Extract Matrix from ABAQUS

Matrix in ABAQUS

Matrices: Stiffness, Mass, Viscous Damping, Structural Damping, Load

Formats: 

  • FORMAT=MATRIX INPUT (default) to specify that the output use the matrix input text format that is consistent with the format used by the matrix definition technique in Abaqus/Standard.
  • FORMAT=LABELS to specify that the output use the standard labeling format.
  • FORMAT=COORDINATE to specify that the output use the common mathematical coordinate format.

Extract Element matrices

It is simple and just edit the keywords in input file. As the *STEP in input file, adding the keywords in the last two lines after the definition of step.

** STEP: Step-1
**
*Step, name=Step-1, nlgeom=NO, perturbation
*Frequency, eigensolver=Lanczos, acoustic coupling=on, normalization=displacement
, , 10., , ,
*Element Matrix Output,Elset=SET-2,
File Name=filename,Frequency=1,Output File=User Defined,Stiffness=Yes,Mass=Yes

Explanation: Elset, means the element set that you want to extract matrix from. File Name, you can name it as what you want and a .mxt file with this name will be generated in your file folder. In a nonlinear analysis, Dload=Yes can be used to extract  the load vector from distributed loads on the element. The exact meanings are detailed in keyword *ELEMENT MATRIX OUTPUT in Abaqus Keywords Reference Guide.

Extract Global Matrices

It is also easy to extract global matrix. You need to add the following codes at the end of the input file or adding these lines before or between step definitions. The difference of the positions in input file between the three lies on the matrices after which step.

**
*STEP
*MATRIX GENERATE, STIFFNESS, MASS
*MATRIX OUTPUT, STIFFNESS, MASS, FORMAT=MATRIX INPUT
*END STEP

After completing the analysis, two .mtx files with the name jobname_STIF2 and jobname_MASS2 (2 is the location number of the this step, i.e. the second step) will be generated in your file folder. Open the jobname_STIF2 file and you will find texts as follows.

1,1, 1,1, 1.000000000000000e+36
1,5, 1,1, 9.283850055777577e-12
1,6, 1,1, -4.181074365176346e+04

The meaning of the five numbers in a line are respectively:

  1. Row node label
  2. Degree of freedom for row node
  3. Column node label
  4. Degree of freedom for column node
  5. Matrix entry
For more details, you can refer to Abaqus Analysis User’s Guide .

Note 1: It is noted that a step containing the mass matrix must be used to extract mass matrix. For example, the under a *Static step, the equation of structure is Kx=F and is not related to mass, and as such the mass matrix can not be extracted. In this example, a *Frequency step is defined.

All structural analyses apart from static will involve calculation and manipulation of the mass matrix. 
Static case: Kx = f
Eigenvalue (modal or free vibration): Ma +Kx = 0
Dynamic (transient): Ma + Cv + Kx = f(t)

Note 2: This keyword is not available in Abaqus/Explicit and the analysis will be terminated.

Codes I often use in abaqus to extract matrices in dynamic implicit analysis

** 
*STEP 
*MATRIX GENERATE, STIFFNESS, MASS, STRUCTURAL DAMPING, VISCOUS DAMPING
*MATRIX OUTPUT, STIFFNESS, MASS, STRUCTURAL DAMPING, VISCOUS DAMPING, FORMAT=COORDINATE
*END STEP

 

103 comments On Extract Matrix from ABAQUS

  • Could you help me to add to my inp. file for extracting stiffness and mass matrix?

    *Heading
    ** Job name: TAN Model name: Model-1
    ** Generated by: Abaqus/CAE 2018
    *Preprint, echo=NO, model=NO, history=NO, contact=NO
    **
    ** PARTS
    **
    *Part, name=Part-1
    *End Part
    **
    **
    ** ASSEMBLY
    **
    *Assembly, name=Assembly
    **
    *Instance, name=Part-1-1, part=Part-1
    0., 2900., 0.
    *Node
    1, 0., -2900.
    2, 0., 1100.
    3, 4000., 1100.
    4, 4000., -2900.
    5, 0., -2500.
    6, 0., -2100.
    7, 0., -1700.
    8, 0., -1300.
    9, 0., -900.
    10, 0., -500.
    11, 0., -100.
    12, 0., 300.
    13, 0., 700.
    14, 400., 1100.
    15, 800., 1100.
    16, 1200., 1100.
    17, 1600., 1100.
    18, 2000., 1100.
    19, 2400., 1100.
    20, 2800., 1100.
    21, 3200., 1100.
    22, 3600., 1100.
    23, 4000., 700.
    24, 4000., 300.
    25, 4000., -100.
    26, 4000., -500.
    27, 4000., -900.
    28, 4000., -1300.
    29, 4000., -1700.
    30, 4000., -2100.
    31, 4000., -2500.
    *Element, type=B21
    1, 1, 5
    2, 5, 6
    3, 6, 7
    4, 7, 8
    5, 8, 9
    6, 9, 10
    7, 10, 11
    8, 11, 12
    9, 12, 13
    10, 13, 2
    11, 2, 14
    12, 14, 15
    13, 15, 16
    14, 16, 17
    15, 17, 18
    16, 18, 19
    17, 19, 20
    18, 20, 21
    19, 21, 22
    20, 22, 3
    21, 3, 23
    22, 23, 24
    23, 24, 25
    24, 25, 26
    25, 26, 27
    26, 27, 28
    27, 28, 29
    28, 29, 30
    29, 30, 31
    30, 31, 4
    *Nset, nset=_PickedSet2, internal, generate
    1, 31, 1
    *Elset, elset=_PickedSet2, internal, generate
    1, 30, 1
    ** Section: Section-1 Profile: Profile-1
    *Beam Section, elset=_PickedSet2, material=Material-1, temperature=GRADIENTS, section=RECT
    100., 100.
    0.,0.,-1.
    *End Instance
    **
    *Nset, nset=_PickedSet4, internal, instance=Part-1-1
    1, 4
    *End Assembly
    **
    ** MATERIALS
    **
    *Material, name=Material-1
    *Density
    7.85e-09,
    *Elastic
    200000., 0.3
    **
    ** BOUNDARY CONDITIONS
    **
    ** Name: BC-1 Type: Symmetry/Antisymmetry/Encastre
    *Boundary
    _PickedSet4, ENCASTRE
    ** —————————————————————-
    **
    ** STEP: Step-1
    **
    *Step, name=Step-1, nlgeom=NO, perturbation
    *Frequency, eigensolver=Lanczos, sim, acoustic coupling=on, normalization=mass
    5, , , , ,
    **
    ** OUTPUT REQUESTS
    **
    *Restart, write, frequency=0
    **
    ** FIELD OUTPUT: F-Output-1
    **
    *Output, field, variable=PRESELECT
    *End Step

    • If you want element matrices, just add the codes as I did. And If you want global matrices, just add the codes as another step which you can find in this article. If you have further questions, please feel free to email me.

  • Hello,

    Thank you so much for this nice-presented work! It’s quite useful. I used the command to generate global mass and stiffnes matrix. But it seems that the mass matrix is only global LUMPED MASS MATRICES. What if I want to generate global CONSISTENT MASS MATRICES using abaqus?
    Looking forward to your reply!

    • Hi Qinbo, if you use consistent mass for the model, you can then get consistent mass matrix. What you mean seems to be related to the matrix, actually the mass will be distributed to nodes and what you get from abaqus is just the right answer. You can calculate the mass matrix of a simple model with consistent mass and compare with what you get from abaqus. If you have further questions, please feel free to reply or email me.

      • Hello Dorothy,
        Thank you so much for your article! I have the same question with Qinbo, and I want to generate global consistent mass matrices too. How can I use or define consistent mass for my model ? Looking forward to your reply and thanks in advance!

        • Hi Zeyu,
          If you defined the material density for your model and did not use point mass, then what you get by generating the global mass matrix will be the consistent mass matrix. The default mass matrix in Abaqus is the consistent one. If there is non-zero non-diagonal element in the generated matrix, then you can be sure you got the consistent mass matrix.

        • Has your problem been solved? I also use ABAQUS to extract the LUMPED mass matrix.

        • Hello Zeyu,
          Have you solved this problem? The mass matrix extracted by ABAQUS now is also a lumped mass matrix, and a consistent mass matrix cannot be obtained.

  • Hello Dorothy,
    Thanks for this article. I have some doubt in further usage of these mass and stiffness matrices. I would like to find natural frequencies using Matlab (e = eig(K,M);) by finding eigenvalues and taking their square roots.
    First of all, my matrices’ size is thrice the number of nodes (actually it is a 3D problem, but DOFs isn’t 6 per node, I need a bit clarification on this too). So, I’m getting the same number of eigenvalues from Matlab as that of the size of mass and stiffness matrices and the results are not the same as that obtained from Abaqus (1st 10 natural frequencies are not matching).
    Please clarify

    • Hi Nikhil,
      Did you compare the mass matrix and stiffness matrix from abaqus and the ones you used in matlab? I suggest you make a comparison.
      Another thing is that the mass calculated in abaqus is distributed mass if you did not add the mass on nodes, while we tend to use lumped mass for convenience.
      Since the dofs per node in your problem is not 6, abaqus magnifies the elements in stiffness matrix for fixed dofs while we prefer to delete the corresponding rows and columns in K matrix.
      The different methods in dealing with mass matrix and stiffness matrix may lead to different eigenvalues. If the relative errors of eigenvalues are within 5%, the results are acceptable.

  • Hello Dorothy,
    Nice article. Thank you.
    I used the 2nd method to generate global mass and stiffness matrices. But what I found is, the total mass calculated in Abaqus and the sum of all the entries from .mtx files are not matching. Analytical way mass calculation (density*volume) is agreeing with Abaqus result, but not with extracted matrix. So, the Abaqus answer is right.
    Can you please help?
    Thank you in advance

    • Hi Dheeraj,
      Do you mean the sum of mass matrix is not consistent with the total mass you calculated with density*volume? It is the right case because you have two/three directions (for 2D/3D problem) in the model and the load applied to it may induce deformation(velocity, acceleration) in two/three directions. So, the different directions have the same mass for distributed mass condition. If mass only exists in gravity, there will be no deformation(velocity, acceleration) in other directions. The sum of mass matrix from abaqus should be two/three times of the total mass you calculated for distributed mass condition.

  • Hello Dorothy,
    Thanks for this article. I followed your instruction and then get the element stiffness matrix successfully. But yet I don’t know the meaning of the stiffness matrix element. For example, when I deal with a beam section from your article “Beam elements in ABAQUS”, it outputs the matrix as:
    1062000.0000000 ,
    0.0000000000000 , 43264.656088429
    0.0000000000000 , 0.0000000000000 , 43264.656088429
    0.0000000000000 , 0.0000000000000 , 0.0000000000000 , 4553.8475200000
    0.0000000000000 , 0.0000000000000 , 21632.328044215 , 0.0000000000000 16736.164022107 ,
    0.0000000000000 , -21632.328044215 , 0.0000000000000 , 0.0000000000000 0.0000000000000 , 6736.164022107
    Can you explain to me how can I associate this matrix with the section property?(EI、EA、etc)
    Looking forward to your reply!

    • Hi Akbjiang,
      The elements in stiffness matrix is associated with node number and the degree of freedoms of each node. You can check the meaning from https://zxding.me/archives/d702tw.html or http://abaqus.software.polimi.it/v6.14/books/usb/default.htm?startat=pt04ch10s03at32.html#usb-anl-amtxgenerationperturbation. You cannot get section properties from stiffness matrix because stiffness matrix is related to both section properties and the length of elements. If you were doing nonlinear analysis, the stiffness matrix will change during the analysis. It seems you were using beam element. You can check E from material property and I and A from the sections you defined in Property Module.

      • Hello Dorothy,
        Thanks for your kindly reply, actually I wonder how abaqus calculate the element stiffness matrix and is there any relation of the element stiffness matrix we derived from abaqus and the section properties we input(for example, we input EA、EI、GJ as section properties when use MESHED), how can I get the stiffness matrix manually if node number and the degree of freedoms is determined?
        Looking forward to your reply!

        • Sorry for the late reply. Something was wrong about the WordPress email. The stiffness matrix is definitely related to the section properties and also the meshing size. You can find the derivation of the stiffness matrix in any finite element book. This is one recommendation for you and you can download the PDF file from this link, http://web.mit.edu/kjb/www/Books/FEP_2nd_Edition_4th_Printing.pdf . You can also watch the lecture videos given by Prof. Bathe from MIT https://ocw.mit.edu/resources/res-2-002-finite-element-procedures-for-solids-and-structures-spring-2010/linear/. There is also course on nonlinear finite element analysis in MIT open course. If you just want to derive the initial stiffness matrix, you can just focus on the linear part which is much easier. There are also many lecture ppts online and you can find the derived matrix and just use it directly. The stiffness matrix of beam element is easier and there are at least three different stiffness matrix because of different consideration such as shear effects and integration method. The stiffness matrix you got from abaqus is also related to your settings about shear stiffness of beam section in Property module. For the setting, you can check the abaqus analysis user’s guide from http://130.149.89.49:2080/v2016/books/usb/default.htm .

      • Hi Dorothy!
        I am also extracting the element stiffness matrix in the analysis. The .mtx file that is given out by Abaqus has the same format as mentioned in the above comment as:
        “1062000.0000000 ,
        0.0000000000000 , 43264.656088429
        0.0000000000000 , 0.0000000000000 , 43264.656088429
        0.0000000000000 , 0.0000000000000 , 0.0000000000000 , 4553.8475200000
        0.0000000000000 , 0.0000000000000 , 21632.328044215 , 0.0000000000000 16736.164022107 ,
        0.0000000000000 , -21632.328044215 , 0.0000000000000 , 0.0000000000000 0.0000000000000 , 6736.164022107”
        I am struggling to understand the pattern in which the matrix element are written. Can you help me understand this matrix? It is for sure the lower or upper triangular format. But what id pattern?

  • Dear All,
    thank you for your very interested post.
    I am aware of how to get out these matrices from Abaqus.
    However I have not found yet any way to get out the MODAL mass/stiffness/damping matrices.
    I am running a frequency analysis (my model has also some damping properties) and I would like to get the modal matrices.
    This means if [M], [K], [C] are the mass,stiffness and damping matrices and [Φ] the eigevectors matrix I would like to get out
    [Φ]'[M][Φ], [Φ]'[K][Φ], [Φ]'[C][Φ].
    Does anyone know the way?
    Thank you in Advanced,
    ddaniel

    • Hi Ddaniel,
      You can try to use the following codes to get the M, K, C matrices, it should work.
      *MATRIX GENERATE, STIFFNESS, MASS, STRUCTURAL DAMPING, VISCOUS DAMPING
      *MATRIX OUTPUT, STIFFNESS, MASS, STRUCTURAL DAMPING, VISCOUS DAMPING, FORMAT=COORDINATE

      To get the eigenvectors, you should first request eigenvectors at all nodes. Here is the link related to this, https://abaqus-docs.mit.edu/2017/English/SIMACAEANLRefMap/simaanl-c-freqextraction.htm. Since I never extracted eigenvector before and abaqus is now not available to me, I am not sure how to do. You can have a try after requesting the eigenvectors.
      Please feel free to contact me if any questions.

      • Dear Doothy,
        thank you very much for your prompt reply.
        What you describe is exactly what I am currently doing.
        However I was hoping for a way to get the modal M,K,C matrices directly from Abaqus (this is something posible to be done for example with Nastran) without the need to multiply them with the eigenvectors matrix my self.
        Best Regards,
        ddaniel

        • Hi Ddaniel,
          Now I clearly understand what you want from abaqus. I think the ‘OUTPUT’ part in this link may be helpful. The generalized mass is written automatically to the output database as history data.

  • Hi Dorothy,

    I would like to extract the stiffness matrix at the initial step of the analysis and then after cracking occurs. I would like to view how the stiffness changed with the cracks.
    Is this possible. Thank you

    • Hi Diana,
      You can add a step to extract the initial stiffness matrix and also a step after your cracking analysis for the final stiffness matrix. As far as I known, it’s not possible to extract stiffness matrix during the analysis for each substep. You can check the abaqus documents.

  • Hi Dorothy,
    I tried using the code for the extraction of element mass and stiffness matrix. The stiffness matrix works fine but not for the mass matrix in which I find a diagonal matrix. The problem is that I cannot calculate the eigenvalues with such a mass matrix. I tried to do the same for a cantilever beam and it works well but not for my 2D model. Can you help me with that? Thank you in advance

    • Hi Katy,
      To my best knowledge, the eigenvalues could be calculated with a lumped mass matrix which is a diagonal matrix. If you want consistent mass matrix, it should work if you avoid using point mass.

      • Hi Dororthy,
        I didn’t find a way to find the eigenvalues with a lumped mass can you share it if you know. And for the second option I would like to know how to do that in Abaqus.

        • Hi Katy,
          I am a little confused with your question, so I will explain what may be useful to you.
          For the eigenvalues given by abaqus, you can go to the location where your abaqus job files are saved, then you search the jobname.dat file and you can find the eigenvalue output with eigenvalues and frequencies.
          For the manual calculation of eigenvalues, you can use the matlab code [eigen_vec, w_square] = eig(K, M), in which the K and M are the stiffness matrix and mass matrix you have, and the w_square is the eigenvalue (which is the eigenvalue in abaqus). You can get the frequency w in rad/s (which is the frequency in rad/time in abaqus) by taking square root of w_square and w/(2*pi) in Hz.
          If you use the material with density and do nothing else in abaqus, you will get consistent mass matrix, which will have non-diagonal elements because of the shape function of the element. If you want to use lumped mass matrix which only have diagonal elements, do not define density in material and go to the ‘Property‘ module and then go to the ‘Special->Inertia‘ to create the point mass/inertia. After successfully defined the point mass at the nodes you want, there will be a green square at the node with point mass.
          Hope these could help you and feel free to contact me if you have further questions.

  • I have extracted the stiffness and mass matrix of an assembly, two beams bolted together. I created one beam as part and the other beam is a copy of this beam. I have to apply boundary conditions on certain nodes in the stiffness matrix. But when I created node-set, both my instances have the same node numbers. How to relate this to the stiffness matrix.

    • Hi Remya,
      I did not deal with this before, but I think one way to get the stiffness matrix related to the node numbers is renumbering the nodes. Here is the link about how to renumber the nodes.

  • hi Dorothy
    i have modeled a 2D-plate using Q4 element in matlab. i have used consistent formulation of mass matrix to form the elemental mass matrix of the plate and then assembled them to creat the Global mass matrix of the plate. to extract the eigenvalues, i used eig(K,M) in matlab. i did the same in abaqus to model a 2D plate using CPS4 element in plane stress condition. the stiffness matrix calculated by abaqus is as same as the matlab. but the mass matrix extarcted from abaqus seems to be lumped mass matrix, because it’s numebr of values are as equal as the number of DOFs. so the first 3 eigenvalues calculated by matlab are 100 times greater than those of calculated by abaqus.
    do you know the reason of this diffrence? is it possible to model a 2D-plate in abaqus whose mass matrix is consistent?
    thank you.

    • Hi Alireza,
      From my understanding, abaqus uses consistent mass matrix by default. One can obtain lumped mass matrix only by create the point mass/inertia. If you only define the material density for your plate, the mass matrix should be the consistent one. You can double check the mass matrix you obtained from abaqus and also the one you have in matlab. I once compared the eigenvalues for a beam element from consistent and lumped mass matrix. The first eigenvalue is the same corresponding to rigid body motion, and the second one is about two times with consistent mass matrix.

      • Thanks for your response.
        I have compared both mass matrices extracted from Matlab and Abaqus. As I mentioned it in my first comment, the number of mass matirx entries calculated by Abaqus are equal to the number of DOFs, which means it is a diagonal mass matrix.
        I have used Abaqus’ mass matrix values to form a diagonal mass matrix in Matlab. I have employed eig(K,M) again to extract the eigenvalues. The extracted eigenvalues didn’t differ from the previous ones (using consistent mass matrix). I was wondered because I used diagonal mass matrix instead of consistent mass matrix. so I have another question. Do you know how Abaqus calculates the eigenvalues? because Abaqus and Matlab gave the same stiffness matrix and the only diffrence between them was in the mass matrix. Actually I couldn’t understand where the problem was.
        Thank you again.

        • Hi Alireza,
          The method for eigenvalue calculation in abaqus depends on which eigensolver you choose in ‘STEP’. It could be Lanczos, subspace or AMS. I used Lanczos method before for a simply supported rectangular plate and the differences of the eigenvalues are within 35% and 10% for the first 10 modes with a coarse and fine mesh respectively. I extracted the mass matrix of this model, and the first ten rows in .mxt file are shown as:
          1,1, 1,1, 1.838929123451831e-03
          2,1, 1,1, 1.837295790156881e-03
          12,1, 1,1, 1.837295790156881e-03
          13,1, 1,1, 1.836479123509406e-03
          1,2, 1,2, 1.838929123451831e-03
          2,2, 1,2, 1.837295790156881e-03
          12,2, 1,2, 1.837295790156881e-03
          13,2, 1,2, 1.836479123509406e-03
          1,3, 1,3, 3.266666589899999e-03
          2,3, 1,3, 1.633333294950000e-03

          You can see the matrix does have off-diagonal elements. Maybe somewhere in your model is not correct.

          • Hello Dorothy,
            I am very thankful for the help I am getting from you. However, I want to use the mass, stiffness, and damping matrices from Abaqus to define a state space system: Xdot= Ax+Bu and Y=Cx+Du
            In this system, the matrices A and B requires the knowledge of Mass, Stiffness and Damping matrices (Which I can get from Abaqus as you described in the previous texts). My problem is how the matrices from Abaqus are arranged? for example, you mentioned that the last column indicates the matrix entry, does this means we ignore other columns you explained as 1st row: Row node label, 2nd row: degree of freedom for row node, 3rd row: Column node label, and 4th row: Degree of freedom for column node? I mean do we only consider the last row i.e. Matrix entry? if yes how does it mean that the matrices are row vectors?
            Kind Regards

          • Hi Dush,
            Sorry for replaying late, I was focusing on my qualifying exams and thankfully it will ends tomorrow. In your case, you need global matrices which you need to form yourself according to the outputs. I would suggest the matrix input format (I used in this post). Let assume you have 10 nodes (indexing from node 1 to node 10) each with 3 dofs for better explanation. Then you will have a 30*30 global matrix. Let’s say in each line we get “n1, d1, n2, d2, v” from the output, then you will have your matrix element with value of v at the [(n1 -1)*3 + d1] th row and [(n2 – 1)*3 + d2] th column.
            Hope this helps. Please feel free to let a comment if you have further questions.

  • Hi Dorothy,
    Thanks a lot for your attention and fast response. Could you please give me your Email? I have some more questions about mesh numbers you used and the first 10 natural frequencies you extracted from Abaqus. I will be appreciated you.
    Best regards.

  • Karthikayen Raju

    Hi Dorothy!
    why cannot we extract matrices in abaqus explcit?

    • Hi Karthikayen,
      I am not sure what the reason is. I tried but the codes could not work. If you know the reason, please let me know. I am also confused.
      One way to extract matrices in abaqus/explicit is to add keywords for one more step.
      **
      *STEP
      *MATRIX GENERATE, STIFFNESS, MASS, STRUCTURAL DAMPING, VISCOUS DAMPING
      *MATRIX OUTPUT, STIFFNESS, MASS, STRUCTURAL DAMPING, VISCOUS DAMPING, FORMAT=COORDINATE
      *END STEP

  • Hi Dorothy,

    I managed to extract the mass and stiffness matrix from my Abaqus model, however, the mass matrix is a lumped (diagonal) matrix. How can I extract the consistent mass matrix instead? I use 3D solid elements.

    Thanks in advance!

    Kind regards.

    Lars

    • Hi Lars,
      I only tried beam element before. To my best knowledge, consistent mass matrix is the default setting in abaqus. To get consistent mass matrix, one needs to avoid defining point mass and use material density only. Hope this helps.

  • Hi Dorothy,

    This is a good article!!! Because I am new in this field. I am confused that how I add the code in .inp file as an input file. Because we will get the .inp file after completing the run of model. Please tell me how to do this.

    Thank you

    • Hi Panida,
      You can right click your model in the model tree, then click ‘Edit Keywords’. Hope this helps.

      • Thank you so much for your kind reply. I read all your comments that replied to everybody. It is very useful. Now I got the mass matrix and stiffness matrix as your article. I modeled a 2D plate in Abaqus to get mass matrix and stiffness matrix, Then these matrices are input to MATLAB. And I have some questions below;

        1. How to extract mass matrix and stiffness matrix that contain only Row node label, Column node label, Matrix entry (like 443 509 6.040995098525574e-04)?
        2. Can the mass matrix and stiffness matrix are used for all mode shapes (like my problem considers only the first five mode shapes)?
        3. Now I have known that I have to use the synx code ( [Phi,Wn]=eig(K,M)) to plot eigenvector but still confused how to write the MATLAB code. If you have the code for plotting mode shape, could you please share to me as an example?
        Look forward to your reply
        Thank you in advance

        • Hi Panida,
          Hope you find the following helpful. Please feel free to leave questions in comments.
          R1: You can switch the format from ‘matrix input’ to ‘coordinate’, like *MATRIX OUTPUT, STIFFNESS, MASS, FORMAT=COORDINATE. Then, you will get matrix like this 1 1 1.962500490625005e+00. The first and second are the row and column numbers in the matrix.
          R2: Of course you can use the mass and stiffness matrices for all mode shapes since mass and stiffness are the properties of a structure. As long as you use the same structure and do not consider the damage after analysis, the mass and stiffness matrices are the same.
          R3: Mode shape is closely related to your structure, so most codes are specific to particular structure. You might need to write your own. You can start with plotting the original structure, and then add the scaled ‘displacements’ from mode analysis to corresponding nodes.

          • Hi Dorothy,
            Thank you for your prompt reply. I really appreciate your kindness.
            I have got mass and stiffness matrices by changing the format to ‘coordinate’. But I wonder that the number of rows and columns is higher than the format ‘matrix input’.

            For example, A model has around 6000 elements (check from mesh). The format ‘matrix input’. also has around 6000 elements, BUT the format to ‘coordinate’ has around 40,000 elements. I think I misunderstand on something. Could you please clarify. Thank you.

          • Hi Panida,
            The 40,000 rows/columns are correct since the ‘coordinate’ format expands the matrix from ‘matrix input’ by ignoring the node numbers and degrees of freedoms.
            You have around 6,000 elements and each element has 6 degrees of freedoms. Then the matrices should have around 6,000*6=36,000 rows/columns.
            If you look at the .mtx files from ‘matrix input’ and ‘coordinate’, you should have the same numbers of lines.
            Hope this helps.

          • Hi Dorothy,
            Thank you so much for your advice. It helps me a lot. I will try to continue my simulation further.

            Stay safe during epidemic 🙂
            Best Regards,

  • Hi Dorothy,
    With your good reference i was able to extract mass matrix for my problem, but i didn’t understood the significance of first 4 terms of the .mtx file (Row node label, Degree of freedom for row node, Column node label, Degree of freedom for column node). How can i get a single mass matrix entry for a single node or How to obtain the value which is assigned to a single node. If my problem is not clear to you i will mail you with the attached .mtx file. Hoping to hear good from your side.

    • Hi Sastha,
      From my understanding to your question, you want to have only the mass on one node instead of the mass at all nodes in the mass matrix. If so, you can search for the entry from the mass matrix according to the number and degrees of freedom of that node. For example, 2,2, 2,2, -4.181074365176346e+04, means this is the mass in the second degree of freedom for node 2 and it is in the diagonal element in the mass matrix. Another way is to extract the mass matrix for all elements that containing that node, so that you can find the element more quickly and also save time in outputting a big global matrix. But in this way you need to calculate the mass element manually or with some software such as matlab. I didn’t try this before, but it should work.
      If this is not what you mean in the question, please feel free to contact me.

      • Hi Dorothy,
        Thank you for your immediate response, actually I need find a single mass value acted on each node, so how to find that singular mass value for that particular node? Here we can get many values of mass attached to a particular node according to different degrees of freedom. So how to obtain the net mass value which is being acted on that particular node.
        Hoping to hear good from your side.

        Regards,
        SASTHA

        • Hi Sastha,
          As far as I know, there is no such a convenient way to just extract one mass value for a node. Feasible way to achieve the mass value on a node would be either the one I mentioned in the previous reply. If you want to extract the mass matrix for all elements that containing that node, you can first define an element set and then generate mass matrix for this set only.

          • Hi Dorothy,
            Thanks for the followup, I will find an alternative way for solving the same. I will definitely update you once i am done. Thank you once again for your support will keep in contact.

            Regards,
            Sastha

          • Hi Dorothy,

            I managed to extract the mass and stiffness matrix from abaqus, please guide me on hw to read the sparse matrix in matlab. I am abit confused on the numbering of the matrices

          • Hi Ivan,
            If you output the matrices with ‘matrix input’ format, the first four numbers are the row node number, degree of freedom of the row node, column node number, degree of freedom of the column node, respectively.
            If you output the matrices with ‘coordinate’ format, the first two numbers are the row number and column number.
            You can assemble the matrices according to the first four or two numbers in a mathematical way.
            Hope this helps.

          • SREESASTHARAM

            Hi Dorothy,
            I was a bit confused with the incorporation of boundary condition for Dynamic Analysis of Cantilever with base excitation. Can you try help me to figure out this. In my analysis there is cantilever with a tip, as we know one end of the cantilever must be fixed but to where we can incorporate displacement boundary condition (base excitation) on to the cantilever. Here i can’t attach my model, if it is possible I can send the model image via email

          • Hi Sreesastharam,
            I am not sure what you are confused about from the description. If you need the stiffness matrix, you can extract the matrix and ABAQUS will assign a large value (1.000000000000000e+36) for fixed nodes. Hope this will help.

  • Hi Dorothy,
    Thanks very much for this article. Just wondering whether you can change the format of the element stiffness matrix output file for use in MATLAB afterwards; currently, the output file has lots of text surrounding the matrix data (e.g. Element number or type) for each element, which is making it challenging to extract only the element stiffness matrix values. Is there a way to make the Abaqus output file more MATLAB-friendly, or alternatively do you know of some MATLAB code that could extract only the element stiffness matrix data, without the text between each element?
    Many thanks for your help!

    • Hi Dan,
      As far as I know, there is no such a way in abaqus to extract only numbers for element matrices. You can do it in matlab with some commands for reading files like fgetl.
      Also, the output matrices from abaqus follow some patterns. You can take advantage of the patterns when read with matlab.
      Hope this helps.

  • `Hi Dorothy,
    Thanks very much for this article. Just wondering whether there was a more MATLAB-friendly output format for the Abaqus element stiffness matrix file. The current output has lots of text between each element (describing element number or type for example), making it challenging to extract only the element stiffness matrix data. Do you know of a way to change the format of the output of Abaqus element stiffness matrices, or alternatively a MATLAB code that can extract only the element stiffness matrix data from the Abaqus file?
    Many thanks!

    • Hi Dan,
      Please check the response under your first comment. Sorry about the late reply. The emails from wordpress keep going into junk folder in my outlook even though I reported this problem. I have to check every a few days and cannot see the comments in time, very annoying.

    • Hi,
      Abaqus2Matlab package enables you to extract stiffness matrix in various formats suitable for MATLAB manipulation. I am not sure but maybe you can use it for your intended post-processing operations. The link to this free tool:

      https://abaqus2matlab.wixsite.com/abaqus2matlab

  • Hi Dorothy,
    Many thanks for putting this nice resource together!
    I am trying to recreate a model from COMSOL in Abaqus. The geometry, material properties and boundary conditions are identical, but there are some discrepancies in the mass and stiffness matrices (and hence the natural frequencies, around 2% difference). Any ideas on why this is the case/how to get them to match? I am using C3D15 elements.
    Thanks,
    Eva

    • Hi Eva,
      From my perspective, 2% difference is totally acceptable. Even though you have two ‘same’ models in different software, the results could differ a little bit. The tolerance for iterations, the precision of numerical calculations, the default method (if you did not specify) for frequency analysis could differ. All these would lead to discrepancies in final results. I would accept both models if the discrepancy is less than 5%.

  • Hi Dorothy,
    Thanks for this great article , I read the comments and questions above. I have another question please
    Is there a way in Abaqus to convert the applied load( point load, line load or distributed load) to masses for it to be accounted in the mass matrix?
    Thanks for your reply

    • Hi Efio,
      Thank you Efio. From my understanding, there is no such a way to convert load to mass in abaqus (load and mass are very different for analysis in governing equation). But you can output the load vectors and then combine the load with mass matrix in Matlab or with python. Hope this helps.

  • Dear Dorothy,

    I hope my email finds you well. Thank you for this great article. I tried to modify the input files (that I got from the analysis in Abaqus) using the codes you wrote in this article. However, I still cannot get the mass and stiffness matrices. The .mtx files with the jobname do not generate after the analysis completes. I have tried many times with different input files, but I still do not get the matrices. I will be grateful if you can advise or direct me on how to proceed. Thank you very much in advance for your help.

    • Hi Ashleyed,
      Did you get any warning or error message when you change input file or run the jobs? You can check the data file when analysis finishes. You can find contents ‘The following global matrices will be written to the following text files’, followed by a list of matrices and corresponding file names. If you cannot find contents like these, the input file was not correctly modified.

      • Dear Dorothy,
        Thank you for your response. The analysis completes perfectly and In the data file, I get one warning message saying
        ***WARNING: THIS OPTION WILL NOT BE STEP-DEPENDENT.
        LINE IMAGE: *matrixgenerate, stiffness, mass

        and one note saying
        ***NOTE: THE MATRIX OUTPUT OPTION IS ONLY VALID IN THE MATRIX GENERATION
        PROCEDURE
        Could you please direct me on how to fix this?

        Here is the .inp file that I added the lines for the matrix generation before End Step. I do not understand what is wrong with it.

        *Heading
        This is the analysis of a simple beam.
        ** Job name: Beam Model name: Model-1
        ** Generated by: Abaqus/CAE 2019
        *Preprint, echo=NO, model=NO, history=NO, contact=NO
        **
        ** PARTS
        **
        *Part, name=Part-1
        *Node
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        858, 0.802105248, 0., 0.
        859, 0.804210544, 0., 0.
        860, 0.80631578, 0., 0.
        861, 0.808421075, 0., 0.
        862, 0.810526311, 0., 0.
        863, 0.812631607, 0., 0.
        864, 0.814736843, 0., 0.
        865, 0.816842079, 0., 0.
        866, 0.818947375, 0., 0.
        867, 0.821052611, 0., 0.
        868, 0.823157907, 0., 0.
        869, 0.825263143, 0., 0.
        870, 0.827368438, 0., 0.
        871, 0.829473674, 0., 0.
        872, 0.83157897, 0., 0.
        873, 0.833684206, 0., 0.
        874, 0.835789502, 0., 0.
        875, 0.837894738, 0., 0.
        876, 0.839999974, 0., 0.
        877, 0.842105269, 0., 0.
        878, 0.844210505, 0., 0.
        879, 0.846315801, 0., 0.
        880, 0.848421037, 0., 0.
        881, 0.850526333, 0., 0.
        882, 0.852631569, 0., 0.
        883, 0.854736865, 0., 0.
        884, 0.856842101, 0., 0.
        885, 0.858947396, 0., 0.
        886, 0.861052632, 0., 0.
        887, 0.863157868, 0., 0.
        888, 0.865263164, 0., 0.
        889, 0.8673684, 0., 0.
        890, 0.869473696, 0., 0.
        891, 0.871578932, 0., 0.
        892, 0.873684227, 0., 0.
        893, 0.875789464, 0., 0.
        894, 0.877894759, 0., 0.
        895, 0.879999995, 0., 0.
        896, 0.882105291, 0., 0.
        897, 0.884210527, 0., 0.
        898, 0.886315763, 0., 0.
        899, 0.888421059, 0., 0.
        900, 0.890526295, 0., 0.
        901, 0.89263159, 0., 0.
        902, 0.894736826, 0., 0.
        903, 0.896842122, 0., 0.
        904, 0.898947358, 0., 0.
        905, 0.901052654, 0., 0.
        906, 0.90315789, 0., 0.
        907, 0.905263186, 0., 0.
        908, 0.907368422, 0., 0.
        909, 0.909473658, 0., 0.
        910, 0.911578953, 0., 0.
        911, 0.913684189, 0., 0.
        912, 0.915789485, 0., 0.
        913, 0.917894721, 0., 0.
        914, 0.920000017, 0., 0.
        915, 0.922105253, 0., 0.
        916, 0.924210548, 0., 0.
        917, 0.926315784, 0., 0.
        918, 0.92842108, 0., 0.
        919, 0.930526316, 0., 0.
        920, 0.932631552, 0., 0.
        921, 0.934736848, 0., 0.
        922, 0.936842084, 0., 0.
        923, 0.93894738, 0., 0.
        924, 0.941052616, 0., 0.
        925, 0.943157911, 0., 0.
        926, 0.945263147, 0., 0.
        927, 0.947368443, 0., 0.
        928, 0.949473679, 0., 0.
        929, 0.951578975, 0., 0.
        930, 0.953684211, 0., 0.
        931, 0.955789447, 0., 0.
        932, 0.957894742, 0., 0.
        933, 0.959999979, 0., 0.
        934, 0.962105274, 0., 0.
        935, 0.96421051, 0., 0.
        936, 0.966315806, 0., 0.
        937, 0.968421042, 0., 0.
        938, 0.970526338, 0., 0.
        939, 0.972631574, 0., 0.
        940, 0.974736869, 0., 0.
        941, 0.976842105, 0., 0.
        942, 0.978947341, 0., 0.
        943, 0.981052637, 0., 0.
        944, 0.983157873, 0., 0.
        945, 0.985263169, 0., 0.
        946, 0.987368405, 0., 0.
        947, 0.989473701, 0., 0.
        948, 0.991578937, 0., 0.
        949, 0.993684232, 0., 0.
        950, 0.995789468, 0., 0.
        951, 0.997894764, 0., 0.
        *Element, type=B31
        1, 1, 12
        2, 12, 13
        3, 13, 14
        4, 14, 15
        5, 15, 16
        6, 16, 17
        7, 17, 18
        8, 18, 19
        9, 19, 20
        10, 20, 21
        11, 21, 22
        12, 22, 23
        13, 23, 24
        14, 24, 25
        15, 25, 26
        16, 26, 27
        17, 27, 28
        18, 28, 29
        19, 29, 30
        20, 30, 31
        21, 31, 32
        22, 32, 33
        23, 33, 34
        24, 34, 35
        25, 35, 36
        26, 36, 37
        27, 37, 38
        28, 38, 39
        29, 39, 40
        30, 40, 41
        31, 41, 42
        32, 42, 43
        33, 43, 44
        34, 44, 45
        35, 45, 46
        36, 46, 47
        37, 47, 48
        38, 48, 49
        39, 49, 50
        40, 50, 51
        41, 51, 52
        42, 52, 53
        43, 53, 54
        44, 54, 55
        45, 55, 56
        46, 56, 57
        47, 57, 58
        48, 58, 59
        49, 59, 60
        50, 60, 61
        51, 61, 62
        52, 62, 63
        53, 63, 64
        54, 64, 65
        55, 65, 66
        56, 66, 67
        57, 67, 68
        58, 68, 69
        59, 69, 70
        60, 70, 71
        61, 71, 72
        62, 72, 73
        63, 73, 74
        64, 74, 75
        65, 75, 76
        66, 76, 77
        67, 77, 78
        68, 78, 79
        69, 79, 80
        70, 80, 81
        71, 81, 82
        72, 82, 83
        73, 83, 84
        74, 84, 85
        75, 85, 86
        76, 86, 87
        77, 87, 88
        78, 88, 89
        79, 89, 90
        80, 90, 91
        81, 91, 92
        82, 92, 93
        83, 93, 94
        84, 94, 95
        85, 95, 96
        86, 96, 97
        87, 97, 98
        88, 98, 99
        89, 99, 100
        90, 100, 101
        91, 101, 102
        92, 102, 103
        93, 103, 104
        94, 104, 105
        95, 105, 2
        96, 2, 106
        97, 106, 107
        98, 107, 108
        99, 108, 109
        100, 109, 110
        101, 110, 111
        102, 111, 112
        103, 112, 113
        104, 113, 114
        105, 114, 115
        106, 115, 116
        107, 116, 117
        108, 117, 118
        109, 118, 119
        110, 119, 120
        111, 120, 121
        112, 121, 122
        113, 122, 123
        114, 123, 124
        115, 124, 125
        116, 125, 126
        117, 126, 127
        118, 127, 128
        119, 128, 129
        120, 129, 130
        121, 130, 131
        122, 131, 132
        123, 132, 133
        124, 133, 134
        125, 134, 135
        126, 135, 136
        127, 136, 137
        128, 137, 138
        129, 138, 139
        130, 139, 140
        131, 140, 141
        132, 141, 142
        133, 142, 143
        134, 143, 144
        135, 144, 145
        136, 145, 146
        137, 146, 147
        138, 147, 148
        139, 148, 149
        140, 149, 150
        141, 150, 151
        142, 151, 152
        143, 152, 153
        144, 153, 154
        145, 154, 155
        146, 155, 156
        147, 156, 157
        148, 157, 158
        149, 158, 159
        150, 159, 160
        151, 160, 161
        152, 161, 162
        153, 162, 163
        154, 163, 164
        155, 164, 165
        156, 165, 166
        157, 166, 167
        158, 167, 168
        159, 168, 169
        160, 169, 170
        161, 170, 171
        162, 171, 172
        163, 172, 173
        164, 173, 174
        165, 174, 175
        166, 175, 176
        167, 176, 177
        168, 177, 178
        169, 178, 179
        170, 179, 180
        171, 180, 181
        172, 181, 182
        173, 182, 183
        174, 183, 184
        175, 184, 185
        176, 185, 186
        177, 186, 187
        178, 187, 188
        179, 188, 189
        180, 189, 190
        181, 190, 191
        182, 191, 192
        183, 192, 193
        184, 193, 194
        185, 194, 195
        186, 195, 196
        187, 196, 197
        188, 197, 198
        189, 198, 199
        190, 199, 3
        191, 3, 200
        192, 200, 201
        193, 201, 202
        194, 202, 203
        195, 203, 204
        196, 204, 205
        197, 205, 206
        198, 206, 207
        199, 207, 208
        200, 208, 209
        201, 209, 210
        202, 210, 211
        203, 211, 212
        204, 212, 213
        205, 213, 214
        206, 214, 215
        207, 215, 216
        208, 216, 217
        209, 217, 218
        210, 218, 219
        211, 219, 220
        212, 220, 221
        213, 221, 222
        214, 222, 223
        215, 223, 224
        216, 224, 225
        217, 225, 226
        218, 226, 227
        219, 227, 228
        220, 228, 229
        221, 229, 230
        222, 230, 231
        223, 231, 232
        224, 232, 233
        225, 233, 234
        226, 234, 235
        227, 235, 236
        228, 236, 237
        229, 237, 238
        230, 238, 239
        231, 239, 240
        232, 240, 241
        233, 241, 242
        234, 242, 243
        235, 243, 244
        236, 244, 245
        237, 245, 246
        238, 246, 247
        239, 247, 248
        240, 248, 249
        241, 249, 250
        242, 250, 251
        243, 251, 252
        244, 252, 253
        245, 253, 254
        246, 254, 255
        247, 255, 256
        248, 256, 257
        249, 257, 258
        250, 258, 259
        251, 259, 260
        252, 260, 261
        253, 261, 262
        254, 262, 263
        255, 263, 264
        256, 264, 265
        257, 265, 266
        258, 266, 267
        259, 267, 268
        260, 268, 269
        261, 269, 270
        262, 270, 271
        263, 271, 272
        264, 272, 273
        265, 273, 274
        266, 274, 275
        267, 275, 276
        268, 276, 277
        269, 277, 278
        270, 278, 279
        271, 279, 280
        272, 280, 281
        273, 281, 282
        274, 282, 283
        275, 283, 284
        276, 284, 285
        277, 285, 286
        278, 286, 287
        279, 287, 288
        280, 288, 289
        281, 289, 290
        282, 290, 291
        283, 291, 292
        284, 292, 293
        285, 293, 4
        286, 4, 294
        287, 294, 295
        288, 295, 296
        289, 296, 297
        290, 297, 298
        291, 298, 299
        292, 299, 300
        293, 300, 301
        294, 301, 302
        295, 302, 303
        296, 303, 304
        297, 304, 305
        298, 305, 306
        299, 306, 307
        300, 307, 308
        301, 308, 309
        302, 309, 310
        303, 310, 311
        304, 311, 312
        305, 312, 313
        306, 313, 314
        307, 314, 315
        308, 315, 316
        309, 316, 317
        310, 317, 318
        311, 318, 319
        312, 319, 320
        313, 320, 321
        314, 321, 322
        315, 322, 323
        316, 323, 324
        317, 324, 325
        318, 325, 326
        319, 326, 327
        320, 327, 328
        321, 328, 329
        322, 329, 330
        323, 330, 331
        324, 331, 332
        325, 332, 333
        326, 333, 334
        327, 334, 335
        328, 335, 336
        329, 336, 337
        330, 337, 338
        331, 338, 339
        332, 339, 340
        333, 340, 341
        334, 341, 342
        335, 342, 343
        336, 343, 344
        337, 344, 345
        338, 345, 346
        339, 346, 347
        340, 347, 348
        341, 348, 349
        342, 349, 350
        343, 350, 351
        344, 351, 352
        345, 352, 353
        346, 353, 354
        347, 354, 355
        348, 355, 356
        349, 356, 357
        350, 357, 358
        351, 358, 359
        352, 359, 360
        353, 360, 361
        354, 361, 362
        355, 362, 363
        356, 363, 364
        357, 364, 365
        358, 365, 366
        359, 366, 367
        360, 367, 368
        361, 368, 369
        362, 369, 370
        363, 370, 371
        364, 371, 372
        365, 372, 373
        366, 373, 374
        367, 374, 375
        368, 375, 376
        369, 376, 377
        370, 377, 378
        371, 378, 379
        372, 379, 380
        373, 380, 381
        374, 381, 382
        375, 382, 383
        376, 383, 384
        377, 384, 385
        378, 385, 386
        379, 386, 387
        380, 387, 5
        381, 5, 388
        382, 388, 389
        383, 389, 390
        384, 390, 391
        385, 391, 392
        386, 392, 393
        387, 393, 394
        388, 394, 395
        389, 395, 396
        390, 396, 397
        391, 397, 398
        392, 398, 399
        393, 399, 400
        394, 400, 401
        395, 401, 402
        396, 402, 403
        397, 403, 404
        398, 404, 405
        399, 405, 406
        400, 406, 407
        401, 407, 408
        402, 408, 409
        403, 409, 410
        404, 410, 411
        405, 411, 412
        406, 412, 413
        407, 413, 414
        408, 414, 415
        409, 415, 416
        410, 416, 417
        411, 417, 418
        412, 418, 419
        413, 419, 420
        414, 420, 421
        415, 421, 422
        416, 422, 423
        417, 423, 424
        418, 424, 425
        419, 425, 426
        420, 426, 427
        421, 427, 428
        422, 428, 429
        423, 429, 430
        424, 430, 431
        425, 431, 432
        426, 432, 433
        427, 433, 434
        428, 434, 435
        429, 435, 436
        430, 436, 437
        431, 437, 438
        432, 438, 439
        433, 439, 440
        434, 440, 441
        435, 441, 442
        436, 442, 443
        437, 443, 444
        438, 444, 445
        439, 445, 446
        440, 446, 447
        441, 447, 448
        442, 448, 449
        443, 449, 450
        444, 450, 451
        445, 451, 452
        446, 452, 453
        447, 453, 454
        448, 454, 455
        449, 455, 456
        450, 456, 457
        451, 457, 458
        452, 458, 459
        453, 459, 460
        454, 460, 461
        455, 461, 462
        456, 462, 463
        457, 463, 464
        458, 464, 465
        459, 465, 466
        460, 466, 467
        461, 467, 468
        462, 468, 469
        463, 469, 470
        464, 470, 471
        465, 471, 472
        466, 472, 473
        467, 473, 474
        468, 474, 475
        469, 475, 476
        470, 476, 477
        471, 477, 478
        472, 478, 479
        473, 479, 480
        474, 480, 481
        475, 481, 6
        476, 6, 482
        477, 482, 483
        478, 483, 484
        479, 484, 485
        480, 485, 486
        481, 486, 487
        482, 487, 488
        483, 488, 489
        484, 489, 490
        485, 490, 491
        486, 491, 492
        487, 492, 493
        488, 493, 494
        489, 494, 495
        490, 495, 496
        491, 496, 497
        492, 497, 498
        493, 498, 499
        494, 499, 500
        495, 500, 501
        496, 501, 502
        497, 502, 503
        498, 503, 504
        499, 504, 505
        500, 505, 506
        501, 506, 507
        502, 507, 508
        503, 508, 509
        504, 509, 510
        505, 510, 511
        506, 511, 512
        507, 512, 513
        508, 513, 514
        509, 514, 515
        510, 515, 516
        511, 516, 517
        512, 517, 518
        513, 518, 519
        514, 519, 520
        515, 520, 521
        516, 521, 522
        517, 522, 523
        518, 523, 524
        519, 524, 525
        520, 525, 526
        521, 526, 527
        522, 527, 528
        523, 528, 529
        524, 529, 530
        525, 530, 531
        526, 531, 532
        527, 532, 533
        528, 533, 534
        529, 534, 535
        530, 535, 536
        531, 536, 537
        532, 537, 538
        533, 538, 539
        534, 539, 540
        535, 540, 541
        536, 541, 542
        537, 542, 543
        538, 543, 544
        539, 544, 545
        540, 545, 546
        541, 546, 547
        542, 547, 548
        543, 548, 549
        544, 549, 550
        545, 550, 551
        546, 551, 552
        547, 552, 553
        548, 553, 554
        549, 554, 555
        550, 555, 556
        551, 556, 557
        552, 557, 558
        553, 558, 559
        554, 559, 560
        555, 560, 561
        556, 561, 562
        557, 562, 563
        558, 563, 564
        559, 564, 565
        560, 565, 566
        561, 566, 567
        562, 567, 568
        563, 568, 569
        564, 569, 570
        565, 570, 571
        566, 571, 572
        567, 572, 573
        568, 573, 574
        569, 574, 575
        570, 575, 7
        571, 7, 576
        572, 576, 577
        573, 577, 578
        574, 578, 579
        575, 579, 580
        576, 580, 581
        577, 581, 582
        578, 582, 583
        579, 583, 584
        580, 584, 585
        581, 585, 586
        582, 586, 587
        583, 587, 588
        584, 588, 589
        585, 589, 590
        586, 590, 591
        587, 591, 592
        588, 592, 593
        589, 593, 594
        590, 594, 595
        591, 595, 596
        592, 596, 597
        593, 597, 598
        594, 598, 599
        595, 599, 600
        596, 600, 601
        597, 601, 602
        598, 602, 603
        599, 603, 604
        600, 604, 605
        601, 605, 606
        602, 606, 607
        603, 607, 608
        604, 608, 609
        605, 609, 610
        606, 610, 611
        607, 611, 612
        608, 612, 613
        609, 613, 614
        610, 614, 615
        611, 615, 616
        612, 616, 617
        613, 617, 618
        614, 618, 619
        615, 619, 620
        616, 620, 621
        617, 621, 622
        618, 622, 623
        619, 623, 624
        620, 624, 625
        621, 625, 626
        622, 626, 627
        623, 627, 628
        624, 628, 629
        625, 629, 630
        626, 630, 631
        627, 631, 632
        628, 632, 633
        629, 633, 634
        630, 634, 635
        631, 635, 636
        632, 636, 637
        633, 637, 638
        634, 638, 639
        635, 639, 640
        636, 640, 641
        637, 641, 642
        638, 642, 643
        639, 643, 644
        640, 644, 645
        641, 645, 646
        642, 646, 647
        643, 647, 648
        644, 648, 649
        645, 649, 650
        646, 650, 651
        647, 651, 652
        648, 652, 653
        649, 653, 654
        650, 654, 655
        651, 655, 656
        652, 656, 657
        653, 657, 658
        654, 658, 659
        655, 659, 660
        656, 660, 661
        657, 661, 662
        658, 662, 663
        659, 663, 664
        660, 664, 665
        661, 665, 666
        662, 666, 667
        663, 667, 668
        664, 668, 669
        665, 669, 8
        666, 8, 670
        667, 670, 671
        668, 671, 672
        669, 672, 673
        670, 673, 674
        671, 674, 675
        672, 675, 676
        673, 676, 677
        674, 677, 678
        675, 678, 679
        676, 679, 680
        677, 680, 681
        678, 681, 682
        679, 682, 683
        680, 683, 684
        681, 684, 685
        682, 685, 686
        683, 686, 687
        684, 687, 688
        685, 688, 689
        686, 689, 690
        687, 690, 691
        688, 691, 692
        689, 692, 693
        690, 693, 694
        691, 694, 695
        692, 695, 696
        693, 696, 697
        694, 697, 698
        695, 698, 699
        696, 699, 700
        697, 700, 701
        698, 701, 702
        699, 702, 703
        700, 703, 704
        701, 704, 705
        702, 705, 706
        703, 706, 707
        704, 707, 708
        705, 708, 709
        706, 709, 710
        707, 710, 711
        708, 711, 712
        709, 712, 713
        710, 713, 714
        711, 714, 715
        712, 715, 716
        713, 716, 717
        714, 717, 718
        715, 718, 719
        716, 719, 720
        717, 720, 721
        718, 721, 722
        719, 722, 723
        720, 723, 724
        721, 724, 725
        722, 725, 726
        723, 726, 727
        724, 727, 728
        725, 728, 729
        726, 729, 730
        727, 730, 731
        728, 731, 732
        729, 732, 733
        730, 733, 734
        731, 734, 735
        732, 735, 736
        733, 736, 737
        734, 737, 738
        735, 738, 739
        736, 739, 740
        737, 740, 741
        738, 741, 742
        739, 742, 743
        740, 743, 744
        741, 744, 745
        742, 745, 746
        743, 746, 747
        744, 747, 748
        745, 748, 749
        746, 749, 750
        747, 750, 751
        748, 751, 752
        749, 752, 753
        750, 753, 754
        751, 754, 755
        752, 755, 756
        753, 756, 757
        754, 757, 758
        755, 758, 759
        756, 759, 760
        757, 760, 761
        758, 761, 762
        759, 762, 763
        760, 763, 9
        761, 9, 764
        762, 764, 765
        763, 765, 766
        764, 766, 767
        765, 767, 768
        766, 768, 769
        767, 769, 770
        768, 770, 771
        769, 771, 772
        770, 772, 773
        771, 773, 774
        772, 774, 775
        773, 775, 776
        774, 776, 777
        775, 777, 778
        776, 778, 779
        777, 779, 780
        778, 780, 781
        779, 781, 782
        780, 782, 783
        781, 783, 784
        782, 784, 785
        783, 785, 786
        784, 786, 787
        785, 787, 788
        786, 788, 789
        787, 789, 790
        788, 790, 791
        789, 791, 792
        790, 792, 793
        791, 793, 794
        792, 794, 795
        793, 795, 796
        794, 796, 797
        795, 797, 798
        796, 798, 799
        797, 799, 800
        798, 800, 801
        799, 801, 802
        800, 802, 803
        801, 803, 804
        802, 804, 805
        803, 805, 806
        804, 806, 807
        805, 807, 808
        806, 808, 809
        807, 809, 810
        808, 810, 811
        809, 811, 812
        810, 812, 813
        811, 813, 814
        812, 814, 815
        813, 815, 816
        814, 816, 817
        815, 817, 818
        816, 818, 819
        817, 819, 820
        818, 820, 821
        819, 821, 822
        820, 822, 823
        821, 823, 824
        822, 824, 825
        823, 825, 826
        824, 826, 827
        825, 827, 828
        826, 828, 829
        827, 829, 830
        828, 830, 831
        829, 831, 832
        830, 832, 833
        831, 833, 834
        832, 834, 835
        833, 835, 836
        834, 836, 837
        835, 837, 838
        836, 838, 839
        837, 839, 840
        838, 840, 841
        839, 841, 842
        840, 842, 843
        841, 843, 844
        842, 844, 845
        843, 845, 846
        844, 846, 847
        845, 847, 848
        846, 848, 849
        847, 849, 850
        848, 850, 851
        849, 851, 852
        850, 852, 853
        851, 853, 854
        852, 854, 855
        853, 855, 856
        854, 856, 857
        855, 857, 10
        856, 10, 858
        857, 858, 859
        858, 859, 860
        859, 860, 861
        860, 861, 862
        861, 862, 863
        862, 863, 864
        863, 864, 865
        864, 865, 866
        865, 866, 867
        866, 867, 868
        867, 868, 869
        868, 869, 870
        869, 870, 871
        870, 871, 872
        871, 872, 873
        872, 873, 874
        873, 874, 875
        874, 875, 876
        875, 876, 877
        876, 877, 878
        877, 878, 879
        878, 879, 880
        879, 880, 881
        880, 881, 882
        881, 882, 883
        882, 883, 884
        883, 884, 885
        884, 885, 886
        885, 886, 887
        886, 887, 888
        887, 888, 889
        888, 889, 890
        889, 890, 891
        890, 891, 892
        891, 892, 893
        892, 893, 894
        893, 894, 895
        894, 895, 896
        895, 896, 897
        896, 897, 898
        897, 898, 899
        898, 899, 900
        899, 900, 901
        900, 901, 902
        901, 902, 903
        902, 903, 904
        903, 904, 905
        904, 905, 906
        905, 906, 907
        906, 907, 908
        907, 908, 909
        908, 909, 910
        909, 910, 911
        910, 911, 912
        911, 912, 913
        912, 913, 914
        913, 914, 915
        914, 915, 916
        915, 916, 917
        916, 917, 918
        917, 918, 919
        918, 919, 920
        919, 920, 921
        920, 921, 922
        921, 922, 923
        922, 923, 924
        923, 924, 925
        924, 925, 926
        925, 926, 927
        926, 927, 928
        927, 928, 929
        928, 929, 930
        929, 930, 931
        930, 931, 932
        931, 932, 933
        932, 933, 934
        933, 934, 935
        934, 935, 936
        935, 936, 937
        936, 937, 938
        937, 938, 939
        938, 939, 940
        939, 940, 941
        940, 941, 942
        941, 942, 943
        942, 943, 944
        943, 944, 945
        944, 945, 946
        945, 946, 947
        946, 947, 948
        947, 948, 949
        948, 949, 950
        949, 950, 951
        950, 951, 11
        *Nset, nset=_PickedSet2, internal, generate
        1, 951, 1
        *Elset, elset=_PickedSet2, internal, generate
        1, 950, 1
        ** Section: SteelBeam Profile: Profile-1
        *Beam Section, elset=_PickedSet2, material=Steel, temperature=GRADIENTS, section=RECT
        0.05, 0.03
        0.,0.,-1.
        *End Part
        **
        **
        ** ASSEMBLY
        **
        *Assembly, name=Assembly
        **
        *Instance, name=Part-1-1, part=Part-1
        *End Instance
        **
        *Nset, nset=_PickedSet6, internal, instance=Part-1-1
        1,
        *Nset, nset=_PickedSet8, internal, instance=Part-1-1, generate
        1, 951, 1
        *Elset, elset=_PickedSet8, internal, instance=Part-1-1, generate
        1, 950, 1
        *Nset, nset=_PickedSet9, internal, instance=Part-1-1
        11,
        *End Assembly
        **
        ** MATERIALS
        **
        *Material, name=Steel
        *Density
        8050.,
        *Elastic
        2e+11, 0.3
        **
        ** BOUNDARY CONDITIONS
        **
        ** Name: BC-1 Type: Displacement/Rotation
        *Boundary
        _PickedSet6, 2, 2
        ** Name: BC-3 Type: Displacement/Rotation
        *Boundary
        _PickedSet8, 1, 1
        _PickedSet8, 3, 3
        _PickedSet8, 4, 4
        ** Name: BC-4 Type: Displacement/Rotation
        *Boundary
        _PickedSet9, 2, 2
        ** —————————————————————-
        **
        ** STEP: Frequency Extraction
        **
        *Step, name=”Frequency Extraction”, nlgeom=NO, perturbation
        *Frequency, eigensolver=Lanczos, sim=NO, acoustic coupling=on, normalization=displacement
        15, , , , ,
        **
        ** OUTPUT REQUESTS
        **
        *Restart, write, frequency=0
        **
        ** FIELD OUTPUT: F-Output-1
        **
        *Output, field, variable=PRESELECT
        **
        *MATRIX GENERATE, STIFFNESS, MASS
        *MATRIX OUTPUT, STIFFNESS, MASS, FORMAT=MATRIX INPUT
        *End Step

  • Hello all,

    first of all a big thank you for the explanation about exporting mass and stiffness matrices. I have created a beam with a fixed restraint and deposited steel as material model.Works great.
    Works great. For a student research project I need the mass and stiffness matrices for a body that consists of a hyperelastic model. The instructions for exporting the matrices also work for this.

    The only problem is that at the beginning a number of entries is zero. As an example: A beam consists of 53 nodes, so I get in the TXT file for the mass matrix in the format(coordinate) 424 entries, of which they are the first 106 entries zero, so

    1 1 0
    2 2 0
    .
    .
    .
    106 106 0
    After that, the entries are shifting from zero, so in the end there are 318 entries different from zero (53 nodes a 6 degrees of freedom = 318 entries).
    so
    107 107 x
    .
    .
    .
    424 424 y

    My question now is, what do the first 106 entries in which there is a zero mean? The mass and stiffness matrix is to be read into MatLab afterwards. Only zeros on the main diagonal are not advantageous, if the matrix has to be inverted. As element type currently C3D4H is used.

    I hope someone has a tip. Thanks a lot !

    Greetings
    Zemos

    Translated with http://www.DeepL.com/Translator (free version)

    • Hi Zemos,
      Sorry about late reply, I was focusing on my qualifying exams. I did not use C3D4H element before and am not sure what are the zeros. I would suggest to output the matrices in matrix input format FORMAT=MATRIX INPUT, and then you will know where the zeros locate, at which node and which dof. Hope this helps.

  • Dear Dorothy’s world
    First of all i want to thank you for your blog , you helped me a lot with some problems i found in ABAQUS.
    i have a question and i Don’t find the ansewer in the internet , can you tell me how do we extract the modeshapes vector in a frequency analysis in Abaqus ?
    I need this vector to do calculation with it.
    thank you very much for your answer
    Regards,

    • Hi Nina,
      As far as I know, abaqus does not output the mode shape vectors automatically. But you can output filed variables (displacements) at each node, then you need to process the data to get it into the format you want. You can output the displacements in Visualization module – creating XY data, then select unique nodal and all the nodes. Hope this helps.

  • Hello, Dorothy
    Thank you for sharing great tips!
    I wonder how to lump mass matrix for shell element.
    So that I’m going to try your method in the case of Abaqus/Explicit, but as you mentioned in note 2.
    This code does not work in Abaqus/Explicit. Do you have any idea about it?
    I need a lumping mass matrix for the shell element. I think that if I could make a lumping mass matrix for modal. or implicit dynamics analysis, your code may work.

    Thank you.
    Regards.

    • Hi Seokmin,
      I am not sure why the codes do not work in Abaqus/Explicit. I searched the official documents and also online, but got no answer.
      I think you are exactly correct about how to get lumping mass matrix for the shell element. Since the mass matrix is a property of structure, you can definitely try from modal analysis.
      Hope this helps.
      Bests.

  • Hi Dorothy,

    I generated mass matrix by Abaqus, but it has nonzero off diagonal values.
    I need to get lumped mass matrix with nonzero values only at the diagonal.
    In Ansys I can turn Lump on and that produces a lumped diagonal mass matrix, but I do not know how to do that in Abaqus.

    • Hi Gokay,
      The default mass matrix in Abaqus is consistent mass matrix. I used point mass for beam elements in order to get lumped mass matrix. I am not sure if there is a similar convenient way as in Ansys (I did not find in official guides). If you are using beam elements, point mass is a good choice. Hope this helps.

  • Hi Dorothy,

    Your blog is very informative, thank you for sharing your experiences.

    In my case, I have a complex 3D model in Abaqus. Since there are very thin parts in my model, I modeled the structure using solid and shell sections.

    I defined some parts of the structure as solids and some parts as shells. After I got the mass matrix, I saw that mass matrix is not diagonal.

    Normally, if I only used 3D solid parts, I would have a 3n*3n diagonal mass matrix because it would have 3 DOFs at each node.

    But now that I’m using both solid and shell structures, the mass matrix is ​​a non-diagonal matrix. How do I find out the total number of nodes and DOFs? What order is there? Which node has 3 DOFs, which has more or less DOFs?

    P.S. I did not use point mass or inertia etc. I just defined the material properties as usual.

    • Thank you Zafer.
      Consistent mass matrix is default in Abaqus, and you used material properties in your model, so you will have off-diagonal elements in mass matrix.
      From my understanding, the 3D solid element will have 6 dofs at each node, including the three rotation dofs, and the number of dofs in shell element depends on the particular element.
      For detailed number of dofs, you can check the element description in Abaqus Analysis User’s Guide.
      You can use select Tools, then Query to check the nodes and elements. To get the total number of nodes or elements, creating a set and then query the set (also select tools and then query) would be a better option.
      The order of node number depends on the order of meshing, but I did not investigate this in detail. I usually use matlab or python to postprocess the node or element data.

  • Hi Dorothy,

    In Abaqus, we can easily see the node numbers by doing the following: View tab–> Assembly display option–>Mesh–>Show node labels.
    However, I would like to see the DOF numbers. When we generate mass and stiffness matrices, what we get is:
    1.Row node label
    2.Degree of freedom for row node
    3.Column node label
    4.Degree of freedom for column node
    5.Matrix entry

    How can I figure out the DOF numbers in the corresponding node numbers?

  • Hi Dorothy,
    In Abaqus, we can easily see the node numbers by doing the following: View tab–> Assembly display option–>Mesh–>Show node labels.

    However, I would like to see the DOF numbers. When we generate mass and stiffness matrices, what we get is:
    1.Row node label
    2.Degree of freedom for row node
    3.Column node label
    4.Degree of freedom for column node
    5.Matrix entry

    How can I figure out the DOF numbers in the corresponding node numbers?
    In my case I have both solid and shell elements. Therefore, there are 3DOF for the solid sections and 6DOF for the shell sections.

    Let’s think together. I want to see the DOF number at node 8 in solid element. Since the DOF numbers for the solid elements are 3n-2,3n-1,3n, they become 22 23 24.
    Same logic.
    I want to see the DOF number at node 4 in the shell element. Since the DOF numbers for the shell elements are 6n-5,6n-4,6n-3,6n-2,6n-1,6n, so they become 19 20 21 22 23 24.

    As you can see here, it’s very confusing to me.

    How can I understand DOF numbers? Since I am implementing Bloch Theory in Abaqus I need corresponding individual DOF numbers for each node.

    • Hi Gokay,
      The dof number could only be 1 to 6 or 1 to 3 depending on the element type. It won’t become 3n-2, 3n-1 or 3n.
      Let’s see one example “1,5, 1,1, 9.283850055777577e-12”. The number 9.283850055777577e-12 is at the matrix row node 1 dof 5 and column node 1 dof 1.
      I think you might need to check a finite element analysis book to see what the elements in a stiffness/mass matrix mean and how to assemble the element matrices into global matrix. These would definitely help you understand the stiffness matrix in abaqus.

      • Hi Dorothy,

        Thank you for your answer. I think I explained it wrong. Let me get this straight.
        The dof number could only be 1 to 6 or 1 to 3 depending on the element type. It is definitely correct and I agree with you.
        For example, the dof number for node 1 would be 1 to 3. (Because the dof number 1 to 3 for solid element).
        So here we can see that n=1(node ​​number), the number of dof should be 3n-2.3n-1.3n. What I mean here is that when we put n=1 into the 3n-2,3n-1,3n equation, we can get 1,2,3 dof numbers.

        This is just a representation. For example, the dof number for node 2 would be 4 to 6. (Because the dof number 1 to 3 for each node). When we put n=2 into the 3n-2,3n-1,3n equation, we can get 4,5,6 dof numbers.

        Same logic applies to shell elements.

        If we have a shell elemet, the dof number should be 1 to 6. For example, the dof number for node 1 would be 1 to 6. (Because the dof number 1 to 6 for shell element).
        So here we can see that n=1(node ​​number), the number of dof should be 6n-5. 6n-4, 6n-3. 6n-2. 6n-1. 6n.
        So, the dof number for node 1( assume node 1 is a shell element), would be 1 to 6. What I mean here is that when we put n=1 into the 6n-5. 6n-4, 6n-3. 6n-2. 6n-1. 6n equation, we can get 1,2,3,4,5,6 dof numbers.

        I think everything is clear so far.

        My previous question was that:
        Let’s assume, I want to see the DOF number at node 8 in solid element. The dof number for the solid element could only be 1 to 3. If I want to see the dof number at node 8 in solid element, the dof number should be 22,23,24 (They come from the 3n-2,3n-1,3n equation. I explained it above).

        Same logic.
        I want to see the dof number at node 4 in shell element. The dof number for the shell element could only be 1 to 6. If I want to see the dof number at node 4 in shell element, the dof number should be 19 20 21 22 23 24. (They come from the 6n-5,6n-4,6n-3,6n-2,6n-1,6n equation. I explained it above).

        As you can see here I have some common DOF numbers used for solid and shell elements. How can I understand which is which?

        • Hi Gokay,
          I did not notice your comment until I got notification for a new one. Sorry about that.
          I now understand what you mean by the equations, the row/column number in the global matrix. You are right about this.
          When there are two or more nodes from different elements, we have the original numbers of dofs (for example you used 6 dofs for one node in shell element). We will then have constraints for the dofs since they have the same displacement or rotation (for example some dofs from the node connecting two elements), which means the displacements or rotations in the u vector are the same (as we all know Ku=F).
          Hope this helps.

  • Hi,
    Thanks for the nice detailing of all the steps.
    I have some queries. I am getting global stiffness matrix but some row and column entries are missing in the matrix. For example
    1 1
    1 2 are there

    but 3 2
    2 3 are not there in the matrix.

    Then without knowing 3 2 and 2 3, how I can form the square mass and stiffness matrix. Without knowing the square mass and stiffness, we cannot do eigen value analysis. Please help.

    • Thank you Kundan 🙂
      The missing ones have a value of zero, and abaqus only outputs those with non-zero values.
      You may safely initialize the matrix with all zeros and then write the elements with values from the output.
      Hope this helps.

  • I have more than one beam model which includes also material damping as alpha and beta coefficient. I used substructure in model. I can obtain reduced mass & stiffness Matrix in .mtx format for substructure. (*Substructure Matrix output, file format= user defined, stiffness=yes, mass=yes)
    But I can’t obtain reduced damping Matrix for substructure. How I can obtain?

    • Hi Keser,
      I did not output matrix for substructure before. I checked the keyword *Substructure Matrix output and it does not contain parameter damping. But since you are using Rayleigh damping, you can postprocess by [C] = alpha*[M] + beta*[K].
      Hope this helps.

      • Yes, I am using Rayleigh damping. How can I postprocess by [C] = alpha*[M] + beta*[K] ? The below part is our model which causes “unknown parameter damping error”.
        *Heading
        *Preprint, echo=NO, model=NO, history=NO, contact=NO
        ** —————————————————————-
        **
        ** PART INSTANCE: PART-1-1
        **
        *Node
        1, 4430.37988, 0.452399999, 1533.67004
        31682, 2463.63989, -873.503662, 726.17688
        170918, 2470.02173, -974.755737, 673.070801
        170919, 2470.02173, -1088.12451, 550.050293
        170920, 2470.02173, -1151.9021, 406.909515
        170921, 2470.02173, -1199.73962, 228.377731
        170922, 2468.96899, -1247.5, 50.1334686
        170923, 1494.91553, -1247.5, 50.1450768
        170924, 4070.02173, -1247.5, 50.1334686
        170925, 4386.68311, -1247.5, 50.1334686
        170926, 4070.02173, -1213.12708, 178.415192
        170927, 4070.02173, -1178.69702, 306.909515
        170928, 4070.02173, -1114.69446, 450.396088
        170929, 4070.02173, -999.773132, 574.43866
        170930, 4070.02173, -852.961121, 652.136353
        170931, 4070.02173, -695.734131, 677.5
        170932, 4070.02173, -656.299744, 677.5
        170933, 2463.63721, 873.432861, 726.134338
        170934, 2470.0188, 974.682312, 673.023376
        170935, 2470.01831, 1088.04517, 549.997314
        170936, 2470.01807, 1151.8158, 406.853455
        170937, 2470.01807, 1199.64453, 228.319321
        170938, 2468.96509, 1247.39624, 50.0727463
        170939, 1494.9115, 1247.39319, 50.0843544
        170940, 4070.01782, 1247.40137, 50.0727463
        170941, 4386.6792, 1247.40234, 50.0727463
        170942, 4070.01807, 1213.03455, 178.35614
        170943, 4070.01807, 1178.61084, 306.852142
        170944, 4070.01831, 1114.61523, 450.341827
        170945, 4070.01855, 999.699951, 574.389954
        170946, 4070.01904, 852.891724, 652.094849
        170947, 4070.01953, 695.666016, 677.466125
        170948, 4070.01978, 656.231567, 677.468079
        170949, 4430.37988, 0.452399999, 1533.67004
        *Element, type=B31H
        146235, 31682, 170918
        146236, 170918, 170919
        146237, 170919, 170920
        146238, 170920, 170921
        146239, 170921, 170922
        146240, 170922, 170923
        146241, 170922, 170924
        146242, 170924, 170925
        146243, 170924, 170926
        146244, 170926, 170927
        146245, 170927, 170928
        146246, 170928, 170929
        146247, 170929, 170930
        146248, 170930, 170931
        146249, 170931, 170932
        146250, 170934, 170933
        146251, 170935, 170934
        146252, 170936, 170935
        146253, 170937, 170936
        146254, 170939, 170938
        146255, 170938, 170937
        146256, 170940, 170938
        146257, 170941, 170940
        146258, 170942, 170940
        146259, 170943, 170942
        146260, 170944, 170943
        146261, 170945, 170944
        146262, 170946, 170945
        146263, 170947, 170946
        146264, 170948, 170947
        146265, 31682, 170933
        146266, 170932, 170948
        *Elset, elset=PART-1-1_PART-1-1_SET-13
        146240, 146241, 146242, 146254, 146256, 146257
        *Elset, elset=PART-1-1_PART-1-1_SET-14
        146235, 146236, 146237, 146238, 146239, 146243, 146244, 146245, 146246, 146247, 146250, 146251, 146252, 146253, 146255, 146258
        146259, 146260, 146261, 146262
        *Elset, elset=PART-1-1_PART-1-1_SET-15
        146248, 146249, 146263, 146264, 146265, 146266
        *Elset, elset=PART-1-1_Set-4
        146240, 146241, 146242, 146254, 146256, 146257
        *Elset, elset=PART-1-1_Set-5
        146235, 146236, 146237, 146238, 146239, 146250, 146251, 146252, 146253, 146255, 146265
        *Elset, elset=PART-1-1_Set-6
        146243, 146244, 146245, 146246, 146247, 146248, 146249, 146258, 146259, 146260, 146261, 146262, 146263, 146264, 146266
        ** Region: (Ön-Çapraz:Set-5), (Beam Orientation:PART-1-1_SET-14)
        *Elset, elset=PART-1-1__I1
        146235, 146236, 146237, 146238, 146239, 146250, 146251, 146252, 146253, 146255
        ** Section: Ön-Çapraz Profile: Profile-Ön-Çapraz
        *Beam Section, elset=PART-1-1__I1, material=MATERIAL-1, temperature=GRADIENTS, section=PIPE
        40., 2.5
        0.,0.,-1.
        ** Section: Yatay Profile: Profile-Yatay
        *Beam Section, elset=PART-1-1_Set-4, material=MATERIAL-1, temperature=GRADIENTS, section=PIPE
        37., 2.
        0.,0.,-1.
        ** Region: (Arka-Çapraz:Set-6), (Beam Orientation:PART-1-1_SET-14)
        *Elset, elset=PART-1-1__I3
        146243, 146244, 146245, 146246, 146247, 146258, 146259, 146260, 146261, 146262
        ** Section: Arka-Çapraz Profile: Profile-Arka-Çapraz
        *Beam Section, elset=PART-1-1__I3, material=MATERIAL-1, temperature=GRADIENTS, section=PIPE
        33., 2.5
        0.,0.,-1.
        ** Region: (Arka-Çapraz:Set-6), (Beam Orientation:PART-1-1_SET-15)
        *Elset, elset=PART-1-1__I4
        146248, 146249, 146263, 146264, 146266
        ** Section: Arka-Çapraz Profile: Profile-Arka-Çapraz
        *Beam Section, elset=PART-1-1__I4, material=MATERIAL-1, temperature=GRADIENTS, section=PIPE
        33., 2.5
        0.,0.,-1.
        ** Region: (Ön-Çapraz:Set-5), (Beam Orientation:PART-1-1_SET-15)
        *Elset, elset=PART-1-1__I5
        146265,
        ** Section: Ön-Çapraz Profile: Profile-Ön-Çapraz
        *Beam Section, elset=PART-1-1__I5, material=MATERIAL-1, temperature=GRADIENTS, section=PIPE
        40., 2.5
        0.,0.,-1.
        *System
        *Elset, elset=LG, generate
        146235, 146266, 1
        *Nset, nset=MASTER_NODE
        170949,
        *Elset, elset=PART-1-1_SET-3
        146240, 146254
        *Elset, elset=PART-1-1_SET-4
        146241, 146256
        *Elset, elset=PART-1-1_SET-5
        146242, 146257
        *Elset, elset=PART-1-1_SET-6
        146239, 146243, 146255, 146258
        *Elset, elset=PART-1-1_SET-7
        146238, 146244, 146253, 146259
        *Elset, elset=PART-1-1_SET-8
        146236, 146237, 146245, 146246, 146251, 146252, 146260, 146261
        *Elset, elset=PART-1-1_SET-9
        146235, 146247, 146250, 146262
        *Elset, elset=PART-1-1_SET-10
        146235, 146247, 146248, 146250, 146262, 146263
        *Elset, elset=PART-1-1_SET-11, generate
        146264, 146266, 1
        *Elset, elset=PART-1-1_SET-12
        146248, 146249, 146263, 146264, 146265, 146266
        *Nset, nset=PART-1-1__PICKEDSET18
        170922,
        *Nset, nset=PART-1-1__PICKEDSET19
        170919,
        *Nset, nset=PART-1-1__PICKEDSET20
        170919,
        *Nset, nset=PART-1-1__PICKEDSET21
        31682,
        *Nset, nset=PART-1-1__PICKEDSET22
        170938,
        *Nset, nset=PART-1-1__PICKEDSET23
        170935,
        *Nset, nset=PART-1-1__PICKEDSET24
        170935,
        *Nset, nset=PART-1-1__PICKEDSET25
        170933,
        *Nset, nset=PART-1-1__PICKEDSET26
        170924,
        *Nset, nset=PART-1-1__PICKEDSET27
        170929,
        *Nset, nset=PART-1-1__PICKEDSET28
        170929,
        *Nset, nset=PART-1-1__PICKEDSET29
        170930,
        *Nset, nset=PART-1-1__PICKEDSET30
        170940,
        *Nset, nset=PART-1-1__PICKEDSET31
        170944,
        *Nset, nset=PART-1-1__PICKEDSET32
        170944,
        *Nset, nset=PART-1-1__PICKEDSET33
        170946,
        *Nset, nset=SET-4
        170922, 170924, 170938, 170940
        *Nset, nset=SLAVE_NODES
        170918, 170930, 170934, 170946
        *Nset, nset=Set-32
        170922, 170924, 170938, 170940
        *Nset, nset=SLAVE_NODES_CNS_
        170918, 170930, 170934, 170946
        *Surface, type=NODE, name=SLAVE_NODES_CNS__CNS_
        SLAVE_NODES_CNS_, 1.
        ** Constraint: CONSTRAINT-1
        *Coupling, constraint name=CONSTRAINT-1, ref node=MASTER_NODE, surface=SLAVE_NODES_CNS__CNS_
        *Distributing, weighting method=LINEAR, coupling=STRUCTURAL
        **
        ** MATERIALS
        **
        *Material, name=MATERIAL-1
        *Damping, alpha=0.1, beta=0.05
        *Density
        2.78e-09,
        *Elastic
        71016., 0.33
        ** —————————————————————-
        **
        ** STEP: Modal
        **
        *Step, name=Modal, nlgeom=NO, perturbation
        *Steady State Dynamics, direct, friction damping=NO
        0., 300., 2,
        **
        ** OUTPUT REQUESTS
        **
        **
        ** FIELD OUTPUT: F-Output-2
        **
        *Output, field, variable=PRESELECT
        **
        ** HISTORY OUTPUT: H-Output-1
        **
        *Output, history, variable=PRESELECT
        *End Step
        ** —————————————————————-
        **
        ** STEP: Substructure
        **
        *Step, name=Substructure, nlgeom=NO
        *Substructure Generate, overwrite, type=Z8789, recovery matrix=YES, nset=MASTER_NODE, mass matrix=YES,
        structural damping matrix=YES, viscous damping matrix=YES
        *Damping Controls, structural=COMBINED, viscous=COMBINED
        **
        ** BOUNDARY CONDITIONS
        **
        ** Name: Fixed Type: Displacement/Rotation
        *Boundary
        Set-32, 1, 1
        Set-32, 2, 2
        Set-32, 3, 3
        Set-32, 4, 4
        Set-32, 5, 5
        Set-32, 6, 6
        *Retained Nodal Dofs, SORTED=NO
        MASTER_NODE, 1, 6
        *SUBSTRUCTURE MATRIX OUTPUT, OUTPUT FILE=USER DEFINED, FILE NAME=Matrix, MASS=YES, STIFFNESS=YES, DAMPING=YES
        *End Step

        • Hi Keser,
          The “unknown parameter damping error” appears since the keyword *Substructure Matrix output does not have parameter damping.
          You may use matlab or python to postprocess [C] = alpha*[M] + beta*[K]. Form a matrix and fill the corresponding element location with the value you got from the output. Then you can do the matrix operation to get [C].
          In the output matrix, you may need to check the node number and dof number to locate the value. But since you are using the substructure matrix, the output format might be different. This web page and the links in it might help.

          • Thanks for comments. What if I used a dashpot element in our model? How can obtain dashpot element damping parameter instead of Rayleigh damping?

          • Hi Keser,
            Sorry for late replay, I was focusing on my finals. I do not have the experience with dashpot element, but I checked the document here and found dashpots cannot be used within substructures. The document recommends to define Rayleigh damping within the substructure definition or on the usage level to create damping within a substructure. So dashpots are not suitable for your case.
            Hope this helps.

          • Thanks for explanation. I tried to use Rayleigh damping also. Mu question is that exporting damping matrix in substructure. How can I extract/export reduced damping Matrix? Which type of word is needed for input file?

          • Hi Keser,
            As I explained before, no damping parameter is available in the keyword *Substructure Matrix output. So I would recommend to get the damping matrix by postprocessing from the mass matrix and stiffness matrix [C] = alpha*[M] + beta*[K]. Please check the previous replay for more details.
            Hope this helps.

  • Hi Dorothy,
    I also added damping=yes in “.inp” file. But I got error “invalid parameter damping”. So, I don’t understand the error😕

  • how does one extrat the eigen vectors directly from abaqus?

  • Hi Dorothy,
    I need to extract the mass and stiffness matrices for a model with the following problem size:

    P R O B L E M S I Z E
    NUMBER OF ELEMENTS IS 249191
    153326 linear line elements of type T3D2
    84141 linear hexahedral elements of type C3D8R
    102 linear line elements of type B31
    11613 linear quadrilateral elements of type S4R
    NUMBER OF NODES IS 267444
    NUMBER OF NODES DEFINED BY THE USER 267240
    NUMBER OF INTERNAL NODES GENERATED BY THE PROGRAM 204
    TOTAL NUMBER OF VARIABLES IN THE MODEL 837207
    (DEGREES OF FREEDOM PLUS MAX NO. OF ANY LAGRANGE MULTIPLIER
    VARIABLES. INCLUDE *PRINT,SOLVE=YES TO GET THE ACTUAL NUMBER.)

    The properties are input as mass density, and I believe they will be used to generate a consistent mass matrix.

    Here’s the input file code I used:
    ** Global Mass and Stiffness matrix
    *Step, name=Export matrix
    *MATRIX GENERATE, STIFFNESS, MASS, VISCOUS DAMPING, STRUCTURAL DAMPING
    *MATRIX OUTPUT, STIFFNESS, MASS, VISCOUS DAMPING, STRUCTURAL DAMPING, FORMAT=coordinate

    I have the following questions regarding my problem:

    Dimensions of M and K matrices
    As indicated above, the number of degrees of freedom is 837,207, but the matrix dimensions are reduced to 354,231*354,231. Shouldn’t the number of degrees of freedom match the matrix dimensions?

    Node numbering
    The model consists of 8 parts, and the nodes start from 1 for each part. However, when I extract the matrices using the FORMAT=matrix input option, a different node numbering system (1 to 241,751) is applied, making it difficult to match the entries to the actual model locations. How can I find the correspondence between the entries in the M and K matrices and the nodes in the model?

    In the coordinate format, I get 5,620,189 rows of data, while in the matrix input format, I get 2,987,210 rows of data. Shouldn’t the number of data entries be the same in both cases?

    When using the matrix input format, the entries are extracted in the following format:
    241751,3, 241751,3, 9.038200770026704e+00
    Can I interpret the corresponding data as follows?
    1: X (translational)
    2: Y (translational)
    3: Z (translational)
    4: RX (rotational)
    5: RY (rotational)
    6: RZ (rotational)

    The modes obtained from modal analysis in ABAQUS CAE GUI and the eigenanalysis results obtained from extracting the M and K matrices and performing the Lanczos method in MATLAB do not match. Is there any way to reconcile them?

    • Hi Chan,
      1) Dimensions of M and K matrices: the matrix dimension should be the total number of dofs in the model theoretically (I am not sure how you got 837,207). It is possible to have a matrix dimension less than this since you used a format of coordinate for output and abaqus will eliminate some zero elements. You might use MATRIX INPUT format instead so that you have the node number and dof in the rows. Then you can easily verify the dimensions.
      2) Node numbering: Honestly I am not sure how to renumber the nodes, but to my best knowledge it is not possible unless you use a python script. Abaqus is not available to me after my graduation, so I cannot help with this. Post processing might also be an option to find the correspondence between the entries in metrices.
      3) Interpreting of element 241751,3, 241751,3, 9.038200770026704e+00 in matrix: row node label, dof for row node, column node label, dof for column node, matrix entry. The last number is the actual element in a matrix, and the first four numbers indicate the location of the element in the matrix.
      4) Reconcile eigen analysis results: when you have the correct matrices from abaqus (you may need to assemble the matrix with a script or compare only the eigenvalues and resemble the eigenvectors), and the results should be very close.
      Hope these could help.

    • Hi Chan, did you get the answer, I am also facing the same issue with my model. The Abaqus and Matlab frequency do not match and not able to understand the obtained matrix from Abaqus.

  • Hi Dorothy,
    have you found a way to extract stiffness matrix, mass matrix for explicit dynamic problem, I am currently stuck on this.
    Thanks and Regards
    Aazim Shafi

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