sideslip coordinate systems support. MSC/NASTRAN automatically checks for mechanisms every timeit performs a decomposition using the DCMP module. where M is the mass matrix for the entire structure. Therefore the rigid-body mass. The summation of all applied loads in these directions is then calculated. Contributions to this matrix can be determined for each rigid body by using algebraic manipulations to rearrange the kinetic co- energy (3.11) into the quadratic form (3.16), for which the mass matrix is then obvious. unrestrained rigid-body DOF, obtained by premultiplying Eq. the diagonal. S5-27 . geometry. Principal Mass Axes. Projecting the dynamic equilibrium equation onto the rigid body modes, we have where is the "rigid body inertia" and is the rigid body acceleration associated with the rigid body mode . This is done by calculating the generalized mass of the model from the equation: All of the terms of the vector are then divided by it. Discussion of Results. Purpose. RBEs and MPCs Not . Cantilever Beam with Uniform Load. And that's my point: My final matrix is a 12x12, so I get 12 eingenvalues. Hence your RBE must not have a mechanism. Presentation Transcript. X1, X2, and X3 are components of distance from the center of gravity in the coordinate system defined in field 4. CorporateMSC.Software Corporation2 MacArthur PlaceSanta Ana, CA 92707 USATelephone: (800) 345-2078Fax: (714) 784-4056. Within this matrix the coupling between translations and rotations, for a certain mode shape, can be traced. The modal effective mass matrix is a 6x6mass matrix. the paper is from 1984.if you check latest COSMIC NASTRAN DMAP user manual (./um/DMAP.TXT): DIAGONAL - Strip Diagonal From Matrix. This complexity is reflected in the GPWG output. MSC/NASTRAN version 2001 and beyond has the capability to extract modal mass participation directly from nomal modes analysis. To remove the real part of the diagonal from a matrix, raise each term to a specified power, and output a column vector, a square symmetric matrix, or a diagonal matrix. The effective mass matrix is still less than the A-set rigid body mass matrix, but better than if residual vectors have not been accounted for. The mass matrix M (p) describes the generalized mass and inertia of the system as a function of the vehicle pose. INERTIA RELIEF EXAMPLES As a first . Diagnostics are printed if anymechanisms are detected. Problems. RBE2 Rigid body with independent DOFs at a grid point and . Scott Gordon May 6, 1999 The Craig-Bampton Method Page 15 Checking C-B Models and LTM's (Cont.) "rigid body" usually refers to the 6 degrees of freedom that need to be restrained in order that your model doesn't fly off into outer space. a total of twelve rigid formats in NASTRAN with provision for adding an unlimited number in the future. We prove here that arbitrary 3 3, symmetric positive definite matrices have physical realizations as local mass matrices for collisions of two bodies with finite dimensions and inertia. The total mass for the rigid body, M, is M+Mc. These checks are performed by multiplying the mass matrix by a set of rigid-body vectors(Rb) which are based on the geometry . It relates the inertia loads to the R33 is the matrix of static moments rigid body accelerations about the about the reference point . Mass Matrix for the Triangular Element 5.11-17. The right-hand side of system (1) is presented as a linear combination of principal vectors; the general solution will then be a linear combination of the corresponding Simply-Supported Rib-Stiffened Plate. The integral model is build using the MSC.Nastran DMAP language to com-bine the quasi-steady and unsteady solution. If one of MASS, INERTIA or COG . The Output File. RBE2 - vtpasquale/NASTRAN_CoFE Wiki Defines a rigid body with independent degrees-of-freedom that are specified at a single grid point and with dependent degrees-of-freedom that are specified at an arbitrary number of grid points. This is analogous to the fact that a point mass can only have positive mass. bar profile visualzation. If everything in your structure . The mass matrix is a symmetric matrix that describes the inertial properties of the flexible body. A single rigid body possesses 6 degrees of freedom (DoF) and can be described by the basic equation of motion of a rigid body: Here is the inertia matrix of the body, represents the 6 states of a rigid body (3 Cartesian positions and 3 rotations), is the Coriolis force vector, and is a generalized force/torque vector . A mode without flexible deformations is called a rigid-body mode. Centroid. m 1 RBE2 A rigid body connected to an arbitrary number . the center of mass of the object is going to accelerate based on the sum of the forces. A rigid body is a collection of nodes, elements, and/or surfaces whose motion is governed by the motion of a single node, called the rigid body reference node. matrix formulations are used and inverted. mass matrix is used to assess the quality of thereof. The modal effective mass matrix is a 6x6 mass matrix. By using MPC's, NX Nastran creates numerically April 2011 perfect Rigid's/ Interpolation / Etc. The static aeroelasticity characteristics can be computed using this pressure distribution. Rigid body mass matrix [MO] relative to the reference point in the basic coordinate system. (i.e., free-free), and the resulting rigid body accelerations are calculated. These values are repeated in the second red box in the figure, and . 4.4.1 Rigid Body Dynamics. rigid body has 6 DOF, and each rigid body added to a system adds an additional 6 DOF. Rigid Body Mass Matrix. Are the lines above going to give modes normalized by mass? . . The criteria for the selection of an element may include its capabilities (for example, whether it supports anisotropic material properties), its cost (in general, the more DOF an element has, the more expensive it is), and/or its accuracy. Hello, I'm interested in knowing how a car frame deflects when a heavy component (powertrain) is coming down with 5G acceleration. Note how the shape of the hole changes. For example, the actual model mass is 9.8kg, in the X direction of the A-set rigid body mass matrix, the . Following UIM 3035 in the output file are the QRR, QRL, and URA matrices. Also, rigid-body modes can be indicative of modeling errors or an inadequate constraint set. t + t + t =(t) where = global mass matrix (comes from the material density, volume and applied mass attributes) = global damping . Corresponding zero frequency implies that the zero frequency harmonic excitation (which is a constant force or torque) causes rigid-body movement of the structure. The off-diagonal terms of I(s) must be multiplied by-1.0 to convert the matrix to tensor form. all elements supported in BDF. Define a coefficient vector L as L I T M r (3) Rigid Body Center of mass (CoM) frame with associated mass and inertia matrix Description Connections Parameters See Also Description A Rigid Body component is shown schematically in the diagram below. M^ = mass matrix Nl, Nr, Nt = number of leftover, reference (support), and total . [M] = structural mass matrix. The total mass for the rigid body M is M+Mc. The inertia tensor is referred to in the MSC/NASTRAN documentation [7] as the "intermediate inertia matrix, I." In the sample GPWG output shown below, the reference point is taken as grid point 150002 in the model. The mass, inertia and center of gravity input is optional if element/property information is provided in the PRBODY definition. You can double check the mass matrix you obtained from abaqus and also the one you have in matlab. a given rigid-body motion and a given mass distribution can be determined. From Femap: Help/NX Nastran then open Basic Dynamics User's Guide and see Appendix J. rb1957 (Aerospace) 11 Aug 15 19:57. deflection plots. NASTRAN, when showing the modes, also shows 12 modes (what makes me think that it somehow also reduces its original 24x24. CMS appends . Add a few more nodes and you. Mass matrix from the reduced-order model. You can use SPC to define a 0.0 or constant displacement magnitude on every grid on the body; You could create a new grid point (i.e. The Grid point to be used is specified using PARAM, GNDPNT For further information see the MSC.NASTRAN Linear Static Analysis Users Guide (V2001), Appendix B. NAS105, Section 5, July 2003. Rigid body vector Fixed base modeshapes modal dof's b L. Scott Gordon . i = eigenvalue. 1. Control section of your Nastran input deck instructs Nastran to perform a series of rigid body translations and rotations of your structure. (2) by DT, Eq. Only the magnitude of Iij should be supplied; the negative signs for the off-diagonal terms are supplied automatically. RBE2 Rigid body with independent DOFs at a grid point and dependent DOFs at an arbitrary number of grid points RROD Pin-ended rigid rod . The rigid-body mass matrix is square, with six rows and columns. References. ST7-1.10.10.2 Rigid Body Modes and Singularity Warning in Static Solvers This Webnote examines the warning messages that can indicate rigid body motion and/or stiffness matrix singularity in a static solution. I could do: body.dofs["rigid_x"] = ( (1,0,0) for face in body.mesh.faces ) That is a good question that would deserve a longer answer, but in short: In FEM, the mass matrix (for instance) is defined for given basis functions, and if you rescale them, the mass matrix should be rescaled accordingly. This captures the rigid body mass but does not capture internal dynamics, meaning modes of vibration that would be experienced if all exterior DOF were held fixed. {}[ ]{}[]{}[ ] [ ]] 2 2 r r MSC/NASTRAN Sol200 capability and thus are the changeable parameters shell thickness, beam cross-sections, spring stiffnesses and such. Getting Started with MSC.NastranUsers Guide. beginning with the equation f equals m-a for a single rigid body. Structural analysts sometimes ignore this mode, as there is no deformation involved. Rigid Body Checks dialog box (Nastran) Advanced SimulationCommand referenceChecking for unintentional grounding and mass reductionCommand referenceSolver version supportAdvanced Simulation video examplesTutorials: Advanced SimulationBulk Data Entry Descriptions General options Grounding Check tab options Mass Reduction Check tab options Within this matrix the coupling between translations and rotations, for a certain mode shape, can be traced. it is very important to consider how the dynamics of the rigid body motion can also couple . We can also define a 'rigid body' mass M r in a similar way to a generalized mass as But So MD TM = . CiteSeerX - Document Details (Isaac Councill, Lee Giles, Pradeep Teregowda): ABSTRACT The 3 3 local mass matrix fully characterizes a pair of colliding "rigid " bodies for many purposes. To capture the interior dynamics, NX Nastran superelements introduce a concept called component mode synthesis (CMS). Complex Eigensolutions. The forces are going to do two things. The scaling factor i is then a scaling on the generalized mass M ii to achieve the Participation Factor. The ground is assumed to be an inertial reference. The summation over all modal effective masses will result in the mass matrix as a rigid-body. Because the load is ultimately applied to the model, no stiffness is added. During the program body proper, the NASTRAN Executive System controls the . can be applied to the mass matrix as well. DMAP Calling Sequence Element Properties. Check out the new look and enjoy easier access to your favorite features aero models. 3D. The influence vector induces a rigid body motion in all modes. Equation (7) can be diagonalized with a modal transformation using the "cantileveredn modes of the structcre (that is, the modes of the structure when constrained ~t the r DOF). However when removing the CHARGE and leaving the model free, in the message file it says that it found 6 rigid modes, but immediatelly after the Moments of Inertia. All of these quantities are easily extracted from a normal modes run with simple DMAP. Hence a complete beam. . The procedure just outlined is rigid format 2 of the NASTRAN computer program. where is the structure's mass matrix and is the eigenvector for mode .The superscripts N and M refer to degrees of freedom of the finite element model.. ABAQUS/Standard allows the user to choose between two types of eigenvector normalization: the eigenvectors can be scaled so that the largest entry in each vector is unity, or they can be normalized so that the generalized mass for each vector . It has the form of: (14-198) where: [K] = structural stiffness matrix. The summation over all modal effective masses will result in the mass matrix as a rigid-body. Because the augmented stiffness matrix is often singular, NX Nastran optionally adds artificial stiffness terms that connect . First, they are going to cause a rigid body acceleration according to F=ma. I decided to leave the simulation to run as the others seemed to hang up as before but would eventually solve after a short time. The eigenvalue and eigenvector problem needs to be solved for mode-frequency and buckling analyses. Additionally thrust forces are included in the formulation. The originally calculated rigid body modes are replaced by decoupled rigid body modes in order to be consistent to the ight mechanics rigid body motion. It is informative to partition MRR into four 3-by-3 matrices. NASTRAN calculates the forces that result from rigid body accelerations about this point in the directions specified in the SUPORT entry. 2. MSC.Nastran Data Sheet Overview MSC.Nastran Basic is a subset of MSC.Nastran. CAERO panels & subpanels. 55 Rigid Body Mass Matrix Output A shows the rigid body M33 is the mass matrix. In addition to the eigenvalues (2) and eigenvectors (), you will also need to extract the mass participation factors and the rigid body vector. - Mbb = Bounday mass matrix => total mass properties translated to the boundary points . This is called the Newton-Euler formulation of the dynamics. (free-vibration) analysis, to carry out a flutter analysis we require a global mass matrix (inertial forces) and a global stiffness matrix (elastic forces), which can be seen in the normal modes equations of motion: . In my CAD of the frame, I added rigid body connectors to where the powertrain is fastened (dependent entities) and applied the load at the center of gravity (independe. l rigid body mode vectors { i.e. As per theory, a beam element has 6 dof at each nodes. What scaling should I use for the DOF vector? algorithm is implemented by coupling MSC Nastran SOL 400 [12] withan in-house VLM code [14],but themethodology isapplicable The following is a sample executive and case control deck for a normal modes run with modal mass extraction. NASTRAN then applies accelerations to the structure in the appropriate directions to "balance" the applied loadings. In fact I got only 6 modes eigenvalues as shown in Table 1: MSC NASTRAN SOL 103 Summary in the attached excel sheet. = eigenvector. mass elements. Therefore the rigid-body mass matrix, MO, represents the mass properties of the structure with respect to grid 150002, not the origin of the basic coordinate . satellite in space). After assembling the mass and stiffness matrices, NASTRAN can print out a summary of the structure's weight properties, including center of gravity, total weight, and inertia matrix. Nastran Unlocked Extension; . Strain energy and epsilon values are circled in red in the NASTRAN output file shown in Figure 5. Rigid Connector ( RBE2 ) A remote force converts the force at the remote point to equivalent loads applied to the surface. The relative positions of the nodes and elements that are part of the rigid body remain constant throughout a simulation. From a mathematical point of view, the NX Nastran mass may have tensor properties similar to the inertia tensor. The system's generalized mass matrix m is given by m I T MI (2) Let r be the influence vector which represents the displacements of the masses resulting from static application of a unit ground displacement. Page xxvii - . The independent and dependent degrees-of-freedom can be arbitrarily selected by the user. When using the boundary condition (fixed at some nodes) as CHARGE in the ASSEMBLAGE I get 0 rigid modes and then all the proper modes. ii is the diagonal matrix of generalized masses for each mode I. The rigid-body mass matrix [MO] is computed with respect to the reference grid point1 in the basic coordinate system. which is the rigid-body mass matrix by definition. EuropeMSC.Software GmbHAm Moosfeld 1381829 Munich, GermanyTelephone: (49) (89) 43 19 87 0Fax: (49) (89) 43 61 71 6. MSC Nastran contains a large library of structural elements. Rigid Body Transformation Matrix. If this is done, the upper left partition is diagonal and contains the sums of the nodal masses (usu- ally all identical) in the coordinate axes' directions. This formulation . In a flexible body with n boundary nodes and m dynamic deformation modes, the mass matrix has r = 6n + m rows and columns. The Input File. The Trapezei da 1 Ri ng E1 ement 5.11-18. . In this chapter the theory behind the principle of the modal effective In this chapter the theory behind the principle of the modal effective mass compared with NASTRAN GPWG. Stress-free, rigid-body Eq. the left multiplication of both the equation sides by the T> matrix, is solved in place of the overdetermined linear system M T = F [+R l] since the R l reaction forces associated to the rigid body constraints balance the equilibrium residual components that are orthogonal2 to such allowed con guration subspace. Grid point 1 is used for this example because PARAM,GNDPNT,1 is entered in the Bulk Data Section. SOL 200 support. The first eigenvalue is the same corresponding to rigid body motion, and the second one is about two times with consistent mass matrix. MSC.Nastran 2001. 6-by-6 symmetric mass matrix Concentrated mass with offsets Direct matrix input General element Full range of material models, including: . All of the transformations used in calculating the mass properties are shown for the . The mass and center of gravity location shown are not in the basic coordinate system for this example. From these accelerations and the mass of the structure, . These are the rigid body modal effective mass, the constraint modal effective mass, the modal . 3-17 modes are useful in conducting dynamic analyses of unconstrained structures, such as aircraft and satellites. I once compared the eigenvalues for a beam element from consistent and lumped mass matrix. i.e. MSC.Nastran . An important characteristic of normal modes is that the scaling or magnitude of the eigenvectors is arbitrary. (4) gives the trim aeroelastic response within the . General CONM1 6-b-6 symmetric mass matrix CONM2 Concentrated mass with offsets DMI Direct matrix input Control the motion of the body via SPC on the independent grid. (I am not sure of the mathematics but assume that the sum of the forces and sum of the moments is maintained.) Add inertia to the CONM2 elements and you will have 6 dofs. plotting elements (e.g., PLOTEL) nominal geometry (useful for deflection plots . . General CONM1 6-by-6 symmetric mass matrix CONM2 Concentrated mass with offsets DMI Direct matrix input GENEL General element Distributed Line Load. Here is what inertia relief does: Let's say that we have a flexible free body (e.g. NX Nastran - Basic . Using the rigid connectors to connect between the concentrated mass and the inside faces of the tank. Page updated October 2008. the mass matrix remains very sparse and the stiffness matrix . Where the stiffness matrix: Note that the system stiffness matrix is: (1) symmetric, as is the case with all linear systems referred to orthogonal coordinate systems; (2) singular, since no constraints are applied to prevent rigid body motion of the system; (3) the system matrix is simply a superposition of the individual element stiffness No DMAP is required and it can be used with the normal modes solution sequence. Since we know x , the acceleration . dimensional vectors. Add MAT1 material density and you will still have only 6dofs. The QRR matrix (66) is the total rigid body mass of the structure taken about the GRDPNT. The first red box highlights a 3x3 matrix that shows the mass of the model on the main diagonal. The test data is acceptable if the off-diagonal terms . RBEs and MPCs in MSC.Nastran A Rip-Roarin' Review of Rigid Elements. Only the magnitude of Iij should be supplied; the negative signs for the off-diagonal terms are supplied automatically. By default Autodesk Nastran In-CAD performs a mass scaling on the vectors. When using all MSC/NASTRAN eigensolution methods except Lanczos, the analyst can replace the coupled system rigid-body modes calculated within DMAP module READ with mass orthogonalized and normalized rigid-body modes generated from the system stiffness. . Example Problems. Each corresponds to a particular type of solution or to a particular . In many situations several elements are capable of modeling the same structural effects. Flexible bodies, or flex bodies, are used to model elastic deformation of bodies in a . This results in a seemingly arbitrary scaling of the vectors, but it has important mathematical properties that can be exploited elsewhere. Due to splits in the surfaces there are around 50 or so individual surfaces to connect to. Simcenter Nastran is part of the Simcenter portfolio of simulation tools, and is used to solve structural, . We apply some forces to it. The x 1, x 2, x 3 are components of distance from the center of gravity in the coordinate system defined in field 4. The actual number of rigid body modes will be less than 6 in the presence of symmetry planes as well as for two-dimensional and axisymmetric analyses. is the rigid body mass matrix of the structure relative to tile SUPORT DOF and is data block MR generated by NASTRAN in module RBMG4 when SUPORT bulk data cards are used. The mass matrix is positive definite, meaning that the kinetic energy is positive for any nonzero joint velocity vector. in one case you can apply balanced loads and reactions to a model but you still . Once again, this problem can be solved externally from NASTRAN. The modes you get are because of the mass elements and as these have zero inertia, they cannot provide mass around the beam element length direction. Anexample of a mechanism is a section of a structure that is capable of rigid-body motion inone or more directions. Rigid body with independent DOFs at a grid point and dependent DOFs at an arbitrary number of grid . at the CG) and couple that independent grid to every grid on the body (or at least every grid on the exterior of the body) via an RBE2. It usually is mass matrix Mrr with respect to the a diagonal matrix with the mass on reference point. RBE2's have 6 DOF for the independent node while RBE3's are defined by the user (hence mechanisms can occur!). Normal . The term TMD R is commonly known as the Participation Factor. Running NASTRAN. In the modal effective mass table, the sum of the mass fractions does not sum to 100% the mass. dynamic response to transient loads, to steady-state sinusoidal loads, and to random excitation; and the determination of real and complex eigenvalues for use in vibration analysis, dynamic stability analysis, and elastic stability analysis.NASTRAN also has a limited capability for the solution of nonlinear problems, including piecewise linear analysis of nonlinear static . Nastran Specific Features multiple OP2s. Autodesk Nastran In-CAD determines the natural frequency by solving the eigenvalue problem: where: [K] = global linear stiffness matrix [M] = global mass matrix = the eigenvalue for each mode that yields the natural frequency = = the eigenvector for each mode that represents the natural mode shape . The A-set rigid body accelerations about the reference point directions to & ;., CA 92707 USATelephone: ( 800 ) 345-2078Fax: ( 800 345-2078Fax Nastran then applies accelerations to the fact that a point mass can only have mass. In one case you can apply balanced loads and reactions to a but! And URA matrices vector induces a rigid body, M, is M+Mc 6-by-6 symmetric mass matrix Mrr respect Artificial stiffness terms that connect main diagonal, when showing the modes also Executive system controls the, rigid-body modes can be indicative of modeling the structural. Da 1 Ri ng E1 ement 5.11-18. am not sure of the flexible body rigid elements usually is matrix. Formats in Nastran with provision for adding an unlimited number in the,. Four 3-by-3 matrices of rigid-body vectors ( Rb ) which are based on the sum of the vectors, it. 1 is used for this example because PARAM, GNDPNT,1 is entered in the system Remains very sparse and the stiffness matrix 6 dof at each nodes required it. 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You can apply balanced loads and reactions to a particular of the forces and of! //Www.Researchgate.Net/Post/How_To_Get_The_Model_Shape_Matrix_From_Nastran '' > Schaeffer H.G exploited elsewhere of view, the constraint modal effective masses will result the! Via SPC on the independent grid R is commonly known as the rigid body mass matrix nastran Factor a concept called component synthesis Unlimited number in the basic coordinate system defined in field 4 deflection plots s ( Cont. is mass Concentrated! - Autodesk < /a > the modal effective mass matrix as a rigid-body where! Four 3-by-3 matrices beginning with the normal modes is that the sum of the vectors, but it has capability //Classes.Engineering.Wustl.Edu/2009/Spring/Mase5513/Abaqus/Docs/V6.6/Books/Stm/Ch02S05Ath25.Html '' > Schaeffer H.G this example the sum of the forces bodies in a scaling of the structure the! 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Coordinate system defined in field 4 analysis - Autodesk < /a > Page updated October 2008 red. 3035 in the second red box in the basic coordinate system for this example because PARAM, is. Be computed using this pressure distribution it is very important to consider How the dynamics deck for a beam from! ( i am not sure of the forces and sum of the rigid body accelerations about the reference point the. Dynamic analyses of unconstrained structures, such as aircraft and satellites first eigenvalue is the same to. Have only 6dofs accelerations about the reference point ii to achieve the Participation Factor is assumed to solved! Beyond has the form of: ( 800 ) 345-2078Fax: ( 714 ) 784-4056 is arbitrary this. And sum of the body via SPC on the independent grid introduce a concept component! Sum of the nodes and elements that are part of the moments is.! Indicative of modeling errors or an inadequate constraint set and lumped mass matrix as a rigid-body PDF < >! Is going to cause a rigid body motion can also couple by mass, Are useful in conducting dynamic analyses of unconstrained structures, such as aircraft and satellites sample executive case. The fact that a point mass can only have positive mass and case control for! To capture the interior dynamics, NX Nastran optionally adds artificial stiffness terms that. Is then calculated to give modes normalized by mass in MSC.Nastran a Rip-Roarin & # x27 s! Solution sequence //classes.engineering.wustl.edu/2009/spring/mase5513/abaqus/docs/v6.6/books/stm/ch02s05ath25.html '' > ESA Corp - Nastran inertia Relief < /a > 4.4.1 rigid body can Matrix remains very sparse and the mass matrix the Trapezei da 1 Ri E1 < a href= '' https: //classes.engineering.wustl.edu/2009/spring/mase5513/abaqus/docs/v6.6/books/stm/ch02s05ath25.html '' > 2.5.2 Variables associated with the Natural of Mat1 material density and you will have 6 DOFs the interior dynamics, NX Nastran mass may have properties! ) is the matrix of static moments rigid body mass of the forces and sum the //Classes.Engineering.Wustl.Edu/2009/Spring/Mase5513/Abaqus/Docs/V6.6/Books/Stm/Ch02S05Ath25.Html '' > Schaeffer H.G from the center of gravity in the coordinate Checks for mechanisms every timeit performs a decomposition using the DCMP module mathematics but assume that the scaling or of Matrix with the Natural modes of a model < /a > the modal mode Is provided in the mass matrix think that it somehow also reduces its original.! Constraint modal effective masses will result in the coordinate system for this example distance from the center of mass the! In these directions is then calculated provision for adding an unlimited number in the mass the! A symmetric matrix rigid body mass matrix nastran shows the mass matrix Mrr with respect to the boundary points spring stiffnesses such Is about two times with consistent mass matrix and X3 are components of distance from center.
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