About HM, Flexible bodies

Hi Lokesh,

Can you point me to the statement for

1) To converting rigid bodies into flexible bodies in hypermesh opti, Why we are going for modal analysis?

 

i am asking why we are going for modal analysis to convert the rigid bodies into flexible bodies

thank you

If you mean Rigid body modes from the Modal analysis,  let me explain what a rigid body mode is. 

A rigid body mode is the free translation and rotation of a body with no deformation. If you have a rigid body it is not possible to calculate internal responses for applied external loads. 

I hope this helps. 

ok sir but my actual doubt is why we are going for modal analysis to convert rigid bodies into flexible bodies ?

Thank You

Modal analysis does not convert a rigid body to flexible body. 

Hi LOKESH KATARI,

you are probably referring to Flexible body generation using the CMS modeling technique, integrated with multibody analysis if the model is set up in OptiStruct for multibody dynamics.

This method uses linear superposition of modes computed using the Component Mode Synthesis (CMS) method. Several variants of CMS exist, each attempting to accurately capture the deformations and boundary conditions with a minimum number of modes. A CMS-based flexible body contributes degrees of freedom equal to the number of CMS modes in addition to the six degrees of freedom associated with the rigid body motion. This body is able to handle small or linear deformations only.

If you are interested in theoretical background refer to the attached file.

Unable to find an attachment - read this blog

Hi LOKESH KATARI,

 

you are probably referring to Flexible body generation using the CMS modeling technique, integrated with multibody analysis if the model is set up in OptiStruct for multibody dynamics.

 

This method uses linear superposition of modes computed using the Component Mode Synthesis (CMS) method. Several variants of CMS exist, each attempting to accurately capture the deformations and boundary conditions with a minimum number of modes. A CMS-based flexible body contributes degrees of freedom equal to the number of CMS modes in addition to the six degrees of freedom associated with the rigid body motion. This body is able to handle small or linear deformations only.

 

If you are interested in theoretical background refer to the attached file.

 

 

Non-Linear Finite Element (NLFE) body:

This method uses the “Absolute Nodal Coordinate Formulation” to obtain a fully non-linear finite element representation of the flexible component. As the name suggests, this body is defined with respect to the global frame and does not have a local part reference frame like the linear flexible body. Each flexible component can be made up of several finite elements that represent flexibility in the component. Similar to traditional finite elements, this flexibility is determined by the geometric and material data specified for the elements. The NLFE body allows you to model geometric non-linearity (large deformations) as well as material non-linearity (hyper-elastic materials like rubber). Current support for the NLFE body is limited to BEAM and CABLE elements only. These elements are useful in modeling long, slender structures.

Since this representation is fully non-linear, no reduction analysis (like CMS) is required to create this body – the body can be created and modified entirely within MotionView/Optistruct without the need for any FE solver based pre-processing. For more information on the NLFE body, refer to the Body: Flexible modeling component.

If this is what you are looking for, CMS is not a modal analysis and this can be used in structural analysis as well. To learn more, please refer to Finite Element Analysis (Superelements)

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hai sir 

can u help me in calculating the stiffness of a body in hypermesh optistruct ?

Thank You

Please refer to this tutorial. OS-T: 2070 Reduced Model using DMIG

. To extract the Global Stiffness and Global Mass Matrices you could activate PARAM, EXTOUT,DMIGPCH this helps in printing the matrices in ASCII.pch files. 

hello

pch file is creating but how to see the matrix 

its showing long rows ?

pls help with this

DMIGPCH will output PCH which can be used in subsequent analysis. 

Please let us know what you are looking for?

i am looking for stiffness

Actually  I want to study the Stiffness matrix in CBN and CB Method by taking chassis and creating ASET points and using CMSMETH card 

load step is generic process, i gave  DMIGPCH  card for stiffness output and also i am not giving any card to create h3d file

Now i want to check whether the stiffness Matrix is coming same for both the methods i.e CBN and CB methods..!!

Is my process correct ?

please help me with this

Awaiting reply

Thank You

Actually  I want to study the Stiffness matrix in CBN and CB Method by taking chassis and creating ASET points and using CMSMETH card 

load step is generic process, i gave  DMIGPCH  card for stiffness output and also i am not giving any card to create h3d file

Now i want to check whether the stiffness Matrix is coming same for both the methods i.e CBN and CB methods..!!

 

Is my process correct ?

please help me with this

Awaiting reply

Thank You

Actually  I want to study the Stiffness matrix in CBN and CB Method by taking chassis and creating ASET points and using CMSMETH card 

load step is generic process, i gave  DMIGPCH  card for stiffness output and also i am not giving any card to create h3d file

Now i want to check whether the stiffness Matrix is coming same for both the methods i.e CBN and CB methods..!!

Is my process correct ?

please help me with this

Awaiting reply

Thank You

Hi Lokesh,

If you are looking for global stiffness, OptiStruct will not write the global stiffness matrix. 

Okay sir then what is that .PCH file ? what does it mean?

It is the stiffness matrix of the GRIDs of interest defined through ASET card. 

okay thank you for clarifying

will there be any stiffness matrix difference in CBN and CB method?