Introduction

Using Adams/Vibration – Adams2Nastran (A2N) feature, you can define the operating point at which exporting the Mass, Stiffness and Damping matrices of the full linearized model and then performing Nastran modal or frequency response analysis: the operating point has been achieved running Adams/Solver, taking into account all the nonlinearities of the system and with the possibility to easily change any parameter or variable for exploring different model configuration and, consequently, to easily recreate full Nastran equivalent model. The Mass, Stiffness and Damping matrices are exported as Nastran DMIG and connected to the system using MPC (Multi Point Constraint) while the location of input channels and output channels (Adams Markers) are exported as Nastran GRIDs and generalized degrees of freedom as SPOINTs.

The following image displays the work flow, starting from an Adams model and getting the Nastran bdf file for Complex Modal Analysis (SOL 107) and Frequency Response Analysis (SOL 108):

To implement the procedure, the MKB (Mass, Stiffness, Damping) system is recovered by Adams/Linear function.

(1)

A Plant Input and a plant output have to be defined to input and output channels, which correspond to u and y respectively in equation (1). The current Adams2Nastran approach requires velocities for output channels, som the feed forward term, D matrix, can be neglected. Then, equation (1) can be written as 1st order differential equation like as follows.

(2)

(3)

where:


:	Displacement of part coordinates
:	Displacement of states
	Displacement of marker coordinates
:	Force to part coordinates
	Force to marker coordinates

Equation (2) can be transformed to 2nd order differential equation.

(4)

(5)

The variable x and M, B and K matrices in equation are expressed by SPOINT and DMIG respectively. A plant input and plant output are always defined on same degree of freedoms, thus P equals the transpose of C; consequently equation (3) can be written as follows.

(6)

A degree of freedom of xm and fm is modeled by GRID, and MPC (Multi Point Constraint) are used to express the relationship between GRID and SPOINT in equation .

Typical analysis (SOL 101: static analysis; SOL 103: modal analysis) into Nastran could not be performed because they require symmetric matrices. DMIG matrices can be not symmetric ones: a customized DMAP has been developed for symmetrization of not symmetric matrices and it has been made available for Nastran users in the Adams2Nastran installation directory.

Full details about the symmetrization procedure can be found in Symmetrization of Not Symmetric matrices paragraph.