04patran nastran教程513g加密所属kafeimao msc官方.pptxVIP

;TABLE OF CONTENTS;We have seen that the Eigenvectors that we calculate in a Normal Modes Analysis are independent of each other and are arbitrarily scaled. Until we apply some kind of loading – either transient or frequency response, then it is very difficult to predict which modes will play a dominant part in a structure. One way we can help predict what are the important modes is to use a technique called Modal Participation Factor. We know that linear combinations of Eigenvectors can be assembled to make arbitrary shapes. In this case we say that the shape to be made is a Rigid Body Vector in the direction of response we are interested in. The Rigid Body Vector is DR And we assume where e is a vector of scaling factors on the eigenvectors F, i.e. a set of Participation Factors.;Pre Multiply by FTM: Where Mii is the diagonal matrix of generalized masses for each mode I The term FTMDR is commonly known as the Participation Factor. The scaling factor ei is then a scaling on the generalized mass Mii to achieve the Participation Factor. We can also define a ‘rigid body’ mass Mr in a similar way to a generalized mass as But So;So the contribution which each mode provides to the rigid body mass Mr is as Mii is a diagonal matrix This is known as the modal effective mass. If we Mass Normalize the so participation Factor is e, Modal Effective Mass is e2 The modal effective weight is modal effective mass factored by g in the appropriate units.;The command has the following form: Examples: MEFFMASS MEFFMASS(GRID=12, SUMMARY,PARTFAC) Describers Meaning PRINT Write output to the print file. (Default) NOPRINT Do not write output to the print file. PUNCH Write output to the punch file. NOPUNCH Do not write output to the punch file. (Default) gid Reference grid point for the calculation of the Rigid Body Mass Matrix. SUMMARY Requests calculation of the Total Effective Mass Fraction, Modal Effective Mass Matrix, and the A-Set Rigid Body Mass Matrix. (Default);De