This special REQUEST allows a user to model a four pole filter within MSC.ADAMS. The filter operates on standard MSC.ADAMS output information to simulate the actual filtering of experimental test data. The filter is modeled by a set of four DIFF statements, which reduce the filter's transfer function to four first order differential equations. Therefore, four DIFF statements are required for each MSC.ADAMS output variable that needs to be filtered. The fourth DIFF statement for each filter model utilizes the user written DIFSUB.
Input:
DIFF/id1, IC=0, FUNC=DIF(id2)
DIFF/id2, IC=0, FUNC=DIF(id3)
DIFF/id3, IC=0, FUNC=DIF(id4)
DIFF/id4, IC=0 , FUNCTION = USER (1101,r1,r2,icd,idi,idj,idr,id1,id2,id3,id4)
REQ/id, FUNCTION = USER (1120,id1)
where:
| id1 | = | identifier of the first DIFF statement | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| id2 | = | identifier of the second DIFF statement | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| id3 | = | identifier of the third DIFF statement | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| id4 | = | identifier of the fourth DIFF statement | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| r1 | = | the cutoff frequency of the filter to be modeled in ertz (see Notes section) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| r2 | = | the capacitance of the filter to be modeled in Farads (see Notes section) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| icd | = | a two digit digital code used to identify the desired information,
which is obtained from MSC.ADAMS and passed through the four pole filter.
The first digit of the code identifies the type of information to be filtered
(i.e. displacement, velocity, acceleration, or force). The second digit
identifies the component (i.e. X, Y, Z, Ax, Ay, or Az).
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| idi | = | identifier of the I MARKER used for requesting information, which passed through the filter | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| idj | = | identifier of the J MARKER used for requesting information, which passed through the filter | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| idr | = | identifier of the Reference MARKER used for requesting information, which passed through the filter | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| id | = | identifier of the MSC.ADAMS REQUEST statement |
Request File Output
Column Number Output:
Notes on Input and Output
It is important to use consistent values for r1 and r2 for a proper functioning filter. This can be accomplished by selecting the cutoff frequency of the filter then selecting the filter capacitance corresponding the cutoff from the table below:
| r1 | r2 |
| Frequency (Hz) | Capacitance (Farads) |
| 8000 | 0.0010 E-6 |
| 6800 | 0.0012 E-6 |
| 4500 | 0.0018 E-6 |
| 3600 | 0.0022 E-6 |
| 2500 | 0.0033 E-6 |
| 1400 | 0.0056 E-6 |
| 800 | 0.0100 E-6 |
| 680 | 0.0120 E-6 |
| 450 | 0.0180 E-6 |
| 360 | 0.0220 E-6 |
| 250 | 0.0330 E-6 |
| 140 | 0.0560 E-6 |
| 80 | 0.1000 E-6 |
| 68 | 0.1200 E-6 |
| 45 | 0.1800 E-6 |
| 36 | 0.2200 E-6 |
| 25 | 0.3300 E-6 |
| 14 | 0.5600 E-6 |
The REQUEST statement shown above contains only one parameter in its call list (aside from the routine number). It is possible to enter up to six DIFF statement id numbers. The first DIFF id entered would cause the output of the DIFF statement to be stored in column 1 of the request file. The second id entered would place the output of the DIFF statement in the second column and so on. This allows a user to write separate filter DIFF statements for say roll angle, yaw rate, etc. but place all (up to six) in one REQUEST statement. In doing so, the size of the request output file is reduced.