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The model is a car-body resting on four coil springs and four viscous dampers. The dampers have zero length why their symbols look like small green circles.
This example consists of a car-body named car_1
supported by four springs kmcb11r, kmcb11l, kmcb12r and kmcb12l
and four dampers cmcb11r, cmcb11l, cmcb12r and cmcb12l.
The following data are valid:
|mc=||50e3 [kg]||#||Weight of car-body|
|kzcb=||500e3 [N/m]||#||Vertical stiffness of coil-springs|
|czcb=||30e3 [Ns/m]||#||Damping coefficient in vertical dampers|
Eigenfrequency of vertical bounce mode can be calculated as:
Relative damping for the vertical bounce mode can be calculated as:
In current example the vertical bounce mode was found to have an eigenfrequency of 1.01 [Hz] with a relative damping of 19.0 %.
Make a quasi-static calculation by running file runf/car_body_quasi.quasif in program QUASI.
The coil-springs have only a stiffness in vertical direction and no pre-stress force. Earth gravity makes the car-body to fall until the coil-springs responds with the weight of the car-body. Program QUASI will find the position of the car-body where the forces in all coil-springs equals the weight of the car-body.
In command accel local_all the user defines the magnitude of earth gravity. As default it is set equal to 9.81[m/s2].
On standard output program quasi writes the vertical equilibrium position and the forces in all coil-springs:
Func print06_quasi kmcb11r.F2z = 1.22625E+05 Func print06_quasi kmcb11l.F2z = 1.22625E+05 Func print06_quasi kmcb12r.F2z = 1.22625E+05 Func print06_quasi kmcb12l.F2z = 1.22625E+05 Func print06_quasi car_1.z = 2.45250E-01
The weight of the car-body is 50e3*9.81[N]. Distributed on four springs, which gives a vertical load of 122625[N] per spring.
The spring stiffnesses are 500e3[N/m] per spring, which leads to a vertical compression of 0.24525[m] for all springs.
Make a time-domain simulation by running file runf/car_body_tsim.tsimf in program TSIM.
In runf/car_body_tsim.tsimf the car-body is excited by a sinusoidal motion of the ground.
Make a modal analysis of the car-body by running file runf/car_body_modal.modalf in program MODAL. In runf/car_body_modal.modalf the coil-springs are modeled with coupling coupl k3_l_preZ which means that the vertical pre-stress forces are calculated automatically, therefore in this case there is need to make an initial calculation with program QUASI
|id/car_body_modal.id||MPdat-file for plotting in MPLOT|
|gp/car_body_modal.gp||GPdat-file for animation in GPLOT|
|calcmod/car_body_modal.mode||mode-file containing all eigenvalues|
|calcmod/car_body_modal.modf||modf-file containing all eigen forms|
|calcmod/car_body_modal.modjac||modjac-file for linear analysis|
Make a frequency responce analysis by running file runf/car_body_fresp.frespf in program FRESP. In runf/car_body_fresp.frespf the car-body is excited by a white noise spectra from ground.
|ground.z||Real part of the vertical position, body ground|
|ground.vz||Imaginary part of the vertical position, body ground|
|car_1.z||Real part of the vertical position, body car_1|
|car_1.vz||Imaginary part of the vertical position, body car_1|
|ground.bz||Absolute value of the vertical position, body ground|
|ground.pz||Phase angle of the vertical position, body ground|
|car_1.bz||Absolute value of the vertical position, body car_1|
|car_1.pz||Phase angle of the vertical position, body car_1|