wikifemfuchde2019:lez

mentat2013.1 -ogl -glflush

Inertia relief and dynamic loadcases theory

Embodiment of the vector shape functions constituting the $\underline{\underline{S}}$ matrix columns.

*FSAE-like chassis*

model at the end of the previous lesson

Inertial elements

monocoque_chassis_2019_inertial_elements_alone.mud

model as at the end of today's lesson (inertia relief crash deceleration loadcase)

Notes:

The pedagogical model proposed does not include sway/antiroll bars, that are instead a critical element for torsional stiffness loadcases.

In particular, torsional stiffness should be evaluated in both the limiting cases of

This second loadcase, which is usually neglected, is however relevant for sizing the sway bar support areas on the chassis structure.

Static test: torsional stiffness;
- preliminary suspension stroke motion test (original Optistruct tutorial version );
- rigid spring or rigid anti-roll bar?
Front, right wheel bump loadcase (inertia relief);
Frontal crash absorber collapse loadcase (inertia relief); at the element faces belonging to the crash_absorber_bearing_area set (an approx. 155×320 mm area at the front bulkhead), a 25 psi = 0,172 MPa distributed pressure is applied which is due to the honeycomb absorber crushing (see datasheet).
Dynamic modal response;
Dynamic harmonic response: vertical harmonic load at the front, right wheel, 1-100 Hz range, sampled at 0.25Hz resolution ((100-1)*4+1 = 397 steps);

RBE3 link kinematics, in a nutshell:

in the standard configuration, the centroidal C node dof.s are set as dependent, whereas the other $P_i$ nodes in the distribution maintain their independent dof. characterization;
a $q_i$ weight is associated to each $P_i$ node of the distribution, uniformly allotted by default;
the C centroidal node rigidly roto-translates with the distribution COG. G;
the distribution COG. G translational motion is defined by the weighted average $P_i$ nodes translations;
the distribution COG. G rotational motion is defined based on the momentum of the $P_i$ nodes translations.