mentat2013.1 -ogl -glflush
Inertia relief and dynamic loadcases theory
Embodiment of the vector shape functions constituting the $\underline{\underline{S}}$ matrix columns.
monoelem_piastra_motielementari_singolidof.mfd
*FSAE-like chassis*
model at the end of the previous lesson
monocoque_chassis_2019_v004.mud
Inertial elements
monocoque_chassis_2019_inertial_elements_alone.mud
inertially_equivalent_cuboid_engine.ods
inertially_equivalent_cuboid_wheel_assemblies.ods
model as at the end of today's lesson (inertia relief crash deceleration loadcase)
monocoque_chassis_2019_v005.mud
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
- rigid springs, disconnected sway bars;
- disconnected springs, rigid sway bar.
This second loadcase, which is usually neglected, is however relevant for sizing the sway bar support areas on the chassis structure.
Loadcases
- 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_areaset (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);
Connectors
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.
