Rider Stiffness (Motorcycle)

[HDFEA]

Hello,
I am trying to model the rider and passanger on a full-vehicle motorcycle FE model. I am representing them as lumped masses at their appropriate c.g.'s and want to hook them up to the vehicle so that during acceleration loading (braking), their masses will load the vehicle appropriatly. I am thinking of hooking the rider up to the handlebars (right and left side), as well as the footboards (right and left side). The passanger I will hook up to the passanger footboards (right and left side and the area of the seat that he/she touches). How do you model the stiffness of the person into the vehicle? I am currently using very soft 3-d springs so that I don't artificially stiffen the structure. Is this appropriate? I am just trying to distribute their masses into the vehicle properly. Any suggestions?

 

[GregLocock]

In the absence of a better answer - I'd pin joint the body to the seat, and then model the arms to give about 75mm of motion under 1 g acceleration.



Cheers

Greg Locock

 

[EnglishMuffin]

It seems to me that the problem with assigning stiffnesses to the human body is that it is an active system (while alive) and can have varying stiffnesses depending on how our brain tells our muscles to behave. The one exception to this is that it is very poor at resisting torsion under any circumstances, which is also true of most other living things. I have never ridden a motorcycle, so I probably have no business answering this thread. But I have ridden a bicycle, and I have witnessed a motorcycle accident up close at an intersection in which the rider was thown from his mount and landed in the road right in front of my stationary car. On the basis of this, I would argue that you should model the body as a linkage capable of sustaining gravity and inertia loads, with the hands pivoted to the handlebars, and with the forarms, upper arms and torso as one connected rigid link. The upper body would be connected to the seat (in the vertical direction only) with a gap element (if you are using FE or something similar), or its equivalent. The lower legs and thighs would then be pivoted to the torso and footrests. Under this scenario, under static conditions the weight of the legs is mostly carried by the footrests, and the weight of the upper body and arms is mostly carried by the seat. Under acceleration or braking, the load on the seat and footrests would then be respectively increased or decreased. In this simplified representation, there would be no forward or rearward relative motion between the riders buttocks and the seat during acceleration or braking. If you could estimate the amount of such relative motion, assuming it occurs in practice, you could then allow for it in the model by introducing some flexibility in the arm-upper body pivot such that the model matches reality. I'm not quite sure what happens during cornering, never having ridden a motorcycle, but there is presumably a transverse force between the rider and machine which has to be resisted somehow. Is this achieved by buttocks-to-seat friction, or the arms , the legs, or all three I wonder ? I do believe, to a first degree of approximation, that the rider's upper arm and forearm should be considered as rigidly connected, based on what happens in a frontal crash. This certainly seems to be true in some race car crashes, judging by what often happens to the steering wheel in such cases.