Load Determination：荷载的确定.doc

Load Determination:Given:(1) geometry of the object or device is given(2) location of the mass center of each link is given(3) Given input force or momentSolving the Problem:(1) Free-body diagram for each member(2) Setup equations for each memberFor 2D problems:- 2 force equations- 1 moment equationFor 3D problems:- 3 force equations- 3 moment equationsFor static problems:- Sum of forces = 0- Sum of moment = 0For dynamic problems:- Sum of forces = m*a- Sum of moment = I*aVibration Loading:- Finite Element Analysis (FEA)- Boundary Element Analysis (BEA)Undamped Natural Frequency:Period of the natural frequency:Tn = 1/ fnSpring Constant (k):Fs = k * d (for linear spring) k = Fs dWhereFs spring forced deflection of the springDamping Coefficient (d, or C):whereDamped Natural Frequency:(For 1 DOF free or forced vibration) (Free Vibration)rad/sHzDynamic forces: (Avoid Resonance)Impact Loading:- the time of load application is less than half of the period of the natural frequency of the system.(Apply load slowly - static load)(Apply load rapidly - impact load)(1) Striking Impact - actual collision of two bodies. (hammering)(2) Force Impact - suddenly applied load with no velocity of collision. (friction clutches and brakes)Energy Method:Elastic energy:Treat the struck body as spring effect.The impact kinetic energy: (for horizontal impact)whereh correction factor for energy dissipationvi impact velocityTherefore, (dynamic force)Static force: W = k * dstFor vertical impact from a height of h:The impact energy: E = mg (hh + di ) = W (hh + di )Therefore, the dynamic force ratio becomesCorrection Factor for ax