New question #698635 on Yade: https://answers.launchpad.net/yade/+question/698635
Hi, while seeking for solution to Rohit John's problem [1], I got confused by inertia and orientation of clumps. I have found a discussion [2] explaining that: > inertia is defined in the space of principal axes > The orientation is internally stored as a quaternion I modified John's code [1] where he uses eccentricAxisEngine() to pin one of the clumps spheres to create a clump pendulum. The weird thing is that behavior of this pendulum depends on its orientation. To visualize this problem I create two clumps. The first one is aligned along the y axis and oscillates in y-z plane. The second one is aligned along x axis and oscillates in x-z plane. Two observations are odd: 1) For both clumps inertia and orientation are the same. If I understand the convention properly, the orientations should be different ( Quaternion((0,1,0),0) in case of the first clump? ) 2) The two pendulums have different periods of oscillations - the one that is x axis aligned move slower (T=3.4s) while the y axis aligned pendulum has period T=2.5s. I think that may be a potential bug, but I would like to confirm this first. Cheers, Karol [1] https://answers.launchpad.net/yade/+question/698572 [2] https://answers.launchpad.net/yade/+question/274324 # ------------------------------------------------------------------------------------------------------------------------------- YADE SCRIPT from math import * from yade import * from yade import utils, geom from yade import plot # ---------------------------------------------------------------------------------- bodies sph1 = sphere((0, 2, 0), radius=.5) sph2 = sphere(center=(0, 0, 0), radius=.5) sph3 = sphere((2, 5, 0), radius=.5) sph4 = sphere(center=(0, 5, 0), radius=.5) sph1_id = O.bodies.append(sph1) sph2_id = O.bodies.append(sph2) sph3_id = O.bodies.append(sph3) sph4_id = O.bodies.append(sph4) g = Vector3([0,0,-10]) stiffnes = 1e7 # ---------------------------------------------------------------- clumps clump1_id = O.bodies.clump([sph1_id, sph2_id]) clump2_id = O.bodies.clump([sph3_id, sph4_id]) # ---------------------------------------------------------------------------------- engines O.engines = [ ForceResetter(), InsertionSortCollider([Bo1_Sphere_Aabb()]), InteractionLoop( [Ig2_Sphere_Sphere_ScGeom()], # collision geometry [Ip2_FrictMat_FrictMat_FrictPhys()], # collision "physics" [Law2_ScGeom_FrictPhys_CundallStrack()] # contact law -- apply forces ), PyRunner(command = "eccentricAxisEngine()", iterPeriod = 1), PyRunner(command = "addPlotData()", iterPeriod = 100), NewtonIntegrator(gravity=g, damping=0.0), ] # ---------------------------------------------------------------------------------- additional engines def eccentricAxisEngine(): pos_01 = O.bodies[sph2_id].state.pos# anchor clump 1 pos_02 = O.bodies[sph4_id].state.pos# anchor clump 2 force1 = -stiffnes*pos_01 force2 = -stiffnes*(pos_02-Vector3(0,5,0)) O.forces.addF(id = sph2_id, f = force1) O.forces.addF(id = sph4_id, f = force2) def addPlotData(): h1 = O.bodies[sph1_id].state.pos[2] h2 = O.bodies[sph3_id].state.pos[2] plot.addData(t = O.time, m1_height = h1, m2_height = h2) # ---------------------------------------------------------------------------------- sim setup O.dt = .5e-2 * PWaveTimeStep() # plot.plots={'t':('m1_height','m2_height')} plot.plot(subPlots =False) ### print information about clumps print("*************** ORIENTATION OF CLUMP NO 1 ***************") print(O.bodies[clump1_id].state.se3[1]) print("*************** ORIENTATION OF CLUMP NO 2 ***************") print(O.bodies[clump2_id].state.se3[1]) print("*************** INERTIA OF CLUMP NO 1 ***************") print(O.bodies[clump1_id].state.inertia) print("*************** INERTIA OF CLUMP NO 2 ***************") print(O.bodies[clump2_id].state.inertia) -- You received this question notification because your team yade-users is an answer contact for Yade. _______________________________________________ Mailing list: https://launchpad.net/~yade-users Post to : [email protected] Unsubscribe : https://launchpad.net/~yade-users More help : https://help.launchpad.net/ListHelp
