[MBDyn-users] Element feedback system

humberto at kot.com.br humberto at kot.com.br
Mon Mar 31 16:56:43 CEST 2014


Dear all,

I am a new user to MBDyn and up to now, I have been exploring the 
software functionalities in order to check if it is a suitable tool for 
my purposes. I must also say that I have used MBDyn with Doug Baldwin's 
Blender script in some examples I have been working on. One of them 
concerns the modelling of a simple pendulum, according to the code 
below:


begin: data;
	problem: initial value;
end: data;

begin: initial value;
	initial time: 0.0;
	final time: 8.3;
	time step: 0.001;
	max iterations: 10;
	tolerance: 1e-06;
	derivatives tolerance: 2.0;
	derivatives coefficient: 0.001;
end: initial value;

begin: control data;
	default orientation: orientation matrix;
	output precision: 6;
	output meter: meter, 0., forever, steps, 33;
	structural nodes: 3;
	joints: 3;
	rigid bodies: 1;
	gravity;
	default output: accelerations;
end: control data;

begin: nodes;
	structural: 0, static,
		reference, global, 0.0, 0.0, 0.0,
		reference, global, matr,
			1.0, 0.0, 0.0,
			0.0, 1.0, 0.0,
			0.0, 0.0, 1.0,
		reference, global, null,
		reference, global, null;
	structural: 1, static,
		reference, global, 0.0, 0.0, 0.0,
		reference, global, matr,
			1.0, 0.0, 0.0,
			0.0, 1.0, 0.0,
			0.0, 0.0, 1.0,
		reference, global, null,
		reference, global, null;
	structural: 2, dynamic,
		reference, global, 3.0, 0.0, 0.0,
		reference, global, matr,
			1.0, 0.0, 0.0,
			0.0, 1.0, 0.0,
			0.0, 0.0, 1.0,
		reference, global, null,
		reference, global, null;
end: nodes;

begin: elements;
	body: 0,
		2,
			1.0,
			0.0, 0.0, 0.0,
			diag, 0.4, 0.4, 0.4,
			inertial, matr,
				1.0, 0.0, 0.0,
				0.0, 1.0, 0.0,
				0.0, 0.0, 1.0;
	joint: 1, clamp,
		0, node, node;
	joint: 3, revolute hinge,
		0, 0.0, 0.0, 0.0,
			hinge, matr,
				1.0, 0.0, 0.0,
				0.0, 1.0, 0.0,
				0.0, 0.0, 1.0,
		1, 0.0, 0.0, 0.0,
			hinge, matr,
				1.0, 0.0, 0.0,
				0.0, 1.0, 0.0,
				0.0, 0.0, 1.0;
	joint: 4, total joint,
		2, position, -3.0, 0.0, 0.0,
			position orientation, matr,
				1.0, 0.0, 0.0,
				0.0, 1.0, 0.0,
				0.0, 0.0, 1.0,
			rotation orientation, matr,
				1.0, 0.0, 0.0,
				0.0, 1.0, 0.0,
				0.0, 0.0, 1.0,
		1, position, 0.0, 0.0, 0.0,
			position orientation, matr,
				1.0, 0.0, 0.0,
				0.0, 1.0, 0.0,
				0.0, 0.0, 1.0,
			rotation orientation, matr,
				1.0, 0.0, 0.0,
				0.0, 1.0, 0.0,
				0.0, 0.0, 1.0,
			position constraint, active, active, active, component,
				null,
				null,
				null,
			orientation constraint, active, active, active, component,
				null,
				null,
				null;
	gravity:
			0.0, -1.0, 0.0, scale, 10.0, unit;
end: elements;

Having this code as basis, I had no problem on introducing a structural 
couple of constant drive of 30.0 N.m on th z-direction of node 1 and 
observing that the system remained static. However I would like to make 
a more general situation, in which the sphere defined by body 0 is 
actually a more complex body that is attached to other moving parts, 
making the couple with respect to node 1 possibly vary with time. For 
this purpose, I was hoping to use some private data of the total joint 
in order to implement a feedback system by means of a element drive, but 
I just cannot figure out what private data I should use. Does anyone 
have a suggestion?

Thanks in advance,
Humberto.












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