View the posts of glenhenshaw

Jan-16-13 19:16:47

Topic: Question: is the openmodelica-to-C external function interface broken?

OMC-generated c files contain invalid C identifiers

Category: Developer

Here's the modelica code. I'm trying to get a very simple collision detection system working. I want to model a soccer ball being kicked.

record objectrecord
type objectType = enumeration(point, sphere, line, plane);
Real[3] x;
end objectrecord;

class obj
extends objectrecord;
Real[3] xdot;
equation
der(x) = xdot;
end obj;

record collision
Boolean colliding;
Real sep[3];
Real distance;
end collision;

function collisionDetection
input objectrecord object1, object2;
output collision info;
external "C" info = distanceObjectToObject(object1, object2);
end collisionDetection;

model World
obj ground(x.start = {0.0, 0.0, 0.0}, xdot = {0.0, 0.0, 0.0}, objectType = objectrecord.objectType.plane);
obj ball(x.start = {0.0, 0.0, 1.0}, xdot.start = {0.0, 0.0, 0.0}, objectType = objectrecord.objectType.sphere);
parameter Real ks = 35000.0;
parameter Real kd = 50.0;
parameter Real g[3] = {0.0, 0.0, -9.8};
collision collisioninfo;
Real[3] contactforce;
equation
collisioninfo = collisionDetection(ball, ground);
contactforce = if collisioninfo.colliding then collisioninfo.sep*ks + ball.xdot*kd else {0.0, 0.0, 0.0};
der(ball.xdot) = -g - contactforce;
end World;

Jan-16-13 01:32:23

Topic: Question: is the openmodelica-to-C external function interface broken?

OMC-generated c files contain invalid C identifiers

Category: Developer

Forum: OpenModelica development

Pardon, I've learned more about preprocessing. However, I'm still left with a bug. If I run gcc -E on the omc output file, I am left with a line that reads:

void eqFunction_7(DATA *data)
{
collisionDetection_rettype tmp0;
tmp0 = omc_collisionDetection($Pball, $Pground);
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
data->localData[0]->booleanVars[0] = tmp0.c1.colliding;
copy_real_array_data_mem(&tmp0.c1.sep, &data->localData[0]->realVars[21]);
data->localData[0]->realVars[27] = tmp0.c1.distance;
}

Any ideas? Is this my problem or omc's?

Jan-16-13 00:58:28

Topic: Question: is the openmodelica-to-C external function interface broken?

OMC-generated c files contain invalid C identifiers

Category: Developer

Forum: OpenModelica development

From an omc-generated C file:

void eqFunction_32(DATA *data)
{
$Pground$Pxdot$lB3$rB = 0.0;
}

...

This code involves calling a C function from within a modelica model. The identifier "$Pground$Pxdot$lB3$rB" is, of course, not valid C syntax. Is this a known bug?

Jan-03-13 20:27:37

Topic: contact modelling

Does OpenModelica support contact dynamics in the MultiBody library?

Category: Usage and Applications

Forum: OpenModelica Usage and Applications

I would like to model a soccer player kicking a ball. Papers by Michael Otter et al indicate that contact dynamics suitable for this problem were included in the Modelica MultiBody library around 2005, but colleagues of mine who use Modelica are not so sure. Does OpenModelica support Otter's (or anyone else's) collision detection and contact modeling?

Dec-14-12 01:25:46

Topic: More Newbie: reinit() with arrays

Converting the BouncingBall demo to use array variables fails...

Category: Usage and Applications

Forum: OpenModelica Usage and Applications

Oh, so it's a bug? That's good to know, won't keep banging my head against it then. Thanks!

Dec-14-12 00:33:25

Topic: More Newbie: reinit() with arrays

Converting the BouncingBall demo to use array variables fails...

Category: Usage and Applications

Forum: OpenModelica Usage and Applications

I would like to modify the BouncingBall demo to be three dimensional instead of one. The cleanest way to do this would seem to be to use 3-vectors for the position and velocity. However, a straightforward rewrite of the demo code fails; the problem is apparently the reinit() command. The code is as follows:

model Ball
Real[3] x(start={0.0, 0.0, 0.0});
Real[3] xdot;
Real[3] xdot_new;

parameter Real g=9.81 "gravitational acceleration";
parameter Real e=0.7 "coefficient of restitution";

Boolean impactWithFloor;
Boolean flying(start=true) "true, if ball is flying";

equation
impactWithFloor = x[3]<=0.0;

der(x) = xdot;
der(xdot) = if flying then {0.0, 0.0, -g} else {0.0, 0.0, 0.0};

when {x[3] <= 0.0 and xdot[3] <= 0.0, impactWithFloor} then
xdot_new = if edge(impactWithFloor) then {0.0, 0.0, -e*pre(xdot[3])} else {0.0, 0.0, 0.0};
flying = xdot_new[3] > 0;
reinit(xdot, xdot_new);
end when;

end Ball;

The simulation fails with the error:

base_array.c: array dimensions sizes are NULL!
Assertion failed: (base_array_ok(source)), function copy_real_array_data_mem, file util/real_array.c, line 142.

Rewriting the Ball object to use three scalar variables x1, x2, x3 works fine. What's going on here?

Dec-13-12 22:17:14

Topic: Newbie: initializing state variables from OMShell