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Improve inheritance of MultiBody forces #4228

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19aadf2
Extend from PartialForce instead of PartialTwoFrames
tobolar Nov 8, 2023
c765353
Introduce orientation object R_rel (in accordance with class' documen…
tobolar Nov 8, 2023
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47 changes: 23 additions & 24 deletions Modelica/Mechanics/MultiBody/Forces/Internal/BasicForce.mo
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Original file line number Diff line number Diff line change
@@ -1,8 +1,9 @@
within Modelica.Mechanics.MultiBody.Forces.Internal;
model BasicForce
"Force acting between two frames, defined by 3 input signals"
extends Modelica.Mechanics.MultiBody.Interfaces.PartialTwoFrames;
extends Interfaces.PartialForce;
import Modelica.Mechanics.MultiBody.Types.ResolveInFrameAB;

Interfaces.Frame_resolve frame_resolve
"The input signals are optionally resolved in this frame"
annotation (Placement(transformation(
Expand All @@ -22,36 +23,34 @@ model BasicForce

SI.Position r_0[3]
"Position vector from origin of frame_a to origin of frame_b resolved in world frame";
SI.Force f_b_0[3] "frame_b.f resolved in world frame";
SI.Force f_b_0[3] "Force frame_b.f resolved in world frame";

equation
assert(cardinality(frame_resolve) > 0, "Connector frame_resolve must be connected at least once and frame_resolve.r_0/.R must be set");
frame_resolve.f = zeros(3);
frame_resolve.t = zeros(3);

if resolveInFrame == ResolveInFrameAB.frame_a then
f_b_0 = -Frames.resolve1(frame_a.R, force);
frame_b.f = Frames.resolve2(frame_b.R, f_b_0);
elseif resolveInFrame == ResolveInFrameAB.frame_b then
f_b_0 = -Frames.resolve1(frame_b.R, force);
frame_b.f = -force;
elseif resolveInFrame == ResolveInFrameAB.world then
f_b_0 = -force;
frame_b.f = Frames.resolve2(frame_b.R, f_b_0);
elseif resolveInFrame == ResolveInFrameAB.frame_resolve then
f_b_0 = -Frames.resolve1(frame_resolve.R, force);
frame_b.f = Frames.resolve2(frame_b.R, f_b_0);
else
assert(false, "Wrong value for parameter resolveInFrame");
f_b_0 = zeros(3);
frame_b.f = zeros(3);
end if;
frame_b.t = zeros(3);
r_0 = frame_b.r_0 - frame_a.r_0;
frame_b.t = zeros(3);

if resolveInFrame == ResolveInFrameAB.frame_a then
f_b_0 = -Frames.resolve1(frame_a.R, force);
frame_b.f = Frames.resolve2(frame_b.R, f_b_0);
elseif resolveInFrame == ResolveInFrameAB.frame_b then
f_b_0 = -Frames.resolve1(frame_b.R, force);
frame_b.f = -force;
elseif resolveInFrame == ResolveInFrameAB.world then
f_b_0 = -force;
frame_b.f = Frames.resolve2(frame_b.R, f_b_0);
elseif resolveInFrame == ResolveInFrameAB.frame_resolve then
f_b_0 = -Frames.resolve1(frame_resolve.R, force);
frame_b.f = Frames.resolve2(frame_b.R, f_b_0);
else
assert(false, "Wrong value for parameter resolveInFrame");
f_b_0 = zeros(3);
frame_b.f = zeros(3);
end if;

// Force and torque balance
r_0 = frame_b.r_0 - frame_a.r_0;
zeros(3) = frame_a.f + Frames.resolve2(frame_a.R, f_b_0);
zeros(3) = frame_a.t + Frames.resolve2(frame_a.R, cross(r_0, f_b_0));
annotation (
Icon(coordinateSystem(preserveAspectRatio=true, extent={{-100,-100},{
100,100}}), graphics={
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43 changes: 20 additions & 23 deletions Modelica/Mechanics/MultiBody/Forces/Internal/BasicTorque.mo
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Original file line number Diff line number Diff line change
@@ -1,15 +1,15 @@
within Modelica.Mechanics.MultiBody.Forces.Internal;
model BasicTorque
"Torque acting between two frames, defined by 3 input signals"
extends Interfaces.PartialForce;
import Modelica.Mechanics.MultiBody.Types.ResolveInFrameAB;
extends Modelica.Mechanics.MultiBody.Interfaces.PartialTwoFrames;

Interfaces.Frame_resolve frame_resolve
"The input signals are optionally resolved in this frame"
annotation (Placement(transformation(
origin={40,100},
extent={{-16,-16},{16,16}},
rotation=90)));

Modelica.Blocks.Interfaces.RealInput torque[3](each final quantity="Torque", each final unit="N.m")
"x-, y-, z-coordinates of torque resolved in frame defined by resolveInFrame"
annotation (Placement(transformation(
Expand All @@ -23,37 +23,34 @@ model BasicTorque

SI.Position r_0[3]
"Position vector from origin of frame_a to origin of frame_b resolved in world frame";
SI.Torque t_b_0[3] "frame_b.t resolved in world frame";
SI.Torque t_b_0[3] "Torque frame_b.t resolved in world frame";

equation
assert(cardinality(frame_resolve) > 0, "Connector frame_resolve must be connected at least once and frame_resolve.r_0/.R must be set");
frame_resolve.f = zeros(3);
frame_resolve.t = zeros(3);

r_0 = frame_b.r_0 - frame_a.r_0;
frame_a.f = zeros(3);
frame_b.f = zeros(3);

if resolveInFrame == ResolveInFrameAB.frame_a then
t_b_0 = -Frames.resolve1(frame_a.R, torque);
frame_b.t = Frames.resolve2(frame_b.R, t_b_0);
elseif resolveInFrame == ResolveInFrameAB.frame_b then
t_b_0 = -Frames.resolve1(frame_b.R, torque);
frame_b.t = -torque;
elseif resolveInFrame == ResolveInFrameAB.world then
t_b_0 = -torque;
frame_b.t = Frames.resolve2(frame_b.R, t_b_0);
elseif resolveInFrame == ResolveInFrameAB.frame_resolve then
t_b_0 = -Frames.resolve1(frame_resolve.R, torque);
frame_b.t = Frames.resolve2(frame_b.R, t_b_0);
else
assert(false, "Wrong value for parameter resolveInFrame");
t_b_0 = zeros(3);
frame_b.t = zeros(3);
end if;
if resolveInFrame == ResolveInFrameAB.frame_a then
t_b_0 = -Frames.resolve1(frame_a.R, torque);
frame_b.t = Frames.resolve2(frame_b.R, t_b_0);
elseif resolveInFrame == ResolveInFrameAB.frame_b then
t_b_0 = -Frames.resolve1(frame_b.R, torque);
frame_b.t = -torque;
elseif resolveInFrame == ResolveInFrameAB.world then
t_b_0 = -torque;
frame_b.t = Frames.resolve2(frame_b.R, t_b_0);
elseif resolveInFrame == ResolveInFrameAB.frame_resolve then
t_b_0 = -Frames.resolve1(frame_resolve.R, torque);
frame_b.t = Frames.resolve2(frame_b.R, t_b_0);
else
assert(false, "Wrong value for parameter resolveInFrame");
t_b_0 = zeros(3);
frame_b.t = zeros(3);
end if;

// torque balance
zeros(3) = frame_a.t + Frames.resolve2(frame_a.R, t_b_0);
annotation (
Icon(coordinateSystem(preserveAspectRatio=true, extent={{-100,-100},{
100,100}}), graphics={
Expand Down
25 changes: 15 additions & 10 deletions Modelica/Mechanics/MultiBody/Interfaces/PartialForce.mo
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Original file line number Diff line number Diff line change
@@ -1,32 +1,37 @@
within Modelica.Mechanics.MultiBody.Interfaces;
partial model PartialForce
"Base model for force elements (provide frame_b.f and frame_b.t in subclasses)"
"Base model for force elements, used for textual modeling, i.e., for elementary models"
extends PartialTwoFrames;

SI.Position r_rel_b[3]
"Position vector from origin of frame_a to origin of frame_b, resolved in frame_b";
Frames.Orientation R_rel
"Relative orientation object from frame_a to frame_b";
equation
// Determine relative position vector between frame_a and frame_b
// Determine relative position and orientation
r_rel_b = Frames.resolve2(frame_b.R, frame_b.r_0 - frame_a.r_0);
R_rel = Frames.relativeRotation(frame_a.R, frame_b.R);

// Force and torque balance between frame_a and frame_b
zeros(3) = frame_a.f + Frames.resolveRelative(frame_b.f, frame_b.R, frame_a.R);
zeros(3) = frame_a.t + Frames.resolveRelative(frame_b.t + cross(r_rel_b, frame_b.f), frame_b.R, frame_a.R);
zeros(3) = frame_a.f + Frames.resolve1(R_rel, frame_b.f);
zeros(3) = frame_a.t + Frames.resolve1(R_rel, frame_b.t + cross(r_rel_b, frame_b.f));

annotation (Documentation(info="<html>
<p>
All <strong>3-dimensional force</strong> and <strong>torque elements</strong>
should be based on this superclass.
All elementary <strong>3-dimensional force</strong> and
<strong>torque elements</strong> should be based on this superclass.
This model defines frame_a and frame_b, computes the relative
translation and rotation between the two frames and calculates
the cut-force and cut-torque at frame_a by a force and torque
balance from the cut-force and cut-torque at frame_b.
As a result, in a subclass, only the relationship between
the cut-force and cut-torque at frame_b has to be defined as
a function of the following relative quantities:
the cut-force and cut-torque at frame_b (i.e., frame_b.f and frame_b.t)
has to be defined as a function of the following relative quantities:
</p>
<blockquote><pre>
r_rel_b[3]: Position vector from origin of frame_a to origin
of frame_b, resolved in frame_b
R_rel : Relative orientation object to rotate from frame_a to frame_b
R_rel : Relative orientation object from frame_a to frame_b
</pre></blockquote>
<p>
Assume that force f = {100,0,0} should be applied on the body
Expand All @@ -42,7 +47,7 @@ the definition should be:
<strong>end</strong> Constant_x_Force;
</pre></blockquote>
<p>
Note, that frame_b.f and frame_b.t are flow variables and therefore
Note, that frame_b.f and frame_b.t are flow variables and, therefore,
the negative value of frame_b.f and frame_b.t is acting at the part
to which this force element is connected.
</p>
Expand Down