Improve force element implementation

- Replace frames type AbstractObject3D -> Object3D.
- Use variable type arguments for force laws of SpringDamperPtP.
- Update test models.

Author: GerhardHippmann

src/Composition/ForceElements/Bushing.jl

@@ -13,15 +13,15 @@ influence the resulting forces.
 """
 mutable struct Bushing <: Modia3D.AbstractForceElement
 
-    obj1::Modia3D.AbstractObject3D
-    obj2::Modia3D.AbstractObject3D
+    obj1::Object3D
+    obj2::Object3D
 
     nominalForce::SVector{3,Float64}
     stiffness::SVector{3,Float64}
     damping::SVector{3,Float64}
 
-    function Bushing(; obj1::Modia3D.AbstractObject3D,
-                       obj2::Modia3D.AbstractObject3D,
+    function Bushing(; obj1::Object3D,
+                       obj2::Object3D,
                        nominalForce::AbstractVector = Modia3D.ZeroVector3D,
                        stiffness::AbstractVector = Modia3D.ZeroVector3D,
                        damping::AbstractVector = Modia3D.ZeroVector3D)

src/Composition/ForceElements/SpringDamperPtP.jl

@@ -1,61 +1,58 @@
 
 """
     force = SpringDamperPtP(; obj1, obj2,
-        nominalLength          = 0.0,
-        nominalForce           = 0.0,
-        stiffness              = 0.0,
-        stiffnessForceFunction = nothing,
-        damping                = 0.0,
-        dampingForceFunction   = nothing )
+        nominalLength  = 0.0,
+        nominalForce   = 0.0,
+        springForceLaw = 0.0,
+        damperForceLaw = 0.0 )
 
 Return a `force` acting as point-to-point parallel spring-damper between
 `obj1::`[`Object3D`](@ref) and `obj2::`[`Object3D`](@ref).
 
 # Arguments
 
-- `nominalLength`: Nominal length, i.e. distance between `obj1` and `obj2`
-  where deflection of stiffness force is zero.
-- `nominalForce`: Nominal force, i.e. force that acts when stiffness and
-  damping forces are zero. Positive values represent tensil forces.
-- `stiffness`: Linear stiffness coefficient of spring. Ignored if
-  `stiffnessForceFunction` is defined.
-- `stiffnessForceFunction`: Univariate function which computes the
-  stiffness force dependent of the stiffness force deflection.
-- `damping`: Linear damping coefficient of damper. Ignored if
-  `dampingForceFunction` is defined.
-- `dampingForceFunction`: Univariate function which computes the
-  damping force dependent of the damper velocity.
+- `nominalLength` defines the nominal length, i.e. the distance between
+  `obj1` and `obj2` where the deflection of the spring is zero.
+- `nominalForce` defines the nominal force, i.e. the force that acts when
+  spring and damper forces are zero. Positive values represent tension.
+- `springForceLaw` defines the force law of the spring:
+  A `Float64` value represents a linear stiffness coefficient.
+  An univariate `Function` is used to compute the spring force dependent
+  of its deflection. Positive values represent tension.
+- `damperForceLaw` defines the force law of the damper:
+  A `Float64` value represents a linear damping coefficient.
+  An univariate `Function` is used to compute the damper force dependent
+  of its deflection velocity. Positive values represent expansion.
 """
 mutable struct SpringDamperPtP <: Modia3D.AbstractForceElement
 
-    obj1::Modia3D.AbstractObject3D
-    obj2::Modia3D.AbstractObject3D
+    obj1::Object3D
+    obj2::Object3D
 
     nominalLength::Float64
     nominalForce::Float64
+    springForceFunction::Function
+    damperForceFunction::Function
 
-    stiffness::Float64
-    stiffnessForceFunction::Union{Function, Nothing}
-
-    damping::Float64
-    dampingForceFunction::Union{Function, Nothing}
-
-    function SpringDamperPtP(; obj1::Modia3D.AbstractObject3D,
-                               obj2::Modia3D.AbstractObject3D,
+    function SpringDamperPtP(; obj1::Object3D,
+                               obj2::Object3D,
                                nominalLength::Float64 = 0.0,
                                nominalForce::Float64 = 0.0,
-                               stiffness::Float64 = 0.0,
-                               stiffnessForceFunction::Union{Function, Nothing} = nothing,
-                               damping::Float64 = 0.0,
-                               dampingForceFunction::Union{Function, Nothing} = nothing)
-
-        nomLength = Modia3D.convertAndStripUnit(Float64, u"m"    , nominalLength)
-        nomForce  = Modia3D.convertAndStripUnit(Float64, u"N"    , nominalForce)
-        stiff     = Modia3D.convertAndStripUnit(Float64, u"N/m"  , stiffness)
-        damp      = Modia3D.convertAndStripUnit(Float64, u"N*s/m", damping)
-
-        return new(obj1, obj2, nomLength, nomForce, stiff, stiffnessForceFunction, damp, dampingForceFunction)
-
+                               springForceLaw::Union{Float64, Function} = 0.0,
+                               damperForceLaw::Union{Float64, Function} = 0.0 )
+
+        nomLength = Modia3D.convertAndStripUnit(Float64, u"m", nominalLength)
+        nomForce  = Modia3D.convertAndStripUnit(Float64, u"N", nominalForce)
+        if (typeof(springForceLaw) == Float64)
+            stiffness = Modia3D.convertAndStripUnit(Float64, u"N/m", springForceLaw)
+            springForceLaw = eval(:(fc(pos) = $stiffness * pos))
+        end
+        if (typeof(damperForceLaw) == Float64)
+            damping = Modia3D.convertAndStripUnit(Float64, u"N*s/m", damperForceLaw)
+            damperForceLaw = eval(:(fd(vel) = $damping * vel))
+        end
+
+        return new(obj1, obj2, nomLength, nomForce, springForceLaw, damperForceLaw)
     end
 end
 
@@ -71,16 +68,8 @@ function evaluateForceElement(force::SpringDamperPtP)
     vel = measFrameDistVelocity(force.obj2; frameOrig=force.obj1)
 
     defl = pos - force.nominalLength
-    if isnothing(force.stiffnessForceFunction)
-        fc = force.stiffness * defl
-    else
-        fc = force.stiffnessForceFunction(defl)
-    end
-    if isnothing(force.dampingForceFunction)
-        fd = force.damping * vel
-    else
-        fd = force.dampingForceFunction(vel)
-    end
+    fc = force.springForceFunction(defl)
+    fd = force.damperForceFunction(vel)
     f12 = (fc + fd + force.nominalForce) * norm
 
     applyFrameForcePair!(force.obj2, force.obj1, f12; frameCoord=force.obj1)

test/ForceElements/BoxNonLinearSpringDamperPtP.jl

@@ -5,10 +5,20 @@ using ModiaLang
 import Modia3D
 using  Modia3D.ModiaInterface
 
+interpolatedForceLaws = false
 l0 = 0.1
 f0 = 5.0
 fc(x) = sign(x) * 100.0 * abs(x)^1.2
 fd(v) = sign(v) *   2.0 * abs(v)^0.8
+if (interpolatedForceLaws)
+    using Interpolations
+    xc = -1.0:0.1:1.0
+    yc = [fc(x) for x in xc]
+    fc(x) = CubicSplineInterpolation(xc, yc)(x)
+    xd = -10.0:0.1:10.0
+    yd = [fd(x) for x in xd]
+    fd(v) = LinearInterpolation(xd, yd)(v)
+end
 
 SpringDamper = Model(
     Length = 0.1,
@@ -25,14 +35,18 @@ SpringDamper = Model(
                               feature=Visual(shape=CoordinateSystem(length=:(Length/2))),
                               translation=:[Length/2, Length/2, Length/2]),
     joint = FreeMotion(obj1=:world, obj2=:box),
-    force = SpringDamperPtP(obj1=:world, obj2=:boxCornerFrame, nominalLength=l0, nominalForce=f0, stiffnessForceFunction=fc, dampingForceFunction=fd)
+    force = SpringDamperPtP(obj1=:world, obj2=:boxCornerFrame, nominalLength=l0, nominalForce=f0, springForceLaw=fc, damperForceLaw=fd)
 )
 
 springDamper = @instantiateModel(buildModia3D(SpringDamper), aliasReduction=false, unitless=true)
 
 stopTime = 5.0
 dtmax = 0.1
-requiredFinalStates = [-0.021471022585945587, -0.021471338063312084, -0.22257979374805176, 0.3258966598257503, 0.3258956068893249, 0.007390650203910464, -0.014365742162847027, 0.014364567804398353, 0.00010407183716342378, -0.2720750966146867, 0.27207423475429426, 8.60986118342952e-7]
+if (interpolatedForceLaws)
+    requiredFinalStates = [-0.018609840194419268, -0.018610063010666804, -0.22128548799442815, 0.3091309586280587, 0.3091307182143652, 0.019491580480008697, -0.01289771100508473, 0.012897263597266288, 8.547830805609731e-5, -0.24873244248570697, 0.2487317559006742, 6.865934996471178e-7]
+else
+    requiredFinalStates = [-0.021471022585945587, -0.021471338063312084, -0.22257979374805176, 0.3258966598257503, 0.3258956068893249, 0.007390650203910464, -0.014365742162847027, 0.014364567804398353, 0.00010407183716342378, -0.2720750966146867, 0.27207423475429426, 8.60986118342952e-7]
+end
 simulate!(springDamper, stopTime=stopTime, dtmax=dtmax, log=true, requiredFinalStates=requiredFinalStates)
 
 @usingModiaPlot

test/ForceElements/BoxSpringDamperPtP.jl

@@ -22,7 +22,7 @@ SpringDamper = Model(
                               feature=Visual(shape=CoordinateSystem(length=:(Length/2))),
                               translation=:[Length/2, Length/2, Length/2]),
     joint = FreeMotion(obj1=:world, obj2=:box),
-    force = SpringDamperPtP(obj1=:world, obj2=:boxCornerFrame, stiffness=:Stiffness, damping=:Damping)
+    force = SpringDamperPtP(obj1=:world, obj2=:boxCornerFrame, springForceLaw=:Stiffness, damperForceLaw=:Damping)
 )
 
 springDamper = @instantiateModel(buildModia3D(SpringDamper), aliasReduction=false, unitless=true)