Variational principles for dissipative systemsurbanski/Madrid.pdf · • A master model for all...
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Variational principles for dissipative systems
W. M. Tulczyjew and P. Urbanski
Faculty of Physics
University of Warsaw
Madrid, 6.09.2006 – p. 1/17
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Credo
• A master model for all variational principles of classicalphysics is provided by the principle of virtual work wellknown in statics of mechanical systems.
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Credo
• A master model for all variational principles of classicalphysics is provided by the principle of virtual work wellknown in statics of mechanical systems.
• Ingredients:
◦ configuration manifold Q,◦ constrained set C1 ⊂ TQ,◦ virtual work function σ : C1 → R,
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Credo
• A master model for all variational principles of classicalphysics is provided by the principle of virtual work wellknown in statics of mechanical systems.
• Ingredients:
◦ configuration manifold Q,◦ constrained set C1 ⊂ TQ,◦ virtual work function σ : C1 → R,
• with the properties:◦ for each q ∈ C0 = τQ(C1) the set C1
q = TqQ ∩ C1 is acone, i.e. λv ∈ C1
q for each v ∈ C1q , λ > 0,
◦ virtual work function is positive homogeneous, i.e.σ : (λv) = λσ(v) for λ > 0.
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The principle of virtual work
is incorporated in the definition of the constitutive set
S = {f ∈ T∗Q; q = πQ(f) ∈ C0, ∀v∈C1
qσ(v) − 〈f, v〉 > 0}.
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The main reference
Włodzimierz M. TULCZYJEW
"The Origin of Variational Principles"
Banach Center Publications 59, "Classical and QuantumIntegrability", Warszawa 2003also math-ph/0405041
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Legendre-Fenchel transformation
Letσ : C → R
be a positive homogeneous function defined on a cone C in avector space V .
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Legendre-Fenchel transformation
Letσ : C → R
be a positive homogeneous function defined on a cone C in avector space V .The set
S = {F ∈ V ∗; ∀v∈C σ(v) − 〈f, v〉 > 0}
is the Legendre-Fenchel transform of σ.
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Legendre-Fenchel transformation
Letσ : C → R
be a positive homogeneous function defined on a cone C in avector space V .The set
S = {F ∈ V ∗; ∀v∈C σ(v) − 〈f, v〉 > 0}
is the Legendre-Fenchel transform of σ.The constitutive set S derived from the work function σ isobtained by applying the Legendre-Fenchel transformation tofunctions
σq : C1q → R.
The Legendre-Fenchel transforms Sq are then combined
S =⋃
q∈C0
Sq
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The inverse Legendre-Fenchel transformation
Let S be a subset of V ∗. We introduce the set
C = {v ∈ V ; supf∈S
〈f, v〉 < ∞}.
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The inverse Legendre-Fenchel transformation
Let S be a subset of V ∗. We introduce the set
C = {v ∈ V ; supf∈S
〈f, v〉 < ∞}.
and the functionσ : C → sup
f∈S
〈f, v〉
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Properties of the L-F transformation
• The L-F transform S of a positive homogeneous functionσ : C → R is convex and closed.
• The inverse L-F transform σ : C → R of a subset S ⊂ V ∗ isconvex and closed (the overgraph of σ is closed).
• The L-F transformation and the inverse L-F transformationestablish a one to one correspondence between positivehomogeneous closed convex functions defined on cones inV and non empty closed convex subsets of V ∗.
It follows that the constitutive setprovides a complete characterization ofa convex static system
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Partially controlled systems
There is the internal configuration space Q and the controlconfiguration space Q
Q
η ��Q
, (1)
�� //
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Partially controlled systems
There is the internal configuration space Q and the controlconfiguration space Q
Q
η �� U //R
Q
, (3)
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Partially controlled systems
There is the internal configuration space Q and the controlconfiguration space Q
Q
η �� U //R
Q
, (4)
The constitutive set S derived from the potential U :
S = {f ∈ T∗Q;∃q∈Q η(q) = πQ(f),∀v∈TqQ 〈dU, v〉 = 〈f, Tη(v)〉}
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Partially controlled systems
There is the internal configuration space Q and the controlconfiguration space Q
Q
η �� U //R
Q
, (5)
The constitutive set S derived from the potential U :
S = {f ∈ T∗Q;∃q∈Q η(q) = πQ(f),∀v∈TqQ 〈dU, v〉 = 〈f, Tη(v)〉}
A point q ∈ Q ’contributes’ to S if and only if 〈dU, v〉 = 0 for eachvertical v ∈ TqQ.
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Generating families
The potential U is interpreted as a family of functions defined onfibres of the fibration η.
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Generating families
The potential U is interpreted as a family of functions defined onfibres of the fibration η.
The family (U, η) is called a generating family of the set S.
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Generating families
The potential U is interpreted as a family of functions defined onfibres of the fibration η.
The family (U, η) is called a generating family of the set S.
The critical set of the family (U, η):
Cr(U, η) = {q ∈ Q;∀v∈TqQ if Tη(v) = 0 then 〈dU, v〉 = 0}
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Convex generating families
Simplified version, without constraints.
�� oo //
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Convex generating families
Simplified version, without constraints.
Q
η �� TQτQ
oo σ //R
Q
, (7)
For each q the function σq : TqQ → R is convex.
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Convex generating families
Simplified version, without constraints.
Q
η �� TQτQ
oo σ //R
Q
, (8)
For each q the function σq : TqQ → R is convex.
S = {f ∈ T∗Q;∃q∈Q η(q) = πQ(f),∀v∈TqQ 〈σ, v〉 > 〈f, Tη(v)〉}
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Convex generating families
Simplified version, without constraints.
Q
η �� TQτQ
oo σ //R
Q
, (9)
For each q the function σq : TqQ → R is convex.
S = {f ∈ T∗Q;∃q∈Q η(q) = πQ(f),∀v∈TqQ 〈σ, v〉 > 〈f, Tη(v)〉}
The critical set
Cr(σ, η) = {q ∈ Q;∀v∈TqQ if Tη(v) = 0 then σ(v) > 0}
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Convex generating families
’Contribution’ of q ∈ Cr(σ, η) to S
Sq = {f ∈ T∗Q;πQ(f) = η(q), ∀v∈TqQ 〈σ, v〉 > 〈f, Tη(v)〉}
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Convex generating families
’Contribution’ of q ∈ Cr(σ, η) to S
Sq = {f ∈ T∗Q;πQ(f) = η(q), ∀v∈TqQ 〈σ, v〉 > 〈f, Tη(v)〉}
Proposition.
Sq = {f ∈ T∗Q;πQ(f) = η(q) = q, ∀v∈TqQ 〈σq, v〉 > 〈f, v〉}
where
σq : TqQ → R : v 7→ infv
σ(v), v ∈ TqQ, Tη(v) = v.
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Convex generating families
’Contribution’ of q ∈ Cr(σ, η) to S
Sq = {f ∈ T∗Q;πQ(f) = η(q), ∀v∈TqQ 〈σ, v〉 > 〈f, Tη(v)〉}
Proposition.
Sq = {f ∈ T∗Q;πQ(f) = η(q) = q, ∀v∈TqQ 〈σq, v〉 > 〈f, v〉}
where
σq : TqQ → R : v 7→ infv
σ(v), v ∈ TqQ, Tη(v) = v.
σq is well defined and convex.
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Convex generating families
’Contribution’ of q ∈ Cr(σ, η) to S
Sq = {f ∈ T∗Q;πQ(f) = η(q), ∀v∈TqQ 〈σ, v〉 > 〈f, Tη(v)〉}
Proposition.
Sq = {f ∈ T∗Q;πQ(f) = η(q) = q, ∀v∈TqQ 〈σq, v〉 > 〈f, v〉}
where
σq : TqQ → R : v 7→ infv
σ(v), v ∈ TqQ, Tη(v) = v.
σq is well defined and convex.
If Cr(σ, η) is a section of η, the family (σ, η) can be reduced to afunction σ : TQ → R
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Example 1
A point with configuration q1 is tied to a fixed point q0 with aspring of spring constant k1. Points q1 and q2 are tied with aspring of spring constant k2. The point q1 is subject to frictionand left free.
η : (q1, q2) 7→ (q2)
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Example 1
A point with configuration q1 is tied to a fixed point q0 with aspring of spring constant k1. Points q1 and q2 are tied with aspring of spring constant k2. The point q1 is subject to frictionand left free.
η : (q1, q2) 7→ (q2)
The work form of the system is
ϑ(q1, q2, v1, v2) = k1(q1 − q0|v1) + µ‖v1‖ + k2(q2 − q1|v2 − v1)
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Example 1
A point with configuration q1 is tied to a fixed point q0 with aspring of spring constant k1. Points q1 and q2 are tied with aspring of spring constant k2. The point q1 is subject to frictionand left free.
η : (q1, q2) 7→ (q2)
The work form of the system is
ϑ(q1, q2, v1, v2) = k1(q1 − q0|v1) + µ‖v1‖ + k2(q2 − q1|v2 − v1)
A point (q1, q2) is critical if ‖k1(q1 − q0) + k2(q1 − q2)‖ 6 µ
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Example 1
For a critical point (q1, q2)
infv1
ϑ(q1, q2, v1, v2) = k2(q2 − q1|v2)
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Example 1
For a critical point (q1, q2)
infv1
ϑ(q1, q2, v1, v2) = k2(q2 − q1|v2)
S(q1,q2) = {f = k2(q2 − q1)}.
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Example 2
A point with configuration q1 is tied to a fixed point q0 with aspring of spring constant k1. Points q1 and q2 are tied with aspring of spring constant k2. The point q1 is left free and point q2
is subject to friction.
η : (q1, q2) 7→ (q2)
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Example 2
A point with configuration q1 is tied to a fixed point q0 with aspring of spring constant k1. Points q1 and q2 are tied with aspring of spring constant k2. The point q1 is left free and point q2
is subject to friction.
η : (q1, q2) 7→ (q2)
The work form of the system is
ϑ(q1, q2, v1, v2) = k1(q1 − q0|v1) + µ‖v2‖ + k2(q2 − q1|v2 − v1)
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Example 2
A point with configuration q1 is tied to a fixed point q0 with aspring of spring constant k1. Points q1 and q2 are tied with aspring of spring constant k2. The point q1 is left free and point q2
is subject to friction.
η : (q1, q2) 7→ (q2)
The work form of the system is
ϑ(q1, q2, v1, v2) = k1(q1 − q0|v1) + µ‖v2‖ + k2(q2 − q1|v2 − v1)
There is one critical point in a fibre
q1 = q0 +k2
k1 + k2(q2 − q0).
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Example 2
For a critical point (q1, q2)
infv1
ϑ(q1, q2, v1, v2) = µ‖v2‖ +k1k2
k1 + k2(q2 − q1|v2)
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Example 2
For a critical point (q1, q2)
infv1
ϑ(q1, q2, v1, v2) = µ‖v2‖ +k1k2
k1 + k2(q2 − q1|v2)
The family can be reduced to the function
(q2, v2) 7→ µ‖v2‖ +k1k2
k1 + k2(q2 − q1|v2).
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Convex relation
Let a relation R : T∗Q1 → T
∗Q2 be generated by a convexfunction G : TK → R, K ⊂ Q1 × Q2, i.e.
b ∈ R(a) if 〈b, v2〉 − 〈a, v1〉 6 G(v1, v2)
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Convex relation
Let a relation R : T∗Q1 → T
∗Q2 be generated by a convexfunction G : TK → R, K ⊂ Q1 × Q2, i.e.
b ∈ R(a) if 〈b, v2〉 − 〈a, v1〉 6 G(v1, v2)
Let D ⊂ T∗Q1 be generated by a function σ : TC1 → R.
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Convex relation
Let a relation R : T∗Q1 → T
∗Q2 be generated by a convexfunction G : TK → R, K ⊂ Q1 × Q2, i.e.
b ∈ R(a) if 〈b, v2〉 − 〈a, v1〉 6 G(v1, v2)
Let D ⊂ T∗Q1 be generated by a function σ : TC1 → R.
Theorem. Let K and C1 × Q2 have clean intersection and letY = K ∩ (C1 × Q2) then the family
ρ : TY → R : (q1, q2, v1, v2) 7→ G(q1, q2, v1, v2) + σ(v1)
is a generating family of R(D).
Madrid, 6.09.2006 – p. 16/17
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Application
Legendre transformation for dissipative systems.
Madrid, 6.09.2006 – p. 17/17