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IEEE TRANSACTIONS ON AUTOMATIC CONTROL, VOL. 50, NO. 5, MAY 2005 631 Semilinear Duhem Model for Rate-Independent and Rate-Dependent Hysteresis JinHyoung Oh, Student Member, IEEE, and Dennis S. Bernstein, Fellow, IEEE Abstract—The classical Duhem model provides a finite-di- mensional differential model of hysteresis. In this paper, we consider rate-independent and rate-dependent semilinear Duhem models with provable properties. The vector field is given by the product of a function of the input rate and linear dynamics. If the input rate function is positively homogeneous, then the resulting input–output map of the model is rate independent, yielding persistent nontrivial input–output closed curve (that is, hysteresis) at arbitrarily low input frequency. If the input rate function is not positively homogeneous, the input–output map is rate depen- dent and can be approximated by a rate-independent model for low frequency inputs. Sufficient conditions for convergence to a limiting input–output map are developed for rate-independent and rate-dependent models. Finally, the reversal behavior and orientation of the rate-independent model are discussed. Index Terms—Duhem, hysteresis, rate dependence. I. INTRODUCTION H YSTERESIS arises in diverse applications, such as struc- tural mechanics, aerodynamics, and electromagnetics. The word “hysteresis” connotes lag, and hysteretic systems are generally described as having memory. Although there is no precise definition of hysteresis, we adopt the notion that hysteresis is effectively nontrivial quasi-dc input–output closed curve, that is, a nontrivial closed curve in the input–output map that persists for an periodic input as the frequency content of the input signal approaches dc. With dynamic, that is, non-dc excitation, both linear and nonlinear systems exhibit nontrivial input–output closed curve, which is generally frequency de- pendent and a natural consequence of the system’s dynamics. However, the input–output map a linear system can approach only a single-valued linear map as the input frequency ap- proaches zero. Consequently no linear system is hysteretic, and thus hysteresis is an inherently nonlinear phenomenon. To illustrate this point of view, consider the mechanism [1] shown in Fig. 1, where the system input is the position of the right end of the spring and the system output is the position of the mass. The equation of motion is given by (1.1) where is a deadzone function with width due to the gap where the spring attaches to the mass. The presence of hysteresis Manuscript received May 27, 2004; revised October 2, 2004. Recommended by Associate Editor M. Reyhanoglu. This work was supported in part by the National Science Foundation under Grant ECS-0225799. The authors are with the Department of Aerospace Engineering, The Univer- sity of Michigan, Ann Arbor, MI 48109-2140 USA (e-mail: [email protected]; [email protected]). Digital Object Identifier 10.1109/TAC.2005.847035 Fig. 1. Mass-dashpot-spring system with gap. Fig. 2. Input–output map for the mass-dashpot-spring system with gap when , and . between and is not readily evident during dynamic operation, since the nontrivial input–output closed curve is a consequence of both the gap and the dynamics. However, Fig. 2 reveals that the nontrivial closed curve persists near dc, that is, in the dc limit at asymptotically low frequency. Alternatively, consider the relationship between the magnetic field strength and the magnetic flux density of a fer- romagnetically soft material of the isoperm type [2] given by (1.2) where are positive constants. Fig. 3 shows the relationship between the magnetic field strength and the magnetic flux density . The presence of nontrivial input–output closed curve for low frequency inputs indicates that this system is hys- teretic. Although the examples discussed above are both hysteretic, they are distinct in several respects. First, the shapes of the hysteresis maps are different, although their orientation is the same, namely, counterclockwise. Next, the response of the 0018-9286/$20.00 © 2005 IEEE

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Page 1: IEEE TRANSACTIONS ON AUTOMATIC CONTROL, VOL. 50, …dsbaero/library/Hysteresis...IEEE TRANSACTIONS ON AUTOMATIC CONTROL, VOL. 50, NO. 5, MAY 2005 631 Semilinear Duhem Model for Rate-Independent

IEEE TRANSACTIONS ON AUTOMATIC CONTROL, VOL. 50, NO. 5, MAY 2005 631

Semilinear Duhem Model for Rate-Independent andRate-Dependent Hysteresis

JinHyoung Oh, Student Member, IEEE, and Dennis S. Bernstein, Fellow, IEEE

Abstract—The classical Duhem model provides a finite-di-mensional differential model of hysteresis. In this paper, weconsider rate-independent and rate-dependent semilinear Duhemmodels with provable properties. The vector field is given by theproduct of a function of the input rate and linear dynamics. If theinput rate function is positively homogeneous, then the resultinginput–output map of the model is rate independent, yieldingpersistent nontrivial input–output closed curve (that is, hysteresis)at arbitrarily low input frequency. If the input rate function isnot positively homogeneous, the input–output map is rate depen-dent and can be approximated by a rate-independent model forlow frequency inputs. Sufficient conditions for convergence to alimiting input–output map are developed for rate-independentand rate-dependent models. Finally, the reversal behavior andorientation of the rate-independent model are discussed.

Index Terms—Duhem, hysteresis, rate dependence.

I. INTRODUCTION

HYSTERESIS arises in diverse applications, such as struc-tural mechanics, aerodynamics, and electromagnetics.

The word “hysteresis” connotes lag, and hysteretic systemsare generally described as having memory. Although there isno precise definition of hysteresis, we adopt the notion thathysteresis is effectively nontrivial quasi-dc input–output closedcurve, that is, a nontrivial closed curve in the input–output mapthat persists for an periodic input as the frequency content ofthe input signal approaches dc. With dynamic, that is, non-dcexcitation, both linear and nonlinear systems exhibit nontrivialinput–output closed curve, which is generally frequency de-pendent and a natural consequence of the system’s dynamics.However, the input–output map a linear system can approachonly a single-valued linear map as the input frequency ap-proaches zero. Consequently no linear system is hysteretic, andthus hysteresis is an inherently nonlinear phenomenon.

To illustrate this point of view, consider the mechanism [1]shown in Fig. 1, where the system input is the position of theright end of the spring and the system output is the positionof the mass. The equation of motion is given by

(1.1)

where is a deadzone function with width due to the gapwhere the spring attaches to the mass. The presence of hysteresis

Manuscript received May 27, 2004; revised October 2, 2004. Recommendedby Associate Editor M. Reyhanoglu. This work was supported in part by theNational Science Foundation under Grant ECS-0225799.

The authors are with the Department of Aerospace Engineering, The Univer-sity of Michigan, Ann Arbor, MI 48109-2140 USA (e-mail: [email protected];[email protected]).

Digital Object Identifier 10.1109/TAC.2005.847035

Fig. 1. Mass-dashpot-spring system with gap.

Fig. 2. Input–output map for the mass-dashpot-spring system with gap w = 1when m = 0:1; k = 10; c = 1, and r(t) = sin!t.

between and is not readily evident during dynamicoperation, since the nontrivial input–output closed curve is aconsequence of both the gap and the dynamics. However, Fig. 2reveals that the nontrivial closed curve persists near dc, that is,in the dc limit at asymptotically low frequency.

Alternatively, consider the relationship between the magneticfield strength and the magnetic flux density of a fer-romagnetically soft material of the isoperm type [2] given by

(1.2)

where are positive constants. Fig. 3 shows the relationshipbetween the magnetic field strength and the magnetic fluxdensity . The presence of nontrivial input–output closedcurve for low frequency inputs indicates that this system is hys-teretic.

Although the examples discussed above are both hysteretic,they are distinct in several respects. First, the shapes of thehysteresis maps are different, although their orientation is thesame, namely, counterclockwise. Next, the response of the

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Fig. 3. Input–output map for a ferromagnetically soft material of the isopermtype when a = 0:02125; b = 0:100; c = 0:04361, and H(t) = 30sin!t.

mass-spring system depends on the input frequency, whereasthe ferromagnetic material model has the same input–output re-sponse for all input frequencies.

In classical terminology [2]–[4], these systems have rate-dependent hysteresis and rate-independent hysteresis, respec-tively. We shall use this traditional terminology despite the factthat it is inconsistent with our view that “hysteresis” per se refersto the response in the dc limit. Since the dynamic response ofa system with rate-independent hysteresis is completely deter-mined by its quasi-dc behavior, such a system is effectively kine-matic.

Examples (1.1) and (1.2) are also different with respectto their dependence on the shape of the input. Considerthe input–output maps corresponding to sinusoidal and tri-angle-wave inputs. Fig. 4 shows that the mass-spring exampleexhibits different input–output maps, while Fig. 5 shows thatthe ferromagnetic material model exhibits the same maps. Thisdistinction suggests a relationship between the rate dependenceof the hysteresis and the dependence of the input–output mapon the shape of the periodic input.

Yet another distinction between these examples is their re-versal behavior. As can be seen in Fig. 6(a), the mass-spring ex-ample exhibits play-type reversal, while the ferromagnetic ma-terial model response converges to a self-similar hysteresis asseen in Fig. 6(b).

One of the most popular hysteresis models is the infinite-di-mensional Preisach model [4]–[9], which is an integral modelwhose kernel involves an infinite number of hysteretic opera-tors. The Preisach model can capture a large class of hysteresismaps with complex reversal behavior. However, simulatingPreisach models requires gridding of the plane and thus iscomputationally demanding. Other integral models of hys-teresis with different kernel functions include the energy-basedhysteresis model [10], the generalized Maxwell-slip hystereticfriction model [11], [12], and the Prandtl-Ishilinskii model [13,pp. 342–367].

In contrast to Preisach models, the examples discussed aboveare finite dimensional. The mass-spring example is suggested

Fig. 4. Input–output map for the mass-dashpot-spring system with deadzoneunder (a) sinusoid input and (b) triangle-wave input when r = sin 5t.

Fig. 5. Input–output map for the model of a ferromagnetically soft material ofthe isoperm type under both sinusoidal and triangle-wave inputs.

in [13, p. 90] as an approximation to a hysteron model, whilethe ferromagnetic material model is a Duhem model, a classof hysteresis models studied in [2] and [14]–[16]. Variations of

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OH AND BERNSTEIN: SEMILINEAR DUHEM MODEL FOR RATE-INDEPENDENT AND RATE-DEPENDENT HYSTERESIS 633

Fig. 6. Reversal behavior for (a) the mass-dashpot-spring system withdeadzone and (b) the ferromagnetically soft material.

the Duhem model have been studied in different contexts undervarious names. For example, the Bouc–Wen model [17], [18],the Madelung model [13, p. 274], the Dahl friction model [19],the LuGre friction model [20], and the presliding friction model[21] are specialized Duhem models as shown in Examples 2.1and 2.2. All of these models are rate independent. Rate-depen-dent models are studied in [3] and [14].

The purpose of this paper is to extend the existing analysisof the Duhem model to further elucidate its properties. In par-ticular we are interested in the rate dependence of the response,convergence, shape, and orientation of the hysteresis map, aswell as the reversal behavior.

The contents of the paper are as follows. In Section II, we in-troduce the generalized Duhem model and define the hysteresismap to be the dc-limiting input–output phase portrait. In Sec-tion III, we discuss the rate-independent generalized Duhemmodel using the concept of positive time-scale invariance. InSections IV and V we introduce the rate-independent and rate-

dependent semilinear Duhem models, respectively, and analyzetheir properties. In Section VI, the reversal behavior of the rate-independent generalized Duhem model is discussed. Finally,the orientation of the limiting periodic input–output map of therate-independent generalized Duhem model is analyzed in Sec-tion VII, followed by the Conclusion.

II. GENERALIZED DUHEM MODEL

Consider the single-input single-output generalized Duhemmodel given by

(2.1)

(2.2)

where is absolutely continuous,is continuous and piecewise is

continuous, is continuous and satisfies, and is continuous. The value of

at a point at which is discontinuous can be assignedarbitrarily. We assume that the solution to (2.1) exists and isunique on all finite intervals. Under these assumptions, andare continuous and piecewise . The following definition willbe useful.

Definition 2.1: The nonempty set is a closed curveif there exists a continuous, piecewise , and periodic map

such that .Definition 2.1 implies that every closed curve is a compact

and connected subset of . For closed curves , definethe Hausdorff metric [22, p. 104]

(2.3)

where is a norm on . Since with the metricis complete, it follows from [23, p. 67] that the set of

closed curves with is a complete metric space.Definition 2.2: Let be contin-

uous, piecewise , periodic with period , and have exactlyone local maximum in and exactly one local min-imum in . For all , define ,assume that there exists that is periodicwith period and satisfies (2.1) with , and let

be given by (2.2) with and . For all, the periodic input–output map is the closed

curve , and thelimiting periodic input–output map is the closed curve

if the limit exists. If there existsuch that , then is a

hysteresis map, and the generalized Duhem model is hysteretic.Example 2.1: Bouc’s hysteresis model [17] is given by

(2.4)

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where and are continuous,and is . Letting , where , itfollows that (2.4) is equivalent to

(2.5)

(2.6)

Now, (2.5) and (2.6) can be rewritten in the form of (2.1) and(2.2) as

(2.7)

(2.8)

where

(2.9)

The Bouc-Wen model [18] is the variation of (2.7) and (2.8)given by (2.10) and (2.11), shown at the bottom of the page,where , and are system parameters, and is therestoring force of a hysteretic structural system due to a dis-placement . Setting , and yields theDahl friction model [19]

(2.12)

where denotes rigid body displacement and is theelastic strain in the frictional contact.

Example 2.2: LuGre friction model [20] is given by

(2.13)

(2.14)

where is monotonically decreasing, denotes therelative position between the two surfaces, denotes the frictionforce, and are stiffness, damping coefficient,and viscous friction coefficient, respectively. The state equation(2.13) can be rewritten as

(2.15)

which is in the form of (2.1). Note that (2.14) depends onand thus cannot be written as (2.2). This model can be inter-preted as an improper generalized Duhem model. Other im-

proper generalized Duhem models include the presliding fric-tion model [21]

(2.16)

(2.17)

where is the current transition curve,models the constant velocity behavior in sliding, is anoffset constant, and is a system parameter. The state equation(2.16) can be written in the form of (2.1) as

(2.18)

III. RATE-INDEPENDENT GENERALIZED DUHEM MODEL

In this section, we consider the rate-independent generalizedDuhem model. The following definition is needed.

Definition 3.1: The continuous and piecewise functionis a positive time scale if is

nondecreasing, and . The generalized Duhemmodel (2.1), (2.2) is rate independent if, for every continuousand piecewise and satisfying (2.1) and for every posi-tive time scale , it follows that and

also satisfy (2.1).Note that there is a slight abuse of notation in defining

in Definition 2.2, and in Definition 3.1. Letting, it follows that and denote and , respectively.

The following definition is needed to characterize the rate-inde-pendent generalized Duhem model.

Definition 3.2: The function is positively homogeneous iffor all and .

The following result generalizes [14, Prop. 9].Proposition 3.1: Assume that is positively homogeneous.

Then, the generalized Duhem model (2.1), (2.2) is rate indepen-dent.

Proof: Let be a positive time scale. Then and,thus, . Now, for all ,consider

(2.10)

(2.11)

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OH AND BERNSTEIN: SEMILINEAR DUHEM MODEL FOR RATE-INDEPENDENT AND RATE-DEPENDENT HYSTERESIS 635

Since is a positive time scale, for all . Hence,it follows from the positive homogeneity of that

which implies that

for all , as required.Let be a positive time scale, assume that (2.1) and (2.2) are

rate independent, let and , where , be inputs as inDefinition 3.1, and let , and satisfy (2.1),(2.2) with and , respectively. Define the input–outputmap

and the scaled input–output map

Then

Hence, is independent of , and thusfor every positive time-scale .

This observation shows that the periodic input–output mapof the rate-independent generalized Duhem model is identicalto the limiting periodic input–output map. Specifically, since

is a positive time scale, the periodic input–outputmap is invariant for all and, thus,

, for all .The rate-independent generalized Duhem model has several

alternative representations. The following lemma is needed forfurther discussion.

Lemma 3.1: Assume is positively homogeneous. Then,there exist such that

,(3.1)

Proof: Let . Since is positively homo-geneous, is also positively homogeneous, . Then,for all , where

. Similarly, for all ,

where . Finally, defineand , which satisfies

(3.1) as required.Assume is positively homogeneous. Then, (2.1) and (2.2)

can be written in the form of the Madelung model [13, p. 282]

(3.2)

(3.3)

where and. Note that (3.2) can be viewed as a switching

system with respect to the sign of . Furthermore, (3.1) canbe written as

(3.4)

and, thus, (3.2) can be written as (2.1) with in the form

(3.5)

for , which is the standard Duhem model[15, p. 131]. Finally, it follows from (3.5) that

where vec is the column-stacking operator and denotes theKronecker product. Hence, the rate-independent generalizedDuhem model (2.1), (2.2) is equivalent to

(3.6)

(3.7)

The following result is needed to analyze the rate-indepen-dent generalized Duhem model (3.2), (3.3).

Proposition 3.2: Assume that is positively homoge-neous and given by (3.1), where , and let

and satisfy

when increaseswhen decreasesotherwise

(3.8)

(3.9)

for and with initial condition ,where , and

. Furthermore, letbe piecewise monotonic, continuous, piecewise , and

. Then, and satisfy(3.2) and (3.3).

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Proof: For , note that

when increaseswhen decreasesotherwise

with the initial condition .Hence, satisfies (3.2). Therefore, for all

and, thus, from (3.3).Proposition 3.2 shows that the rate-independent generalized

Duhem model (3.2), (3.3) can be reparameterized with as theindependent variable. Note that (3.8) and (3.9) can be viewedas a time-varying dynamical system with nonmonotonic time

. Hence, reparameterization of the rate-independent general-ized Duhem model implies that the input–output map ofand consists of a positive orbit arising from and anegative orbit arising from . We exclude pathologicalinputs by assuming that is piecewise monotonic.

Assume that the forward-time and backward-time solutionsof (3.8) exist and are unique on all finite intervals. If ,then the positive and negative orbits of (3.8) are identical andthus the limiting periodic input–output map is not hysteretic.Therefore, the existence of hysteresis requires thatand be different.

Example 3.1: Let be the triangle wave

for , and consider the positive time scales

for and . Fig. 7 shows the triangle waveand the positive time-scaled triangle waves , and

. Note that and change the period of , while andchange the shape of . Now, consider the generalized Duhem

model

(3.10)

(3.11)

and let . Since is positively homogeneous, Propo-sition 3.1 implies that (3.10), (3.11) is rate independent. Fig. 8

Fig. 7. Time histories of u; u ; u ; u , and u . The inputs u and uare identical to u except for their periods, u (t) = sin(�t=2��=2), and uis a triangle wave with the same period as u but different slope.

Fig. 8. Input–output maps of (u; y); (u ; y ); (u ; y ); (u ; y ), and(u ; y ) with g( _u) = j _uj. All of the input–output maps are identical sincethe model is rate independent.

shows that the input–output maps of (3.10) and (3.11) with dif-ferent positive time scales are identical. Next, let ,which is not positively homogeneous. Fig. 9 shows that theinput–output maps of (3.10) and (3.11) depend on the positivetime scales.

Example 3.2: Reconsider Example 3.1 with .Since the model is rate independent, we can reparameterize(3.10) and (3.11) in terms of to obtain

when increaseswhen decreasesotherwise

(3.12)

(3.13)

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OH AND BERNSTEIN: SEMILINEAR DUHEM MODEL FOR RATE-INDEPENDENT AND RATE-DEPENDENT HYSTERESIS 637

Fig. 9. Input–output maps of (u; y); (u ; y ); (u ; y ); (u ; y ), and(u ; y ) with g( _u) = _u . In this case, the input–output map changes withdifferent positive time scales.

Fig. 10. Input–output map of Example 3.2 with g( _u) = j _uj and u(t) = sin t.

Consider the piecewise monotonic sinusoidal input. When increases from 0 to is given by the

forward-time ramp response of

(3.14)

which yields the branch from (0, 0) to of the input–outputmap shown in Fig. 10. Now, when decreases from 1 to

is given by the backward-time ramp response of

(3.15)

which yields the branch from to of theinput–output map shown in Fig. 10.

IV. RATE-INDEPENDENT SEMILINEAR DUHEM MODEL

As a specialization of (3.6) and (3.7), we now consider therate-independent semilinear Duhem model

(4.1)

(4.2)

where, and . Note that (4.1) is

a rate-independent generalized Duhem model of the form(3.6), (3.7) with

, and. Reparameterizing (4.1)

and (4.2) in terms of yields

when increaseswhen decreasesotherwise

(4.3)

(4.4)

where . Note that the forward and backward solutionsof (4.3) are each given by the sum of a ramp response and a stepresponse. For the following lemma, let denote the Drazingeneralized inverse of and let denote the index of[24, p. 122].

Lemma 4.1: Let and . Then thesolution of (4.3) for increasing is given by

(4.5)

and the solution of (4.3) for decreasing is given by

(4.6)

where

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Proof: First, we recall from [24, p. 176] that, for

where . Now, suppose is increasing. Then, with theinitial condition , the solution of (4.3) is givenby

which proves (4.5). Now suppose is decreasing and let. Then, the solution of (4.3) with

decreasing from is equivalent to with increasingfrom . For all , it follows from (4.3) that

that is

Therefore

Hence, with the initial condition is givenby

Since , we have, for

Remark 4.1: If , then # and thus# and

# , where # is thegroup generalized inverse of [24, p. 124]. If ,that is, is nonsingular, then and, thus,

. Similarly, if #

and thus # and# . Furthermore, if ,

then and .For the following result, let the limiting input–output

map be the set of points such thatthere exists a divergent sequence in satisfying

. Furthermore, let denotethe spectral radius of . We now state the main resulton the existence of the limiting periodic input–output map of arate-independent semilinear Duhem model.

Theorem 4.1: Consider the rate-independent semilinearDuhem model (4.1), (4.2), where iscontinuous, piecewise , and periodic with period and hasexactly one local maximum in and exactly one localminimum in . Furthermore, defineand assume that . Then, for all , (4.1)has a unique periodic solution , the limitingperiodic input–output map exists, and the limitinginput–output map is given by .Specifically

(4.7)

where

(4.8)

and

(4.9)

(4.10)

(4.11)

(4.12)

(4.13)

(4.14)

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OH AND BERNSTEIN: SEMILINEAR DUHEM MODEL FOR RATE-INDEPENDENT AND RATE-DEPENDENT HYSTERESIS 639

Proof: Let , define , anddefine

when increaseswhen decreases

Since

and

and since continuous, piecewise , and periodic with pe-riod , it follows that is continuous, piecewise , and peri-odic with period . Furthermore, Lemma 4.1 implies thatis the solution of (4.3) with and for in-creasing and is the solution of (4.3) withand for decreasing . Hence is a periodic solutionof (4.1), (4.2) with and, thus, the periodic input–outputmap is given by

. Since (4.1), (4.2) is rate independent,it follows that , for all .

Now, to prove that is the unique periodic solution of (4.1),(4.2), let satisfy (4.1) with . Let

and, and for define

and . Without loss of generality, let. Analogous arguments hold for the case

. Since is periodic and has exactly one local max-imum and exactly one local minimum in each period, Lemma4.1 implies that is given by (4.5) with as

and, for is given by (4.5) with, and as

Similarly, for is given by (4.6) with, and as

Since is obtained by a sequence of forward and backwardsolutions of (4.3) for is given by the affinemap

Similarly, for , since is also obtained by asequence of backward and forward solutions of (4.3), isgiven by the affine map

Since and hence , itfollows that

and

Therefore, Lemma 4.1 implies that, as and, thus,converges to the forward solution of (4.3) with

, and , and the backward solution of(4.3) with , and , which is .Therefore, is the unique periodic solution of (4.1) and (4.2)with .

Finally, to prove , letand let without loss of generality. Analogous ar-guments hold for the case . Let

, and define . Then,, and

thus . Since the model is rate inde-pendent, for all

, as required.As a special case of (4.1), (4.2), consider the rate-independent

semilinear Duhem model

(4.15)

(4.16)

where , and . Then,(4.15) and (4.16) can be rewritten as

(4.17)

(4.18)

where is given by (3.1). The following result is the specializa-tion of Theorem 4.1 to (4.15) and (4.16).

Corollary 4.1: Consider the rate-independent semilinearDuhem model (4.15), (4.16), whereis continuous, piecewise , and periodic with period and

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Fig. 11. Illustration of positively homogeneous functions g for asymptoticallystable A. (a) Not hysteretic. (b) May not converge toH since h > h . (c),(d) Will converge to H .

has exactly one local maximum in and exactly onelocal minimum in . Furthermore, suppose thatis asymptotically stable and . Then, for all ,(4.15) has a unique periodic solution , thelimiting periodic input–output map exists, and thelimiting input–output map of (4.1) and (4.2) is givenby . Specifically

(4.19)

where

(4.20)

(4.21)

and

(4.22)

(4.23)

(4.24)

(4.25)

Proof: First note that

Since and is asymptotically stable, it follows that. The result is now a consequence of The-

orem 4.1.Consider the rate-independent semilinear Duhem model

(4.17), (4.18) and assume that is asymptotically stable. ThenCorollary 4.1 implies that the convergence of the input–outputmap to the limiting input–output map depends on the left-and right-hand slopes of at the origin. Fig. 11 illustratesseveral positively homogeneous functions . If as inFig. 11(a), then the positive orbit and the negative orbit of the

reparameterized model are identical and thus the model is nothysteretic. If , it follows from Corollary 4.1 that forthe functions shown in Fig. 11(c) and (d) the rate-independentsemilinear Duhem model has a limiting periodic input–outputmap.

Example 4.1: The ferromagnetic material model (1.2) can berewritten as

(4.26)

where and .Note that (4.26) is a rate-independent semilinear Duhem modelof the form (4.1). Consider the parameters from [2]

and let . Since ,it follows from Theorem 4.1 that the limiting periodicinput–output map exists and converges to thelimiting input–output map as , as shown in Fig. 3.

Example 4.2: Consider the rate-independent semilinearDuhem model (4.15) and (4.16) with

Suppose and let and .Then since is asymptotically stable and , Corollary4.1 implies that the limiting periodic input–output map existsand the input–output map converges to the limiting input–outputmap as , as shown in Fig. 12(a). Now, let and

. Then and the input–output map ofand does not converge, as shown in Fig. 12(b). In this case,

.

V. RATE-DEPENDENT SEMILINEAR DUHEM MODEL

As an alternative specialization of (2.1) and (2.2), we considerthe rate-dependent semilinear Duhem model

(5.1)

(5.2)

where, and , and where

and are continuous and satisfyfor , and for . Note that (5.1), (5.2)is a rate-independent semilinear Duhem model (4.1), (4.2) if

and . Furthermore, notethat (5.1), (5.2) is a generalized Duhem model of the form (2.1),(2.2) with

and . Sinceis not necessarily positively homogeneous, (5.1) and (5.2) are

generally rate dependent.

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OH AND BERNSTEIN: SEMILINEAR DUHEM MODEL FOR RATE-INDEPENDENT AND RATE-DEPENDENT HYSTERESIS 641

Fig. 12. Input–output maps of Example 4.2 under sinusoidal input with(a) h = 1 and h = �1 and (b) h = 1 and h = 1:1.

For the following result, we assume thatand exist,

where and denote the left- and right-hand limitsat 0, respectively.

Proposition 5.1: Consider the rate-dependent semilinearDuhem model (4.1) and (4.2), whereis , periodic with period , and has exactly one local max-imum in and exactly one local minimumin . Furthermore, define and assumethat . Then, the unique lim-iting periodic input–output map exists and is given

by (4.7)–(4.14) with and replacedwith , and

, respectively.Proof: Let , let , and consider the

rate-independent semilinear Duhem model

(5.3)

(5.4)

where

, and .Since (5.3), (5.4) is rate independent and since

, Theorem 4.1 impliesthat the limiting periodic input–output map for (5.3),(5.4) exists, is periodic, and the limiting input–outputmap is given by . Our goal is to showthat is the limiting input–output map for (5.1), (5.2).To do this we need to show thatas uniformly for all , so that the periodicinput–output map of (5.1) and (5.2) converges to withrespect to the Hausdorff metric (2.3).

For , let , satisfy (5.1),(5.2) with and , define

, and define

Furthermore, define , whichsatisfies

(5.5)

with . Letand . For convenience,assume . Then, for , (5.6) impliesthat is given by (5.6), as shown at the bottom of the page,where and

. Since is and thus is bounded,it follows thatuniformly for all . Furthermore, since is continuous at

(5.6)

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Fig. 13. Illustration of nonpositively homogeneous functions g forasymptotically stable A. (a) Not hysteretic. (b) May not converge toH sinceg (0) > g (0). (c), (d) Will converge to H .

uniformly for all. Therefore

uniformly for all and . Likewise,uniformly for all and .

Furthermore, since and exist

it follows thatuniformly for all .

Therefore, since and are bounded, it follows thatuniformly for all and, thus,

uniformly for all . Finally

As a special case of (5.1), (5.2), consider the rate-dependentsemilinear Duhem model

(5.7)

(5.8)

where , and , and where isgiven by

The following result is the specialization of Proposition 5.1 to(5.7) and (5.8).

Corollary 5.1: Consider the rate-dependent semilinearDuhem model (5.1), (5.2) whereis , and periodic with period and has exactly one localmaximum in and exactly one local minimumin . Suppose that is asymptotically stable and assume

, where and . Then, theunique limiting periodic input–output map exists andis given by (4.19)–(4.25).

Assuming that is asymptotically stable, Corollary 5.1 im-plies that the existence of a limiting periodic input–output mapfor the rate-dependent semilinear Duhem model (5.7) and (5.8)depends on the slopes of at the origin. Fig. 13 illustrates sev-eral nonpositively homogeneous functions . Ifas in Fig. 13(a), then the linearized rate-independent semilinearDuhem model is not hysteretic and, thus, (5.7) and (5.8) are

not hysteretic. If , it follows from Corollary5.1 that for the functions shown in Fig. 13(c) and (d) therate-dependent semilinear Duhem model has a limiting periodicinput–output map.

VI. REVERSAL BEHAVIOR OF THE RATE-INDEPENDENT

SEMILINEAR DUHEM MODEL

In this section, we discuss the reversal behavior of the rate-in-dependent semilinear Duhem model, that is, the change of theinput–output map when the range of the input changes. Specifi-cally, consider the rate-independent semilinear Duhem model(4.1), (4.2), where is piecewise monotonic. Letand suppose that, for is periodic with period

and has exactly one local maximum in and ex-actly one local minimum in . Letand suppose . Then, it follows from The-orem 4.1 that, for sufficiently large , the input–output mapof and converges to a limiting input–output map for

. Now, let ,and suppose that for is periodic with period andhas exactly one local maximum in and exactlyone local minimum in . Let .If , then the input–output map ofand converges to another limiting input–output map for

as . The limiting input–outputmap for is the major loop and the limitinginput–output map for is a minor loop [2].

Note that if is asymptotically stable,, and if ,

and , the existence of the minor loop is guaranteedfor all from Corollary 4.1.

Example 6.1: Reconsider Example 4.2 with and. Let for , and

for . Since the range of the input changesfrom to , we can determine the major andminor loops from (4.20) and (4.21). As shown in Fig. 14(a), theinput–output map changes from the major loop to a minor loopafter a transient response, as shown Fig. 14(b).

VII. ORIENTATION OF THE INPUT–OUTPUT MAP OF THE

RATE-INDEPENDENT GENERALIZED DUHEM MODEL

In this section, we analyze the orientation of the input–outputmap of the rate-independent generalized Duhem model (3.2)and (3.3). For the following discussion, we adopt standard ter-minology from complex analysis [25]. Let be a closed curve,and let , where bethe periodic map with period associated with as definedin Definition 2.1. Then, is simple if for all dis-tinct . Furthermore, letting ,where , then the winding number of about

is defined as

(7.1)

Assume that is a simple closed curve. Then it follows from theJordan curve theorem [25, p. 111] that consists of two

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OH AND BERNSTEIN: SEMILINEAR DUHEM MODEL FOR RATE-INDEPENDENT AND RATE-DEPENDENT HYSTERESIS 643

Fig. 14. (a) Major and minor loop of Example 6.1 from (4.20) and (4.21).(b) Transient response of Example 6.1 from the major loop to the minor loop.

disjoint connected open sets. The inside of the simple closedcurve is the bounded open set of these disjoint sets. Notethat not every hysteretic limiting periodic input–output mapis a simple closed curve, since can cross itself as shown inFig. 12(a). The following definition is needed.

Definition 7.1: Let be contin-uous, piecewise , and periodic with period and have ex-actly one local maximum in and exactly one localminimum in . Let be periodic withperiod and suppose that and satisfy the rate-inde-pendent generalized Duhem model (2.1), (2.2). Furthermore,define and assume that the limiting peri-odic input–output map exists, and ishysteretic and simple. Then is clockwise (respectively,counterclockwise) if (respectively, )for every in the inside of .

Let be piecewise monotonic andconsider the reparameterized rate-independent generalizedDuhem model (3.8), (3.9). Assume that the limiting periodic

Fig. 15. Relationship between clockwise orientation (CW) andcounterclockwise orientation (CCW) of the input–output map and the sign of(d y(u))=(du ).

input–output map exists, and is hysteretic and simple.Now, suppose the positive orbit of (3.8), (3.9) is concave andthe negative orbit of (3.8), (3.9) is convex or, equivalently

when increaseswhen decreases

(7.2)

which implies is clockwise. Similarly, suppose the pos-itive orbit of (3.8), (3.9) is convex and the negative orbit of (3.8),(3.9) is concave, or equivalently

when increaseswhen decreases

(7.3)

which implies that is counterclockwise. Fig. 15 showsthe relationship between the orientation of the trajectory and thesigns of . This observation shows that the orien-tation of the limiting periodic input–output map of the rate-in-dependent generalized Duhem model can be determined by theconcavity and convexity of , or by the sign of the secondderivative of with respect to . We thus obtain the fol-lowing result for the input–output map of the rate-independentgeneralized Duhem model.

Proposition 7.1: Let be contin-uous, piecewise , and periodic with period and have exactlyone local maximum in and exactly one local min-imum in . Consider the rate-independent generalizedDuhem model (3.2), (3.3). Assume that is with respect to

and . Also assume that the limiting periodic input–outputmap exists, and is hysteretic and simple. Furthermore,for , define

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If and for all , thenis clockwise. Similarly, if and

for all , then is counterclockwise.Proof: For , it suffices to show

that when increases, andwhen decreases. Suppose is

increasing. Then

The proof is similar for decreasing .Remark 7.1: For the semilinear Duhem model (4.1), (4.2),

and are given by

(7.4)

(7.5)

Example 7.1: Consider the generalized Duhem model

(7.6)

(7.7)

Let . Then Corollary 4.1 implies that the lim-iting periodic input–output map exists for all .First, let . Then, it can be seen that and

for all . Hence, it follows from Proposi-tion 7.1 that is counterclockwise, as shown in Fig. 16(a).Now, let . Then, it can be seen that and

for all . Hence, it follows from Proposi-tion 7.1 that is clockwise, as shown in Fig. 16(b).

VIII. CONCLUSION

In this paper, we introduced the rate-independent and rate-de-pendent semilinear Duhem model. The analysis of the rate-inde-pendent model was facilitated by a reparameterization in termsof the control input. By analyzing the iterated ramp response,

Fig. 16.Input–output map of Example 7.1 with (a) b = 1 and (b) b = �1.The orientation of the input–output map is counterclockwise when b = 1, andclockwise when b = �1.

we obtained sufficient conditions for convergence to a limitinginput–output map. We then approximated the rate-dependentmodel with low frequency inputs by a rate-independent semi-linear Duhem model and developed a sufficient condition forconvergence. We then analyzed the orientation of the rate-in-dependent hysteresis map in terms of its clockwise or counter-clockwise evolution. The reversal behavior of the rate-indepen-dent semilinear Duhem model was characterized by applyingthese results to a restricted input range. Future research possi-bilities include developing conditions for the existence of hys-teresis for the generalized Duhem model.

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OH AND BERNSTEIN: SEMILINEAR DUHEM MODEL FOR RATE-INDEPENDENT AND RATE-DEPENDENT HYSTERESIS 645

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JinHyoung Oh (S’02) was born in Taegu, SouthKorea, in 1971. He received the B.S. degree incontrol and instrumentation engineering from KoreaUniversity, Chochiwon, Korea, in 1993, and the M.S.degrees in aerospace engineering and applied math-ematics from the Georgia Institute of Technology,Atlanta, in 1999 and 2001, respectively. He willreceive the Ph.D. degree in aerospace engineeringfrom the University of Michigan, Ann Arbor, inApril 2005. His Ph.D. thesis focuses on modeling,identification, and control of hysteresis.

He is currently a Research Fellow with the University of Michigan.

Dennis S. Bernstein (M’82–SM’99–F’01) receivedthe Sc.B. degree in applied mathematics from BrownUniversity, Providence, RI, in 1977, and the Ph.D.degree in control engineering from the University ofMichigan, Ann Arbor, in 1982.

He is currently a Professor in the Aerospace En-gineering Department at the University of Michigan.His interests encompass all aspects of control foraerospace applications, with emphasis on identifi-cation and adaptive control for vibration and flowcontrol. He is the author of Matrix Mathematics:

Theory, Facts, and Formulas with Application to Linear Systems Theory(Princeton, NJ: Princeton Univ. Press, 2004).