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HAL Id: hal-01874134

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Submitted on 14 Sep 2018

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Two-temperature homogenized eigenfunctions of conduction through domains with jump interfaces

Isabelle Gruais, Dan Poliševski, Alina Stefan

To cite this version:

Isabelle Gruais, Dan Poliševski, Alina Stefan. Two-temperature homogenized eigenfunctions of con- duction through domains with jump interfaces. Applicable Analysis, Taylor & Francis, 2020, 99 (13), pp.2361-2370. �10.1080/00036811.2018.1563292�. �hal-01874134�

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Two-temperature homogenized eigenfunctions of conduction through

domains with jump interfaces

Isabelle Gruais, Dan Poliˇsevski and Alina S¸tefan

Abstract. In this paper we study the asymptotic behavior of the eigen- value problem solutions of the conduction process in an ε-periodic domain formed by two components separated by a first-order jump interface. We prove that when ε → 0 the limits of the eigenvalues and eigenfunctions of this problem verify a certain (effective) two-temperature eigenvalue prob- lem. Moreover, we show that the effective eigenvalue problem has only eigenvalues which come from the homogenization process.

Keywords: interfacial jump, conduction, eigenvalue, two-scale conver- gence, homogenization

MSC 2010: 35B27, 35P15, 49R05, 74A50, 80M40

1 Introduction

During the last decades there was a steady interest for the homoge- nization of problems with interfacial thermal barriers (see [2], [14], [7], [5]) or equivalent (see [13], [11], [8], [15]). Meanwhile, it was also studied the asymptotic behavior of the eigenvalue problems in ε-periodic domains (see [12]) , even for ε-periodically perforated domains (see [17]), where the key ingredient was the prolongation operator which was introduced by [6].

Here we continue our works [9], [10] and [16] by studying the asymptotic behavior of the eigenvalue problem solutions of the conduction process in an ε-periodic domain formed by two components separated by a first-order jump interface. We prove that when ε→0 the limits of the eigenvalues and eigenfunctions of this problem verify a certain (effective) two-temperature eigenvalue problem. Moreover, we show that the effective eigenvalue problem has only eigenvalues which come from the homogenization process. Our key ingredient is a pair of prolongation operators, corresponding to each component of the domain. Otherwise, we mainly follow the methods of the two-scale theory (see [1]). We have to remark that the procedure presented here can straightforwardly be generalized to any n-component ε-periodic domain with interfacial jumps of the first order.

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The paper is organized as follows: in Section 2 we study the eigenvalue problem in theε-periodic domain; in Section 3 we present the key prolonga- tion operators, the a priori estimates and the specific compactness results;

Section 4 is devoted to the derivation of the effective eigenvalue problem and its connection with the homogenization process.

2 The eigenvalue problem

Let Ω be an open connected bounded set in RN (N ≥ 3), locally lo- cated on one side of the boundary ∂Ω, a Lipschitz manifold composed of a finite number of connected components. For any ε ∈ (0,1),Ω has two ε-periodically ditributed components. For convenience, the periodicity is described by using the cubeY = (0,1)N,as follows:

LetYa⊂⊂Y be a Lipschitz open set such thatYb=Y\Yais connected.

For anyε∈(0,1) we denote

Zε={k∈ZN : εk+εY ⊆Ω}. (1) The twoε−periodic components of Ω are defined by:

εa= int

 [

k∈Zε

(εk+εYa)

 (2)

εb = Ω\Ωεa. (3)

Denoting Γ :=∂Ya=∂Ya∩∂Yb, the interface between Ωεaand Ωεb have the property:

Γε:= [

k∈Zε

(εk+εΓ) =∂Ωεa=∂Ωεa∩∂Ωεb. (4) Let us remark that Ωεb is connected and all the boundaries are at least locally Lipschitz. Also, the inward normal on ∂Ya, denoted by ν, has the property

νε(x) =ν

ε−1x , ∀x∈Γε, (5) where

ε−1x is formed by the fractional parts of the components of ε−1x.

We have to introduce the Hilbert space Hε=

n

u∈L2(Ω) :u

εa∈H1(Ωεa), u

εb∈H1(Ωεb), u= 0 on ∂Ω o

(6) endowed with the scalar product

(u, v)Hε = Z

εa

∇u∇v+ Z

εb

∇u∇v+ε Z

Γε

[u][v], (7)

where [u] =γεau−γεbu and γεau, γεbu are the traces of u on Γε defined in H1(Ωεa) and H1(Ωεb),respectively.

Our domain has the following well-known property [8]:

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Lemma 2.1. For any v ∈ Hε there exists C > 0, independent of ε, such that

|v|L2(Ωεb)≤C|∇v|L2(Ωεb), (8) ε1/2εαv|L2ε)≤C

|v|L2(Ωεα)+ε|∇v|L2(Ωεα)

, α ∈ {a, b}, (9)

|v|L2(Ωεa)≤C

ε1/2εav|L2ε)+ε|∇v|L2(Ωεa)

. (10)

Remark 2.1. Taking in account theL2−norm of the jump onΓε the results of the previous Lemma have important consequences:

ε1/2 [v]

L2ε)≤C

v

L2(Ω)

∇v

L2(Ωεa)

∇v L2(Ωεb)

, (11)

|v|L2(Ωεa)≤C|v|H

ε,∀v∈Hε. (12)

Next, we introduce the data of our problem: the transmission factor hε(x) = h(x/ε) and the symmetric conductivities aεij(x) = aij(x/ε) and bεij(x) =bij(x/ε),whereh, aij and bij belong toLper(Y) and have the prop- erty that there exists δ >0 such that

h≥δ, a.e. on Y, (13)

aijξjξi≥δξiξi and bijξjξi ≥δξiξi, ∀ξ∈RN, a.e. on Y. (14) We consider the following eigenvalue problem:

Find λε∈R such that ∃uε∈Hε\ {0}verifying the equations

−div (aε∇uε) =λεuε, in Ωεa, (15)

−div (bε∇uε) =λεuε, in Ωεb, (16) and the transmission conditions

aεij∂uε

∂xjνiε=bεij∂uε

∂xjνiε=εhεεauε−γεbuε) on Γε. (17) The variational formulation of the problem (15)-(17) is the following:

Find λε∈R such that ∃uε∈Hε\ {0}verifying

Gε(uε, v) :=

Z

εa

aεij∂uε

∂xj

∂v

∂xi

+ Z

εb

bεij∂uε

∂xj

∂v

∂xi

+ε Z

Γε

hε[uε][v] =λε(uε, v),

∀v∈Hε (18)

where (·,·) denotes the inner product in L2(Ω).

Using the procedure of [3], we introduce the operatorTε ∈ L L2(Ω), Hε by denotig with Tε(u), foru∈L2(Ω), the unique solution of the problem Z

εa

aεij∂Tε(u)

∂xj

∂v

∂xi

+ Z

εb

bεij∂Tε(u)

∂xj

∂v

∂xi

+ε Z

Γε

hε[Tε(u)][v] = Z

uv,∀v∈Hε.

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Defining ˜Tε:L2(Ω)→L2(Ω) by ˜Tε=Jε◦Tε,whereJεis the inclusion of Hε into L2(Ω), we see that the eigenvalue problem (18) is equivalent to the eigenvalue problem

εuεεuε, viaµε= 1 λε.

Lemma 2.2. The inclusion Jε:Hε→L2(Ω) is a compact operator.

Proof. As for anyv∈Hε we have Jεv

Lε(Ω)= v

εa+ v

εb ≤C v

H

ε,

is sufficient to prove that the bounded sequences fromHεcontain a conver- gent subsequence inL2(Ω).

Let {vn}n a bounded sequence in Hε. We note van = vn

εa and vnb = vn

εb. Since {vna}n is a bounded sequence in H1(Ωεa), from the Rellich’s theorem there existva∈H1(Ωεa) and a subsequence, still denoted by{n}, such that

vna→va strongly inL2(Ωεa).

Further, {vnb}n being bounded in H1(Ωεb), again the Rellich’s theorem implies the existence of somevb ∈H1(Ωεb) such that on a sub-subsequence it holds

vbn→vb strongly inL2(Ωεb).

It follows that v0 =

va in Ωεa, vb in Ωεb

⇒v0∈Hε⊂L2(Ω).

The proof is completed as

vn−v0

2

L2(Ω) =

vna−va

2

L2(Ωεa)+

vbn−vb

2

L2(Ωεb)→0.

We see now that ˜Tε is a self-adjoint, compact operator in L2(Ω) and recalling for instance [4] it follows that there exist{λεk}k, eigenvalues of the problem (18), with the property

0< λε1 ≤λε2 ≤...→ ∞

and {uεk}k, the corresponding eigenfunctions, which are complete and or- thonormal inL2(Ω).

In the following sections we shall study the behaviour of (λεk, uεk) when ε→0.

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3 A priori estimates

We begin this section by proving the boundedness of {λεk}ε, the eigen- values of (18). For every k∈N let us denote

Hε,k ={S subspace ofHε,dimS=k}.

Applying the Minimum-maximum principle (see [3]), λεk can be estimated via the Rayleigh quotient:

λεk = min

S∈Hε,kmax

v∈S

Gε(v, v) v

2 L2(Ω)

≤ C min

S∈Hε,kmax

v∈S

∇v

2

L2(Ωεa)+

∇v

2

L2(Ωεb)+ε [v]

2 L2ε)

v

2 L2(Ω)

. (19)

In order to further estimate λεk with respect to εwe introduce two prolon- gation operators.

First, for any v ∈ H1(Ya) let w ∈ H1(Yb) be the only solution of the Dirichlet problem:

−∇w= 0 in Yb, (20)

w= 0 on ∂Y, w=v on Γ. (21)

We have to introduce here Pa(v)∈H1(Y) by Pa(v) =

v inYa, w inYb. It has the property

Pa(v)

H1(Y) ≤C v

H1(Ya). (22) Denoting uεk(y) := u(εk+εy), for any k∈Zε,y∈Ya and u∈H1(Ωεa), we define our first prolongation operator, Paε :H1(Ωεa)→H01(Ω), by

Paε(u)(x) =

u(x) forx∈Ωεa

Pa(uεk) {xε}

forx∈(εk+εYb), k∈Zε

0 forx∈Ω\S

k∈Zε(εk+εY) Rescaling (22) we easily obtain

Paε(u)

H1(Ω) ≤C

u

L2(Ωεa)

∇u L2(Ωεa)

, ∀v∈H1(Ωεa). (23) Second, for any v ∈H1(Yb) let w ∈H1(Yb) be the only solution of the Dirichlet problem:

−∇w= 0 inYa, (24)

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w=v on Γ. (25) For this component we introducePb(v)∈H1(Y) by

Pb(v) =

w inYa, v inYb, which has a property similar to (22):

Pb(v)

H1(Y)≤C v

H1(Yb). (26) Denoting uεk(y) := u(εk +εy), for any k ∈ Zε, y ∈ Yb, u ∈ H1(Ωεb), u = 0 on∂Ω, we define our second prolongation operator, Pbε : {u ∈ H1(Ωεb), u=0 on∂Ω} →H01(Ω), by

Pbε(u)(x) =

u(x) forx∈Ωεb Pb(uεk) {xε}

forx∈(εk+εYa), k∈Zε. Rescaling (26) we get

Pbε(u)

H1(Ω)≤C u

L2(Ωεb)

∇u L2(Ωεb)

,

∀u∈H1(Ωεb), u=0 on∂Ω. (27) We can now estimate the terms of (19).

The first term gives:

∇v

2 L2(Ωεa)

v

2 L2(Ω)

∇Paε(v)

2 L2(Ωεa)

Paε(v)

2 L2(Ω)

· Paε(v)

2 L2(Ω)

v

2 L2(Ω)

< C Paε(v)

2 L2(Ω)

v

2 L2(Ω)

,

the constant being the first eigenvalue of the problem (20)-(21). Using (23) we obtain

∇v

2 L2(Ωεa)

v

2 L2(Ω)

< C12C2

Z

εa

aε∇v∇v

v

2 L2(Ω)

. (28)

The second term gives:

∇v

2 L2(Ωεb)

v

2 L2(Ω)

∇Pbε(v)

2 L2(Ωεb)

Pbε(v)

2 L2(Ω)

· Pbε(v)

2 L2(Ω)

v

2 L2(Ω)

< C Pbε(v)

2 L2(Ω)

v

2 L2(Ω)

,

the constant being the first eigenvalue of the problem (24)-(25). Using (27) we obtain

∇v

2 L2(Ωεb)

v

2 L2(Ω)

< C12C2

Z

εb

bε∇v∇v v

2 L2(Ω)

. (29)

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The third term can be estimated from (11), that is

[v]

2 L2ε)

v

2 L2(Ω)

< C12C2 Z

εa

aε∇v∇v

v

2 L2(Ω)

2C2 Z

εb

bε∇v∇v

v

2 L2(Ω)

. (30)

Adding the estimates (28)-(30) we get λεk ≤C12C2λεk,

which obviously implies that λεk is bounded for sufficiently smallε.

Setting v = uεk in (18) and using the coerciveness of Gε(·,·) and the orthonormality of {uεk}k we find

Gε(uεk, uεk) = Z

εa

aεij∂uεk

∂xj

∂uεk

∂xi

dx+ Z

εb

bεij∂uεk

∂xj

∂uεk

∂xi

dx+

+ε Z

Γε

hε[uεk]2ds=λεk, ∀uε ∈Hε. (31) As {λεk}ε is bounded, we find that

{uεk}ε is bounded in Hε. (32) Using the previously obtained result together with inequalities (8)-(10), it follows that there exists C >0 such that

|∇uεk|L2(Ωεa)≤C, |∇uεk|L2(Ωεb)≤C, |[uεk]|L2ε)≤C. (33) Applying to the properties of the two-scale convergence theory [1], a specific compactness result follows.

Theorem 3.1. There exist λk ∈ R?+, uak∈H1(Ω), ubk ∈ H01(Ω) and ηkα∈ L2

Ω;Heper1 (Yα)

, α ∈ {a, b}, such that the following convergences hold on some subsequence

χεαuεk* χ2s αuαk, (34) χεα∇uεk* χ2s α(∇xuαk +∇yηαk(·, y)), (35)

λεk→λk, (36)

where χεα :L2(Ωεα)→L2(Ω)andχα :L2(Ω×Yα)→L2(Ω×Y), α∈ {a, b}, denote the straight prolongations with zero; sometimes they can be identified with the corresponding characteristic functions.

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4 The homogenization process

Passing (18) to the limit on the subsequence on which the convergences of Theorem 3.1 hold, we obtain like in [8]:

Lemma 4.1. For any ϕa ∈C( ¯Ω), ϕb ∈ D(Ω) and ψα ∈ D(Ω;Cper(Yα)), α∈ {a, b}, it holds

Z

Ω×Ya

aij ∂uak

∂xj +∂ηak

∂yj

∂ϕa

∂xi + ψa

∂yi

+ Z

Ω×Yb

bij ∂ubk

∂xj +∂ηbk

∂yj

∂ϕb

∂xi + ψb

∂yi

+ +eh

Z

(uak−ubk)(ϕa−ϕb) =λk

Z

Ω×Y

χauakϕabubkϕb (37) where eh is defined by

eh= Z

Γ

h(y)ds. (38)

Proof. Forϕα and ψα, α∈ {a, b}like in the hypotheses, we set v in (18) as follows:

v(x) =

ϕa(x) +εψa x,x

ε

, ϕb(x) +εψb x,x

ε

. (39)

We obtain

λεεauε, ϕa) +λεεauε, ϕb) +O(ε) = X

α∈{a,b}

Z

εα

αεij∂uε

∂xj ∂ϕα

∂xi + ∂ψα

∂yi

+

+ε Z

Γε

hεεauε−γεbuε) [ϕa−ϕb+ε(ψa−ψb)]. (40) The proof is completed by following the same steps as in the proof presented in [8].

In order to present the next results we have also to introduce the Hilbert space

H:=

H1(Ω)×H01(Ω)

×h

L2(Ω,Heper1 (Ya)×L2(Ω,Heper1 (Yb))i

, (41) endowed with the scalar product

(((ua, ub),(ηa, ηb)),((ϕa, ϕb),(ψa, ψb)))H = X

α∈{a,b}

Z

∇uα∇ϕα+

+ Z

(ua−ub) (ϕa−ϕb) + X

α∈{a,b}

Z

Ω×Yα

yηαyψα. (42) Using density arguments, Lemma 4.1 yields:

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Theorem 4.1. λk∈R+ and (uak, ubk),(ηa, ηb)

∈H\ {0} verify:

Z

Ω×Ya

aij ∂uak

∂xj +∂ηak

∂yj

∂ϕa

∂xi + ψa

∂yi

+ Z

Ω×Yb

bij ∂ubk

∂xj +∂ηkb

∂yj

∂ϕb

∂xi + ψb

∂yi

+

+eh Z

(uak−ubk)(ϕa−ϕb) =λk Z

Ω×Y

χauakϕabubkϕb ,

∀((ϕa, ϕb),(ψa, ψb))∈H. (43) We can present now the main result of this paper.

Theorem 4.2. If (λεk, uεk) is a solution of (18) then the limits of the con- vergences (34)-(36), that isλk∈R+and (uak, ubk)∈

H1(Ω)×H01(Ω)

\ {0}, put together a solution of the following effective eigenvalue problem:

Find (λk,(uak, ubk))∈R+×

H1(Ω)×H01(Ω)

\ {0} such that

Ghom((uak, ubk),(ϕa, ϕb)) =λk Z

m uakϕa+ (1−m)ubkϕb,

∀(ϕa, ϕb)∈H1(Ω)×H01(Ω), (44) where m=

Ya

,

Ghom((uak, ubk),(ϕa, ϕb)) = Z

ˆ aij

∂uak

∂xj

∂ϕa

∂xi + Z

ˆbij

∂ubk

∂xj

∂ϕb

∂xi +eh Z

(uak−ubk)(ϕa−ϕb), (45) the effective coefficients αˆij,α∈ {a, b}, are defined by

ˆ αij =

Z

Yα

αijik∂eaj

∂yk

dy, ∀i, j∈ {1,2, ..., N}, (46) and eαk ∈ Heper1 (Yα), k ∈ {1,2, ..., N}, is the unique solution of the local- periodic problem

− ∂

∂yi

αij

∂(eαk +yk)

∂yj

= 0 in Yα, (47)

αij∂(eαk+yk)

∂yj νi = 0 on Γ. (48)

Moreover, there are no eigenvalues of the problem (44) except those ob- tained as limits of the homogenization process.

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Proof. The first assertion follows from Theorem 4.1 using standard homog- enization procedures.

Next, suppose that there exists an eigenvalue of the problem (44), µ ∈ R+, µ6=λk, ∀k≥1, where{λk}krepresents the eigenvalues of the problem (44) obtained as limits of the homogenization process. It follows that there existsk such that λk < µ < λk+1. Let w= (wa, wb)∈

H1(Ω)×H01(Ω)

\ {0} be an eigenfunction associated toµ.

Let us introducewε∈Hε, the unique the solution to the problem Gε(wε, v) =µ

Z

εa

wav+µ Z

εb

wbv, ∀v ∈Hε. (49) Settingv=wε in the previous relation we find that

Gε(wε, wε)≤C wε

L2(Ω).

Applying the coercivity property ofGε, we find that the sequence {wε}ε is bounded in Hε. Under these circumstances, there exists w = (wa, wb) ∈ H1(Ω)×H01(Ω) such that

Paεwε* wa inH1(Ω) and Pbεwε * wb inH01(Ω).

Homogenizing the problem (49) we obtain

ε→∞lim Gε(wε, v) =Ghom(w, v) =µ(w, v) =Ghom(w, v),∀v∈H01(Ω), from which follows

w=w and Z

(wε)2→ Z

m(wa)2+ (1−m)(wb)2 6= 0. (50)

Next, we define ˆwε = wε

k

X

i=1

Z

wεuεi

uεi, where uεi ∈ Hε is an eigen- function associated toλi. We note that

Z

ˆ

wεuεj = 0, ∀j ≤k,and hence Gε( ˆwε,wˆε)≥λεk+1

Z

( ˆwε)2. (51)

As Z

wεuεi = Z

χεaPaεwεuεi + Z

(1−χεa)Pbεwεuεi, ∀i∈ {1, ..., k}, the passage to the limit yields

Z

wεuεi → Z

mwauai + (1−m)wbubi = 0,

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which obviously implies Z

( ˆwε)2→ Z

m(wa)2+ (1−m)(wb)2. (52) Passing (49) to the limit in we finally get

Gε( ˆwε,wˆε)→Ghom(w, w) =µ Z

m(wa)2+ (1−m)(wb)2 <

< λk+1

Z

m(wa)2+ (1−m)(wb)2, (53)

which is in contradiction with (51), via (52).

Remark 4.1. The formulation of the effective two-temperature eigenvalue problem follows from Theorem (4.2):

Find λ∈R such that ∃(ua, ub)∈

H1(Ω)×H01(Ω)

\ {0} verifying

−div (ˆa∇ua) =m λ ua in Ω, (54)

−div ˆb∇ub

= (1−m)λ ub in Ω, (55) and the boundary condition

ˆ aij∂ua

∂xj

ni= 0 on ∂Ω, (56)

where n is the outward normal on ∂Ω.

Acknowledgements. The authors gratefully acknowledge partial sup- port from the International Network GDRI ECO-Math.

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