Wave Interactions of the Aw-Rascle Model for Generalized Chaplygin Gas ()
1. Introduction
In the present paper, we study the Aw-Rascle (AR) macroscopic model of traffic flow
(1)
where
is the density,
is the velocity, P is the velocity offset which is called as the “pressure” inspired from gas dynamics. The derivation process of the above AR model and the application can be discovered in [1] - [7].
In [8], Aw and Rascle studied the limit behavior and found that the pressure term is active. In [9], Shen and Sun investigated the limit behavior without the constraint of the maximal density.
In [10] [11], M. N. Sun studied the following model
(2)
In [10] [11], they studied the elementary wave interactions and obtained the stability of the Riemann solutions under such a perturbation on the initial data.
In [12], G. D. Wang investigated the Riemann problem of (1) and
(3)
where
,
. This is the so-called generalized Chaplygin gas for (1).
In the present paper, we investigate the elementary wave interactions for (1) and (3). In our paper [13], we study the wave interactions containing no delta shock, so we just consider the wave interactions for (1) containing delta shock wave with the three piecewise constants
(4)
where the perturbation parameter
is sufficiently small. (4) can be regarded as a local perturbation on the initial values
(5)
where
.
This paper is arranged as follows. In Section 2, we give curtly the Riemann problem for the model (1) (3) and (5) for the convenience of the readers. In Section 3, we investigate the elementary wave interactions by the characteristic analysis method. In Section 4, we summarize our main conclusion.
2. Preliminaries
We give briefly the Riemann problem for (1) (3) and (5) [12].
The characteristic roots of (1) are
,
which shows that (1) is strictly hyperbolic. The corresponding right characteristic vector of
and
is respectively given by
(6)
If
, we get
(7)
which indicates that
is genuinely nonlinear and the associated wave is either shock wave or rarefaction wave,
is always linearly degenerate and the associated wave is the contact discontinuity, where
denotes the gradient.
We construct the self-similar solution
,
. The Riemann problem (1) (5) becomes the following boundary value problem of the ordinary differential equations
(8)
and
. For smooth solutions, let
, (8) becomes
(9)
where
Besides the constant state solution
, (9) has a rarefaction wave solution. For the given left state
, the rarefaction wave curve is given by
(10)
For a bounded discontinuity at
, it holds the Rankine-Hugoniot conditions
(11)
where
,
,
, etc.
For the given left state
, the shock wave is given by
(12)
Since
is linearly degenerate, from (9) or (11) we know the contact discontinuity
(13)
All the above rarefaction waves R, shock waves S, and contact discontinuities J are the elementary waves for (1). Notice the shock curves coincide with the rarefaction curves in the phase plane
[14]. It is very important because it can simplify the process of the elementary wave interactions.
According to the right state
in the different region (Figure 1), we obtain the unique Riemann solution. When
or II, the unique Riemann solution is
, when
or IV, the unique Riemann solution is
, when
, i.e.,
, we should construct the delta shock wave solution as follows.
Consider a piecewise smooth solution of (1) with the form
(14)
where
(15)
-measure solutions
of (1) (3) and (5) is given
(16)
here
,
is the Heaviside function.
The measure solution (14) and (15) satisfies the generalized Rankine-Hugoniot condition
(17)
where
is the jump of u across the discontinuity
, etc.
The
-entropy condition is
(18)
which is
(19)
We know that all the characteristics on both sides of the
-shock wave curve are incoming.
In order to consider the interaction of elementary waves containing delta shock wave, we briefly recall the concept of left- and right-hand side delta functions as follows.
Let
be divided into two disjoint open sets
and
with a piecewise smooth boundary curve L, which satisfies
and
. Let
and
be the space of bounded and continuous real-valued functions equipped with the
-norm and the space of measures on
, respectively. Let us assume that
and
, then the product of
and
is defined as an element
, where
can be defined as the usual product of a continuous function and a measure. Thus, it is obvious that the above-defined product makes sense.
We view the measure on
as a measure on
with support in
. Then the mapping
can be obtained by taking
. In a similar way, we have
. The solution concept used in our paper when we consider the delta shock can be described as follows: carry out the multiplication and composition in the space
and take the mapping
before differentiation in the space of distributions.
Based on the above analysis, we have the following conclusion.
Theorem 2.1 The Riemann solution of the initial value problem (1) (3) and (5) is unique.
3. Interactions of Elementary Waves Containing Delta Shock Wave
Now we study the elementary wave interactions for (1) (3) with (4). (4) is regarded as the perturbation on the Riemann initial values (5). In order to cover all the cases containing delta shock completely, we have three possibilities according to the different combinations from
and
as follows:
and
,
and
,
and
.
Case 1:
and
.
We consider the interaction of a delta shock wave
emanating from
and a delta shock wave
emanating from
. When t is small enough, the solution of the initial value problem (1) (3) and (4) is expressed as (Figure 2).
The propagation speed of
and
satisfy respectively the
-entropy conditions
and we know that
where
and
are respectively the propagating speed of
and
,
and
are respectively the strength of
and
.
It easy to see that
which shows that
will overtake
at a point
which is determined by
(20)
which yields
(21)
At the intersection point
, a new initial data is formed as follows
(22)
where
is the sum of the strengths of the incoming delta shock wave
and
. A new delta shock wave will generate after interaction and we denote it by
, which is given by
(23)
where H is the Heaviside function and
is a split delta function. All of them are supported by the line
,
is the propagating speed of
. Although they are supported by the same line,
is the delta measure on the set
and
is the delta measure on the set
respectively.
From (23), we obtain
(24)
(25)
Substituting (24) and (25) into the first equation of (1), we obtain
From (15), we get
Case 2:
and
.
In this case, a shock wave followed by a contact discontinuity emits from
and a delta shock wave emits from
(Figure 3). The propagating speed of the contact discontinuity is
, and the propagating speed of the delta shock wave satisfies the
-entropy condition
. It easy to see that J will overtake
at
which given by
(26)
From (26), we get
(27)
The delta shock wave
will pass through J with the same speed as before but the strength changes due to the difference between
and
. We still denote it with
after the time
, and
.
From the
-entropy condition
and the shock entropy condition
we know that S will overtake
at
which satisfies
(28)
thus
(29)
The new initial data will be formulated at
as follows
(30)
denotes the strength of
at the time
and from
and
we can determine the value of
.
A new delta shock wave will be generated after the interaction of S and
, denoted by
here. It satisfies that
(31)
The Heaviside function H and the split delta function
are supported by the line
,
is the propagating speed of
. From (31), similarly with the above case we obtain that the strength of
after the interaction of S and
is
As
, the delta shock wave
will propagate with the invariant speed
which is given by (15) with
and
as its right and left state. Furthermore, from the condition
we know the
-entropy condition for the new delta shock wave
holds which shows
is an overcompresive wave.
Case 3:
and
.
When t is small enough, the solution of the initial value problem (1) (3) and (5) can be described by (Figure 4)
Similar with the above case, the contact discontinuityJ will overtake the delta shock wave
at the point
given by (27). The delta shock wave
will pass through J with the same speed as before but the strength changes due to the difference between
and
. We still denote it with
after the time
, and
. Since the propagation speed of wave front in the rarefaction wave is
and that of the delta shock wave
satisfies the
-entropy condition
it is shown that R will interact with
at
which is determined by
(32)
it follows that
. The strength of
at
can be calculated by
. At the same time, a new delta shock wave
with varying speed is generated. Here we use
to express the curve of
and it is given in the following form
(33)
(34)
where
is a split delta function on the new delta shock, and
is the strength of the new delta shock at the time t.
When
, the delta shock wave cannot penetrate the rarefaction wave; when
, the delta shock wave can penetrate the rarefaction wave completely.
4. Conclusions
Now we construct the unique solution of the elementary wave interactions and get the following main conclusion. Using the characteristic analysis method, i.e., by analyzing the elementary wave curves in the phrase plane, we get the unique solution of the initial problem (1) with the state equation (3) and the initial values (4). We observe that the elementary wave interactions have a much simpler structure for Temple class than general systems of conservation laws since the wave interaction of the same family does not generate wave of other families for Temple systems. It is important to study the elementary waves interactions for (1) not only because of their significance in practical applications in the traffic flow system for the generalized Chaplygin gas, but also because of their basic role as building blocks for the general mathematical theory of the traffic flow system.
Theorem 4.1 The Riemann solutions of the initial value problem (1) (3) with the initial data (4) are constructed which are stable under such small perturbation on the initial data.
Funding
Supported by the Foundation for Young Scholars of Shandong University of Technology (No. 115024).