CoInvestigator(Kenkyūbuntansha) 
SAKATA Sadahisa Faculty of Engineering, Osaka ElectroCommunication University Associate Professor, 工学部, 助教授 (60175362)
YAMAHARA Hideo Faculty of Engineering, Osaka ElectroCommunication University Associate Professor, 工学部, 助教授 (30103344)
MANDAI Takeshi Faculty of Engineering, Osaka ElectroCommunication University Professor, 工学部, 教授 (10181843)

Budget Amount *help 
¥3,400,000 (Direct Cost: ¥3,400,000)
Fiscal Year 2000: ¥1,600,000 (Direct Cost: ¥1,600,000)
Fiscal Year 1999: ¥1,800,000 (Direct Cost: ¥1,800,000)

Research Abstract 
1.Stability of the Maxwell States in ThermoElasticity : In the isothermal elasticity, the Maxwell states can be defined by the equalarea principle. We proved in this research that these Maxwell states are asymptotically stable in time. Moreover, the entropy function is expressed by means of the mechanical Gibbs function, even if the states are not stationary. In the polytropic thermoelasticity, on the other hand, the Maxwell states are defined to constitute a phase boundary such that the entropy of the both sides coincides. We proved that there exists a unique transitional map in a neighborhood of a pair of Maxwell states together with the kinetic condition. However, we have shown that the Riemann problem has at least two solutions under certain condition. In this case, if we prescribe the increase or decrease of the temperature after the phase transition, we can single out a unique solution. The above study indicates in the polytropic elasticity, different from the isothermal elast
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icity, the Maxwell states must be unstable. 2.Geometric Uniqueness Theorem in the Riemann Problem : We obtain a uniqueness theorem for the Riemann problem for general 2x2system of conservation laws in a strictly hyperbolic domain whose boundary contains an isolated umbilic point. The condition for uniqueness is given by the following : for j=1 and 2, the gradient of the jcharacteristic direction and the secant from the center of the jHugoniot curve to the point on the curve are confined to fixed disjoint sectors for j=1 or 2, respectively. This condition is a generalization of that obtained by T.P.Liu in 70's. Moreover, in the process of our study, we gave a proof of the theorem declared by him but the details of its proof are not yet published. 3.Admissible Discontinuous Solutions for Nonstrictly Hyperbolic Conservation Laws : We carried out a geometric study of the Hugoniot curves for conservation laws whose flux vector is a quadratic function of the state variables and has an isolated umbilic point. We found precise regions where the Lax entropy condition holds. In particular, for the SchaefferShearer's class I, where the geometric structure is most complicated, we gave a mathematical proof of claims that had been postulated only by numerical studies. Here, it is essential that the Hugoniot curves are rational curves. Less
