Abstract: Japan Aerospace Exploration Agency (JAXA) has studied Space Solar Power Systems (SSPS) using laser and microwave beams for years since 1998. Current SSPS study undertaken by JAXA consists of three main subjects, SSPS concepts and architectures study, technology demonstration and elemental technology development. In current research of Laser based SSPS (L-SSPS), we have studied some elemental technologies such as ultralight film mirror, wavelength selective mirror, laser generator based on direct solar pumping solid-state laser diode, laser transmission property in atmosphere, photovoltaic generation converting laser energy to electricity and photocatalytic hydrogen generation. This paper presents the introduction of SSPS concepts and architectures study and elemental technology development of L-SSPS.
Abstract: Laser medium for solar-pumped solid laser of 10MW-1GW power is a key to realize Laser Space Solar Power System (L-SSPS). Since it is an ultrahigh power system operated in space, the laser medium must satisfy the conditions such as high efficiency, high power per weight or volume, excellent durability and maintainability, thermal equilibrium operation, and excellent long-range propagation of oscillated laser. YAG (Y3Al5O12) ceramics doped doubly with Nd and Cr is considered to be a suitable laser medium for L-SSPS at present. There are the following important points for L-SSPS application: 1) Optimization of the doping amount, 2) Process, 3) Temperature control. Feasibility of YAG ceramics is discussed from a view point of material science and proposed a YAG ceramics structure with graded distribution of dopants.
Abstract: Transient dynamic behavior of a three-dimensional (3D) homogeneous cantilever beam under sinusoidal loading at the free end is verified using the finite element method (FEM). Explicit central difference technique is used for the time integration of finite elements. The tip displacement and maximum stress at the fixed end obtained using the FEM agree well with exact solutions. Modal analysis of a functionally graded (FG) 3D cantilever beam is investigated using Rayleigh-Ritz (RR) method and the FEM. The natural frequencies obtained using the RR method converges as the number of terms in the assumed base function increases. The natural frequencies vary considerably with the gradation of the beam, more for lower modes than for higher modes. Wave propagation in a fixed-free 3D bar is studied using the FEM. Axial stress results for the homogeneous bar with zero Poisson’s ratio agree closely with 1D exact solution. For the FG bar, we see that gradation affects stresses considerably more so at the fixed end than at other locations.
Abstract: The plane strain problem for a functionally graded solid cylinder with thermal energy generation under the effect of convective heat transfer is considered. In previous studies on FGM cylinders in the literature, the modulus of elasticity, the thermal conductivity and the thermal expansion coefficient are represented by using either exponential or power functions. However, this study considers different functions for these material properties, which results in a more realistic representation of the problem. The stress and strain components are evaluated analytically and their dependencies on the radially varying material parameters are presented at the elastic state. Critical values of the volumetric thermal energy generation evaluated for a homogeneous solid cylinder and for an FGM cylinder are compared by using the Tresca’s Yield Criterion. Numerical results are generated by considering a W/Cu FGM solid cylinder which has potential applications as an International Thermonuclear Experimental Reactor (ITER) component.
Abstract: Minimum interlayer numbers of functionally graded materials (FGMs) are studied based on the empirical analysis of thermal stress due to the differences in the thermal expansion coefficient and temperature T between sintering and room temperatures. It is found the maximum , and the minimum interlayer number necessary to produce a NiCr / Fly ash FGM structure without interface cracking were 4.0×10-6 K-1, 1080 K, 0.043 and 2, respectively. The condition < 0.043 was derived and confirmed to be valid for available FGM systems.
Abstract: This paper is aimed to numerically evaluate the effective thermal conductivity of randomly distributed spherical particle composite with imperfect interface between the constituents. A numerical homogenization technique based on the finite element method (FEM) with representative volume element (RVE) was used to evaluate the effective properties with periodic boundary conditions. Modified random sequential adsorption algorithm (RSA) is applied to generate the three dimensional RVE models of randomly distributed spheres of identical size with the volume fractions up to 50%. Several investigations have been conducted to estimate the influence of the imperfect interfaces on the effective conductivity of particulate composite. Numerical results reveal that for the given composite, due to the existence of an interfacial thermal barrier resistance, the effective thermal conductivity depends not only on the volume fractions of the particle but on the particle size.
Abstract: In this work, hypersonic aero-thermo post-buckling and thermal flutter behaviors of Functionally Graded (FG) panels under thermal and aerodynamic loads are investigated. The volume fractions of constitutive materials of the panels are gradually varied from ceramic to metal in the thickness direction based on a simple power law distribution. Thus, the material properties of the panel are also changed by a linear rule of mixture. Furthermore, the material properties are assumed to be temperature dependent because the panels are mainly used in the high temperature environments. Using the principle of virtual work, the equations of motion of the first-order shear deformation plate theory (FSDPT) are derived and the finite element method is applied to get the solution. In the formulation, the von Karman strain-displacement relationship is used for structural nonlinearity, and the partial second-order piston theory is adopted to consider the aerodynamic nonlinearity. Newton-Raphson iterative technique is used to solve the governing equations, and linear eigenvalue analysis is performed to obtain the hypersonic flutter boundaries.
Abstract: Asphalt concrete pavements are inherently graded viscoelastic structures. Oxidative aging of asphalt binder and temperature cycling due to climatic conditions are the major cause of such graded non-homogeneity. Current pavement analysis and simulation procedures either ignore or use a layered approach to account for non-homogeneities. For instance, the recently developed Mechanistic-Empirical Design Guide (MEPDG) , which was recently approved by the American Association of State Highway and Transportation Officials (AASHTO), employs a layered analysis approach to simulate the effects of material aging gradients through the depth of the pavement as a function of pavement age. In the current work, a graded viscoelastic model has been implemented within a numerical framework for the simulation of asphalt pavement responses under various loading conditions. A functionally graded generalized Maxwell model has been used in the development of a constitutive model for asphalt concrete to account for aging and temperature induced property gradients. The associated finite element implementation of the constitutive model incorporates the generalized iso-parametric formulation (GIF) proposed by Kim and Paulino , which leads to the graded viscoelastic elements proposed in this work. A solution, based on the correspondence principle, has been implemented in conjunction with the collocation method, which leads to an efficient inverse numerical transform procedure.
This work is the first of a two-part paper and focuses on the development, implementation and verification of the aforementioned analysis approach for functionally graded viscoelastic systems. The follow-up paper focuses on the application of this approach.