Vertical Nonlinear Temperature Gradient and Temperature Load Mode of Ballastless Track in China

In the process of heat exchange with the external environment, the internal temperature of ballastless track structure presents a nonlinear distribution. The vertical temperature gradient will cause repeated warping and deformation of track slab, resulting in mortar layer separation, which will affect driving comfort and track durability. The traditional temperature field analysis method of concrete structure based on thermodynamics has the disadvantages of too many assumptions, difficult parameter selection and too much calculation of energy consumption. In this paper, based on the finite element software ANSYS, the heat exchange was transformed into the boundary condition of heat flux, which was applied to the thermodynamic analysis model to study the nonlinear temperature distribution law of ballastless track. The accuracy of the analysis method was verified by the measured data. On this basis, the regional distribution law of temperature gradient of ballastless track under different geographical coordinates and climatic conditions was studied. By adding a regional adjustment coefficient, the vertical temperature load model of ballastless track suitable for typical areas in China was proposed. The proposed temperature load model makes up for the lack of refinement of climate division and temperature load model in relevant specifications, and has strong engineering application and popularization value.

On the Stefan Problem With Nonlinear Thermal Conductivity

The solution is obtained and validated by an existence and uniqueness theorem for the following nonlinear boundary value problem \[ \frac{d}{dx}(1+\delta y+\gamma y^{2})^{n}\frac{dy}{dx}]+2x\frac{dy}{dx}=0,\,\,\,x>0,\,\,y(0)=0,\,\,\,y(\infty)=1, \] which was proposed in 1974 by [1] to represent a Stefan problem with a nonlinear temperature-dependent thermal conductivity on the semi-infinite line (0;1). The modified error function of two parameters $\varphi_{\delta,\gamma}$ is introduced to represent the solution of the problem above, and some properties of the function are established. This generalizes the results obtained in [3, 4].

Vibration Characteristics of Hybrid Honeycomb Core Sandwich Structure with FG-CNT Reinforced Polymer Composite Faces under Various Thermal Fields

This paper presents the free and forced vibration characteristics of a hybrid honeycomb core sandwich structure consisting of a top and bottom FG-CNT reinforced polymer composite face sheet in a thermal environment. Different thermal fields like the uniform, linear and nonlinear temperature fields in the thermal environment along the thickness direction are considered to study the dynamic characteristics of the hybrid honeycomb core sandwich structure. The mathematical model is developed using Hamilton’s principle along with the third-order shear deformation theory. Five unknown modal coefficients are found using the modal superposition principle to calculate the forced vibration response. From the free and forced vibration results, it is observed that the FG-V[Formula: see text] grading pattern face sheets with lower cell size honeycomb core and with higher cell wall thickness honeycomb core show better vibration characteristics. It is noticed that the sandwich structure with honeycomb core and FG-V[Formula: see text] CNT reinforced polymer composite face has a higher critical buckling temperature in the thermal environment. Furthermore, for different percentages of critical buckling temperature, the natural frequencies and vibrating patterns for uniform, linear and nonlinear temperature fields are the same for the sandwich structure with UD, FG-V[Formula: see text] and FG-[Formula: see text]V CNT reinforced polymer composite faces. In addition, the resonant peak of the sandwich structure with FG-V[Formula: see text] CNT reinforced polymer composite face in nonlinear temperature field shifts more toward the right, while that of the uniform temperature field shifts more toward the left in the velocity response.