Non-parallel Layers Research Articles

Burning Rate Enhancement Analysis of End-Burning Solid Propellant Grains Based on X-Ray Real-Time Radiography

Unexpected pressure rise may occur in the end-burning grain solid rocket motor. It is generally believed that this phenomenon is caused by the nonparallel layer combustion of the burning surface, resulting in the increase of burning rate along the inhibitor. In order to explain the cause of this phenomenon, the experimental investigation on four different end configurations were carried out. Based on the X-ray real-time radiography (RTR) technique, a new method for determining the dynamic burning rate of propellant and obtaining the real-time end-burning profile was developed. From the real-time images of the burning surface, it is found that there was a phenomenon of nonuniform burning surface displacement in the end-burning grain solid rocket motor. Through image processing, the real-time burning rate of grain center line and the real-time cone angle are obtained. Based on the analysis of the real-time burning rate at different positions of the end surface, the end face cone burning process in the motor working process is obtained. The closer to the shell, the higher the burning rate of the propellant. Considering the actual structure of this end-burning grain motor, it is speculated that the main cause of the cone burning of the grain may be due to the heat conduction of the metal wall. By adjusting the initial shape of the grain end surface, the operating pressure of the combustion chamber can be basically unchanged, so as to meet the mission requirements. The results show that the method can measure the burning rate of solid propellant in real time and provide support for the study of nonuniform combustion of solid propellant.

Molecular basis for coke strength: Stacking-fault structure of wrinkled carbon layers

A macromolecular model with formula C60468H2193O527N468S49 was constructed for Pingyao coke by using microstructural characteristics and theoretical calculations. The coke model geometry was obtained by simulated annealing algorithm in molecular dynamics simulations with reactive force field (ReaxFF). ReaxFF parameters were modified iteratively until the model geometry agreed with X-ray photoelectron spectroscopy and X-ray diffraction data. The model indicates that the carbon matrix in coke is composed of wrinkled carbon layers, which agrees with reported high-resolution transmission electron microscope results. Neighboring carbon layers are not synclastic and have some stacking faults (such as arch-shaped moieties and screw dislocation), which result in increased layer spacing or non-parallel layers. To investigate the molecular basis for coke strength, ReaxFF simulations of the coke compression process were performed at 300 K and 3500 K, respectively. Results showed that the stacking-fault structure of wrinkled carbon layers was the main microscopic cause of coke strength. Wrinkled carbon layers can disperse the external force, and stacking-fault moieties restrained the interface slippage of carbon layers. Coke structural changes that were caused by the external force presented different characteristics at different temperatures. High temperatures aid the coke matrix reconstruction and prompt the formation of large and planar carbon layers.

Ultrasonic non-destructive testing of complex titanium/carbon fibre composite joints

Ultrasonic inspection is widely used for non-destructive evaluation of composite adhesive joints. However, there are serious challenges in applying ultrasonic testing on metal to composite hybrid joints, because they are multi-layered, made out of dissimilar materials and relatively thin. The ultrasonic signals reflected by different layers are overlapped, scattered and attenuated. The aim of this research was to develop an ultrasonic inspection technique suitable for defect detection in hybrid metal to composite joints where the metal part has pin arrays, which entangle with the composite part. The immersion pulse echo technique was used to collect data. In order to overcome the problems related to the rough surface and non-parallel layers a novel signal post-processing algorithm for reconstruction of the joint area was developed and validated experimentally. It is shown that using the proposed technique the positions of different defects can be determined.

Seafloor sound-speed profile characterization with non-parallel layering by the image source method: Application to CLUTTER'09 campaign data.

The image source method was originally developed to estimate sediment sound speed as a function of depth assuming plane-layered sediments. Recently, the technique was extended to treat dipping, i.e., non-parallel layers and was tested using synthetic data. Here, the technique is applied to measured reflection data with dipping layers and mud volcanoes. The data were collected with an autonomous underwater vehicle towing a source (1600-3500 Hz) and a horizontal array of hydrophones. Data were collected every 3 m criss-crossing an area about 1 km(2). The results provide a combination of two-dimensional sections of the sediment sound-speeds plotted in a three-dimensional picture.

Seismic response of laterally inhomogeneous geological region by boundary integral equations

The proposed study deals with synthesis of seismograms by BIEM (boundary integral equation method) taking into account all three base components-seismic source, wave path and local region of interest. Consider a laterally inhomogeneous geological profile situated in a half-plane with non-parallel layers. Seismic load is time-harmonic or transient in time. It is presented by incident SH wave or wave radiating from an embedded line seismic source. Two types of lateral inhomogeneities with arbitrary shape and located in the inhomogeneous half-plane are considered: (i) free-surface relief as a canyon or a hill; (ii) alluvial basin with properties different from those of the layered half-plane. The computational tool is BIEM based on the frequency-dependent elastodynamic fundamental solutions. A relation between displacements and tractions along the free surface and arbitrary interface of the soil stratum is derived, which is applicable for arbitrary geometry of the interfaces between soil layers. Validation and convergence study is presented. All simulations reveal the sensitivity of the synthetic seismic signals on the type and characteristics of the seismic time-harmonic or transient load, on the wave path inhomogeneity and on the specific geotechnical properties of the local geological region.

Seismic wave propagation in laterally inhomogeneous geological region via a new hybrid approach

2D seismic wave propagation in a local multilayered geological region rested in an inhomogeneous half-space with a seismic source is studied. Plane strain state is suggested. The vertical variation of the soil properties in the half-space is modelled by a set of horizontal flat isotropic, elastic and homogeneous layers. The finite local region is with non-parallel layers and free surface relief. Efficient hybrid wavenumber integration-boundary integral equation method (WNI-BIEM) is proposed, validated and applied for synthesis of seismic signals in the finite soil stratum. The numerical simulation reveals that the developed hybrid method is able to demonstrate the sensitivity of the obtained synthetic signals to the seismic source properties, to the heterogeneous character of the wave path and to the relief peculiarities of the local stratified geological deposit. The advantages and disadvantages of the proposed method are discussed.

Site effects due to wave path inhomogeneity by BEM

The time-harmonic response of a multi-layered soil deposit resting on the elastic half-plane under the influence of incoming pressure and shear waves is numerically investigated by a hybrid boundary integral equation-plane wave decomposition method. The multi-layered deposit is finite-sized, with non-parallel layers and contains a free-surface relief, while the half-plane into which it is embedded is elastic, isotropic and inhomogeneous. Two basic types of material inhomogeneity are considered for the half-plane, namely a shear modulus that varies (a) quadratically and (b) exponentially with respect to the depth coordinate. In all cases, Poisson's ratio is fixed at one-quarter and conditions of plane strain are assumed to hold. This boundary-value problem is solved by using the direct boundary element method, while free-field motions in the surrounding inhomogeneous half-plane that include contributions of incident as well as of reflected waves, are computed by an analytical plane wave decomposition method. In order to handle both internal (the multi-layered region) and external (the half-plane domain) components of this problem, boundary conditions in the form of displacement and stress field continuity along the common interface between these two regions are imposed. Finally, a detailed simulation study of a complex geological region is conducted in the frequency domain, and the results clearly demonstrate the importance of local site effects on the propagation of obliquely incident waves following a wave path that is continuously inhomogeneous.

Particle transport through two-dimensional, saturated porous media: influence of physical structure of the medium

Recent work in the transport of particulate matter (e.g. bacteria, viruses, colloids, mineral grains, etc.) through saturated porous media has indicated that the physical structure of the porous medium plays an important role in both the ability of the particles to be transported and the distribution of the particles deposited within the medium. The present paper addresses the influence on particle transport within saturated porous media of high-permeability pathways and contacts between different grain size distributions. The experiments discussed in the present paper were conducted in two dimensions. The porous media were constructed from glass beads and the tracer utilized consisted of latex spheres in the size range 2–90 μm (2–30 μm in most experiments). Among the media designs investigated were simple layers in which flow was parallel to layers, simple layers in which flow was at an angle to layers, a simple form of heterogeneity including non-parallel layers and disjoint inclusions, and a complex heterogeneity involving three interconnected permeabilities. Results from these experiments demonstrated that significantly greater numbers of particles were deposited at media contacts where water moved from larger to smaller diameter glass beads. Further, it was observed that outflow concentrations of particles for media containing continuous flow paths within the coarse glass beads were substantially higher than outflow concentrations of particles for media containing a number of interfaces between different-sized glass beads. Specifically, a comparison of the results for a medium in which flow was parallel to layers with results from a medium in which flow was at an angle to the layers led to the observation of higher concentrations of latex particles in the outflow from the former medium and high concentrations of particles remaining in the region of layer contacts within the latter medium. Similar observations were made in a comparison of the simple and complex heterogeneities. Based on these results and prediction of straining based on the filtration literature, it is argued that the enhanced deposition observed near contacts results from sorption leading to increased straining in regions of lower uniformity in the glass bead distribution. These results demonstrate the importance of particle transport along high-permeability pathways and the enhanced deposition which may occur at contact surfaces within heterogeneous porous media.

Magnetotelluric theory of the sinusoidal interface

Most of the theoreticians working on the magnetotelluric method have concentrated on models of the earth which are flat and composed of parallel layers of material having differing conductivities. The purpose of this paper is to demonstrate the effect which nonparallel layers have on the electric and magnetic fields. We simulate the earth by two conducting layers which are joined at an interface which is sinusoidal. The incident waves are plane and of two polarizations chosen to make the electric or the magnetic field parallel to the corrugations of the interface. The electromagnetic field is found for both polarizations by formulating a set of integral equations which are solved by a perturbation technique in conjunction with an established Fourier transform method. The resulting electromagnetic fields are used to form the ratios Ey/Hx and Ex/Hy. When the interface is flat, these ratios are equal, but when it is sinusoidal, they are not, in general. Although usually small, this difference may be diagnostic for some cases of geological significance. The amplitude of the perturbed part of the electromagnetic field also has the interesting property of decaying or increasing above the surface of the earth, depending upon whether the ratio of the wavelength of the incident wave to the wavelength of the interface is greater or less than unity.