The strength of a natural clay is affected by its structure and anisotropy. The consolidated-undrained shear test with a constant principal stress axis deflection angle is conducted, where the consolidation pressure is 100 kPa and the constant deflection angle of the principal stress axis is 0°, 15°, 30°, 45° and 60°. And the influences of different constant principal stress axis deflection angles on the consolidated-undrained shear strength and the cumulative pore pressure of the saturated soft clay are analyzed. The total stress path of the total stress-controlled constant principal stress axis deflection angle shear test is derived. The integration program of the total stress-controlled shear three-dimensional point is developed. By comparing the calculated and test results of the shear strength at the constant principal stress axis deflection angle of the saturated soft clay under consolidated-undrained conditions, it is shown that the influence of the anisotropy on the shear strength of the soil is well revealed.
The transverse seismic response analysis of immersed tunnels is the key for the seismic design of immersed tunnel structures. According to the structure characteristics of immersed tunnels and the dynamic shear performance of the joints, a multibody dynamic model composed of the multi-rigid body, the shear hinge, and the viscous damping hinge is proposed for immersed tunnels based on reasonable assumptions. The mathematical models and formulae of each element and the system are deduced based on the discrete time transfer matrix method (MS-DT-TMM) of the multibody dynamics theory. The new method is applied in an example. The results agree well with benchmark simulation results from the finite element method (FEM). This method could provide a rapid seismic analysis for the transverse dynamic response of immersed tunnels.
In the numerical simulation of hydraulic fracturing in a shale gas reservoir, both the shale rock's properties and the multistage hydro-fracking technique of the horizontal well should be considered, which is a difficult problem of mechanics. In this paper, the mechanical characteristics of the shale rock and the multistage fracking technology of the horizontal well in the shale gas reservoir are discussed, as well as the applications of the extended finite element method, the boundary element method and the discrete element method in hydraulic fracturing and their advantages and limitations. It is indicated that the three dimensional displacement discontinuity method of the boundary element method is an effective approach to model the propagation of multistage fractures.
Mechanics, as the basic discipline of engineering sciences, plays a very important role in the design of the launch vehicle. Structure Dynamics, as an important part of mechanics, is especially important, and its developments reflect the level of the LV's (launch vehicle's) design in some extent. This paper discusses the interactions between structure dynamics and the launch vehicle technology, in the context of their development, and puts forward some proposals for the further development.
The magnetohydrodynamic technology becomes a research hotspot since the "AJAX" concept was proposed by Russia in the early 1990s. This paper reviews the advances of the studies of magenetohydrodynamic turbulence, mainly in two parts: the characteristics of magenetohydrodynamic turbulence and the numerical models of magenetohydrodynamic turbulence. Magnetohydrodynamic turbulence has some peculiar characteristics such as the anisotropy induced by the magnetic field, the Joule dissipation, the relaminarization of turbulence, which are different from common turbulence. This paper also discusses the effects of the magnetic field on the turbulence structures and the turbulence intensities. Two methods of numerical simulations are addressed for engineering applications: the Reynolds average Navier-Stokes equations and the large eddy simulation. Almost all studies are conducted for incompressible fluid, and it is not the case for aerospace applications since most of air vehicles operate in a medium of high Mach number, that is compressible.
The Circular Synthetic Aperture Radar (CSAR) is a special spotlight SAR (synthetic aperture radar) with an all-directional high spatial resolution. The feasibility of its space-borne implementation by a space-borne platform is analyzed based on a dynamical method. A trajectory model with the constraint of CSAR's operating conditions is built. And an active control force on the space-borne platform to keep its trajectory is determined by analyzing the motion and the load of the platform by a basing-point method. Results show that for any latitude area, the magnitude and the direction of the force needed vary too frequently to be actualized. For the north and south pole areas, to keep the platform moving along a circular trajectory with a certain angular velocity, the magnitude and the direction of the active control force needed vary slightly and are easy to be actualized.
A comprehensive comparison of the stiffness characteristics is made for the bolted flange and socket joints of two typical connected structures between cabins. First, the finite element results of a 3D fine model reveal that the static axial stiffness of the two bolted joints is asymmetric and symmetric in tension and compression, respectively. With a larger average static stiffness of tension and compression, the bolted flange joint has a higher natural vibration frequency. Then, a unified dynamic model of the two bolted joints is established, the motion of the flange joint is shown to be coupled because of the asymmetric axial stiffness. By approximating the nonlinear stiffness by high precision power functions, under the transverse dynamic load, numerical solutions of the impact response demonstrate that the frequency of the coupled longitudinal vibration is twice of the transverse frequency. Finally, for the flange joint, the double-frequency coupling longitudinal vibration is confirmed by the impact experiments. The socket joint can provide a high modal damping ratio despite the lower frequency for the first mode according to experimental results.
Using the PAM-CRASH software for transient dynamics, a constitutive model of bird is established based on the equation of state. The calculated dynamic response agrees well with experimental results for the aluminum plate under the bird impact. Two different structure types and the same structure with different thicknesses are simulated to model the dynamic response under the bird impact for the leading edge structure. Then, the energy absorptions are compared and analyzed. The research result can be used for the design of leading edge structures.
In order to study the effect of a transonic rotor blade static aeroelastic deformation on the aerodynamic performance, a time domain numerical simulation method for the Two-Way Fluid-Structure Interaction is applied to simulate the flow field and the solid domain of one-stage transonic compressor blades, The comparison of the aerodynamic performance and the natural frequency is analyzed in 100% rotating speed. The results show that the total aeroelastic deformation is dominated by the torsional deformation under aerodynamic and centrifugal forces. The aerodynamic force contribution to the total deformation at the leading edge is up to 20%, the flow capacity of the blade passage is enhanced and the aerodynamic characteristic map is shifted to the larger flow rate direction after the static deformation.
The temperature oscillation and the free surface deformation are two essential phenomena for the fluid with free surface. In this paper, an annular pool with upper opening is constructed to obtain critical conditions of the onset of temperature oscillations and free surface oscillations when the horizontal radial temperature gradient is given. The experimental pool is cooled from the outer cylinder walls by 6 semiconductor coolers and linearly heated from the inner cylinder walls at the rate of 0.5℃/min, resulting in a horizontal radial temperature difference. The T-type thermocouple is used here to measure the temperature at a single point in the liquid layer and the free surface deformation is obtained by the CCD (charge-coupled device) displacement sensor at the same time. The temperature and the free surface begin to oscillate when the temperature exceeds a threshold value with the increase of the temperature difference. Experimental results show that for the same kind of silicone oil, the Macr is proportional to the Bond number; the enhancement of the buoyancy convection can stabilize the whole flow; on the other hand, with the same thickness, the silicone oil of 1.5cSt has a larger Macr than that of 2cSt; the decrease of the viscosity makes the flow more stable.
The interior flow-field of the water saving faucet bubbler is simulated by the Fluent software to study the flow characteristics of a two phase flow. According to the flow characteristics in the faucet bubbler, an Eulerian-model with the two phase flow and the RNG (re-normalization group) κ-ε turbulence model are established separately to analyze the distribution of the gas-liquid phase volume fraction and the velocity at the exit section. Results show that the increased velocity of the inlet flows accelerates the dispersion of the gas and liquid at the exit section. Furthermore, the commute-net disperses the flow and reduces the flow velocity at the same time. Additionally, staggering the grid of the commute-net between the adjacent layers improves the distribution of the liquid phase in the exit section, and the commute-net with a 3-level grid achieves an even better flow effect.