大位移水平井两层不稳定岩屑传输模型研究

本文在Martins提出的两层模型基础上,考虑了悬浮层岩屑颗粒的扩散,建立了与时间相关的两层不稳定岩屑传输数学模型。用有限容积法求解了此偏微分方程组。研究结果表明:在一定条件下,环空岩屑传输流动达到稳定状态需要很长的时间,这表明用稳定流动模型来模拟环空中岩屑传输问题有其局限性;粘度的增加、环空返速的提高和机械钻速的降低有助于水平环空中岩屑的传输。

颅颈交界区不稳定三维有限元模型的建立

目的建立颅颈交界区[枕骨髁(C0)～C2]不稳定的三维有限元模型,并验证其有效性。方法在国人解剖学数据基础上选取1例健康成年男性志愿者,对C0～C2进行CT连续薄层扫描,导入相应软件进行三维几何模型重建,优化模型结构,生成骨性三维有限元模型,补充建立相关韧带结构。设定载荷1.5 N.m测定各脊柱节段单位(C0～C1、C1～C2)的前屈、后伸、侧屈、旋转的三维运动范围,位于文献测试结果范围内认为模型建立成功。删减横韧带、寰枕、寰枢关节囊的单元结构,模拟相应损伤,建立颅颈交界区不稳定模型,并进行有限元网格划分。再次测量各脊柱节段的三维运动范围,若较正常运动范围增大,则认为模型构建成功。结果成功建立正常成人颅颈交界区的三维有限元模型,整个模型共包括86 050个节点和55 371个单元。模型与实体组织具有良好的几何相似性。通过对单元结构的删减,各脊柱节段活动范围均较正常增大,成功建立颅颈交界区不稳定的三维有限元模型,共包括82 650个节点和53 370个单元。结论成功建立颅颈交界区不稳定三维有限元模型,该模型具有较高的真实性,可以用于相关生物力学试验研究。

双重介质模型在岩溶地下水流动系统模拟中的应用

文章采用不稳定层状裂隙水流模型,应用有限元-卷积结合法,模拟了岩溶地下水流动系统。相对于等效多孔介质模型,双重介质模型模拟的水位下降速度更小,达到稳定的时间更长。距抽水井较近的观测孔处,双重介质模型模拟的水位变化过程阶段性较明显,水位变化过程类似于承压含水层-弱透水层的释水过程,裂隙和孔隙基质分别相当于承压含水层和弱透水层。然后讨论了影响裂隙和孔隙基质间水流交换项的因素,分析了孔组抽水后的渗流场特征。

大位移井岩屑动态运移计算简便方法研究

对现有岩屑运移稳定和不稳定模型优缺点进行了分析,基于大位移井岩屑运移机理和连续性定理提出了一种半经验半理论的岩屑动态运移计算新方法,可以将稳定模型方便地用于大位移井岩屑动态运移计算中,可以简单描述岩屑实际运移和累积过程,同时计算简便,易于编程,适合工程应用。计算结果表明,使用稳定模型计算大位移井环空岩屑运移状态将会产生较大误差。使用该方法可以方便地分析不同间隔洗井操作所带来的效果,为工程洗井操作提供指导。

横韧带损伤的上颈椎不稳定三维有限元模型的建立研究

目的建立高仿真度的横韧带损伤的上颈椎(C_1~C_2)不稳定三维有限元模型。方法选取健康成年男性志愿者1名,对上颈椎进行薄层C_T检查,图片采用Dicom形式存储。将图片文件导入Mimics10.0三维重建软件,勾选出上颈椎的骨结构外形,以此重建三维几何。使用Freefrom 5.0结构优化软件对几何模型进行处理后录入Ansys10.0有限元软件,重建出上颈椎(C_1~C_2)的骨性有限元模型。根据相关数据资料构建各韧带结构。在建立完善的正常模型上通过删除寰椎横韧带的单元结构模拟相应损伤,以此建立横韧带损伤的上颈椎不稳定三维有限元模型,并对模型进行网格划分。结果建立了具有高仿真度的横韧带损伤的上颈椎(C_1~C_2)不稳定三维有限元模型,整个模型共有58 360个节点和31 020单元。结论建立的横韧带损伤的上颈椎(C_1~C_2)不稳定三维有限元模型具有较高的真实性,可以用于相关试验研究。

活动星系核在光学波段的光度及光谱斜率变化

利用盘不稳定模型和星爆模型,模拟活动星系核在光学B、V波段的光变,分析光变时光谱斜率的变化情况,并将模拟的结果和观测进行比较,结果表明,这两种模型是定性解释活动星系核光学波段光度、光谱变化的合理模型.

Experiments of Brittle-Plastic Transition and Instability Modes of Juyongguan Granite at Different Temperatures and Pressures

Three groups of experiments on brittle-plastic transition and instability modes of granite were performed in a triaxial vessel with solid pressure medium at high temperature and high pressure. The results of experiments show that brittle faulting is the major failure mode at temperature <300℃, but crystal-plastic deformation is dominate at temperature >800℃, and there is a transition with increasing temperature from semi-brittle faulting to cataclastic flow and semi-brittle flow at temperatures of 300～800℃. So, temperature is the most influential factor in brittle-plastic transition of granite and confining pressure is the second factor. The results also show that progressive failure of granite occurs at lower pressure or high temperature where there is crystal plasticity, and sudden instability occurs at room temperature and high pressure (>300MPa) or high temperature and great pressure(550℃600MPa ～650℃700MPa), and a broad regime of quasi-sudden instability exists between the T-P condition of progressive failure and sudden instability. So, instability modes of granite depend simultaneously on the pressure and temperature.

Multiple-Relaxation-Time Lattice Boltzmann Approach to Richtmyer-Meshkov Instability

The aims of the present paper are twofold. At first, we further study the Multiple-Relaxation-Time （MRT） Lattice Boltzmann （LB） model proposed in [Europhys. Lett. 90 （2010） 54003]. We discuss the reason why the Gram Schmidt orthogonalization procedure is not needed in the construction of transformation matrix M; point out a reason why the Kataoka-Tsutahara model [Phys. Rev. E 69 （2004） 035701（R）] is only valid in subsonic flows. The yon Neumann stability analysis is performed. Secondly, we carry out a preliminary quantitative study on the Richtmyer- Meshkov instability using the proposed MRT LB model. When a shock wave travels from a light medium to a heavy one, the simulated growth rate is in qualitative agreement with the perturbation model by Zhang-Sohn. It is about half of the predicted value by the impulsive model and is closer to the experimental result. When the shock wave travels from a heavy medium to a light one, our simulation results are also consistent with physical analysis.

Comparisons between unsteady sediment-transport modeling

The comparative study between unsteady flow models in alluvial streams shows a chaotic residue as for the choices of a forecasting model. The difficulty resides in the choice of the expressions of friction resistance and sediment transport. Three types of mathematical models were selected. Models of type one and two are fairly general, but require a considerable number of boundary conditions, which related to each size range of sediments. It can be a handicap during rivers studies which are not very well followed in terms of experimental measurements. Also, the use of complex models is not always founded. But then, the model of type three requires a limited number of boundary conditions and solves only a system of three equations at each time step. It allows a considerable saving in calculating times.

Performance enhancement of IMC-PID controller design for stable and unstable second-order time delay processes

An IMC-PID controller was proposed for unstable second-order time delay system which shows the characteristics of inverse response(RHP zero). A plot of Ms versus λ was suggested to calculate the suitable tuning parameter λ, which provides a trade-off between performance and robustness. Six different forms of process models were selected from literature to show the applicability of the present method. Performance of controller was calculated by ITAE and total variation TV and compared with recently published tuning rules. Undesirable overshoot was removed by using a set-point weighting parameter. Robustness was tested by introducing a perturbation into the various model parameters and closed-loop results show that the designed controller is robust in the case of model uncertainty. The proposed method shows an overall better closed-loop response as compared to other recently reported methods.

Two Approaches of Substance Flow Analysis—An Inspiration from Fluid Mechanics

That flow is the common feature of substance flow and fluid flow is the viewpoint emphasized in the paper. Some notes on fluid mechanics, including the two approaches of fluid flow description, were given. The concepts of the chain and the chain group of product life cycles, which are essential for understanding the specific features of substance flow, were advanced. Taking the specific feature of substance flow into consideration, on the analogy of the two approaches in fluid mechanics, two approaches of substance flow analysis, i.e. L method and E model, were formulated. Illustrative models of steady and unsteady substance flow were sketched by both methods, and comparison between them was made in general.

Low-speed instability analysis for hydraulic motor based on nonlinear dynamics

A nonlinear dynamics model and a mathematical expression were set up to investigatethe mechanism and conditions of vibration creep acceleration.The model showsthat hydraulic spring and nonlinear friction are major factors that can affect low-speed instability.The mathematic model was established to obtain the change rule of speed andinstantaneous acceleration of the hydraulic motor.Then, Matlab was used to simulate theeffect of nonlinear friction force and hydraulic motor parameters such as coefficient of leakand compression ratio, etc., under low speed.Finally, some measures were proposed toimprove the low-speed stability of the hydraulic motor.

Unsteady lubrication modeling of inlet zone in metal rolling processes

An unsteady lubrication model of inlet zone in metal rolling was established. The simulation computations show that for the variation amplitude of the inlet film thickness, the variation of the inlet angle contributes the largest, the surface mean speed contributes the second and the back tension stress the least. The higher the input frequency is, the smaller the amplitude output of the inlet film thickness will be. For a sinusoidal input, the inlet film thickness varies periodically but is not a sine wave because the system is not linear.

Gas-Fluid and Fluid-Solid Phase Instability for Restricted Primitive Model

By considering the fluctuation of grand potential f~ around equilibrium with respect to small one-particle density fluctuations δpα（r→）, the phase instability of restricted primitive model （RPM） of ionic systems is investigated. We use the integral equation theory to calculate the direct correlation functions in the reference hypernetted chain approximation and obtain the spinodai line of RPM. Our anaiysis explicitly indicates that the gas-fluid phase instability is induced by k = 0 fluctuation mode, while the fluid-solid phase instability is related to k ≠ 0 fluctuation modes. The spinodai line is qualitatively consistent with the result of computer simulations by others.

Non-Topological Domain Walls in a Model with Broken Supersymmetry

We study non-topological, charged planar walls （Q-walls） in the context of a particle physics model with supersymmetry broken by low-energy gauge mediation. Analytical properties are derived within the fiat-potential approximation for the flat-direction raising potential, while a numerical study is performed using the fall two-loop supersymmetric potential. We analyze the energetics of finite-size Q-walls and compare them to Q-balls, non-topological solitons possessing spherical symmetry and arising in the same supersymmetric model. This allows us to draw a phase diagram in the charge-transverse length plane, which shows a region where Q-wall solutions are energetically favored over Q-balls. However, due to their finiteness, such finite-size Q-walls are dynamically unstable and decay into Q-balls in a time which is less than their typical scale-length.

Impacts of NBTI/PBTI on power gated SRAM

A signal probability and activity probability (SPAP) model was proposed firstly, to estimate the impacts of the negative bias temperature instability (NBTI) and positive bias temperature instability (PBTI) on power gated static random access memory (SRAM). The experiment results show that PBTI has significant influence on the read and write operations of SRAM with power gating, and it deteriorates the NBTI effects and results in a up to 39.38% static noise margin reduction and a 35.7% write margin degradation together with NBTI after 106 s working time. Then, a circuit level simulation was used to verify the assumption of the SPAP model, and finally the statistic data of CPU2000 benchmarks show that the proposed model has a reduction of 3.85% for estimation of the SNM degradation after 106 s working time compared with previous work.

A Simple Model for Earthquake Instability

Based on the heterogeneity of fault plane strength,the macro rupture process of a fault plane can be treated as the rupture accumulation process of local micro-elements in the fault surface.Assuming that the strength of the local micro-elements follows the Weibull probability distribution,the macro-fault constitutive relationship of the complete load-deformation process is derived from a statistical mechanics viewpoint.Applying a one-dimensional earthquake mechanics model and using far-field displacement a as the control variable,the problem of earthquake instability is investigated by employing the stability theory.The results show that the system stiffness ratio(stiffness ratio of fault to surroun-ding rock) β is the important parameter that affects the occurrence of earthquakes.Earthquake instability occurs only when β < 1,and the sudden stress jump appears at the displacement turning point of the equilibrium path curve.The expression of three important parameters for earthquakes(fault half-dislocation distance after earthquake,earthquake stress drop and elastic energy release) is also given.When β≥1,the earthquake does not occur and the fault only slips slowly without an earthquake.

R-Parity Violation Effects on b_1 → bχ_1~0 in Minimal SupersymmetricStandard Model

We investigate in detail the effects of R-parity lepton number violation onthe decay b_1 → bχ_1~0 in the R-parity violating minimal supersymmetric standard model (R_p-MSSM)under the present experimental constraints on R_p parameters. In our numerical calculations weconsider two cases of input parameters of the squark and slepton sectors, M_(squark) 【 M_(slepton)and M_(squark) 】 M_(slepton), for comparison. The results show that the relative R-parity violatingcorrection is not very sensitive to the mass of the lightest neutralino bχ_1~0 the degenerateR-parity violating coupling parameter λ′_2 but strongly depends on M_(squark), M_(slepton) tan βand tie degenerate R-parity violating coupling parameter λ′_1. The relative correction is about -4～ 3% and can exceed -6% in some region of parameter space. Therefore, precise experiment analyseson the decay b_1 → bχ_1~0 may provide a probe of the R-parity violation.

Application of gravity inversion focused in Changbai Mountain

Focusing inversion is accomplished by the iterative of abnormal source to make the image gradually focused. It can better reflect the underground geological geometry and physical parameters. The model experiments in the study show that gravity focusing inversion allows inversion image stabilization and polymerization,which solves the multiple solutions and instability of inversion and so on. The method is applied to measured gravity data processing of certain region of Changbai Mountain,compared to Euler deconvolution,the results show that the method for determining the horizontal position and depth of underground anomalies has good efforts.

On Relative Stability in 4-Dimensional Duck Solution

This paper gives the existence of a relatively stable duck solution in a slow-fast system in R2＋2 with an invariant manifold. The slow-fast system in R2＋： has a 2-dimensional slow vector field and a 2-dimensional fast vector field. The fast vector field restricts a feasible region of the slow vector field strictly. In the case of the slow-fast system in R2＋1 , that is, the fast vector field is l-dimension, it is classified according to its sign, because it gives only negative（-）, positive（＋） or zero sign. Then it is attractive, repulsive or stationary. On the other hand, in R2~2 , the fast vector field has combinatorial cases. It causes a complex state to analyze the system. First, we introduce a local model near the pseudo singular point on which we classify the fast vector field attractive（-,-）, attractive-repulsive（-,＋） or repulsive（＋,＋）, simply as possible. We prove the existence of a 4-dimensional duck solution in the local model. Secondarily, we assume that the slow-fast system has an invariant manifold near the pseudo singular point. When the invariant manifold has a homoclinic point near the pseudo singular point, we show that the slow-fast sytem has a 4-dimensional duck solution having a relatively stable region.