Torsional Surface Waves in Nonhomogeneous Anisotropic Medium under Initial Stress

This paper studies the possibilities of propagation of torsional surface waves in nonhomogeneous anisotropic half-space under compressive initial stress. Two types of variations in nonhomogeneity, mainly hyperbolic and quadratic, have been discussed, and it is observed that in both cases the torsional surface wave will propagate in the media under consideration. The velocities of propagation have been computed and are presented in graphs. The study shows that for hyperbolic variation of nonhomogeneity, the increase of the anisotropic factor, increases the velocity of propagation, always keeping it more than that of shear wave in homogeneous medium. The presence of initial stress increases the velocity of propagation. In the case of quadratic variation it is found that the presence of initial stresses increases the velocity of propagation. The increase of anisotropy decreases the velocity, and the decrease in the nonhomogeneity factor increases the velocity, always keeping the velocity of torsional surface waves less than that of shear wave in the homogeneous medium.     

Torsional Surface Waves in an Initially Stressed Anisotropic Porous Medium

It is well known that the homogeneous elastic half space does not allow the torsional surface wave to propagate. The present article attempts to study the possibility of propagation of such waves in a liquid-filled initially stressed poroelastic layer over nonhomogeneous half space. The study concludes that torsional surface waves may propagate in the poroelastic layer. The presence of fluid in pores and initial compressive stresses diminishes the velocity. The nonhomogeneity in rigidity and density of the half space also has a certain role to play in initiating, enhancing, or diminishing the velocity of torsional surface waves.     

Degradation of Sands due to Combined Sinusoidal Loading

Dynamic loading due to earthquakes is made up of very complicated combinations of different types of waves including compressive waves, shear waves, etc. If a soil specimen is subjected to a combined longitudinal and torsional excitation, significant degradation of the specimen occurs, wherein the modulus is reduced and the damping increased more than for single excitation. This paper presents equations based on test results on clean sands for the determination of the shear modulus and damping of sandy soils for single and combined sinusoidal loadings. From the equations, the degree of specimen degradation can be determined, as well as the threshold strain ratio needed for the degradation to occur. The dynamic properties obtained from combined loadings will be more representative of actual field conditions than those from single-loading conditions.     

Water Well Resonance Induced by Preearthquake Signals

This study elucidates the water well resonance induced by preearthquake signals using an analytic approach. Weak pressure waves passing through a confined aquifer are considered as the incoming preearthquake signal. Owing to the hardness of the porous skeleton, the pressure waves are simply the limiting case of the second kind of dilatational waves of poroelasticity. Because the driving signals of a weak preearthquake pressure wave transmitting through a confined aquifer are too weak to significantly affect the solid skeleton, we believe that this phenomenon is attributed to the effect of resonant amplification of water levels in wells. The flow inside the well is assumed to be incompressible, inviscid, and irrotational, while that outside the well is treated as a porous-media flow with a rigid skeleton. The flows inside and outside the well are analyzed using the potential flow theory under the assumption of small-amplitude waves and Darcy’s law of porous-media flow, respectively. The well-posed boundary value problem is solved using the regular perturbation expansion based on a small gauge function k0R, where k0 = wave number and R = well radius. The results of this study demonstrate that the weak preearthquake longitudinal pressure wave is only a triggering mechanism for the resonance of transverse gravity surface water waves inside the well.     

Effective Soil Density for Propagation of Small Strain Shear Waves in Saturated Soil

This technical note defines an “effective soil density” that controls the velocity of small strain shear waves in saturated soil. Biot theory indicates that the ratio of effective density to saturated density will generally range from 0.75 to 1.0 and is a function of specific gravity of solids, porosity, hydraulic conductivity, and shear wave frequency. For many geotechnical applications, effective density will be equal to saturated density for low hydraulic conductivity soils (clays and silts) and may be less than saturated density for high hydraulic conductivity soils (clean sands and gravels). The findings are relevant to applications involving the propagation of small strain shear waves through saturated soil, and in particular for laboratory and field tests in which shear modulus is back-calculated from measured shear-wave velocity.     

Shallow Water Wave Propagation in Convectively Accelerating Open-Channel Flow Induced by the Tailwater Effect

Propagation of shallow water waves in viscous open-channel flows that are convectively accelerating or decelerating under gradually varying water surface profiles is theoretically investigated. Issues related to the hydrodynamics of wave propagation in a rectangular open channel are studied: the effect of viscosity in terms of the Manning coefficient; the effect of gravity in terms of the Froude number; wave translation and attenuation characteristics; nonlinearity and wave shock; the role of tailwater in wave propagation; and free surface instability. A uniformly valid nonlinear solution to describe the unsteady gradually varying flow throughout the complete wave propagation domain at and away from the kinematic wave shock as well as near the downstream boundary that exhibits the tailwater effect is derived by employing the matched asymptotic method. Different scenarios of hydraulically spatially varying surface profiles such as M1, M2, and S1 type profiles are discussed. Results from the nonlinear wave analysis are further interpreted and the influence of the tailwater effect is identified. In addition to the nonlinear wave analysis, a linear stability analysis is introduced to quantify the impact from such water surface profiles on the free surface instability. It is shown that the asymptotic flow structure is composed of three distinct regions: an outer region that is driven by gravity and channel resistance; a near wave shock region dominated by the convective inertia, pressure gradient, gravity and channel resistance; and a downstream boundary impact region where the convective inertia, pressure gradient, gravity and channel resistance terms are of importance. The tailwater effect is demonstrated influential to the flow structure, free surface stability, wave transmission mechanism, and hydrostatic pressure gradient in flow.     

Microporodynamics of Bones: Prediction of the “Frenkel–Biot” Slow Compressional Wave

Understanding of ultrasonic wave propagation in bones is essential for further development of related techniques in clinical practice. As any other saturated porous medium, bone is characterized by different forms of longitudinal wave propagation, either undrained waves or fast and (Frenkel–Biot) slow compressional waves. We here study the wave propagation in the framework of poromicromechanics. A continuum micromechanics model allows for the prediction of the anisotropic poroelastic properties, Biot’s coefficients, and moduli, from tissue-specific composition data, on the basis of tissue-independent (“universal”) elastic properties of the elementary components of all bones. These poroelastic properties enter the governing equations for wave propagation in anisotropic porous media. They allow for the prediction of undrained, fast and slow waves, as is verified by comparison of model results with experimental findings.     

Kinematic principles of primate rotational vestibulo-ocular reflex. II. Gravity-dependent modulation of primary eye position

The kinematic constraints of three-dimensional eye positions were investigated in rhesus monkeys during passive head and body rotations relative to gravity. We studied fast and slow phase components of the vestibulo-ocular reflex (VOR) elicited by constant-velocity yaw rotations and sinusoidal oscillations about an earth-horizontal axis. We found that the spatial orientation of both fast and slow phase eye positions could be described locally by a planar surface with torsional variation of <2.0 +/- 0.4 degrees (displacement planes) that systematically rotated and/or shifted relative to Listing's plane. In supine/prone positions, displacement planes pitched forward/backward; in left/right ear-down positions, displacement planes were parallel shifted along the positive/negative torsional axis. Dynamically changing primary eye positions were computed from displacement planes. Torsional and vertical components of primary eye position modulated as a sinusoidal function of head orientation in space. The torsional component was maximal in ear-down positions and approximately zero in supine/prone orientations. The opposite was observed for the vertical component. Modulation of the horizontal component of primary eye position exhibited a more complex dependence. In contrast to the torsional component, which was relatively independent of rotational speed, modulation of the vertical and horizontal components of primary position depended strongly on the speed of head rotation (i.e., on the frequency of oscillation of the gravity vector component): the faster the head rotated relative to gravity, the larger was the modulation. Corresponding results were obtained when a model based on a sinusoidal dependence of instantaneous displacement planes (and primary eye position) on head orientation relative to gravity was fitted to VOR fast phase positions. When VOR fast phase positions were expressed relative to primary eye position estimated from the model fits, they were confined approximately to a single plane with a small torsional standard deviation ( approximately 1.4-2.6 degrees). This reduced torsional variation was in contrast to the large torsional spread (well >10-15 degrees ) of fast phase positions when expressed relative to Listing's plane. We conclude that primary eye position depends dynamically on head orientation relative to space rather than being fixed to the head. It defines a gravity-dependent coordinate system relative to which the torsional variability of eye positions is minimized even when the head is moved passively and vestibulo-ocular reflexes are evoked. In this general sense, Listing's law is preserved with respect to an otolith-controlled reference system that is defined dynamically by gravity.     

Improved Prediction of Lateral Deformations due to Installation of Soil-Cement Columns

A modified method is proposed for predicting the lateral displacements of the ground caused by installation of soil-cement columns. The method is a combination of the original method derived on the basis of the theory of cylindrical cavity expansion in an infinite medium and a correction function introduced to consider the effect of the limited length of the columns. The correction function has been developed by comparing the solutions obtained using the spherical and the cylindrical cavity expansion theories for a single column installation. Both the original and the modified methods have been applied to a case history reported in the literature, which involves clay soils, and the predictions are compared with field measurements. The advantage of the modified method over the original method is demonstrated. Finally, the modified method has also been applied to a case history involving loose sandy ground, and the calculations show that the method can also be used for this type of soil provided that appropriate consideration is given to the volumetric strain occurring in the plastic zone of soil surrounding the soil-cement columns.     

Effects of Weakly Nonlinear Water Waves on Soft Poroelastic Bed with Finite Thickness

Since porous material is usually of a finite thickness in nature, the effects of periodically nonlinear water waves propagating over a soft poroelastic bed with finite thickness are hence noticed and studied in this work. The water waves are simulated by potential theory while the porous bed is governed by Biot’s theory of poroelasticity herein. The conventional Stokes expansion of water waves based on a one-parameter perturbation expansion fails to solve the soft poroelastic bed problem; therefore, the boundary layer correction approach combined with a two-parameter perturbation expansion is proposed, which enables us to solve the problem of soft poroelastic bed with finite thickness. The results are compared to the similar problem with an infinite-thickness porous bed. The boundary effects of the impervious rock are significant on wave-induced pore water pressure and effective stresses, but are of very little significance on wave profiles at the free surface and the porous bed surface. However, the rigid boundary is insignificant to the pore water pressure and effective stresses when the thickness of porous bed is larger than about one wavelength.     

基于无线传感器扭矩检测的轧机扭振前馈控制

 针对轧机轧辊反复正反转咬钢抛钢受到突然强有力的冲击时扭振现象极为严重的情况,研究采用扭矩无线传感器实时采回负载干扰值,解决了现有的扭振抑制方法中采用扭振预估器计算扭振时容易出现偏差的问题;利用前馈能在扰动发生时提前做出干扰补偿的原理,在大型轧机交交变频调速系统定子转矩电流与转速双闭环的基础上,在转矩控制器的输入端加入负载扭矩扰动补偿,提前控制定子电流转矩分量而达到控制扭振的目的,并用Simulink对上述过程进行仿真。结果表明：基于无线传感的扭振前馈抑制方式对扭振的控制效果非常明显,几乎可以彻底消除扭振,更贴近实际。     

The ex vivo expansion capacity of normal human bone marrow cells is dependent on experimental conditions: role of the cell concentration, serum and CD34+ cell selection in stroma-free cultures

The present study was conducted to establish defined culture conditions for ex vivo expansion of normal human bone marrow cells. We investigated the role of three experimental expansion parameters: the cell concentration in the initial culture medium, the role of animal serum, human plasma and serum-free substitute, and the expansion potential of mononucleated cells (MNC) versus CD34+ cells. Cells were cultured in suspension with stem cell factor (SCF), IL3, IL6 and Erythropoietin (Epo) for 10 days. 1) Reducing the cell concentration from 3 x 10(4) to 1.5 x 10(3)/ml increased total cell expansion almost 20 fold, progenitor expansion more than 3 fold, and the maintenance of long term culture-initiating cells (LTC-IC). 2) In medium containing a serum-free substitute, total and CD34+ cell expansion was 3 times greater than in medium containing 1-10% human AB plasma or 25% animal serum. 3) The expansion potential of selected CD34+ cells was significantly greater than that of the total MNC population. However, taking into account the cell loss due to CD34+ selection, the overall results for quantitative expansion in relation to the initial number of MNCS favor the use of non-selected MNCS. 4) SCF + IL3 + IL6 was clearly the best combination of early cytokines for LTC-IC maintenance, with or without lineage-restricted cytokines, whereas the presence of IL1 beta in any combination augmented the decrease in LTC-IC. Addition of G-CSF to the medium resulted in 1 log increase in total cell expansion and a 2-fold increase in CFU-GM expansion. Addition of Epo always induced a dramatic proliferation of erythroid cells (up to 2000 fold) as well as of CFU-GM (up to 4 fold), without exhausting the LTC-IC pool. We concluded that the expansion of hemopoietic cells for clinical purposes needs establishment of controlled, reproducible and reliable culture conditions.     

Coupling Behavior of Wire Ropes Subjected to Tensile Impulses

To determine the stress state of a wire rope is tedious although analytical solution of a simple rope subjected to static load is available. While facing the problems involving complex ropes, it is usual practice to take approximations based upon the concepts of an average stress state for the constitutive ropes or for every wire. For a statically loaded cable superimposed with a tensile impulse, practically in sudden lifting of a heavy weight, the coupled axial-shearing strain waves in the cable has rarely been studied and explored through analytical approaches. Based on Costello’s force-deformation relationship and elastic wave propagation theory, analysis procedures and results are presented in this paper. Time-dependent coupled axial-torsional displacements and axial-shearing strain waves in a simple straight wire rope, due to a longitudinal impact at one end, are obtained. At the instance of the strike, a pair of coupled primary axial-torsional waves is created and begins to travel in the cable independently with different speed. Meanwhile, a coupling induced secondary torsional wave and an axial wave were observed to travel with the primary axial wave and the primary torsional wave, respectively. Phenomenon such as the traveling, reflections from ends, and intersections of the primary waves as well as the secondary wave are presented. Information provided in this paper would be useful in the study of unexpected overstress and/or fatigue problems.     

利用超重力富集和分离Sn-3％Fe熔体中的杂质元素铁

在粗锡精炼过程中引入超重力场,运用超重力技术研究Sn-3% Fe（质量分数）熔体中杂质元素铁在超重力场中的定向富集和过滤分离的规律,达到提纯净化粗锡的目的.结果表明,对于超重力场G=500以10℃·min-1冷却速率凝固后的Sn-3% Fe熔体,超重力场极大强化富铁相在粗锡熔体中的沉降运动,使先析出富铁相全部富集到试样的下部区域,上部几乎找不到富铁相颗粒.下部尾锡中的铁质量分数达到4.817%,而上部精锡中的铁质量分数降低到0.036%,精锡中铁的脱除率高达98.78%.在超重力场中过滤的Sn-3% Fe熔体可实现富铁相杂质和精锡液的有效分离,当重力系数大于30时,精锡的回收率随重力系数的增大而提高.在超重力场G=100,240℃条件下,Sn-3% Fe熔体过滤1 min后,精锡液几乎全部被分离到坩埚底部,富铁相杂质被截留在过滤碳毡上部,下部精锡中找不到富铁相杂质的颗粒,精锡中铁质量分数降至0.253%,富铁渣中铁质量分数高达11.528%.精锡中铁的脱除率高达91.44%,超重力场中精锡的回收率高达82.69%.      

超重力方向调节电沉积镍箔表面形貌和力学性能

在电场方向与超重力方向相同和相反条件下电沉积制备金属镍箔.利用扫描电镜和原子力显微镜对镍箔表面形貌和粗糙度进行了表征, 并测试和对比了各种重力条件下电沉积镍箔硬度和拉伸强度.结果表明, 在超重力场作用下电沉积镍箔表面变得更加致密、平整, 晶粒细化, 粗糙度明显降低.特别是, 当超重力与电场方向相反(电极C)时, 镍箔表面更为平整致密.当超重力方向和电场方向相同(电极B)时, 镍箔的HV硬度可达839, 抗拉强度可达944 MPa, 性能优于电极C镍箔片, 且远高于常重力条件下电沉积镍箔HV硬度的294和抗拉强度298 MPa.      

Complex Dielectric Permittivity of Soil–Organic Mixtures (20 MHz–1.3 GHz)

The dielectric permittivity of soils can be significantly modified by the presence of organic contaminant in the pore fluid. Thus, nondestructive techniques based on the propagation of electromagnetic waves may be used to detect contaminant plumes and to evaluate decontamination processes. Ground penetrating radar (GPR) and time domain reflectometry are two of the most relevant geophysical tools working in the frequency range of interest here. In this work, the complex dielectric permittivity of some soil–organic mixtures are measured in the frequency range of 20 MHz to 1.3 GHz. Tests are conducted in samples of silica sand, loess, and kaolinite mixed with varied amount of paraffin oil and lubricant oil. Additional tests are performed in soil–water samples for comparison. Mixtures formulas reported in the literature are extended from two to three and four phases in order to model the measured dielectric response of the contaminated soil samples. The results allow us to study the effect of the volumetric liquid content, organic type, mineral composition, and specific surface of soil particles on the dielectric permittivity of the mixtures. It is concluded in this work that the value of dielectric permittivity in soils is sensitive to the detection of contaminants when the organic concentration is high. On the other hand, the organic content can be determined providing that the total volume of fluid in the pores is known. The detection limits of organics in soils are discussed. Finally, a contamination process is monitored with GPR at the frequency of 1 GHz in a laboratory cell. The results show that organic contaminants are easily detected in dry sand, yet detection becomes very difficult in wet sand.     

核电用316奥氏体不锈钢钢丝扭转性能分析

针对核电用奥氏体不锈钢钢丝研制过程中存在的单向扭转性能不均匀及异常断裂问题,利用光学显微镜(OM)与扫描电镜(SEM)等手段,对该钢丝的金相组织、单向扭转断口及断口附近表面形貌进行了分析。研究发现,产生单向扭转性能不均匀与异常断裂的主要原因是钢丝表面质量较差及钢丝用钢棒焊接连接处局部过烧。通过将拉拔模具由钨钢模更换为聚晶模、润滑剂由润滑粉更换为水性油等措施,改善了钢丝表面质量;通过适当降低焊接接头处焊接时的热输入,消除了单向扭转时异常断裂的问题。改进后钢丝单向扭转圈数趋于均匀且最大扭转圈数可达169 圈,远高于技术要求值。     

Fatigue life prediction analysis of surface cracked straight pipes

In piping components, for the stability assessment it is important to calculate the point of initiation of the crack and to monitor the subsequent crack propagation behaviour. The objective of this paper is to use the finite element method backed up with experimental results to determine the crack initiation stage and to subsequently predict the crack propagation behaviour under fatigue loading. With reference to full scale surface cracked carbon steel pipes tested data, the accuracy of the numerical procedure is judged. It is concluded that semi-elliptical SIFs solutions should not be used to assess the fatigue life when straight pipe is having constant depth crack profile.     

Wave Attenuation over a Rigid Porous Medium on a Sandy Seabed

In this study, an analytic solution of wave interaction with a rigid porous medium above a poro-elastic sandy bottom is derived to investigate the attenuation of the surface wave and the wave-induced soil response. In the model, both inertial and damping effects of the flow are considered in the rigid porous region using the potential theory, while the consolidation theory is adopted in the sand region. A new complex dispersion relation involving parameters of the rigid porous and the poro-elastic medium is obtained. The analytic solutions are verified by some special cases, such as wave interaction with a porous structure over an impermeable bottom or wave interaction with a poro-elastic medium only. Numerical results indicate that the wave attenuation is highly dependent upon the thickness of the rigid porous layer, the soil stiffness, and their respective coefficients of permeability. Increasing the thickness of the rigid porous layer will shorten the wavelength of the surface wave regardless of the sand coarseness. The pore pressure in fine-sand is larger than in coarse sand, with both decaying with wave progression. It is also found that increasing the thickness of the rigid porous medium will effectively reduce the pore pressure in the sand. For the applications, an extended hyperbolic mild-slope equation is finally obtained, based on the basic analytic solutions. Examples of the wave height transformation over submerged permeable breakwaters on a slope sandy seabed are given. The simulated results show that the wave decay of the coarse sand seabed is larger than those of fine-sand and impermeable seabeds when waves pass after the submerged porous breakwater. The wave damping versus the friction factor for various height of the submerged breakwater is discussed.     

Short-Wave and Wave Group Scattering by Submerged Porous Plate

An analytical solution for waves propagating through a horizontal porous plate of finite thickness is obtained. The objective of the plate is to reduce the incident short-wave energy and the long-wave energy as well. Consequently, in this study the plate is analyzed in a global perspective [i.e., considering its response to obliquely incident short waves (both regular and irregular) and wave groups (with the consequent generation of free and locked long waves)]. To solve the propagation of regular and irregular waves, an eigenfunction expansion is used and the results are verified with experimental data showing good agreement. The propagation of a wave group past a horizontal porous plate is studied using a multiple-scale perturbation method, and an analytical solution is presented. The results show that the generated long waves are present on both sides of the plate and that maximum short-wave reflection is associated with maximum long-wave transmission.