Near Crack Line Elastic-Plastic Analysis for an Infinite Plate Loaded by a Pair of Point Shear Forces

The near crack line analysis method was used to investigate a crack loaded by a pair of point shear forces in an infinite plate in an elastic-perfectly plastic solid. The analytical solution was obtained, that is the elastic-plastic fields near crack line and law that the length of the plastic zone along the crack line is varied with external loads. The results are sufficiently precise near the crack line and are not confined by small scale yielding conditions.

Comparison of point and two-dimensional shear wave elastography of the spleen in healthy subjects

BACKGROUND Few systematic comparative studies of the different methods of physical elastography of the spleen are currently available.AIM To compare point shear wave and two-dimensional elastography of the spleen considering the anatomical location(upper,hilar,and lower pole).METHODS As part of a prospective clinical study,healthy volunteers were examined for splenic elasticity using four different ultrasound devices between May 2015 and April 2017.The devices used for point shear wave elastography were from Siemens(S 3000)and Philips(Epiq 7),and those used for two-dimensional shear wave elastography were from GE(Logiq E9)and Toshiba(Aplio 500).In addition,two different software versions(5.0 and 6.0)were evaluated for the Toshiba ultrasound device(Aplio 500).The study consisted of three arms:A,B,and C.RESULTS In study arm A,200 subjects were evaluated(78 males and 122 females,mean age 27.9±8.1 years).In study arm B,113 subjects were evaluated(38 men and 75 women,mean age 26.0±6.3 years).In study arm C,44 subjects were enrolled.A significant correlation of the shear wave velocities at the upper third of the spleen(r=0.33088,P<0.0001)was demonstrated only for the Philips Epiq 7 device compared to the Siemens Acuson S 3000.In comparisons of the other ultrasound devices(GE,Siemens,Toshiba),no comparable results could be obtained for any anatomical position of the spleen.The influencing factors age,gender,and body mass index did not show a clear correlation with the measured shear wave velocities.CONCLUSION The absolute values of the shear wave elastography measurements of the spleen and the two different elastography methods are not comparable between different manufacturers or models.

Elastic-plastic analytical solution for centric crack loaded by two pairs of point shear forces in finite plate

The near crack line analysis method was used to investigate a centric crack loaded by two pairs of point shear forces in a finite plate, and the analytical solution was obtained. The solution includes the unit normal vector of the elastic-plastic boundary near the crack line, the elastic-plastic stress fields near the crack line, the variations of the length of the plastic zone along the crack line with an external load, and the bearing capacity of a finite plate with a centric crack loaded by two pairs of point shear forces. The results are sufficiently precise near the crack line because the assumptions of small scale yielding theory have not been made and no other assumptions are taken.

An application of interacting shear flows theory: exact solution for unsteady oblique stagnation point flow

An analytical solution of the governing equations of the interacting shear flows for unsteady oblique stagnation point flow is obtained. It has the same form as that of the exact solution obtained from the complete NS equations and physical analysis and relevant discussions are then presented.

Shear modulus of shock-compressed LY12 aluminium up to melting point

Asymmetric plate impact experiments are conducted on LY12 aluminium alloy in a pressure range of 85-131 GPa. The longitudinal sound speeds axe obtained from the time-resolved particle speed profiles of the specimen measured with Velocity Interferometer System for Any Reflector （VISAR） technique, and they are shown to be good agreement with our previously reported data of this alloy in a pressure range of 20-70 GPa, and also with those of 2024 aluminium reported by McQueen. Using all of the longitudinal speeds and the corresponding bulk speeds calculated from the Gruneisen equation of state （EOS）, shear moduli of LY12 aluminium alloy are obtained. A comparison of the shear moduli in the solid phase region with those estimated from the Steinberg model demonstrate that the latter are systematically lower than the measurements. By re-analysing the pressure effect on the shear modulus, a modified equation is proposed, in which the pressure term of P/η^1/3 in the Steinberg model is replaced by a linear term. Good agreement between experiments and the modified equation is obtained, which implies that the shear modulus of LY12 aluminium varies linearly both with pressure and with temperature throughout the whole solid phase region. On the other hand, shear modulus of aluminium in a solid-liquid mixed phrase region decreases gradually and smoothly, a feature that is very different from the drastic dropping at the melting point under static conditions.

The Effect of Near-Wall Vortices on Wall Shear Stress in Turbulent Boundary Layers

The objective of the present study is to explore the relation between the near-wall vortices and the shear stress on the wall in two-dimensional channel flows. A direct numerical simulation of an incompressible two-dimensional turbulent channel flow is performed with spectral method and the results are used to examine the relation between wall shear stress and near-wall vortices. The two-point correlation results indicate that the wall shear stress is associated with the vortices near the wall and the maximum correlation-value location of the near-wall vortices is obtained. The analysis of the instantaneous diagrams of fluctuation velocity vectors provides a further expression for the above conclusions. The results of this research provide a useful supplement for the control of turbulent boundary layers.

Rheological Properties of Waxy Crude at a Low Temperature in the Presence of Pour Point Depressants

Pour point depressants （PPD） are used to improve the theology of waxy crude. The affect of various factors on the theological properties, and the thermal characteristics of waxy crude treated by PPD have been investigated. The conclusions are as follows： PPD can reduce the pour point and abnormal point of waxy crude, broaden the temperature range of Newtonian fluid of waxy crude, and lower greatly the viscosity of non-Newtonian fluid of waxy crude. The influence of reheating and high-rate shear on the effect of PPD mainly depends on their temperature. When the reheating temperature is more than the abnormal point of crude by 10℃, the reheating process has little effect on the modification effect of PPD. However, when the reheating temperature is below the abnormal point of crude, the reheating process will reduce the modification effect of PPD. When temperature is above the abnormal point of crude, the high-rate shear has little effect on the modification effect of PPD. At a temperature range where a lot of wax is precipitating, high-rate shear will greatly reduce the modification effect of PPD.

Relationship between wall shear stresses and streamwise vortices in turbulent flows over wavy boundaries

The relationship between wall shear stresses and near-wall streamwise vortices is investigated via a direct numerical simulation(DNS) of turbulent flows over a wavy boundary with traveling-wave motion. The results indicate that the wall shear stresses are still closely related to the near-wall streamwise vortices in the presence of a wave. The wave age and wave phase significantly affect the distribution of a two-point correlation coefficient between the wall shear stresses and streamwise vorticity. For the slow wave case of c/Um = 0.14, the correlation is attenuated above the leeward side while the distribution of correlation function is more elongated and also exhibits a larger vertical extent above the crest. With respect to the fast wave case of c/U_m=1.4, the distribution of the correlation function is recovered in a manner similar to that in the flat-wall case. In this case, the maximum correlation coefficient exhibits only slight differences at different wave phases while the vertical distribution of the correlation function depends on the wave phase.

体外预应力节段式UHPC无腹筋梁抗剪性能试验研究

体外预应力节段式超高性能混凝土(UHPC)无腹筋桥梁由于其施工工业化水平高且构造简单,得到广泛地关注,但其抗剪性能研究尚不成熟,相关规范也相对滞后。为了研究体外预应力节段式UHPC无腹筋梁的抗剪性能,开展了静力破坏试验,共制作了5根体外预应力节段式UHPC无腹筋梁、2根体外预应力节段式UHPC有腹筋梁和1根体外预应力整体式UHPC无腹筋梁,选取了剪跨比、钢纤维掺量、箍筋间距为研究参数进行试验。结果表明:接缝张开后梁刚度明显下降;添加钢纤维的试验梁的裂缝多而密;钢纤维的掺入可以提高梁的开裂强度、极限强度和裂后性能,2%钢纤维掺量的梁开裂强度比1.5%和0%掺量的增大8.20%和1.16倍;配箍筋的梁在钢纤维失效后箍筋开始受力,并且很快达到屈服,箍筋的存在可以提高梁极限承载力,无腹筋梁的极限承载力比箍筋间距为150 mm和75 mm的梁低15.9%和19.6%。采用AASHTO GSCB INTERIM-2003标准中计算干接缝节段式梁的折减系数0.85。在不考虑安全系数的情况下,法国规范NF P 18-710中UHPC梁抗剪承载力计算公式可以准确地预测含钢纤维体外预应力节段式UHPC无腹筋梁的抗剪强度,其试验值和预测值比值的平均值为1.04,标准差为0.28。

蜂窝板几何参数对芯子剪切模量测量值的影响

为了通过三点弯曲试验获得蜂窝芯子较准确的剪切模量,基于商用铝蜂窝夹层板几何参数与典型剪切模量值,对三点弯曲试验有限元仿真模型进行校验,研究了蜂窝夹层板几何参数对测得芯子剪切模量值的影响规律。利用Sobol法对各影响因素进行灵敏度分析,拟合得到简化代理模型。基于简化代理模型,给出了三点弯曲试验中蜂窝夹层板几何参数适用可行域。研究结果表明,蜂窝夹层板几何参数对芯子剪切模量测量值的影响程度由大到小的顺序为芯子密度、面芯厚度比和面板厚度。在给定的可行域内,通过三点弯曲方法测得的蜂窝芯剪切模量精度良好,可为实际工程提供参考。

Evaluation of Red Blood Cell Contribution to Platelet Activation in the Bulk Applying Red Blood Cell—Platelet Thrombus as a Point Source Model

In this study, a point source mathematical model is proposed to describe the diffusion of adenosine di-phosphate (ADP) from either damaged red blood cell (RBC) or activated platelet. The convective diffusion equation is reduced to describe the suggested problem. The final differential equation is solved using Laplace transforms and ADP concentration profiles around the source are obtained. Thrombi of 5 to 20 μm3 containing platelets and a range of red blood cells (RBCs) (0%, 25%, 50%, 75%, 100%) concentrations are used to apply the model. Reported ADP concentrations in the literature are used and its dynamic release from the point source is calculated. Results suggest that RBC chemical contribution to platelet aggregation in the bulk is much less than that of platelet (almost) negligible. However, the physical effect of RBCs is dominant in the bulk through augmentation of released ADP and platelets diffusivities. Moreover, the chemical contribution reported in previous studies is suggested to be as a result of interaction of RBC with the surface under the influence of shear stresses in the boundary region.

Study on the Shear Effect on Dye Patches Diffused in Wall-Bounded Shear Flow

This paper focuses on the high intensity filaments (dye patches) embedded in dye plumes in a wall-bounded shear flow, to investigate the shear effect on the dye patch distribution. Motivated by the widely concerned inverse estimation of the source location, we try extracting useful information to know the source location from down-stream dye patches. Accordingly, we changed the dye injection location at different distances from the wall and made observations at different downstream (diffusion) distances from the source. The orientation angle and roundness of dye patches were concerned to examine the shear effect and dye patch characteristics. To capture the dye plume images, a planar laser induced fluorescence (PLIF) technique was used. The orientation and roundness of each dye patch were calculated by least-square fitting. The statistics of both the orientation angle and the roundness were compared with those in homogeneous turbulent cases to reveal the shear effect. Different from uniformly-orientated dye patches in the homogeneous flow, larger occurrence probabilities with positive orientation angles of dye patches are observed in wall-bounded shear flow, in particular, when the injection location is near the wall. As with information extraction for the inverse estimation of source location, it is found that the orientation distribution of dye patches is independent of the diffusion distance, but related with the injection location from the wall. While for the homogeneous flow cases, a strong dependence on the diffusion distance is observed in the orientation distribution profiles. As for the roundness, similar aspects are found regarding the dependencies on the injection location in shear flow and on diffusion distance in homogeneous flow.

Study on Fluid Shear Flow on Osteoblast-like Cells in Their Tensile Loading Experiments

In vitro cell loading experiments are used to investigate stimulation of strain to cellular proliferation. As the flowing conditions of culture fluid in loading systems has been little known, strictly people can not detect the influence of strain to cellular proliferation exactly because shear flow can enhance cell proliferation either. Based on the working principle and cyclic loading parameters, we simplify Navier-Stokes equation to describe the flow of culture fluid on substrates of uniaxial and equi-biaxial flat tensile loading systems and four point bending system. With approximate solutions, the distributions of velocity field and wall shear flow to cells are gained. Results show: shear flows are zero in the middle (or fixed point or line) of substrate for all systems, and they get larger proportionally to distance from middle and substrate elongate; the shear flow on the substrate of four point bending system is much greater than those of others. This shear flow in four point bending system, confirmed by Owan, I., et al with OPN mRNA increase in their experiment, could cause more influence to osteoblast-like cells than that caused by strain. We estimate the average magnitude of shear stress in Owan’s device, the results are consistent with other experimental data about shear flow. In conclusion our study makes it possible to differentiate the influence of strain on cellular proliferation to that of shear flow in loading experiments with the devices mentioned above quantitatively.

超声引导下针刀松解激痛点治疗腰背肌筋膜疼痛综合征临床观察

目的观察超声引导下针刀松解激痛点治疗腰背肌筋膜疼痛综合征(myofascial pain syndrome,MPS)的临床疗效。方法将60例腰背MPS患者随机分为常规组和超声组,每组30例。常规组采用普通针刀疗法进行治疗,超声组在超声引导下行针刀疗法治疗,两组均每周治疗1次,连续治疗4次为1个疗程。分别于治疗前后采用简化McGill疼痛问卷(short-form McGill pain questionnaire,SF-MPQ)评估患者疼痛程度,采用多裂肌杨氏模量值评估患者肌肉状态变化,并于治疗后观察两组临床疗效。结果与治疗前比较,两组患者治疗后SF-MPQ评分及杨氏模量值均显著降低(P<0.05);与常规组比较,超声组SF-MPQ评分及杨氏模量值降低程度更显著(P<0.05);超声组临床疗效显著优于常规组(P<0.05)。结论超声引导下针刀松解激痛点治疗腰背MPS,能显著缓解患者疼痛症状,显著改善肌肉组织弹性。

含水率对黄土高原地区几种主要类型土壤流变特性的影响

[目的]研究含水率对土壤浆体流变特性的影响机理,为黄土高原地区泥浆体流动规律的认识和泥石流防治提供科学依据。[方法]以黄土高原地区4种主要类型土壤为研究对象,通过流变振荡剪切测试,探究含水率对土壤流变特性的影响。[结果](1)[土娄]土、褐土和黑垆土的储能模量、损耗模量、剪切应力随含水率的增加(40%~80%)均呈减小趋势,剪切应力分别从229.85,193.38,96.46 Pa减小到2.25,2.65,2.32 Pa;在含水率较大(>50%)的条件下,黄绵土表现出强应变过冲现象。(2)4种土壤浆体的储能模量随剪切应变的增加出现两个平台区,表现出两步屈服现象;随着含水率的增加,浆体出现两步屈服向一步屈服的转变。第一步屈服与初始网络结构的破坏有关,第二步屈服表明浆体结构被完全破坏。(3)当土壤含水率≤50%,土壤细颗粒可通过形成絮凝体增加絮凝程度从而提高土壤浆体流动点剪切应力;当含水率>50%时,土壤中的粗颗粒通过增加颗粒间摩擦力提高流动点剪切应力,此时黄绵土流动点剪切应力大于其他土壤。[结论]土壤流变特性不仅与其自身性质有关,而且受土壤含水率的重要影响;细颗粒含量较大的土壤,在高含水率条件下其浆体更易发生流动。

干湿循环作用下嵊州-新昌地区红层软岩崩解及强度弱化特性

红层软岩遇水易崩解并造成其强度弱化,在边坡工程建设中易造成其稳定性弱,导致经济损失,甚至人员伤亡。揭示红层软岩干湿循环作用下黏聚力与内摩擦角的变化特征对于针对性设计边坡处理措施具有重要意义。以浙江嵊州-新昌地区下白垩统朝川组3组红层软岩为研究对象,通过干湿循环试验、崩解岩块点荷载强度试验和崩解颗粒直剪试验研究了红层软岩崩解及强度弱化特性。结果表明:试样在干湿循环作用下呈碎块状-粒渣状-泥糊状依次崩解的形态,其主要崩解过程可分为初始崩解、快速崩解、细微再崩解和崩解稳定4个阶段;试样的点荷载强度I_(s(50))随干湿循环次数的增加而降低,耐崩解指数I_(dn)与点荷载强度I_(s(50))呈正指数关系,试样的点荷载强度I_(s(50))在耐崩解指数I_(dn)为80%~100%之间急速弱化,在耐崩解指数I_(dn)为50%~80%之间表现缓慢弱化特性;试样的峰值抗剪强度介于0.567~1.219 MPa之间,其多发生在剪切位移3 mm前后,同组试样在相同轴压下,峰值抗剪强度随循环次数的增加而减小,试样崩解颗粒内摩擦角在22.28°~33.03°之间,黏聚力在0.46~0.74 MPa之间。试样的摩擦角和黏聚力随着干湿循环次数增加,都呈负指数关系。试验结果表明砂质比泥质胶结的耐崩解性更好,黏土矿物高的岩石更容易崩解,而“白色矿物”钠长石的吸水膨胀能力远不及黏土矿物,其含量差异对耐崩解性的影响不及黏土矿物。

基于激光雷达低空风切变监测的逐点滑动分析

针对激光测风雷达低空风切变识别率不高的现状,文章利用陕西榆林机场激光测风雷达的数据产品,开展数据质量控制,引入风切变强度因子构建滑动分析方法,使得低空风切变被有效识别。利用沙尘天气、持续大风天气和日变化天气下的风切变过程,结合航空器风切变报告、机场自动观测站气象报文,对下滑道上顶风和侧风廓线的风速进行逐点滑动判别与风切变强度识别,验证滑动分析方法的可用性与有效性。3个不同天气背景下的举例验证结果表明:通过逐点滑动分析,可判断下滑道上风切变强度因子最大值对应的高度位置与机组报告的风切变发生高度相吻合;风切变发生时,下滑道上侧风的时空变化明显大于顶风;在同一高度上,风速在短时间内存在较强的波动是造成风切变的原因之一。

基于动态振荡剪切的砒砂岩浆体流变行为研究

[目的]随着全球变暖及强降水极端事件频发,砒砂岩区滑塌泥流灾害可能将不断增加。为探明水-土互馈作用如何导致脆弱岩土松动变形进而发展为泥流,系统认识其演化过程的关键科学问题。[方法]以4种典型砒砂岩为研究对象,采用流变学方法,开展动态振荡剪切下砒砂岩浆体的流变特性研究,探索砒砂岩浆体的液化过程及流变特性。[结果](1)随着剪切应变增加,4种砒砂岩浆体储能模量和损耗模量减小,表现出应变变稀特点。(2)在含水率较低(w<50%)的样品中,紫、棕色砒砂岩浆体与红、白色砒砂岩浆体相比,线性黏弹区的应力和应变更大。在含水率较高(w≥50%)的样品中,红、白色砒砂岩浆体与紫、棕色砒砂岩浆体相比,流动点的应力和应变更大。(3)随含水率增加,4种砒砂岩浆体的储能模量和损耗模量降低,线性黏弹区的应力和应变降低。[结论]细颗粒物质可增加浆体在线性黏弹区的抗剪强度和弹性,但细颗粒浆体受含水率影响较大,水分加入后,浆体结构破坏、抵抗变形的能力立即减弱,同时,更容易发生相态转变。粗颗粒的存在使浆体非线性黏弹区弹性主导的范围增大,阻碍浆体的相态转变。该研究结果为砒砂岩区泥流灾害的认识和防治提供一定的科学基础。

某工程剪力墙混凝土点状爆裂问题研究分析

某在建高层剪力墙住宅工程在剪力墙混凝土浇筑完成6个月后,发生由内向外的点状爆裂,爆裂表现为外大内小的圆锥形缺陷,圆锥形缺陷顶部为黄褐色颗粒。本文通过对爆裂区与非爆裂区凝胶体进行X衍射物相半定量与显微偏光分析,判断该黄褐色颗粒为硅酸二钙,混凝土爆裂的原因为硅酸二钙吸水膨胀崩裂,产生由内向外的推力将混凝土拉裂,并同时对剪力墙混凝土强度、爆裂点分布状态等进行检测,评估该爆裂对结构安全的影响,提出相应的治理方法,为其他混凝土工程提供可靠借鉴。

剪切波弹性成像技术对低强度脉冲超声刺激足三里穴引起肌张力变化的评估

目的:应用剪切波弹性成像技术(SWE)评估低强度脉冲超声(LIPUS)刺激足三里穴位时肌张力的变化特点,初步探讨LIPUS刺激穴位的可行性,以期为LIPUS在外周神经调控研究中提供定量评估信息。方法:实验动物为16只雄性SD大鼠,随机分为胫骨前肌组和腓肠肌组各8只,应用LIPUS刺激大鼠足三里穴20 min,通过SWE连续监测胫骨前肌和腓肠肌的肌张力变化。酶联免疫吸附试验(ELISA)测定刺激前后血清5-羟色胺(5-HT)水平变化。结果:胫骨前肌在LIPUS刺激足三里穴后3 min的剪切波速度和杨氏模量值均较刺激前显著升高(均P<0.05);腓肠肌在刺激足三里穴后13、14 min的剪切波速度和杨氏模量值均较刺激前显著升高(均P<0.001)。血清5-HT水平较刺激前显著升高(P<0.05)。结论:SWE可为评估LIPUS刺激足三里穴位引起的肌张力变化提供客观依据,为LIPUS的经穴效应的研究提供更多信息。