脑动静脉畸形供血动脉内压力测量准确性的分析

对脑动静脉畸形供血动脉内压力测量的准确性进行了定量的分析,分析结果认为,以介入导管方法测量脑动脉畸形患者供血动脉内压力时,导管的影响可以导致测量结果偏低,这一结论支持了脑动静脉畸形患者低压灌注的程度一般不易于导致部分脑组织缺血的观点。     

导管对动脉中脉动流生理参数的影响

导管在循环生理学和临床医学中已得到广泛的应用。血管中介入导管后必然会影响测量的准确性和受检者的正常生理状态。许多学者讨论过导管的介入对压力测量结果的影响,但还未见有讨论导管介入对正常生理状态影响的文章报导。本文基于动脉中血液流的刚性管分析模型,从理论上讨论了血流量和纵向阻抗等生理状态参数在导管介入前后的变化情况,为进一步全面分析导管介入对动脉中血液脉动流的影响提供了理论基础。     

相变滞后对裂纹屏蔽效应的数值分析

本文针对奥氏体-马氏体双相材料,研究裂纹尖端区弥散分布的奥氏体颗粒在应变诱发时发生的相变对裂纹的屏蔽效应。鉴于实验中已发现的不同相变滞后对裂纹屏蔽效应的不同影响,本研究通过在裂纹尖端区不同位置嵌入相变颗粒,考虑到裂纹尖端区应力应变场的奇异分布及其诱发的相变,将裂纹尖端区相变滞后问题转化为相变颗粒在裂纹尖端区的位置问题。计及奥氏体-马氏体相变的体积膨胀效应进行了平面应力裂纹问题数值模拟,得到了单个相变夹杂对裂纹屏蔽效应的影响规律。结果表明：裂纹尖端区相变夹杂的位置对裂纹的屏蔽效应在距裂尖2倍夹杂直径以内影响极大,且以裂尖86度方向为界。其影响规律与McMeeking 和 Evans理论预言的60度方向不同。     

基于应力测试的汽轮机高导管焊区失效研究

对125MW汽轮机高压导汽管进口焊区进行了应力测试，从应力角度分析了高导管早期失效的原因，能够为采取防止失效措施、合理设计高导管焊区结构提供参考。     

横向振荡圆柱绕流的格子Boltzmann方法模拟

基于格子Boltzmann方法(LBM)对不可压横向振荡圆柱绕流问题进行了数值研究. 与传统的求解宏观的N-S方程的数值方法不同, LBM求解此类问题不需要采用动网格, 而且不需要对网格进行特殊处理, 从而节约了计算成本. 结果显示, 当振荡频率增加到相应的静止圆柱绕流的自然涡脱落频率附近时, 圆柱后最新形成的集中涡距离柱体越来越近, 直到达到一个极限位置. 随后, 集中涡突然转向圆柱体另一侧脱落. 当振荡频率接近于静止圆柱的自然涡脱落频率时, 发生频率同步的现象. 随着振荡频率远离自然涡脱落频率, 同步现象消失. 在几种次谐振荡和超谐振荡下, 尾流区的涡脱落频率仍为相应的静止圆柱绕流的自然涡脱落频率.      

植物导水模型初探

目前世界上对于植物长距离水分运输的微观机理假说存在争论。据此本文初步讨论了植物的导水模型。从流体力学角度讨论了水分在植物体内的运动状态,得出导管中的水分流动是在层流的状态下进行,且必须考虑粘性的作用;通过分析流体的层流运动,建立了导管中一维的流体模型,并简化导管以连续的梯形圆柱排列;分析受力,列出N-S方程,并求解出了一维导管模型的半径与压力梯度和各节管长的关系表达式。研究结果表明,模型中每一节导管的水受力都是平衡的,且各节之间相互独立。     

微裂纹屏蔽问题中守恒积分投影关系

对连续体损伤力学在微裂纹屏蔽问题中应用的Ｊ积分守情理假设提出质疑，用理论分析和电算实践证明了远场Ｊ积分在微裂纹损伤区中的再分配关系。即ＪＫ矢量的投影守恒关系。在这一关系中，被Ｈｅｒｒｍａｎｎ所轻视的Ｊ２分量起着十分重要的作用，本文的研究表明，Ｏｒｔｉｚ理论应考虑到远场Ｊ积分在损伤区中的损失，并通过计及这一损失做出必要的修正。     

某调距导管桨系泊工况水力性能和流激直发声预报

采用经验证的计算流体力学方法,对某艏辅推调距导管桨设计螺距和系泊工况螺距的水动力性能进行了有效预报,并对系泊工况装船桨流激噪声进行了分析。系泊工况下,由于导管桨的抽吸作用在导管外壁近壁面区域存在与导管内部流动方向相反的逆向流动,且导管桨尾流场速度梯度分布不均匀、流动紊乱,此时桨叶与导管的推力之比约为1.2∶1。系泊工况船+桨的瞬态流场脉动信息表明,导管桨各部件噪声源强度均表现出从1倍到4倍叶频依次下降的规律,最强幅值集中在桨叶导边和导管内壁;在远场声源级频谱曲线中轴向测点线谱较高峰值位置体现出导管桨进流流场的流动特性。对比分析该艏辅推整体和各部件宽带声源级指向性,可知旋转部件(桨叶、桨榖)对总噪声级的贡献较大,静止部件是径向测点噪声的主要贡献源。     

圆盘状裂纹前缘塑性区尺寸及张开位移估计

将Ｄｕｇｄａｌｅ模型推广到三维裂纹问题计算了圆盘状裂纹前缘塑性区尺寸,并结合断裂力学中的Ｂａｒｅｎｂｌａｔｔ－Ｄｕｇｄａｌｅ裂纹模型和三维Ｊ－积分原理计算了圆盘状裂纹前缘张开位移,得到了Ｊ－积分与裂纹张开位移的关系,最后用非线性有限元方法对圆盘状裂纹的前缘塑性区尺寸作了数值分析,确定了公式中的未知常数,并对其正确性作了数值验证,本文的工作推广了Ｄｕｇｄａｌｅ模型的应用范围。     

椭圆微孔端面机械密封泄漏率与几何收敛点的关系

采用解析法和数值计算相结合的方法,解释椭圆微孔端面机械密封的方向角所引起的几何特性改变如何影响到泄漏率.首先,得到了不同方向角下,椭圆沿速度方向上的几何收敛点的解析解.然后,基于质量守恒的JFO空化边界条件建立数值计算模型,分析了液膜的压力分布,并使用最高压力点的坐标来近似表征高压区的位置,得到了方向角与最高压力点的关系.接着,通过对比,发现几何收敛点和最大压力点位置一致,并分析了原因.最后,分析了在不同结构参数和操作参数下方向角对泄漏率的影响规律,通过分析得到,方向角的改变,使几何收敛点的位置发生改变,从而改变高低压区的分布,当高压区靠近泄漏出口时,泄漏率大;当高压区远离泄漏出口时,泄漏率小.     

Effects of sub-millimeter-bubble injection on transition to turbulence in natural convection boundary layer along a vertical plate in water

Temperature and velocity measurements are performed to clarify the effects of sub-millimeter-bubble injection on the transition to turbulence in the natural convection boundary layer along a vertical plate in water. In particular, we focus on the relationship between the bubble injection position L and the transition to turbulence in the natural convection boundary layer. The bubble injection positions used in our experiments are L = 1.6 and 3.6 mm. Bubble injection at L = 1.6 mm delays the transition to turbulence in the natural convection boundary layer, while that at L = 3.6 mm accelerates the transition to turbulence in the boundary layer. In the case of L = 1.6 mm, the appearance region of the liquid velocity fluctuation in the bubble-induced upward flow in the upstream unheated section is restricted to near the wall, although the peak of the liquid velocity fluctuation is high. In contrast, in the case of L = 3.6 mm, the relatively large liquid velocity fluctuation is distributed widely over the laminar boundary layer width. These results suggest that the effect of the liquid velocity fluctuation on the laminar boundary layer is quite different between L = 1.6 and 3.6 mm. It is therefore expected that the transition to turbulence in the natural convection boundary layer for the case with bubble injection is dependent on the magnitude and appearance region of the liquid velocity fluctuation in the bubble-induced upward flow in the upstream unheated section.     

Numerical simulation of multiphase cavitating flows around an underwater projectile

The present simulation investigates the multiphase cavitating flow around an underwater projectile. Based on the Homogeneous Equilibrium Flow assumption, a mixture model is applied to simulate the multiphase cavitating flow including ventilated cavitation caused by air injection as well as natural cavitation that forms in a region where the pressure of liquid falls below its vapor pressure. The transport equation cavitating model is applied. The calculations are executed based on a suite of CFD code. The hydrodynamics characteristics of flow field under the interaction of natural cavitation and ventilated cavitation is analyzed. The results indicate that the ventilated cavitation number is under a combined effect of the natural cavitation number and gas flow rate in the multiphase cavitating flows.     

Configuration-dependent modal analysis of a Cartesian parallel kinematics manipulator: numerical modeling and experimental validation

In the design optimization of a robot the configuration-dependent modal analysis can be a powerful tool to be exploited when high stiffness and high dynamic performances are concurrently required. In this paper the elastodynamics of a lower-mobility Parallel Kinematic Machine for pure translational motions is analyzed. The vibrational modes and the natural frequencies of the robot are evaluated as functions of the end effector position inside the workspace. A finite element model including kinematic joints is used to perform a series of modal analyses in a grid of points inside the workspace. A polynomial regression gives continuous volume maps of the natural frequencies distributions. The numerical model is validated by comparison with experiments: a modal analysis is conducted on a set of inertance Frequency Response Functions acquired on several points of the machine components as a result of an excitation given by an instrumented hammer. A Natural Frequency Difference analysis validates the model under certain conditions and highlights some critical issues to be focused on in future works.     

Mathematical modelling of couple stresses on fluid flow in constricted tapered artery in presence of slip velocity-effects of catheter

This paper explores the mathematical model for couple stress fluid flow through an annular region. The above model is used for studying the blood flow be-tween the clogged （stenotic） artery and the catheter. The asymmetric nature of the stenosis is considered. The closed form expressions for the physiological parameters such as impedance and shear stress at the wall are obtained. The effects of various geomet-ric parameters and the parameters arising out of the fluid considered are discussed by considering the slip velocity and tapering angle. The study of the above model is very significant as it has direct applications in the treatment of cardiovascular diseases.     

Exact Solutions for Nonlinear High Retention-Concentration Fines Migration

The paper discusses migration of natural reservoir fines lifted by high-rate or low-salinity water injection. The previous papers used linear analytical model, which is valid for low retention of mobilised fine particles in order to determine the model parameters from breakthrough fines concentration and pressure drop across the core during laboratory corefloods. The current work derives exact analytical solutions for the nonlinear case of high retention-concentration fines migration. The solution exhibits uniform profiles of suspended and retained concentrations ahead of the particle front and steady-state retained concentration behind the front. The obtained type curves allow distinguishing between linear and nonlinear fines migration. The laboratory data exhibit close agreement with the nonlinear model predictions, whereas the linear model poorly matches the laboratory data.     

Engineering of drug nanoparticles by HGCP for pharmaceutical applications

This paper reviews our work on the fundamental principles of high gravity controlled precipitation (HGCP) technology, and its applications in the production of drug nenoparticles, which was carded out in a rotating packed bed (RPB). Several kinds of drug nanoparticles with narrow particle size distributions (PSDs) were successfully prepared via HGCP, including the 300-nm Cefuroxirne Axetil (CFA) particles, 200-400-nm cephradine particles, 500-nm salbutamol sulfate (SS) particles (100 nm in width), end 850-nm beclomethasone dipropionate (BDP) particles, etc. Compared to drugs available in the current market, all the drug nanoparticles produced by HGCP exhibited advantages in both formulation end drug delivery, thus improving the bioavailability of drugs. HGCP is essentially a platform technology for the preparation of poorly water-soluble drug nanoparticles for oral and injection delivery, and of inhalable drugs for pulmonary delivery. Consequently, HGCP offers potential applications in the pharmaceutical industry due to its cost-effectiveness, efficient processing end the ease of scaling-up.     

Vibrational self-alignment of a rigid object exploiting friction

In this paper, one-dimensional self-alignment of a rigid object via stick-slip vibrations is studied. The object is situated on a table, which has a prescribed periodic motion. Friction is exploited as the mechanism to move the object in a desired direction and to stop and self-align the mass at a desired end position with the smallest possible positioning error. In the modeling and analysis of the system, theory of discontinuous dynamical systems is used. Analytic solutions can be derived for a model based on Coulomb friction and an intuitively chosen table acceleration profile, which allows for a classification of different possible types of motion. Local stability and convergence is proven for the solutions of the system, if a constant Coulomb friction coefficient is used. Next, near the desired end position, the Coulomb friction coefficient is increased (e.g. by changing the roughness of the table surface) in order to stop the object. In the transition region from low friction to high friction coefficient, it is shown that, under certain conditions, accumulation of the object to a unique end position occurs. This behavior can be studied analytically and a mapping is given for subsequent stick positions.     

双集中荷载下一次超静定梁的加载过程分析

对双集中荷载作用下一次超静定梁的弹塑性加载全过程进行了分析．根据变形特点可把加载过程分成四个阶段．第一阶段是常规的弹性阶段,第二阶段是固支端附近单个塑性变形区扩展的阶段,第三阶段是固支端和一个集中荷载附近两个塑性变形区同时扩展的阶段,第四阶段是固支端保持为塑性铰从而引起固支端附近区域卸载而梁中间的塑性变形区继续扩展直至形成第二个塑性铰的阶段．在第一阶段,弯矩内力和挠度与外荷载均是线性比例递增关系;在第二、第三两个阶段,弯矩和挠度与外荷载是不同的非线性关系;在第四阶段,弯矩与外荷载是非比例的线性关系,但挠度与外荷载却是复杂的非线性关系．给出了加载各阶段的弯矩及挠度计算公式,具有理论意义,也可供对应的结构设计应用．     

DESIGN OF LATERAL SOIL PRESSURE MODEL TEST SCHEME FOR ADJACENT COMPOSITE FOUNDATION1)

为了研究刚性桩复合地基对邻近支护结构侧土压力的影响,在室内模型试验方案设计前,通过有限元软件建立了邻近天然地基与复合地基模型进行数值模拟研究,对不同地基形式下静止挡墙侧土压力分布规律进行预估。两组数值模拟结果对比表明：复合地基土压力分布规律不同于天然地基,当复合地基褥垫层下方桩间土应力与天然地基土应力相同时,天然地基对挡墙相同位置处的墙侧土压力的附加作用效果要明显大于复合地基,但在"载荷传递效应"作用下,复合地基对挡墙侧向土压力的影响随着加载量的增加,逐步向更深处土体传递;与天然地基相比,复合地基对挡墙侧向土压力的影响在浅部土层相对较弱,但在深部土层中较强,并且在桩端应力集中对挡墙底部侧向土压力影响尤为显著。