DYNAMIC RESPONSE AND ENERGY DISSIPATION ANALYSIS OF THE WALL WITH HORIZONTAL SHORT KEYWAYS AND LOWRISE SHEARWALL

A new type of ductile lowrise shearwall with many short horizontalkeyways is proposed in this paper in order to improve the earthquake resistant behav-ior of ordinary lowrise shearwall.The behavior of this wall is studied through low-frequency cyclic loading test.Based on the test results,the paper puts forward thedifferent restoring force models for different lowrise shearwalls,and a program fortheir nonlinear dynamic analysis is worked out.Thr(?)h directly inputting earth-quake waves,the paper analyses the dynamic response and energy dissipation of 3types of lowrise shearwalls.The calculation results dem(?)strate that the newly de-vised ductile shearwall has good earthquake resistant behavior.

Size-dependent sinusoidal beam model for dynamic instability of single-walled carbon nanotubes

In this study, a model for dynamic instability of embedded single-walled car- bon nanotubes （SWCNTs） is presented. SWCNTs are modeled by the sinusoidal shear deformation beam theory （SSDBT）. The modified couple stress theory （MCST） is con- sidered in order to capture the size effects. The surrounding elastic medium is described by a visco-Pasternak foundation model, which accounts for normal, transverse shear, and damping loads. The motion equations are derived based on Hamilton＇s principle. The differential quadrature method （DQM） in conjunction with the Bolotin method is used in order to calculate the dynamic instability region （DIR） of SWCNTs. The effects of differ- ent parameters, such as nonlocal parameter, visco-Pasternak foundation, mode numbers, and geometrical parameters, are shown on the dynamic instability of SWCNTs. The re- sults depict that increasing the nonlocal parameter shifts the DIR to right. The results presented in this paper would be helpful in design and manufacturing of nano-electromechanical system （NEMS） and micro-electro-mechanical system （MEMS）.

Computational fluid dynamics modeling in intracranial atherosclerotic disease

Intracranial atherosclerotic disease(ICAD)is an important cause for ischemic stroke and transient ischemic stroke(TIA)throughout the world,especially in Asians,which is not fully appreciated,partly due to its inaccessibility and limitations of current neuroimaging methods.The computational fluid dynamics(CFD)modeling technique provides a novel approach to reveal the hemodynamic characteristics in ICAD,e.g.,the distributions of pressure,wall shear stress and flow velocity.In this review article,we aim to provide an overview of the general methodology of CFD modeling in arterial stenotic diseases,the established application of this technique in coronary artery disease,and more importantly,perspectives and challenges of this technique in the investigation of ICAD.Promising findings of preliminary studies using a CFD model for hemodynamic analysis in ICAD warrant verifications.Further studies in this area will help rectify loopholes in the current secondary prevention strategy,and inform individualized treatment for ICAD patients in the near future.

Computational Fluid Dynamics Simulation on Biomedical Stent Design

The stent was a major breakthrough in the treatment of atherosclerotic vascular disease. The permanent vascular implant of a stent, however, changes the intra-stent blood flow hemodynamics. There is a growing consensus that the stent implant may change the artery wall shear stress distribution and hence lead to the restenosis process. Computational fluid dynamics （CFD） has been widely used to analyze hemodynamics in stented arteries. In this paper, two CFD models （the axisymmetric model and the 3-D stent model） were developed to investigate the effects of strut geometry and blood rheology on the intra-stent hemodynamics. The velocity profile, flow recirculation, and wall shear stress distribution of various stent strut geometries were studied. Results show strong correlations between the intra-stent hemodynamics and strut geometry. The intra-stent blood flow is very sensitive to the strut height and fillet size. A round strut with a large fillet size shows 36% and 34% reductions in key parameters evaluating the restenosis risk for the axisymmetric model and the 3-D stent model, respectively. This suggests that electrochemical polishing, a surface-improving process during stent manufacturing, strongly influences the hemodynamic behavior in stented arteries and should be controlled precisely in order to achieve the best clinical outcome. Rheological effects on the wall shear stress are minor in both axisymmetric and 3-D stent models for the vessel diameter of 4 mm, with Newtonian flow simulation tending to give more conservative estimates ofrestenosis risk. Therefore, it is reasonable to simulate the blood flow as a Newtonian flow in stented arteries using the simpler axisymmetric model. These findings will provide great insights for stent design optimization for potential restenosis improvement.

Influence of Strut Cross-section of Stents on Local Hemodynamics in Stented Arteries

Stenting is a very effective treatment for stenotic vascular diseases, but vascular geometries altered by stent implantation may lead to flow disturbances which play an important role in the initiation and progression of restenosis, especially in the near wall in stented arterial regions. So stent designs have become one of the indispensable factors needed to be considered for reducing the flow disturbances. In this paper, the structural designs of strut cross-section are considered as an aspect of stent designs to be studied in details. Six virtual stents with different strut cross-section are designed for deployments in the same ideal arterial model. Computational fluid dynamics（CFD） methods are performed to study how the shape and the aspect ratio（AR） of strut cross-section modified the local hemodynamics in the stented segments. The results indicate that stents with different strut cross-sections have different influence on the hemodynamics. Stents with streamlined cross-sectional struts for circular arc or elliptical arc can significantly enhance wall shear stress（WSS） in the stented segments, and reduce the flow disturbances around stent struts. The performances of stents with streamlined cross-sectional struts are better than that of stents with non-streamlined cross-sectional struts for rectangle. The results also show that stents with a larger AR cross-section are more conductive to improve the blood flow. The present study provides an understanding of the flow physics in the vicinity of stent struts and indicates that the shape and AR of strut cross-section ought to be considered as important factors to minimize flow disturbance in stent designs.

Distribution of wall shear stress in carotid plaques using magnetic resonance imaging and computational fluid dynamics analysis： a preliminary study

Background Wall shear stress is an important factor in the destabilization of atherosclerotic plaques. The purpose of this study was to assess the distribution of wall shear stress in advanced carotid plaques using high resolution magnetic resonance imaging and computational fluid dynamics.Methods Eight diseased internal carotid arteries in seven patients were evaluated. High resolution magnetic resonance imaging was used to visualize the plaque structures, and the mechanic stress in the plaque was obtained by combining vascular imaging post-processing with computational fluid dynamics.Results Wall shear stresses in the plaques in all cases were higher than those in control group. Maximal shear stresses in the plaques were observed at the top of plaque hills, as well as the shoulders of the plaques. Among them,the maximal shear stress in the ruptured plaque was observed in the rupture location in three cases and at the shoulder of fibrous cap in two cases. The maximal shear stress was also seen at the region of calcification, in thrombus region and in the thickest region of plaque in the other three cases, respectively.Conclusion Determination of maximal shear stress at the plaque may be useful for predicting the rupture location of the plaque and may play an important role in assessing plaque vulnerability.

Effect of coronary artery dynamics on the wall shear stress vector field topological skeleton in fluid–structure interaction analyses

In this paper,we investigate the impact of coronary artery dynamics on the wall shear stress(WSS)vector field topology by comparing fluid–structure interaction(FSI)and computational fluid dynamics(CFD)techniques.As one of the most common causes of death globally,coronary artery disease(CAD)is a significant economic burden;however,novel approaches are still needed to improve our ability to predict its progression.FSI can include the unique dynamical factors present in the coronary vasculature.To investigate the impact of these dynamical factors,we study an idealized artery model with sequential stenosis.The transient simulations made use of the hyperelastic artery and lipid constitutive equations,non‐Newtonian blood viscosity,and the characteristic out‐of‐phase pressure and velocity distribution of the left anterior descending coronary artery.We compare changes to established metrics of time‐averaged WSS(TAWSS)and the oscillatory shear index(OSI)to changes in the emerging WSS divergence,calculated here in a modified version to handle the deforming mesh of FSI simulations.Results suggest that the motion of the artery can impact downstream patterns in both divergence and OSI.WSS magnitude is also decreased by up to 57%due to motion in some regions.WSS divergence patterns varied most significantly between simulations over the systolic period,the time of the largest displacements.This investigation highlights that coronary dynamics could impact markers of potential CAD progression and warrants further detailed investigations in more diverse geometries and patient cases.

Non-invasive assessment of intracranial wall shear stress using high-resolution magnetic resonance imaging in combination with computational fluid dynamics technique

In vivo studies on association between wall shear stress(WSS)and intracranial plaque are deficient.Based on the three-dimensional T1-weighted high-resolution magnetic resonance imaging(3DT1 HR-MRI)data of patients with low-grade stenotic(<50%)atherosclerotic middle cerebral artery(MCA)and subjects with normal MCA,we built a three-dimensional reconstructed WSS model by computational fluid dynamics(CFD)technique.Three-dimensional registration of the CFD model to the HR-MRI was performed with projections based on the resolution and thickness of the images.The relationships between the Wss at each side of the vessel wall and plaque location were analyzed.A total of 94 MCA plaques from 43 patients and 50 normal MCAs were analyzed.In the normal MCAs,WSS was lower at the ventral-inferior wall than at the dorsal-superior wall(proximal segment,p<0.001;middle segment,p<0.001)and lower at the inner wall than at the outer wall of the MCA curve(p<0.001).In atherosclerotic MCAs,similar low Wss regions were observed where plaques developed.The WSS ratio of the ventral-inferior wall to the dorsal-superior wall in atherosclerotic MCAs was lower than that in normal MCAs(p=0.002).The WSS_(inmer-outer)ratio in atherosclerotic MCAs was lower than that in normal MCAs(p=0.002).Low WSS was associated with MCA atherosclerosis formation and occurred mainly at the ventral inferior wall,which was anatomically opposite the orifices of penetrating arteries,and at the inner wall of the MCA curve.Overall,the results were well consistent with the low WSS theory in atherosclerosis formation.The reconstructed WSS model is a promising novel method for assessing an individualized vascular profile once validated by further studies.

Seismic performance evaluation of hybrid coupled shear wall system with shear and flexural fuse-type steel coupling beams

Replaceable flexural and shear fuse-type coupling beams are used in hybrid coupled shear wall(HCSW)systems,enabling concrete buildings to be promptly recovered after severe earthquakes.This study aimed to analytically evaluate the seismic behavior of flexural and shear fuse beams situated in short-,medium-and high-rise RC buildings that have HCSWs.Three building groups hypothetically located in a high seismic hazard zone were studied.A series of 2D nonlinear time history analyses was accomplished in OpenSees,using the ground motion records scaled at the design basis earthquake level.It was found that the effectiveness of fuses in HCSWs depends on various factors such as size and scale of the building,allowable rotation value,inter-story drift ratio,residual drift quantity,energy dissipation value of the fuses,etc.The results show that shear fuses better meet the requirements of rotations and drifts.In contrast,flexural fuses dissipate more energy,but their sectional stiffness should increase to meet other requirements.It was concluded that adoption of proper fuses depends on the overall scale of the building and on how associated factors are considered.

On the role of hemodynamics in predicting rupture of the abdominal aortic aneurysm

Hemodynamics plays a crucial role in the growth of an abdominal aortic aneurysm(AAA)and its possible rupture.Due to the serious consequences that arise from the aneurysm rupture,the ability to predict its evolution and the need for surgery are of primary importance in the medical field.Furthermore,the presence of intraluminal thrombus(ILT)strongly affects the evolution of the pathology.In this study,we analyzed the influence of hemodynamics on the growth and possible rupture of AAAs.Numerical investigations of pulsatile non-Newtonian blood flow were performed in six patient-specific AAAs reconstructed from diagnostic images,having different sizes and shapes,and with or without ILT.Wall shear stress and vorticity distribution in the bulge and their evolution during the cardiac cycle were analyzed.The results indicate that blood flow dynamics acts synergistically with atherosclerotic degeneration in the development of the disease.The high surface complexity and tortuosity of the aneurysms significantly affect the blood motion,and the presence of inflection in the aneurysm centerline has a noticeable effect on the vortex dynamics.Links between regions of slow recirculating flows,low values of time-averaged wall shear stress,high values of oscillatory shear index,and zones of ILT deposition were found.In the absence of ILT,possible thrombus accumulation areas and consequent aneurysm growth were identified.The findings of this study highlight the importance of hemodynamics in assessing the vulnerability of the aortic wall and underline the crucial role of patient-specific investigations in predicting the rupture of individual aneurysms.

FREE VIBRATION ANALYSIS OF SHEAR WALLS WITH SHORT PIERS

The equations of the lateral deflection curve of the short pier shear wall under a lateral concentrated load at any level are derived by employing a continuous approach. Lateral flexibility matrixes for the dynamic analysis are also obtained by repeatedly calculating the lateral unit load on the wall at each level where a lumped mass located. Dynamic analyses are implemented for short pier shear walls with different parameters, called the integrative coefficient and the pier strength coefficient related to the dimensions of walls. The influences of two coefficients on the dynamic performances of the structure are studied. Results indicate that with the increase of the integrative coefficient, the periods of top two modes apparently decrease but the other periods of higher frequency modes show little variation when the pier strength coefficient remains constant. Similarly, if the integrative coefficient is constant, the top two periods of the free vibration decrease with the increase of the integrative coefficient but the other periods of higher frequency modes show less variation.

Influence of aortic branch arteries on the hemodynamics of patient-specific type B aortic dissection following TEVAR

Objective:Because of the difficulty in obtaining patient specific flow data,branch arteries are often neglected in the flow simulations of a patient-specific type B aortic dissection(AD)following thoracic endovascular repair(TEVAR).This study aims to investigate the influence of the aortic branch arteries on the hemodynamics and physical flow phenomena commonly associated with aortic modeling of an AD after TEVAR.Methods:The three-dimensional geometry of a type B AD following TEVAR was generated from a high-quality CT dataset.Simulations were performed with all branch arteries,without the four visceral arteries of the abdominal aorta(FVAoAA),and without the upper three branches of the aortic arch(UTBoAA).Results:The removal of the UTBoAA has marginal effect on the flow patterns and hemodynamic parameters in the false lumen(FL);however,regardless of whether there are aorta branches supplied to the FL or not,the omission of FVAoAA will result in a wrong prediction of the flow direction at tears and flow volume to the FL.Conclusions:The omission of aorta branch arteries has great impact on the hemodynamic prediction including flow field and wall shear stress related parameters in a type B AD after TEVAR,which may induce misleading estimates of the potential thrombus in the FL.It is strongly recommended to keep aorta branches in the computational model to predict the post-operative hemodynamic performance in a type B AD following TEVAR.

Seismic Analysis of Shear-Wall Structures with Vertically Installed Dampers

Shear-wall structures are quite common in seismic areas because of their successful seismic behavior during severe earthquakes. But shear walls are prone to brittle failure. This study proposes a new method of vertically installed dampers （VID） to reduce the vibration in shear-wall structures. The motion characteristic of a vertical damping system is that every mass has horizontal and rotational displacements simultaneously, The establishment of dynamic equations should take into account the equilibrium conditions of both horizontal and rotational vibrations. Dynamic equilibrium equations of VID systems are derived from a model of a structure with VID. An example shear-wall structure, with and with- out VID, is studied. There are some changes in the characteristics of the maximum horizontal displacement response. Without dampers, the relative displacements between different floors in the shear wall increase with height. With dampers, the relative displacements are more uniformly distributed, and lateral displacements at the top and at the bottom are closer. When the damping coefficient is 1 000 kN · s/ m, the numerical results reveal that the maximum horizontal displacement and the maximum rotational displacement of the top floor have reduced by 59.3 % and 54.8 % respectively.

西咸自由贸易企业服务中心超高层建筑结构设计

西咸自由贸易企业服务中心地处高烈度区,与渭河断裂之间的距离约2km,应考虑近场效应。项目采用钢管混凝土框架(钢梁)+钢筋混凝土核心筒混合结构,存在扭转不规则、刚度突变、有加强层和通高层等不规则项。为提高结构刚度,在避难层设置了2道伸臂桁架加强层。采用YJK、MIDAS Building软件进行了小震弹性对比分析,采用YJK进行了小震弹性时程分析。根据设定的抗震性能目标,对主体结构主要部位和关键构件进行了性能化设计;采用SAUSAGE软件进行了罕遇地震作用下的动力弹塑性时程分析;采用ANSYS软件对伸臂桁架关键节点进行有限元分析。结果表明:各项指标均符合设计要求,结构及构件均达到预设性能目标,结构体系合理,安全可靠。本工程部分墙体为钢板混凝土剪力墙,设计中应注重钢板混凝土剪力墙的构造措施,施工中应采取措施控制钢板变形。

微孔的磨料水射流抛光CFD模拟及试验

为解决飞秒激光微孔难以抛光的问题,结合磨料水射流去除函数稳定、自适应性强等特点,采用磨料水射流抛光方法提高飞秒激光微孔质量。利用Fluent软件对不同工艺参数下的磨料水射流微孔抛光过程进行计算流体力学(computational fluid dynamics,CFD)模拟,分析不同参数下的流场分布、侵蚀速率及壁面剪切力作用规律;然后通过响应面法对射流靶距、射流压力及磨料粒径等3因素进行优化试验,以微孔内壁面剪切力均方差为响应值,建立其响应面方程,获得最佳抛光参数组合并进行试验验证。结果表明:射流压力对微孔内壁面剪切力的影响最大,当射流压力从0.80 MPa增至1.50 MPa时,微孔内壁面剪切力增大2倍以上。射流的不同结构段因性质不同可适用于不同工况。利用响应面法分析得到水射流微孔抛光的最佳工艺参数组合是:射流冲击角,90°;射流靶距,3.5 mm;射流压力,1.10 MPa;磨料粒径,15.0μm。在该条件下抛光微孔内壁面的表面粗糙度R_a降至0.354μm。磨料水射流抛光可显著改善微孔壁面质量,且响应面法预测的数据模型有较高准确性。

主余震序列作用对剪力墙结构动力响应影响分析

为了研究主余震序列作用对高层剪力墙结构动力响应的影响,以某超高层作为研究基础建立了其动力弹塑性分析模型,开展了相关研究工作。选取10个真实主余震序列作用事件,构造了14条主余震序列作用作为输入的地震荷载;以PGA、PGV、PGA/PGV等作为表征地震动强度的指标,计算了结构在主余震序列作用及仅主震作用下的结构塑性耗能、最大残余层间位移角的增量损伤比及Karl Pearson相关系数;分析了主余震序列作用下结构塑性耗能及最大残余层间位移角的特点和地震动强度指标与增量损伤比的相关性。结果表明,主余震序列作用加剧了结构损伤,其塑性耗能增量平均达24%~28%;主余震序列作用下结构最大残余层间位移角有可能增大,也有可能减少。基于塑性耗能的结构主余震增量损伤比与PGV、SED、SI等速度相关的地震动强度表征指标均表现出了较强的相关性,可考虑作为选择和调整主余震序列作用地震波的指标;基于最大残余层间位移角的结构主余震增量损伤比则与地震动强度指标相关性较弱。

广州某超限连体高层结构设计

广州某超限高层为带连体的部分框支剪力墙结构,两栋结构高度分别为9725、9275m,在4层、11~13层通过连廊连接。为了验证结构布置的可靠性和安全性,采用YJK和ETABS软件对建筑结构进行整体计算分析及弹性时程分析,同时借助Perform-3D软件,对结构的动力弹塑性进行深入分析,并对连接体结构受力情况做专项分析。结果表明,两栋塔楼的转换构件及连接体结构受力体系合理可靠。根据结构的受力特征,通过对关键构件及其他受力构件的加强处理,确保结构整体上满足各项预先设定的抗震性能目标的要求。

广州某部分框支剪力墙结构设计

广州市某超限高层项目采用部分框支剪力墙结构,属于A级高度的超限高层建筑,结构同时存在扭转不规则、组合平面及构件间断共3项不规则情况。设计基于性能化进行抗震设计,采用YJK、SATWE两个有限元程序进行小震弹性分析、中震等效弹性分析、大震等效弹性分析,Perform-3D对超限结构进行了罕遇地震作用下的弹塑性动力时程分析,并采取了针对超限的加强措施。计算及研究分析结果表明,通过对部分关键构件的加强,结构整体的抗震性能满足“小震不坏、中震可修、大震不倒”,结构体系安全可行。

某超限高层剪力墙结构分析与设计

8度区某办公楼项目采用剪力墙结构体系,房屋总高度143.7m,存在两项超限,分别为高度超限和第四层刚度突变。设计时在保证超限结构满足现行规范要求的同时,还要使结构两个方向的动力特性相近。选用YJK和Midas-building软件对结构进行计算,计算内容包括多遇地震反应谱分析、多遇地震弹性时程分析、设防地震下墙肢名义拉应力验算、罕遇地震弹塑性时程分析。并对结构关键部位进行了剪力墙模型以及实体单元模型的补充验算,保证了结构设计的可靠性。结果表明:通过合理的结构平面布置,提高了结构效率,使结构在多遇地震和罕遇地震作用下都能保证良好的抗震性能,安全可行。

增幅冲击下钢筋混凝土剪力墙的动态响应分析

在冲击荷载下,钢筋混凝土剪力墙的动态响应是一个复杂的非线性过程,采用LS-DYNA对钢筋混凝土剪力墙进行了3次连续冲击荷载下的数值模拟试验,验证了CSCM本构模型的可靠性,分析3次冲击破坏模式得到位移时程曲线。研究结果表明,在增幅冲击荷载作用下,混凝土的损伤范围逐次增大,放射状裂缝逐次增多,冲击响应复杂程度加剧;随着冲击能量的增加,剪力墙吸收能量的效率逐渐降低。墙体中心峰值位移随着冲击头速度的增加而增大,中心位移从12.83 mm增至49.08 mm;峰值位移周期随着墙体损伤程度的加剧而增长。