基于网格变换技术的9岁儿童C4-C5颈椎有限元模型开发与验证

针对通过手动画高质量网格的传统有限元建模方法存在建模周期长的问题,应用网格变换技术,结合开发的一套自动识别并提取标识点的方法,快速地建立了9岁儿童C4-C5颈椎有限元模型.应用材料缩放的方法,获得了9岁儿童颈部材料参数,并参考尸体试验数据,在拉伸、前屈及后伸工况下对模型进行了验证.结果显示,与全部人工识别并提取标志点的方法相对比,该套取点方法节约了2/3~3/4的时间.开发的有限元模型网格质量高,平均几何模型精度误差是0.46mm.模型仿真输出值与试验值吻合良好,精度达到90%以上.通过该方法开发有限元模型可节省大量的时间,并且模型具有较高的生物逼真度.同时该方法具有较强的适应性,可应用于各类复杂几何的快速有限元建模.     

基于人体生物力学的颈椎动力外骨骼的设计与运动学分析

针对神经根型与交感神经型颈椎病,基于颈椎牵引、前屈/后伸、左/右侧屈及旋转运动康复治疗方式,设计了一种基于6-SPS/CS型并联机构的可穿戴式颈椎动力外骨骼.首先,基于人体生物力学进行外骨骼机构设计与颈椎运动分析,采用空间坐标变换方程和闭环矢量法对外骨骼等效并联机构进行运动学逆解分析;其次,利用ADAMS软件对外骨骼等...     

行人下肢有限元模型的建立与验证研究

下肢损伤是行人与车辆碰撞事故中的主要损伤形式之一,建立具有较高生物逼真度的行人下肢有限元模型,可以为下肢保护提供有效的研究手段.在下肢长骨(股骨、胫骨、腓骨)、韧带(ACL,PCL,MCL,LCL)及膝关节得到全面验证的基础上,建立了包含骨骼、韧带、肌肉及皮肤等详细解剖学结构的行人下肢有限元模型,并定义了各组织间的接触.利用行人下肢弯曲的生物力学实验,对下肢有限元模型进行了整体弯曲验证.结果显示,下肢有限元模型的损伤形式、损伤发生时刻、膝关节弯矩和弯曲角度均与实验结果吻合较好,能够较真实地反映行人下肢的损伤和生物力学响应,具有较好的生物逼真度.     

内镜下经椎板间联合椎间孔入路减压治疗腰椎管狭窄症生物力学评价

为了解决单纯应用椎板间或椎间孔入路,对于多部位、多因素、多层面致压的腰椎管狭窄症(lumbar spinal stenosis, LSS)病例,往往存在减压不彻底的情况,通过建立人体腰椎L4-L5节段有限元模型M0,构建精确的腰椎仿真模型,模拟经椎板间联合椎间孔入路减压,即Endo-LOVE (endoscopic LOVE decompression)联合PTED(percutaneous transforaminal endoscopic decompression)形成的环绕关节突周围减压M3模型,研究经椎板间联合椎间孔入路治疗腰椎管狭窄症术后生物力学变化及对责任节段稳定性影响。结果表明：M3处于前屈、后伸、左侧弯、右侧弯、左旋转、右旋转六种工况下时,其L4-L5责任节段活动度相对M0分别增加7.28%、11.29%、0.51%、0.27%、1.17%、0.51%,未发生节段失稳;M3处于前屈、后伸、左侧弯、右侧弯、左旋转、右旋转六种不同条件下时,其椎间盘Von Mises应力极值相对M0分别增加3.20%、9.51%、0.55%、0.10%、0.39%、-0.44%,未发生应力...     

内固定器对人体颈椎运动生物力学性能的影响

在失稳颈椎内安装固定器后,其稳定性的生物力学评价是医学研究的一个重要课题。该文提出了一种双目三维光学精密运动测量方法对其进行评价。采用该方法分别对保存良好的人体颈椎标本在失稳、内固定以及疲劳3种状态下的三维运动情况(包括前屈、后伸、左侧弯、右侧弯4种运动)进行了测量,并以每种运动情况下的颈椎C 1-C 2节相互旋转角度衡量其内固定的效果。实验结果表明,内固定后颈椎的旋转角度明显小于失稳时的旋转角度;内固定后模拟远期效果的疲劳加载后测试结果证实内固定的效果仍然是可靠的。     

人体下肢有限元动力学分析模型的建立和验证

为了研究行人碰撞事故中人体下肢的生物力学响应和损伤机理,建立了一个人体下肢有限元模型．模型按人体解剖学结构建立,由髋骨、股骨、胫骨、腓骨、膑骨、足骨、韧带、腱、关节囊以及髋关节、膝关节和踝关节构成．采用了壳单元和线性弹簧-阻尼单元来模拟骨骼和软组织．模型的边界和载荷条件根据汽车行人侧碰撞实验条件确定．通过比较仿真和实验在横向碰撞载荷条件下的剪切、弯曲响应结果,验证了模型的生物逼真度．分析了在不同加载条件下有限元模型的生物力学响应和应力分布,以及与下肢损伤风险的关系．     

不同骨密度轨迹内固定系统对腰椎L4-L5节段的影响

为了评价改良皮质骨螺钉技术(modified cortical screw technique,MCBT)与其他传统内固定系统对腰椎骨质疏松湿标本L4-L5节段的生物力学影响.通过运用计算机体层摄影(computed tomography,CT)数据建立4种不同的有限元模型,比较三种置钉模型在相同生理负荷下的内固定系统应力的变化和腰椎L4-L5节段椎间活动度的变化.结果表明:改良模型组在前屈、后伸、侧弯、扭转工况下内固定系统的最大应力值明显大于传统椎弓根螺钉技术(traditional pedicle screw technique,TT)模型组和传统皮质骨螺钉技术(cortical bcrew technique,CBT).MCBT螺钉模型在前屈、后伸、扭转工况下的椎间活动度最小,侧弯工况下大于TT模型组和CBT模型组.可见与TT和CBT相比,MCBT的机械稳定性更好,且在临床应用方面具有一定价值.     

Numerical simulation of the temperature fields of stainless steel with different roller parameters during twin-roll strip casting

The temperature field of stainless steel during twin-roll strip casting was simulated by experiment and a finite element (FE) model. By comparing the measured result with the simulated values, it is found that they fit close to each other, which indicates this FE model is effective. Based on this model, the effects of roll gap (t) and roll radius (R) on solidification were simulated. The simulated results give the relationship between t or R and the position of the freezing point. The larger the t is and the smaller the R is, the closer the position of the freezing point is to the exit.     

微动椎弓根螺钉的生物力学仿真评测

利用有限元法评估一种微动椎弓根螺钉的生物力学性能.基于人体脊柱CT图像数据建立腰椎L3-L4节段有限元模型,并在此基础上建立坚强固定(M1)、微动固定(M2)、混合固定(M3)3种内固定有限元模型,对有限元模型施加模拟生理载荷,计算内固定节段各项生物力学参数.仿真结果表明,微动椎弓根螺钉在屈伸方向增大了内固定节段的椎间活动度,其中前屈工况增大95%,后伸工况增大83%;改善了载荷在椎间的传递,增大终板正常生理性刺激应力4.25%~5.7%;降低了植入体上的应力集中效应,在前屈、后伸和侧弯工况下降低椎弓根螺钉应力9.2%~16.2%.     

Further results on generalized LCM matrices

Let S={x_1,x_2,...,x_n } be a set of n distinct positive integers and f be an arithmetic function.By(f[S])(resp.( f[S])),we denote the n*n matrix whose i,j entry is Σ[x_i,x_j]|l l∈S f(l) (resp.Σx∈Sf(x)-Σ x_i,|l l∈S f(l)-Σ x_j,|l l∈S f(l)+Σ[x_i,x_j]|l l∈S f(l)).In this paper,we first investigate the structures of the matrices ( f[S]) and( f[S]),then we give the formulae for the determinants of these matrices.These extend the results obtained by Bege in 2011.Finally,we give two examples to demonstrate the validity of our main results.     

Super-Edge-Connectivity of G(k,d,s)(s≥k/2)

A graph G is super-edge-connected,for short super-λ,if every minimum edge-cut consists of edges adjacent to a vertex of minimum degree.Alphabet overlap graph G(k,d,s)is undirected,simple graph with vertex set V={v|v=1()kv…v;vi∈{1,2,…,d},i=1,…,k}.Two vertices u=(u1…uk)and v=(v1…vk)are adjacent if and only if us+i=vi or vs+i=ui(i=1,…,k-s).In particular G(k,d,1)is just an undirected de Bruijn graph.In this paper,we show that the diameter of G(k,d,s)is k s,the girth is 3.Finally,we prove that G(k,d,s)(s≥k/2)is super-λ.     

铝合金薄壁矩形管绕弯成形起皱极限的预测

失稳起皱是铝合金薄壁矩形波导管绕弯成形过程中的主要缺陷之一,严重制约着薄壁矩形管绕弯成形极限的提高。笔者采用有限元数值模拟结合正交回归分析的方法,建立了薄壁矩形管绕弯成形起皱波纹度回归预测模型,并通过实验验证了该模型的可靠性;在此基础上推导出了基于失稳起皱成形极限的解析模型。研究获得了芯头个数、防皱块与管坯间隙及芯模与管坯间隙对起皱极限的影响规律,并获得了铝合金薄壁矩形管绕弯成形起皱极限图。该研究为提高实际生产中薄壁矩形管绕弯成形质量提供了依据和指导。     

A logic-based safety analysis algorithm for discretionary access control

For the issue of the discretionary access control(DAC) model safety analysis,a logic method is proposed.This method takes the GD model as the classic DAC model and Prolog as the basic language to describe system states and state transfer rules.A general program based on this logic method is proposed for DAC safety analysis,but this program may never be terminal for some safety analysis goal.The safety analysis algorithm is achieved by simplifying the general program according to the property of the DAC model state transfer rules.This safety analysis algorithm is easier to understand and implement than the previous algorithms and its time complexity is O(N+M+T),in which N,M,and T are the numbers of the rights with copy flag,the policies for right transferring,and the policies for right permitting,respectively.     

体外预应力钢－混凝土组合梁在负弯矩作用下的稳定系数研究

摘要：对组合梁施加体外预应力,可有效提高截面的开裂弯矩。负弯矩作用下体外预应力组合梁的极限承载力受失稳控制,其侧扭失稳表现为与纯钢梁不同的畸变失稳模式。本文考虑钢梁初始几何缺陷影响和残余应力影响,对体外预应力组合梁进行了有限元非线性稳定分析,计算结果与试验实测值吻合。通过改变截面参数,对25组组合梁在初始几何缺陷、不同残余应力分布和不同综合力比下的承载力进行计算,给出了预应力组合梁的长细比计算公式,与我国现行钢结构规范钢柱稳定曲线进行了比较。研究表明：承受负弯矩作用的体外预应力组合梁可用文中提出的长细比做参数采用钢柱稳定曲线进行计算。     

Texture evolution of commercial pure Ti during cold rolling and recrystallization annealing

X-ray diffraction (XRD) was employed to analyze the texture evolution of commercial pure (CP) Ti during cold rolling and recrystallization annealing. The texture components were measured by electron backscattered diffraction (EBSD) after recrystallization annealing. The CP Ti tends to form a texture with the basal pole tilted 30°-40° away from the normal direction toward the transverse direction. The texture of the initial hot-rolled plate can be classified into three kinds, i.e., the pyramid texture (1013)[5230] and (2021)[1015], the basal plane texture (0001)[2110], and the stronger prism texture (1120)[0001]. After cold rolling and annealing (700℃, 60 min), the main texture components are the cold-rolled texture (1125)[1123] and the recrystallized texture (1013)[5230]. The texture (2021)[1015] is inherited from the texture of the initial hot-rolled plate with the decrease of orientation density gradually. The volume contents of the cold-rolled texture {2115} <0110> and the recrystallized texture {1013} <1210> are calculated by EBSD. After recrystallization annealing, the specimen is rich in the recrystallized texture and inherits some of texture components from the cold-rolled texture. When the annealing time is prolonged, the anisotropic value decreases.     

自锚式混凝土悬索桥的动力分析

研究自锚式混凝土悬索桥的动力学性能 .以一新建自锚式混凝土悬索桥为背景 ,首先运用有限元分析获得其动力特性并与地锚式悬索桥进行比较 ,然后利用实桥环境振动试验验证有限元动力特性分析结果 ,最后由地震反应分析进一步考察自锚式悬索桥的振动特点 .结果表明 :自锚式悬索桥由于主缆直接锚固于主梁端 ,主塔纵向弯曲振动频率明显降低 ;因结构耗能方式也随之发生了变化 ,主塔和主梁在纵向地震输入下的各种反应均呈不同程度的增加 .     

新管幕结构受力模式及关键技术分析

沈阳地铁九号线奥体中心站采用Steel Tube Slab管幕工法建造覆土超浅埋暗挖地铁车站.对新管幕结构的纵向和横向受力模式进行研究，阐述了管幕结构的作用机理，并对管幕结构的抗弯承载力和抗剪承载力计算理论进行讨论，给出了相应的计算公式.结合奥体中心的施工工况，对管幕结构的内力进行计算.随着右侧导洞贯通时，与左侧导洞相比较，跨中正弯矩增加8%，最大负弯矩减小17.8%.管幕结构沿纵向跨中最大变形为6.46mm.研究结果对新管幕工法的应用和推广具有参考意义.     

Correlation of morphological anisotropy and Lankford value of deep drawing sheets hot-rolled by compact strip production

Cold-rolled steel sheets in automotive applications require an excellent deep draw ability, which is characterized by the Lankford value (r-value). In this study, a correlation was identified between r-value and pancake-shaped grain flatness which is indicated as the ratio of grain diameter in the rolling direction (RD) and normal direction (ND) of sheets (d_r/d_n). A mathematical model (r=e0.345(d_n-1/2-d_r-1/2)) was developed to calculate r-value by the microstructure of steel sheets hot-rolled by compact strip production (CSP). It is shown that the r-value is higher, if the microstructure of steel sheet is of pancake-shaped grains elongated in the rolling direction. The calculated r-value is confirmed to fit exactly to the measured one from the large-scale production.     

Corrosion of magnesium and magnesium –calcium alloy in biologically-simulated environment

A study of biocompatibility and corrosion of both metallic magnesium(Mg) and a magnesium alloy containing 1% calcium(Mg–Ca) were investigated in in vitro culture conditions with and without the presence of bone marrow derived human mesenchymal stem cells(h MSCs).Chemical analysis of the degraded samples was performed using XRD and FEGSEM. The results from the XRD analysis strongly suggested that crystalline phase of magnesium carbonate was present on the surface of both the Mg and Mg–Ca samples. Flame absorption spectrometry was used to analyse the release of magnesium and calcium ions into the cell culture medium. Magnesium concentration was kept consistently at a level ranging from 40 to 80 m M for both Mg and Mg–Ca samples. No cell growth was observed when in direct contact with the metals apart from a few cells observed at the bottom of culture plate containing Mg–Ca alloy. In general, in vitro study of corrosion of Mg–Ca in a biologicallysimulated environment using cell culture medium with the presence of h MSCs demonstrated close resemblances to in vivo corrosion. Although in vitro corrosion of Mg–Ca revealed slow corrosion rate and no immediate cytotoxicity effects to h MSCs, its corrosion rate was still too high to achieve normal stem cell growth when cells and alloys were cultured in vitro in direct contact.