A Virtual Puncture Surgery System Based on Multi-Layer Soft Tissue and Force Mesh

Puncture is a common operation in surgery, which involves all kinds of tissue materials with different geometry and mechanical properties. As a new cross-disciplinary research area, Virtual Surgery (VS) makes simulation of soft tissue in puncture operation possible in virtual environment. In this paper, we introduce a VS-based puncture system composed by three-layer soft tissue, simulated with spherical harmonic function (SHF), which is covered with a force mesh, constructed by mass spring model (MSM). The two models are combined together with a parameter of SHF named surface radius, which provides MSM with real-time deformation data needed in force calculation. Meanwhile, force calculation, divided into the surface spring force and the puncture damping force, makes the force presentation better accord to the corresponding tissue characteristics. Moreover, a deformation resumption algorithm is leveraged to simulate the resumption phenomenon of the broken tissue surface. In evaluation experiment, several residents are invited to grades our model along with other four mainstream soft tissue models in terms of 7 different indicators. After the evaluation, the scores are analyzed by a comprehensive weighted grading method. Experiment results show that the proposed model has better performance during puncture operation than other models, and can well simulate surface resumption phenomenon when tissue surface is broken.     

Simulation of Coupling Process of Flexible Needle Insertion into Soft Tissue Based on ABAQUS

In order to get to the desired target inside the body, it is essential to investigate the needle-tissue coupling process and calculate the tissue deformation. A cantilever beam model is presented to predicting the deflection and bending angle of flexible needle by analyzing the distribution of the force on needle shaft during the procedure of needle insertion into soft tissue. Furthermore, a finite element (FE) coupling model is proposedto simulate the needle-tissue interactive process. The plane and spatial models are created to relate the needle and tissue nodes. Combined with the cantilever beam model and thefinite element needle-tissue coupling model, the simulation of needle-tissue interaction was carried out by the ABAQUS software. The comparing experiments are designed to understand the needle-tissue interactions, by which the same points in the experiments and simulation are compared and analyzed. The results show that the displacements in x and z directions in the simulation can accord with the experiments, and the deformation inside the tissue mainly occurs in the axial direction. The study is beneficial to the robotassisted and virtual needle insertion procedure, and to help the physicians to predict the inside tissue deformation during the treatments.     

An Integrated Suture Simulation System with Deformation Constraint Under A Suture Control Strategy

Current research on suture simulation mainly focus on the construction of suture line, and existing suture simulation systems still need to be improved in terms of diversity, soft tissue effects, and stability. This paper presents an integrated liver suture surgery system composed of three consecutive suture circumstances, which is conducive to liver suture surgery training. The physically-based models used in this simulation are based on different mass-spring models regulated by a special constrained algorithm, which can improve the model accuracy, and stability by appropriately restraining the activity sphere of the surrounding mass nodes around the suture points. We also studied the kinematic model to update the status of suture points in real time, according to an external force exerted by the operators, which can sense synchronous force feedback in return as well. Moreover, in case that the sutured wounds tear open again, a suture control strategy is designed to ensure the stability of the whole suturing procedure. Several experiments are carried out to validate the model performance in terms of model accuracy, suture control effects, and comprehensive training effects. The experiment results show that the proposed models have realistic visual and haptic feedback, stable control on the suture, as well as good training effects as an integrated liver suture surgery system compared to other suture simulation systems which only simulate suture on a single kind of soft tissue.     

Simulation of deformations in the membranes of pressure transducers

Analytic and numerical simulation of deformations in flat membranes and membranes with hard center are considered. A simplified algorithm based on the bending equation of a beam is proposed. The equation may be used to calculate the tangential and radial deformations of different membranes by means of the method of finite differences. Translated from Izmeritel’naya Tekhnika, No. 3, pp. 33–36, March, 2009.     

Simulation of Coupled Processes of Deformation and Cracking in Elastic Brittle Materials

We propose an approximate model of combined deformation and microcracking of elastic brittle materials leading to the formation of a system of stochastically distributed shallow microcracks.     

弹塑性变形阶段力磁效应的有限元模拟

金属磁记忆研究的是由铁磁材料内部应力和应变引起的材料磁性质的变化,而不同类型的形变(弹性和塑性)对材料磁化的影响机制各不相同.本文利用线性强化弹塑性模型,结合材料不同变形阶段对材料磁化影响的物理模型,提出了贯穿所有变形阶段的力磁耦合模型.为了研究不同变形阶段金属磁记忆检测信号的变化,基于上述模型利用ANSYS有限元分析软件,对不同应力载荷下铁磁材料试件表面漏磁场的分布进行了模拟研究.模拟结果表明,弹性变形对金属磁记忆信号的影响并不明显,而小的塑性形变会使磁信号发生锐变.     

ECAPT过程中载荷变化规律的数值模拟

为了掌握纯铝在ECAPT过程中的力学变化规律,利用刚塑性有限元技术对纯铝1100的ECAPT变形行为进行数值模拟,重点分析了载荷在挤压过程中的变化规律及产生变化的原因。结果表明:ECAPT过程大致分为载荷骤升、2次小幅度升高和载荷下降4个阶段;载荷峰值随着摩擦因数的增大迅速增大,应采取有效的润滑措施减小摩擦从而降低载荷峰值,提高模具寿命;随着摩擦因数的增大,载荷在达到各阶段峰值后下降趋势越来越明显。     

ITER装置环向场线圈盒焊接变形调控数值模拟研究

目的 对国际热核聚变装置中环向场线圈盒AU1段的焊接过程进行有限元数值模拟分析,探究焊接坡口类型和焊接工装对侧板焊接角变形的影响。方法 基于ABAQUS有限元计算平台,建立等截面尺寸简化的线圈盒AU1模拟件的有限元模型,通过二次开发移动单元体热源模型实现多层多道焊接模拟。在AU1模拟件的基础上设计对称和非对称的2种焊接坡口,并分析2种坡口结构侧板角变形的大小和规律。通过将防角变形工装抽象为边界条件,实现了该工装的功能,研究了防角变形工装调控焊接角变形的效果。结果 非对称坡口和对称坡口结构产生的侧板角变形规律基本相同,但前者的最终角变形为22.5 mm,大于后者的18.1 mm;在AU1结构焊接过程中,当焊接至约76 mm厚度时,角变形先是变化较快,而后逐渐趋于稳定;在焊接至约76mm厚度之前对焊接工装进行调整,可使焊接厚度为280mm时的侧板角变形由同期的22.7 mm降低至4.0 mm。结论 移动单元体热源模型很好地平衡了计算效率与准确性,使用对称坡口可以获得更小的角变形,对防角变形工装进行及时调整可以大幅度减小侧板的角变形。     

新型等径角挤压工艺下的5052 铝合金变形行为的有限元模拟

目的采用新型复合大塑性变形技术正挤压-等径角挤压工艺(FE-ECAP),研究5052铝合金在室温条件下的变形行为。方法基于有限元分析软件DEFORM-3D,在FE-ECAP工艺下对5052铝合金进行有限元模拟,研究变形过程中挤压载荷、等效应变、金属流动速度等场量的分布规律。结果 5052铝合金在FE-ECAP变形过程中,挤压载荷曲线呈双峰形态分布,在挤压模口附近达到第一次峰值,第二次出现在转角处,挤压载荷值为347 k N,同时也是整个挤压过程的最大值;经过FE-ECAP变形后,等效应变大量累积,使得主要变形区达到了高度均匀的变形状态;坯料外转角处金属的流动速度值大于内转角处的流动速度值。结论根据以上结果分析,在FE-ECAP工艺下,为使变形坯料性能优越,应尽量提高坯料变形的均匀性。     

Ti2AlNb合金电子束焊接头残余应力及变形的数值模拟

目的 研究平板对接电子束焊接过程中Ti2AlNb合金接头的残余应力及变形规律。方法 采用高斯圆柱体和高斯面组合热源模型模拟了6.6 mm厚的Ti2AlNb合金平板对接电子束焊过程,对比研究了高焊速高束流和低焊速低束流2种工艺参数下焊接接头的残余应力和变形分布规律,并用小孔法测量了焊缝中心及距焊缝中心10 mm位置的残余应力值。结果 在高焊速高束流参数下,获得了熔池体积小、熔池宽度窄(为3.62 mm)、深宽比高的焊缝;在该参数下焊缝横截面上的高应力集中区(应力在900 MPa以上)尺寸较小,其宽度仅为低焊速低束流参数下的89%;同时,在高焊速高束流参数下,焊缝法向变形最大值为0.79 mm,低于低焊速低束流参数下的0.82 mm;模拟计算所得残余应力与实测值的误差在5.64%以内。结论 高束流高焊速工艺具有热输入小、热量集中、加工效率高的特点,有助于获得高应力集中区域小、深宽比高、变形小的焊缝,比低束流低焊速工艺更具优势。     

TA1钛合金药型罩剪切旋压成形塑性变形规律的数值模拟研究

目的 TA1钛合金作为药型罩材料,具有提高穿深和侵彻孔径的优异表现,但其剪切旋压成形过程中塑性变形规律复杂且难于控制,以期通过有限元数值计算解析多工艺参数的协同作用。方法 建立了TA1薄壁锥形件结构旋压加工过程的三维非线性热-力耦合有限元模型,研究了TA1从圆形板坯到锥形件旋压全过程的金属塑性变形行为、应力及应变的变化。采用正交实验分析了旋轮进给速率、芯轴转速与板坯厚度对成形过程的旋压力以及成形样件的内径偏差和壁厚偏差的影响规律。结果 结果表明,锥形件侧壁的塑性应变沿母线方向逐渐减小,最大应变值出现在靠近锥形件顶部的小端面位置。旋压载荷随旋轮进给速率与板坯厚度增加而增加,随芯轴转速增加而减小。内径偏差随进给速率与板坯厚度的增加而减小,与芯轴转速的相关性较小。壁厚偏差随进给速率的增加先减小后增大,随芯轴转速与板坯厚度的增加而减小。结论 基于数值模拟结果,获得TA1薄壁锥形件的优化工艺参数为:旋轮进给速率300 mm/min,芯轴转速260 r/min,板坯初始厚度4 mm。开展了TA1钛合金剪切旋压成形实验,所得锥形件尺寸与模型计算结果一致,验证了模型的准确性。     

热轧能耗模型及其计算机仿真

作者根据能耗曲线的形态,应用数学方法,建立了如下热轧能耗模型——样条模型:式中,E是累计能耗;x=ln(H_0/h),H_0是来料厚度,h是轧件出口厚度;γ是能耗曲线形态指数,0<γ≤2;m是轧制总道次(对可逆轧机)或机架总数(对连轧机);k=[(m-1)/3];β_1,β_2,…,β_(k+2)是由产品规格和轧制条件决定的参数。用可逆式精轧机轧制16Mn、20G、3C和A3四种钢板的实测数据,进行了计算机仿真。经过仿真确定了γ的值,对于16Mn和A3,γ=1/2;对于20G和3C,γ=2/3。对样条模型和得到较多重视的今井一郎模型、幂函数模型和抛物线模型进行了数学论证和实验数据验证,结果表明:样条模型的理论曲线能适应不同形态的能耗实验曲线,而另外三个模型只能适应没有拐点的能耗曲线,拟合实测数据时,样条模型的精度比其他三个模型的精度高得多。     

A direct Numerical Simulation Approach to the Study of Intrusion Fronts

A direct numerical simulation approach for the study of gravity currents in a plane channel is described. The numerical method employed is based on a mixed spectral/spectral-element discretization in space together with finite differences in time. For the validation of the code, simulations of Rayleigh–Bénard convection are performed and the results are compared with theoretical predictions and reference data from the literature. The dynamics of gravity currents is then studied by simulations of two-dimensional lock-exchange flow. The results obtained in these simulations are in good agreement with recent experimental data. By a systematic variation of the Grashof number the influence of viscous diffusion on the characteristics of the propagating fronts is assessed.     

基于留量模型的加工仿真技术

数控加工仿真和验证是CAM系统的重要组成部分。通过仿真实现数控程序的模拟加工,可以节省大量的人力和物力。本文阐述了一种新的基于留量几何模型的数控加工智能仿真和验证系统的建模、体系结构及其实现。     

A selective smoothed finite element method with visco-hyperelastic constitutive model for analysis of biomechanical responses of brain tissues

Brain tissues are known for exhibiting complex nonlinear and time-dependent properties, which require visco-hyperelastic constitutive models for proper simulation. In this paper, a Total Lagrangian Explicit Selective Smoothed Finite Element Method (Selective S-FEM) is formulated to analyze the dynamic behavior of incompressible brain tissues undergoing extremely large deformation. The proposed Selective S-FEM deals with three-dimensional problems using four-node tetrahedron elements that can be automatically generated for geometrically complex soft tissues. It consists of the three key ingredients. (i) A visco-hyperelastic constitutive model is developed within the framework of S-FEM in the first time, allowing adequate modeling of the dynamic brain tissue behavior. (ii) Selective S-FEM strategy is used for overcome the mesh distortion and the volumetric locking that often occurs in soft tissues. (iii) Total Lagrangian formulation is used in an explicit algorithm allowing rigorous simulation of extreme large deformation. (iv) A combined implementation of Selective S-FEM with the visco-hyperelastic constitutive model for dynamic simulations. The shear deformation is calculated by Face/Edge-based S-FEM, and the volume deformation is calculated by NS-FEM. Numerical experiments show that Selective S-FEM is a robust solver with good accuracy, and excellent ability to reduce element distortion effects in simulate time-dependence behavior of bio-tissues.     

A Random Pairing Collision Model (RPCM) for Improving the DEM Simulation of Particle-Bed Collisions in Aeolian Sand Transport

The impact of sand particles with bed is the key process in aeolian sand transport. In this article, the discrete element method (DEM) is embedded to the large-eddy simulation (LES) method for simulating the wind-blown sand two-phase flow. A numerical model is developed to stochastically describe collisions between sand particles and bed within the DEM approach. Statistical features of major simulated motion parameters are undertaken and compared with measured data to verify the model. The probability distribution of the kinetic energy restitution coefficient is normal, and the probability density functions of the impact and lift-off angles are consistent with reported results. The probability density functions of three-dimensional impact and lift-off velocities are addressed in further detail.     

变形温度对镁合金等通道转角挤压晶粒尺寸演变影响的有限元模拟

目的研究变形温度对AZ31B镁合金等通道转角挤压(ECAP)过程中晶粒尺寸演变的影响。方法建立AZ31B镁合金动态再结晶和晶粒长大数学模型,采用Fortran语言编写晶粒演变子程序,并通过商用有限元软件MARC的二次开发接口,建立耦合微观组织演变的AZ31B镁合金等通道转角挤压有限元模型,研究变形温度对等通道转角挤压过程应变场、再结晶百分数和晶粒尺寸的影响规律,并与实验结果进行比较。结果随变形温度从200℃增至400℃,原子热激活效应增强,再结晶百分数从75.37%增加至99%,平均晶粒尺寸从6.67μm增加至25.7μm,且晶粒尺寸分布均匀性增大,但是200℃变形的ECAP试样出现开裂。结论在250~300℃温度区间内进行ECAP变形,有助于获得细小均匀的微观组织,同时避免出现变形开裂。     

涡量-流函数法模拟不同高宽比和角度的腔内自然对流

采用涡量-流函数方程,对FLUENT软件进行二次开发,对重力作用下封闭空腔内的二维自然对流换热流场、温度场进行了数值模拟.对非正方形的矩形空腔内的自然对流换热进行了数值计算,结果表明不同的高宽比例对自然对流换热有很大的影响;该文还对Ra=104时放置不同角度的封闭腔进行了数值计算,揭示了重力作用下不同角度时的自然对流换热变化,发现在某一倾斜角度时(θ=45°左右),平均换热系数Numean存在极大值.