A finite-element model of two-layer ocean circulation

A mixed finite-element formulation is applied to solve the quasi-geostrophic equations in a two-layer ocean domain enclosed by solid boundaries. A combination of leap-frog and θ-schemes is used to integrate the equations in time. Wood's formula of the wall vorticity is derived in our formulation for the case of square elements adjacent to the boundaries. Long-term computations with and without lumping have been carried out.     

A finite-element model for the study of vibration of a beam with a closing crack

We present a finite-element model to be used in a study of vibration of a beam with a closing crack. Some special features of numerical solution and methods for its fast realization are discussed. The results of experimental verification of the model are provided. __________ Translated from Problemy Prochnosti, No. 5, pp. 114–120, September–October, 2008.     

A finite-element model with closed-form solutions to workpiece deflections in turning

Simulation models for workpiece deflections play an important role in determining conditions to maximize the part accuracy in machining processes as well as in analysing the dynamic response of the machining system. In this paper, the crosssectional deflection of the workpiece due to all cutting force components (radial, axial and tangential) is determined using the finite-element method. Three workpiece mounting types generally used in industrial practice are considered. The change in the workpiece diameter during machining can easily be taken into account with this model. Furthermore, the finite-element reponses are derived in closed form which enables rapid and continuous solutions along the part length. Numerical examples are treated for which the workpiece deflections calculated from this model are compared with those computed only from the radial cutting force component as usually done by several simplified models. From the results obtained, the proposed model is generally recommended to improve turning simulations.     

A finite-element formulation for the study of ultrasonic NDT systems

The authors present a finite-element formulation for an overall ultrasonic NDT (nondestructive testing) system, including appropriate models for transmitter and receiver transducers. Transducer considerations are discussed. Results are given for two-dimensional plane-strain geometry simulations that agree qualitatively with corresponding experimental measurements and show the potential of the method.     

A finite-element study on constitutive relation HM-V for elastic polycrystals

Through a semi-phenomenological approach, we have recently derived a simple constitutive relation (HM-V) for aggregates of cubic crystallites with arbitrary texture symmetry. This constitutive relation is quadratic in the texture coefficients of the polycrystal, and it carries four elastic constants. The derivation delivers four explicit formulae which express the four elastic constants of the polycrystal in terms of the three elastic constants of the single cubic crystal and one undetermined parameter. In this paper we use finite-element calculations to check the adequacy of constitutive relation HM-V and to determine the undetermined parameter for copper and iron polycrystals, respectively.     

A finite-element method model of soft tissue response to impulsive acoustic radiation force

Several groups are studying acoustic radiation force and its ability to image the mechanical properties of tissue. Acoustic radiation force impulse (ARFI) imaging is one modality using standard diagnostic ultrasound scanners to generate localized, impulsive, acoustic radiation forces in tissue. The dynamic response of tissue is measured via conventional ultrasonic speckle-tracking methods and provides information about the mechanical properties of tissue. A finite-element method (FEM) model has been developed that simulates the dynamic response of tissues, with and without spherical inclusions, to an impulsive acoustic radiation force excitation from a linear array transducer. These FEM models were validated with calibrated phantoms. Shear wave speed, and therefore elasticity, dictates tissue relaxation following ARFI excitation, but Poisson's ratio and density do not significantly alter tissue relaxation rates. Increased acoustic attenuation in tissue increases the relative amount of tissue displacement in the near field compared with the focal depth, but relaxation rates are not altered. Applications of this model include improving image quality, and distilling material and structural information from tissue's dynamic response to ARFI excitation. Future work on these models includes incorporation of viscous material properties and modeling the ultrasonic tracking of displaced scatterers.     

Use of two-dimensional schemes in the finite-element method in calculating the coil system for the toroidal magnetic field in a tokamak

Strength of Materials -     

日志检查点回卷恢复策略的检查点周期求解模型

基于Markov链进程状态模型和拉普拉斯变换,提出了一种日志检查点回卷恢复容错策略的最佳检查点周期求解模型,该模型充分考虑了日志检查点回卷恢复策略中进程回卷恢复与正常运行期间执行速度存在的差别,同时允许进程检查点和回卷恢复期间发生故障事件.通过求解进程状态Markov链转移概率和权重,得到完成检查点间隔的期望执行用时,...     

A digital process for additive manufacturing of occlusal splints: a clinical pilot study

The aim of this study was to develop and evaluate a digital process for manufacturing of occlusal splints. An alginate impression was taken from the upper and lower jaws of a patient with temporomandibular disorder owing to cross bite and wear of the teeth, and then digitized using a table laser scanner. The scanned model was repaired using the 3Data Expert software, and a splint was designed with the Viscam RP software. A splint was manufactured from a biocompatible liquid photopolymer by stereolithography. The system employed in the process was SLA 350. The splint was worn nightly for six months. The patient adapted to the splint well and found it comfortable to use. The splint relieved tension in the patient''s bite muscles. No sign of tooth wear or significant splint wear was detected after six months of testing. Modern digital technology enables us to manufacture clinically functional occlusal splints, which might reduce costs, dental technician working time and chair-side time. Maximum-dimensional errors of approximately 1 mm were found at thin walls and sharp corners of the splint when compared with the digital model.     

A study on time schemes for DRBEM analysis of elastic impact wave

 The precise integration and differential quadrature methods are two new unconditionally stable numerical schemes to approximate time derivative with more than the second order accuracy. Recent studies showed that compared with the Houbolt and Newmark methods, they produced more accurate solutions with large time step for the problems where response is primarily dominated by low and intermediate frequency modes. This paper aims to investigate these time schemes in the context of the dual reciprocity BEM (DRBEM) formulation of various shock-excited scalar elastic wave problems, where high modes have important affect on traction response. The Houbolt method was widely recommended in many literatures for such DRBEM dynamic formulations. However, this study found that the damped Newmark algorithm was the most efficient and accurate for impact traction analysis in conjunction with the DRBEM. The precise integration and differential quadrature methods are shown inapplicable for such shock-excited problems due to the absence of numerical damping. On the other hand, we also found that to achieve the same order of accuracy, the differential quadrature method required much less computing effort than the precise integration method due to the use of the Bartels–Stewart algorithm solving the resulting Lyapunov matrix analogization equation. Received 6 November 2000     

Dynamic analysis of large-scale SSI systems for layered unbounded media via a parallelized coupled finite-element/boundary-element/scaled boundary finite-element model

An algorithm for a parallelized coupled model based on finite element method (FEM), boundary element method (BEM), and scaled boundary FEM (SBFEM) for harmonic and transient dynamic response of large-scale 2D structures embedded in or on layered soil media is presented. The BEM and SBFEM are used for modelling the dynamic response of the unbounded media. The standard FEM is used for modelling the finite region and the embedded structure. The objective of the development of this parallelized coupled model is to use the power of high performance computing, and to take into account the advantages and evade the disadvantages of the above mentioned numerical methods for modelling of the unbounded media in soil-structure interaction (SSI) systems. The development of the parallel algorithm for this model is essential for solving arbitrarily shaped large-scale SSI problems, which cannot be solved within reasonable elapsed times by a serial algorithm. The efficiency of the proposed parallel algorithm and the validity of the coupled model are shown by means of three numerical examples, indicating the excellent accuracy and applicability of the parallel algorithm with considerable time-savings in large-scale problems.     

A comparative study on various time integration schemes for heat wave simulation

The performance of several explicit and implicit time advancement schemes of first-order ODEs are examined for heat wave simulation with different boundary conditions. It is found that the boundary conditions have a considerable influence on the stiffness property of the hyperbolic heat conduction equation, due to the occurrence of thermal shock waves, and hence, according to the type of the enforced boundary conditions, a specific time integration scheme has to be performed in order to obtain an accurate and efficient solution. The results of the considered time integration schemes are also compared with analytical solution and based on the obtained results, some recommendations regarding the numerical simulation of hyperbolic heat conduction are presented.     

Thermomechanics of structures made of elastomers in cyclic loading on the basis of a finite-element model

Finite-element discretization of equations of thermoviscoelasticity in solving problems of dissipative heating of elastomers carried out. The FEM equations produced on the basis of the moment system of finite elements can be used to calculate elastomer structures with an arbitrary degree of compressibility. Examples of solving test problems are used to analyze the convergence of numerical solutions for linear, quadratic, and cubic loss of approximation of displacements. Calculations are carried out of the self-heating temperature in a trapezoidal shock absorber with a hole under complicated loading and also a shock absorber of AKS type. The effect of relaxation processes and geometrical dimensions on heating a solid cylindrical shock absorber is examined.Voroshilovgrad Agricultural Institute. Translated from Problemy Prochnosti, No. 10, pp. 74–82, October, 1989.     

A finite-element method for computing three-dimensional electromagnetic fields in inhomogeneous media

A finite-element method is presented that is particularly suited for the computer modeling of three-dimensional electromagnetic fields in inhomogeneous media. It employs a new type of linear vectorial expansion functions. Across an interface where the constitutive coefficients are discontinuous, they have the following properties: (1) the continuity of the tangential components of the electric and the magnetic field strengths is exactly preserved, (2) the normal component of the electric and the magnetic field strengths are allowed to jump and (3) the electric and the magnetic fluxes are continuous within the pertaining degree of approximation. The system of equations from which the expansion coefficients are obtained is generated by applying a Galerkin-type weighted-residual method. Numerical experiments are described that illustrate the efficiency of our elements, and the computational costs of the method.     

A comparison of two correlation schemes

Processes involving the cross-correlation of two noisy data streams are frequently encountered in signal processing. The performances of two commonly used correlators, the simple and complex correlators, are examined. The conventional view is that the complex correlator is superior to the simple correlator by a factor of the square root of two in output signal-to-noise ratio (SNR). However, by modifying the simple correlator to utilize all the available information, its performance is improved. The development of the modified correlator is explained, and a computer simulation shows that this modified correlator is approximately equivalent to the complex correlator in noise performance