Quantification and simulation of fluid-filled catheter/transducer systems

Optimization of fluid-filled catheter/transducer systems for blood pressure measurement requires a prior knowledge of how each component affects overall dynamic response. This paper presents a method to measure resistance, inertance, and compliance of individual components by investigating the causal relationships between added known compliances and resonance. Additionally, a computer simulation that combines individual component values to synthesize practical blood pressure monitoring systems is presented. Complete monitoring systems are modeled through the combination of characterized components such as transducers, monitoring lines, and catheters and used to predict overall system response to any input function.     

Prediction of the transient energy response for complex vibro-acoustic systems

As research works of the transient statistical energy analysis (TSEA) and transient local energy approach (TLEA) mostly focus on simple structures, TSEA and TLEA are adopted to quantify the transient response of a complex vibro-acoustic system at the mid-high frequency range in this paper. Numerical examples of a coupled oscillator system, an L-shaped plate, and a launch vehicle fairing model are conducted to demonstrate the effectiveness and accuracy of TSEA and TLEA. The computational precision of TSEA and TLEA is verified by the analytical solution and finite element method. Furtherly, the transient energy responses of subsystems with different coupling ratios between subsystems are investigated. Results show that TLEA has a better performance than TSEA. With the increasing coupling ratio between subsystems, the rise time and peak energy of transient energy response of subsystems decrease gradually. Both ratios of rise time and peak energy predicted by TLEA to these of the TSEA increase as the rising of the coupling ratio.

     

Substructuring and model reduction of pipe components interacting with acoustic fluids

This paper presents a model reduction and substructure technique for reduced dynamical models of fluid-filled pipe components. Both linear acoustical domain and structural domain are modelled by finite elements (FE), and they are fully coupled by a fluid–structure interface. The discretised dynamic FE-equations, which use the acoustic pressure as field variable in the fluid, render both non-symmetric mass and stiffness matrices due to the FSI-coupling. Since the partial solutions to the eigenproblem of the coupled system are of special interest, either numerical preconditioning or non-dimensionalisation of the physical quantities is performed to improve the condition and to accelerate the numerical computation. An iterative subspace solver is adopted to generate a sufficient approximate of the low-frequency eigenspace of the constrained problem. Model reduction for component mode synthesis uses constraint modes together with the computed eigenspace. Single-point constraints for the nodal degrees of freedom hold at the interface between substructures. The null space resulting from a QR-decomposition of the single-point constraints at the interface is used as explicit coupling matrix to prevent the deterioration of the conditioning. Partitioning of the reduction space and coupling matrices leads to a structure of the coupled global system matrices, which is similar to the original system structure in physical quantities. Therefore, the iterative subspace eigensolver is used again for numerical modal analysis. Modal analysis is performed for a pipe segment assembled by fully coupled two-field substructures. The results are compared to the results obtained from the full model and to experimentally determined mode shapes.     

压缩机出口管系振动分析及结构改进

针对某炼油厂压缩机管道在生产中,由于剧烈振动而导致开裂泄漏问题,进行了管系结构模态分析,结果表明管道开裂泄漏的原因为管系结构固有频率与激发主频率相近,形成了共振。共振使得管系薄弱环节处出现裂纹,经过累积损伤和裂纹扩展后,导致管道开裂泄漏。在此基础上提出了在不改变管系主特征条件下,进行减振设计和结构改进。管道结构经改进后,共振现象得到抑制,振幅明显减小,管道的安全性得到了保障。     

An efficient way of including thermal diffuse scattering in simulation of scanning transmission electron microscopic images

We propose an improved image simulation procedure for atomic-resolution annular dark-field scanning transmission electron microscopy (STEM) based on the multislice formulation, which takes thermal diffuse scattering fully into account. The improvement with regard to the classical frozen phonon approach is realized by separating the lattice configuration statistics from the dynamical scattering so as to avoid repetitive calculations. As an example, the influence of phonon scattering on the image contrast is calculated and investigated. STEM image simulation of crystals can be applied with reasonable computing times to problems involving a large number of atoms and thick or large supercells.     

Determination of eigenfrequencies for arbitrary multicomponent piping systems in a fluid

Computational determination of the effect(s) of an attached mass or the variation of the relative vibration eigenfrequencies in arbitrary multicomponent hydroelastic systems of tubes or bars is considered. The approach is intended for the entire range of variation of the system parameters. The developed program code allows a user to rapidly determine these parameters for all types of heat exchange devices. Generalized data can be used for design and computations of the vibration strength as well as frequency detuning of the considered structures.     

On the vibrations of three-dimensional angled piping systems conveying fluid

The vibrations of three dimensional angled pipe systems conveying fluid are studied by using the finite element method. Extended Hamilton's principle is applied to derive the equations of motion. The characteristics matries consisting of inertia, stiffness, and Coriolis terms are derived by variational method, in which the effects of the internal flow velocity and pressure are considered. The change of dynamic characteristics of the piping system due to the variation of flow velocity, pressure and the geometry of the system is investigated. As a result, it can be found that the natural frequency of the system decreases generally as the flow velocity and pressure increase and that the tendency is more significant as the geometry of the system is similar to the straight pipe.     

A simulation model including intake and exhaust systems for a single cylinder four-stroke cycle spark ignition engine

A comprehensive simulation model is presented for a spark ignition engine including intake and exhaust systems. The power cycle simulation requires only one empirical factor to correct for turbulent speed of the flame front in order to complete the cycle calculation including NO. The exhaust pipe gas dynamics include chemical reactions along path lines. Calculations are presented which compare well with experimental results. The model predictions compare favourably with previous work.     

Effect of piping systems on surge in centrifugal compressors

There is a possibility that the exchange of the piping system may change the surge characteristic of a compressor. The piping system of a plant is not always the same as that of a test site. Then it is important to evaluate the effect of piping systems on surge characteristics in centrifugal compressors. Several turbochargers combined with different piping systems were tested. The lumped parameter model which was simplified to be solved easily was applied for the prediction of surge point. Surge lines were calculated with the linearlized lumped parameter model. The difference between the test and calculated results was within 10%. Trajectory of surge cycle was also examined by solving the lumped parameter model. Mild surge and deep surge were successfully predicted. This study confirmed that the lumped parameter model was a very useful tool to predict the effect of piping systems on surge characteristics in centrifugal compressors, even though that was a simple model. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju, Korea, October 16–19, 2007.     

Verifying common-cause reduction rules for fault tolerant systems via simulation using a stress-strength failure model

Redundant programmable electronic systems are commonly used in many industrial processes for safety protection and high availability process control. Common-cause failures can significantly reduce the benefits of the redundancy designed into this equipment. To improve on this situation, a number of qualitative design rules for reducing common cause failures have been put forth. However, these rules have not previously been subjected to quantitative verification. It is important to understand the magnitude of common cause failures and how this varies with design changes. This information can be used to show how system designs can be improved by lowering common cause failure rates. A stress-strength simulation was created to simulate the failures of a programmable electronic system under different design scenarios and the common cause failure rate was computed for each case. The simulation results not only confirm that the qualitative design rules lowered common cause failure rates but also provide some quantitative assessment of how large the improvements can be in various cases.     

Nanorefrigerants for energy efficient refrigeration systems

Journal of Mechanical Science and Technology - Nanorefrigerants, which are a new class of nanofluids, are mixtures of nanoparticles and refrigerants. They have several potential applications in...     

一种接收仿真数据的通用高层体系结构的接口研究

为提高基于高层体系结构的仿真工具的通用性,在分析高层体系结构接口数据流程的基础上,提出了一种通用的高层体系结构接口模型.该模型建立了一种通用的高层体系结构接口数据表示、存储和访问的方法,实现了对象类属性的动态订购和反射.此外,利用联邦对象模型文档自动解析技术,实现联邦对象模型信息动态获取,减少了高层体系结构接口代码中仿真应用与运行时间框架之间的静态连接,实现了仿真应用与运行时间框架之间的松耦合.最后,以虚拟样机可视化虚拟环境的高层体系结构接口开发为例,验证了该高层体系结构接口模型的有效性.     

Numerical simulation of concrete pumping process and investigation of wear mechanism of the piping wall

A numerical simulation has been conducted to study the solid-fluid multi-phase flow problem in concrete pumping process. The kinematics and trajectory of the discrete particles as well as the particle-particle interaction were predicted by DEM while the motion of the continuous fluid phase was evaluated by a Navier-Stokes solver, and a pressure gradient force model was adopted to calculate the solid-fluid interaction force. A case of pneumatic conveying was utilized to demonstrate the capability of the coupling model. The concrete pumping process was then simulated, where several flow features were observed such as roping, particle segregation and particle concentration. The frequency of the particles impacting on the bended pipe was monitored, a new time average collision intensity model based on impact force has been proposed to investigate the wear mechanism of the elbow. The location of maximum erosive wear damage in the elbow was predicted. Statistical results were in good agreement with that observed in actual pumping process. It is found that the present multi-phase coupling model can predict the wear behavior of the bended pipe accurately, and consequently provide an effective guidance for the design of concrete pumping pipe.     

Multilevel simulation for advanced manufacturing systems

This paper focuses on the techniques used to generate a multilevel simulation system that can optimise the design, layout, control and performance of a flexible manufacturing system (FMS). It discusses the software structures used to design and implement the simulator, which operates in the following modes: Off-line system-layout optimisation Off-line part-schedule evaluation Off-line control-algorithm evaluation/optimisation On-line state extrapolation and “what if?” testing All of these modes of operation are essential to the efficient running of a complex FMS. The techniques described have been applied and tested on an FMS at the Key Centre for Computer Integrated Manufacture at Swinburne Institute of Technology in Melbourne, Australia.     

An efficient mode-based alternative to principal orthogonal modes in the order reduction of structural dynamic systems with grounded nonlinearities

An alternative order reduction technique, based on the local equivalent linear stiffness method (LELSM), is suggested in this paper and compared with the principal orthogonal decomposition (POD) and the linear-based order reductions of structural dynamic systems with grounded cubic and dead-zone nonlinearities. It is shown that the updated LELSM modes approximate the principal orthogonal modes (POMs) of these systems with high accuracy especially at initial conditions corresponding to the linear modes of these systems. The use of the POMs for order reduction of nonlinear structural dynamic systems, while previously shown to be effective, requires that the solution response matrix in space and time should be obtained a priori while the alternative LELSM technique in this paper has no such requirement. The methods are applied to illustrative 2-dof (two degree-of-freedom) and 40-dof spring-mass systems with cubic and dead-zone nonlinearities. The reduced models of these systems in physical coordinates, obtained via updated LELSM modes, have been found nearly equivalent to POD modal-based reduced models and more accurate than the linear-based reduced models. Like POD modal-based order reduction, LELSM modal-based order reduction gives in-phase time histories with the exact numerical solution of the full model for long time periods of simulation. As a result, the updated LELSM modes are proposed as an alternative to POMs in order reduction of structural dynamic systems with grounded nonlinearities.     

An efficient method to predict steady-state vibration of three-dimensional piping system conveying a pulsating fluid

The dynamic equations of motion for a three-dimensional piping system conveying a harmonically pulsating fluid contain time-varying terms attributable to the fluid pulsating in the pipe. In this study, finite element formulation for this three-dimensional piping system was performed. The stiffness and damping matrices in the finite element modeling vary according to time because of the effects of the harmonically pulsating fluid. The frequency-domain method based on eigenvalue analysis cannot be used in this kind of problem. Conventional numerical time-domain methods require substantial computational efforts. An efficient numerical method to predict the steady-state time response of the piping system was presented. In this method, simultaneous equations were constructed by comparing the coefficients of a Taylor series expansion instead of directly solving the problem in the time domain. The accuracy and efficiency of this method were validated by comparison with a conventional numerical integration method.     

机械装配耦合动刚度的逆子结构辨识方法

为检测机械装配的动态质量,基于子结构法分析装配工艺对部件动态传递特性的影响作用,明确装配耦合动刚度是影响机械装配动态质量的唯一决定性关键因素。在阐述装配耦合动刚度的直接逆子结构辨识方法(直接法)并分析其在生产实践应用中存在的缺陷之后,建立五类装配耦合动刚度的基于频率响应函数(Frequency response function,FRF)谱的间接逆子结构辨识方法(间接法),并给出单点耦合和多点耦合计算公式及其工程适用条件。分析表明,五类间接法完全或部分避免直接法存在的测试操作困难,第一类间接法辨识精度受FRF谱测量误差影响最低且与直接法相近,可作为机械装配耦合动刚度辨识的最优间接法选项。逆子结构辨识方法的理论完备性和第一类间接法的应用有效性分别经机械装配二级子结构集总参数模型及其类比试验模型予以检验,为机械装配耦合动刚度辨识及其动态质量检测提供新的有效技术方法。     

Reliability simulation for assemblies of airplane functional systems

The possibility of using an exponential distribution in calculations of assembly reliability is considered. It is shown that the failure probability determined by an exponential distribution estimates the probability of one or more failures. The justification of using a distribution with a uniform probability density for reliability calculations is proved.     

An efficient numerical algorithm for stability testing of fractional-delay systems

This paper presents a numerical algorithm for BIBO stability testing of a certain class of the so-called fractional-delay systems. The characteristic function of the systems under consideration is a multi-valued function of the Laplace variable s which is defined on a Riemann surface with finite number of Riemann sheets where the origin is a branch point. The stability analysis of such systems is not straightforward because there is no universally applicable analytical method to find the roots of the characteristic equation on the right half-plane of the first Riemann sheet. The proposed method is based on the Rouche’s theorem which provides the number of the zeros of a given function in a given simple closed contour. One advantage of the proposed method over previous works is that it gives the number and the location of the unstable poles. The algorithm has a reliable result which is illustrated by several examples.     

Enhancement of an efficient liveness-enforcing supervisor for flexible manufacture systems

This paper presents an enhanced efficient control method to obtain a maximally permissive deadlock prevention policy for flexible manufacturing systems (FMSs) based on Petri nets and the theory of regions. It is well known that the marking/transition-separation instances (MTSIs) method with the theory of regions has been extensively studied as one of optimal policies (i.e., maximally permissive) in FMS deadlock problems. However, all MTSIs are required to identify for controlling the deadlock problems. Therefore, this paper proposes novel crucial MTSIs (CMTSIs) to alleviate the computation cost due to the involvement of few MTSIs. This article elucidates CMTSI is the foundation of MTSI. Moreover, a maximally permissive liveness-enforcing supervisor with efficient computation can be implemented based on the experimental results, demonstrating that the proposed control policy is the most efficient algorithm among the closely related approaches.