Search results

Simple methods for the steady‐state analysis of a flow network are readily available, but the dynamic behavior of a large‐scale flow network is difficult to study due to the complex differential‐algebraic equation system resulting from its modeling. It is the aim of this paper to present two simple methods for the dynamic analysis of large‐scale flow networks and to demonstrate their use by examining the dynamics of a self‐similar branching tree network.

Two numerical projection methods are proposed for one‐dimensional dynamic analysis of large piping networks. Both are extensions of that suggested by Chorin for the nonlinear differential‐algebraic system resulting from the Navier‐Stokes equations. Each numerical algorithm is discussed and verified for turbulent flow in a nonlinear, self‐similar, branching tree network with constant friction factor for which an exact solution is available.

The dynamics of this network are calculated for more realistic friction factors and described as system parameters are varied. Self‐excited oscillations due to laminar‐turbulent transition are found for some parameter values and dynamic component behavior is observed in the network which is not observable in components apart from it.

It is shown that the dynamics of a flow network can exhibit unexpected behavior, reinforcing the need for simple methods to perform dynamic analysis.

This paper presents two numerical projection schemes for dynamic analysis of large‐scale flow networks to aid in their study and design.

This paper discusses algorithms for large displacement analysis of interconnected flexible and rigid multibody systems. Hydrostatic and hydrodynamic loads for systems being submerged in water are also considered. The systems may consist of cables and beams and may combine very flexible parts with rigid parts. Various ways of introducing structural joints are discussed. A special implementation of the Hilber‐Hughes‐Taylor time integration scheme for constrained non‐linear systems is outlined. The formulation is general and allows for displacements and rotational motion of unlimited size. Aspects concerning efficient solution of constrained dynamic problems are discussed. These capabilities have been implemented in a general purpose non‐linear finite element program. Applications involving static and dynamic analysis of a bi‐articulated tower and a floating tripod platform kept in place by three anchor lines are discussed.

The purpose of this paper is to show that the computation of time-periodic signals for coupled antenna-circuit problems can be substantially accelerated by means of the single shooting method. This allows an efficient analysis of nonlinearly loaded coupled loop antennas for near field communication (NFC) applications.

For the modelling of electrically small coupled field-circuit problems, the partial element equivalent circuit (PEEC) method shows to be very efficient. For analysing the circuit-like description of the coupled problem, this paper developed a generalised modified nodal analysis (MNA) and applied it to specific NFC problems.

It is shown that the periodic steady state (PSS) solution of the resulting differential-algebraic system can be computed very time efficiently by the single shooting method. A speedup of roughly 114 to conventional transient approaches can be achieved.

The proposed approach appears to be an efficient alternative for the computation of time PSS solutions for nonlinear circuit problems coupled with discretised conductive structures, where the homogeneous solution is not of interest.

The present paper explores the implementation and application of the shooting method for nonlinearly loaded coupled antenna-circuit problems based on the PEEC method and shows the efficiency of this approach.

To provide a reliable numerical technique for the time integration of the electromagnetic models with sinusoidal excitation.

The numerical integration of an electrotechnical problem is commonly carried out using adaptive time stepping. For one particular selected time step, Runge‐Kutta (RK) adaptive integration methods deliver two approximations to the solution with different order of approximation. The difference between both is used to estimate the local error.

Standard error‐controlled RK time integration fails for electromagnetic problems with sinusoidal excitation when the adaptive time step selection relies upon the comparison of a main solution and an embedded solution where the difference of orders is one. This problem is overcome when the embedded solution differs by two orders of approximations. Such embedded solution is efficiently constructed by putting appropriate order conditions on the coefficients of the Butcher table.

Using the technique proposed in the paper, electromagnetic problems with sinusoidal dynamics can also be effectively tackled.

The purpose of this paper is to provide an accurate dynamic model for the flexible cable capture mechanism and to analyze the dynamic characteristics in the capturing process.

The absolute nodal coordinate formulation (ANCF) that based on the continuum mechanics approach is applied in the capture task using flexible cables. An ANCF cable element in which axial and bending strain energy are taken into account is presented to model the flexible cables. The generalized coordinates of ANCF are absolute displacements and slopes and make no small deformation assumptions; therefore, this element has a remarkable superiority in the large rotation and deformation analysis of flexible cables compared to the conventional floating frame of reference formulation (FFRF). The mass matrix of the cable element is constant, which will reduce the degree of non-linearity of the dynamic equations. The contact force between the steel cables and capture rod is calculated by the non-linear contact dynamic model, in which material and geometry properties of contact bodies are considered.

The stress distribution of steel cables is investigated in the numerical studies which show that the closer to the ends of the cable, the larger axial forces and smaller bending moments they will be. The reduction of grasping velocity will lead to a decrease in the contact force and the oversize peak value of contact force is more likely to be avoided when reducing the elastic modulus of steel cables to obtain a greater soft capture capability.

The work shows a practical possibility to improve modeling accuracy of the capture mechanism. Results of the analyses can provide references for the design and analysis of the capture task.

The ANCF is first used in the analysis of the capture task with flexible cables, and some useful results which have not been published before are obtained.

Radio-frequency circuits often possess a multi-rate behavior. Slow changing baseband signals and fast oscillating carrier signals often occur in the same circuit. Frequency modulated signals pose a particular challenge. The paper aims to discuss these issues.

The ordinary circuit differential equations are first rewritten by a system of (multi-rate) partial differential equations in order to decouple the different time scales. For an efficient simulation the paper needs an optimal choice of a frequency-dependent parameter. This is achieved by an additional smoothness condition.

By incorporating the smoothness condition into the discretization, the paper obtains a non-linear system of equations complemented by a minimization constraint. This problem is solved by a modified Newton method, which needs only little extra computational effort. The method is tested on a phase locked loop with a frequency modulated input signal.

A new optimal frequency sweep method was introduced, which will permit a very efficient simulation of multi-rate circuits.

The purpose of this study is to use the method of lines to solve the two-dimensional nonlinear advection–diffusion–reaction equation with variable coefficients.

The strictly positive definite radial basis functions collocation method together with the decomposition of the interpolation matrix is used to turn the problem into a system of nonlinear first-order differential equations. Then a numerical solution of this system is computed by changing in the classical fourth-order Runge–Kutta method as well.

Several test problems are provided to confirm the validity and efficiently of the proposed method.

For the first time, some famous examples are solved by using the proposed high-order technique.

This study aims to use new formula derived based on the shifted Jacobi functions have been defined and some theorems of the left- and right-sided fractional derivative for them have been presented.

In this article, the authors apply the method of lines (MOL) together with the pseudospectral method for solving space-time partial differential equations with space left- and right-sided fractional derivative (SFPDEs). Then, using the collocation nodes to reduce the SFPDEs to the system of ordinary differential equations, which can be solved by the ode45 MATLAB toolbox.

Applying the MOL method together with the pseudospectral discretization method converts the space-dependent on fractional partial differential equations to the system of ordinary differential equations.

This paper contributes to gain choosing the shifted Jacobi functions basis with special parameters a, b and give the authors this opportunity to obtain the left- and right-sided fractional differentiation matrices for this basis exactly. The results of the examples are presented in this article. The authors found that the method is efficient and provides accurate results, and the authors found significant implications for success in the science, technology, engineering and mathematics domain.

The flexible automatic transportation and manual assembly jobs for large aircraft components demand an automated guided vehicle (AGV) system with heavy-duty capacity and omnidirectional movability. This paper aims to propose a four driving-steering wheels-four supporting-steering wheels (4DSW-4SSW) layout plan to enhance the controllability and moving stability of AGV.

The anti-vibration structure of DS wheels and high-torque steering mechanism of SS wheels with tapered rolling bearings are rigorously designed to meet the functional requirements. Based on the specific wheel layout and vehicle dynamics, the rotational kinematic model as well as the straight and rotational dynamic models of AGV are established by the authors. To well verify the motion characteristics of wheels under heavy load in three motion states including straight motion, self-rotation and rotation around a certain point, the simulations in ADAMS and factory experiments have all been conducted.

Simulation results indicate that normal and friction forces of DS wheels and SS wheels are very stable except for some small oscillations, which are caused by non-center load distribution on AGV. Experimental results on driving speed of AGV have directly demonstrated that its positioning accuracy is enough for use in real aircraft assembly lines.

The designed AGV system has been applied to the final assembly line of a certain aircraft in Aviation Industry Corporation of China, Ltd, whose assembly efficiency and flexibility have been significantly improved.

A new layout plan of wheels for an omnidirectional heavy-duty AGV is proposed, which enhances the operating and moving capacity of AGV. A function of human-machine collaboration is also offered by the AGV for transporting large workpieces intelligently and economically in aerospace and other heavy industries.

This paper presents an application of the dual reciprocity boundary element method (DRBEM) to transient advection‐diffusion problems. Radial basis functions and augmented thin plate splines (TPS) have been used as coordinate functions in DRBEM approximation in addition to the ones previously used in the literature. Linear multistep methods have been used for time integration of differential algebraic boundary element system. Numerical results are presented for the standard test problem of advection‐diffusion of a sharp front. Use of TPS yields the most accurate results. Further, considerable damping is seen in the results with one step backward difference method, whereas higher order methods produce perceptible numerical dispersion for advection‐dominated problems.