Calculation Of Transient Response Research Articles

Mechanism of extraordinary stress on blade during start-up of the Francis turbine

This paper describes the mechanism of extraordinary transient stress that occurs during start-up of a Francis turbine by investigating the detailed analysis with measured stress of prototype runner and transient response calculation. According to the dynamic stress measurement with high sampling frequency, it has been clear that a unique phenomenon occurs during start-up especially at the low rotation speed. From the macro perspective, impulsive stress occurred at blade outlet instantaneously and sporadically. Time interval of the event can be considered close to random, and there is no synchronization with the rotation speed. From the micro perspective, the strain occurs owing to the entire vane vibration, and the impulsive loads bump blade outlet from the side of the pressure surface. A Blade shows dumped free vibration in its natural mode in water. As the conclusion, the phenomenon that runner blades are struck by impulsive load on the pressure surface during start-up is compared to a drum beaten by drumsticks randomly in short time, and we named the unique phenomenon “Hydro Drum”

FEATURES AND PRINCIPLES OF THE DEVELOPMENT OF BRUSHLESS MAGNETOELECTRIC SYSTEMS OF THE RETURN-ROTARY MOTION

The paper reviews the results of studies of brushless magnetoelectric systems of return-rotary motion, carried out for many years at the Electrodynamics Institute of the National Academy of Sciences of Ukraine. Structures of specialized brushless magnetoelectric motors with elastic magnetic coupling between the stator and the rotor are presented. An example of structural optimization of the motor is given. The electromechanical characteristics of the motors of the return-rotary motion are described and the indexes of their efficiency are proposed. An example of the formation of functional dependences for motor control in an open-loop system is given. Structures of the system for automatic control of the rotor oscillations angle amplitude and stator current limitation, as well as a system for vector control of the auxiliary winding current for active compensation of reactive alternating torque of the main rotor are presented. Examples of calculation of transient responses of the main parameters of the motor are given. Reference 11, figure 9.

Transient analysis of leaky Lamb waves with a semi-analytical finite element method

We previously formulated a semi-analytical finite element technique for Lamb waves in a plate surrounded by fluids and investigated the dispersion curves and wave structures for leaky Lamb waves. Herein, this technique is extended to the calculation of transient responses both in a plate and in fluids for dynamic loading on the plate surface. To gain fundamental insights into guided wave inspection for a water-filled pipe or tank, guided waves generated upon transient loading of a flat plate water-loaded on one side were analyzed. The results show that a quasi-Scholte mode propagating at the plate-water interface is useful for the long-range inspection of a water-loaded plate because of its non-attenuation and minimal dispersion; moreover, this mode has superior generation efficiency in the low-frequency range, while it is localized near the plate-water interface at higher frequencies.

Gas pipeline modelling and control

The distributed parameter modelling of the gas flow through long pipelines is considered. Procedures which incorporate the gas stream energy storage, the pipeline frictional resistance and pressure attenuation characteristics are introduced. The pipeline input–output, transfer function, pressure and volume flow representations are formulated. An optimum, least effort, closed loop regulation strategy is proposed. Frequency response techniques are invoked enabling the derivation of simple, robust control algorithms. Confirmation of the results obtained, from the transient response computation of the outputs following input reference and load disturbance changes, are presented. The accuracy and novelty of the approach presented is commented upon.

保存系支配方程式の高解像度スキームによる非定常層流圧力損失の高速高精度計算法

A highly accurate unified computation of transient response in pipelines is desirable in order to improve pneumatic components. This paper deals with a high resolution simulation of transient response in laminar pipe flow by solving the governing equations directly. The authors employed a TVD scheme for computation of its stable and less diffusive properties. To apply this scheme, the governing equations must be described for a conservative system. The time-dependent friction loss in laminar pipe flow, which had only been discussed for a non-conservative system, was therefore transformed into a conservative system and solved with the Chakravarthy-Osher TVD scheme. Computations for a pneumatic pipeline with several pipe diameters were performed. The computations for the developed method were compared with the standard CIP method, and showed higher resolution, more stable computation and shorter computation time than the CIP method. The developed method can be easily applied to turbulent or high-amplitude pipe flow by simply changing the friction term.

Full density-matrix numerical renormalization group calculation of impurity susceptibility and specific heat of the Anderson impurity model

Recent developments in the numerical renormalization group (NRG) allow the construction of the full density matrix (FDM) of quantum impurity models (see A. Weichselbaum and J. von Delft) by using the completeness of the eliminated states introduced by F. B. Anders and A. Schiller (2005). While these developments prove particularly useful in the calculation of transient response and finite temperature Green's functions of quantum impurity models, they may also be used to calculate thermodynamic properties. In this paper, we assess the FDM approach to thermodynamic properties by applying it to the Anderson impurity model. We compare the results for the susceptibility and specific heat to both the conventional approach within NRG and to exact Bethe ansatz results. We also point out a subtlety in the calculation of the susceptibility (in a uniform field) within the FDM approach. Finally, we show numerically that for the Anderson model, the susceptibilities in response to a local and a uniform magnetic field coincide in the wide-band limit, in accordance with the Clogston-Anderson compensation theorem.

Study on Dynamic Simulation of 4-Bundle Ice-Coated Conductor Galloping Based on 3-D Model

Galloping of power transmission lines is a low frequency self-oscillation with large amplitude. The aerodynamic effect on each sub-conductor of 4-bundle conductor is different due to wake-flow-influence. In order to explore the reasons leading to galloping, a 3-D model for power transmission line is built. A two-node quadratic beam element in 3-D and a structure mass element are applied to establish the finite element model of iced 4-bundle conductor in ANSYS software. Then dynamic transient response calculations are made on this model. According to the results, difference in vibration of sub-conductors and frequency coupling of torsional and transverse vibration can be confirmed. The simulation results illustrate the wake-flow-influence effect and the coupled motions effect on galloping of 4-bundle conductor.

FIR modeling of voltage instrument transformers with iron core for the study of fast transients

Modern electronics found in various measuring equipment is sensitive to the effect of transient over-voltages. This paper treats the measurement procedure for the estimation of Finite Impulse Response (FIR) models of voltage instrument transformers, dedicated for the study of fast electromagnetic transients, with the special concern to its influence on the equipment connected to the secondary. A black-box approach is applied, and the model identification is based solely on a single measurement with the impulse excitation. The paper proposes two different procedures for the estimation of the analytical expression of the excitation, based on the parameters of the impulse generator or its estimation using a least-squares procedure. The frequency response of the transformer is used for the design of an initial FIR model, which was further reduced using corrected Akaike information criterion. This way the duration of the transient response calculation is further decreased, and the computation complexity reduced. Once determined, the FIR model allows, through the digital filtering operation (closely related to the concept of recursive convolution), a very easy time-domain calculation of the system’s response at any excitation.

Computer Modeling and Simulation of Thickness Mode Piezoelectric Transducers Under Different Driving Conditions

A global model for the pulsed ultrasonic responses of piezoelectric probes is presented. It allows the evaluation of transducers electrical impedance, transfer functions, impulse responses, emission and pulse-echo transient responses (neglecting diffraction effects) for different electrical pulsed driving waveforms (spike, sine-wave burst, square-wave burst, …). In addition, an approximate approach allows the computation of transient responses of piezoelectric transducers driven by efficient pulsers, which usually include a power switching device (e.g. SCR elements or nowdays MOS-FET transistors) and some rectifier components. Attenuation of ultrasonic waves in the different piezoelectric and non-piezoelectric layers are taken into account. A Visual Fortran Program has been developed for computer simulation. This program, with an interactive graphic interface, allows an easy simulation of electrical and ultrasonic responses of thickness mode piezoelectric transducers having different structures, material parameters, dimensions, tuning components, coaxial cables and electrical driving conditions.

Analytical solutions of one-dimensional macrodispersion in stratified porous media by the quadrupole method: convergence to an equivalent homogeneous porous medium

In this article, the quadrupole method is implemented in order to simulate the effects of heterogeneities on one dimensional advective and diffusive transport of a passive solute in porous media. Theoretical studies of dispersion in heterogeneous stratified media can bring insight into transport artefacts linked to scale effects and apparent dispersion coefficients. The quadrupole method is an efficient method for the calculation of transient response of linear systems. It is based here on the Laplace transform technique. The analytical solutions that can be derived by this method assists understanding of upscaled parameters relevant to heterogeneous porous media. First, the method is developed for an infinite homogeneous porous medium. Then, it is adapted to a stratified medium where the fluid flow is perpendicular to the interfaces. The first heterogeneous medium studied is composed of two semi-infinite layers perpendicular to the flow direction each having different transport properties. The concentration response of the medium to a Dirac injection is evaluated. The case studied emphasises the importance in the choice of the boundary conditions. In the case of a periodic heterogeneous porous medium, the concentration response of the medium is evaluated for different numbers of unit-cells. When the number of unit cells is great enough, depending on the transport properties of each layer in the unit cell, an equivalent homogeneous behaviour is reached. An exact determination of the transport properties (equivalent dispersion coefficient) of the equivalent homogeneous porous medium is given.

A Study on Vibration and Noise Reduction of Stepping Floor of Movable Seat Used in Dome.

This paper describes the vibration and noise reduction of a stepping floor of a movable seat used in a dome. This seat is made of steel because of being movable. Consequently the vibration and noise occur due to the walking and the jumping of spectators and the problems appear to be that the noise makes it difficult to hear the announcer and the seat is uncomfortable to sit on. Then, the prediction of the reduction effect of the damping material is performed by the transient response calculation and the modal analysis, and the predicted values are compared with the experimental results. As a result, the calculation result is in good agreement with the experimental one and the reduction effect is simply expressed by the ratio of loss factors before and after countermeasures in case of being able to neglect the mass of the damping material.

LASER-BASED TRANSIENT SURFACE ACCELERATION OF THERMOELASTIC LAYERS

The removal of particles from elastic substrates has been an important practical problem in the electronics industry especially as the sizes of electronic units shrink. In recent years, there has been an interest in removingsubmicron level particles from surfaces. The use of traditional surface cleaning methods, such as ultrasonically induced fluid flow, vibrational methods, centrifugal techniques, is limited to particles that require surface acceleration lower than 107m/s2. For the effective removal of submicron particles, a higher level surface acceleration is needed since the adhesion forces (mainly van der Waals force for dry surfaces) are related to the particle size and increase approximately linearly as the characteristic radius of small particles that are to be removed decreases. In current work, based on the generalized dynamic theory of thermoelasticity reported, a transfer matrix formulation including the second sound effect is developed for a thermoelastic layer. The transfer matrix for axisymmetric wave propagation in a thermoelastic layer is obtained by adopting a double integral transform approach. The second sound effect is included to eliminate the thermal wave travelling with infinite velocity as predicted by the diffusion heat transfer model, and, consequently, the immediate arrival of waves. Using the current formulation and the periodic systems framework, a transfer function formulation for calculating the accelerations is developed for transient analysis. A double integral transform inversion method is used for transient response calculations. Acceleration levels, sufficient for submicron particle removal, are reported. Various processes such as thermoelastic stresses, surface evaporation, and optical breakdown may be responsible for surface acceleration components and particle removal. In current work, only the surface acceleration due to transient thermoelastic wave propagation is under investigation.

A boundary element formulation in time domain for viscoelastic solids

Viscoelastic solids may be effectively treated by the boundary element method (BEM) in the Laplace domain. However, calculation of transient response via the Laplace domain requires the inverse transform. Since all numerical inversion formulas depend heavily on a proper choice of their parameters, a direct evaluation in the time domain seems to be preferable. On the other hand, direct calculation of viscoelastic solids in the time domain requires the knowledge of viscoelastic fundamental solutions. Such solutions are simply obtained in the Laplace domain with the elastic–viscoelastic correspondence principle, but not in the time domain. Due to this, a quadrature rule for convolution integrals, the ‘convolution quadrature method' proposed by Lubich, is applied. This numerical quadrature formula determines their integration weights from the Laplace transformed fundamental solution and a linear multistep method. Finally, a boundary element formulation in the time domain using all the advantages of the Laplace domain formulation is obtained. Even materials with complex Poisson ratio, leading to time-dependent integral free terms in the boundary integral equation, can be treated by this formulation. Two numerical examples, a 3D rod and an elastic concrete slab resting on a viscoelastic half-space, are presented in order to assess the accuracy and the parameter choice of the proposed method. Copyright © 1999 John Wiley & Sons, Ltd.

Torsional Vibrations of Synchronous Motor Driven Trains Using p-Method

Synchronous motors produce damaging oscillating torques during startup. If the system is not properly analyzed and designed, the torsional excitation can be very destructive. This paper presents a systematic approach to the dynamic analysis of synchronous motor driven rotating machinery. The p-version of the finite element method is used in the formulation of the equations of motion which provides a great deal of simplicity in the modeling process. The convergence is achieved by increasing the polynomial order of the basis functions of the geometric elements. The system damping matrix can be constructed from the element level or can be calculated by specifying the critical damping factors for a given number of modes of interest. A modified Newmark integration method is employed in the nonlinear transient response calculation. The nonlinearity of the flexible resilient couplings can be easily implemented into this direct numerical integration algorithm. The dynamic stiffness and damping of the resilient couplings are updated at each time step to ensure the dynamic equilibrium. Two examples have been employed to illustrate the validity of the proposed algorithm. The effectiveness, accuracy, and simplicity of the use of p-method on the torsional vibration of synchronous motor driven trains are demonstrated in this paper.

CALCULATION OF TRANSIENT ELECTROMAGNETIC FORCES IN AN AXISYMMETRICAL ELECTROMAGNET WITH CONDUCTIVE SOLID PARTS

The paper describes the analysis and the calculation of transient response of a voltage fed electromagnet. This calculation is based on the simultaneous solution of the magnetic field equations and the electrical circuit equations. In the modelling of the magnetic fields, eddy currents in solid conductive parts and saturation of magnetic parts are taken into account. This modelling uses Finite Element Method for the calculation of magnetic fields and forces with special quadrilateral elements. Experimental and simulation results for an axisymmetrical electromagnet are presented and compared.

The application of Kirchhoff's formula to the numerical calculation of transient response in an enclosure.

This paper is concerned with the use of Kirchhoff's time-retarded potential boundary integral equation in the numerical calculation of the transient response in an enclosure with rigid or absorbent boundary. The sound pulse reflected from the absorbent boundary, consisted of a porous layer on a rigid backing, is calculated by using the time-dependent “impulse admittance” (inverse Laplace transform of the normal admittance). Next, the numerical integration method of Kirchhoff's integral equation and some problems arising in the calculation are discussed. Finally, transient responses for a rigid and an absorbent cubic rooms are calculated numerically by Kirchhoff's integral equation and compared with the precise results given by the image sources method.

How to Start Transient Response Calculations for Rotating Structures Without Causing Centrifugal Force Shocks

In computer programs for transient response calculations often only homogeneous and not more complicated, inhomogeneous initial conditions can be considered. The initial conditions assumed here are the stresses or displacements generated by the centrifugal force field in rotating structures. Nevertheless, calculations can be started with homogeneous initial conditions. The system has then to be transferred to operating conditions in a precalculation by a suitable rotational speed characteristic. Only then can the actual simulation begin. The rotational speed characteristic must have the additional capability of establishing the inhomogeneous initial conditions in minimum time. Precise imitation of the long technical run-up procedure is undesirable because of high computer cost and numerical inaccuracy. Modal equations are taken as the basis for formulation of an optimization problem whose solution determines the optimum speed characteristic. For the technically important case where a single prevailing natural vibration has to be controlled, it is possible to state the solution explicitly. With several natural vibrations, the control must be determined numerically. The procedure is used in calculating the effects of bird strike on rotating turbine blades.

Equivalent Dominant Pole Approximation of Capacitively loaded VLSI Interconnection

The equivalent dominant pole approximation including delay term is proposed for the transient response calculation of an uniformly distributed URC line loaded with capacitance. Transfer functions for voltage and current excitations have been derived and their applications for modeling of VLSI interconnections have been discussed.

Structural dynamic analysis on a parallel computer: The finite element machine

The development of general-purpose finite element computer software systems has provided the capability to analyze a wide range of linear and non-linear structural problems. However, these software systems are severely limited for non-linear response calculations because of the available speed on current sequential computers. Recent and projected advances in parallel multiple instruction multiple data (MIMD) computers provide an opportunity for significant gains in computing speed and for broadening the range of structural problems which may be solved. The key to these gains is the effective selection and implementation of algorithms which exploit parallel computing. This paper documents experiences solving transient response calculations on an experimental MIMD computer, termed the Finite Element Machine. The paper describes the algorithm used, its implementation for parallel computations, and results for representative one- and two-dimensional dynamic response test problems. The results show computation speedups of up to 7.83 for eight processors, and indicate that significant speedups of solution time are possible for non-linear dynamic response calculations through the use of many processors and appropriate parallel integration algorithms. The results are extremely encouraging and suggest that significant speedups in structural computations can be achieved through advances in parallel computers.

Modal analysis for random vibration of hysteretic frames

AbstractAn algorithm is presented for the direct stiffness formulation of hysteretic frames which is suitable for random vibration analysis under zero mean or non‐zero mean random excitation. A modal transformation is used to reduce the number of active degrees of freedom. First and second order response statistics are presented for two example frames using stochastic equivalent linearization and Monte Carlo simulation. The modal transformation stabilizes the stationary response calculation algorithm by eliminating superfluous higher modes. The iterations for transient response calculations under non‐zero mean excitations are destabilized by elimination of too many modes. The modal transformation allows reasonable response estimates to be obtained with significant reductions in computing time. The expected lower modes dominate the response, but inclusion of several higher modes is necessary to provide reasonable response estimates.