Simulation Of Transient Response Research Articles

Transient kinetic analysis of multipath reactions: An educational module using the IPython software package

A large number of industrial catalytic reactions proceeds via multiple pathways. A transient response method has been successfully utilized for the analysis of kinetics and mechanism of multipath reactions. In this paper, we describe an educational module for teaching kinetics of complex heterogeneously-catalyzed reactions based on the software package for simulation of transient responses in a tubular packed-bed reactor. The module includes the reactor model description, derivation and verification of kinetic equations, analysis of steady-state kinetics, numerical simulation of transient responses, and visualization and analysis of results utilizing the developed IPython notebooks. The use of the module helps students to acquire theoretical knowledge as well as the practical and analytical skills related to the kinetic analysis of multipath reactions.

Determination of draw resonance onsets in tension-controlled viscoelastic spinning process using transient frequency response method

Draw resonance onsets of actual viscoelastic spinning processes with secondary forces operated by constant draw ratio are determined via transient frequency response simulations under a constant tension or force boundary condition, which causes the system to be always stable. Transfer function data between the spinline velocity and the tension at the take-up position in the frequency domain, which are transformed from the transient responses of the take-up velocity with respect to a step change of the take-up force, play a key role in the determination of the onset points for various spinning cases. It is confirmed that the critical draw ratios established in this study are almost the same as those decided by linear stability or direct transient simulation methods for velocity-controlled spinning systems. The transfer function data for the stability analysis can be readily and beneficially applied to an analysis of sensitivity of a spinning process with respect to a sinusoidal disturbance.

Linearized State-Space Model of a Self-Excited Induction Generator Suitable for the Design of Voltage Controllers

The complexity and strong nonlinearity of the model of a self-excited induction generator hinder the systematic design of a voltage regulation system. Using a special reference frame aligned with the stator voltage vector, the paper succeeds in developing a control-oriented linearized model that relates small deviations of the capacitance, load admittance, and angular velocity, to corresponding deviations of the voltage amplitude. Transfer functions are also computed based on the linear model. A stability analysis predicts rapidly decaying oscillatory transients combined with a primary component with slower exponential decay. Simulated transient responses of the full and linearized models demonstrate the validity of the approximation and are in good agreement with experiments.

Mathematical modeling of Lamb wave scattering for structural health monitoring

The ability to estimate and suppress part of the reflected energy from the structural boundaries in the received signal to obtain the reflections solely due to damage is explored. When the ultrasound transducer transmits a pulse into the structure to be interrogated, a reflected wave from the structural boundaries and/or damage is detected by the ultrasound receiver. In typical Lamb wave simulation practices, with a view to simplify the wave signal interpretations, effects of structural boundary reflections are often not considered. Although such Lamb wave simulation practices are effective in case of infinite plates, the same method is inapplicable in case of finite plates, because the effect of structural boundaries causes intricacies especially for transient response simulations. In this paper, a specific statistical method is used to model the reflections from structural boundaries. Indeed, this modeling is efficient in case of finite plates. Such a modeling can also be used to examine and suppress part of the reflected energy from the structural boundaries in received signal to procure the signal containing the reflections only due to damage. The proposed algorithm has been evaluated in both simulation and experimental tests on an 6061 aluminum plate with dimensions 300 mm × 300 mm × 3 mm. The tests yield considerable improvement in the accuracy of estimating the position of the flaw.

Evaluation of passive autocatalytic recombiners operation efficiency by means of the lumped parameter approach*

Abstract The problem of hydrogen behavior in containment buildings of nuclear reactors belongs to thermal-hydraulic area. Taking into account the size of systems under consideration and, first of all, safety issues, such type of analyses cannot be done by means of full-scale experiments. Therefore, mathematical modeling and numerical simulations are widely used for these purposes. A lumped parameter approach based code HEPCAL has been elaborated in the Institute of Thermal Technology of the Silesian University of Technology for simulations of pressurized water reactor containment transient response. The VVER-440/213 and European pressurised water reactor (EPR) reactors containments are the subjects of analysis within the framework of this paper. Simulations have been realized for the loss-of-coolant accident scenarios with emergency core cooling system failure. These scenarios include core overheating and hydrogen generation. Passive autocatalytic recombiners installed for removal of hydrogen has been taken into account. The operational efficiency of the hydrogen removal system has been evaluated by comparing with an actual hydrogen concentration and flammability limit. This limit has been determined for the three-component mixture of air, steam and hydrogen. Some problems related to the lumped parameter approach application have been also identified.

Structure‐preserving, stability, and accuracy properties of the energy‐conserving sampling and weighting method for the hyper reduction of nonlinear finite element dynamic models

SummaryThe computational efficiency of a typical, projection‐based, nonlinear model reduction method hinges on the efficient approximation, for explicit computations, of the scalar projections onto a subspace of a residual vector. For implicit computations, it also hinges on the additional efficient approximation of similar projections of the Jacobian of this residual with respect to the solution. The computation of both approximations is often referred to in the literature as hyper reduction. To this effect, this paper focuses on the analysis and comparative performance study for nonlinear finite element reduced‐order models of solids and structures of the recently developed energy‐conserving mesh sampling and weighting (ECSW) hyper reduction method. Unlike most alternative approaches, this method approximates the scalar projections of residuals and/or Jacobians directly, instead of approximating first these vectors and matrices then projecting the resulting approximations onto the subspaces of interest. In this paper, it is shown that ECSW distinguishes itself furthermore from other hyper reduction methods through its preservation of the Lagrangian structure associated with Hamilton's principle. For second‐order dynamical systems, this enables it to also preserve the numerical stability properties of the discrete system to which it is applied. It is also shown that for a fixed set of parameter values, the approximation error committed online by ECSW is bounded by its counterpart error committed off‐line during the training of this method. Therefore, this error can be estimated in this case a priori and controlled. The performance of ECSW is demonstrated first for two academic but nevertheless interesting nonlinear dynamic response problems. For both of them, ECSW is shown to preserve numerical stability and deliver the desired level of accuracy, whereas the discrete empirical interpolation method and its recently introduced unassembled variant are shown to be susceptible to failure because of numerical instability. The potential of ECSW for enabling the effective reduction of nonlinear finite element dynamic models of solids and structures is also highlighted with the realistic simulation of the nonlinear transient dynamic response of a complete car engine to thermal and combustion pressure loads using an implicit scheme. For this simulation, ECSW is reported to enable the reduction of the CPU time required by the high‐dimensional nonlinear finite element dynamic analysis by more than four orders of magnitude, while achieving a very good level of accuracy. Copyright © 2015 John Wiley & Sons, Ltd.

Wind-Induced Vibration Control for Transmission System Using Steel-Lead Viscoelastic Damper

For wind-induced vibration of transmission tower-line system, the vibration reduction effects are studied based on a new type steel-lead viscoelastic damper. Firstly, Calculate damped coefficient basing on the test of the new type steel-lead viscoelastic damper under slow reversed cyclic horizontal loads. Then, a finite element model of transmission tower was built by using ANSYS. And the time history samples of random fluctuating wind load is obtained with the linear auto-regressive filter law principle. Next, three installation plans of dampers on tower were proposed based on analyzing the working principle damper and the structure of tower. Finally, a wind-induced vibration transient response simulation was performed respectively for the different plans. The influences of SLVD dampers on the displacement and on the acceleration of the controlled nodes were compared. SLVD damper can reduce the top node displacement by about 37.89%. The results indicated that the SLVD damper can suppress the wind-induced vibration. And through comparison, the optimal installation scheme of SLVD dampers is obtained.

Coupled circuit numerical analysis of eddy currents in an open MRI system

We performed a new coupled circuit numerical simulation of eddy currents in an open compact magnetic resonance imaging (MRI) system. Following the coupled circuit approach, the conducting structures were divided into subdomains along the length (or width) and the thickness, and by implementing coupled circuit concepts we have simulated transient responses of eddy currents for subdomains in different locations. We implemented the Eigen matrix technique to solve the network of coupled differential equations to speed up our simulation program. On the other hand, to compute the coupling relations between the biplanar gradient coil and any other conducting structure, we implemented the solid angle form of Ampere’s law. We have also calculated the solid angle for three dimensions to compute inductive couplings in any subdomain of the conducting structures. Details of the temporal and spatial distribution of the eddy currents were then implemented in the secondary magnetic field calculation by the Biot–Savart law. In a desktop computer (Programming platform: Wolfram Mathematica 8.0®, Processor: Intel(R) Core(TM)2 Duo E7500 @ 2.93GHz; OS: Windows 7 Professional; Memory (RAM): 4.00GB), it took less than 3min to simulate the entire calculation of eddy currents and fields, and approximately 6min for X-gradient coil. The results are given in the time–space domain for both the direct and the cross-terms of the eddy current magnetic fields generated by the Z-gradient coil. We have also conducted free induction decay (FID) experiments of eddy fields using a nuclear magnetic resonance (NMR) probe to verify our simulation results. The simulation results were found to be in good agreement with the experimental results. In this study we have also conducted simulations for transient and spatial responses of secondary magnetic field induced by X-gradient coil. Our approach is fast and has much less computational complexity than the conventional electromagnetic numerical simulation methods.

1D34 NMPC Approach on Nonlinear Model Reduction Techniques : Application to an ultrasonic motor(The 12th International Conference on Motion and Vibration Control)

This paper proposes a nonlinear control design methodology using nonlinear model order reduction (MOR) techniques on a practical complex system. As the typical controlled object, we take ultrasonic motor that has strong nonlinearity and needs precise control. In control design phase, Nonlinear Model Predictive Control (NMPC) is applied. In this paper, MOR of Finite Element method is described first. Generally, it is very difficult to apply MOR to a nonlinear finite element model. However, it may be possible by focusing to the character of the model. The key point of this MOR technique is separation with linear space and nonlinear space for system from the composition view point of ultrasonic motor. When the techniques apply to a certain system appropriately, the degree of freedom of the finite element model will be reduced substantially. This model will be called the reduction model, and it has tried to apply this technique to the transient response simulation of ultrasonic motor. A strong nonlinearity appears because ultrasonic motor is driven by the contact friction. We identify the nominal model for the control design from the reduction model. In order to get this nominal model, the conditions of an input and load are changed to a reduction model, and two or more simulations are performed. As a result, the gain constant and the time constant can be found. This gain constant and time constant turn into a nonlinear function whose variables are the input and load. The proposed method tries to carry out speed follow-up control with the application of model prediction control to the model. Finally, the control rule of a nominal model is applied also to reduction model, and the speed servo performance is checked.

Transient Behavior of an Active Indirect Two-tank Thermal Energy Storage System During Changes in Operating Mode – An Application of an Experimentally Validated Numerical Model

Solar thermal power plants are a promising way of providing renewable electricity, particularly, due to their ability to store thermal energy. At today's parabolic trough collector plants, the only commercially applied thermal energy storage system is an active indirect two-tank thermal energy storage, based on molten salts. This work focuses on the transient response simulation of such a thermal energy storage system during changes in operation. Modelica is used as modeling language. Simulation results show that there are certain limitations regarding instantaneous thermal power demand or supply, which still requires heat transfer fluid buffer storage in order to provide the thermodynamic power cycle of the plant with a continuous thermal power input.

Combustion Property Analysis and Control System for the Dynamics of a Single Cylinder Diesel Engine

Corresponding to global environment problems in recent year, the technology for reducing fuel consumption and exhaust gas emission of engine was needed. Simulation of transient engine response is needed to predict engine performance that frequently experience rapid changes of speed. The aim of this research is to develop a non-linear dynamic control model for direct injection single cylinder diesel engine which can simulate engine performance under transient conditions. In this paper, the combustion model with multistage injection and conducted experiments in the transient conditions to clarify the combustion characteristics was proposed. In order to perform the analysis of acceleration operation characteristics, it was built a Model Predictive Control (MPC) to reproduce the characteristic values of the exhaust gas and fuel consumption from the control parameters in particular. Finally, MPC is an effective method to perform the analysis of characteristic in diesel engine under transient conditions.

Object-oriented modeling for the transient response simulation of multi-pass shell-and-tube heat exchangers as applied in active indirect thermal energy storage systems for concentrated solar power

This work focuses on the transient numerical modeling of multi-pass shell-and-tube heat exchangers that apply single-phase fluids. A one-dimensional modeling approach is used for the heat exchanger ducts. The governing partial differential equations are solved numerically by applying the finite volume method. In particular, the commonly applied cell-method is used, which is presented in a flexible, intuitive and simulation-platform-independent way. Simulation results are checked for consistency by comparing them to theoretical as well as experimental data available in the literature. Subsequently, the presented modeling approach is used for a specific case study, showing the transient behavior of a typical heat exchanger train configuration currently used at active indirect thermal energy storage systems for CSP (concentrated solar power). Typical process parameters (process gain, dead time and time constant) are given for charging as well as for discharging mode at different heat exchanger loads. Furthermore, transient response simulation results are discussed in detail, providing all used boundary conditions and assumed heat exchanger specifications, thus enabling future model comparison studies. Finally, suitable degrees of discretization are discussed for transient CSP performance simulations on system level, offering a good trade-off between simulation speed and accuracy. Modelica is used as modeling language.

Domain of validity of the perturbative approach to femtosecond optical spectroscopy

We have performed numerical nonperturbative simulations of transient absorption pump-probe responses for a series of molecular model systems. The resulting signals as a function of the laser field strength and the pump-probe delay time are compared with those obtained in the perturbative response function formalism. The simulations and their theoretical analysis indicate that the perturbative description remains valid up to moderately strong laser pulses, corresponding to a rather substantial depopulation (population) of the initial (final) electronic states.

The sensitivity of flowline models of tidewater glaciers to parameter uncertainty

Abstract. Depth-integrated (1-D) flowline models have been widely used to simulate fast-flowing tidewater glaciers and predict change because the continuous grounding line tracking, high horizontal resolution, and physically based calving criterion that are essential to realistic modeling of tidewater glaciers can easily be incorporated into the models while maintaining high computational efficiency. As with all models, the values for parameters describing ice rheology and basal friction must be assumed and/or tuned based on observations. For prognostic studies, these parameters are typically tuned so that the glacier matches observed thickness and speeds at an initial state, to which a perturbation is applied. While it is well know that ice flow models are sensitive to these parameters, the sensitivity of tidewater glacier models has not been systematically investigated. Here we investigate the sensitivity of such flowline models of outlet glacier dynamics to uncertainty in three key parameters that influence a glacier's resistive stress components. We find that, within typical observational uncertainty, similar initial (i.e., steady-state) glacier configurations can be produced with substantially different combinations of parameter values, leading to differing transient responses after a perturbation is applied. In cases where the glacier is initially grounded near flotation across a basal over-deepening, as typically observed for rapidly changing glaciers, these differences can be dramatic owing to the threshold of stability imposed by the flotation criterion. The simulated transient response is particularly sensitive to the parameterization of ice rheology: differences in ice temperature of ~ 2 °C can determine whether the glaciers thin to flotation and retreat unstably or remain grounded on a marine shoal. Due to the highly non-linear dependence of tidewater glaciers on model parameters, we recommend that their predictions are accompanied by sensitivity tests that take parameter uncertainty into account.

Dynamic Behavior of Multiport Power Electronic Interface Under Source/Load Disturbances

This paper presents the dynamic behavior of multiport power electronic interface (MPEI) under load/source disturbances. A cascaded topology for MPEI is considered. This system is capable of power management for local generations, loads, and storage systems. Large-signal and small-signal models for MPEI are developed. These models are combined with corresponding control algorithms. Simulated and experimental transient responses to disturbances on each port are presented. The behavior of MPEI in response to each disturbance is analyzed. Simulation and experimental results are compared in order to verify the model.

Calculation of design sensitivity for large-size transient dynamic problems using Krylov subspace-based model order reduction

Nowadays, transient dynamic responses of a large-size finite element (FE) model can be solved within a reasonable computation time owing to rapid improvement in both numerical schemes and computing resources. However, increasing demands for accurate simulation and complicated modeling have led to larger and more complex finite element models, which consequently result in considerably high computational cost. In addition, when structural optimizations include transient responses such as displacement, velocity, and acceleration, the optimizations often do not end within a reasonable process time because the large-size simulation must be repeated many times. In order to reduce the computational cost in this respect, model order reduction (MOR) for the original full-order model (FOM) can be used for the transient response simulation. In this paper, a transient dynamic response analysis using Krylov subspace-based MOR and its design sensitivity analysis with respect to sizing design variables is suggested as an approach to the handling of large-size finite element models. Large-size finite element models can incur the problem of a long computation time in gradient-based optimization iterations because of the need for repeated simulation of transient responses. In the suggested method, the reduced order models (ROMs) generated from the original FOMs using implicit moment-matching via the Arnoldi process are used to calculate the transient response and its design sensitivity. As a result, the speed of numerical computation for the transient response and its design sensitivity is maximized. Newmark’s time integration method is employed to calculate transient responses and their design sensitivities. In the case of the transient sensitivity analysis, we apply a temporal discretization scheme to the design sensitivity equation derived by directly differentiating the governing equation with respect to design variables. This methodology has been programmed on the MATLAB with the FE information extracted from the FE package ANSYS. Two application examples are provided to demonstrate the numerical accuracy and efficiency of the suggested approach. The relative errors of transient response and design sensitivity between the FOMs and ROMs are also compared according to the orders of the reduced model. Calculation of transient dynamic responses and their sensitivities using Krylov subspacebased MOR shows a sizeable reduction in computation time and a good agreement with those provided by the FOM.

Simulated Transient Electromagnetic Response for the Inspection of GFRP-Wrapped Concrete Cylinders Using Radar NDE

Assessing the subsurface condition of glass fiber reinforced polymer (GFRP)-retrofitted concrete structures is an important inspection problem for the maintenance of reinforced concrete structures retrofitted with high performance composites like GFRP. The objective of this paper is to investigate the radar response of GFRP-concrete cylinders through a parametric study, using the finite difference time domain (FDTD) method. Intact and artificially damaged GFRP-wrapped concrete cylinders were modeled in a two dimensional domain. Considered parameters include the thickness of GFRP wrap/layer, width and depth of artificial defects, and the incident frequency. Modulated Gaussian signals with a carrier frequency ranging from 8 GHz to 18 GHz were used as the incident wave. Field and power responses in both time and frequency domains were investigated. A nonlinear effect due to the variation of defect dimensions is found in both time and frequency responses, indicating the multiple, interlayer scattering effect in the system.

State-space model for transient behavior of water-to-air surface heat exchanger

Adequately representing the dynamic performance of a water-to-air heat exchanger under transient conditions would help design optimized control strategies for a high-energy-efficiency HVAC system. In this paper, the water-to-air heat exchanger is considered as a multi-input-and-multi-output system (MIMO), and the corresponding dynamic model is developed with the mass and energy balance equations based on which the state-space model for transient behavior of the heat exchanger is derived.The model has been validated by a series of dynamic response experiments including the transient responses of exit air temperature and humidity as well as exit water temperature subjected to the disturbances of inlet water temperatures (Case I: Start up the chiller; and Case III: Stop the chiller) and a sudden change in the water flow rate (Case II: The water flow rate increases by 0.058kg/s). The time of experimental validation on the transient response simulation is set as 1200s in all the cases. The simulated results obtained by the state-space model have been compared with the experimental data, which shows that the state-space model developed in this study is capable of predicting the transient performance of the water-to-air heat exchangers satisfactorily (the average error is less than 15.0%). Meanwhile, the influence of input disturbances and initial conditions on the transient behaviors of the heat exchanger is discussed through the model simulation. The results show that the input disturbances and the initial conditions will produce significant influence on the proportionality coefficient of the response variables, but little influence on the time constant of the response ones.

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.

Optimization of Hydraulic Digital Governor parameters using EMTP-RV

Application of hydraulic digital governor is an important step in achieving a fully integrated system for stability studies. In this paper, EMTP-RV model of hydraulic digital governor is used in order to perform optimization of hydraulic digital governor parameters. The simulated transient response characteristics of a digital governor, obtained by the EMTP-RV model, give us much more realistic insight into optimization of hydraulic digital governor parameters such as transient droop time constant (Tr) and temporary droop coefficient (δ). Optimization of essential hydraulic digital governor parameters gives us possibility to improve transient response characteristics of governing system relating to long-term stability of a power system.