Modeling Of Transient Response Research Articles

Accurate modeling of thermal-optical performance for a lightweight SiC mirror

The SiC mirror has excellent structural rigidity and thermal stability, making it widely applicable in high-power optical systems. This manuscript aims to establish a coupled analysis model of thermal-optical performance for a lightweight SiC reflector under high-power laser irradiation. First, based on the Fourier principle, the transient temperature rise of the mirror is analyzed using the finite element method, considering boundary conditions such as heat source and convective radiation. A transient thermal response model for the mirror is established. Then, the reflective surface deformation is solved based on the mirror temperature field. By processing the data of node deformation, the decrease in the mirror surface shape accuracy (RMS) value is obtained. Finally, the experimental platform is built to measure the transient temperature rise and wavefront aberration change of the mirror after high-power laser excitation. Based on the deviation between the calculated data of the analysis model and the measured data, thermodynamic parameters in the analysis model are adjusted according to the principle of minimum residual. The research findings of this manuscript can be utilized for accurately predicting the temperature rise and optical degradation of SiC mirrors under high-power laser irradiation and provide a theoretical basis for the subsequent design of actively compensating methods for thermal-induced distortions.

Thermal and mechanical investigation of proton exchange membrane fuel cells under combined loading conditions

Mechanical performance of PEM fuel cells under combined loadings is one of critical issues in improving cell performance and reliability. In this study, thermal and mechanical performance of the PEM fuel cell under clamping force and temperature load are investigated by experiments and three-dimensional dynamic simulations. In experiments, pressure distributions between gas diffusion layer and flow field are measured by pressure sensitive films. The experimental results show that the local pressure increases with clamping load, and pressure distribution is much uneven in the midstream. Meanwhile, a three-dimensional model of the cell combined transient heat transfer and mechanical response of components is developed, which is validated by experimental data. The modeling results show that under combined loadings, the porosity of gas diffusion layer under the rib decreases, attributed to compressive deformation caused by thermal gradient and clamping pressure, leading to higher effective thermal conductivity and electrical conductivity. When at a higher temperature, the overall stresses of gas diffusion layer decrease and the minimum stress is located under the center rib, forming a concave stress distribution pattern. Distribution and variation patterns of local deformations and stresses for the membrane are similar to those of gas diffusion layer, but the maximum stress and deformation are much lower. A dimensional stress coefficient is proposed to determine the stress distribution uniformity under the rib. With the increase of clamping torque, dimensionless stress coefficients under lower ambient temperature change slightly. As temperature increases, dimensionless stress coefficients increase significantly and decrease with the clamping torque, indicating the decreasing role of temperature load on mechanical response of the cell.

3-D Numerical Modeling of Transient Electromagnetic Responses in Anisotropic Formation With Cement-Coated Steel Casing Borehole

3-D Numerical Modeling of Transient Electromagnetic Responses in Anisotropic Formation With Cement-Coated Steel Casing Borehole

A semi-analytical solution for the transient response of one-dimensional saturated single-layer porous media with general boundary conditions

Based on the basic equations for saturated porous media wave equations proposed by Biot, a mathematical model for one-dimensional transient response of single-layer saturated porous media were established with general boundary condition, arbitrary initial conditions and arbitrary vertical load. Firstly, the independent parameters total stress σ, fluid pressure p, soil absolute displacement u and fluid relative displacement w were advised to describe the boundary conditions by linear combination in pairs. Through adjusting the parameters, the linear combination boundary conditions could represent various boundary conditions. The eigenvalues and the eigenfunctions of the undamped governing equations were obtained by means of the variable separation method. With the help of undetermined coefficients and orthogonality of eigenfunctions methods, the solution to the problem could be converted to solve the initial value problem of a series of ordinary differential equations. The semi-analytical solutions were approached by the precise time-integration method. Compared with previous research, the semi-analytical solutions of this research were more general and could be degenerated into various conditions exactly. Several numerical simulations were carried out to validate this method. Finally, the one-dimensional transient responses of single-layer saturated soil with general boundary conditions under step load were analyzed. The results demonstrate that the responses of semi-permeable condition are between permeable condition and impermeable condition and the solid and fluid displacement increase first and then decrease with time.

Analytical workload dependence of self-heating effect for SOI MOSFETs considering two-stage heating process

Dynamic self-heating effect (SHE) of silicon-on-insulator (SOI) MOSFET is comprehensively evaluated by ultrafast pulsed I–V measurement in this work. It is found for the first time that the SHE complete heating response and cooling response of SOI MOSFETs are conjugated, with two-stage curves shown. We establish the effective thermal transient response model with stage superposition corresponding to the heating process. The systematic study of SHE dependence on workload shows that frequency and duty cycle have more significant effect on SHE in first-stage heating process than in the second stage. In the first-stage heating process, the peak lattice temperature and current oscillation amplitude decrease by more than 25 K and 4% with frequency increasing to 10 MHz, and when duty cycle is reduced to 25%, the peak lattice temperature drops to 306 K and current oscillation amplitude decreases to 0.77%. Finally, the investigation of two-stage (heating and cooling) process provides a guideline for the unified optimization of dynamic SHE in terms of workload. As the operating frequency is raised to GHz, the peak temperature depends on duty cycle, and self-heating oscillation is completely suppressed.

Probe beam influence on spin polarization in spin-exchange relaxation-free co-magnetometers

Spin-exchange relaxation-free (SERF) co-magnetometers have promising applications in both inertial navigation and fundamental physics experiments. However, the fluctuation in the spin polarization caused by the probe beam has a non-negligible influence on the co-magnetometer signal. In this paper, a theoretical model containing three parameters of the probe beam is established by extending the coupled Bloch equation. Based on this model, the influence of probe power density on the transient and steady-state response of the SERF co-magnetometer is analyzed. According to the transient response model, a new measurement method for transverse optical pumping of the probe beam is proposed. Then, for the steady-state response model, a steady-state error suppression method is suggested by adjusting the degree of circular polarization of the probe beam. Eventually, the suppression method is used to refine the SERF co-magnetometer, achieving a suppression rate of 70.31% in transverse electron spin polarization fluctuations, thus improving the co-magnetometer to a stability of 0.0079∘ h−1. To our knowledge, this is better than what has been reported so far.

A Nonisolated High Step-Down DC–DC Converter With Low Voltage Stress and Zero Voltage Switching

This article introduces a general method to modify the traditional buck converter to become a high step-down dc–dc converter, which has a lower voltage gain without changing the voltage stress of switches. From the analysis, an auxiliary circuit is proposed to implement this method. In addition, triangular conduction mode operation is also analyzed to derive zero-voltage switching (ZVS) model of the modified buck converter, which is beneficial for high-frequency applications. Coupled inductor, which is established from two inductors of auxiliary circuit and buck converter, is employed to improve both steady-state and dynamic response performances. By analyzing the influence of coupling coefficient, and the rate between two inductances into inductor current ripple, transient response, and ZVS model, a suitable coupling structure is recommended to employ in the proposed converter. As a result, the design considerations are presented to get the maximum benefits of coupled inductor for this proposed converter. Finally, a prototype of 48 W is built and tested to verify its feasibility.

Infrared thermography observations of crystallization fouling in a plate heat exchanger

Heat exchanger performance is significantly reduced in the presence of impurities in one or both fluid streams, frequently by deposits of inversely soluble salts. Accordingly, immense efforts were and still are spent to combat, predict, and investigate such fouling problems to mitigate the reduction of heat transfer performance. In this study, calcium carbonate crystallization fouling in a corrugated plate heat exchanger was investigated. Fouling was monitored using temperature and flow measurements, and, for the first time, coupled with infrared thermography observations. We show a clear and measurable local difference between clean and fouled conditions, regardless of operating conditions. Infrared measurements of temperature permit conclusions about flow distribution and the spatial location of areas with severe fouling. Compared to the clean state, completely skewed isotherms after fouling point out channel blockage and flow obstructions, resulting in large scale flow re-distribution within the channel. The presented results exhibit a clear benefit of this approach for heat exchanger fouling studies and serve as a foundation for future research of dynamic operation, transient response, and computational models.

Method to Estimate Thermal Transients in Reactors and Determine Their Parameter Sensitivities without a Forward Simulation

Thermal response time is an important parameter for the control of fast reactors. Modern thermal hydraulic codes allow for the modeling of transient responses and can also be used to understand the dominant factors that affect them. However, simulations can be computationally expensive, particularly for performing parametric analyses of how thermophysical properties affect transient behavior. Here, we present a method for using linear stability analysis to estimate thermal response time and determine the key parameters that affect transient behavior without performing a forward simulation. The approach can also be used to corroborate simulation results and is tested against simulation results produced with a 2D finite difference model. The results show that this approach produces time-dependent temperature profiles that are within 2 × 10−5–0.1% of the numerical results for a single node perturbation. Changes in temperature have the greatest effect on thermal response time, followed by changes to thermal conductivity.

Improvement of the delayed neutron precursor transport model in RELAP5 for liquid-fueled molten salt reactor

The Liquid-Fueled Molten Salt Reactor (LF-MSR) with high-temperature molten salt is one of the Generation IV nuclear power systems. One of the significant differences between the LF-MSR and the Pressurized Water Reactor (PWR) is that the delayed neutron precursors (DNP) circulate in the primary loop of the LF-MSR and leads to different neutron kinetics between LF-MSR and PWR. Consequently, a system code for PWR is not applicable to LF-MSR, and the safety analysis code RELAP5-TMSR is modified by adding a one-dimensional DNP transport model to improve its applicability to LF-MSR. A second-order Godunov method is adopted in this 1-D DNP model. Then the improved code is tested with experimental benchmarks from Molten Salt Reactor Experiment (MSRE) designed and operated by Oak Ridge National Laboratory (ORNL) and the results show good consistency. Moreover, the modified RELAP5-TMSR code is applied to analyzing transient characteristics of the single-fluid Molten Salt Breeding Reactor (MSBR) so that the applicability of the modified RELAP5-TMSR code is further verified. It is concluded that the one-dimensional DNP transport model can describe effectively the movement of the DNP and the improved RELAP5-TMSR code is suitable for modeling and simulation of reactor transient responses in LF-MSR.

Three-dimensional modeling of ground-airborne transient electromagnetic responses of typical models based on the finite difference approach

Ground-airborne transient electromagnetic (GATEM) methods combine the advantages of ground TEM and airborne TEM, which can simultaneously fulfill the requirements of detection depth and work efficiency. In this study, the GATEM responses of typical models were numerically modeled using the finite-difference time-domain (FDTD) approach. The traditional FD approach of TEM uses the upward-continuation boundary condition at the surface of the earth but does not model complex terrains with an air layer. In this study, the FDTD approach was used to directly mesh and calculate the air layer. Specifically, based on the quasi-static conditions of the electromagnetic field and the frequency spectral features of the transmitting current waveform, the choice method for obtaining the fictitious permittivity in the air layer was studied, and the stability problem in the calculation of the air layer was addressed. The convolutional perfectly matched layer boundary conditions were used at the air and underground boundaries to improve the accuracy of the solution in the late field. Moreover, the results of this approach were compared with the analytical solution and the results of other algorithms, and the accuracy and reliability of the approach were verified. Next, this approach was used to perform three-dimensional forward simulations on the GATEM responses of typical models such as the 3-D body model, rugged topography model, and low-resistivity overburden model. The modeling results show that the GATEM response is significantly affected by flight altitude in the early stage, whereas the late response is less affected by the flight altitude. The sensitivity of the GATEM response was smaller than that of the ground TEM. Signal reversal is observed in the ∂Bz/∂t response curve under the influence of a hill. However, the influence of the hill can be treated as a background field in the late period. The ∂Bz/∂t curve observed above the goaf is higher than that without the goaf, but the difference between them will be reduced due to the influence of the low-resistivity overburden and measurement noise.

Static and dynamic NURBS-based isogeometric analysis of composite plates under hygrothermal environment

In this paper, a computationally efficient isogeometric plate model, employing nonpolynomial shear deformation theory (NPSDT), for static and dynamic analysis of laminated and sandwich composite plates under hygrothermal environment is presented. Transient and steady-state response using Rayleigh damping model and fast Fourier transformation of transient response have also been obtained for the hygrothermal environment. The non-uniform rational B-splines (NURBS) based formulation has been considered, which attribute only five-degree of freedom and satisfies the stringent continuity requirement of the NPSDT model (C1-continuity) without any additional variables. A total Lagrangian approach in conjunction with Hamilton’s principle is utilized to formulate the governing equations for thermal bending and subsequent dynamic analysis of multilayered composite plates. To model stress stiffening effect due to hygrothermal load, both von Kármán and Green–Lagrange strain displacement relations are incorporated and obtained solutions are compared. It has been shown that at higher temperature (around one fourth of the critical buckling temperature), the consideration of Green–Lagrange strain relationship for modeling stiffening effect due to hygrothermal load is important for better accuracy. Further, it has been shown that bending strip is essential in case of higher-order shear deformation theory (HSDT) to get more accurate solution. In addition, the obtained transient damped/undamped solutions may be used to get the natural frequency from their FFT solution.

Significance Level and the Strength of Test Shift Through the Finite Rate of the Transient Response

A significance level and the strength of test shifts are studied then the error function as a transient response model of logical gate is used for testing of statistical hypothesis with Neumann-Pearson criterion. Shifts are rated for Rayleigh accumulated distributions. The generalized signalto-noise ratio is used as one of the variable parameters. The paper reveals that the finite slope of the transient response curve of logical gate results in a type I error increase. The significance level lock leads to bottom of critical region increase and the strength of test decrease in return. The twofold increase of the slope of the transient response curve leads to both the type I error and the bottom of critical region and the strength of test shifts decrease about 12 dB. The twofold increase of generalized signal-to-noise ratio causes the rise of the maximum displacement of a test power functions more than 3 dB up. As this takes place the extremum abscissa is diminished.

Hybrid model for the damped transient response of giant dipole resonances

We suggest the hybrid model for the description of the dipole spreading widths, in which the strength function is built on the one-phonon strength distribution folded with the energy-dependent Lorentzian. Its energy dependence is brought about by (i) the energy-dependent smearing parameter and (ii) the energy-dependent shift of the one-phonon states. These variables are estimated by means of the two-phonon density, provided by a modified Fermi gas model with uniformly spaced states, and with the aid of the weak constant interaction between the one-phonon states and the two-phonon states, considered as background states. Based on calculated one-phonon states, the model is analytically solvable. To explore the validity of the model we analyze the properties of the ${1}^{\ensuremath{-}}$ spectrum in $^{206}\mathrm{Hg}$, $^{206}\mathrm{Pb}$, and $^{210}\mathrm{Po}$ nuclei. Our results demonstrate that the description of the decay widths within the latter approach is in good agreement with that obtained in the quasiparticle random phase approximation, by means of the random distribution of the coupling between microscopic one-phonon states and two-phonon states, generated by the Gaussian orthogonal ensemble distribution.

Transient response of functionally graded carbon nanotubes reinforced composite conical shell with ring-stiffener under the action of impact loads

The mathematical model of transient response of functionally graded carbon nanotubes reinforced conical shell with ring-stiffener is derived. The deformation state of the conical shell is described by the Reddy higher-order shear deformation theory. The deformation of the isotropic ring-stiffener is described by the Euler-Bernoulli hypotheses. The Rayleigh-Ritz method is used to analyze the eigenmodes of the nanocomposite structure. Displacements projections and rotations of middle surface normal are the main unknowns of the problem.The mathematical model of the structure transient response is obtained as the linear dynamical system with respect to generalized coordinates. The assumed mode method is used to obtain this dynamical system.The influence of the type of carbon nanotube composite reinforcement on the amplitudes of the transient responses is analyzed. As follows from the numerical simulations, the top ring-stiffener significantly decreases the amplitudes of the transient response of the nanocomposite structure.

A new nonlinear finite element model for transient dynamic response of a micro composite plate embedded with micro SMA wires considering the size effects

In this research, a nonlinear dynamic analysis of micro plate containing micro shape memory alloy (SMA) wires, taking into account the material and geometric nonlinear effects and also considering the instantaneous changes of martensitic volume fraction (MVF) in different points of the micro plate, has been investigated. In this study, using the first-order shear deformation theory (FSDT) and applying Hamilton's principle, the governing equations of micro plate are extracted such the kinematic equations of micro SMA wires are coupled with governing equations. In this regard, von Karman nonlinear strain-displacement relation is used to consider large displacements and the model proposed by Hernandez and Lagoudas is employed to model the pseudoelastic behavior and also to capture the size effect of the SMA wires at micro scale. The modified couple stress theory is also employed to consider the size effect on the matrix material of micro plate. In addition, it is assumed that the micro wires are arranged in FG forms in the direction of the thickness of the micro plate. Using the return mapping algorithm and nonlinear finite element method, the governing equations of motion, are solved. In the results section, the study of parameters such as size effects, different boundary conditions, taking into account nonlinear strain field, diameter change and type of arrangement of micro SMA wires, length scale factor and thickness of micro plate, have been implemented. To evaluate the validity of the present work, some of the results are compared with the articles available in the literature. New results show that the bigger diameter of the micro SMA wires (considering the total volume fraction constant) and the smaller length scale factor, the higher damping ratio of the micro plate is obtained. Also, the vibration damping ratio increases when more micro SMA wires are arranged in form.

Transient aeroelastic response of a rotor on a sea-based oil rig during engagement operations

An aeroelastic simulation of a helicopter rotor on a sea-based oil rig during engagement operations is investigated to explore the influence of the location of the rotor and the geometry of the superstructure on the transient aeroelastic response. The transient aeroelastic response model of the rotor on the sea-based oil rig during the engagement is derived and validated by the test data. The flow field on the deck is obtained by using the CFD method. Parametric investigations illustrate that the location of the rotor and the geometry of the superstructure have significant influence on the maximum negative displacement of the blade tip. When the inflow angle is 0° and the inflow speed is 30 m/s, the change of the maximum blade tip deflection is more than 190%. By changing the geometry of the superstructure at 30 m/s and 240° inflow, the maximum blade tip deflection can be reduced by 29.7%. Optimizing the location and the shape of the superstructure is an effective means to reduce the risk of the blade touching the fuselage or the deck.

Transient response modeling of reactant concentration in polymer electrolyte membrane fuel cells during load change

ABSTRACT This paper outlines a semi-empirical model to account for the transient response of Polymer Electrolyte Membrane Fuel Cells (PEMFC) during load changes. In this work, we investigated the voltage undershoots of the PEMFC system with a current step-up given as the input. The dynamic response of PEMFC during stepwise load changes is a vital factor that indicates cell performance. We present a model based on mass balance equations, various transport phenomena, and experimental conditions for these voltage undershoots. This model’s response highlights the impact of reactant starvation inside the fuel cell stack during step increase in current. A single fuel cell is divided into two domains to analyze the availability of reactant gases. The model can anticipate the impact of different operating conditions on the magnitude of voltage undershoots. Validation of the model with experimental data resulted in a maximum relative error of 4.59%, with the goodness of fit in the range of 0.96 to 0.99, making the model statistically significant.

Modal identification using bandpass filters based on an ARX model of transient response

The interarea modes of a power system can be identified from a transient response in the frequency data of the phasor measurement units during a power system event. An effective impulse response of the modes can be obtained from the transient response, which contains measurement noise. In this paper, a modal identification method that is insensitive to the measurement noise is proposed using an autoregressive exogenous (ARX) model and bandpass filters. To remove the noise, the effective impulse response is filtered through a combined system of bandpass filters with narrow bandwidths centered on the oscillation frequencies of each mode. Modal identification is fulfilled by estimating the coefficients of the ARX model from the filtered impulse response. The identification accuracy of the proposed method is compared with that of the Prony method with singular value decomposition and discrete Fourier transform method. First, the identification accuracy of the three methods is investigated through simulations on modal spacing and measurement noise. Next, an IEEE 39-bus system is simulated to compare the identification accuracy of the three methods. Finally, the feasibility of the proposed method is demonstrated by identifying interarea modes of power systems in North America from transient responses of their frequency data.

Meshfree model for earthquake-induced transient response in a porous seabed

The earthquake-induced seabed instability is one of critical issues that need to be considered in the offshore structure design procedure. However, the investigations of the earthquake-induced seabed behaviour are limited. Most previous studies regard to the seabed response are adopting the traditional mesh-based method (such as finite element method). In this study, to overcome the drawbacks existing in mesh-based methods (for example, time-consuming and mathematical sophistication), a meshfree method is adopted to predict the soil response under the Japan 311 earthquake, based on the “u−p” approximation. The numerical results conclude that the earthquake-induced transient response, including the acceleration and the pore pressure were amplified from the top to the bottom of the seabed. The high values of the degree of saturation lead to a large magnitude of the pore pressures, while the amplification for the seismic wave become slightly extensive as the soil permeability increases.