Transient Simulation Method Research Articles

A generalized alternating direction implicit method for transient thermal simulation of 2-D structures with locally refined grids

In this article, a generalized alternating direction implicit (ADI) method for transient thermal simulation of two-dimensional structures with locally refined grids is proposed. First, a flexible approach is employed to generate the semistructured grids with local refinement. The generalized ADI method is then derived based on these semistructured grids, in which two new directions are added to deal with the grid points in the transition regions. By this means, the ADI scheme is successfully extended to handle the transient simulation of objects with locally refined grids while maintaining the property of linear complexity in computation. The accuracy and high efficiency of the proposed method are verified by several typical examples.

Voltage Stability Analysis of Power System with Photovoltaic Power Plant

Photovoltaic power plants usually do not provide reactive power output; hence the application of large photovoltaics in power systems will decrease the voltage stability level of the power system. Capacitor banks can provide reactive power to compensate the photovoltaic plants; therefore, capacitor banks can overcome the reactive power deficiency of photovoltaic plants. However, the effect of capacitor bank installation on the system’s voltage stability is unknown. Therefore, the research aims to investigate whether installing a capacitors bank can restore the level of system voltage stability. The study employs the method of Voltage Stability Margin and transient stability simulation to the IEEE 9 bus system. The IEEE 9 bus system is modified where one generator of the system is replaced with a photovoltaic plant, and a capacitor bank is also installed. The study results show that the modified system voltage stability level is lower than the original system. When the capacity of the capacitor bank is increased to the maximum allowable value, the voltage stability level rises. However, it is still unable to be restored to its original value.

Detection of former goaf and analysis of deformation characteristics of overburden in Dameidong coal mine

In order to analyze the deformation of the old goaf in Dameidong Coal Mine and its influence on the surrounding rock and soil layer, it provides guidance for the prevention and control of geological disasters in the region. In this paper, the transient electromagnetic method and numerical simulation method were used to study the deformation law of the overlying strata in the mining area. The results of transient electromagnetic detection showed that the subsidence area of the goaf in Dameidong Coal Mine was within the range of the elliptical water-rich area, and the average buried depth of the goaf was expected to be 90 m. The model was established by discrete element numerical simulation to study the variation law of mining overburden rock. The results showed that the stress change in coal mining was mainly reflected at both ends of the goaf, which was a stress concentration phenomenon. Overburden rock deformation changed with the mining process. The stress concentration area and the displacement change area were highly coincident, consisted with the displacement monitoring map, showing a “U”-type distribution. The results proved that the numerical simulation results do have theoretical guidance for mining subsidence control.

Investigation on the Influence of Flap Valve Area on Transition Process of Large Axial Flow Pump System

The large axial flow pump systems used in coastal pump stations are often required to add flap valves to the gates to improve the quality of the transition process. However, due to the unclear mechanism of the additional flap valve on the transition process of the large axial flow pump system, there are many difficulties in the design and application of this feature. In this paper, six kinds of flap valves with different areas are designed. On the basis of the secondary development of the Flomaster software, the transient simulation method is used to study the impact of flap valves with different areas on the large axial flow pump system synchronous start-up process, the asynchronous start-up process, the synchronous stop process and the asynchronous stop process. The research results show that when the AOF is less than 38% Ag during the asynchronous startup, increasing the AOF can significantly improve the shunt ability of the flap valve during startup. However, in the process of asynchronous starting, the working capacity of the flap valve is less affected by the AOF. During the asynchronous shutdown process, the additional flap valve can effectively delay the attenuation of the LAPS flow and reduce the instantaneous head and power. However, when the AOF reaches 38% Ag, further increasing the AOF has no obvious gain in reducing the maximum instantaneous head and power of the LAPS. When the AOF increases from 38% Ag to 49% Ag, the maximum instantaneous head and the power of the LAPS only decrease by 2.7% and 1.4%, respectively.

Novel Parallelization of Discontinuous Galerkin Method for Transient Electromagnetics Simulation Based on Sunway Supercomputers

A novel parallelization of discontinuous Galerkin time-domain (DGTD) method hybrid with the local time step (LTS) method on Sunway supercomputers for electromagnetic simulation is proposed. The proposed method includes a minimum number of roundtrip (MNR) strategy for processor-level parallelism and a double buffer strategy based on the remote memory access (RMA) of the Sunway processor. The MNR strategy optimizes the communication topology between nodes by recursively establishing the minimum spanning tree and the double buffer strategy is designed to make communication overlapped computation when RMA transmission. Combining the two methods, the proposed method achieves an unprecedented massively parallelism of the DGTD method. Several examples of radiation and scattering are used as cases to study the accuracy and validity of the proposed method. The numerical results show that the proposed method can effectively support 16,000 nodes (1,040,000 cores) parallelism on the Sunway supercomputer, which enables the DGTD method to solve the transient electromagnetic field in a very short time.

Combined transient 3D simulation and experimental methods to assess a slow heat-up curve used to dry a refractory concrete

Explosive spalling is a major concern when drying refractory concretes. For safety, empirically defined overestimated slow heat-up curves are used in industry. Polypropylene fibres reduce spalling; however, they are inconvenient for certain castables due to properties deterioration, such as slag penetration. There is neither a generally accepted methodology to define monolithic refractories dry-out schedules nor agreement about a mathematical model to predict spalling phenomena. This paper presents original numerical and experimental results of castable drying investigation using slow heating. Modifications in experimental methods were made to reproduce refractory lining boundary conditions. A conservative fully implicit finite volume method in three-dimensions was developed to predict pressure and moisture migration. The influence of the methods used to characterize the properties needed for the mathematical model was discussed. The combined analyses suggest that the first holding time used was not productive for drying; however, its effect on curing must be reviewed.

Electromechanical transient simulation model of low frequency flexible transmission system based on modular multilevel matrix converter

Low frequency AC transmission has broad prospects in the future power system. How to establish its electromechanical transient simulation model and provide basic research means for its adaptability analysis after connecting to the large power grid is an urgent problem to be solved. Based on the existing electromechanical transient simulation methods, the mathematical model of modular multilevel matrix converter (M3C) is simplified, and an electromechanical transient simulation model composed of virtual DC circuit and equivalent AC circuit is proposed. On this basis, the power and voltage controller is designed according to the power decoupling characteristics of M3C. Further considering the operation requirements of the offshore wind power transmission system through low frequency AC transmission, an island control is designed to make M3C have the ability of passive control. Numerical examples verify the effectiveness of the proposed simulation model, which can effectively respond to short-circuit faults and power loss. This model can better meet the calculation requirements of large power grid simulation.

Modeling and simulation for transient thermal analyses using a voltage-in-current latency insertion method

This article presents a modeling and simulation method for transient thermal analyses of integrated circuits (ICs) using the original and voltage-in-current (VinC) latency insertion method (LIM). LIM-based algorithms are a set of fast transient simulation methods that solve electrical circuits in a leapfrog updating manner without relying on large matrix operations used in conventional Simulation Program with Integrated Circuit Emphasis (SPICE)-based methods which can significantly slow down the solution process. The conversion from the thermal to electrical model is performed first by using the analogy between heat and electrical conduction. Since electrical inductance has no thermal equivalence, a modified VinC LIM formulation is presented which removes the requirement of the insertion of fictitious inductors. Numerical examples are presented which show that the modified VinC LIM formulation outperforms the basic LIM formulation, both in terms of stability and accuracy in the transient thermal simulation of ICs.

Optimization of Process Parameters for ESR Waspaloy Superalloy by Numerical Simulation.

A transient numerical simulation method is used to investigate the temperature field, velocity field, and solidified field of large-size Waspaloy superalloy during the electroslag remelting (ESR) process. The effects of melting rate, filling rate, and thickness of the slag layer on the molten pool shape and dendrite arm spacing evolution have been discussed. The temperature in the slag pool is high and relatively uniformly distributed, the temperature range is 1690-1830 K. The highest temperature of the melt pool appears in the center of the slag-metal interface, 1686 K. There are two pairs of circulating vortices in the slag pool, the side vortices are caused by the density difference caused by the buoyancy of the slag, the center vortices are the result of the combined action of electromagnetic force and the momentum of the falling metal droplets. The molten pool depth and dendrite arm spacing increase with the increase of melting rate, but the slag layer thickness and electrode filling rate have little effect on the molten pool morphology and dendrite arm spacing if the droplet effect is not taken into account. Considering the morphology and depth of the molten pool as well as the size and distribution uniformity of the dendrite arm spacing, it is appropriate to maintain the melting rate at 5.8 kg/min for the industrial scale ESR process with the ingot diameter of 580 mm.

Comparison of simulation methods for dynamic internal air distribution in naturally ventilated livestock buildings

Accurate internal air distribution prediction facilitates the analysis of occupant thermal comfort and the control of gaseous contaminants within naturally ventilated livestock buildings (NVLB). However, the dynamic and random change in external wind conditions makes it difficult to predict the air distribution. This study compares three scenarios based on real-time monitored external wind conditions: the quasi-static simulation method with moving average data, the transient simulation method with raw data, the transient simulation method with Kalman filtering, and the continuous fast Fourier transform. The quasi-static simulation was verified for computational efficiency and reliability within different time spans. The simulation results were validated with measurement data in a low-rise stand-alone NVLB surrounding a low-density building complex. The quasi-static simulation results of internal air distribution in oblique wind directions partially agreed with the hourly averaged wind speed measurements and turbulent kinetic energy. Additionally, the quasi-static simulation agrees with the direct transient method for predicting the air distribution within a long-time span. The quasi-static simulation shows promise for the future simulation of internal air distribution in naturally ventilated livestock buildings under dynamic boundary conditions.

Fast and accurate evaluation method of commutation failure in line‐commutated converter‐based high‐voltage direct current systems considering probability characteristics

Line-commutated converter-based high-voltage direct current (LCC-HVDC) systems suffer from commutation failure (CF) when receiving-end AC grid faults occur, which is a major drawback and threatens the security and stability of power systems. This paper presents a fast and accurate evaluation method of CF for the LCC-HVDC systems, considering the CF probability characteristics. Firstly, based on the analysis of the CF probability characteristics from the view of short-circuit impedance, the CF tolerance index (CFTI) and CF vulnerability index (CFVI) are proposed to quantitatively evaluate the LCC-HVDC systems' risk of the possible- and inevitable-occurrence CF, respectively. Secondly, four factors, that is, commutation voltage, fault occurrence time, DC current and firing angle command, are considered to calculate CF evaluation indices (CFEIs) and identify the CF risk area boundaries based on the theoretical analysis. Moreover, the relationships among short-circuit impedance, fault position, and extinction angle are established based on the AC/DC decoupling method, which helps realize the decoupling of multi-factors affecting CF during fault. Compared to earlier methods, this evaluation method combines the advantages of the accuracy of the electromagnetic transient simulation method and the rapidity of theoretical derivation. Finally, the validity and accuracy of the evaluation method are verified in the CIGRE HVDC benchmark model and IEEE 39-bus system.

GPU and CPU-Based Parallel FDTD Methods for Frequency-Dependent Transmission Line Models

Finite-difference time-domain (FDTD) is a popular method utilized for solving frequency-dependent transmission line structures. It is also conveniently applicable to nonuniform wires. The FDTD algorithm discretizes the transmission line problem into a finite number of space-segments and solve for the voltage and current of each segment at every time-step. Therefore, they inherently involve more computations per timestep than conventional terminal based models. In this letter, parallel implementations of a modified FDTD algorithm for a frequency-dependent transmission line problem using multicore CPU and GPU architectures are proposed in order to increase its computational efficiency. Accuracy and performance of the parallel FDTD methods are discussed with examples. The results indicate that a speedup of a few folds compared to serial execution is achieved by the parallel implementation using multicore CPU architecture whereas a massive speedup is achieved by using GPU. The proposed model is also suitable for modelling transmission lines in massively parallel electromagnetic transient (EMT) simulation methods.

Study on vortex flow and pressure fluctuation in dustpan-shaped conduit of a low head axial-flow pump as turbine

In the plain river network area, the constructed axial-flow pumping station is used to generate electricity by reversing as turbine when the upstream water is abundant, which can reduce the environmental pollution caused by coal-fired power generation while making full use of water resources. When the axial-flow pump as turbine (PAT) operates, there are severe flow instability and obvious pressure pulsation in the dustpan-shaped conduit. In this paper, the transient numerical simulation method is used to study the evolution characteristics and pressure pulsation of the vortex in the dustpan-shaped conduit when the axial-flow PAT runs, and the pressure pulsation signal of simulation is compared with the pressure pulsation result of model test. The formation of the spiral vortex rope in the dustpan-shaped conduit is related to the velocity circulation at the impeller outlet and the axial velocity of the fluid. The axial velocity and tangential velocity near the vortex center are close to zero. The inlet of the dustpan-shaped conduit is subjected to the dynamic and static interaction effect of impeller domain and conduit domain. Further downstream, rotor and static interaction effect weakens gradually. As the distance from the impeller increases, the dominant frequency of pressure pulsation changes from 3 times the rotational frequency to 0.5 times the rotational frequency. The dominant frequency of pressure pulsation at the monitoring points near the vortex rope are 0.5 times the rotational frequency, and massive low frequency near the vortex rope are generated by the vortex rope rotation.

EI-NK: A Robust Exponential Integrator Method With Singularity Removal and Newton–Raphson Iterations for Transient Nonlinear Circuit Simulation

In this article, we propose an exponential-integrator-Newton–Krylov (EI-NK) method for transient simulation of large-scale nonlinear circuits. This method aims to address two long-standing problems that affect the performance and robustness of EI in handling nonlinear circuits. First is the numerical instability caused by the singularity in the differential-algebraic equation system. We provide an in-depth analysis of the problem and propose a systematic, algebraic, and sparsity preserving regularization technique to eliminate the unstable modes in the system to be solved. Next, we develop a scheme to enable the iterative Newton–Raphson solution in the EI framework for enhanced nonlinearity handling capability. With the two techniques, we wish to elevate EI’s robustness and performance and make it a competitive alternative to the existing SPICE-type simulators in practical applications.

Numerical study of unsteady flow and cooling characteristics of turbine blade cutback trailing edges integrated with pin fins and film holes

Accurate prediction of the unsteady flow mixing process and its effects on cooling performance in the turbine blade trailing edge (TE) is essential to improving TE cooling designs. This paper used high accuracy transient Scale Adaptive Simulation (SAS) method to investigate the unsteady flow and cooling characteristics of two novel turbine blades cutback TEs under blowing ratios BRs=0.65 and 1.25. The two novel TEs have five rows of pin fins in the cooling slot and two rows of either cylindrical or fan-shaped film holes on the pressure side upstream of the cutback region. The results were compared against those of the baseline TE with only pin fins and the data obtained from Shear Stress Transport (SST) k-ω model.The results revealed that: 1) the coolant issued from upstream cylindrical or fan-shaped holes has significantly disturbed the Brown-Roshko vortices shedding off the lip of the top wall, but only largely reduced the magnitude of normal velocity fluctuation in the cutback region. The alternating vortices in the cutback region are stretched flat. The changes brought to the flow structures are more significant by the fan-shaped holes than the cylindrical holes; 2) Although increasing blowing ratio enhances flow unsteadiness in the cutback region of the three TEs, the differences in the magnitude of velocity fluctuations are much reduced among the three TEs; 3) The TE cutback with fan-shaped holes achieves a higher adiabatic wall cooling effectiveness ηaw on the cutback wall at BR=0.65, and also a lower reduction in ηaw at BR=1.25 than the TE cutback with cylindrical holes; 4) Transient SAS method demonstrates a better agreement of ηaw with the experimental data for the baseline TE on the cutback wall, and higher values of ηaw than the results of the SST k-ω model on the top wall.

Power system solution based on root matching method in FPGA environments

Digital electromagnetic transient simulation is an important means to analyze the operation, planning and control of power systems. Numerical integration algorithm is the core of electromagnetic transient simulation analysis. By analyzing the existing electromagnetic transient simulation methods of power systems, it is difficult to solve the numerical oscillation and decoupling problems, and the root matching method is proposed to solve such problems. From the perspectives of basic component modeling methods and basic simulation algorithms, the disadvantages of mainstream algorithms in solving electromagnetic oscillations are analyzed. Combining the calculation and simulation features in FPGA, the three-phase two-level inverter model of the power system built is verified.

Multi-dimensional performance analysis and efficiency evaluation of paper-based microfluidic fuel cell

As a mainstream power storage and supply device, batteries are continuously upgraded. The microfluidic fuel cell has great development potential, and the paper-based microfluidic fuel cell is the latest achievement of its lightweight, which can be applied in the field of medical and biological detection. In this work, the cell models with various folding forms and unconventional absorption pads are creatively constructed, then the influence mechanism on cell performance is revealed by numerical simulation. Both transient and steady-state simulation methods are employed to monitor the whole process of paper-based microfluidic fuel cell. Conclusions show that the cell performance decreases with the increase of folding angle, the peak power density is as low as 1.71 mW/cm2, and the corresponding fuel utilization is only 2.73%. The changes in the absorbent pad shapes have little improvement on cell performance, thus the most direct way is increasing the absorbent pad volume. Moreover, materials with better water absorption capacity can increase the maximum current density to 28.70 mA/cm2, and the appropriate increase of operating temperature can also increase the peak power density to 2.36 mW/cm2, but the effect on the cell is significantly weakened if the temperature exceeds a certain limit.

Combined Transient 3d Simulation and Experimental Methods to Evaluate a Slow Heat-Up Curve Used to Dry a Refractory Concrete

Combined Transient 3d Simulation and Experimental Methods to Evaluate a Slow Heat-Up Curve Used to Dry a Refractory Concrete

A Novel Electromagnetic Transient Simulation Method of Large-Scale AC Power System With High Penetrations of DFIG-Based Wind Farms

With the ever-expanding deployment of renewable energy sources (RESs), the short-time transients have more significant impacts on shaping the characteristics of large power grids. However, the electro-mechanic transient simulation cannot reflect the short-time transients, while the current electromagnetic transient simulation cannot tackle large power systems due to the huge computational burden. This paper presents a novel simplified electromagnetic transient simulation method for large-scale power systems with high penetrations of doubly fed induction generator (DFIG)-based wind farms. Firstly, a DFIG-based wind generator (WG) model is built to simplify the detailed switching process of power electronic devices as well as reproduce external characteristics to the power system. Secondly, an initialization technique is further adopted using the power flow results, aiming to avoid the long and unnecessary computation process for starting the simulation with traditional methods. Finally, a simulation tool is developed based on the proposed method, and a real power system with 9889 buses and 898 wind farms is simulated. Results show that the simulation can start smoothly with good accuracy. Therefore, the proposed method can be employed in electromagnetic transient simulation of large-scale AC power systems with high penetrations of RESs.

Study on Thermal Damage of Large-Span Ice Shell Structure Based on Thermal-Mechanical Coupling

The large-span ice shell is a novel building style with the aid of inflatable formwork and water-spraying method. Ice material has strong temperature sensitivity, and the ice shell experiences complicated environmental conditions during the operation stage. A thermal-mechanical coupling analysis framework is presented to explore the thermal effect of the ice shell. The transient simulation method for the non-uniform temperature field is established. A thermoelastic damage model for fibre-reinforced ice is derived and the thermal damage analysis method is conducted. Subsequently, the non-uniform temperature field is mapped into the mechanical field of the ice shell structure to carry out the temperature effect and further evaluate the thermal damage. A large-span ice shell built in Harbin Ice and Snow World expounds the applicability of the proposed method in practice. The distribution of non-uniform temperature field on the ice shell is investigated and thermal damage is further studied.