Transient Analysis Simulation Research Articles

HPR1000 pressurizer degassing system design and analysis

In the Hualong-1 Unit (HPR1000), the hydrogen (H2) concentration should be reduced to 15 mL (STP)/kg 24 h before reactor shutdown when the reactor vessel is scheduled to be opened. The traditional degassing method, i.e., letting down the reactor coolant through a chemical and volume control system, will take longer, and its operation is more complicated. To shorten the degassing time and simplify the operation, this paper proposes a pressurizer degassing system design for HPR1000 by applying the pressurizer as thermal degassing equipment. Then, the degassing system optimization analysis is carried out under a full range of steady operating conditions during shutdown, and the optimal size of the flow-limiting orifice plate is obtained. Meanwhile, in order to verify the transient characteristic during the degassing process to ensure operating safety, a dedicated transient degassing program based on an improved non-equilibrium multi-region pressurizer model and a transient degassing model is used to carry out a transient simulation analysis of this process. The transient simulation results show that, under bounding conditions of hot–zero-power operation, during the degassing process, the pressure of the pressurizer decreases by a maximum of 0.038 MPa and the water level increases by 0.016 m above the normal level. As can be seen, both the pressure and water level are within the normal operation band and shall not initiate any safety signal. Meanwhile, the entire transient process lasts approximately 24 min and then enters a stable degassing period. It takes approximately 5.2 h to remove the gas dissolved in the reactor coolant from 35 mL (STP)/kg to 15 mL (STP)/kg. The analysis shows that the pressurizer degassing system designed for HPR1000 is safe, effective, and reliable.

Simulation and experimental study on rope driven artificial hand and driven motor.

Prosthetic hands have the potential to replace human hands. Using prosthetic hands can help patients with hand loss to complete the necessary daily living actions. This paper studies the design of a bionic, compact, low-cost, and lightweight 3D printing humanoid hand. The five fingers are underactuated, with a total of 9 degrees of freedom. In the design of an underactuated hand, it is a basic element composed of an actuator, spring, rope, and guide system. A single actuator is providing power for five fingers. And the dynamic simulation is carried out to calculate the motion trajectory effect. In this paper, the driving structure of the ultrasonic motor was designed, and the structural size of the ultrasonic motor vibrator was determined by modal and transient simulation analysis, which replace the traditional brake, realize the lightweight design of prosthetic hand, improve the motion accuracy and optimize the driving performance of prosthetic hand. By replacing traditional actuators with new types of actuators, lightweight design of prosthetic hands can be achieved, improving motion accuracy and optimizing the driving performance of prosthetic hands.

Construction and simulation of a joint scale model for power electronic converters based on wavelet decomposition and reconstruction algorithms.

In power electronics systems, system design and operation often involve multiple time and space scales, ranging from nanosecond switching dynamics to hour-level system operation behavior. Due to the complexity of these systems and the rise of wide-gap semiconductor technology, a series of multi-scale phenomena have emerged that are difficult to ignore. The high frequency of switching operations makes multi-scale effects particularly significant, including the fast dynamic response of the power loop, EMI, and heat conduction problems. They are key factors that must be considered in the design to ensure the efficient and reliable operation of power electronic devices. This study proposes the construction and simulation of a joint scale model for power electronic converters based on wavelet decomposition and reconstruction algorithms to address the multi-scale phenomenon and limitations of single-scale power electronic converters. Firstly, a joint scale model for power electronic converters at both macro and micro-scales was established, targeting both single-scale models and simple combinations of multiple scale models for power electronic converters. The traditional single-scale model is sufficient to describe the average behavior of the converter, but it has serious limitations in capturing fast transient processes and high-frequency switching behavior in power electronic systems. These limitations often manifest themselves when there is a need to capture fine timescales of detail. By transforming between the time domain and the frequency domain, wavelet decomposition enables the model to capture both macroscopic average characteristics and microscopic transient dynamics. The wavelet reconstruction algorithm can simulate all kinds of fast changes in the actual working process more accurately and compress irrelevant information while retaining key signal features, so as to optimize the simulation performance of the model. Secondly, this algorithm is used to analyze BC in short time scale. Finally, the short time scale characteristics of power electronic converters are analyzed. Experimental results show that the fusion of wavelet decomposition and reconstruction algorithm enhances the accuracy of the power electronic converter model and improves the performance of the system. The model achieves an error reduction of nearly 3% in the calculation step size of 10-7s, which has a significant impact on the high precision requirements of high-frequency operations. In addition, the optimal calculation step size of 8×10-8s achieves an error reduction of more than 14%, making an important contribution to the transient analysis and fine structure simulation. The wavelet algorithm can improve the accuracy of multi-scale modeling in power electronic system and reduce the simulation time. The reduction of error not only shows the improvement of the accuracy of the model, but also shows its practical significance in the design and test of the actual power electronic system. The reduction in error reveals the ability to more accurately predict and mitigate potential performance problems in matching tests with actual hardware, as well as its ability to adapt to emerging wide bandgap semiconductor materials and structures.

Precise modeling of lithium-ion battery in industrial applications using Walrus optimization algorithm

This research article demonstrates how to get a precise lithium-ion battery (LIB) model using one of the artificial intelligence algorithms called the Walrus optimization algorithm (WaOA). The model's accuracy affects several transient and dynamic analysis simulations, which are carried out for power systems, electric vehicles, and many transportation applications. The LIB model may have one, two, or three resistance-capacitance (RC) models, signifying the complexity of the optimization challenge. Therefore, the WaOA is used to minimize the cost function that relies on an integral square error criterion. This criterion calculates the error between the estimated and experimental voltages. The proposed method is validated under several conditions, taking into account load variation, battery degradation, temperature fluctuation, and different RC models. The numerical results of the WaOA method are compared with their experimental results for a 2.6 Ah LIB. In addition, the proposed WaOA model has undergone validation alongside numerous optimization algorithms-based models. It is worth noting that utilization WaOA with battery modeling stands as a reliable tool for attaining precise model.

Design of a new cantilevered cylindrical traveling wave ultrasonic motor

In this paper, a composite excitation method is used to optimize the design of an existing cantilevered cylindrical ultrasonic motor to avoid vibration interference. Modal and transient simulation analysis of the stator structure was carried out by the finite element method. Optimized stator structure is simpler than the original motor. Simulation analysis results show that the circumferential amplitude is increased by more than 35% with 55.7% reduction in ceramic usage.

Transient Simulation Analysis of Needle Roller Bearing in Oil Jet Lubrication and Planetary Gearbox Lubrication Conditions Based on Computational Fluid Dynamics

The transient lubrication conditions of rolling bearings are different in gearboxes and bearing testers. It has been observed that samples of qualified rolling bearings tested in rolling bearing testers often fail and do not meet lifespan requirements when employed in other lubrication conditions. This may be caused by different factors affecting the bearing in testing and applying lubrication. Needle roller bearings were selected for this study to investigate the causes of this phenomenon in terms of lubrication. Based on the computational fluid dynamics (CFD) method, fluid domain models for the same type of rolling bearings with different lubrication conditions were established. The transient flow fields of rolling bearings with oil jet lubrication in a tester and splash lubrication in a planetary gearbox were simulated. The air–oil transient distribution of rolling bearings in two kinds of lubrication was analyzed. The results indicate that the rotational speed significantly affected the oil jet lubrication of the needle roller bearing. The average oil volume fraction rose by 0.2 with the increase in the bearing speed from 1200 r/min to 6000 r/min and by 0.06 with the increase in the oil jet velocity from 8 m/s to 16 m/s. The splash lubrication of the bearings in the planetary gearbox was directly related to the immersion depth of the rolling bearings in the initial position. Meanwhile, the splash lubrication of the bearings was also affected by other factors, including the initial layout of the planetary gears. The increase in speed from 1200 r/min to 6000 r/min made the average oil volume fraction of splash lubrication decrease by 4.4%. The average oil volume fraction of the bearings with splash lubrication was better than that with oil jet lubrication by an average of 41.9% when the bearing speed was in the low-speed stage, ranging from 1200 r/min to 3600 r/min. On the contrary, the bearings with oil jet lubrication were better than those with splash lubrication by an average of 31.8% when the bearing speed was in the high-speed stage, ranging from 4800 r/min to 6000 r/min.

Simulation of the fluid dynamic and thermal behavior of an experimental passive cooling system of photovoltaic panels

Solar energy capacity has increased significantly globally, with values above 800 GW produced by different systems. Among these, PVT panels can generate either electricity, heat, or both. As these systems present various issues associated with excessive temperature increases, cooling systems have been developed to control the temperature using fluids such as water. The article uses previous data from the Technologic Institute of Sonora, which analyzed various cooling device configurations and selected the best two options (B1 and B4) based on the panel efficiency. Using the boundary conditions and the predicted streamlines, a simulation was made in CFD programs, determining the correct parameters to replicate the system fluid dynamics. Several simulations were carried out using different turbulence models. After comparing the temperature contour diagram and the streamline, it was obtained that the k-ω turbulence model best describes the fluid's behavior. The transient analysis simulations allow us to determine that the B1 configuration delivers the best cooling effect as it presents the most homogeneous temperature profile. BIAS and RMSE were calculated to validate and contrast the results obtained experimentally, obtaining values of 0.8675 and 1.8981, respectively.

Simulation Analysis of a Sandwich Cantilever Ultrasonic Motor for a Dexterous Prosthetic Hand.

Currently, the driving motor used in a dexterous prosthetic hand is limited by the driving principle, and it has the characteristics of a complex structure, slow response, low positioning accuracy, and excessive volume. There are special requirements in terms of quality and quality, and traditional motor drives have greatly affected the progress of prosthetic robots. A motor (ultrasonic motor) has been developed over more than 30 years. It has the advantages of a small size, small mass, simple structure, accurate positioning, high power density, and fast response time, which is enough to improve the driving mechanism performance of the prosthetic hand with a connecting rod. In this paper, the structural characteristics of the prosthetic hand will be analyzed, and the modal analysis, harmonic response analysis, and transient analysis simulation of the longitudinal vibration linear motor stator used in the prosthetic hand with a connecting rod will be carried out in order to provide preliminary preparation for the feasible design and manufacture of the size of the ultrasonic driver structure used for the prosthetic hand with a connecting rod.

Encoding Time Series as Images: A Robust and Transferable Framework for Power System DIM Identification Combining Rules and VGGNet

Digital simulation is very important for the safe and economic operation of power systems. Power system dominant instability mode (DIM) identification is an intractable problem in large-scale transient simulation analysis, because transient instability and short-term voltage instability are often intertwined. Deep learning is a promising way to achieve accurate DIM identification. By encoding time series as images, this paper proposes a robust and transferable DIM identification framework combining curve filtering rules and a dual-channel VGGNet (DCVGG) image recognition network. The curve filtering rules can effectively reduce the redundancy of massive time-domain features, the model parameters, and training time. A skillfully designed method is proposed to encode time series as images and improve the feature extraction capability of convolutional neural networks. The proposed DCVGG network is capable of processing rotor angle and voltage images simultaneously and has the potential to become a pre-trained model, making transfer learning between different power systems possible. Case studies conducted on 8-machine 36-bus system and Northeast China Power Grid demonstrate the proposed framework has better performance, scalability, robustness, and transferable ability than contrastive machine learning methods.

Analysis of Automatic and Fast Switching Scheme for Closed Loop Point of the Power Grid in the Baotou Area

The influence of the access of different power source unloop points on the power grid is summarized. Transient simulation analysis is carried out on voltage fluctuation, power flow fluctuation, short-circuit current, and voltage unbalance degree after the power grid is closed. The feasibility of the fast-switching device configured on the distribution network side is demonstrated, and the possible problems of the fast-switching device in the operation process and their influence on the power grid are analyzed. Ultimately, it lays a theoretical foundation for researching automatic and fast-switching devices under specific operating modes.

Numerical simulation and testing of laser-MIG hybrid-welding angle-structure sheets.

Numerical simulation and experimental investigation of laser-MIG hybrid angle-welding low-carbon 1.5-mm-thin SPCC steel sheets are presented in this work. The transient simulation analysis provides an access to the thermal-fluid phenomena prediction by employing a hybrid three-dimensional heat source model. Special attention is paid to the melt dynamic behaviors within the triangular molten pool affected by the Marangoni convection. The simulation results show that the temperature and its gradient distribution are symmetrical with respect to the laser beam, which is validated well by the experimental study. The microstructure of the welded joints was analyzed by scanning electron microscopy and transmission electron microscopy. The results show that the cross-section microstructures of welded joint are mainly composed of the weld zone, narrow heat-affected zone, and substrate. The semielliptic-like molten pool shape is consistent with that of the simulated results. The finer microstructure in the weld bead results from the rapid cooling rate of laser welding confirmed by the FEM calculation. The columnar and equiaxed dendrites are formed in the peripheral and central region of the molten pool, which is beneficial for the improvement of the microhardness.

Single phase to ground arcing fault identification based on wavelet packet energy

With the increasing proportion of cable lines in the distribution network, the capacitance current in the system increases, which leads to the single phase to ground arcing fault in the distribution network. However, at present, there is less research on single phase to ground arcing fault, and the type of grounding fault is always assumed to be metallic or resistive grounding, and the arcing ground fault is not identified in time, which leads to further expansion of the fault. In this paper, the transient simulation analysis of a single phase to the ground is carried out, and a new method to distinguish arcing ground fault from metal grounding fault using wavelet packet energy is proposed, which solves the problem of fault type identification. Through a large number of simulation data analyses and practical verification, it is shown that the method is not affected by the time of fault occurrence and neutral grounding mode, and has a strong anti-interference ability and high reliability.

An approach on nonlinear integration of MMC to linear model of ROPS in transient analysis

SummaryThe modular multilevel converter (MMC) is a novel prospective multilevel converter topology for high‐voltage or high‐power applications. This paper presents the 3‐ model integrated into a linear model in transient analysis and the design of current controller for MMC. This paper analyzes the control interactions of MMC on nearby turbine generator. The eigenvalue analysis is used to evaluate the impact of different controller modes of MMC. The impact of converter control with nonlinear switches is analyzed through the transient simulation. The eigenvalue analysis and controller design are carried out on a linear model, and the transient simulation analysis is performed on both the D‐Q model and a three‐phase model of MMC using MATLAB‐Simulink. The results show that the transient simulation of three‐phase model on the proposed approach is consistent with the transient simulation of D‐Q model. Also, the transient simulation results show a satisfactory response with the current controller parameters of the MMC at various operating cases. To validate the results of MATLAB‐Simulink model, the proposed system is implemented in hardware‐in‐the‐loop (HIL) simulation with an integrated subsystem built in two real‐time simulators. The subsystem of mathematical model is implemented in dSPACE, and the subsystem of 3‐ MMC with controller is implemented in Typhoon. The HIL simulation results show a satisfactory response and consistent with MATLAB‐Simulink model results.

Analysis and Preliminary Design of Primary Heat Exchanger Failure Testing Facility for Lead-Cooled Fast Reactors

This paper presents an assessment aimed at evaluating primary heat exchanger (PHE) failure of the Westinghouse Electric Company Lead-cooled Fast Reactor (LFR) and at designing a facility for testing phenomena involved in such failure. The system thermal-hydraulic code RELAP5/MOD3.3 was used to develop a transient analysis simulation at reactor scale. Because of RELAP5/MOD3.3’s inability to mix working fluids, the steam injection effect was evaluated using the SIMMER-III code. The limits and strengths of both codes are highlighted throughout the paper. The reactor-scale steady-state results are in good agreement with the nominal operating condition. The transient results show that lead pool surface level variation and primary system pressurization during the PHE failure event are limited. The PHE failure testing facility was characterized, and a preliminary layout was developed. A separate-effects transient inside the vessel was analyzed with SIMMER-III and RELAP5/MOD3.3 runs. The simulation outcomes have provided useful data to inform subsequent design stages for the test facility. Different configurations of the facility have been assessed, highlighting the strengths and weaknesses of each design. The most important issue was identified to be lead pool swelling, reaching the vessel’s lid and blocking the pressure relief vent. This poses a safety hazard that must be addressed and has been raised for resolution in subsequent design stages. The so-called V4 configuration is suggested as a starting point for further improvement of the facility. Furthermore, a smaller failure opening and lower lead level in the vessel are suggested.

Protection scheme for multi-terminal HVDC system with superconducting cables based on artificial intelligence algorithms

This paper presents the development of a novel data-driven fault detection and classification scheme for DC faults in multi-terminal HVDC transmission system which incorporates superconducting cables and modular multi-level converters. As the deployment of superconducting cables for bulk power transmission from remote renewable generation is progressively increasing in the future energy grids, many fault-related challenges have been raised (i.e., fault detection, protection sensitivity/stability). In this context, the applications of Artificial Intelligence techniques have started to be considered as a powerful tool for the development of robust fault management solutions. The proposed artificial intelligence-based method utilizes local current and voltage measurements to detect and classify all types of faults on the DC cables and DC buses, without the requirement of measurements exchange among different DC substations. The performance of the proposed scheme has been assessed through detailed transient simulation analysis and the results confirmed its effectiveness against a wide range of fault conditions (i.e., various fault types, fault locations and fault resistances). Furthermore, the feasibility of the developed scheme for real-time implementation has been validated using real-time software in the loop testing. The results revealed that the proposed algorithm can correctly, and within a very short period of time (i.e. less than 2 ms) detect and classify the faults within the protected zone and concurrently remain stable during external faults. Additionally, the generalization capability of the algorithm has been verified against influencing factors such as the addition of noise, highlighting the robustness of the presented scheme.

A comprehensive Thermo-hydraulic neutronic and safety analysis of a 100MWth pebble bed reactor core

The HTMR100 is a 100MWth High Temperature Gas-cooled Reactor (HTGR), which is helium-cooled and graphite moderated. This reactor is of the Pebble Bed type featuring a Once-Through-Then-Out (OTTO) fuelling scheme, this cycle was chosen for the simplicity of the fuel handling system.The HTMR100 Pebble Bed Reactor (PBR) has a core volume of 27.73 m3 (core diameter 2.6 m, core height ∼ 5.2 m) which results in an average core power density of 3.6 MW/m3. This reactor utilizes uranium dioxide fuel (UO2) at a U-235 enrichment of 10 wt% and 10 g of heavy metal (total uranium) per Fuel Sphere (FS). Although there are various types of fuel options that can be utilized in the HTMR100 reactor, ranging from LEU to mixtures of Th/LEU, Th/HEU and Th/Pu, this study will only focus on LEU in the form of UO2 fuel.This study investigates the neutronic and thermal–hydraulic modelling of the 100MWth HTMR100 at equilibrium (100% power with the control rods situated at the nominal position for a core having an equilibrium fuel burnup profile) and at transient/accident conditions. The purpose of the investigation is to determine if the maximum fuel temperature remains below the set limit of 1600 °C during a design-base accident event that is defined as a Loss of Coolant Accident (LOCA).The equilibrium core was simulated using the Very Superior Old Programs (VSOP99) suite of codes to obtain burnup results. The transient behaviour of the core was modelled by a code called Multi-group Time Dependent Neutronics and Temperatures (MGT). MGT assesses the dynamic transient results of the accident scenarios such as the Depressurized Loss of Forced Cooling (DLOFC), Pressurized Loss of Forced Cooling (PLOFC), Control Rod Withdrawal (CRW) and a Control Rod Ejection (CRE) as well as normal operating transients of which a Load Following (LF) operation is a typical example.The HTMR100 reactor utilizing the enrichment and heavy metal loading as specified does indeed produce the targeted 80 000 MWD/THM burnup for the OTTO fuel cycle. The study also proves that the VSOP99 and the MGT codes do in fact yield similar results for the HTMR100 reactor with regards to fuel centreline temperatures, outer sphere surface temperatures as well as moderator temperatures for the postulated accident scenarios that were analysed. The results also indicate that the design-base transient safety analysis simulations prove that the fuel temperatures remain below the set value of 1600 °C for the oxide-based fuel. A temperature-volume analysis of a DLOFC design-base event shows that only ∼ 2 % of the fuel reaches the higher temperatures of 1500 °C to 1600 °C in a DLOFC event.The beyond-design base events with a very low probability of occurrence do however exceed the set value of 1600 °C but the fuel only exceeds this set limit for short periods of time while the transient occurs. The probability that this will lead to fuel damage should be very small since the time at these high temperatures is short and the volume fraction of the core exposed to these high temperatures is small.

Study on electromagnetic transient numerical simulation of single-phase inverter circuit

With the continuous progress and development of new energy power generation technology, new energy grid and power electronic devices are widely used in power system, and the modeling requirements for electromagnetic transient simulation analysis of power system are higher and higher. Combined with the research status at home and abroad, this paper first analyzes the single-phase inverter circuit model, and establishes the mathematical model of single-phase inverter circuit in different switching states. Based on the stability, accuracy and efficiency of numerical integration algorithm, different numerical integration substitution methods are applied to the mathematical model established in each state of the circuit, and the electromagnetic transient analysis of single-phase inverter circuit is carried out the correctness and feasibility of the experimental results are verified by comparing with the results in Simulink.

Reduced Model of Droop-controlled Converters for Transient Simulation Analysis

In recent years, the transient stability problems encountered by power grids have increasingly attracted interest due to the connection of renewable energy resources. One of the effective methods for studying the transient characteristics of a system is transient simulation analysis. To reduce the simulation time, especially in a system with numerous renewable energy resources, model reduction has been widely employed. However, when a general reduced model is adopted to analyze different transient characteristics, a tradeoff between accuracy and simulation speed emerges. In this study, reduced model selection is implemented to resolve this problem. Considering the droop-controlled converter as an example, this approach allows the transient simulation analysis of voltage, frequency, and power angle characteristics. First, a full-order model of the droop-controlled inverter is formulated. Thereafter, the singular perturbation method is applied to derive different reduced-order models. Then, considering accuracy and simulation speed simultaneously, the most suitable reduced models for transient angle, voltage, and frequency simulation analyses are determined through time-domain simulation comparison. Finally, the simulation results based on Matlab/Simulink are used to verify the correctness of the reduced model selection.

Engineering electronic platinum–carbon support interaction to tame carbon monoxide activation

CO oxidation has been studied for more than a century; however, molecular-level understanding of its activation protocol and related intermediates remains elusive. Here, we present a unified mechanistic and kinetic picture of various electronic metal–support interactions within platinum–carbon catalysts via in situ spectroscopic/kinetic analyses and multi-scale simulations. Transient kinetic analysis and molecular dynamics simulations with a reactive force field provided a quantitative description of the competition between the oxygen association and oxygen dissociation mechanisms tuned by the interfacial charge distribution and CO coverage. Steady-state isotopic transient kinetic analysis and density functional theory calculations revealed a simultaneous shift in the rate-determining step (RDS) from O2* dissociation to O* and CO* and O2* and CO* association. A de novo strategy from the interfacial charge distribution to the reaction mechanism, kinetics/thermodynamics of RDS, and, ultimately, catalytic performance was developed to quantitatively map the above CO activation mechanism with an order-of-magnitude increase in reactivity. The proposed catalytic picture and de novo strategy are expected to prompt the development of theories and methodologies for heterogeneous catalysis.

Vibration and Constitutive Relations of Viscoelastic Cantilever Beam of HTPB Propellant

A cantilever beam test specimen of a viscoelastic material, which is sourced from the hydroxy-terminated polybutadiene (HTPB) propellant, has been made. The traditional experimental modal analysis (EMA) is performed using the SIEMENS TESTLAB software to obtain the first six orders of modal frequencies based on the Poly MAX method, thereby determining the frequency range associated with the frequency domain analysis. The relaxation modulus of this viscoelastic material is first measured using a thermo-viscoelasticity analyzer (DMA); subsequently, the relaxation modulus is adopted to fit the 19-parameter Prony series of conformational models that characterize this viscoelastic material. Sinusoidal frequency sweep is then conducted on the SIEMENS TESTLAB platform, and the corresponding measured signals are obtained. Using the finite element method, a transient analysis simulation of the experimental conditions is performed. The dynamic response of this viscoelastic material under sinusoidal frequency sweep is evaluated by comparing it with the experimental data. It is observed that the overall acceleration peak error and the finite element simulation result are less than 3%. This study verifies that the obtained static constitutive equation (19-parameter Prony series) can describe the dynamic responses at low frequencies (<80 Hz).