Traditional Simulation Methods Research Articles

A Direct Bounded Control Method for Transient Stability Assessment

Abstract The paper proposes a direct method for transient stability assessment, which is more efficient than traditional time-domain simulation methods. To achieve this objective, a new bounded control law for the model of a power system is designed. This yields superior closed-loop transient performances when compared to those achievable with traditional automatic voltage regulators and power system stabilizers. The designed control law allows defining an energy-based Lyapunov function which is instrumental in assessing transient stability properties of the post-fault system. A case study on a single machine infinite bus power system model is presented to illustrate the merits of the proposed method.

A Wave Digital Newton-Raphson Method for Virtual Analog Modeling of Audio Circuits with Multiple One-Port Nonlinearities

The digital implementation of a nonlinear audio circuit often employs the Newton-Raphson (NR) method for solving the corresponding system of implicit ordinary differential equations in the discrete-time domain. Although its quadratic convergence speed makes NR attractive for real-time audio applications, quadratic convergence is not always guaranteed, since it depends on initial conditions, and also divergence might occur. For this reason, especially in the context of Virtual Analog modeling, techniques for increasing the robustness of NR are in order. Among the various approaches, the Wave Digital (WD) formalism recently showed potential to rethink traditional circuit simulation methods. In this manuscript, we discuss an original formulation of the NR method in the WD domain for the solution of audio circuits with multiple one-port nonlinearities. We provide an in-depth theoretical analysis of the proposed iterative method and we show how its quadratic convergence strongly depends on the free parameters (called port resistances) introduced when modeling the reference circuit in the WD domain. In particular, we demonstrate that the size of the basin where the WD NR solver can be initialized to converge on a solution with quadratic speed is a function of the free parameters. We also show that by setting each port resistance value as close as possible to the derivative w.r.t. current of the nonlinear element v-i characteristic we keep the basin size large. We finally implement an audio ring modulator circuit with four diodes in order to test the proposed iterative method.

A new bivariate Archimedean copula with application to the evaluation of VaR

Abstract In this paper, a new generator function is proposed and based on this function a new Archimedean copula is introduced. The new Archimedean copula along with three representatives of Archimedean copula family which are Clayton, Gumbel and Frank copulas are considered as models for the dependence structure between the returns of two stocks. These copula models are used to simulate daily log-returns based on Monte Carlo (MC) method for calculating value at risk (VaR) of the financial portfolio which consists of two market indices, Ford and General Motor Company. The results are compared with the traditional MC simulation method with the bivariate normal assumption as a model of the returns. Based on the backtesting results, describing the dependence structure between the returns by the proposed Archimedean copula provides more reliable results over the considered models in calculating VaR of the studied portfolio.

Influence of turbulence integral length scale on aerostatic coefficients of bridge sections

This study investigates the influence of turbulence on the aerostatic coefficients of typical bridges by obtaining force measurements via the simulation of turbulence in wind tunnels. The traditional simulation method for turbulence based on spires and grilles cannot be employed for the accurate simulation of the large integral scale of turbulence in an actual wind field. Thus, in this study, the turbulence integral length scale was effectively increased using an active control grid. The wind fields of different turbulence integral scales were generated by controlling the vibration frequency of the active control grid. The aerostatic coefficients of five typical bridge sections (single-box girder, twin-box girder, truss girder, edge girder, and edge-box girder) were measured under turbulent and uniform flow. The test results were compared and analyzed, which revealed that the drag coefficients increased in accordance with a decrease in the reduced turbulence integral length scale, and they were lower under turbulent flow than under uniform flow.

Prediction Method of Three‐Dimensional Crack Propagation Path Based on Deep Learning Application

In engineering, most structural components suffer from local damage in service or fabrication. Under different loading conditions, such local damage will further expand to large cracks and structural collapse. For ensuring longevity and reliability, the study of brittle crack growth is important. In structural damage prediction, various methodologies are commonly used and have demonstrated success in the past. Most traditional simulation methods, however, have the problems of large calculation quantities and long calculation times. At the same time, the mutual influence of crack opening stress and crack image on crack widening is rarely considered in existing works based on the deep learning framework. Herein, a deep learning model is developed to predict the spread of fracture of brittle materials under stress to improve the aforementioned problems. By developing a nonlinear relationship between crack stress and damage effects, this approach predicts crack growth, thus avoiding the loss of required information on crack growth behavior. The model emphasizes repeatability and extensibility, which is verified using extended finite element method (XFEM) Abaqus software through multiple sets of material crack data generated. This model's potential applications are material design and evaluation of residual life.

Simulation of a Synchronous Planar Magnetically Levitated Motion System Based on a Real-Time Analytical Force Model

The existing simulation method for the control of linear or planar magnetically levitated actuators always ignores the characteristics of the real physical object, which deteriorates the accuracy of the simulation. In this work, the proposed emulator for the magnetically levitated actuator is developed to consider both the force characteristics and the control algorithm. To model the real controlled object, the mathematical model for 1D (one-dimensional) and 2D (two-dimensional) magnetic arrays is derived where the yaw angle is taken into consideration using the coordinate transformation. The solution of the mathematical model is compared with the commercial BEM (boundary element method) software and the measurements from a force and torque testing setup to highlight the accuracy of the proposed mathematical model. Compared with the traditional simulation method of the motion control systems founded on the simplified system transfer function, the proposed simulation method has higher consistency and is closer to reality. The accuracy and efficiency of the proposed magnetic force model are further verified by the emulator based on the numerical force model and the testing data of the real setup.

An accelerated conservative sharp-interface method for multiphase flows simulations

In this paper, we develop an accelerated conservative sharp-interface method for multiphase flows simulations. Traditional multiphase simulation methods use the minimum time step of all fluids obtained according to the CFL conditions to evolve the fluid states, which limits the computational efficiency, as the sound speed of one fluid may be much larger than of others. To address this issue, based on the original conservative sharp-interface methods, the present method is proposed by solving the governing equations of each individual fluid with the corresponding time step. Without violating the numerical stability requirement, the states of one fluid containing larger time-scale features will be evolved with a larger time step. The interaction step between two fluids is solved for synchronization, which is handled by interpolating the intermediate states of the fluid with larger time steps. In addition, an interfacial flux correction is applied to maintain the conservative property. The present algorithm has be coupled with a wavelet-based adaptive multi-resolution (MR) algorithm to achieve additional computational efficiency. A number of numerical tests indicate that the accuracy of the results obtained by the present method is comparable to of the original costly method, with a significant speedup. The speedup increases with the dimensions and resolution, which indicates its applications in 3D high resolution simulations of multiphase flows.

An improved method for analyzing shear-lag in thin-walled girders with rectangular ribs

Because the traditional bar simulation method (BSM) cannot directly analyze the shear lag effect of thin-walled steel box girders with rectangular ribs on their top and bottom plates, this paper presents a new method to derive equivalent bar areas and governing differential equations to assess the shear lag effect. On the basis of this, an improved bar simulation method (I-BSM) is proposed for shear lag analysis. In addition, the paper analyzes the influence on the shear lag effect of the thickness of the top and bottom plates, the thickness of the rectangular ribs, and the height of the girder's cross-section. The results show that an increase in the thickness of the top and bottom plates will increase the shear lag effect of the top plate, but decrease the shear lag effect of the bottom plate. The thickness of the rectangular ribs, however, has little effect on the shear lag effect. An increase in the height of the cross-section will reduce the shear lag effect of the top plate and increase the shear lag effect of the bottom plate. In future, it is recommended to change the height of the cross-section and thickness of the top or bottom plate to adjust the shear lag effect while designing structures. The study also demonstrates the strong applicability of I-BSM as an effective approach to analyzing the shear lag effect of thin-walled steel box girders with rectangular ribs.

Assessing the Impact of an EV Battery Swapping Station on the Reliability of Distribution Systems

This paper proposes a comprehensive methodological framework to investigate the potential role of the grid-connected battery swapping station (BSS) with vehicle-to-grid (V2G) capability in improving the reliability of supply in future distribution networks. For this aim, we first develop an empirical model for describing the energy demand of electric vehicles (EVs) and their resultant available generation capacity (AGC) that can be utilized for BSS operation. Then, on this basis, a quantitative method to quantify the effect of grid-connected BSS on distribution system reliability is proposed. In order to capture the uncertainties associated with EV users’ behaviors, Latin Hypercube Sampling (LHS) methods were utilized to obtain the time series of the BSS traffic flow and initial State of Charge (SOC) of each EV battery, according to the probability distribution of corresponding uncertain factors whose statistics are obtained from real-world historical data. Compared with existing works in this research field, the main contributions of this paper are threefold. (i) A comprehensive and efficient method to assess the reliability benefits of BSS with an explicit consideration of BSS characteristics (including physical structure, charging strategy, and swapping model) is proposed, which is in contrast to most of the extant studies that only focus on the EV fast-charging paradigm and thus provide a practical tool to analyze the potential value of BSS resources in future distribution systems. (ii) The randomness of EV user behaviors in BSS operation is explicitly modeled and considered. (iii) The LHS-based sequential simulation is used to improve the accuracy and convergence performance of the evaluation, as compared to the traditional Sequential Monte Carlo Simulation (SMCS) method. To verify the effectiveness of the proposed approach, numerical studies are conducted based on a modified IEEE 33-bus distribution network. The simulation results show that with V2G capabilities, BSS can improve reliability to a certain extent and reduce the adverse impact on the reliability of the distribution network. In addition, EV resources should be orderly managed and exploited; otherwise, uncoordinated charging activities could impose a negative impact on the reliability performance of distribution networks. Finally, it is also shown that under the same sampling time, LHS-based sequential simulation could be better than SMCS in the accuracy and convergence speed of the procedure.

Molecular Dynamics Study of Bubble Nucleation on an Ideally Smooth Substrate.

Questions regarding bubble nucleation on an ideally smooth surface are seemingly endless, but it can not be adequately verified yet because of the scale limitation (microscopic scale). Hence, in this study, bubble nucleation on an ideally smooth substrate is explored using the molecular dynamics simulation method. An ideally smooth hydrophilic platinum substrate at 145 K is conducted to heat the simple L-J liquid argon. Results show that a visible bubble nucleus successfully forms on the ideally smooth substrate without any additional disturbance, which is common in boiling studies using the traditional numerical simulation methods. However, the nucleation position is unpredictable. At the atomic level, the thermal energy transfer from an ideally smooth substrate to liquid atoms is inhomogeneous due to atomic inhomogeneous distribution and irregular movement, which are the key influencing factors for achieving bubble nucleation. The inhomogeneity will be highlighted with the heating process. As a result, some local liquid atoms near the ideally smooth surface absorb more thermal energy to overcome their potential barrier at a specific moment, causing the emergence of a distinct nucleus there. Furthermore, nanostructure substrates are introduced to make a comparison with the smooth substrate in bubble nucleation. There is no significant difference in the inception temperature of nucleation between the ideally smooth and nanostructure substrates, but the latter has better performance in improving the bubble nucleation rate.

Lipofuscin-Type Pigment as a Marker of Colorectal Cancer

The study of the optical properties of biological tissues for a wide spectral range is necessary for the development and planning of noninvasive optical methods to be used in clinical practice. In this study, we propose a new method to calculate almost all optical properties of tissues as a function of wavelength directly from spectral measurements. Using this method, and with the exception of the reduced scattering coefficient, which was obtained by traditional simulation methods, all the other optical properties were calculated in a simple and fast manner for human and pathological colorectal tissues. The obtained results are in good agreement with previous published data, both in magnitude and in wavelength dependence. Since this method is based on spectral measurements and not on discrete-wavelength experimental data, the calculated optical properties contain spectral signatures that correspond to major tissue chromophores such as DNA and hemoglobin. Analysis of the absorption bands of hemoglobin in the wavelength dependence of the absorption spectra of normal and pathological colorectal mucosa allowed to identify differentiated accumulation of a pigment in these tissues. The increased content of this pigment in the pathological mucosa may be used for the future development of noninvasive diagnostic methods for colorectal cancer detection.

A robust data simulation technique to improve early detection performance of a classifier in control chart pattern recognition systems

The quality control process is essential in maintaining the stability of production systems and proactively detecting abnormalities that may result in high mechanical and labor costs. In this study, a new data simulation strategy was devised to improve the early prediction performance (EPP) of an algorithm. Traditional control chart data simulation methods work based on creating abnormal patterns consisting of only abnormal signals. However, a classifier trained with data samples consisting of only abnormal data signals may fail to early detect abnormality in a real-time production line, in which abnormal signals is obscured by volume of normal signals. From this perspective, training a model by imitating real-world cases can improve the performance of an algorithm in terms of early detection of an abnormality. Normal and abnormal patterns were simulated by implementing a new approach called Mix Ratio Data Simulation (MRDS). The proposed methodology MRDS is compared with the customary data simulation method under the predefined scenarios in terms of EPP. The findings indicated that changing the way of simulating dataset increases the EEP of the machine-learning algorithm regardless of abnormality types and parameters.

Distributed Watershed Hydrological Simulation Method Based on SWAT Model

Liu, D. and Gao, J.N., 2020. Distributed watershed hydrological simulation method based on SWAT model. In: Guido Aldana, P.A. and Kantamaneni, K. (eds.), Advances in Water Resources, Coastal Management, and Marine Science Technology. Journal of Coastal Research, Special Issue No. 104, pp. 738–741. Coconut Creek (Florida), ISSN 0749-0208.Aiming at the problems of large simulation error and long time consumption in traditional distributed hydrological simulation methods, a distributed hydrological simulation method based on SWAT model is proposed in this paper. This paper analyzes the working principle of SWAT model and constructs SWAT model; uses baseline drift method and variable storage coefficient model to extract typical characteristics of groundwater runoff, soil moisture evaporation and water surface concentration of distributed watershed hydrological characteristic data; on this basis, analyzes the spatial distribution characteristics of precipitation, modifies the precipitation coefficient, and through the coefficient of linear regression equation and efficiency coefficient and adjust the root mean square error to realize the distributed hydrological simulation. The experimental results show that the minimum error of the proposed method is about 0.01%, and the maximum simulation time is about 5.8 s.

Shale gas transport mechanisms in inorganic and organic pores based on lattice Boltzmann simulation

A better understanding on the mechanism and difference of shale gas transport through inorganic and organic pores is critical to accurately predicting shale gas recovery. Due to the complicated gas flow dynamics in such narrow pores, traditional experimental methods or simulation methods is difficult to accurately describe these processes. Here, a regularized lattice Boltzmann (LB) model coupled with the slippage boundary condition and gas adsorption effect is employed to simulate shale gas transport in the inorganic and organic pore. The adsorption parameters of shale gas in the LB model are obtained from the molecular dynamics (MD) simulations. Effects of the adsorption effect, pore size, pore wall roughness and gas rarefaction effect on the shale gas transport are studied. The simulation results show that the shale gas transport mechanism heavily depends on the pore size. Basically, in the nano-scale pore, the gas slippage and Knudsen flow are the dominated transport mechanism, but the gas transport is dominated by the surface diffusion in the organic pore width with less than 5 nm owing to the gas adsorption effect. The surface roughness effect plays an important role in the gas transport, and this effect significantly increases with the decreasing of the Knudsen number. At the same time, the gas adsorption effect can also cause a significant increase of the friction factor and a slight decrease of the mass flow rate, which indicates that the gas adsorption effect must be considered in the organic roughness pores.

Mode transmission analysis method for photonic lantern based on FEM and local coupled mode theory.

In this paper, a novel full vector numerical simulation method based on the finite element method (FEM) and local coupled mode theory (LCMT) for analyzing the mode transmission characteristics of photonic lantern (PL) with arbitrary input mode field is proposed. Compared with the traditional numerical simulation methods for PL, our method can greatly reduce the computational complexity and ensure high precision. Taking a three-core PL as an example, we verify the validity of our method. The advantages and properties of our method are also discussed in detail and found instructive for optimization design of PL. Through specifically optimizing the geometric parameters of the PL according to the properties, mode selectivity of LP01 and LP11 can be respectively improved up to 44.5 dB and 54.7 dB with more than 95% coupling efficiency.

Predicting Loads and Dynamic Responses of An Offshore Jacket Wind Turbine in A Nonlinear Sea

In order to improve the simulation efficiency, a novel transformed linear Gaussian model has been first proposed in this paper for generating equivalent “nonlinear” irregular waves. It is demonstrated by calculation examples that for obtaining equivalent “nonlinear” waves with the same accuracy, the transformed linear Gaussian model is about 2.7 times faster than the traditional nonlinear simulation method and is about 2.14 times faster than the method proposed by Agarwal and Manuel (2011). The loads and dynamic responses calculation results regarding an offshore jacket wind turbine in this paper demonstrate that nonlinearly simulated irregular waves with bottom effects should be considered in order to design an un-conservative support structure for the offshore wind turbine. Furthermore, by studying the calculation results in this article we have found that the loads and dynamic responses of the offshore wind turbine when inputting transformed linearly simulated waves with bottom effects are almost identical to the corresponding values when inputting nonlinearly simulated waves with bottom effects. All these calculation results clearly demonstrate the superiority and effectiveness of using our novel transformed linear Gaussian model for predicting the wave loads and dynamic responses of an offshore wind turbine operating in a realistic nonlinear sea with bottom effects.

Dynamic reliability and variance-based global sensitivity analysis of pipes conveying fluid with both random and convex variables

Purpose This paper aims to solve the problem that pipes conveying fluid are faced with severe reliability failures under the complicated working environment. Design/methodology/approach This paper proposes a dynamic reliability and variance-based global sensitivity analysis (GSA) strategy with non-probabilistic convex model for pipes conveying fluid based on the first passage principle failure mechanism. To illustrate the influence of input uncertainty on output uncertainty of non-probability, the main index and the total index of variance-based GSA analysis are used. Furthermore, considering the efficiency of traditional simulation method, an active learning Kriging surrogate model is introduced to estimate the dynamic reliability and GSA indices of the structure system under random vibration. Findings The variance-based GSA analysis can measure the effect of input variables of convex model on the dynamic reliability, which provides useful reference and guidance for the design and optimization of pipes conveying fluid. For designers, the rankings and values of main and total indices have essential guiding role in engineering practice. Originality/value The effectiveness of the proposed method to calculate the dynamic reliability and sensitivity of pipes conveying fluid while ensuring the calculation accuracy and efficiency in the meantime.

Dynamic Simulation Analysis of Port Economic Throughput Difference in Marine Environment

Wang, G. and Zhang, Y., 2020. Dynamic simulation analysis of port economic throughput difference in marine environment. In: Yang, Y.; Mi, C.; Zhao, L., and Lam, S. (eds.), Global Topics and New Trends in Coastal Research: Port, Coastal and Ocean Engineering. Journal of Coastal Research, Special Issue No. 103, pp. 268–272. Coconut Creek (Florida), ISSN 0749-0208.A large number of sample data are needed in the dynamic simulation analysis of port economic throughput difference in the marine environment. In the traditional dynamic simulation method, the distribution of sample data is unbalanced, which affects the reliability of the simulation results. Therefore, the dynamic simulation analysis of port economic throughput difference in the marine environment is proposed. This paper analyzes the influencing factors of port economic throughput, determines the appropriate influencing factors by calculating the correlation coefficient, constructs the port economic throughput difference model, takes the predicted value and the original number series obtained by the model as the input, uses the trend extrapolation method and the linear regression model to realize the dynamic simulation of port economic throughput difference. The experimental results show that: compared with the traditional dynamic simulation method, the sample data of the dynamic simulation method of port economic throughput difference under the designed marine environment is evenly distributed, and this method is suitable for practical projects.

Design of Dynamic Diffusion Simulation System for Atmospheric Pollutants in Coastal Cities under Persistent Inverse Temperature

Gong, Y. and Luo, X., 2020. Design of dynamic diffusion simulation system for atmospheric pollutants in coastal cities under persistent inverse temperature. In: Yang, Y.; Mi, C.; Zhao, L., and Lam, S. (eds.), Global Topics and New Trends in Coastal Research: Port, Coastal and Ocean Engineering. Journal of Coastal Research, Special Issue No. 103, pp. 526–529. Coconut Creek (Florida), ISSN 0749-0208.The prediction of the dynamic diffusion of atmospheric pollutants in coastal cities under continuous inverse temperature is the key to establish the dynamic treatment of atmospheric pollutants. In view of the low accuracy of the traditional nonlinear feature estimation simulation method, a continuous inverse temperature simulation model for the dynamic diffusion of atmospheric pollutants in coastal cities under continuous inverse temperature is proposed. A self-similar regression model is constructed for the statistical information of atmospheric pollutant dynamic diffusion in coastal cities under continuous inverse temperature, and a multi-scale decomposition and factor analysis are carried out for the time series of atmospheric pollutant dynamic diffusion in coastal cities under continuous inverse temperature. The simulation results show that the model has high accuracy and good convergence in the simulation and prediction of atmospheric pollutant dynamic diffusion in coastal cities.

An allowance allocation method based on dynamic approximation via online inspection data for deformation control of structural parts

Deformation resulting from residual stress has been a significant issue in machining. As allowance allocation can directly impact the residual stress on part deformation, it is essential for deformation control. However, it is difficult to adjust allowance allocation by traditional simulation methods based on residual stress, as the residual stress cannot be accurately measured or predicted, and many unexpected factors during machining process cannot be simulated accurately. Different from traditional methods, this paper proposes an allowance allocation method based on dynamic approximation via online inspection data for deformation control of structural parts. An Autoregressive Integrated Moving Average (ARIMA) model for dynamic allowance allocation is established so as to approach the minimum deformation, which is based on the in-process deformation inspection data during the alternative machining process of upside and downside. The effectiveness of the method is verified both by simulation cases and real machining experiments of aircraft structural parts, and the results show that part deformation can be significantly reduced.