Time-domain Simulation Method Research Articles

Different optical properties in different periodic slot cavity geometrical morphologies**Project supported by the National Natural Science Foundation of China (Grant No. 61178044), the Natural Science Foundation of Jiangsu Province, China (Grant No. BK20160969), and the University Postgraduate Research and Innovation Project of Jiangsu Province, China (Grant No. KYLX_0723).

In this paper, optical properties of two-dimensional periodic annular slot cavity arrays in hexagonal close-packing on a silica substrate are theoretically characterized by finite difference time domain (FDTD) simulation method. By simulating reflectance spectra, electric field distribution, and charge distribution, we confirm that multiple cylindrical surface plasmon resonances can be excited in annular inclined slot cavities by linearly polarized light, in which the four reflectance dips are attributed to Fabry–Perot cavity resonances in the coaxial cavity. A coaxial waveguide mode TE11 will exist in these annular cavities, and the wavelengths of these reflectance dips are effectively tailored by changing the geometrical pattern of slot cavity and the dielectric materials filled in the cavities. These resonant wavelengths are localized in annular cavities with large electric field enhancement and dissipate gradually due to metal loss. The formation of an absorption peak can be explained from the aspect of phase matching conditions. We observed that the proposed structure can be tuned over the broad spectral range of 600–4000 nm by changing the outer and inner radii of the annular gaps, gap surface topography. Meanwhile, different lengths of the cavity may cause the shift of resonance dips. Also, we study the field enhancement at different vertical locations of the slit. In addition, dielectric materials filling in the annular gaps will result in a shift of the resonance wavelengths, which make the annular cavities good candidates for refractive index sensors. The refractive index sensitivity of annular cavities can also be tuned by the geometry size and the media around the cavity. Annular cavities with novel applications can be implied as surface enhanced Raman spectra substrates, refractive index sensors, nano-lasers, and optical trappers.

Plasmonic Directional Couplers Based on Multi-Slit Waveguides

We propose and investigate the performance of the plasmonic directional couplers based on two dimensional multi-slit plasmonic waveguides, employing the finite difference time domain simulation method. The idea behind the directional properties of the directional couplers is the interference of two wave components, in and out of phase, at the coupled and isolated ports, respectively. The coupler is also analyzed by an analytic method. The simulation results comply well with those of the analytic considerations. The effects of variations of the coupler structural parameters, crosstalk between the input and output ports, and the overall structure loss are also investigated.

Computational comparative study of microwave probes for plasma density measurement

A microwave probe is known to be a suitable method to measure plasma density, even in the processing condition and is widely used in various environments of low-temperature processing plasmas. Various types of microwave probes have been researched and developed to measure the precise plasma density. Extensive research has been conducted to investigate each probes characteristic responding to the plasma parameters (plasma density, electron temperature, pressure, sheath width, and so forth) based on both experiments and simulations. However, a comparative study elucidating the relative characteristics of each probe has not been completed yet, despite the wide applications of the probes in processing plasma. We conduct a comparative study among the microwave probes using the numerical method of three-dimensional finite-difference time-domain simulation. In this study, the microwave probes are compared by investigating the precision of plasma density measurement under a comprehensive range of plasma parameters (plasma density, pressure, and sheath width).

Chatter stability of micro end milling by considering process nonlinearities and process damping

The micro end milling uses the miniature tools to fabricate complexity microstructures at high rotational speeds. The regenerative chatter, which causes tool wear and poor machining quality, is one of the challenges needed to be solved in the micro end milling process. In order to predict the chatter stability of micro end milling, this paper proposes a cutting forces model taking into account the process nonlinearities caused by tool run-out, trajectory of tool tip and intermittency of chip formation, and the process damping effect in the ploughing-dominant and shearing-dominant regimes. Since the elasto-plastic deformation of micro end milling leads to large process damping which will affect the process stability, the process damping is also included in the cutting forces model. The micro end milling process is modeled as a two degrees of freedom system with the dynamic parameters of tool-machine system obtained by the receptance coupling method. According to the calculated cutting forces, the time-domain simulation method is extended to predict the chatter stability lobes diagrams. Finally, the micro end milling experiments of cutting forces and machined surface quality have been investigated to validate the accuracy of the proposed model.

Time-domain simulation of berthing problem between FPSO and shuttle tanker in waves

A time-domain simulation method based on potential flow model has been developed to investigate the berthing problem between two floating bodies in wave. The boundary value problem is formulated with respect to an earth-fixed coordinate system because the relative positions of the two vessels continuously change during the berthing operation. The classical finite element method is used to solve the Laplace equation in the fluid domain with moving boundary. The linearized free-surface boundary conditions are integrated in time by applying 4th-order Adams–Bashforth–Moulton method. A simple re-mesh algorithm with local and global mesh systems is introduced to update mesh by considering large horizontal movement of the berthing vessel. The developed numerical method is used to investigate the berthing problem between a FPSO and shuttle tanker in waves. The focus is on the wave-induced motion response during the berthing process. The characteristics of the motion responses in berthing operation are examined with various wave frequencies, berthing speeds and wave headings.

Hybrid plasmonic electro-optical modulator

A high-performance CMOS compatible electro-optical modulator (EOM) is proposed, simulated and analyzed. The EOM is based on an asymmetric hybrid plasmonic waveguide on a silicon-on-insulator platform. Using the finite difference time domain simulation method, we obtained the transmission spectrum of the modulator. An insertion loss of 0.25 dB is achieved for a 5-μm-short modulator. The extinction ratio is optimized to be as high as 30 dB at a wavelength of 1.55 μm. Broadband operation of 600 nm is feasible since no resonator is deployed .

Prediction of parametric rolling of ships in single frequency regular and triple frequency group waves

A 3D nonlinear time domain simulation method based on the impulse response function concept is applied to the investigation of parametric rolling of the ITTC-A1 containership. In the numerical simulation, the hydrodynamic coefficients are determined beforehand by a 3D frequency domain panel code on the basis of linear potential theory, whereas the most nonlinear terms in the equations of motion are taken into account, such as the excitation by large amplitude waves (exact Froude–Krylov forces/moments), exact restoring forces/moments resulting from integration of the hydrostatic pressures over the actually wetted surface of the ship and the semi-empirical nonlinear viscous damping correction. In addition, all nonlinear inertia terms are retained when considering solution of large amplitude motions. The parametric rolling is predicted by solving the 6 degrees of freedom (DoF) nonlinear equations of ship motion in the time domain in response to single frequency regular waves and triple frequency group waves. The obtained numerical results are compared with corresponding experimental measurements and numerical predictions of an earlier conducted international benchmark study proving the good performance of the developed method in terms of the predictability of parametric roll phenomena and to a lesser degree to the accuracy of predicted roll amplitude values.

Three-Dimensional Manipulations of Surface Plasmon Polariton Wave Propagation

The plasmonic integrated circuit, a potential application of surface plasmon polaritons (SPPs), can manipulate an SPP wave propagating on a metal surface in a way similar to electronic circuits. Here, we propose the concept of three-dimensional (3D) SPP wave manipulation: control of an SPP wave propagating in both the horizontal direction and the vertical direction. A hole set in the film can guide an SPP wave in the vertical direction. In the horizontal direction, two holographic groove patterns are used to focus an incident SPP wave on one surface of the film to the hole and control the divergent SPP waves transmitted from the hole on the other metal surface, respectively. The holographic groove patterns are designed via the methodology of surface electromagnetic wave holography. 3D finite-difference time-domain method simulations show a good performance of the 3D manipulation via these designed holographic groove patterns.

Plasmon induced transparency in MIM waveguide side coupled slot resonators system with high sensing sensitivity

In this paper, electromagnetically induced transparency (EIT)-like window is found in plasmonic waveguide side coupled slot resonator system. Finite-difference time-domain simulation method is used to investigate the transmission spectra. The simulation results demonstrate the bandwidth of the EIT-like spectrum and the operating wavelength can be flexible handled by varying the geometric parameters of the plasmonic structures. Additionally, both symmetrical and asymmetrical plasmonic slot resonators coupled structures show high order resonance mode, which results in a higher sensitivity. The results in our paper may have potential application in optical switching, highly integrated optical circuits and biological medicine.

Time-domain simulation of MIMO fractional systems

The paper proposes an original method for time-domain simulation of MIMO fractional systems based on their rational approximation using Oustaloup’s method. Both commensurate and incommensurate fractional systems are tackled. The main contribution is to propose straightforward formulae allowing to approximate a pseudo-state-space representation of a fractional system with a state-space representation of a rational one whatever the dimension of the original system and whatever the number of poles and zeros used in the approximation.

Fast Assembly of Gold Nanoparticles in Large-Area 2D Nanogrids Using a One-Step, Near-Infrared Radiation-Assisted Evaporation Process.

When fabricating photonic crystals from suspensions in volatile liquids using the horizontal deposition method, the conventional approach is to evaporate slowly to increase the time for particles to settle in an ordered, periodic close-packed structure. Here, we show that the greatest ordering of 10 nm aqueous gold nanoparticles (AuNPs) in a template of larger spherical polymer particles (mean diameter of 338 nm) is achieved with very fast water evaporation rates obtained with near-infrared radiative heating. Fabrication of arrays over areas of a few cm(2) takes only 7 min. The assembly process requires that the evaporation rate is fast relative to the particles' Brownian diffusion. Then a two-dimensional colloidal crystal forms at the falling surface, which acts as a sieve through which the AuNPs pass, according to our Langevin dynamics computer simulations. With sufficiently fast evaporation rates, we create a hybrid structure consisting of a two-dimensional AuNP nanoarray (or "nanogrid") on top of a three-dimensional polymer opal. The process is simple, fast, and one-step. The interplay between the optical response of the plasmonic Au nanoarray and the microstructuring of the photonic opal results in unusual optical spectra with two extinction peaks, which are analyzed via finite-difference time-domain method simulations. Comparison between experimental and modeling results reveals a strong interplay of plasmonic modes and collective photonic effects, including the formation of a high-order stopband and slow-light-enhanced plasmonic absorption. The structures, and hence their optical signatures, are tuned by adjusting the evaporation rate via the infrared power density.

Angle Stability Analysis of Power System with Multiple Operating Conditions Considering Cascading Failure

A method to analyze the angle stability of power system with multiple operating conditions considering cascading failure is proposed in this paper. First, considering stochastic events such as uncertain operation of protection/breaker and system hardware failure, the system operating condition set is determined based on the flow transfer theory and the matrix of transfer probability between different operating conditions is calculated. On this basis, the discrete Markov power system model with multiple operating conditions considering cascading failure is established. And then, construct the Lyapunov functional containing the Markov model, and derive the robust stochastic stability criterion which satisfies the disturbance attenuation degree γ by iteration and the angle stability of power system could be identified according to the criterion using linear matrix inequality tools. Finally, stability index μ is defined to establish the relationship between transfer probability and system stability. Time-domain simulation tests on the IEEE 16-machine 68-bus system verify that, the proposed method could identify the stability of power system with multiple operating conditions effectively, with no need to obtain the operating trajectory of the system. Compared with traditional time-domain simulation method, the computation amount is reduced. Besides, it is simple and easy to implement.

Time domain simulation of vortex-induced vibrations in stationary and oscillating flows

This paper focuses on the further development of a previously published semi-empirical method for time domain simulation of vortex-induced vibrations (VIV). A new hydrodynamic damping formulation is given, and the necessary coefficients are found from experimental data. It is shown that the new model predicts the observed hydrodynamic damping in still water and for cross-flow oscillations in stationary incoming flow with high accuracy. Next, the excitation force model, which is one component of the total hydrodynamic force model, is optimized by simulating the VIV response of an elastic cylinder in a series of experiments with stationary flow. The optimization is performed by repeating the simulations until the best possible agreement with the experiments is found. The optimized model is then applied to simulate the cross-flow VIV of an elastic cylinder in oscillating flow, without introducing any changes to the hydrodynamic force modeling. By comparison with experiment, it is shown that the model predicts the frequency content, mode and amplitude of vibration with a high level of realism, and the amplitude modulations occurring at high Keulegan–Carpenter numbers are well captured. The model is also utilized to investigate the effect of increasing the maximum reduced velocity and the mass ratio of the elastic cylinder in oscillating flow. Simulations show that complex response patterns with multiple modes and frequencies appear when the maximum reduced velocity is increased. If, however, the mass ratio is increased by a factor of 5, a single mode dominates. This illustrates that, in oscillating flows, the mass ratio is important in determining the mode participation at high maximum reduced velocities.

Time-domain analyses of the layered soil by the modified scaled boundary finite element method

The dynamic response of two-dimensional unbounded domain on the rigid bedrock in the time domain is numerically obtained. It is realized by the modified scaled boundary finite element method (SBFEM) in which the original scaling center is replaced by a scaling line. The formulation bases on expanding dynamic stiffness by using the continued fraction approach. The solution converges rapidly over the whole time range along with the order of the continued fraction increases. In addition, the method is suitable for large scale systems. The numerical method is employed which is a combination of the time domain SBFEM for far field and the finite element method used for near field. By using the continued fraction solution and introducing auxiliary variables, the equation of motion of unbounded domain is built. Applying the spectral shifting technique, the virtual modes of motion equation are eliminated. Standard procedure in structural dynamic is directly applicable for time domain problem. Since the coefficient matrixes of equation are banded and symmetric, the equation can be solved efficiently by using the direct time domain integration method. Numerical examples demonstrate the increased robustness, accuracy and superiority of the proposed method. The suitability of proposed method for time domain simulations of complex systems is also demonstrated.

풍하중에 의한 바지선의 예인 시 거동특성 변화에 관한 연구

This paper presents the results of a numerical study on the towing characteristics of a barge under various wind conditions. First, stability criteria, including the wind force, were derived based on the linear motion equations of a towed vessel. The effect of the wind force on the towing stability was investigated using stability criteria. Next, towing simulations were carried out using a nonlinear time-domain simulation method. In this case, the towline was modeled as a simple spring-damper, and the wind force was computed using the wind coefficient from CFD calculations. Simulations were conducted for a barge under a constant towing speed and constant wind speed conditions. The effect of the wind direction on the slewing motion was also observed. In addition, a series of numerical simulations using variable wind speeds were performed for the present barge with and without a skeg.

Hydrodynamic interaction between two barges during berthing operation in regular waves

In this study, the berthing problem in waves is numerically investigated by a time-domain simulation method based on a potential flow model. The boundary value problem for a berthing operation is formulated with respect to an earth-fixed coordinate system. The Laplace equation of a moving boundary problem is solved using the finite element method by adopting an efficient re-mesh algorithm. The developed numerical method is applied to investigate the berthing problem between two rectangular barges, with particular focus on the hydrodynamic forces acting on the barges during the berthing process. It is assumed that the two barges correspond to installation and transportation barges. To simplify the berthing problem, the transportation barge is assumed to approach the installation barge along a straight path at constant speed. The hydrodynamic force responses during berthing operation are investigated via a series of numerical computations. Further, the effects of wave heading and wave frequency are investigated. To validate present numerical results, model tests were conducted in the Ocean Engineering Basin of KRISO. The berthing tests were performed using two barge models under the head and beam sea conditions. Fairly good agreement is observed between the numerical simulation and experimental results.

Transient response of a ship to an abrupt flooding accounting for the momentum flux

Numerical non-linear time domain simulation method for damaged ship motions is presented. Floodwater motion modelling is based on the lumped mass method with a moving free surface. The ship and floodwater motions are fully coupled. The variation of the floodwater mass is accounted for. A model to account for the flooding ingress transporting the momentum is presented. The experiments of abrupt flooding have shown that the ship may experience the first large roll towards the undamaged side, especially when a large undivided compartment is flooded. The presented time domain model is validated against the experimental data on the roll damping of the flooded ship and transient flooding. Two different initial stability conditions and two different compartment layouts are studied. Viscous dissipation of the floodwater motions is modelled with an equivalent friction coefficient. The impact of the viscous damping is studied. Transient flooding tests show that the inflow momentum has to be accounted for when the undivided compartment is flooded. The simulation model is capable of capturing the impact of the inflooding jet and the first roll on the opposite side of the damage is reproduced.

Online critical clearing time estimation using an adaptive neuro-fuzzy inference system (ANFIS)

Abstract This paper describes an approach using an adaptive neuro-fuzzy inference system (ANFIS) for the assessment of online critical clearing time (CCT). The ANFIS can integrate neural networks and fuzzy logic principles, and has a potential to combine the advantages of both in a single framework. In this paper, the ANFIS is applied for the prediction of CCT by varying load levels and fault locations in buses and transmission lines. The IEEE 39-bus system and 9-bus western system coordinating council are tested and implemented in this study. All machines of the IEEE 39-bus system are considered as the classical model without considering any generator’s exciters. While three machines in the 9-bus western system coordinating council are considered as detailed models, forth-order differential equation is described for all machines by considering the excitation system controller. CCT values obtained by the time domain simulation method using step-by-step calculation are used as the benchmark. The power world version 17 is used for transient simulation, and the ANFIS is implemented using MATLAB version 2014B. The results obtained from the ANFIS approach are quite satisfied with high accurate solutions and much lower computation time. Finally, the graphical user interface in MATLAB is applied for the online CCT estimation of two test power systems by using appropriate ANFIS models obtained from simulations.

Study of HVDC System and Subsynchronous Oscillation

With the application and development of Power Electronics, HVDC is applied more widely China. However, HVDC system has the possibilities to cause subsynchronous torsional vibration interaction with turbine generator shaft mechanical system. This paper simply introduces the mechanism, analytical methods and suppression measures of subsynchronous oscillation. Then it establishes a power plant model in islanding model using PSCAD, and analyzes the effects of the number and output of generators to SSO, and verifies the effect of SEDC and SSDC using time-domain simulation method. Simulation results show that the more number and output of generators is detrimental to the stable convergence of subsynchronous oscillation, and SEDC、SSDC can restrain unstable SSO, avoid divergence of SSO, ensure the generators and system operate safely and stably

Fatigue damage from time domain simulation of combined in-line and cross-flow vortex-induced vibrations

A semi-empirical method for time domain simulation of vortex-induced vibrations (VIV) is used to calculate the in-line and cross-flow fatigue damage of a tensioned riser in uniform and sheared flow. Simulations are run for flow velocities ranging from 0.3 m/s to 2.4 m/s, and a detailed comparison with experimental observations is performed. Results are reported in terms of dominating frequency, mode of vibration and mean of r.m.s. of displacement, as well as fatigue damage distribution along the length of the structure and maximum fatigue damage rates for each case. Fatigue damage is calculated by rainflow counting of the strain time series together with an idealized S–N curve with slope m = 3. The results show that the model reproduces the measured fatigue damage with a satisfactory level of realism, using a consistent set of parameters. This indicates that the model is usable for calculation of riser VIV fatigue damage in various current conditions, assuming the Reynolds number is in the subcritical range.