time domain simulation
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Crystals ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 82
Author(s):  
Mei Ge ◽  
Yi Li ◽  
Youhua Zhu ◽  
Meiyu Wang

The light extraction behavior of an AlGaN-based deep-ultraviolet LED covered with Al nanoparticles (NPs) is investigated by three-dimensional finite-difference time-domain simulation. For the transmission spectra of s- and p-polarizations in different emission directions, the position of maximum transmittance can be changed from (θ = 0°, λ = 273 nm) to (θ = 0°, λ = 286 nm) by increasing the diameter of Al NPs from 40 nm to 80 nm. In the direction that is greater than the critical angle, the transmittance of s-polarization is very small due to the strong absorption of Al NPs, while the transmittance spectrum of p-polarization can be observed obviously for the 80 nm Al NPs structure. For a ~284 nm AlGaN-based LED with surface plasmon (SP) coupling, although the luminous efficiency is significantly improved due to the improvement of the radiation recombination rate as compared with the conventional LED, the light extraction efficiency (LEE) is lower than 2.61% of the conventional LED without considering the lateral surface extraction and bottom reflection. The LEE is not greater than ~0.98% (~2.12%) for an SP coupling LED with 40 nm (80 nm) Al NPs. The lower LEE can be attributed to the strong absorption of Al NPs.


2021 ◽  
Vol 1201 (1) ◽  
pp. 012020
Author(s):  
N O Hauge ◽  
L Li

Abstract This study compares deployment of a subsea template simulated as a coupled model and as an uncoupled model in the time domain simulation software Orcaflex. Defining vessel motion as prescribed simplifies the model and will therefore also decrease the simulation time. Models with predefined vessel motions are called uncoupled models. Vessel motion in a coupled model is a continuously calculated reaction to the forces acting on the vessel. Some software might struggle to run coupled models. The deployment simulations are narrowed down to focus on the incident where the template crosses the splash zone when lifted with an offshore construction vessel. Noticeable differences between the allowable sea state results are observed from the two different simulation methods. Running the time domain simulation as an uncoupled model gives lower allowable sea states than the results from the coupled time domain simulation model.


2021 ◽  
Vol 2076 (1) ◽  
pp. 012116
Author(s):  
Mengxue Sun ◽  
Ruixin Gao ◽  
Yuhui Ji ◽  
Xin Long ◽  
Changzhi Yao ◽  
...  

Abstract Aiming at the sub-synchronous oscillation (SSO) problem of the grid-connected system of multiple DFIGs, most of the existing theoretical studies take the entire wind farm as a single-machine model, the stand-alone model cannot reflect the inside-wind-farm oscillation mode produced by the interactions among DFIGs in the wind farm. Therefore, this paper takes the equivalent value of DFIG-based wind farm to three DFIGs, establishes a mathematical model of the grid-connected system of three DFIGs, and studies the sub-synchronous oscillation modes existing in the system through eigenvalue analysis and participation factor analysis. The results show: When the length of transmission line increases, the oscillation frequency of the inside-wind-farm/wind-farm-grid sub-synchronous oscillation mode increases, the damping decreases and the stability weakens; when the number of grid-connected DFIGs increases, the oscillation frequency of the inside-wind-farm/wind-farm-grid sub-synchronous oscillation mode decreases, the damping increases and the stability enhances. Finally, a time-domain simulation model of the grid-connected system of multiple DFIGs was built in PSCAD/EMTDC to verify the correctness of the theoretical analysis results.


2021 ◽  
Vol 2087 (1) ◽  
pp. 012053
Author(s):  
Weili Liang ◽  
Jiguang Wu

Abstract Since series-compensated grid-connected system of doubly fed induction generator (DFIG) may cause sub-synchronous oscillation, with the purpose of improving the system stability, in this paper, the mechanism of sub-synchronous oscillation (SSO) is analyzed from the perspective of system damping, according to the mechanism, an additional damping controller is designed to suppress SSO. The controller uses rotor speed as the input signal and adds it into the d-axis current inner loop of the grid-side converter through filtering and proportional amplification, with the purpose of providing positive damping to the system. Finally, the model of DFIG series-compensated grid-connected system is established on PSCAD/EMTDC simulation platform to verify the suppression effect of the additional damping controller through time-domain simulation. The simulation results show that the device has good respond speed and suppression effect.


2021 ◽  
pp. 1-11
Author(s):  
Jinhui He ◽  
Haibin Zhang ◽  
Renchuan Zhu

Offshore structures floating at sea should use their dynamic positioning (DP) system to maintain position and heading against environmental loads, including wave loads, current loads, and wind loads. It is difficult to calculate environmental loads accurately and quickly, especially for wind loads due to the shielding effect of different parts on offshore structures. To improve the accuracy of wind load calculation, a new method considering shielding effect is proposed. With the new method, calculated wind force becomes much closer to wind tunnel test than the traditional method. As input data of DP capacity analysis, the environmental loads have critical impact on the design of DP system. A static method and a time-domain simulation method of DP capacity are also proposed, and a case study of drillship is carried out. The results of both static analysis and time-domain simulation of DP capacity show that the new wind load calculation method has improved the accuracy of environmental load calculation and DP capacity analysis. Introduction As the offshore oil and gas exploitation is going further into deep sea, offshore structures are to be used in harsh marine environments, including strong wind, current, and waves. Especially for wind, it can make great effect on the dynamic positioning (DP) system of offshore structures, which is designed to maintain position and heading. Once the DP system is not able to keep the offshore structures’ position and heading, it will cause an accident such as oil leakage and oil pollution in the ocean. Because of the wind shielding effect among all parts on offshore structures, such as deckhouse, derricks, cranes, pipe racks, the wind load is difficult to calculate accurately and quickly.


2021 ◽  
Vol 17 ◽  
pp. 69-74

In this paper, the LLE and ISOMAP algorithms in manifold learning are applied them to the analysis of vowel signals in time and frequency domain. Time domain simulation results show that the two dimensionality reduction methods can implement two-dimensional visualization of signals while preserving the high-dimensional manifold structure of original signals as much as possible. The time-frequency domain dimension reduction analysis of vowel signal manifold effectively solves the problem that high-dimensional speech signals can’t be intuitively felt, and provides a new potential way for signal classification. The frequency domain analysis is further optimized on the basis of time domain simulation. Because half of the amplitude values in DFT is used in the simulation, the two-dimensional manifold of the signal is roughly linearly distributed, which can effectively reduce redundancy and make the signal more compactly expressed in the frequency domain


2021 ◽  
Author(s):  
Emerson Andrade ◽  
Joel Sena Sales Jr. ◽  
Antonio Carlos Fernandes ◽  
Mario Luis Ribeiro ◽  
Pedro Teixeira

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