scholarly journals Time-domain simulation of ultrasound propagation with fractional Laplacians for lossy-medium biological tissues with complicated geometries

2019 ◽  
Vol 145 (1) ◽  
pp. 589-596 ◽  
Author(s):  
Junjian Zhang ◽  
Zhongquan Charlie Zheng ◽  
Guoyi Ke
Keyword(s):  
Time Domain ◽  
Biological Tissues ◽  
Time Domain Simulation ◽  
Ultrasound Propagation ◽  
Lossy Medium ◽  
Complicated Geometries

scholarly journals Time-Domain Simulation of Ultrasound Propagation in a Tissue-Like Medium Based on the Resolution of the Nonlinear Acoustic Constitutive Relations

2016 ◽  
Vol 102 (5) ◽  
pp. 876-892 ◽  
Author(s):  
Nóe Jiménez ◽  
Francisco Camarena ◽  
Javier Redondo ◽  
Víctor Sánchez-Morcillo ◽  
Yi Hou ◽  
...  
Keyword(s):  
Time Domain ◽  
Constitutive Relations ◽  
Time Domain Simulation ◽  
Ultrasound Propagation ◽  
Nonlinear Acoustic

Time-Domain Simulation of Ultrasound Propagation With Fractional Laplacian

2016 ◽  
Author(s):  
Junjian Zhang ◽  
Guoyi Ke ◽  
Z. Charlie Zheng
Keyword(s):  
Fractional Derivative ◽  
Time Domain ◽  
Fractional Laplacian ◽  
Homogeneous Medium ◽  
Biological Tissues ◽  
Immersed Boundary ◽  
Derivative Operator ◽  
Ultrasound Propagation ◽  
Dispersion Effects ◽  
Absorption And Dispersion

The simulation is developed for the purpose of simulating ultrasound propagation through biological tissues. The simulation is based on the time-domain conservation laws with the governing equations for acoustic pressure and velocity, with frequency dependent absorption and dispersion effects. We use forward differencing for velocity and backward differencing for pressure on the non-fractional derivative operator terms in spatial discretization. The fractional Laplacian operators are treated as Riesz derivatives. The shifted standard Grunwald approximation method is used to solve fractional derivative operator terms. To accommodate complicated biological tissue geometries, an immersed boundary method is developed that enables a Cartesian computational grid mesh to be used. The results are compared with those for a non-absorption homogeneous medium to discuss absorption and dispersion effects of biological material.

scholarly journals Convolution-based time-domain simulation for fluidelastic instability in tube arrays

2021 ◽  
Author(s):  
Mingjie Zhang ◽  
Ole Øiseth
Keyword(s):  
Impulse Response ◽  
Response Function ◽  
Time Domain ◽  
Impulse Response Function ◽  
Time Domain Simulation ◽  
Unit Step ◽  
Tube Arrays ◽  
Unit Impulse ◽  
The Time Domain ◽  
Unit Impulse Response

AbstractA convolution-based numerical algorithm is presented for the time-domain analysis of fluidelastic instability in tube arrays, emphasizing in detail some key numerical issues involved in the time-domain simulation. The unit-step and unit-impulse response functions, as two elementary building blocks for the time-domain analysis, are interpreted systematically. An amplitude-dependent unit-step or unit-impulse response function is introduced to capture the main features of the nonlinear fluidelastic (FE) forces. Connections of these elementary functions with conventional frequency-domain unsteady FE force coefficients are discussed to facilitate the identification of model parameters. Due to the lack of a reliable method to directly identify the unit-step or unit-impulse response function, the response function is indirectly identified based on the unsteady FE force coefficients. However, the transient feature captured by the indirectly identified response function may not be consistent with the physical fluid-memory effects. A recursive function is derived for FE force simulation to reduce the computational cost of the convolution operation. Numerical examples of two tube arrays, containing both a single flexible tube and multiple flexible tubes, are provided to validate the fidelity of the time-domain simulation. It is proven that the present time-domain simulation can achieve the same level of accuracy as the frequency-domain simulation based on the unsteady FE force coefficients. The convolution-based time-domain simulation can be used to more accurately evaluate the integrity of tube arrays by considering various nonlinear effects and non-uniform flow conditions. However, the indirectly identified unit-step or unit-impulse response function may fail to capture the underlying discontinuity in the stability curve due to the prespecified expression for fluid-memory effects.

Study of HVDC System and Subsynchronous Oscillation

2015 ◽  
Vol 1092-1093 ◽  
pp. 356-361
Author(s):  
Peng Fei Zhang ◽  
Lian Guang Liu
Keyword(s):  
Power Plant ◽  
Time Domain ◽  
Simulation Method ◽  
Time Domain Simulation ◽  
Stable Convergence ◽  
Turbine Generator ◽  
Plant Model ◽  
Subsynchronous Oscillation ◽  
Hvdc System ◽  
Simulation Results

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

scholarly journals Enhancing Oscillation Damping in an Interconnected Power System with Integrated Wind Farms Using Unified Power Flow Controller

Energies ◽  
2019 ◽  
Vol 12 (2) ◽  
pp. 322 ◽  
Author(s):  
Ping He ◽  
Seyed Arefifar ◽  
Congshan Li ◽  
Fushuan Wen ◽  
Yuqi Ji ◽  
...  
Keyword(s):  
Power Systems ◽  
Power System ◽  
Time Domain ◽  
Power Flow ◽  
Unified Power Flow Controller ◽  
Time Domain Simulation ◽  
Interconnected Power System ◽  
Dynamic Time ◽  
Oscillation Damping ◽  
Power Flow Controller

The well-developed unified power flow controller (UPFC) has demonstrated its capability in providing voltage support and improving power system stability. The objective of this paper is to demonstrate the capability of the UPFC in mitigating oscillations in a wind farm integrated power system by employing eigenvalue analysis and dynamic time-domain simulation approaches. For this purpose, a power oscillation damping controller (PODC) of the UPFC is designed for damping oscillations caused by disturbances in a given interconnected power system, including the change in tie-line power, the changes of wind power outputs, and others. Simulations are carried out for two sample power systems, i.e., a four-machine system and an eight-machine system, for demonstration. Numerous eigenvalue analysis and dynamic time-domain simulation results confirm that the UPFC equipped with the designed PODC can effectively suppress oscillations of power systems under various disturbance scenarios.

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