scholarly journals Linear and nonlinear acoustics in the time domain: Long‐range pulse propagation

1988 ◽  
Vol 84 (S1) ◽  
pp. S50-S51
Author(s):  
B. Edward McDonald
Keyword(s):  
Long Range ◽  
Time Domain ◽  
Pulse Propagation ◽  
Nonlinear Acoustics ◽  
Linear And Nonlinear ◽  
The Time Domain

scholarly journals Computation of Nonlinear Hydrodynamic Loads on Floating Wind Turbines Using Fluid-Impulse Theory

2015 ◽  
Author(s):  
Godine Kok Yan Chan ◽  
Paul D. Sclavounos ◽  
Jason Jonkman ◽  
Gregory Hayman
Keyword(s):  
Free Surface ◽  
Green Function ◽  
Wind Turbines ◽  
Time Domain ◽  
The Body ◽  
Nonlinear Loads ◽  
Frequency Wave ◽  
Linear And Nonlinear ◽  
The Time Domain ◽  
Nonlinear Free Surface

A hydrodynamics computer module was developed to evaluate the linear and nonlinear loads on floating wind turbines using a new fluid-impulse formulation for coupling with the FAST program. The new formulation allows linear and nonlinear loads on floating bodies to be computed in the time domain. It also avoids the computationally intensive evaluation of temporal and spatial gradients of the velocity potential in the Bernoulli equation and the discretization of the nonlinear free surface. The new hydrodynamics module computes linear and nonlinear loads — including hydrostatic, Froude-Krylov, radiation and diffraction, as well as nonlinear effects known to cause ringing, springing, and slow-drift loads — directly in the time domain. The time-domain Green function is used to solve the linear and nonlinear free-surface problems and efficient methods are derived for its computation. The body instantaneous wetted surface is approximated by a panel mesh and the discretization of the free surface is circumvented by using the Green function. The evaluation of the nonlinear loads is based on explicit expressions derived by the fluid-impulse theory, which can be computed efficiently. Computations are presented of the linear and nonlinear loads on the MIT/NREL tension-leg platform. Comparisons were carried out with frequency-domain linear and second-order methods. Emphasis was placed on modeling accuracy of the magnitude of nonlinear low- and high-frequency wave loads in a sea state. Although fluid-impulse theory is applied to floating wind turbines in this paper, the theory is applicable to other offshore platforms as well.

A Moving Zonal Method in the Time-Domain Simulation for Acoustic Propagation

2010 ◽  
Author(s):  
Z. Charlie Zheng ◽  
Guoyi Ke
Keyword(s):  
Long Range ◽  
Time Domain ◽  
Region Of Interest ◽  
Acoustic Propagation ◽  
Coordinate Frame ◽  
Computational Domain ◽  
Perfectly Matched Layers ◽  
Zonal Method ◽  
Moving Domain ◽  
The Time Domain

Conventional time-domain schemes have limited capability in modeling long-range acoustic propagation because of the vast computer resources needed to cover the entire region of interest with a computational domain. Many of the long-range acoustic propagation problems need to consider propagation distances of hundreds or thousands of meters. It is thus very difficult to maintain adequate grid resolution for such a large computational domain, even with the state-of-the-art capacity in computer memory and computing speed. In order to overcome this barrier, a moving zonal-domain approach is developed. This concept uses a moving computational domain that follows an acoustic wave. The size and interval of motion of the domain are problem dependent. In this paper, an Euler-type moving domain in a stationary coordinate frame is first tested. Size effects and boundary conditions for the moving domain are considered. The results are compared and verified with both analytical solutions and results from the non-zonal domain. Issues of using the moving zonal-domain with perfectly-matched layers for the free-space boundary are also discussed.

Experimental Study and Modeling of Nonlinear Scattering in Polymer Dispersed Liquid Crystals

1999 ◽  
Vol 597 ◽  
Author(s):  
M. Pacilli ◽  
P. Sebbah ◽  
P. Sixou ◽  
C. Vanneste ◽  
H. Guillard
Keyword(s):  
Experimental Study ◽  
Liquid Crystal ◽  
Composite Materials ◽  
Time Domain ◽  
Nonlinear Scattering ◽  
Polymer Dispersed Liquid Crystals ◽  
Polymer Dispersed ◽  
Linear And Nonlinear ◽  
The Time Domain ◽  
Nonlinear Light Scattering

AbstractWe investigate the optical limiting capabilities of composite materials consisting of nematic liquid crystal inclusions within a polymer matrix in the millisecond and CW regime. Preparation of the composite has been optimized to decrease the operation voltage. Clear evidence of light induced reorientation is observed. A numerical model is proposed to describe multiple linear and nonlinear light scattering in the time domain in this medium. Numerical simulations are compared to experiment and confirm promising limiting characteristics of such materials.

Green function method for the time domain simulation of pulse propagation

2014 ◽  
Vol 53 (16) ◽  
pp. 3533 ◽  
Author(s):  
Jing Huang ◽  
Jianquan Yao ◽  
Degang Xu ◽  
Runhua Li
Keyword(s):  
Green Function ◽  
Time Domain ◽  
Function Method ◽  
Pulse Propagation ◽  
Time Domain Simulation ◽  
Green Function Method ◽  
The Time Domain

scholarly journals Impact of Waves on Dangerous Stability of Vessels on the Oceanic Route

2018 ◽  
Vol 1 (1) ◽  
pp. 469-477
Author(s):  
Tadeusz Szelangiewicz ◽  
Katarzyna Żelazny
Keyword(s):  
Numerical Methods ◽  
Mathematical Models ◽  
Time Domain ◽  
Loss Of Stability ◽  
Beam Wave ◽  
Irregular Wave ◽  
Linear And Nonlinear ◽  
Ship Capsize ◽  
The Time Domain

Abstract Stability is one of the most important properties of the ship. The greatest influence on stability and thus on the possibility of loss of stability have the rolling of the ship on the wave. Mathematical models describing rolling on wave are complicated, and their solution, especially in the irregular wave, is only possible with numerical methods in the time domain. Large rolling, until the ship capsize, formation not only on the beam wave, but also on the following wave. Various models describing rolling (linear and nonlinear, regular and irregular wave, and constant or variable restoring moment) are presented. The predicted level hazard of stability of the ship depends on the direction of the wave and the cases where the level of hazard will be greatest.

ASYMPTOTIC APPROXIMATION OF OCEAN-ACOUSTIC PULSE PROPAGATION IN THE TIME DOMAIN

2004 ◽  
Vol 12 (02) ◽  
pp. 197-215 ◽  
Author(s):  
G. N. MAKRAKIS ◽  
E. K. SKARSOULIS
Keyword(s):  
Time Domain ◽  
Pulse Propagation ◽  
Acoustic Pulse ◽  
Normal Modes ◽  
Descent Method ◽  
Steepest Descent Method ◽  
Phase Method ◽  
Stationary Phase Method ◽  
Fourier Synthesis ◽  
The Time Domain

Broadband and narrowband time-domain asymptotics are proposed for pulse propagation in range-independent ocean environments. The broadband approximation results by applying the stationary-phase method to the Fourier transform of the Green's function, expressed in terms of normal modes. The narrowband approximation is obtained by incorporating the shape function of the emitted signal — assumed Gaussian — into the phase term and applying the steepest-descent method. The roots of the frequency-derivative of the phase are located in the complex plane by using a second-order expansion of the eigenvalues. The performance of the two approximations is studied numerically. While the broadband approximation improves with increasing bandwidth, the narrowband approximation improves when the bandwidth decreases. Both approximations improve with increasing range, and they can be used for delivering time-domain results more efficiently than with standard Fourier synthesis.

INCLUDING DISPERSION AND ATTENUATION IN TIME DOMAIN MODELING OF PULSE PROPAGATION IN SPATIALLY-VARYING MEDIA

2004 ◽  
Vol 12 (04) ◽  
pp. 501-519 ◽  
Author(s):  
GUY V. NORTON ◽  
JORGE C. NOVARINI
Keyword(s):  
Wave Equation ◽  
Time Domain ◽  
Pulse Propagation ◽  
Acoustic Pulse ◽  
Dispersive Media ◽  
Linear Wave ◽  
Domain Modeling ◽  
Time Domain Modeling ◽  
Media Work ◽  
The Time Domain

Modeling of acoustic pulse propagation in nonideal fluids requires the inclusion of attenuation and its causal companion, dispersion. For the case of propagation in a linear, unbounded medium Szabo developed a convolutional propagation operator which, when introduced into the linear wave equation, accounts for attenuation and causal dispersion for any medium whose attenuation possesses a generalized Fourier transform. Utilizing a one dimensional Finite Difference Time Domain (FDTD) model Norton and Novarini showed that for an unbounded isotropic medium, the inclusion of this unique form of the convolutional propagation operator into the wave equation correctly carries the information of attenuation and dispersion into the time domain. This paper addresses the question whether or not the operator can be used as a basic building block for pulse propagation in a spatially dependent dispersive environment. The operator is therefore used to model 2-D pulse propagation in the presence of an interface separating two dispersive media. This represents the simplest description of a spatially dependent dispersive media. It was found that the transmitted and backscattered fields are in excellent agreement with theoretical expectations demonstrating the effectiveness of the local operator to model the field in spatially dependent dispersive media. [Work supported by ONR/NRL.]

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