scholarly journals Horizontal circulation and jumps in Hamiltonian wave models

2013 ◽  
Vol 20 (4) ◽  
pp. 483-500 ◽  
Author(s):  
E. Gagarina ◽  
J. van der Vegt ◽  
O. Bokhove
Keyword(s):  
Velocity Field ◽  
Water Wave ◽  
Hamiltonian Dynamics ◽  
Hamiltonian Formulation ◽  
Three Dimensional ◽  
Wave Model ◽  
Wave Dispersion ◽  
Flow Profile ◽  
New Model ◽  
Wave Models

Abstract. We are interested in the modelling of wave-current interactions around surf zones at beaches. Any model that aims to predict the onset of wave breaking at the breaker line needs to capture both the nonlinearity of the wave and its dispersion. We have therefore formulated the Hamiltonian dynamics of a new water wave model, incorporating both the shallow water and pure potential flow water wave models as limiting systems. It is based on a Hamiltonian reformulation of the variational principle derived by Cotter and Bokhove (2010) by using more convenient variables. Our new model has a three-dimensional velocity field consisting of the full three-dimensional potential velocity field plus extra horizontal velocity components. This implies that only the vertical vorticity component is nonzero. Variational Boussinesq models and Green–Naghdi equations, and extensions thereof, follow directly from the new Hamiltonian formulation after using simplifications of the vertical flow profile. Since the full water wave dispersion is retained in the new model, waves can break. We therefore explore a variational approach to derive jump conditions for the new model and its Boussinesq simplifications.

Field Verification of Linear and Nonlinear Hybrid Wave Models for Offshore Tower Response Prediction

1997 ◽  
Vol 119 (3) ◽  
pp. 158-165 ◽  
Author(s):  
A. T. Couch ◽  
J. P. Conte
Keyword(s):  
Velocity Field ◽  
Response Time ◽  
Wave Model ◽  
Linear Wave ◽  
Surface Boundary ◽  
Wave Steepness ◽  
Hybrid Wave ◽  
Time Histories ◽  
Wave Models ◽  
Measured Response

Accuracy of the prediction of the dynamic response of deepwater fixed offshore platforms to irregular sea waves depends very much on the theory used to determine wave kinematics. A common industry practice consists of using linear wave theory, which assumes infinitesimal wave steepness, in conjunction with empirical wave stretching techniques to provide a more realistic representation of near-surface water kinematics. The current velocity field is then added to the wave-induced fluid velocity field and the wave-and-current forces acting on the structure are computed via Morison’s equation. The first objective of this study is to compare the predicted responses of Cognac, a deepwater fixed platform, obtained from several popular empirical wave models with the response Cognac predicted based on the hybrid wave model. The latter is a recently developed higher-order, and therefore more accurate, wave model which satisfies, up to the second-order in wave steepness, the local mass conservation and the linear free surface boundary conditions at the instantaneous wave surface. The second objective of this study is to correlate the various analytical response predictions with the measured response of Cognac. Availability of a set of oceanographic and structural vibration data for Cognac provides a unique opportunity to evaluate the prediction ability of traditional analytical models used in designing such structures. The results of this study indicate that (i) the use of the hybrid wave model provides predicted platform response time histories which overall are in better agreement with the measured response than the predictions based on the various stretched linear wave models; and (ii) the Wheeler stretching technique produces platform response time histories which overall are more accurate than those obtained by using the other stretching schemes considered here.

The Effect of Reduced Water Depth on the Description of Extreme Waves and the Prediction of the Water Particle Kinematics

2005 ◽  
Author(s):  
Vasiliki Katsardi ◽  
Chris Swan
Keyword(s):  
Water Depth ◽  
Wave Model ◽  
Wave Dispersion ◽  
Linear Dispersion ◽  
Wave Groups ◽  
Relative Significance ◽  
Water Particle ◽  
Applied Design ◽  
Wave Models ◽  
Water Particle Kinematics

This paper concerns the description of large waves in intermediate and shallow water depths. In deep water it is well known that the evolution of the largest waves is governed by linear dispersion. In contrast, as the water depth reduces the effects of wave dispersion are weakened and the relative significance of wave modulation shown to be increasingly important. This leads to very different extreme wave groups, the properties of which are critically dependent upon the directionality of the wave field. The paper also concerns the water particle kinematics arising beneath these nonlinear wave groups and contrasts fully non-linear predictions based on a state-of-the-art wave model with the results of the commonly applied design wave solutions. To explore these effects, and to provide a physical explanation for their occurrence, two wave models are employed. The first, proposed by Bateman, Swan & Taylor [1, 2], allows fully-nonlinear descriptions of the evolution of large waves in realistic seas, involving a significant spread of wave energy in both frequency and direction. The second is a wave evolution equation based upon the early work of Zakharov [3] and written in Hamiltonian form by Kasitskii [4]. This model is only valid to a fourth-order of wave steepness, but has the over-riding advantage that it gives physical insight into the evolution process.

A NEW MODEL FOR REFRIGERANT CONDENSATION ON THE OUTSIDE OF THREE-DIMENSIONAL ENHANCED TUBES

1998 ◽  
Author(s):  
Alberto Cavallini ◽  
Davide Del Col ◽  
Luca Doretti ◽  
Luisa Rossetto ◽  
Giovanni Antonio Longo
Keyword(s):  
Three Dimensional ◽  
New Model ◽  
Enhanced Tubes

Long waves in a straight channel with non-uniform cross-section

2015 ◽  
Vol 770 ◽  
pp. 156-188 ◽  
Author(s):  
Patricio Winckler ◽  
Philip L.-F. Liu
Keyword(s):  
Boundary Layer ◽  
Wave Propagation ◽  
Cross Section ◽  
Three Dimensional ◽  
Channel Cross Section ◽  
Cross Sectional ◽  
New Model ◽  
One Dimensional ◽  
Uniform Channel ◽  
The Cross

A cross-sectionally averaged one-dimensional long-wave model is developed. Three-dimensional equations of motion for inviscid and incompressible fluid are first integrated over a channel cross-section. To express the resulting one-dimensional equations in terms of the cross-sectional-averaged longitudinal velocity and spanwise-averaged free-surface elevation, the characteristic depth and width of the channel cross-section are assumed to be smaller than the typical wavelength, resulting in Boussinesq-type equations. Viscous effects are also considered. The new model is, therefore, adequate for describing weakly nonlinear and weakly dispersive wave propagation along a non-uniform channel with arbitrary cross-section. More specifically, the new model has the following new properties: (i) the arbitrary channel cross-section can be asymmetric with respect to the direction of wave propagation, (ii) the channel cross-section can change appreciably within a wavelength, (iii) the effects of viscosity inside the bottom boundary layer can be considered, and (iv) the three-dimensional flow features can be recovered from the perturbation solutions. Analytical and numerical examples for uniform channels, channels where the cross-sectional geometry changes slowly and channels where the depth and width variation is appreciable within the wavelength scale are discussed to illustrate the validity and capability of the present model. With the consideration of viscous boundary layer effects, the present theory agrees reasonably well with experimental results presented by Chang et al. (J. Fluid Mech., vol. 95, 1979, pp. 401–414) for converging/diverging channels and those of Liu et al. (Coast. Engng, vol. 53, 2006, pp. 181–190) for a uniform channel with a sloping beach. The numerical results for a solitary wave propagating in a channel where the width variation is appreciable within a wavelength are discussed.

A new model for predicting three-dimensional beach changes by expanding Hsu and Evans' equation

2010 ◽  
Vol 57 (2) ◽  
pp. 194-202 ◽  
Author(s):  
Takaaki Uda ◽  
Masumi Serizawa ◽  
Takayuki Kumada ◽  
Kazuya Sakai
Keyword(s):  
Three Dimensional ◽  
New Model

The Efficiency of Tidal Fences: A Brief Review and Further Discussion on the Effect of Wake Mixing

2013 ◽  
Author(s):  
Takafumi Nishino ◽  
Richard H. J. Willden
Keyword(s):  
Energy Balance ◽  
Theoretical Investigation ◽  
Three Dimensional ◽  
Physical Factors ◽  
Balance Equations ◽  
Order Model ◽  
Near Wake ◽  
New Model ◽  
Actuator Disk ◽  
Limiting Efficiency

Recent discoveries on the limiting efficiency of tidal fences are reviewed, followed by a new theoretical investigation into the effect of wake mixing on the efficiency of ‘full’ tidal fences (i.e. turbines arrayed regularly across an entire channel span). The new model is based on the momentum and energy balance equations but includes several unclosed terms, which depend on the actual (three-dimensional) characteristics of turbine near-wake mixing and therefore need to be modelled empirically. The new model agrees well with three-dimensional actuator disk simulations when those unclosed terms are assessed based on the simulations themselves, suggesting that this low-order model could serve as a basis to analyse how various physical factors (such as the design of turbines) affect the limiting efficiency of tidal fences via changes in those terms describing the characteristics of turbine near-wake mixing. Also discussed is the effect of wake mixing on the efficiency of ‘partial’ tidal fences.

Effect of Initial Velocity Field on Smoke Diffusion Characteristic in Subway Tunnel

2009 ◽  
Author(s):  
Hui Yang ◽  
Li Jia ◽  
Lixin Yang
Keyword(s):  
Velocity Field ◽  
Field Condition ◽  
Initial Conditions ◽  
Three Dimensional ◽  
Wind Effect ◽  
Diffusion Characteristic ◽  
Subway Tunnel ◽  
Air Velocity ◽  
Initial Field ◽  
Fire Disaster

In this paper, piston wind effect on smoke diffusion characteristic in subway tunnel is studied by using three-dimensional transient computational fluid dynamics (CFD) method. In the first simulation case, fire disaster is simulated with homogeneous resting initial field condition. In the second simulation case, the train’s decelerating process till stopping in the tunnel is simulated for getting three-dimensional tunnel air velocity field distribution. Then the final heterogeneous air velocity field when the train stops in the tunnel is taken as initial field condition and the same fire scenario as the first case is simulated again. The data obtained under both initial conditions are compared by detecting people evacuation safety and the influence of initial air velocity field is analyzed. The results show that the inertial air velocity field caused by train’s movement has significant influence on smoke diffusion at the first few minutes of fire disaster, which is the key time for people’s evacuation. The adopted method in this paper and the simulation result could be used in establishing more effective subway fire evacuation plan.

A new model-based framework for lung tissue segmentation in three-dimensional thoracic CT images

2017 ◽  
Vol 12 (2) ◽  
pp. 339-346 ◽  
Author(s):  
Zeinab Naseri Samaghcheh ◽  
Fatemeh Abdoli ◽  
Hamid Abrishami Moghaddam ◽  
Mohammadreza Modaresi ◽  
Neda Pak
Keyword(s):  
Lung Tissue ◽  
Three Dimensional ◽  
Ct Images ◽  
Tissue Segmentation ◽  
New Model ◽  
Model Based ◽  
Thoracic Ct
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