Download or read book Numerical Simulations of Internal Waves Generated by Flow Over a Ridge written by Hui Qian and published by . This book was released on 2010 with total page 57 pages. Available in PDF, EPUB and Kindle. Book excerpt: Keywords: internal wave generation, barotropic tides, ridges.
Download or read book Numerical Simulations of Internal Waves Generated by Flow Over a Ridge written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: QIAN, HUI. Numerical Simulations of Internal Waves Generated by Flow over a Ridge. (Under the direction of Dr. Ping-Tung Shaw). A three-dimensional nonhydrostatic numerical model is used to study the generation of internal wave energy by barotropic tidal flow over a steep ridge. Numerical experiments are carried out over ridges of three different heights in an ocean with strong stratification at shallow depths. The topographic width, stratification, and amplitude of the barotropic tide are varied to examine the dependence of the normalized energy flux on the slope parameter, the ratio of the ridge slope to that of the wave beam. Over a tall ridge reaching the strongly stratified depths of the water column, the non-dimensional energy flux increases with the slope parameter and becomes constant when the slope parameter exceeds a critical value. For a small ridge confined at weakly stratified depths, the non-dimensional energy flux reaches a maximum with increase in the slope parameter but decreases with further increase in the slope parameter. The two regimes of dependence on the slope parameter can be described in terms of a local Froude number. The results show that internal wave generation is most efficient when the ridge is steep and the ridge top reaches the strongly stratified upper ocean. Comparison between the parameterization scheme and the estimated energy flux at several locations in the ocean shows reasonable agreement. The non-dimensional relation provides a way to estimate the baroclinic energy flux using topographic scales, stratification, and strength of the barotropic tides in the ocean.
Download or read book Numerical Simulations of Nonlinear Internal Waves in the South China Sea written by Zhonghua Zhang and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Field observations and satellite imagery have demonstrated the ubiquitous nature of internal waves, and substantial evidence indicates that they play a significant role in nutrient transport, energy distribution and mixing throughout the world's oceans. As a result, internal waves have attracted a great deal of interest in the past few decades. However, because of the complex nature of internal waves, particularly in regard to their nonlinear and nonhydrostatic characteristics, basic properties of internal waves still lack satisfactory explanation, including how they are generated, how they propagate, and how they dissipate their energy in the open ocean and on continental margins. To obtain a better understanding of internal waves, we use SUNTANS, a three-dimensional, unstructured-grid, nonhydrostatic Navier-Stokes code, to simulate internal waves in the South China Sea (SCS), where extremely large-amplitude internal waves have been observed. To capture the nonlinear features of internal waves, a total variation diminishing method has been developed to accurately solve the three-dimensional scalar transport equation with unstructured grids in SUNTANS. Taking advantage of this scheme, we employ both two- and three-dimensional numerical simulations with idealized and real bathymetry and perform detailed analyses of internal wave energetics and dynamics to understand how they are generated in the SCS and how they evolve into trains of weakly nonlinear solitary-like waves. The simulation results indicate that nonlinear internal waves in the SCS are generated by strong barotropic flow over complex topography at a ridge on the eastern edge of the Luzon Strait, which connects the eastern boundary of the SCS to the Pacific Ocean. Idealized two-dimensional simulations show that the internal Froude number over the topography, or the ratio of the barotropic currents to the first-mode internal wave speed, can be the most important parameter governing the generation with a strong effect both on the amplitude of the generated waves and the phase in the barotropic tide at which internal waves are generated. For low-Froude number generation, linear first-mode waves are always generated at the end of the ebb tide, and increasing the Froude number causes waves to be generated earlier given the flow is subcritical. However, because the internal Froude number in the SCS is small, the three-dimensional simulations with real topography and stratification indicate that the excursion parameter, which is the ratio of the tidal excursion to the topographic scale, is the most important parameter governing the generation mechanism. With small tidal excursion parameters in the SCS, the well-known A and B waves are both likely generated by the internal tide mechanism. The A waves evolve from the formation of diurnal internal tidal beams at critical topography along the eastern ridge of the two ridge-system in the southern portion of the Luzon Strait. The B waves, on the other hand, are generated due to the formation of internal tides resulting from semidiurnal barotropic currents along the eastern ridge in the northern portion of the Luzon Strait. An analysis of the energetics indicates that half of the baroclinic or internal tidal energy dissipates locally over the ridge within the Strait, while the other half radiates away from the generation site and into the SCS basin. As the waves propagate across the SCS basin, they develop into trains of rank-ordered solitary-like internal waves under the effects of nonlinear steepening and nonhydrostatic dispersion. Because it employs the nonhydrostatic pressure, the SUNTANS model accurately captures these effects as well as the complex processes of wave diffraction, refraction, and wave-wave interaction on the continental shelf at the western edge of the SCS.
Download or read book Simulation of Stratified Turbulent Flows in Complex Geometry written by Narsimha Reddy Rapaka and published by . This book was released on 2015 with total page 92 pages. Available in PDF, EPUB and Kindle. Book excerpt: Direct and Large Eddy Simulation approaches are used to study internal tide generation and turbulence at a model topography. A three dimensional finite difference code using an immersed boundary method is developed to simulate stratified turbulent flows over complex geometry on a Cartesian grid. The thesis is comprised of two phases. In the first phase, a mixed spectral/finite difference code is used to solve the governing equations in generalized coordinates. Direct and large eddy simulations are performed using a body fitted grid (BFG) to study the internal waves generated by the oscillation of a barotropic tide over a model ridge of triangular shape. The objective is to assess the role of nonlinear interactions including turbulence in situations with low tidal excursion number. The criticality parameter, defined as the ratio of the topographic slope to the characteristic slope of the tidal rays, is varied from subcritical to supercritical values. The barotropic tidal forcing is also systematically increased. In laminar flow at low forcing, numerical results of the energy conversion agree well compared to linear theory in subcritical and supercritical cases but not at critical slope angle. In critical and supercritical cases with higher forcing, there are convective overturns, turbulence and significant reduction (as much as 25%) of the radiated wave flux with respect to laminar flow results. The phase dependence of turbulence within a tidal cycle is examined and found to differ substantially between the ridge slope and the ridge top where the beams from the two sides cross. In the second phase, a sharp-interface Immersed Boundary Method (IBM) is developed to simulate high Reynolds number density-stratified turbulent flows in complex geometry. The basic numerical scheme corresponds to a central second-order finite difference method, third-order Runge-Kutta integration for the advective terms and an alternating direction implicit (ADI) scheme for the viscous and diffusive terms. Both direct numerical simulation (DNS) and large eddy simulation (LES) approaches are considered. The focus is on accurate computation of the internal gravity wave field and turbulence near an underwater obstacle in a model problem where a tide oscillates over the obstacle. Methods to enhance the mass conservation and numerical stability of the solver to simulate high Reynolds number flows are discussed. The solver is validated using Direct Numerical Simulations (DNS) of channel flow with and without stratification, and tidal flow over a laboratory-scale (order of few meters) smoothed triangular ridge. The results including baroclinic energy flux, mean flow properties and turbulent kinetic energy agree reasonably well with our previous results obtained using a body-fitted grid (BFG). The deviation of IBM results from BFG results is found to increase with increasing steepness of the topography relative to the internal wave propagation angle. LES is performed on a large scale ridge, of the order of few kilometers in length, at significantly larger Reynolds number. A non-linear drag law is utilized to parameterize turbulent losses due to bottom friction. The large scale problem exhibits qualitatively similar behavior to the laboratory scale problem with some differences: slightly larger intensification of the boundary flow and somewhat higher nondimensional values for conversion, baroclinic wave flux and turbulent kinetic energy. The phasing of wave breaking and turbulence exhibits little difference between small and large scale obstacles. We conclude that IBM is a viable approach to the simulation of internal waves and turbulence in high Reynolds number stratified flows over topography.
Download or read book Turbulence and Internal Waves in Tidal Flow Over Topography written by Bishakhdatta Gayen and published by . This book was released on 2012 with total page 192 pages. Available in PDF, EPUB and Kindle. Book excerpt: Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES) are used to investigate and quantify the dynamical processes underlying turbulence formed during the generation of an internal wave beam and its subsequent interaction with a realistically stratified upper ocean. As a part of the thesis, a three-dimensional mixed spectral/finite difference code was developed, parallelized, validated and employed to study several geophysical problems relevant to internal tide generation and its nonlinear breaking. The thesis research has four phases. In the first phase, a study of a stratified non-sloping bottom boundary layer under an oscillating tide was completed. The focus is on the boundary layer response to an external stratification based on LES. Flow instabilities and turbulence in the bottom boundary layer are found to excite internal gravity waves that propagate away into the ambient with phase angle varying over the tidal cycle. Subsequent studies as part of the second phase consider a stratified oscillating flow over a sloping bottom wall to mimic the generation of baroclinic internal waves (IW) from the tide-topography interaction at a model continental slope. The DNS study shows transition to turbulence, which is present along the entire extent of the near-critical region of the slope in the regime of low background excursion number and Reynolds number. The transition is found to be initiated by a convective instability, which is closely followed by shear instability. The peak value of the near-bottom velocity is found to increase with increasing length of the critical region of the topography. The scaling law that is observed to link the near-bottom peak velocity to slope length is explained by an analytical boundary layer solution that incorporates an empirically obtained turbulent viscosity. As an extension of the second phase, the objective of the third phase work is to numerically model a near-bottom beam with a larger, more realistic width using LES and characterize its turbulence statistics. Maximum turbulent kinetic energy and dissipation rate are found just after the zero velocity point when flow reverses from downslope to upslope motion. The phasing and other characteristics of the turbulent mixing in the present simulations show remarkable similarity with that observed off Kaena Ridge in Hawaii taken during the hawaiian ocean mixing experiment (HOME), and may be explained by the beam-scale convective overturns found here. The objective of the final phase is to understand the interaction process between an IW beam and an upper ocean pycnocline and to further characterize the cascade to small scales in the context of IW beam degradation observed in the ocean.
Download or read book Ocean Mixing written by Michael Meredith and published by Elsevier. This book was released on 2021-09-16 with total page 386 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ocean Mixing: Drivers, Mechanisms and Impacts presents a broad panorama of one of the most rapidly-developing areas of marine science. It highlights the state-of-the-art concerning knowledge of the causes of ocean mixing, and a perspective on the implications for ocean circulation, climate, biogeochemistry and the marine ecosystem. This edited volume places a particular emphasis on elucidating the key future questions relating to ocean mixing, and emerging ideas and activities to address them, including innovative technology developments and advances in methodology. Ocean Mixing is a key reference for those entering the field, and for those seeking a comprehensive overview of how the key current issues are being addressed and what the priorities for future research are. Each chapter is written by established leaders in ocean mixing research; the volume is thus suitable for those seeking specific detailed information on sub-topics, as well as those seeking a broad synopsis of current understanding. It provides useful ammunition for those pursuing funding for specific future research campaigns, by being an authoritative source concerning key scientific goals in the short, medium and long term. Additionally, the chapters contain bespoke and informative graphics that can be used in teaching and science communication to convey the complex concepts and phenomena in easily accessible ways. - Presents a coherent overview of the state-of-the-art research concerning ocean mixing - Provides an in-depth discussion of how ocean mixing impacts all scales of the planetary system - Includes elucidation of the grand challenges in ocean mixing, and how they might be addressed
Download or read book Numerical Simulations of Atmospheric Internal Waves with Time dependent Critical Levels and Turning Points written by Brian P. Casaday and published by . This book was released on 2010 with total page 114 pages. Available in PDF, EPUB and Kindle. Book excerpt: Just as water surface waves are found everywhere on the ocean's surface, internal waves are ubiquitous throughout the atmosphere. These waves constantly propagate and interact with other flows, but these interactions are difficult to observe due to inadequate current technology.
Download or read book Numerical Simulations of Internal Waves in Stratified Fluids written by Andy K. O. Law and published by . This book was released on 1999 with total page 195 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Instabilities Turbulence and Mixing from Internal Waves at Bottom Topography written by Vamsi Krishna Chalamalla and published by . This book was released on 2015 with total page 155 pages. Available in PDF, EPUB and Kindle. Book excerpt: This study of nonlinear processes and turbulence associated with internal gravity waves has three phases. In the first phase, the reflection problem is studied with simulations involving laboratory-scale slopes whose inclination varies between critical (resonant case with slope angle equal to wave propagation angle) and somewhat off-critical values. We start with three-dimensional direct numerical simulation (DNS) and find strong nonlinearity in the response if the off-criticality is not too large: harmonics in the radiated wave field and cyclical near-bottom turbulence. Subharmonic frequencies are found slightly away from the interaction region in some cases, prompting a followup study with two-dimensional simulations where the underlying mechanism is identified as parametric subharmonic instability (PSI) of the reflected wave beam: the sum of the frequencies and the sum of the wave numbers of the daughter subharmonic waves equal the corresponding quantities for the reflected wave. This is the first demonstration that the reflected wave formed when a small-amplitude linear wave is incident on a slope becomes sufficiently nonlinear so as to suffer PSI. In the second phase, DNS and large eddy simulation (LES) are employed to study the turbulent dissipation and mixing brought about by convective overturns in a stratified, oscillatory bottom layer underneath internal waves. The phasing of turbulence, the onset and breakdown of convective overturns, and the pathway to irreversible mixing are quantified. $L_T$ decreases during the convective instability while $L_O$ increases, which implies that $L_T$ is not linearly related to $L_O$. Thus, the instantaneous Thorpe-inferred dissipation rates are quite different from the actual values. However, the ratio of their cycle-averaged values is found to be O(1). In the third phase, a novel modeling technique called SOMAR-LES has been developed wherein a three-dimensional, body-conforming Large Eddy Simulation (LES) model that resolves turbulence scales is coupled with the large-sale Stratified Ocean Model with Adaptive Refinement (SOMAR) to accurately represent small scale turbulence as well as its effect on flow evolution at large scale. Numerical simulations are performed with coupled SOMAR-LES to examine the flow at model Kaena ridge, a steep supercritical generation site.
Download or read book Internal Waves and Mean Flow in the Presence of Topography written by Keshav Jayakrishnan Raja and published by . This book was released on 2018 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Internal waves play an important role in many processes in oceans. The interaction be-tween internal waves and ocean topography has been an active field of research for long. Yetthere are many questions remaining on the topic. In this thesis, two main processes are ex-amined namely, the reflection of internal wave beams on a slope, and generation of lee wavesover a three-dimensional obstacle, using laboratory experiments and numerical simulations.The nonlinear reflection of an internal wave beam on a uniform slope is studied using two-dimensional inviscid theory and numerical simulations. The resonant triadic interactionsamong the incident, reflected and second harmonic wave beams are investigated developingon existing theory and verifying them with results for numerical simulations.In the case of reflection of three-dimensional internal wave beams, a strong mean horizon-tal flow is found to be induced by the wave beam, which perturbs the wave field and weakensthe second harmonics. The generation of this wave-induced mean flow is examined usingresults from experiments and three-dimensional numerical simulations. Furthermore, theeffects of background rotation on the wave induced mean flow are also studied using numer-ical simulations.The Antarctic Circumpolar Current is considered as one of the main sources of mixing inoceans. Laboratory modelling of the Antarctic Circumpolar Current was done in the Coriolisplatform at LEGI to study the topography induced drag on the current. The experiment andits results are also presented.
Download or read book Environmental Hydraulics Volume 1 written by Georgos C. Christodoulou and published by CRC Press. This book was released on 2022-03-07 with total page 649 pages. Available in PDF, EPUB and Kindle. Book excerpt: Over the last two decades environmental hydraulics as an academic discipline has expanded considerably, caused by growing concerns over water environmental issues associated with pollution and water balance problems on regional and global scale. These issues require a thorough understanding of processes related to environmental flows and transport phenomena, and the development of new approaches for practical solutions. Environmental Hydraulics includes about 200 contributions from 35 countries presented at the 6th International Symposium on Environmental Hydraulics (Athens, Greece, 23-25 June 2010). They cover the state-of-the-art on a broad range of topics, including: fundamentals aspects of environmental fluid mechanics; environmental hydraulics problems of inland, coastal and ground waters; interfacial processes; computational, experimental and field measurement techniques; ecological aspects, and effects of global climate change. Environmental Hydraulics will be of interest to researchers, civil/environmental engineers, and professional engineers dealing with the design and operation of environmental hydraulic works such as wastewater treatment and disposal, river and marine constructions, and to academics and graduate students in related fields.
Download or read book Journal of Physical Oceanography written by and published by . This book was released on 2005 with total page 1410 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Advances in Numerical Simulation of Nonlinear Water Waves written by Qingwei Ma and published by World Scientific. This book was released on 2010 with total page 700 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ch. 1. Model for fully nonlinear ocean wave simulations derived using Fourier inversion of integral equations in 3D / J. Grue and D. Fructus -- ch. 2. Two-dimensional direct numerical simulations of the dynamics of rogue waves under wind action / J. Touboul and C. Kharif -- ch. 3. Progress in fully nonlinear potential flow modeling of 3D extreme ocean waves / S.T. Grilli [und weitere] -- ch. 4. Time domain simulation of nonlinear water waves using spectral methods / F. Bonnefoy [und weitere] -- ch. 5. QALE-FEM method and its application to the simulation of free-responses of floating bodies and overturning waves / Q.W. Ma and S. Yan -- ch. 6. Velocity calculation methods in finite element based MEL formulation / V. Sriram, S.A. Sannasiraj and V. Sundar -- ch. 7. High-order Boussinesq-type modelling of nonlinear wave phenomena in deep and shallow water / P.A. Madsen and D.R. Fuhrman -- ch. 8. Inter-comparisons of different forms of higher-order Boussinesq equations / Z.L. Zou, K.Z. Fang and Z.B. Liu -- ch. 9. Method of fundamental solutions for fully nonlinear water waves / D.-L. Young, N.-J. Wu and T.-K. Tsay -- ch. 10. Application of the finite volume method to the simulation of nonlinear water waves / D. Greaves -- ch. 11. Developments in multi-fluid finite volume free surface capturing method / D.M. Causon, C.G. Mingham and L. Qian -- ch. 12. Numerical computation methods for strongly nonlinear wave-body interactions / M. Kashiwagi, C. Hu and M. Sueyoshi -- ch. 13. Smoothed particle hydrodynamics for water waves / R.A. Dalrymple [und weitere] -- ch. 14. Modelling nonlinear water waves with RANS and LES SPH models / R. Issa [und weitere] -- ch. 15. MLPG_R method and Its application to various nonlinear water waves / Q.W. Ma -- ch. 16. Large Eddy simulation of the hydrodynamics generated by breaking waves / P. Lubin and J.-P. Caltagirone -- ch. 17. Recent advances in turbulence modeling for unsteady breaking waves / Q. Zhao and S.W. Armfield -- ch. 18. Freak waves and their interaction with ships and offshore structures / G.F. Clauss
Download or read book Oceanic Internal Tides Observations Analysis and Modeling written by Eugene G. Morozov and published by Springer. This book was released on 2018-02-08 with total page 317 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents a detailed study of the structure and variability of internal tides and their geographical distribution in the ocean. Based on experimental analysis of oceanic measurements combined with numerical modeling, it offers a comprehensive overview of the internal wave processes around the globe. In particular, it is based on moored buoys observations in many regions in all oceans (Atlantic, Pacific, Indian, Arctic, and Southern) that have been carried out by researchers from different countries for more than 40 years as part of various oceanographic programs, including WOCE and CLIVAR. However, a significant portion of the data was collected by the author, who is a field oceanographer. The data was processed and interpreted on the basis of the latest knowledge of internal wave motion. The properties of internal waves were analyzed in relation to the bottom topography and mean state of the ocean in specific regions. Internal waves play a major role in the formation of seawater stratification and are responsible for the main processes of ocean dynamics, such as energy transfer and mixing. One of the most significant ideas presented in this book is the generation of internal tides over submarine ridges. Energy fluxes from submarine ridges related to tidal internal waves greatly exceed the fluxes from continental slopes. Submarine ridges form an obstacle to the propagation of tidal currents, which can cause the creation of large amplitude internal tides. Energy fluxes from submarine ridges account for approximately one fourth of the total energy dissipation of the barotropic tides. Model simulations and moored measurements have been combined to generate a map of global distribution of internal tide amplitudes. This book is of interest to oceanographers, marine biologists, civil engineers, and scientists working in climate research, fluid mechanics, acoustics, and underwater navigation.
Download or read book Environmental Fluid Mechanics written by Wolfgang Rodi and published by CRC Press. This book was released on 2012-05-28 with total page 456 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book contains the written versions of invited lectures presented at the Gerhard H. Jirka Memorial Colloquium on Environmental Fluid Mechanics, held June 3-4, 2011, in Karlsruhe, Germany. Professor Jirka was widely known for his outstanding work in Environmental Fluid Mechanics, and 23 eminent world-leading experts in this field contributed to
Download or read book Environmental Hydraulics Two Volume Set written by George C. Christodoulou and published by CRC Press. This book was released on 2010-06-09 with total page 1288 pages. Available in PDF, EPUB and Kindle. Book excerpt: Over the last two decades environmental hydraulics as an academic discipline has expanded considerably, caused by growing concerns over water environmental issues associated with pollution and water balance problems on regional and global scale. These issues require a thorough understanding of processes related to environmental flows and transport
Download or read book Internal Gravity Waves written by Bruce R. Sutherland and published by Cambridge University Press. This book was released on 2010-09-02 with total page 395 pages. Available in PDF, EPUB and Kindle. Book excerpt: The study of internal gravity waves provides many challenges: they move along interfaces as well as in fully three-dimensional space, at relatively fast temporal and small spatial scales, making them difficult to observe and resolve in weather and climate models. Solving the equations describing their evolution poses various mathematical challenges associated with singular boundary value problems and large amplitude dynamics. This book provides the first comprehensive treatment of the theory for small and large amplitude internal gravity waves. Over 120 schematics, numerical simulations and laboratory images illustrate the theory and mathematical techniques, and 130 exercises enable the reader to apply their understanding of the theory. This is an invaluable single resource for academic researchers and graduate students studying the motion of waves within the atmosphere and ocean, and also mathematicians, physicists and engineers interested in the properties of propagating, growing and breaking waves.
