A numerical study of tidal asymmetry in Okatee Creek, South Carolina

An unstructured mesh tidal model of the west coast of Britain, covering the Celtic Sea and Irish Sea is used to compare tidal distributions computed with finite element (F.E.) and finite volume (F.V.) models. Both models cover an identical region, use the same mesh, and have topography and tidal boundary forcing from a finite difference model that can reproduce the tides in the region. By this means solutions from both models can be compared without any bias towards one model or another. Two dimensional calculations show that for a given friction coefficient there is more damping in the F.V. model than the F.E. model. As bottom friction coefficient is reduced the two models show comparable changes in tidal distributions. In terms of mesh resolution, calculations show that for the M2 tide the mesh is sufficiently fine to yield an accurate solution over the whole domain. However in terms of higher harmonics of the tide, in particular the M6 component, its small scale variability in near shore regions which is comparable to the mesh of the model, suggests that the mesh resolution is insufficient in the near coastal regions. Even with a finer mesh in these areas, without detailed bottom topography and a spatial varying friction depending on bed types and bed forms, which is not available, model skill would probably not be improved. In addition in the near shore region, as shown in the literature, the solution is sensitive to the form of the wetting/drying algorithm used in the model. Calculations with a three dimensional version of the F.V. model show that for a given value of k, damping is reduced compared to the two dimensional version due to the differences in bed stress formulation, with the three dimensional model yielding an accurate tidal distribution over the region. (1) Description of models slightly enhanced. As a detailed description is given in published papers, these are cited, as we do not wish to repeat information. In addition since a functional form of the solution is given over each finite element or finite volume this can be used to interpolate solutions (e.g. water elevations) to any location. This point made in text. (2) It is made clear that the staircase representation of the coastline only relates to a certain class of finite difference model. (3) The k-0.003 calculations are mentioned "early on". (4) Possibility of lack of mesh resolution influencing solution of higher harmonics is discussed in context of the fact that this could also be influenced by "wetting and drying". Additional references added. (5) Abstract rephrased to suggest this, rather than claim that it has been shown. Similar in text. (6) Elaborated to show that in the near short region the amplitude of the higher harmonics changes very rapidly from one mesh element to another. A sure sign of a lack of spatial convergence. The confusion between temporal convergence, where iteration ensures that a converged solution does occur and spatial convergence is now clarified. (7) The realistic nature of these coefficients is c...

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“…model based on FVCOM (Chen et al 2003, Huang et al 2008, with those derived from a F.E. model namely TELEMAC (e.g.…”

Section: Introductionmentioning

confidence: 99%

A model study of tidal distributions in the Celtic and Irish Sea regions determined with finite volume and finite element models

2011

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“…FVCOM uses unstructured triangular cells in the horizontal plane and a sigma-stretched coordinate system in the vertical direction to better represent the complex horizontal geometry and bottom topography of an estuary. FVCOM has been applied to simulate tidal dynamics and circulations in many estuarine and coastal waters (Zheng et al 2003;Zhao et al 2006;Weisberg and Zheng 2006;Hu et al 2008;Huang et al 2008;Chen et al 2009;Yang and Khangaonkar 2010;Lai et al 2010;Yang et al 2011;Xing et al 2011). …”

Section: Numerical Modelmentioning

confidence: 99%

Assessment of Tidal Energy Removal Impacts on Physical Systems: Development of MHK Module and Analysis of Effects on Hydrodynamics

Yang¹,

Wang²

2011

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In this report we describe 1) the development, test, and validation of the marine hydrokinetic energy scheme in a three-dimensional coastal ocean model (FVCOM); and 2) the sensitivity analysis of effects of marine hydrokinetic energy configurations on power extraction and volume flux in a coastal bay. Submittal of this report completes the work on Task 2. Project OverviewEnergy generated from the world's oceans and rivers offers the potential to make substantial contributions to the domestic and global renewable energy supply. The U.S. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE) Wind and Water Power Program supports the emerging marine and hydrokinetic (MHK) energy industry. As partners in an emerging industry, MHK project developers face challenges with siting, permitting, construction, and operation of pilot-and commercial-scale facilities, as well as the need to develop robust technologies, secure financing, and gain public acceptance.In many cases, little is known about the potential effects of MHK energy generation on the aquatic environment from a small number of devices or a large-scale commercial array. Nor do we understand potential effects that may occur after years or decades of operation. This lack of knowledge affects the solvency of the industry, the actions of regulatory agencies, the opinions and concerns of stakeholder groups, and the commitment of energy project developers and investors.To unravel and address the complexity of environmental issues associated with MHK energy, Pacific Northwest National Laboratory (PNNL) is developing a program of research and development that draws on the knowledge of the industry, regulators, and stakeholders and builds on investments made by the EERE Wind and Water Power Program. The PNNL program of research and development-together with complementary efforts of other national laboratories, national marine renewable energy centers, universities, and industry-supports DOE's market acceleration activities through focused research and development on environmental effects and siting issues. Research areas addressed include  categorizing and evaluating effects of stressors -Information on the environmental risks from MHK devices, including data obtained from in situ testing and laboratory experiments (see other tasks below) will be compiled in a knowledge management system known as Tethys to facilitate the creation, annotation, and exchange of information on environmental effects of MHK technologies.Tethys will support the Environmental Risk Evaluation System (ERES) that can be used by developers, regulators, and other stakeholders to assess relative risks associated with MHK technologies, site characteristics, waterbody characteristics, and receptors (i.e., habitat, marine mammals, and fish). Development of Tethys and the ERES will require focused input from various stakeholders to ensure accuracy and alignment with other needs. effects on physical systems -Computational numerical modeling will be used to understan...

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“…However, in very shallow water areas, "wetting and drying" occurred over the tidal cycle and was implemented in both the FE and FV models in a similar manner (e.g. see Chen et al 2003Chen et al , 2008Huang et al 2008;Greenberg et al 2005, for detail). At a closed boundary, the normal component of velocity was set to zero, while at an open boundary identical tidal forcing was applied in both models and was the same as that used by Davies and Jones (1992) and Jones and Davies (2007).…”

Section: Form Of the Fundamental Equationsmentioning

confidence: 99%

“…The notable exception to this is when a boundary fitted coordinate is used. An alternative approach to finite elements is to use a finite volume method on an unstructured mesh (Chen et al 2003(Chen et al , 2007Huang et al 2008). This again avoids nesting and yields a smooth representation of the coast.…”

Section: Introductionmentioning

confidence: 99%

Modelling tide–surge interaction effects using finite volume and finite element models of the Irish Sea

et al. 2011

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An unstructured mesh model of the west coast of Britain, covering the same domain and using topography and open boundary forcing that are identical to a previous validated uniform grid finite difference model of the region, is used to compare the performance of a finite volume (FV) and a finite element (FE) model of the area in determining tide-surge interaction in the region. Initial calculations show that although qualitatively both models give comparable tidal solutions in the region, comparison with observations shows that the FV model tends to underestimate tidal amplitudes and hence background tidal friction in the eastern Irish Sea. Storm surge elevations in the eastern Irish Sea due to westerly, northerly and southerly uniform wind stresses computed with the FV model tend to be slightly higher than those computed with the FE model, due to differences in background tidal friction. However, both models showed comparable nonlinear tide-surge interaction effects for all wind directions, suggesting that they can reproduce the extensive tide-surge interaction processes that occur in the eastern Irish Sea. Following on from this model comparison study, the physical processes contributing to surge generation and tide-surge interaction in the region are examined. Calculations are performed with uniform wind stresses from a range of directions, and the balance of various terms in the hydrodynamic equations is examined. A detailed comparison of the spatial variability of time series of nonlinear bottom friction and non-linear momentum advection terms at six adjacent nodes at two locations in water depths of 20 and 6 m showed some spatial variability from one node to another. This suggests that even in the near coastal region, where water depths are of the order of 6 m and the mesh is fine (of order 0.5 km), there is significant spatial variability in the non-linear terms. In addition, distributions of maximum bed stress due to tides and wind forcing in nearshore regions show appreciable spatial variability. This suggests that intensive measurement campaigns and very high-resolution mesh models are required to validate and reproduce the non-linear processes that occur in these regions and to predict extreme bed stresses that can give rise to sediment movement. High-resolution meshes will also be required in pollution transport problems.

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A numerical study of tidal asymmetry in Okatee Creek, South Carolina

Cited by 61 publications

References 24 publications

A model study of tidal distributions in the Celtic and Irish Sea regions determined with finite volume and finite element models

A model study of tidal distributions in the Celtic and Irish Sea regions determined with finite volume and finite element models

Assessment of Tidal Energy Removal Impacts on Physical Systems: Development of MHK Module and Analysis of Effects on Hydrodynamics

Modelling tide–surge interaction effects using finite volume and finite element models of the Irish Sea

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