|عنوان فارسی مقاله:||سیر تکاملی اثر پیوسته موج و جریان در پوشش گیاهی|
|عنوان انگلیسی مقاله:||Development of a coupled wave-flow-vegetation interaction model|
|رشته های مرتبط:||زمین شناسی و آب شناسی|
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|نشریه||الزویر – Elsevier|
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|جستجوی ترجمه مقالات||جستجوی ترجمه مقالات زمین شناسی|
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4.2.3. هزینه محاسباتی، موانع و ملاحظات آینده
بخشی از مقاله انگلیسی:
Emergent and submerged vegetation can significantly affect coastal hydrodynamics. However, most deterministic numerical models do not take into account their influence on currents, waves, and turbulence. In this paper, we describe the implementation of a wave-flow-vegetation module into a Coupled-Ocean-AtmosphereWave-Sediment Transport (COAWST) modeling system that includes a flow model (ROMS) and a wave model (SWAN), and illustrate various interacting processes using an idealized shallow basin application. The flow model has been modified to include plant posture-dependent three-dimensional drag, in-canopy wave-induced streaming, and production of turbulent kinetic energy and enstrophy to parameterize vertical mixing. The coupling framework has been updated to exchange vegetation-related variables between the flow model and the wave model to account for wave energy dissipation due to vegetation. This study i) demonstrates the validity of the plant posture-dependent drag parameterization against field measurements, ii) shows that the model is capable of reproducing the mean and turbulent flow field in the presence of vegetation as compared to various laboratory experiments, iii) provides insight into the flow-vegetation interaction through an analysis of the terms in the momentum balance, iv) describes the influence of a submerged vegetation patch on tidal currents and waves separately and combined, and v) proposes future directions for research and development.
4.2.3. Computational expense, obstacles and future considerations
We compared the computational costs of using the vegetation module relative to a simplified approach that uses bottom roughness to account for increased drag in the model domain. The increase in the computational costs arises in different parts of the model, mainly in the 2D and 3D kernels, and the GLS vertical mixing model which computes turbulent quantities (Table 2). Overall, the vegetation module increases computational costs by 6% over a run where the vegetation patch is represented by coarser sediment. The increase occurs from the calculation of the vegetation drag and turbulence terms in the vegetation module. These terms are then added to the 2D kernel, 3D momentum equations, and vertical mixing parameterization. The implementation of this functionality in COAWST was met by several numerical and conceptual obstacles, which will require future investigation and troubleshooting. For example, the ROMS hydrodynamic model required a reduced time step with the vegetation module (e.g. 1 s instead of 10 s) to eliminate instabilities resulting from sharp velocity gradients. We also found that horizontal buoyancy and shear terms in the turbulence model needed to be unsmoothed to avoid perturbations at the corner of the vegetation patch. One possible solution is to gradually ramp up vegetation density into the patch, which can either be accomplished through modification of the initialization file, or through a coding modification. The SWAN model currently does not account for multiple vegetation types, and does not dissipate wave energy (due to vegetation) spectrally; i.e. dissipation is applied uniformly across the wave spectra. In the case of multiple vegetation types an equivalent shoot density is defined in ROMS and SWAN. Future versions of SWAN will account for spatially-variable plant properties as in ROMS. Lastly, a systematic parameter study would constrain the uncertainty of the numerous model parameterizations implemented here. The development of this open-source tool will allow such studies to commence.
5. Summary and conclusion
We have developed a coupled wave-flow-vegetation module in the COAWST modeling system applicable to vegetated flows in riverine, lacustrine, estuarine and coastal environments. New vegetative components were implemented in the flow model ROMS, namely plant posture-dependent three-dimensional drag, vertical mixing, and waveinduced streaming. The model reproduces key features of flow-vegetation hydrodynamic interaction, in particular the strong shear layer at the top of a submerged canopy which varies in height as the plants bend. The coupling framework has also been updated to exchange vegetation-related variables between the flow and the wave model SWAN to account for wave dissipation by vegetation in the presence of currents and water level fluctuations. Results from the idealized test case in shallow water highlight the nonlinear interdependency between (tidal) flow and wave characteristics in the presence of a vegetation patch. In particular, the coupled wave-flow-vegetation model shows that the vegetation modifies the wave characteristics (height, period, steepness, and direction) primarily by wave energy dissipation resulting from the work done by drag force on the vegetation stems, and secondarily by influencing the water level and current fields: i) any (positive or negative) gradient of free surface elevation across the vegetation patch reduces vegetation-induced wave damping; ii) wave dissipation rate decreases/increases when waves propagate along/ against the current, while the (intrinsic) wave frequency increases/ decreases to conserve wave action density which enhances/diminishes wave dissipation by bed friction and vegetation drag. In parallel, waves influence the flow; therefore, waves alter the capacity of vegetation to reduce current speed and adjust water level. This model contributes to an improved understanding of how aquatic vegetation influences the physical environment and, more generally, provides a multidisciplinary tool for informing decision-making of the potential ecologic and economic benefits of aquatic vegetation.