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51.
Internal pressure gradient estimation is problematic in σ-coordinate ocean models and models based on more generalised topography following coordinate systems. Artificial pressure
gradients in these models may create artificial flow. In recent literature, several methods for reducing the errors in the
estimated internal pressure gradients are suggested. A basin with a bell-shaped seamount in the middle has often been applied
as a test case. To supplement the findings from these more idealised experiments, the internal pressure gradient errors in
a σ-coordinate ocean model for the Nordic Seas are discussed in the present paper. Three methods for estimating internal pressure
gradients are applied in these experiments. The sensitivity of the results to the subtraction of background stratification
and to the horizontal viscosity are also investigated. For the extended Nordic Seas case, basin scale modes dominate after
a few days of simulation. The errors in the transports across some sections may be larger than 1 Sv (1 Sv = 106 m3 s − 1) in these studies with 16-km grid resolution. The order of magnitude of the errors in the transports of Atlantic water into
the Nordic Seas is approximately 0.5 Sv or between 5 and 10 % of recent transport estimates based on measurements. The results
do not indicate that the errors are generally reduced if the background stratification is subtracted when estimating internal
pressure gradients in terrain following models. However, the results from the experiments initialised with the background
stratification show that the erroneous flows may be reduced considerably by using more recent techniques for estimating internal
pressure gradients, especially for higher values of horizontal viscosity. 相似文献
52.
Dmitry Eydinov Sigurd Ivar Aanonsen Jarle Haukås Ivar Aavatsmark 《Computational Geosciences》2008,12(2):209-225
A method for history matching of an in-house petroleum reservoir compositional simulator with multipoint flux approximation
is presented. This method is used for the estimation of unknown reservoir parameters, such as permeability and porosity, based
on production data and inverted seismic data. The limited-memory Broyden–Fletcher–Goldfarb–Shanno method is employed for minimization
of the objective function, which represents the difference between simulated and observed data. In this work, we present the
key features of the algorithm for calculations of the gradients of the objective function based on adjoint variables. The
test example shows that the method is applicable to cases with anisotropic permeability fields, multipoint flux approximation,
and arbitrary fluid compositions. 相似文献
53.
The nonhydrostatic pressure effects on the generation and propagation of wind-forced internal waves are studied with a two-dimensional
numerical ocean model. A one-way directed wind pulse over a stratified ocean initiates surface and internal waves in a closed
basin. The studies are performed with horizontal grid sizes in the range from 1 km to 62.5 m. The experiments are performed
with both a hydrostatic and a nonhydrostatic model, facilitating systematic studies of the sensitivity of the numerical model
results to the grid size and to the nonhydrostatic pressure adjustments. The results show that the nonhydrostatic pressure
effects are highly dependent on the grid size and grow with increased resolution. In the internal depression wave, the horizontal
nonhydrostatic pressure gradients reach the same order of magnitude as the hydrostatic gradients in the high-resolution nonhydrostatic
studies. In these studies, the nonhydrostatic pressure gradients approximately balance the corresponding hydrostatic pressure
gradients in the internal depression wave, and the wave degenerates into a train of soliton waves. The time for the soliton
form to develop agrees with the steepening timescale calculated from Korteweg-de Vries theory. In the high-resolution hydrostatic
model, the internal depression wave takes the form of a single wave front. When the internal waves are generated in the boundary
layers, the nonhydrostatic pressure gradients are much smaller than the hydrostatic gradients and the generation processes
are not effected by the nonhydrostatic pressure with the present range of grid sizes. 相似文献
54.
The effect of horizontal grid resolution on the horizontal relative dispersion of particle pairs has been investigated on
a short time scale, i.e. one tidal M
2 cycle. Of particular interest is the tidal effect on dispersion and transports in coastal waters where small-scale flow features
are important. A three-dimensional ocean model has been applied to simulate the tidal flow through the Moskstraumen Maelstrom
outside Lofoten in northern Norway, well known for its strong current and whirlpools (Gjevik et al., Nature 388(6645):837–838,
1997; Moe et al., Cont Shelf Res 22(3):485–504, 2002). Simulations with spatial resolution down to 50 m have been carried out. Lagrangian tracers were passively advected with
the flow, and Lyapunov exponents and power law exponents have been calculated to analyse the separation statistics. It is
found that the relative dispersion of particles on a short time scale (12–24 h) is very sensitive to the grid size and that
the spatial variability is also very large, ranging from 0 to 100 km2 over a distance of 100 m. This means that models for prediction of transport and dispersion of oil spills, fish eggs, sea
lice etc. using a single diffusion coefficient will be of limited value, unless the models actually resolves the small-scale
eddies of the tidal current. 相似文献
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