Coupled Hydrodynamic Model Research Articles

Prediction of Water Quality of Huangpu River Using a Tidal River Network Model

The Huangpu River is the largest river in Shanghai. It exerts great influence on this metropolitan due to the role of the metropolitan's largest drinking water source and the direct scenery waters bordering the venues of World Exposition Shanghai China 2010 (World EXPO 2010), so a series of water environment rehabilitation projects will be carried out during the eleventh five-year plan (2006–2010). The one-dimensional and two-dimensional coupling hydrodynamic and water quality model—RMA2 and RMA4—developed by the United States Army Corps of Engineers, was modified and applied to develop a Shanghai tidal river network model in order to assess the Huangpu River's water quality by 2010; in which the COD decaying rate, nitrification rate, BOD5 decaying rate, sediment oxygen demand, and re-aeration rate were calibrated. The calibrated results of these coefficients were 0.10–0.25 d−1, 0.03–0.07 d −1, 0.10–0.15 d −1, 1.0–10.0 g m −2 d −1, and 0.15–0.20 d −1, respectively. According to China's National Surface Wa...

Calibration of an estuarine sediment transport model to sediment fluxes as an intermediate step for simulation of geomorphic evolution

Modeling geomorphic evolution in estuaries is necessary to model the fate of legacy contaminants in the bed sediment and the effect of climate change, watershed alterations, sea level rise, construction projects, and restoration efforts. Coupled hydrodynamic and sediment transport models used for this purpose typically are calibrated to water level, currents, and/or suspended-sediment concentrations. However, small errors in these tidal-timescale models can accumulate to cause major errors in geomorphic evolution, which may not be obvious. Here we present an intermediate step towards simulating decadal-timescale geomorphic change: calibration to estimated sediment fluxes (mass/time) at two cross-sections within an estuary. Accurate representation of sediment fluxes gives confidence in representation of sediment supply to and from the estuary during those periods. Several years of sediment flux data are available for the landward and seaward boundaries of Suisun Bay, California, the landward-most embayment of San Francisco Bay. Sediment flux observations suggest that episodic freshwater flows export sediment from Suisun Bay, while gravitational circulation during the dry season imports sediment from seaward sources. The Regional Oceanic Modeling System (ROMS), a three-dimensional coupled hydrodynamic/sediment transport model, was adapted for Suisun Bay, for the purposes of hindcasting 19th and 20th century bathymetric change, and simulating geomorphic response to sea level rise and climatic variability in the 21st century. The sediment transport parameters were calibrated using the sediment flux data from 1997 (a relatively wet year) and 2004 (a relatively dry year). The remaining years of data (1998, 2002, 2003) were used for validation. The model represents the inter-annual and annual sediment flux variability, while net sediment import/export is accurately modeled for three of the five years. The use of sediment flux data for calibrating an estuarine geomorphic model guarantees that modeled geomorphic evolution will not exceed the actual supply of sediment from the watershed and seaward sources during the calibration period. Decadal trends in sediment supply (and therefore fluxes) can accumulate to alter decadal geomorphic change. Therefore, simulations of future geomorphic evolution are bolstered by this intermediate calibration step.

Different modelling tools of aquatic ecosystems: A proposal for a unified approach

Over the last few decades, several modelling tools have been developed for the simulation of hydrodynamic and biogeochemical processes in aquatic ecosystems. Until late 70's, coupling hydrodynamic models to biogeochemical models was not common and today, problems linked to the different scales of interest remain. The time scale of hydrodynamic phenomena in coastal zone (minutes to hours) is much lower than that of biogeochemistry (few days). Over the last years, there has been an increasing tendency to couple hydrodynamic and biogeochemical models in a clear recognition of the importance of incorporating in one model the feedbacks between physical, chemical and biological processes. However, different modelling teams tend to adopt different modelling tools, with the result that benchmarking exercises are sometimes difficult to achieve in projects involving several institutions. Therefore, the objectives of this paper are to provide a quick overview of available modelling approaches for hydrodynamic and biogeochemical modelling, to help people choose among the diversity of available models, as a function of their particular needs, and to propose a unified approach to allow modellers to share software code, based on the object oriented programming potentiality. This approach is based on having object dynamic link libraries that may be linked to different model shells. Each object represents different processes and respective variables, e.g. hydrodynamic, phytoplankton and zooplankton objects. Some simple rules are proposed to link available objects to programs written in different source codes.

Numerical problems associated with coupling hydrodynamic models in shelf edge regions: the surge event of February 1994

A coarse grid three dimensional model of the north west European Continental shelf, and a finer grid model of the region off the west coast of Scotland and the Irish Sea are used to examine flow through the North Channel of the Irish Sea. The period of the storm event of February 1994 is considered. Comparisons of computed and observed currents in the North Channel show that the shelf wide model can reproduce the main features of the flow, although the grid of the model is too coarse to resolve the detailed topography in the region. Calculations with the fine grid model alone, show that at times of strong meteorological forcing in the North Channel region (at the start of the storm) this model can accurately reproduce the flow. However at times of reduced wind forcing (later in the storm period) when shelf wide elevation gradients are important in determining flow along the west coast of Britain, the limited area fine grid model fails to reproduce the flow, to such an extent that the current is in the wrong direction. Nesting the fine grid model within the shelf wide model, using a conventional radiation condition, produces a slight improvement, although in the shelf edge region there are problems. Also, the nested model fails to reproduce the correct current direction in the North Channel to a similar extent to that found using the west coast model alone. A simple adjustment to the radiation condition to take account of the transport computed with the shelf wide model is developed. When this condition is applied to nest the west coast model to the shelf model, there is a significant improvement in the currents in the shelf edge region. Also, the flow through the North Channel is correctly reproduced. Results from the calculations show that at times of strong winds off the west coast, the North Channel flow can be explained in terms of local wind forcing. However, at times of weak winds following a strong wind period the flow is related to shelf wide elevation gradients. Including their effect in a limited area model where the open boundary crosses steep topography (namely the shelf edge) is shown to produce some problems, although these can be overcome.

Coupled hydrodynamic and transport models of Port Phillip Bay, a semi-enclosed bay in south-eastern Australia

Coupled hydrodynamic and transport models of Port Phillip Bay were developed as part of the Port Phillip Bay Environmental Study. Model coupling was achieved via a particle tracking method, giving great flexibility in both geometry and time step for the transport model. This technique allowed ecological (water quality) modules to be included efficiently, so that long-term management scenarios could be adequately addressed. Validation of the hydrodynamic model was done primarily against observed sea-level and current meter data. For the transport model, comparisons were made with data on salinity in the bay observed over five years. Despite some disagreement between the hydrodynamic model and observations of longer-term (non-tidal) currents, the transport model provided good simulations of salinity throughout the bay. Transport-model flushing time for the bay was about 270 days (similar to estimates obtained from salinity and radionuclide measurements), varying with model geometry and with position inside the bay. As well as providing physical forcing for ecological simulations (described elsewhere in this issue), the models identified a systematic bias in the known freshwater budget for the bay.

FX2-POOL—A Two-Dimensional Coupled Hydrodynamic Thermodynamic and Neutronic Computer Model for Hypothetical Core Disruptive Accident Analysis

Subroutine POOL was developed for the study of hypothetical core disruptive accidents in nuclear reactors and, as such, is set up for use as a subroutine in the FX-2 Dynamic Neutronics Code. This combination permits scoping studies of the total neutronic/hydrodynamic interactions and is capable of performing phenomenological investigations of hypothetical problems ranging from the high ramp disassembly calculations, performed in the past by the Lagrangian code VENUS, to the study of recriticality in boiling pools of fuel and steel. POOL specifically includes, in at least parametric fashion, the following phenomena: (1) intra- and inter-element heat transfer by diffusion, convection, and radiation for both fuel and steel inside the pool and at the boundaries; (2) local vapor generation and concurrent local pressurization; and (3) hydrodynamic behavior using the inviscid Navier-Stokes equations in a Eulerian formulation. Sample results are shown for boil-up of an initially quiescent dense pool of fuel and steel. Subroutine POOL was modified by removing the free surface portion of the calculation and the associated expansion of the Eulerian Grid. The combined code, known as FX2-POOL, was used to perform prompt burst calculations for two comparison cases for a 1000-MW(t) demo-like reactor. Good agreement is shown between FX2-POOLmore » and VENUS II for these two hypothetical situations, indicating that the hydrodynamic and thermodynamic assumptions made in POOL are accurate enough for prompt burst analysis and compare well with the VENUS models.« less