scholarly journals Stabilized Formulation for Modeling the Erosion/Deposition Flux of Sediment in Circulation/CFD Models

Water ◽  
2019 ◽  
Vol 11 (2) ◽  
pp. 197 ◽  
Author(s):  
Yi-Ju Chou ◽  
Yun-Chuan Shao ◽  
Yi-Hao Sheng ◽  
Che-Jung Cheng
Keyword(s):  
Transport Model ◽  
Three Dimensional ◽  
Circulation Model ◽  
Sediment Concentration ◽  
Dry Density ◽  
Deposition Flux ◽  
Model Stability ◽  
Cfd Models ◽  
Bottom Boundary Condition ◽  
Coastal Circulation Model

In field-scale modeling, when the resuspension of sediment is modeled using a hydrodynamic model, a standard and common approach is to add a resuspension flux as the bottom boundary condition in the transport model. In this study, we show that the way of simply imposing an empirical bottom erosion formula as the flux is actually unrealistic. Its inability to stabilize the sediment concentration can cause excessive suspension fluxes in some extreme cases. Moreover, we present a modified erosion/deposition formula to model the resuspension of sediment. The formulation is based on volume conservation in the presence of erosion/deposition near the bottom. By taking into account the prescribed dry density of the bed material, the proposed formulation is able to produce realistic near-bed concentrations while ensuring model stability. The formulation is then tested in a one-dimensional vertical model and field modeling cases using a three-dimensional coastal circulation model. We show that the modified formulation is particularly important in modeling mud resuspension subject to the large bottom stress, which can be a result of waves or a strong river discharge.

Predictability of Total Ozone Using a Global Three-Dimensional Chemical Transport Model Coupled with the MRI/JMA98 GCM

2005 ◽  
Vol 133 (8) ◽  
pp. 2262-2274 ◽  
Author(s):  
T. T. Sekiyama ◽  
K. Shibata
Keyword(s):  
Total Ozone ◽  
General Circulation ◽  
Transport Model ◽  
Three Dimensional ◽  
Circulation Model ◽  
Chemical Transport ◽  
Japan Meteorological Agency ◽  
High Latitudes ◽  
Chemical Transport Model ◽  
Mean Square Errors

Abstract A global three-dimensional chemical transport model is being developed for forecasting total ozone. The model includes detailed stratospheric chemistry and transport and couples with a dynamical module of the Meteorological Research Institute/Japan Meteorological Agency 1998 (MRI/JMA98) general circulation model, which can yield realistic atmospheric fields through a meteorological assimilation system. Its predictability on total ozone is investigated for up to 4 weeks from 1997 to 2000. Global root-mean-square errors (rmses) of a control run are approximately 10 DU (3% of total ozone) throughout a year; the control run results are used as initial values for hindcast experiments. Rmses of the hindcast experiments globally range from 10 to 30 DU. The anomaly correlation between the 5-day forecasts and satellite measurements is approximately 0.6 throughout a year in the mid- and high latitudes of both the Northern and Southern Hemispheres. Thus, the model has potential for utilization on total ozone forecasts up to 5 days. In the northern mid- and high latitudes, the model produces better total ozone forecasts than the persistence up to 2 weeks, indicating that the deterministic limit of the total ozone forecasts is durationally comparable to that of weather forecasts. Good correlations between changes in total ozone and 100-hPa geopotential height reveal that the predictability of the dynamical field in the lower stratosphere critically affects the predictability of total ozone.

scholarly journals Three-dimensional modelling of wave-induced current from the surf zone to the inner shelf

2011 ◽  
Vol 8 (6) ◽  
pp. 2417-2478 ◽  
Author(s):  
H. Michaud ◽  
P. Marsaleix ◽  
Y. Leredde ◽  
C. Estournel ◽  
F. Bourrin ◽  
...  
Keyword(s):  
Surf Zone ◽  
Transport Model ◽  
Spatial Scales ◽  
Three Dimensional ◽  
Circulation Model ◽  
Good Representation ◽  
Depth Range ◽  
Littoral Drift ◽  
Inner Shelf ◽  
The Impact

Abstract. We develop and implement a new method to take into account the impact of waves into the 3-D circulation model SYMPHONIE (Marsaleix et al., 2008, 2009a), following the simplified equations of Bennis et al. (2011) which use glm2z-RANS theory (Ardhuin et al., 2008b). These adiabatic equations are completed by additional parameterizations of wave breaking, bottom friction and wave-enhanced vertical mixing, making the forcing valid from the surf zone through to the open ocean. The wave forcing is performed by wave generation and propagation models WAVEWATCH III® (Tolman, 2008, 2009; Ardhuin et al., 2010) and SWAN (Booij et al., 1999). The model is tested and compared with other models for a plane beach test case, previously tested by Haas and Warner (2009) and Uchiyama et al. (2010). A comparison is also made with the laboratory measurements of Haller et al. (2002) of a barred beach with channels. Results fit with previous simulations performed by other models and with available observational data. Finally, a realistic case of energetic waves travelling over a coast of the Gulf of Lion (in the northwest of the Mediterranean Sea) for which currents are available at different depths as well as an accurate bathymetric database of the 0–10 m depth range, is then simulated. A grid nesting approach is used to account for the different forcings acting at different spatial scales. The simulation coupling the effects of waves and currents is successful to reproduce the powerful northward littoral drift in the 0–15 m depth zone. More precisely, two distinct cases are identified: when waves have a normal angle of incidence with the coast, they are responsible for complex circulation cells and rip currents in the surf zone, and when they travel obliquely, they generate a northward littoral drift. These features are more complicated than in the test cases, due to the complex bathymetry and the consideration of wind and non-stationary processes. Wave impacts in the inner shelf are less visible since wind and regional circulation seem to be the predominant forcings. Besides, a discrepancy between model and observations is noted at that scale, possibly linked to an underestimation of the wind stress. Lastly, this three-dimensional method allows a good representation of vertical current profiles and permits to calculate the shear stress associated with wave and current. Future work will focus on the combination with a sediment transport model.

2D multi-layer hydrodynamic and sediment transport modelling in a tidal estuary

2020 ◽  
Author(s):  
Kai-Yi Bai ◽  
Jiing-Yun You
Keyword(s):  
Sediment Transport ◽  
Shallow Water ◽  
Finite Volume ◽  
Stokes Equations ◽  
Transport Model ◽  
Three Dimensional ◽  
Sediment Concentration ◽  
Computational Domain ◽  
Operation Rules ◽  
Sediment Transport Model

<p>This study developed a multi-layer hydrodynamic and sediment transport model for simulating tides and the estuarine flows. The flow circulation in an estuary shows complicated mixing and stratification patterns due to the combined effects from currents and tides. This kind of issues becomes more important in Taiwan in line with the more and more frequent sediment flushing operation which led to high sediment concentration flow at the estuary. In some applications,  three-dimensional (3D) models solving full Navier-Stokes equations were used. However, the extremely high computational cost, especially for the large-scale environmental problems, is always a serious concern. In the past years, continuous efforts have been devoted to the development of efficient quasi-three-dimensional models under hydrostatic and Boussinesq assumptions. Following the same state-of-the-art modelling strategy, this study develops a multi-layer shallow-water and sediment transport model with finite volume method. In this model, a terrain following coordinate with high local resolution is used to vertically divide the computational domain into multiple layers to better addressing bottom topography and velocity profile. Our model is rigorously validated against several benchmark cases including winddriven circulation, subcritical flow over a hump, tidal wave propagation, and sediment transport. The grid convergence test and accuracy both are in good agreement with analytical solutions. Subsequently, the model is applied to investigate the estuary dynamics and sediment transport under different conditions, e.g., flow discharges, bottom slopes, wind shears and tidal variations. Overall, the results show a relationship between flow conditions and sediment transport. Later, some scenarios for various upstream inflow and sediment concentration will be examined to assess the reservoir operation rules. </p><p><strong>Keywords: shallow water, sediment transport, multi-layer, hydrostatic, Boussinesq Assumption, a finite volume characteristics (FVC) method </strong><br> </p><p><br> <br> <br><br> </p>

scholarly journals Investigating Suspended-Sediment Transport in a Shallow Lake Using a Three-Dimensional Model

2017 ◽  
Author(s):  
Hong-Ming Liu ◽  
Wen-cheng Liu ◽  
Chih-Yu Chiu
Keyword(s):  
Sediment Transport ◽  
Suspended Sediment ◽  
Shallow Lake ◽  
Suspended Sediment Concentration ◽  
Transport Model ◽  
Three Dimensional ◽  
Sediment Concentration ◽  
Suspended Sediment Transport ◽  
Sediment Distribution ◽  
Mean Current

A three-dimensional, unstructured grid, hydrodynamic and suspended-sediment transport model (i.e., SELFE-SED) was developed to simulate temporal and spatial variations of suspended sediment and was applied to the subtropical subalpine Tsuei-Feng Lake (TFL) of Taiwan. The model was validated with measured water level and suspended‑sediment concentration in 2009, 2010, and 2011. The overall model simulation results are in quantitative agreement with the observational data. The validated model was then applied to explore the most important parameter that affects the suspended-sediment concentration and to investigate the effect of wind stress on the mean current and suspended‑sediment distribution in this shallow lake. Modeling results of sensitivity analysis reveal that the settling velocity is a crucial parameter and erosion rate is less important in the suspended-sediment transport model. Remarkable lake circulation was found based on the strength of wind speed and wind direction. Strong wind would result in higher mean current in the top layer and suspended-sediment distribution in the top and bottom layers. This study demonstrated that the wind stress played a significant influence on mean circulation and suspended-sediment transport in a shallow lake.

scholarly journals Local-time Dependence of Chemical Species in the Venusian Mesosphere

2022 ◽  
Vol 3 (1) ◽  
pp. 3
Author(s):  
Wencheng D. Shao ◽  
Xi Zhang ◽  
João Mendonça ◽  
Thérèse Encrenaz
Keyword(s):  
Local Time ◽  
General Circulation ◽  
Transport Model ◽  
Three Dimensional ◽  
Chemical Species ◽  
Circulation Model ◽  
Chemical Transport Model ◽  
Local Maxima ◽  
Time Patterns ◽  
Time Variations

Abstract Observed chemical species in the Venusian mesosphere show local-time variabilities. SO2 at the cloud top exhibits two local maxima over local time, H2O at the cloud top is uniformly distributed, and CO in the upper atmosphere shows a statistical difference between the two terminators. In this study, we investigated these local-time variabilities using a three-dimensional (3D) general circulation model (GCM) in combination with a two-dimensional (2D) chemical transport model (CTM). Our simulation results agree with the observed local-time patterns of SO2, H2O, and CO. The two-maximum pattern of SO2 at the cloud top is caused by the superposition of the semidiurnal thermal tide and the retrograde superrotating zonal (RSZ) flow. SO2 above 85 km shows a large day–night difference resulting from both photochemistry and the subsolar-to-antisolar (SS-AS) circulation. The transition from the RSZ flows to SS-AS circulation can explain the CO difference between two terminators and the displacement of the CO local-time maximum with respect to the antisolar point. H2O is long-lived and exhibits very uniform distribution over space. We also present the local-time variations of HCl, ClO, OCS, and SO simulated by our model and compare to the sparse observations of these species. This study highlights the importance of multidimensional CTMs for understanding the interaction between chemistry and dynamics in the Venusian mesosphere.

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