Model Description

The CCHE-TIDE provides an add-in module for CCHE2D to add the capability of simulating tidal flows in estuaries and coastal areas. The CCHE-TIDE extends the use of the CCHE2D for simulating tidal waves, tidal currents, and residual currents under the conditions of incident tidal waves (non-reflective), tributary flows, non-uniform wind force, and Coriolis force. The incident tidal waves at open-sea boundaries can be specified as time series of observed tidal levels or a combination of tidal constituents. In particular, the model provides non-reflective open boundary conditions for the cases that the reflective waves need to be taken into consideration. The CCHE-TIDE has been tested and validated using various laboratory and field data.

One of the ongoing projects in the research group is to develop a module for the CCHE3D model for simulation of three-dimensional tidal flows in large-scale and complex bathymetries. The CCHE3D hydrodynamic model together with the tide simulation module can simulate three-dimensional tidal waves, tidal currents, and residual currents under the conditions of incident tidal waves (non-reflective), tributary inflows, wind field, and Coriolis force.

Both 2D and 3D tidal models can simulate long-wave tidal flows and short-wave oscillatory free-surface flows. 

Main Features of CCHE-TIDE

The two-dimensional CCHE-TIDE module has the ability to

• Simulate tidal levels, tidal currents, residual currents in estuaries and coastal areas with complex bathymetries and boundary conditions;

• Consider different external forces, e.g., non-uniform wind forces, Coriolis force, complex tributary inflows, etc;

• simulate non-reflective open boundary conditions for the cases that the reflective waves need to be taken into consideration;

• Simulate sediment transport by different empirical models in riverine and coastal/estuarine region.

The three-dimensional CCHE-TIDE module has the ability to

• Simulate three-dimensional unsteady free surface flows with the assumption of hydrostatic pressure or non-hydrostatic pressure;

• Simulate three-dimensional oscillatory free surface flows with long and/or short periods

• Model three-dimensional tidal flows in large-scale complex bathymetries and boundaries;

• Ability to handle non-reflective boundary conditions on open boundaries.

Application Examples of CCHE-TIDE

1. Verification of CCHE-TIDE by Simulating Standing Wave Propagation in a Semi-Closed Channel with Reflective Straight Wall

(a) Schematic illustration of wave propagation in a semi-closed channel

(b) Comparison of wave elevations at the open boundary (TL=duration of incident wave reflected back from wall to the open boundary, Red line = the analytical solution of the developed standing wave)

Figure 1 Simulation of wave propagation in a channel with reflective wall. Due to the complete wall reflection, the amplitude of the incident wave will be amplified twice as much as the incident wave.

2. Validation of CCHE-TIDE by Simulating Tidal Currents in Hudson River, NY

The validation of CCHE-TIDE was done by using the real-time data provided by USGS sites in the Hudson River, NY. The computational domain covered the tidal river reach from HASTING (USGS Site# 01376304) to GREEN ISLAND (USGS Site# 01358000). The obtained results about tidal levels, tidal currents, and discharge through a cross section are shown as follows.

(a) Ebb tide at 7:30am, 06/07/2004

(b) Slack tide at 10:30am, 06/07/2004

Figure 2 Computed tidal currents in the lower Hudson River, New York

Figure 3 Comparison of tidal elevations between simulation and observation at Albany in the upper Hudson River, NY (USGS Site#: 01359139)

Figure 4 Comparison of stream discharge between simulation and observation at Poughkeepsie in the middle Hudson River, NY (USGS Site #: 01372058). Sign of discharge: (+) ebb tide, (-) flood tide

3. Simulation of Residual Currents in Tokyo Bay

Figure 5 Comparisons of residual currents in Tokyo Bay: the black arrows show the observed residual currents

Figure 6 Comparisons of tidal levels between simulation and observation at Anesaki in Tokyo Bay

4. 2D Simulations of Tidal Currents in the Yangtze River Estuary

Figure 7 A snapshot of computed tidal current at a neap tide in the Yangtze River Estuary. The picture in the left hand side is a close-up view of the current. The time series of tidal elevations show the incident tidal waves at the offshore, in which the circle stands for the tidal elevation at the time of the picture at the offshore boundary.

5. Verification of 3D Tidal Model by Simulating a Standing Wave

Figure 8 A snapshot of computed standing wave profile in a channel (the contour lines show the vertical velocities (m/s)). Wave conditions: period=100.0s, amplitude=0.1m, still water depth=10.0m

6. 3D Simulations of Tidal Currents in the Yangtze River Estuary

Figure 9. 3D Computed water surface at a high tide in the Yangtze River Estuary. The time-series of tidal elevations show the tidal waves at the offshore, in which the black circle stands for the tidal elevation at the time of the picture at the offshore boundary.

Figure 10 Comparison of tidal elevations in the Yangtze River Estuary at Zhong Jun. Observed Duration: August 29 – Sept. 9, 2000

(a) At Zhuyuan

(b) At Mid- Bai Cao

Figure 11 3D-tidal current ellipses during a spring tide in the Yangtze River estuary. Red=bottom layer, Green=middle layer, Blue=surface, black=2D computed ellipse

References

Kawahara, M., Kodama, T., and Ding, Y. (2004), Test case of tidal current analysis of Tokyo Bay for numerical model verification on 3-D free surface flow, to appear in Chapter 5 of the ASCE Monograph on 3D Free Surface Flow Model Verification and Validation.

Wang, S. S. Y., and Ding, Y. (2003). “On the verification and validation of coastal process simulation models”, In: Proceeding of the International Conference on Estuaries and Coasts (ICEC-2003), Nov.9-11, 2003, Hangzhou, China (Keynote Lecture).

Ding, Y., and Wang, S.S.Y. (2003). “Test Case Database of Tidal Currents in Tokyo Bay for Numerical Model Verification on 3-D Free Surface Flow”, Technical Report No. NCCHE-TR-2002-11, National Center for Computational Hydroscience and Engineering, The University of Mississippi, Oxford, MS.

Ding, Y. (2002). “Enhancement of CCHE2D model for predicting tidal flows”, Joint Seminar of NCCHE and U.S. Department of Agriculture-Agricultural Research Service, Sept. 2002 (presentation file available).

Kawahara, M., and Ding, Y. (1998), Bifurcation analysis of Brown tide in tidal flow using finite element method, Computer Methods in Applied Mechanics and Engineering, vol.151, no. 1-2, p.195-213.