Volume 2 Issue 2

Authors: Khlifa Maalel; Zouhaier Hafsia; Zeineb Saoudi

Abstract: A numerical model is proposed of forced sloshing with obstacles through solving the Reynolds averages Navier-Stokes equation and the standard k–epsilon turbulence model. The Volume of Fluid method is adopted for capturing the free surface flow. The transport equations are solved by the CFX (spell it out) code in a moving domain to take into account the harmonic excitation of the sloshing tank. This model is validated through a case study for non linear sloshing inside a partially filled oscillating in a two dimensional rectangular tank without baffles and at resonance condition. The numerical results and previously developed analytical solution agree very well. When the frequency of the external excitation is close to the 0.98 natural sloshing motion frequency, the free surface displacement becomes larger than the case of excitation frequency close to 1.1 sloshing natural frequency. The simulated results of sloshing motion of internal vertical baffles located at the middle of the tank show thatunder harmonic excitation and at resonance condition, the displacement amplitude decreases and the sloshing frequency increases. When the vertical baffle height equal 0.75 of the still water depth, the numerical results from this study and Liu’s (2009) match agree very well. To eliminate the beating phenomenon, a slat screen is proposed. Numerical simulation results show that when the slat screen solidity increases, the displacement amplitude will decrease and the beating phenomenon will be eliminated. When, the screen solidity equals the area of the vertical baffle, the screen is more efficient to reduce the sloshing response than the vertical baffles. This reduction is attributed to the evolution of vortex shedding near the tip baffle.

Keywords: Beating Motion;Forced Sloshing; Free Surface; Non-Linear; Resonance; Slat Screen; Vertical Baffles; Vortex Shedding


Authors: Helen Wu; Tim Kuo; Charlie Matsubara

Abstract: Abstract- In this study, different turbulent models were used (k - ε, k - ω, and zero equation models) to characterize the permeability of turbulent water flows (hydraulic conductivity) in an artificial crack. The results were compared to a “universal” equation of flow in porous media based on empirical fit (Barr’s model) of a simple general check. The results showed that while the simulations did not match the empirical model, they follow the same trends. The values of the empirical constants in Barr’s model can be modified to match that of the simulation results. The results then were compared against the simulation results and were found to be mildly sensitive to the type of turbulent model used. In this problem, k - ω was considered to be most suitable model, due to limitations of the other models. The discrepancies between the k - ε, k - ω and zero equation models were small, less than 5%. These discrepancies may be due to the nature of the scenario of interest and simplifications that were applied to it.

Keywords: Turbulent Models; Darcy’s Law; Hydraulic Conductivity; Porous Media; CFD


Authors: M. Scott Forrester; Brian L. Benham; Kevin J. McGuire; Karen S. Kline

Abstract: Modeling groundwater hydrology is critical in low-gradient, high water table watersheds where ground-water is the dominant contribution to streamflow. The Hydrological Simulation Program-FORTRAN (HSPF) model has two different subroutines available to simulate ground water, the traditional groundwater (TGW) subroutine and the high water table (HWT) subroutine. The HWT subroutine has more parameters and requires more data but was created to enhance model performance in low-gradient, high water table watershed applications. The objective of this study was to compare the performance and uncertainty of the TGW and HWT subroutines when applying HSPF to a low-gradient watershed in the Coastal Plain of northeast North Carolina. Monte Carlo simulations were performed to generate data needed for model performance comparison. Both models performed well when simulating the 10% highest daily average flow rates. However, neither model performed well when simulating the 50% lowest daily average flow rates. The HWT model significantly outperformed the TGW model when simulating daily average flow over the full three-year simulation period, an indication that the HWT model out-performed the TGW over the full range of simulated flows. Model uncertainty was assessed using the Average Relative Interval Length (ARIL) metric. The HWT model exhibited slightly more combined model structure and parameter uncertainty than the TGW model. Based on the results, the HWT subroutine is preferable when applying HSPF to a low-gradient watershed and the accuracy of simulated stream discharge is the paramount concern.

Keywords: Modeling; HSPF; High Water Table; Uncertainty


Authors: Guanghua Shao; Lei Bian; Xipeng Wang; Qun Miao

Abstract: During the research of Xinxue River artificial wetland of Nansi Lake, through consulting literature and inferred analysis, BP neural network forecasting model of Xiaosha River artificial wetland is selected to carry on follow-up study. Because Xiaosha River artificial wetland is in the planning and design stage, and the establish of BP neural network forecasting model requires large amounts of data, therefore this paper built virtual data of influent quantity and quality and effluent quality, and studied on the modeling of Xiaosha River artificial wetland and the scheduling program of water quality and quantity.

Keywords: BP Neural Network; Virtual Data; Construction of Model; Scheduling of Water Quantity and Quality