J. S. Lai

Hybrid Flux-Splitting Finite-Volume Scheme for the Shallow Water Flow Simulations with Source Terms

The extension of the hybrid flux-splitting finite-volume (HFF) scheme to the shallow water equations with source terms is presented. Based on the monotonic upstream schemes for conservation laws (MUSCL) method, the scheme is second-order-accurate both in space and time. An accurate and efficient surface gradient method (SGM), in conjunction with the HFF scheme, is adopted for the discretization of source terms, including the bed slopes and friction slopes. The resulting scheme has several desirable properties: ease of implementation, satisfaction of entropy condition, sharp shock resolution and preservation of well-balancing. The HFF scheme with SGM is verified through the simulations of steady transcritical flow over a hump and steady flow over an irregular bed. Besides, the effects of the limiter functions, the grid sizes and the Manning roughness coefficients on the simulated results are investigated for the steady transcritical flow problems. Using the laboratory measurements, the scheme is also applied to the dam-break flows: with an adverse slope, with a triangular hump, and with a constriction. Furthermore, the HFF scheme is employed in the simulation of typhoon flood flow with natural-irregular river topography to demonstrate the practical engineering application. The results show good agreements compared with the exact solutions, the experimental data and the field measurements.

Simulation of Hydraulic Shock Waves by Hybrid Flux-Splitting Schemes in Finite Volume Method

In the framework of the finite volume method, a robust and easily implemented hybrid flux-splitting finite-volume (HFF) scheme is proposed for simulating hydraulic shock waves in shallow water flows. The hybrid flux-splitting algorithm without Jacobian matrix operation is established by applying the advection upstream splitting method to estimate the cell-interface fluxes. The scheme is extended to be second-order accurate in space and time using the predictor-corrector approach with monotonic upstream scheme for conservation laws. The proposed HFF scheme and its second-order extension are verified through simulations of the 1D idealized dam-break problem, the 2D oblique hydraulic shock-wave problem, and the 2D dam-break experiments with channel contraction as well as wet/dry beds. Comparisons of the HFF and several well-known first-order upwind schemes are made to evaluate numerical performances. It is demonstrated that the HFF scheme captures the discontinuities accurately and produces no entropy-violating solutions. The HFF scheme and its second-order extension are proven to achieve the numerical benefits combining the efficiency of flux-vector splitting scheme and the accuracy of flux-difference splitting scheme for the simulation of hydraulic shock waves.

Measurement of solid suspension concentration and flow velocity with temperature compensation using a portable ultrasonic device

Abstract Ultrasonic spectroscopy is highly suitable for real-time measurement, in particular for dense particle systems. In the present study, a novel measurement device, namely a portable ultrasonic device (PUD), is designed and manufactured for measuring solid suspension concentration and flow velocity simultaneously with respect to the propagation of ultrasound waves in a solid–liquid mixture at different temperatures. A series of experiments were conducted in the laboratory to obtain the ultrasonic attenuation of kaolin and reservoir sediment solutions within a wide range of concentrations (1000–300 000 mg/L) at various temperatures (15–27°C). The resulting data were regressed to establish linear functions of attenuation and temperature for concentration. The experimental data were compared with theoretical simulated results to show the effect of particle size distribution on concentration measurement. The flow meter part of the PUD was verified by a standard-speed carriage in the towing tank. According to experimental tests by PUD, it was demonstrated that the accuracy for concentration in full scale is ±5%, and the accuracy for flow velocity is ±2%. Compared with sampled data, good agreements were also found by employing the PUD for sediment concentration and flow velocity measurements in turbidity currents during typhoon floods in a reservoir, which demonstrates that the PUD is operable and reliable on site. Editor D. Koutsoyiannis; Associate editor K. Heal Citation Huang, Y.J., Sung, C.C., Lai, J.S., Lee, F.Z., Hwang, G.W., and Tan, Y.C., 2013. Measurement of solid suspension concentration and flow velocity with temperature compensation using a portable ultrasonic device. Hydrological Sciences Journal, 58 (3), 615–626.

Reliability-Based Delineation of Debris-Flow Deposition Areas

In this paper, a methodology is proposedfor the delineation of debris-flow deposition areas.First, based on the theory of reliability,the delineated hazardous area is defined. Then,uncertainty analyses of all the uncertainparameters affecting the probable maximum length,width and thickness are performed. Finally,the proposed methodology is applied to an actualsite susceptible to debris flow. It is foundthat the maximum deposition length is much moreuncertain than the maximum deposition width.The delineated hazardous areas for variousreliability are obtained using the inversefirst-order second moment method. The proposedmethodology is recommended for the delineation ofdebris-flow hazardous areas, because theinfluence of all the uncertainparameters is considered.

CHARACTERISTICS OF HYDRAULIC SHOCK WAVES IN AN INCLINED CHUTE CONTRACTION - EXPERIMENTS

This paper presents the experimental results of the characteristics of hydraulic shock waves in an inclined chute contraction with consideration of the effects of sidewall deflection angle φ, bottom inclination angle θ and approach Froude number Fr 0 . Seventeen runs of laboratory experiments were conducted in the range of 27.45° ≤φ ≤ 40.17°, 6.22° ≤ θ ≤ 25.38° and 1.04 ≤ Fr 0 ≤ 3.51. Based on the experimental data, three empirical dimensionless relations for the shock angle, maximum shockwave height, and corresponding position of maximum shockwave were obtained by regression analyses, respectively. These empirical relations would be useful for hydraulic engineers in designing chute contraction structures.

Ultrasonic attenuation in solutions of kaolin and samples from reservoir with various thermal conditions

Multiphase suspensions systems are extensively used in hydrology, biochemical, and food industry. Ultrasonic spectroscopy is a rapid, on-line, and non-invasive measurement technique for the characterization of suspension over a wide range of particle size and concentration. Although kaolin has already been investigated extensively the ultrasonic attenuation property of kaolin against concentration with various temperatures has not been reported yet. This paper provides a series measurement results of ultrasonic attenuation of kaolin under a wide range of concentrations (0 ~ 300,000 ppm) and various temperatures (5 ~ 25degC). Besides, the ultrasonic attenuation of silt of Shihmen reservoir in Taiwan has been measured. The mean radii for the silt ranged from 4 to 8 mum. Results show that the variation of attenuation is driven by concentration and temperature. Based on these results as calibration data, an ultrasonic system is then designed and manufactured for real-time monitoring the silt concentration of the Shihmen reservoir.