Froude Criterion for Ice-Block Stability

The conditions under which a floating fragment of ice is either entrained under the upstream edge of a down-stream ice cover or accumulated up-stream are examined by means of dimensional analysis and a simplified analysis of the moments acting on an idealized ice fragment. The significant parameter descriptive of the critical conditions is found to be a Froude number based on block thickness. The influence of the ratio of thickness to flow depth is shown to be due to the effect of the block constricting the flow cross-section, thus amplifying the velocity in accordance with simple continuity. Under-turning instability occurs at a lower critical velocity than required for vertical submergence. Comparison of experimental data with the theoretical results show good agreement and demonstrates the vital dependence on fragment thickness as well as providing a criterion readily applicable to special flow conditions where a Froude number based on flow depth is illogical.

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Comparison Between Theoretical Predictions of Wave Resistance and Experimental Data for the Wigley Hull

Journal of Ship Research ◽

10.5957/jsr.1983.27.4.215 ◽

1983 ◽

Vol 27 (04) ◽

pp. 215-226

Author(s):

C. Y. Chen ◽

F. Noblesse

Keyword(s):

Experimental Data ◽

Froude Number ◽

Resistance Coefficient ◽

Wave Resistance ◽

Number Range ◽

Theoretical Predictions ◽

Wigley Hull ◽

Sinkage And Trim ◽

Theoretical Results ◽

Good Agreement

A number of theoretical predictions of the wave-resistance coefficient of the Wigley hull are compared with one another and with available experimental data, to which corrections for sinkage and trim are applied. The averages of eleven sets of experimental data (corrected for sinkage and trim) and of eleven sets of theoretical results for large values of the Froude number, specifically for F 0.266, 0.313, 0.350, 0.402, 0.452, and 0.482, are found to be in fairly good agreement, in spite of considerable scatter in both the experimental data and the numerical results. Furthermore, several sets of theoretical results are fairly close to the average experimental data and the average theoretical predictions for these large values of the Froude number. Discrepancies between theoretical predictions and experimental measurements for small values of the Froude number, specifically for F = 0.18, 0.20, 0.22, 0.24, and 0.266, generally are much larger than for the above-defined high-Froude-number range. However, a notable exception to this general finding is provided by the first-order slender-ship approximation evaluated in Chen and Noblesse [1],3 which is in fairly good agreement with the average experimental data over the entire range of values of Froude number considered in this study.

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Investigating the Nonlinear Optical Response of Pepper Oil under Low Power Irradiation with Continuous Wave Visible Laser Beam

10.32792/utq/utjsci/vol7/2/29 ◽

2020 ◽

pp. 131-138

Keyword(s):

Refractive Index ◽

Nonlinear Refractive Index ◽

Nonlinear Optical ◽

Continuous Wave ◽

Diffraction Integral ◽

Visible Laser ◽

Limiting Property ◽

Kirchhoff Diffraction Integral ◽

Theoretical Results ◽

Good Agreement

The nonlinear optical properties of pepper oil are studied by diffraction ring patterns and Z-scan techniques with continuous wave beam from solid state laser at 473 nm wavelength. The nonlinear refractive index of the sample is calculated by both techniques. The sample show high nonlinear refractive index. Based on Fresnel-Kirchhoff diffraction integral, the far-field intensity distributions of ring patterns have been calculated. It is found that the experimental results are in good agreement with the theoretical results. Also the optical limiting property of pepper oil is reported. The results obtained in this study prove that the pepper oil has applications in nonlinear optical devices.

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Modeling of mass transfer in biofilms in oscillatory flow conditions using k-ɛ turbulence model

Water Science & Technology Water Supply ◽

10.2166/ws.2003.0104 ◽

2003 ◽

Vol 3 (1-2) ◽

pp. 201-207

Author(s):

H. Nagaoka ◽

T. Nakano ◽

D. Akimoto

Keyword(s):

Numerical Simulation ◽

Mass Transfer ◽

Turbulence Model ◽

Uptake Rate ◽

Oscillatory Flow ◽

Substrate Uptake ◽

Flow Conditions ◽

Mass Transfer Mechanism ◽

Substrate Uptake Rate ◽

Good Agreement

The objective of this research is to investigate mass transfer mechanism in biofilms under oscillatory flow conditions. Numerical simulation of turbulence near a biofilm was conducted using the low Reynold’s number k-ɛ turbulence model. Substrate transfer in biofilms under oscillatory flow conditions was assumed to be carried out by turbulent diffusion caused by fluid movement and substrate concentration profile in biofilm was calculated. An experiment was carried out to measure velocity profile near a biofilm under oscillatory flow conditions and the influence of the turbulence on substrate uptake rate by the biofilm was also measured. Measured turbulence was in good agreement with the calculated one and the influence of the turbulence on the substrate uptake rate was well explained by the simulation.

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Modelling solid transport in building drainage systems

Water Science & Technology ◽

10.2166/wst.1996.0164 ◽

1996 ◽

Vol 33 (9) ◽

pp. 9-16 ◽

Cited By ~ 4

Author(s):

John A. Swaffield ◽

John A. McDougall

Keyword(s):

Decision Making ◽

Boundary Conditions ◽

Numerical Solution ◽

Water Conservation ◽

Transient Flow ◽

Drainage System ◽

System Model ◽

Flow Depth ◽

Flow Conditions ◽

Solid Transport

The transient flow conditions within a building drainage system may be simulated by the numerical solution of the defining equations of momentum and continuity, coupled to a knowledge of the boundary conditions representing either appliances discharging to the network or particular network terminations. While the fundamental mathematics has long been available, it is the availability of fast, affordable and accessible computing that has allowed the development of the simulations presented in this paper. A drainage system model for unsteady partially filled pipeflow will be presented in this paper. The model is capable of predicting flow depth and rate, and solid velocity, throughout a complex network. The ability of such models to assist in the decision making and design processes will be shown, particularly in such areas as appliance design and water conservation.

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Optimization of the flow conditions in the spawning ground of the Chinese sturgeon (Acipenser sinensis) through Gezhouba Dam generating units

Scientific Reports ◽

10.1038/s41598-021-93903-4 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Anyang Huang ◽

Jinzhong Yao ◽

Jiazhi Zhu ◽

Xingchen Gao ◽

Wei Jiang

Keyword(s):

Spawning Ground ◽

Chinese Sturgeon ◽

Flow Conditions ◽

Velocity Measurements ◽

Acipenser Sinensis ◽

Critically Endangered Species ◽

Gezhouba Dam ◽

Opening Mode ◽

Suitable Area ◽

Good Agreement

AbstractChinese sturgeon (Acipenser sinensis) is a critically endangered species, and waters downstream from Gezhouba Dam are the only known spawning ground. To optimize the velocity conditions in the spawning ground by controlling the opening mode of Gezhouba Dam generator units, a mathematical model of Chinese sturgeon spawning ground was established in FLOW-3D. The model was evaluated with velocity measurements, and the results were determined to be in good agreement. By inverting the 2016–2019 field monitoring results, the model shows that the preferred velocity range for Chinese sturgeon spawning is 0.6–1.5 m/s. Velocity fields of different opening modes of the generator units were simulated with identical discharge. The suitable-velocity area was maximal when all units of Dajiang Plant of Gezhouba Dam were open. For discharges below 12,000 m3/s, most of the area was suitable; for discharges above 12,000 m3/s, the suitable area rapidly decreased with increasing discharge. A comparison of suitable areas under high-flow showed that at discharges of 12,000–15,000 m3/s, opening 11–13 units on the left side was optimal. For discharges above 15,000 m3/s, all units should be open. We used these results to recommend a new operation scheme to support the conservation of Chinese sturgeon.

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Studies of local structures for Cu2+ centers in M2Zn(SO4)2·6H2O (M = NH4 and Rb) crystals

Zeitschrift für Naturforschung A ◽

10.1515/zna-2020-0326 ◽

2021 ◽

Vol 76 (4) ◽

pp. 299-304

Author(s):

Fu Chen ◽

Jian-Rong Yang ◽

Zi-Fa Zhou

Keyword(s):

Crystal Field ◽

Elongation Ratio ◽

Paramagnetic Resonance ◽

Local Structures ◽

Epr Parameters ◽

Structure Constants ◽

Crystal Field Parameters ◽

Electron Paramagnetic ◽

Theoretical Results ◽

Good Agreement

Abstract The electron paramagnetic resonance (EPR) parameters (g factor g i , and hyperfine structure constants A i , with i = x, y, z) and local structures for Cu2+ centers in M2Zn(SO4)2·6H2O (M = NH4 and Rb) are theoretically investigated using the high order perturbation formulas of these EPR parameters for a 3d 9 ion under orthorhombically elongated octahedra. In the calculations, contribution to these EPR parameters due to the admixture of d-orbitals in the ground state wave function of the Cu2+ ion are taken into account based on the cluster approach, and the required crystal-field parameters are estimated from the superposition model which enables correlation of the crystal-field parameters and hence the studied EPR parameters with the local structures of the Cu2+ centers. Based on the calculations, the Cu–H2O bonds are found to suffer the axial elongation ratio δ of about 3 and 2.9% along the z-axis, meanwhile, the planar bond lengths may experience variation ratio τ (≈3.8 and 1%) along x- and y-axis for Cu2+ center in (NH4)2Zn(SO4)2·6H2O and Rb2Zn(SO4)2·6H2O, respectively. The theoretical results show good agreement with the observed values.

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On the Flow Fields of Inertial Impactors

Journal of Fluids Engineering ◽

10.1115/1.3447176 ◽

1974 ◽

Vol 96 (4) ◽

pp. 394-400 ◽

Cited By ~ 28

Author(s):

V. A. Marple ◽

B. Y. H. Liu ◽

K. T. Whitby

Keyword(s):

Flow Field ◽

Stokes Equations ◽

Relaxation Method ◽

Water Model ◽

Navier Stokes ◽

Visualization Technique ◽

Navier Stokes Equations ◽

Theoretical Results ◽

Plate Distance ◽

Good Agreement

The flow field in an inertial impactor was studied experimentally with a water model by means of a flow visualization technique. The influence of such parameters as Reynolds number and jet-to-plate distance on the flow field was determined. The Navier-Stokes equations describing the laminar flow field in the impactor were solved numerically by means of a finite difference relaxation method. The theoretical results were found to be in good agreement with the empirical observations made with the water model.

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An approach to the modeling of a virtual thermal manikin

Thermal Science ◽

10.2298/tsci130115115r ◽

2014 ◽

Vol 18 (4) ◽

pp. 1413-1423 ◽

Cited By ~ 4

Author(s):

Dragan Ruzic ◽

Sinisa Bikic

Keyword(s):

Turbulence Models ◽

Thermal Conditions ◽

Heat Fluxes ◽

Thermal Manikin ◽

Flow Conditions ◽

Body Segments ◽

Nominal Size ◽

Natural Flow ◽

Good Agreement ◽

Made In

The aim of the research described in this paper, is to make a virtual thermal manikin that would be simple, but also robust and reliable. The virtual thermal manikin was made in order to investigate thermal conditions inside vehicle cabins. The main parameters of the presented numerical model that were investigated in this paper are mesh characteristics and turbulence models. Heat fluxes on the manikin's body segments obtained from the simulations were compared with published results, from three different experiments done on physical thermal manikins. The presented virtual thermal manikin, meshed with surface elements of 0.035 m in nominal size (around 13,600 surface elements) and in conjunction with the two-layer RANS Realizable k-? turbulence model, had generally good agreement with experimental data in both forced and natural flow conditions.

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Explanation of the Influence of Inflow Air Content on the Lift of Cavitating Hydrofoils

Journal of Fluids Engineering ◽

10.1115/1.4039252 ◽

2018 ◽

Vol 140 (8) ◽

Cited By ~ 1

Author(s):

Eduard Amromin

Keyword(s):

Experimental Data ◽

Theoretical Study ◽

Lift Coefficient ◽

Cavity Surface ◽

Air Bubbles ◽

Incoming Flow ◽

Fluid Density ◽

Air Content ◽

Theoretical Results ◽

Good Agreement

According to several known experiments, an increase of the incoming flow air content can increase the hydrofoil lift coefficient. The presented theoretical study shows that such increase is associated with the decrease of the fluid density at the cavity surface. This decrease is caused by entrainment of air bubbles to the cavity from the surrounding flow. The theoretical results based on such explanation are in a good agreement with the earlier published experimental data for NACA0015.

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