Physical Model Study Research Articles

Limiting the development of riparian vegetation in the Isère River: A physical modelling study

Physical modelling experiments are conducted to investigate if a modification of the Isère River (French Alps) hydrology by changing dams management is able to foster riverbed morphodynamic and, thus limiting riparian plant development. The experimental setup is a 1:35 scale, undistorted movable bed designed to ensure the Froude number similarity and initial conditions for sediment particle motion. The physical model is 35 m long, 2.6 m wide, with a sand mixture composed of three grain size classes. Two runs with different flow and bed load conditions are simulated. Preliminary results show an intense riverbed activity when the system reaches a dynamic equilibrium state. Under these conditions, bar mobility is strong enough to limit vegetation encroachment only when water discharges are higher than the discharge of a 5-years flood during more than 10 days. These results indicate that the hydrological characteristics of the Isère River and the actual configuration of the hydropower structures could be not able to release annually the flow conditions needed to control riparian plant development.

A preliminary study of physical energy distribution model of Sciaenops ocellatus under swimming conditions

This study focused on Sciaenops ocellatus in deep-water cage culture studying the changes of the main energy substances and metabolites during swimming. Based on our results, a physical energy distribution model was constructed. The main conclusions were as follows: (1) A power function relationship between the maximum swimming time and swimming speed of the red drum was found. (2) At high swimming speed, there was a significant increase in red drum blood glucose concentration, a slight decrease in the amount of muscle glycogen, and a significant decrease in hepatic glycogen. When fish were close to fatigue, hepatic glycogen concentration was close to depletion, so hepatic glycogen concentration in the red drum can be used as an important indicator to determine sustained swimming ability in the fish. (3) There was a significant increase in lactic acid and lactic acid concentration during swimming at a high speed, which indicated that the process of high-speed swimming in the red drum was accompanied by anaerobic respiration and aerobic respiration. (4) This study established a simple swimming physical energy distribution model of red drum based on the energy consumption of hepatic glycogen. The model shows a linear relationship between time and swimming speed. (5) A calculation method for the maximum tidal current velocity in red drum farming areas was put forward based on the physical energy distribution model of the red drum and the rules of the tidal currents. Thish may give practical reference for farming site selection.

Physical water model and CFD studies of fluid flow in a single strand tundish

Flow characteristics in a continuous casting tundish is one of the key parameters producing a high quality clean steel. In this study, the fluid flow analyses of a single-strand tundish model were carried out using the commercial CFD software ANSYS FLUENT 14.0 and experimentally verified by physical water model. The realizable k-ɛ equation was utilized to model turbulent phenomenon. The behavior and performance of the flow in tundish with and without flow modifiers were investigated by the residence time distribution (RTD) curves which were obtained from the tracer concentration measurement at the outlet. The results from CFD are in agreement with the experiment results. The results show that the flow modifier plays an important role in increasing residence time and enhancing flow performance which could feasibly promote the inclusion removal potentials in the tundish process. The peak and the minimum residence time of RTD curves of the tundish model with flow modifiers were improved for more than 20%. With the comparison of the four flow modifier configurations (bare tundish, dam, baffle and turbostop) in the current tundish model, it could be concluded that the turbostop could provide the optimal flow characteristic in which could improve the level of inclusion removable.

Comparison of Large Woody Debris Prototypes in a Large Scale Non-flume Physical Model

Due to excessive rainfall in June of 2013, several rivers located in and near the City of Calgary, Canada experienced significant flooding events. These events caused severe damage to infrastructure throughout the city, precipitating a renewed interest in flood control and mitigation strategies for the area. A major potential strategy involves partial diversion of Elbow River flood water to the proposed Springbank Off-Stream Storage Reservoir. A large scale physical model study was conducted to optimize and validate the design of a portion of the new project. The goals of the physical model were to investigate diversion system behaviors such as flow rates, water levels, sediment transport and, debris accumulation, and optimize the design of new flow control structures to be constructed on the Elbow River. In order to accurately represent the behavior of debris within the system due to flooding, large woody debris created from natural sources was utilized in the physical model and its performance was compared to that of debris of the same size fabricated from pressed cylindrical wood dowels. In addition to comparing the performance of these two debris types, the impact of root wads on debris damming was also investigated. Significant differences in damming behavior was shown to exist between the natural debris and the fabricated debris, while the impact of root wad on damming affected the dam structure and formation. The results of this experiment indicate that natural debris is preferred for studies involving debris accumulation.

A physical modelling study to determine the influence of slag on the fluid flow in the AOD converter process

ABSTRACTA 1:4.6 scale physical model of a production argon oxygen decarburisation (AOD) converter was used to study the influence of top slag on the AOD process. Specifically, the gas penetration depth, fluid flow and slag behaviour under different nozzle diameters, nozzle numbers and gas flow rates were studied. The results show that the relative gas penetration depth generally increases linearly with an increased gas flow rate and a decreased nozzle size. Furthermore, the slag thickness increases linearly with an increased gas flow rate. In addition, the open-eye size was found to increase exponentially with an increased gas flow rate. Overall, three kinds of fluid flow patterns were found in the experiments: (i) a counter-clockwise rotation, (ii) a clockwise rotation and (iii) a double circulation with the plume in the middle of the converter. A counter-clockwise rotation was most common for the current experimental conditions.

Physical Modeling of the Polyfrequency Filter-Compensating Device Based on the Capacitor-Coil

The paper presents the results of physical modeling and experimental study of the frequency characteristics of the polyfrequency filter-compensating device (PFCD) based on a capacitor-coil. The amplitude- frequency and phase-frequency characteristics of the physical PFCD model were constructed and its equivalent parameters were identified. The feasibility of a PFCD in the form of a single technical device with high technical and economic characteristics was experimentally proven. In the paper, recommendations for practical applications of the capacitor-coil-based PFCD are made and the advantages of the device over known standard passive filter-compensating devices are evaluated.

Assessing the effectiveness of an airshaft for dropshaft air re-circulation and depressurization

Dropshafts are commonly used to convey water to deep tunnels. Plunging flow dropshafts have been reported to cause downstream air pressurization and subsequent sewer odor issues. A retrofit by connecting the dropshaft to an airshaft with several horizontal pipes for air re-circulation has been implemented in Edmonton, Canada. Tools for predicting the performance of this retrofit are needed. In the current work, physical model study and prediction were conducted to assess the effectiveness of the retrofit. Experiments were run with the dropshaft connected to the airshaft with different numbers of horizontal pipes. Predictions of air pressure and air entrainment of the retrofitted dropshaft were in good agreement with the experimental data. The effect of the airshaft became more important under a pressurized downstream condition with a larger sized airshaft. The prediction was also applied to simulate the performance of the retrofitted prototype dropshaft in Edmonton, regarding the bottom air pressure and the air flow rates in horizontal pipes. The prediction compared well with the field monitoring results, and the airshaft was found to be effective in depressurizing the downstream sewers, which helped to reduce the downstream pressure by about 60%.

Insight of Bridge Scour during Extreme Hydrologic Events by Laboratory Model Studies

The occurrence of extreme weather events that lead to flooding are expected to worsen in frequency and intensity. During such extreme events with high water levels, bridges may be subjected to submerged orifice flow and overtopping because they were not designed for such large flows. As a result, bridges over the water course are vulnerable to unexpected excessive scour of the foundations and possible failure. This study presents the results of clear-water local scour and contraction scour experiments using full bridge geometry and river bathymetry and especially their separations from the total scour depth. Three bridge sites were selected for the physical model studies and constructed in a hydraulic laboratory that included upstream and downstream river reaches and bridge structure based on the Froude number similarity between field and laboratory. From observations, the experimental studies elucidated the interaction among the various types of scour, including long-term aggradation or degradation, vertical and/or lateral contraction scour, and local pier and abutment scour. This study proposes a method of separating each scour component from the total scour depth and qualitatively address the effect of vertical contraction to the average contraction scour.

Sustainable Utilization of Scrap Tire Derived Geomaterials for Geotechnical Applications

Use of scrap tire derived (STD) geomaterials in geotechnical engineering applications has received growing interest to prevent creation of wastes and conserve natural resources towards achieving sustainability. STD geomaterials and their mixtures with soils are being used in highway embankments, retaining walls, landfills and other applications as lightweight fill, backfill, compressible inclusion, vibration absorber, and drainage material. The use of STD geomaterials in these applications has been affirmed by characterization of the engineering properties based on laboratory tests and performance assessment based on physical model studies. This paper provides a review of engineering properties of STD geomaterials and their mixtures with soil (predominantly sand) based on published studies. Further, laboratory model and field studies on typical applications of STD geomaterials/mixtures such as retaining walls, foundations, embankments, and landfills are discussed. Overall, STD geomaterial alone or sand mixed with optimal STD content of 30–40% by weight has been shown to be effective for geoengineering applications.

Longwall surface subsidence control by technology of isolated overburden grout injection

Surface subsidence is a typical ground movement due to longwall mining, which causes a series of environmental problems and hazards. In China, intensive coal extractions are commonly operated under dense-populated coalfields, which exacerbates the negative subsequences resulted from surface settlement. Therefore, effective approaches to control the ground subsidence are in urgent need for the Chinese coal mining industry. This paper presents a newly developed subsidence control technology: isolated overburden grout injection, including the theory, technique and applications. Relevant procedures such as injection system design, grouting material selection, borehole layout, grout take estimation and injection process design are proposed. The applicability of this technology has been demonstrated through physical modelling, field measurements, and case studies. Since 2009, the technology has been successfully applied to 14 longwall areas in 9 Chinese coal mines. The ultimate surface subsidence factors vary from 0.10 to 0.15. This method has a great potential to be popularized and performed where longwall mining are implemented under villages and ground infrastructures.

Numerical modelling of downstream migrating antidunes

AbstractA numerical model is presented that compute the geometrical dimensions and movement of downstream migrating antidunes. The model solves the Navier–Stokes equations together with the k‐epsilon turbulence model to find the water flow field over the bedforms. A two‐dimensional width‐averaged grid is used. The bed elevation changes are computed by solving the convection–diffusion equation for suspended sediments and bedload, together with the Engelund–Hansen sediment transport formula. The free surface is computed with an algorithm based on water continuity in the surface cells. Non‐orthogonal adaptive grids were used, moving vertically with the computed location of the bed and the free water surface. The numerical model was tested on data from a physical model study where regular downstream migrating antidunes had been observed. The numerical model started out with a flat bed and the trains of antidunes formed over time. Many of the physical processes observed in earlier studies were replicated by the numerical model. Four dune parameters were computed in the current tests: The antidune wavelength, height and celerity, together with the average water depth. The antidune wavelengths were best predicted with an accuracy of 3 to 8% compared with the measurements. The antidune heights were computed with a deviation of 11 to 25% compared with an empirical formula. The water depths over the antidunes were predicted with an accuracy of 3 to 9% related to the measured values. The average antidune celerity was the parameter with largest deviation: For the coarsest grid it was overpredicted with 37%. Copyright © 2017 John Wiley & Sons, Ltd.

Scour at wind turbine tripod foundation under steady flow

Results of a physical modelling study of clear-water scour at a tripod obstacle in uniform bed sediment under steady flow conditions are presented. 4 flow depths, 2 flow velocities and 3 angles of attack were considered. Maximum scour depth increased with increase in flow depth or velocity. For deep flows and high flow rate, the maximum value of the ratio of the equilibrium scour depth to the diameter of the tripod’s leg was 3.5, which is significantly greater than values of 1.3 or 2.5 suggested by guidelines for offshore wind turbine monopiles design. This ratio may be even larger because of the increased shear stress when waves are superimposed on current. All maximum equilibrium scour depths occurred at the upstream surface of a tripod leg despite the centre pile having a larger diameter. The alignment angle had a small effect on scour depth. But it is notable that there is an increase in scour development depth at 60° alignment angle. Equations are suggested for estimating the clear-water scour depth at wind turbine tripod foundations.

DETERMINATION OF WAVE CREST ELEVATIONS FOR SLAMMING FORCES ON JETTY WITH VERTICAL WALL END

Wave disturbance study for a closed end jetty conducted both in laboratory and through a numerical model is presented in this study. Shore protection structures and the structures at the end of the piers are considered for the calculation of the wave disturbance map. The connection locations of the jetties have been designed as vertical walls. These vertical structures and armored waterfront structures would affect the wave behavior in the study area along jetty axis causing reflection of waves and therefore the wave height in front of the structures might increase. This study intends to clarify wave agitation problem by using a numerical model with the help of physical model study.

Source wavelet and local wave propagation effects on the amplitude-variation-with-offset response of thin-layer models: A physical modeling study

In target layers with thicknesses below the vertical seismic resolution as thin layers, the tuning effect/interference between the wave propagation modes may increase the challenge of doing amplitude-variation-with-offset (AVO) analysis because it is difficult to recover the primary PP amplitudes embedded in the data by further seismic data processing. Thus, we have investigated the importance of the primary PP reflections, locally P-SV converted waves, and internal multiple reflections in the amplitude response of two thin-layer seismic physical models. One model consists of a thin water layer embedded between two nylon plates, and another model with a thin acrylic layer surrounded by water. Numerical modeling using the reflectivity method was applied to analyze each wave propagation mode and the source waveform role in the experimental data. Before the experimental reflection data acquisition, we characterized two source and receiver piezoelectric transducer (PET) pairs: one with a circular plane face and the other with a semispherical face. We measured the source wavelet, its dominant frequency, and the PETs’ directivity pattern. Semispherical PETs were chosen to acquire common midpoint reflection data. Thereafter, a processing workflow was applied to remove linear events interfering with the target reflections and to correct amplitudes due to transmission losses, source/receiver directivity, and geometric spreading effects. Finally, we investigated the thin-layer targets near incidence angle amplitude and the AVO response. The results showed that the interference between the primary PP reflections and the locally converted shear waves may considerably affect the observed amplitude response. The source wavelet bandwidth appeared as a second-order effect, and the internal multiple reflections were practically negligible. These results suggested that in real data sets, it is important to investigate the wave propagation modes and source wavelet role in the amplitudes observed, before deciding the AVO analysis/inversion workflow that should be adopted.

Experimental Study on Submerged Sand Erosion through a Slot on a Defective Pipe

AbstractA physical model study was conducted to examine the development of submerged sand erosion through a slot on a defective sewer pipe. Various parameters that affect the erosion process were s...

Physical Model Study of the Seismic Performance of Highway Embankments with and without Geotextile

In order to ensure structural safety and integrity in earthquake conditions, it may be useful or even necessary to increase the seismic safety of the highway embankments with reinforcement inclusions. The inclusion of geosynthetics in highway embankments may provide an additional tensile strength and durability to construct more stable and earthquake resistant embankments. In this study, the contributions of the primary factors as inclusion of the geotextile reinforcement, slope inclination and dynamic motion characteristics affecting the seismic performance of the highway embankments are evaluated. Shake table models of the unreinforced and geosynthetic reinforced highway embankments with different slope inclinations are designed. An extensive series of shake table tests were performed under dynamic motions with different predominant frequencies. Test results revealed that inclusion of geotextiles in the embankment model causes deamplification of the transmitted accelerations traveling through the reinforced embankment models. Thus, the geosynthetic reinforcement successfully enhances the seismic performance and mitigates earthquake-related hazards. Contribution of this study to the literature is that the efficiency of the geosynthetic reinforcement by means of energy absorption properties is highly dependent on the dynamic motion characteristics but less dependent to the degree of slope inclination.

Design diagrams for wavelength discrepancy in tank testing with inconsistently scaled intermediate water depth

The well-known dispersion relation links the length and period of a water wave with the depth in which it propagates. When model testing in tanks, the water depth should be consistently scaled to correctly replicate the waves. While this is done routinely by scaling foreshore bathymetry in coastal engineering physical model studies, and is not significant for deep water scenarios, this is not always considered when testing marine renewable energy devices, which are often in intermediate depth. Where water depth is not scaled consistently there will be resulting errors in wave parameters including wavelength, steepness, celerity, group velocity, and power. Design diagrams are presented to quantify and visualise these discrepancies over a typical range for testing offshore renewable energy devices. This design tool will facilitate experimental planning, quantification of uncertainties, and correlation of model test results with field data.

Centrifuge modeling of mitigation-soil-foundation-structure interaction on liquefiable ground

Significant progress has been made in recent years toward a better understanding of the liquefaction phenomena. Yet, the combined effects of excess pore pressure generation, permanent soil deformation, and ground shaking, with and without mitigation, on the performance of the soil-foundation-structure system remain poorly understood. Moreover, there is a lack of physical model studies incorporating these important effects for a range of conditions to validate numerical models. This paper presents an experimental study of the performance of 3-story structures with shallow foundations on a saturated soil profile including a thin liquefiable layer. The influence of three different mitigation techniques was evaluated: 1) ground densification; 2) enhanced drainage with prefabricated vertical drains (PVDs); and 3) reinforcement with in-ground structural walls. Densification was observed to slightly reduce excess pore pressures and permanent foundation settlement and tilt, but amplified the demand transferred to the superstructure. Use of PVDs reduced permanent foundation settlement and rotation by reducing the duration of large excess pore pressures, but amplified roof accelerations and flexural drift. The performance of the stiff structural wall depended on the properties of the earthquake motion. During more intense, longer-duration motions, confining the soil and inhibiting flow inside the structural wall led to liquefaction, larger settlements, and larger translational and rotational accelerations on the foundation. In this case, the dissipation of seismic energy through additional foundation movements reduced the moment-rotation demand on the columns. These experimental results emphasize the importance of evaluating the potential tradeoffs of liquefaction mitigation, which may reduce settlement and sometimes tilt, but result in larger transient drifts and damage to the superstructure.

Physical hydrodynamic propulsion model study on creeping viscous flow through a ciliated porous tube

The present investigation focusses on a mathematical study of creeping viscous flow induced by metachronal wave propagation in a horizontal ciliated tube containing porous media. Creeping flow limitations are imposed, i.e. inertial forces are small compared to viscous forces and therefore a very low Reynolds number (Re ≪ 1) is taken into account. The wavelength of metachronal wave is also considered to be very large for cilia movement. The physical problem is linearized and exact solutions are developed for the differential equation problem. Mathematica software is used to compute and illustrate numerical results. The influence of slip parameter and Darcy number on velocity profile, pressure gradient and trapping of bolus are discussed with the aid of graphs. It is found that with increasing magnitude of the slip parameter, the trapped bolus inside the streamlines increases in size. The study is relevant to biological propulsion of medical micromachines in drug delivery.

Numerical investigation of the influence of extreme hydrodynamic forces on the geometry of structures using OpenFOAM

The main focus of the present study is to numerically examine the effects of tsunami-like-induced hydrodynamic loading applied to free-standing structures with various architectural geometries. To accomplish these goals, the authors employed a multi-phase numerical model utilizing the volume of fluid method in the three-dimensional space. The second objective of the present study is to improve the understanding of hydrodynamic loads on structural components in order to develop practical guidelines for the engineering design of structures located in areas with a high risk of tsunami hazards. In order to evaluate the performance of the numerical model, the results of the simulation are compared with various available experimental data and physical modeling studies. The tsunami-like wave was reproduced via a sudden release of water located in an impounding reservoir located at the upstream part of a flume in the form of a dambreak wave. The shear force exerted by the hydrodynamic force on the square and round structures in the downstream area is estimated to obtain the value of tsunami loading. Finally, the validated numerical model is employed to examine the influence of the structure’s geometry on the hydrodynamic loads exerted on it.