Laboratory Physical Model Research Articles

Simulation of extended optical paths in a convective cell with water

A laboratory experiment on studying the statistics of the intensity fluctuation field associated with laser radiation after passing a convective cell filled with water was carried out. It is shown that the action of the cell can be compared in the relative fluctuation dispersion and Rytov index with the influence of turbulence on an extended path. The extended and short paths are numerically simulated and probability density functions of the intensity logarithm are considered. The laboratory cell can serve as a laboratory physical model of long atmospheric paths.

Behavior of circular footing resting on laterally confined granular reinforced soil

Three dimensional physical laboratory models were examined to investigate the influence of soil confinement on circular footing behavior resting on granular soil. A total of 23 model footing tests were performed. Nine hollow cylinders with various heights and diameters were installed around the footing model for soil confinement purpose. Square geogrid layers were placed at different depths beneath the bottom edge of the cylinder. Different parameters such as height, diameter, and depth of the cylinder were studied. Moreover, number, width, and position of the geogrid layers were, also, investigated. The response of a non-confined footing model was set as reference for comparison purpose. The results showed enhancement in the bearing capacity of the soil as well as a reduction in its settlement in all used configurations compared with the reference case. It is, however, observed that on increasing the number of geogrid layers more than one layer had a small significant effect on the footing behavior. Moreover, placing geogrid layers underneath the cylinders improves the bearing capacity up to 7.5 times that of the non-confined case. Footing with cylinder of a diameter nearly equal to the footing diameter behaves as one unit like a deep foundation. This behavior pattern was no longer observed with large cylinder diameter and small height. Finally, the study ends up with recommendations for selection of cylinder dimensions to maximize the bearing capacity. The benefits of using geogrid layers were also highlighted.

A simple method for numerical modelling of mechanical behaviour of an energy pile

A commercial numerical code was used to simulate the mechanical behaviour of energy piles under thermo-mechanical loadings. The thermal load was simply simulated by imposing on the pile volumetric strains calculated from the coefficient of thermal expansion of the material. Simulations were performed for two existing in situ experiments and one experiment performed using a physical laboratory model. Comparison between the simulations and experimental results shows that this decoupling method can satisfactorily predict the experimentally observed phenomena of pile head movement under thermal cycles at various mechanical loads and change of pile axial load along the pile under thermal cycles. The results highlight the important role played by thermal volume change of the pile on the mechanical behaviour of the energy pile under thermo-mechanical loadings.

Evaluation of coefficient of consolidation for dilatory dissipation in piezocone test in overconsolidated cohesive soils

The interpretation method for dilatory dissipation, showing an initial temporary increase in pore pressure, in piezocone tests in overconsolidated clayey soils was investigated in this study. Finite difference analyses on the dissipation after cone penetration were performed with various ground conditions. The spatial distribution of initial excess pore pressure induced by cone penetration was determined from experimental estimations through in-situ tests and laboratory physical model tests and theoretical predictions by the cavity expansion theory and critical state soil mechanics. A method to evaluate the coefficient of consolidation from dilatory dissipation results was developed through the assessment of numerical simulation results. Comparing the application results with the laboratory-determined values, it was verified that the proposed approach provided a reliable and consistent evaluation of the coefficient of consolidation.

Investigation of concentrating and nonconcentrating evacuated tube solar water heaters using 2D particle imaging velocimetry

Abstract Under transient climatic conditions, solar water heaters using heat pipes are more effective at capturingincident solar radiation than other equivalent sized solar water heaters. The cost must be reduced toimprove uptake of such systems. To investigate two methods were considered by this study: thermosyphonfluid flow and reflective concentrators. A physical reconfigurable laboratory model of the manifold andassociated condensers of a heat-pipe-evacuated tube system were fabricated; fluid circulation was viathermosyphonic action, particle imaging velocimetry derived velocity maps and the use of concentratorswas simulated. When condenser spacing was doubled, the Nusselt number increased by 43%, the velocityby 55% but the heat transfer efficiency of the model manifold decreased by 9%. Potential annual energysavings of 10207 GWh could be realized if such systems could be successfully fabricated. Keywords: thermosyphon; fluid flow visualization; solarenergy; particle imaging velocimetry;compound parabolicconcentrators; evacuated tube solar water heaters

Estimation of elastic stiffness coefficients of an orthorhombic physical model using group velocity analysis on transmission data

We acquired 3C ultrasonic transmission seismograms, measured group velocities associated with the three quasi-body wave types, and determined density-normalized stiffness coefficients ([Formula: see text]) over an orthorhombic physical (laboratory) model. The estimation of [Formula: see text] is based on an approximate relationship between the nine orthorhombic [Formula: see text] and group velocities. Estimation of the anisotropic [Formula: see text] is usually done using phase velocities with well-known formulas expressing their theoretical dependence on [Formula: see text]. However, on time-domain seismograms, arrivals are observed traveling with group velocities. Group velocity measurements are found to be straightforward, reasonably accurate, and independent of the size of the transducers used. In contrast, the accuracy of phase velocities derived from the [Formula: see text] transform analysis was found to be very sensitive to small differences in picked arrival times and to transducer size. Theoretical phase and group velocities, calculated in a forward manner from the [Formula: see text] estimates, agreed with the originally measured phase and group velocities, respectively. This agreement confirms that it is valid to use easily measured group velocities with their approximate theoretical relationship to the [Formula: see text] to determine the full stiffness matrix. Compared to the phase-velocity procedure, the technique involving group velocities is much less prone to error due to time-picking uncertainties, and therefore is more suitable for analyzing physical model seismic data.

Partitioning characteristics of gas channel of coal-rock mass in mining space and gas orientation method

In order to research the influence of coal-rock mass morphology of mining space on the flow law of gas, the laboratory physical model and numerical computation methods were adopted to simulate coal mining activities. The simulation results indicate that, after coal seam mining, the loose rock accumulation body of free caving, ordered rock arrangement body of plate damage rich in longitudinal and transverse fractures and horizontal fissure body formed by rock mass deformation imbalance are formed from bottom to top in the mining space. For these three types of accumulation bodies, there are essential differences in the accumulation state, rock size and gas breakover characteristics. According to this, the coal-rock mass in the mining space is classified into gas turbulence channel area, gas transitional flow channel area and gas seepage channel area. In the turbulence channel area, the gas is distributed transversely and longitudinally and gas diffuses in the form of convection with Reynolds number Re more than 100; in the transitional flow channel area, one-way or two-way gas channels are crisscross and gas is of transitional flow regime with Re between 10 and 100. In the seepage channel area, there are a few vertical gas channels with Re less than 10. In this paper, the researches on the gas orientation method in different partitions were further carried out, gas orientation methods of low-level pipe burying, middle-level interception and high-level extraction were determined and an on-site industrial test was conducted, achieving the effective diversion of gas and verifying the reasonableness of gas channel partition.

High- and low-solids anaerobic digestion in laboratory model fermenter made from silage bags

A laboratory physical model of a new type of anaerobic fermenter for “dry” and “wet” anaerobic digestion consisting of silage bags was designed. In the model, the experiment based on high-solids discontinuous anaerobic co-fermentation of agricultural substrates was carried out. It was verified that a horizontal fermenter constructed from silage bags is a suitable type of equipment for the production of biogas. The biogas production peaked at 4th day and was completed by 18th day. Within 18 days of discontinuous high-solids process (18.5-20.0 wt. %TS) the intensity of biogas production reached 1.18 mN3. m-3 . d-1, or 0.0012 mN3. kg-1 . d-1, and the specific methane production 0.01 mN3. kg-1, or 0.07 mN3. kgVS-1. After conversion of the modeling process to a semi-continuous low-solids mode (3.5-5. 5 wt. %TS) during the daily dosage of 87 wt % mixture of biscuit meal EKPO-EB with 13 wt % CaO, the intensity of biogas production reached the value 2.42 mN3 . m-3 . d-1, or 0.0105 mN3 . kg-1 . d-1. The fermentation bag appears to be a more efficient device in the semi-continuous “low-solids” Laboratory model: “(2 inches)”.

Mini-magnetosphere: Laboratory experiment, physical model and Hall MHD simulation

Magnetosphere with a size comparable to the ion kinetic scales is investigated by means of laboratory experiment, analytical analysis and Hall MHD simulation. In experiment a specific magnetic field was observed which is non-coplanar to dipole field, does not change sign at dipole moment inversion and could be generated only via the quadratic Hall term. Magnetopause position and plasma stand off distance were found to be profoundly different between the experimental regimes with small and large ion inertia length. In the previous studies of a mini-magnetosphere by kinetic codes such novel features were observed as absence of the bow shock and plasma stopping at the Stoermer particle limit instead of the pressure balance distance. Proposed analytical model explains these features by Hall currents which tend to cancel magnetic field convection by ions. Performed numerical simulation shows a good agreement with experiment and analytical model. It gives detailed spatial structure of the Hall field and reveals that while ions penetrate deep inside mini-magnetosphere electrons overflow around it along magnetopause boundary.

A cement-based method for fixing sand in laboratory channels

A method to fix movable beds in river-related laboratory research or physical model studies is proposed and investigated. The motivation was to develop a method that would: (1) not involve the use of harsh chemicals and (2) ensure that the granular roughness of the original movable bed was maintained. The method involves coating the surface with a mixture of sand and Portland cement. Laboratory tests were conducted to determine the amount of cement, and investigate the best method of application, effect on roughness, shear strength and durability. It is found that the method can be used to fix both flat and deformed beds. The method is particularly effective for sands up to 1.1 mm, when it is possible to ensure that the granular roughness of the fixed bed is comparable to that of the movable bed by merely using in the coating mixture a coarser sand than the original one.

Analyses on docking dynamic characteristics of the jack-up platform with two-piece units guide cable

Abstract To meet the requirements of deeper offshore oil and gas exploration, a two-piece units mode jack-up rig is employed to upgrade the existing cylindrical leg jack-up rig which works in shallow areas of 50 m deep. A set of mat support structure is added to the bottom of the cylindrical leg jack-up rig and the upper piece of rig and the bottom piece of rig are connected by a docking assembly, making the two pieces become a mat jack-up rig. This paper studies the equilibrium position and displacement response of the upper unit in docking procedure under different environmental condition and different ballast mode based on the three dimensional time domain linear potential flow theory and Morison theory, and analyses the dynamic response of the guide cable under different docking positions through physical models in laboratory. If the environment load acts from the stem direction, longitudinal oscillation affects mostly on the displacement of the guide cable. With the increment of water depth, the axial tension of the guide cable and the vertical angle of deviation decreases. Under the condition of separately floating, the guide cable is mostly affected by the mass of the platform; the forces acting on the guide cable of the lower unit is much smaller than that of the upper unit. Once one of the units was fixed, the towing force dropped obviously. The bearing force of the guide cable is obviously affected by the wave period and wave height and will increase with the increment of wave period and wave height in general.

A feasibility study on solar-wall systems for domestic heating – An affordable solution for fuel poverty

A Solar Wall Heating (SWH) system was developed to provide low cost space heating in traditional solid stone-walled tenement buildings in Scotland. The SWH system uses the internal solid walls to store the solar heat collected during the day and heat the bedrooms during the night.A physical laboratory model with attached solar hot water system and a computational model of it were developed to investigate the dynamic performance of the system in use and test the cost benefits of iterations of its modes of use. The temperatures throughout the wall structure were measured under the variant solar input of a 24-h cycle. An unsteady state CFD model was developed and validated using the measured data and setup to test a number of key variables of the solar wall heating system in use. These included optimisation control strategies and maximisation strategies for the collection and storage of solar heat under various conditions. This paper presents the modelled results of the solar thermal storage and optimisation system and strategies for internal solid stone walls in a typical Scottish tenement flat in the Scottish climate.In addition the study analysed the solar availability, heating demand and domestic water supply of two typical dwellings based on two reliable methods: (a) a purpose built dynamic thermal model and (b) data collected in previous studies.The study demonstrated that the solar collection of current solar hot water systems can be improved upon so that, even in Scotland, more solar power can be harvested to contribute not only to domestic hot water, but also domestic space heating, particularly in buildings occupied over 24h with heavy thermal mass. The cost analysis of the system in use suggested a 16year payback period for such a system for a tenement flat.

An Experimental Study of the Effect of the Water Injection Process on Rock Structure and Permeability Reduction

The estimation and assessment of formation damage on reservoir core samples is an important measurement. Laboratory tests were set up to investigate the effects of injection pressure, flow rate, and induced fracture on the rock sample with respect to formation damage. In this research, selected rock samples from one of Iranian giant oil fields were used as the laboratory physical model. Permeability reduction was observed for unfractured samples: however, it was more interesting that no injection pressure buildup was detected in fractured samples. It appears that fractures in sandstones, especially with weak cementation, can play the role of an agent for particle movement and cause damage far from injection wells over a long period of time.

Impacts of Epistemic Uncertainty in Operational Modal Analysis

AbstractField experimentation on constructed systems demands consideration of many mechanisms of epistemic and aleatory uncertainties as well as human errors and subjectivity. This is especially true in operational modal analysis (OMA) applications that aim to identify the dynamic properties of a structure. Although statistics and probability theory are sufficient for quantifying aleatory uncertainty and bounding the resulting errors in OMA results, there is much debate as to whether the same tools may also be used to quantify epistemic uncertainty. This study explored a framework for better understanding the distinctions and impacts of these two types of uncertainties in OMA and how human errors and subjectivity may be classified. A physical laboratory model was designed to simulate four key sources of epistemic uncertainty that represented the primary test variables: structural complexity (changing boundary conditions, nonlinearity), ambient excitation characteristics (magnitude, directionality, and ban...

Laboratory investigation of wave run-up caused by landslides in dam reservoirs

Waves generated by underwater landslides are studied in a physical laboratory model. A total of 102 laboratory tests were carried out. The experimental data measured generation, propagation and run-up of water waves. A wide range of effective parameters are considered in the experimental tests. Based on laboratory data, an empirical method is presented for prediction of impulse wave run-up caused by an underwater landslide in a dam reservoir. This method is developed using only the information about landslide geometry, initial submergence, water depth and sidewall slopes in the dam reservoir. The presented equation is successfully verified using laboratory-based and analytical equations from the literature. The equation is also applied in a real case study for a dam reservoir in Iran in which the impulse wave characteristics are available, and good reliability is obtained.

Evaluation of undrained shear strains in multi-directional horizontal shaking

The evaluation of shear strains under multi-directional shaking is an important issue in interpreting dynamic soil behavior for both laboratory physical modeling and in situ monitoring. Shear strain components evaluated from Cartesian coordinates in undrained conditions have limitations to fully capture the coupled shear strain-pore pressure responses with an individual expression. In the present study, radial and rotational shear strain components derived from particle motions described with cylindrical polar coordinates are proposed. The proposed radial and rotational shear strains are verified with data from a bi-directional laminar shear box and a free field downhole array. Comparison results show that the proposed expressions of shear strain effectively capture the coupled strain-pore pressure responses in terms of the frequency content, amplitude variation, phase difference, and oscillation behavior. Comparison results reveal that the radial shear strain is the dominant shearing mode and the amplitude of the rotational shear strain is only 6.5–14.5% of the radial component. This provides quantitative data for the correction factor for multi-directional shaking and suggests that a simple shear system capable of inducing the radial shear strain on the vertical plane is a better approach than other shearing modes for physically modeling the behavior of soil subjected to undrained seismic loadings.

Performance of geocomposite and granular drains under irrigation canal linings

ABSTRACT: In many irrigation projects, where the groundwater table is high, part of the canal may be located below the water table. In such cases the groundwater would apply uplift pressure to the bottom and side panels of the lining. This phenomenon may cause deformation, displacement or rupture of the concrete panels, or other damage, which would cause high maintenance costs for the project. The most effective way to control the uplift pressure is to provide a filter drainage system under the canal lining. At present, granular filters are the most common material in use. However, the application of granular materials is not an easy task in some cases, owing to the high costs involved, and the environmental impacts. Therefore, in recent years, geosynthetic materials (geocomposites) have been employed as a replacement for granular filters. In the present study, the behaviour of geocomposite material as a filter drainage layer under canal lining has been investigated, using a physical laboratory model. The results of the experiments show that a geocomposite layer with adequate thickness can fully relieve the uplift pressure and discharge the drained water effectively. The efficiencies of the filter drainage under the bottom concrete panels, as well as under the bottom and side concrete panels, were studied. The results show that providing a filter under the side panels has no significant effect on the drainage capacity of the system.

Stability analysis of a copper tailings dam via laboratory model tests: A Chinese case study

The upstream method is a popular method for raising tailings dams. Currently in China there are more than 12,000 tailings impoundments and almost 95% of them use the upstream method for the construction of the dam. Statistical data has shown that the tailings impoundment is one of the main sources of risk in the mining industry. Failures of tailings impoundments have resulted in the loss of many lives, considerable property damage, and irreversible pollution in downstream areas. Therefore, the safety of tailings management facilities has been of increasing concern to governments and local communities. The management of a conventional tailings storage facility requires the maintenance of a high level of structural stability. Therefore, according to the relevant mine Acts, the mine operators are required to conduct stability analyses for all types of tailings facilities, whether they are new, active, or decommissioned. For the stability analysis of tailings dams, the accurate profile of the tailings dam is very important. The profiles are easily obtained for both active and decommissioned tailings facilities because their data can be collected through field investigations. However, collecting basic data from newly constructed tailings facilities is difficult. In this paper, a laboratory physical model test has been performed. The construction process for new tailings impoundment has been physically simulated in the laboratory, where the tailings particle composition and distribution below a beach, the change of phreatic surface of the dam, and the engineering properties of the tailings of the dam profiles have been measured. A new tailings facility, Yangtianqin tailings impoundment, owned by Tongchang copper mine of Yuxi Mine Co., was used as a case study to illustrate the physical modeling of the tailings dam. In the model test, the geometrical model of pond area was constructed according to the scale factor, λL, of 1:200 (model:prototype), and the tailings discharge system was also established, the tailings slurry then being discharged based on the design data. Finally, on the basis of the model test results on profiles, the stability analysis of the tailings dam at different heights was conducted under different conditions. The model test results and stability analysis show that the height of the tailings dam should be less than that originally planned. The original design of Yangtianqing tailings impoundment should therefore be revised for the safety of the tailings impoundment.

Fiber Optic Displacement Monitoring in Laboratory Physical Model Testing

For physical models, conventional techniques have difficulties in monitoring internal displacements during laboratory testing. In this paper, based on fiber Bragg grating (FBG) sensing technology, a bar-type fiber optic displacement sensor is developed for small-scale models. When the model deforms due to loading or unloading, the embedded displacement sensor can capture the displacement profile along the bar length using the strain data from quasi-distributed FBGs. Laboratory calibration tests have showed that the displacements measured by the FBG sensing bar are in good agreement with those from conventional displacement transducers. For the physical models of a gravity dam and a cavern group, the FBG sensing bars were successfully installed in predefined holes, together with conventional gauges. During testing, the FBG sensing bars measured the displacement distributions within the models. The fiber optic monitoring results demonstrate the deformation characteristics of surrounding rock masses induced by overloading and underground excavation and indicate the overall stability conditions of these two geo-structures.

Behaviour of prestressed geotextile-reinforced sand bed supporting a loaded circular footing

In the past, the beneficial effects of prestressing the geosynthetic in reinforced soil foundations have been studied mathematically. It is timely to experimentally investigate the degree of improvement generated by prestressing the geosynthetic layer for several embedment depths of a footing resting on a reinforced sand bed. Therefore, laboratory physical model tests and finite element analyses were conducted to study the behaviour of prestressed geotextile-reinforced sand bed supporting a loaded circular footing. The addition of prestress to the geotextile reinforcement results in significant improvement to the settlement response and the load-bearing capacity of the foundation. For a surface footing, the load-carrying capacity at 5 mm settlement for the prestressed case (with prestress equal to 2% of the allowable tensile strength of the geotextile) is approximately double that of the geotextile-reinforced sand without prestress. The beneficial effects of the prestressed geotextile configuration were evident for greater footing depths, in comparison with unreinforced and reinforced (without prestress) counterparts. Experimental and numerical results were also used to validate a few empirical relationships, which are commonly used for solving soil-structure interaction problems. The results obtained from finite element analysis using the program, PLAXIS are generally found to be in reasonabaly good agreement with experimental results.