Reduced-scale Model Research Articles

A test method for analyzing the deformation of landslide model

In order to study the overall deformation of geotechnical model conveniently, the worksite of landslide bridge foundation reinforced by the front and rear row anti-slide piles in Chenglan railway was taken as an example. On the basis of shaking tabe test of a 1/40 reduced scale model, the landslide deformation caused by vibration waves was monitored through burying self-made phosphor bronze strips in soil. Combined with the horizontal and vertical coordinates of the bending strain points on the phosphor bronze strips, the digital matrix was converted by applying Renka Cline random matrix generation method, and the two-dimensional contour plots were drawn based on it. The results showed that the two-dimensional contour plots reflected the basic law of landslide deformation reasonably, and it revealed the evolution process of landslide deformation and failure. The research conclusions were consistent with the test phenomenon, which met the basic requirements of overall deformation analysis of landslide model. This proposed method can monitor multiple cross sections and was practical for model test.

Physical and Virtual Simulation of the Experiment of Bridge Structure under Static Load

Simulation experiment is an important method to study the performance of bridge structure, among which the simulation experiment of the structure under static load is an effective way to evaluate bridge quality and bearing capacity. In this paper, a 1:25 reduced-scale model of vehicle and bridge is used to simulate the performance of the practical bridge under static load. The finite element analysis is used for virtual simulation, and scale model experiment is used for physical simulation. Comparing the results of physical simulation and virtual simulation for the experiment, it is found that the two are basically the same, verifying the accuracy and effectiveness of this method. Physical simulation and virtual simulation complement each other, which plays an important role in promoting the experimental research and teaching in bridge engineering.

Economic design of alternative system to reduce the water distribution losses for sustainability

Water companies and their consumers affected with leakages in water distribution system worldwide. This has attracted many practitioner’s attention as well as researchers over the past years. Selected study area suffers from water losses of about 10 to 15% which accounts to loss of about 9 to 9.75 million liters per month. The present study was under taken to understand, analyze and evaluate the losses and suggest preventive measures of wrapping and repair clamping for control of these losses. The assessment of water losses is done through comparative analysis of data using Microsoft Excel software. Population forecasting is done in context of assessing the amount of water lost that can be prevented in future decades, adjusting to increased water demand and losses. For better efficiency of the suggested methods, experimental analysis was carried out on a reduced scale model of a single stretched pipeline. Cost estimation of the preventive measures was done by obtaining information about the materials used by trading professionals.

Numerical Simulation on Effects of Horizontal Natural Opening Area and Heat Release Rate on Temperature Distribution and Vent Flow in Small Compartment

In this study, the numerical simulation to investigate the effects of horizontal natural opening areas and heat release rates on temperature distribution and vent flow in a small compartment was performed using a fire dynamics simulator. The reduced scale model of a stage in a real scale theater with horizontal natural opening was selected for this study. The horizontal opening areas were 0.0196, 0.1024, and 0.2025 m<sup>2</sup> (1, 5, and 10% of the floor area, respectively), and the heat release rates were 0.46, 1.35, and 2.61 kW. By decreasing the horizontal opening area and increasing the heat release rate, the temperature in the compartment increased. Additionally, by increasing the heat release rate, the average velocity near the center of the opening increased. For the increase in the horizontal opening area from 0.0196 to 0.1024 m<sup>2</sup>, the velocity near the center of the opening increased. However, when the horizontal opening area increased from 0.1024 to 0.2025 m<sup>2</sup>, the variation in velocity was not noticeable. Considering the analyses of temperature and velocity distributions of vent flow, the bidirectional flow pattern was observed, where the outflow and inflow occurred at the center and edge of the horizontal opening, respectively. The mass flow rate through the horizontal opening increased with the increase in the horizontal opening area and heat release rate. The previous correlation for mass flow rate under-predicted the present numerical simulation data.

Development of the Reduced-Scale Vehicle Model for the Dynamic Characteristic Analysis of the Hyperloop

This study addresses the Hyperloop characterized by a capsule-type vehicle, superconducting electrodynamic suspension (SC-EDS) levitation, and driving in a near-vacuum tube. Because the Hyperloop is different from conventional transportation, various considerations are required in the vehicle-design stage. Particularly, pre-investigation of the vehicle dynamic characteristics is essential because of the close relationship among the vehicle design parameters, such as size, weight, and suspensions. Accordingly, a 1/10 scale Hyperloop vehicle system model, enabling the analysis of dynamic motions in the vertical and lateral directions, was developed. The reduced-scale model is composed of bogies operated by Stewart platforms, secondary suspension units, and a car body. To realize the bogie motion, an operation algorithm reflecting the external disturbance, SC-EDS levitation, and interaction between the bogie and car body, was applied to the Stewart platform. Flexible rubber springs were used in the secondary suspension unit to enable dynamic characteristic analysis of the vertical and lateral motion. Results of the verification tests were compared with simulation results to examine the fitness of the developed model. The results showed that the developed reduced-scale model could successfully represent the complete dynamic characteristics, owing to the enhanced precision of the Stewart platform and the secondary suspension allowing biaxial motions.

Optimization of fishway attraction flow based on endemic fish swimming performance and hydraulics

Attracting fish to fishway entrances is vital for ensuring successful and timely passage at dams and other in-stream barriers. This requires knowledge of both the target species' swimming ability and the hydrodynamics near the entrance. However, such knowledge is not always available during the initial design phase. The objective of this study is to propose suitable hydraulic conditions for the entrance of a fish passage facility to be built on the Jing River in China. We measured the swimming ability of three endemic cyprinid species (Phoxinus lagowskii, Triplophysa stoliczkae and Opsariich thysbidens) using three metrics: 1) induced flow velocity, 2) critical swimming speed, and 3) burst swimming speed. We then used a reduced-scale physical model of the fish passage facility and a verified 3D numerical hydrodynamic model to simulate the flow field under three fish collecting channel (FCC) operation scenarios. Connecting the fish swimming ability and the flow conditions in the river allowed to define the migration corridors present downstream of the FCC entrance under the different operation scenarios. Although the local velocity in the river near the fish passage entrance never exceeded the burst swimming speed of the target species, large backflow areas developed below the entrance in scenarios 1 and 2. The addition of a spur dike downstream of the entrance decreased the development of backflows, optimizing the width of the migration corridor by nearly 32%. This research presents a reliable and quantitative approach that combines fish swimming ability metrics and hydraulic characterization for optimizing attraction flows at fishway entrances.

Comparative analysis of Piled Raft Foundation System (PRFS) settlements placed on soft soils via geotechnical centrifuge

The use of Piled Raft Foundations Systems (PRFS) has been extended to different types of soils, including soft clay soils. In this type of soil it is possible that, in addition to the consolidation process due to the presence of loads, a subsidence process is generated, associated with variations in pore pressure with depth. In many cases, these variations are associated with the loss of recharge of the aquifers or with the extraction of water from deep soil layers. In this work, the behaviour of some PRFS built on soft clay soils, which are subjected to the double consolidation process, are evaluated, both by loading and by the extraction of water from deep soil layers. The research is based on the implementation of reduced-scale models in a geotechnical centrifuge; the influence of the separation and number of piles on the deformation or settlement of the system is analysed. It is shown that, normally, groups of piles with greater separation control settlement more effectively. However, the settlements are greater when the soil is subjected to the weight of the structure in addition to a process of depletion of the pore pressure, because the settlement depends on the distribution of the piles, which is described using the Filling Factor (FF).

Joints for treelike column structures based on generative design and additive manufacturing

Joint design is always of particular interest and important to treelike column structures in view of their structural integrity and cost. In this work, an integrated method based on generative design and additive manufacturing is presented to obtain an optimal joint structure. This method is applied to design a three-branch joint, and hundreds of models are automatically generated from a cloud computing platform. Then, two representative joint models with the lowest mass are selected for further static behavior analysis. Furthermore, the analysis results are compared to three other types of joints, namely the topologically optimized joint generated by Optistruct software, the hollow spherical joint commonly used in engineering applications and the bionic joint developed by simulating a branching plant in nature. Finally, reduced-scale models of the above joints are produced by the additive manufacturing technique using both polylactic acid plastic and stainless steel. The effects of parameter settings and support methods on the quality of additive manufacturing are discussed. The results show that the representative joints obtained by the generative design exhibit more uniform stress distribution and better static behavior than the other joints. Additive manufacturing technology can not only improve the accuracy of joint production but also solve the key problem that complex shapes formed by generative design are difficult to be produced by traditional processes. Thus, it is effective and promising for combine generative design with additive manufacturing to design and manufacture joints for treelike column structures.

Numerical modeling of Reynolds scale effects for filling/emptying system of Panama Canal locks

Significant scale effects have been detected on the filling/emptying time measured with a reduced-scale physical model of the Third Set of Locks of the Panama Canal. During the design phase, corrections were made to compensate for these effects. However, the measurements at the prototype scale indicated that the corrections were insufficient because they only accounted for the differences in skin friction. In this study, a general methodology was proposed to evaluate scale effects using three-dimensional numerical models. This methodology was validated and then applied to a portion of the filling/emptying system of the Panama Canal to quantify its scale effects. The results showed that this technique can consider all sources of scale effects that affect head losses, such as skin friction and flow separation, and thereby correctly simulate the filling/emptying time at the prototype scale. The proposed methodology for scale effect quantification can be used to correct the results of physical models, and it can be expected to improve estimation of the performance of prototypes.

Experimental facility for reduced scale model testing of hydraulic machines hybridized with a battery energy storage system

With a continuously growing share of non-dispatchable renewable energy sources in the power mix, flexibility in hydropower provision is becoming fundamental. The major role played by hydropower in frequency regulation in the last years has underlined the possible drawbacks of fast regulation impacting the hydraulic system health. Two of the most promising solutions to address this problem are the hybridisation of hydropower with battery energy storage systems and the variable speed technology. Batteries have already proved to be able to provide multiple services to the power system, and their coupling with hydropower is a possible interdisciplinary solution to increase flexibility provision in power systems. In this respect, one of the main challenges to address is the control of the hybrid system. While research is heading towards this direction, it becomes necessary to have experiment facilities able to test and validate the upcoming solutions. Testing platforms are nowadays decoupling the hydraulic and the electric components, testing them separately, therefore, they are not suitable for the validation of the control strategy under real grid conditions. The scope of this paper is to present an experimental facility where different joint control techniques can be tested on reduced scale models of hydraulic machines hybridized with a battery energy storage system. The presented test-rig combines all the fundamental components, both on the hydraulic and on the electrical side, within the same testing facility. The platform is an adaptation of the already existing laboratory of hydraulic machines at EPFL in Switzerland.

Emergency gates - model scale tests at turbine runaway condition

Emergency gates are the last link in the chain of safety of turbo-groups in case of distributor failure, safeguarding the power station from severe damage. These gates can be located at the turbine intake or at the outlet of the draft tube and can be controlled by gantry cranes or hoist hydraulic cylinders. Gates must descend with high flow for a short time to prevent the turbine from spinning at runaway velocity for periods longer than admissible, as that would entail the rise of uplift and downpull forces that may jeopardize their stability. Indeed, at the prototype scale, the closing maneuver entails a certain risk, because of which it is usually tested avoiding extreme conditions.In this work, the operation of emergency gates was tested against more severe conditions on a reduced-scale physical model. The case study involves three emergency gates controlled by gantry cranes and located at the intake of a large Kaplan turbine which underwent high levels of vibration when operated at prototype scale.Model tests were aimed at detecting and quantifying hydraulic phenomena that might emerge during operation with an eye on the proposal of alternative designs. Unlike most tests of this sort, the experimental setup includes the runner of the turbine assembled on a test rig, which allows for a more realistic flow distribution along the vanes during the gate closure under runaway conditions.Steady state tests were carried out under runaway conditions, while stems of servomotors enabled the regulation of the position of the gate. Downpull forces were found to start at 12 % of the gate opening. Flow asymmetry was observed, gate on the left of the semi-spiral casing being the most affected by higher flow velocities. The runner vortex rope frequency was measured also at gate lip for some particular conditions.

Experimental investigation on extinguishing characteristics of liquid nitrogen in underground long and narrow space

As an efficient and environmentally friendly cryogenic extinguishing agent, liquid nitrogen (LN2) is highly promising for fire extinguishing in narrow and long underground confined spaces. It is difficult to tackle the urban utility tunnel fire due to its complex and narrow structural characteristics. Thus work aims to study the feasibility and effectiveness of LN2 fire suppression in urban utility tunnel. An experimental study on the fire extinguishing characteristics of LN2 in urban underground utility tunnel was carried out in a 1/3.6 reduced-scale model tunnel with different injection parameters, such as the direction of the LN2 nozzle and the distance between the LN2 nozzle and the fire source. The results show that LN2 can quickly extinguish a utility tunnel fire. The rapid extinguishing mechanism of LN2 involves the combined effect of cooling and inerting. When the LN2 release distance is 2 m and 4 m, the fire extinction time increases by 8.7% and 27.5% respectively for the horizontal injection. On the contrary, the vertical injection is more effective when the LN2 nozzle is far from the fire source. By injecting LN2 into the utility tunnel, an abrupt evaporation occurs, followed by a thermal expansion. The vaporizing cryogen forms a low temperature nitrogen cloud, which rapidly cools the gas. As the cloud spreads, the pyrolysis gas is rendered inert, and the fire is isolated from oxygen and finally extinguished.

Experimental Research Into Influence of Discontinuity Angle on Roof Breaking

This study investigates the influence of pre-existing discontinuities on the roof breaking behaviors under Longwall (LW) mining condition. Taking the Meiyukou Coal Mine’s 82,002 working face as the engineering background, a series of similar experiments were conducted for the purpose. To be specific, mica powder was schematically set above the coal seam, simulating the angled discontinuities in the overlaying strata (α = 30° and 60°). Markers and gauges were employed to monitor the strata displacement and relevant stress variation. The results show that the prefabricated discontinuity leads to an early first weighting and frequent periodical weightings. Besides, discontinuities provide favorable conditions for the crack formation and propagation in the overlaying strata. As a result, the final roof caving height has almost doubled, which may aggravate the bearing pressure of the hydraulic pillars at the working surfaces if in the real situation. Hopefully, these information from the reduced-scale models could serve as a reference for the future practical designs of LW face supporting system.

Behaviour of geocell-reinforced strip footings on slopes

ABSTRACT This study presents the results of a series of reduced scale model tests carried out to investigate the bearing capacity and displacement behaviour of strip footings resting near both unreinforced and geocell-reinforced sand slopes. Impacts of some contributing factors such as slope angle, depth of geocell embedment, geocell pocket size and the arrangement of double layer reinforcement are presented and discussed thoroughly. Results indicate that placing a single geocell layer at a depth to footing width ratio of 0.1 (d/B = 0.1) leads to the highest bearing capacity and the lowest settlement ratio. It was observed that steepening the reinforced slope always reduces the bearing capacity and this reduction is remarkable if the slope angle approaches the soil internal friction angle. The optimum depth of the first geocell layer (µ) in a double-layer reinforced slope was found to be approximately 0.5B. At large settlements (s/B > 25%) double geocell reinforcement is always superior to single-layer reinforcement. However, at smaller settlements (s/B < 15%), double geocell reinforcement is effective provided that the spacing of the geocell layers is smaller than 0.5B.

On the influence of Reynolds number and ground conditions on the scaling of the aerodynamic drag of trains

The present study examines the possibilities of transferring drag measurement results on reduced-scale train models to the respective full-scale vehicle. A comprehensive experimental and numerical study of the boundary layer and skin friction along trains is performed, focusing on Reynolds number effects. The data are supplemented by an extensive literature study and compared with different approaches from flat plate theory. Good agreement can be found when using the appropriate empiric coefficients and boundary conditions. Simultaneously, the difficulties in determining the skin friction drag of trains due to three-dimensional effects and surface roughness become apparent. The ground simulation analysis, including the effects of ground roughness due to ballast and sleepers, reveals a significant effect of the ground conditions on the vehicle’s aerodynamic drag. Additionally, the effects of elements mounted on the train roof are investigated for different upstream flow conditions. Finally, a scaling method is proposed to transfer drag results from model-scale to full-scale trains based on the findings.

Instrumental Uncertainty of Conductance Transducers for Maritime Reduced-Scale Models

This paper aims to determine the instrumental measurement uncertainty of conductance transducers for maritime reduced-scale models developed in hydraulic experimental facilities. These transducers are used for the measurements of wave levels and their variations under a dynamic regime (being the measurement principle and method briefly described in the paper). Several metrological characterization methods are also presented, aiming to identify and quantify measurement uncertainty components, namely electrical stability, linearity, reversibility, repeatability, and thermal influence. The obtained results were applied in the evaluation of the transducer instrumental measurement uncertainty.

Dynamic impact experiment and response characteristics analysis for 1:2 reduced-scale model of hydraulic support

It is significant to research the impact resistance properties of hydraulic support due to its key support role in the fully mechanized mining face. However, it is difficult for the entire hydraulic support to implement the impact experiment underground and analyze the response characteristic. Therefore, a dynamic impact experiment for the entire hydraulic support was proposed in this paper, where a 1:2 reduced-scale model of hydraulic support was designed and its response characteristics under dynamic impact load were analyzed. Firstly, a comprehensive monitoring scheme was proposed to achieve an effective monitoring for dynamic response of hydraulic support. Secondly, a multi-scale impact experiment was carried out for the entire hydraulic support and dynamic behaviors of hydraulic support under the multi-scale impact load were revealed by experimental data. Then a dynamic impact experiment of the entire hydraulic support was simulated in ADAMS with the same experiment conditions, and the experimental and simulation data were verified mutually. Finally, the characteristics of energy conversion and dissipation of the entire experiment system after impact were analyzed. The experiment results showed that the impact resistance properties of hydraulic support largely depended on the initial support conditions and different vertical rigidities affected energy distribution proportion of the entire support system.

An Analysis of Floating Geogrid-Reinforced Pile-Supported Embankments Containing Deep Softened Soil

Floating geogrid-reinforced piles provide economic solutions when constructing embankments over areas with soft soil. The combination of piles and geogrids allows for the transfer of stress between the piles and adjacent soil through soil arching and tensioned membrane effects. Furthermore, floating geogrid-reinforced pile foundations can also significantly reduce embankment settlement. However, it has been found that in many cases, the ends of the piles may not be anchored due to layers of thick softened soil. Therefore, reduced scale model tests and numerical simulations were conducted in the current study for the purpose of evaluating the performances of different types of end-bearing and floating piles. The effects of different parameters were considered, including embankment filling heights; pile spacing ratios; stiffness ratios between the piles and the adjacent subsoil; internal friction angles of the embankment fill; and the effects of the tensile stiffness of the geogrids on the bearing capacities of the embankments. The results showed that the absence of firmly supported layers could transfer loads and reduce settlement. The results of this study’s numerical simulations revealed that enlarging the pile-soil stiffness ratios or tensile stiffness, and improving the shear properties of embankment fill could successfully improve the performances of geogrid-reinforced pile-supported embankments. This study’s findings can potentially be used to guide future analyses of floating pile load transfer mechanisms and settlement patterns.

Zoning strategy of zonal modeling for thermally stratified large spaces

Large space buildings play a significant role in modern society because of their environmental advantages and market value. While the zonal model is promising for the efficient and rapid evaluation of the stratified thermal environment, there is a lack of a reasonable and convenient zoning strategy with the advent of modern computing. This paper presents a universal and practical zonal model, in which a simplified momentum equation is applied to consider air momentum preservation, transformation, and dissipation. Hence, the zoning structure is generalized and flexible. Moreover, limiting the dimensionless temperature constraint between adjacent zones establishes the connection between thermal nonuniformity and zoning results automatically. Simultaneously, the dimension and number of zones should be restricted within reasonable ranges to satisfy the characteristics of zonal simulation and reach the criteria of convergence. To further explore and validate the zonal model, a reduced-scale experimental model was constructed to replicate the thermal stratification in a mechanically ventilated large space by considering many crucial realistic factors. A particle image velocimetry (PIV) measurement was then conducted to visualize the airflow pattern and support the partition of zones. The results showed that the zonal simulation with adaptive zoning method can realize a similar accuracy with fewer zones and exhibit a better tolerance for zoning results compared to the conventional empirical zoning method. Furthermore, a case study of an atrium was performed to demonstrate the practicality and efficiency of the method for long-term dynamic simulations of complex thermal environments and building energy use.

Influence of longitudinal ventilation on the mass flow rate distribution of fire smoke flow in tunnels

Experimental investigation on the fire plume mass flow rate distribution in the upstream and downstream direction of fire is performed. Series of tests were conducted in a reduced-scale tunnel model with longitudinal ventilation. The ceiling temperatures along the tunnel were measured under different heat release rate of the fire source and longitudinal velocity. Based on the ceiling temperature decay coefficients, the ratios of the upstream fire plume mass flow rate to the total fire plume mass flow rate released by the fire, δ=ṁupṁ0, were calculated. The results show that the value of δ is significantly affect by the longitudinal velocity (Va). When Va is smaller than 0.50Vc(Vc is the velocity at which the fire smoke is fully confined at the impinging point.), that is Va≤0.50Vc, δ would attain constant value, being 0.5. When Va>0.50Vc, δ would decrease with longitudinal velocity. Once Va excesses Vc, δ will be zero in terms of no fire smoke presence in the upstream side of the fire. Thus a correlation between δ and Va is obtained. A verification of the correlation is also presented at last by comparing to other experimental data.