Scale Model Experiments Research Articles

Meteorological effects on the noise reducing performance of a low parallel wall structure

Numerical calculations, scale model experiments and real-life implementations have shown that the insertion of a closely spaced array of low parallel walls of finite dimension beside a road is potentially useful for road traffic noise abatement. However, previous studies did not consider atmospheric effects. In this work, numerical techniques have been used to predict the sound reduction provided by a low parallel wall structure, subject to wind and temperature related atmospheric effects. Three full-wave prediction schemes show very good agreement when looking at the insertion loss of a low 6m wide parallel wall structure, consisting of 24 regularly spaced 0.2-m high rigid walls. Meteorological effects are predicted not to deteriorate the insertion loss (relative to rigid flat ground) of the parallel wall array in the low frequency range. However, at high sound frequencies the insertion loss is strongly reduced by downward refraction at a distance of 50m in case of strong wind. Consequently, overall A-weighted road traffic noise insertion loss will be significantly lower during wind episodes. Although weak turbulence does not alter the energy time-averaged insertion losses, strong turbulence reduces the noise shielding in the high frequency range also. As with conventional noise walls, when considering use of low parallel wall structures for noise reduction outdoors, even at short distances, atmospheric effects should be considered.

Extension of the Rusck Model for Calculating Lightning-Induced Voltages on Overhead Lines Considering the Soil Electrical Parameters

The validity of the Rusck coupling model and its equivalence to the model by Agrawal, Price and Gurbaxani have already been demonstrated for the case of a perfectly conducting ground and a vertical stroke channel. However, in spite of its popularity, the restriction of an infinite soil conductivity imposes a strong limitation on the use of the model for the analysis of realistic situations. In this paper, a procedure is proposed to extend the Rusck's model to the case of a finite ground conductivity so as to enable the calculation of lightning-induced transients on overhead lines taking into account the soil electrical parameters. The validity of the model is demonstrated through comparisons of simulation results with measured lightning-induced voltages and currents obtained from scale model and rocket-triggered lightning experiments.

In-situ orifice calibration for reversing oscillating flow and improved performance prediction for oscillating water column model test experiments

Performance characterization of oscillating water column (OWC) wave energy converters (WEC) is commonly assessed by conducting physical scale model experiments of OWC models fitted with orifice plates to the air chamber to both; simulate the power take off (PTO), and measure the air flow rate. Generally it is assumed that a single calibration factor can be used for bi-directional air flow measurement, however this paper shows the assumption can be in-accurate and that it is necessary to have separate inflow and outflow calibration factors. This paper presents (i) a novel method for in-situ calibration of an orifice and (ii) a simple algorithm to reduce noise during air flow reversal (low air chamber pressure differential). Application of this technique results in more accurate flow rate prediction and consequently, better prediction of the power absorbed by the power take-off for OWCs.

2.5-Dimensional finite-difference time-domain analysis for propagation of conventional railway noise: Application to propagation of sound from surface railway and its verification by scale model experiments

2.5-Dimensional finite-difference time-domain analysis for propagation of conventional railway noise: Application to propagation of sound from surface railway and its verification by scale model experiments

MPS法による大型船舶の津波中挙動と構造物に作用する衝突荷重特性に関する研究

Most of the loss suffered in the Great East Japan Earthquake was due to the tsunami rather than to the earthquake itself. An unusual aspect of these disasters was that much of the structural wreckage that was swept up by the tsunami remained and drifted on the sea. Some of the wreckage caused subsequent damage to coastal structures. These drifting objects caused by the tsunami included containers, boats and ships, cars, caissons, and other objects from the harbors. Thus, it is necessary to solve these problems in order to plan the safe coastal zone. However, there is no effective method in order to verify this subject, and few reports are available on characteristics of collision behavior of huge ship in tsunami. These problems can be resolved by the hydraulic model experiment. However, it is difficult to verify the scale model experiment, in addition these need enormous cost. On the other hand, numerical simulation method is suitable for analyze the collision phenomena of huge ship in tsunami. The MPS method is a particle based method originally proposed by Koshizuka et al. and is a Lagrangian procedure for simulating a flow field employing the moment-to-moment motions of particles distributed in a space. The most distinctive aspect of particle methods is that they do not require consideration of connections between calculation points. Because of this, the MPS method is well suited for analysis of strongly non-linear phenomena accompanying large deformations of free surfaces. The objective in this paper is following items, 1) to propose and evaluate the friction elastic body model for collision phenomena using MPS method, 2) to clarify characteristics of collision behavior of huge ship. The present numerical model of the MPS method is applied the dynamic analysis of elastic solids developed by Koshizuka et al. And, the authors approach the new method of the MPS which can analisys friction phenomena between solid in this research. As these results, the authors found that present model is suitable for calculation of collision phenomena through the verifications of the wave tank experiment and the analytical solution. In addition, the authors confirmed basic characteristics of behavior of collision phenomena of huge ship in tsunamis. Further, it was concluded that, the impulse due to collision force without friction force on the surface of the huge ship is 55% larger than the impulse of only tsunami waves in case of reflection tsunami flow from the land structure is small.

Aerodynamics and Conceptual Design Studies on an Unmanned Combat Aerial Vehicle Configuration

The ability to accurately predict both static and dynamic stability characteristics of air vehicles using computational fluid dynamics methods could revolutionize the air vehicle design process, especially for military air vehicles. A validated computational fluid dynamics capability would significantly reduce the number of ground tests required to verify vehicle concepts and, in general, could eliminate costly vehicle “repair” campaigns required to fix performance anomalies that are not adequately predicted before full-scale vehicle development. This paper outlines the extended integrated experimental and numerical approach to assess the stability and control prediction method capabilities, as well as the design and estimation of the control device effectiveness, for highly swept low observable unmanned combat aerial vehicle configurations. The aim of the AVT-201 Task Group is to provide an assessment of the computational fluid dynamics capabilities using model-scale experiments and transfer this knowledge to real-scale applications.

Smoke spreading analysis from an experimental subway scale model

The aim of this study is to experimentally investigate buoyancy-induced upward flow interaction with forced convection by mechanical ventilation. We consequently tried to determine optimal ventilation strategy in case of fire arising in a confined subway station. To do so, a subscale approach was developed and measurements from Picture Imaging Velocimetry and thermal field investigations were carried out to provide comprehensive flow field analysis. The flow patterns involved have been described for several geometric configurations i.e. first without and then with passenger staircases. In staircases, limits of the momentum ratio determining presence of the stack phenomenon were identified for two staircase configurations. A need for compromise between smoke-free staircases and a globally stratified platform environment was underscored. Extraction tends to decrease by 22% the safety height parameter in the station, but a concomitant 50% ventilation mass flow rate increase ensures that the two passenger accesses will be smoke-free. The results of this study correspond to the existing guidelines for prevention and ventilation in case of underground station fire.

Influence of constraint effect of sidewall on maximum smoke temperature distribution under a tunnel ceiling

A sequence of tests and simulations with varying transverse fire locations were conducted in a full-scale tunnel to investigate the constraint effect of sidewall on the maximum smoke temperature distribution under a tunnel ceiling. Then, the simulated results were comprehensively compared with both those of the full-scale tests and the model-scale experiments from previous studies. The results of the full-scale experiment show that the longitudinal maximum smoke temperature rise distribution decreases can be approximated by a power function. However, the numerical simulation results indicate that an exponential distribution may be plausible. The normalized ceiling jet temperature rise at the impingement point displays an exponential variation with the distance between the fire source and the sidewall. Meanwhile, regression models taking the constraint effect of sidewall into account was developed to predict the ceiling jet impingement temperature in tunnel fires.

Numerical energy balance analysis for an onshore oscillating water column–wave energy converter

The hydrodynamic performance of Oscillating Water Column (OWC) wave energy converters depends mainly on the behaviour of the wave–OWC interaction. In this paper, a fully nonlinear 2D RANS–based computational fluid dynamics (CFD) model was used to carry out an energy balance analysis of an onshore OWC. Chamber differential air pressure and free surface elevation from published physical measurements were used to validate the CFD model. Additional validation was carried out via PIV data from available model–scale experiments to validate the CFD model's capability in capturing the flow field and the turbulent kinetic energy. The validated CFD model was then used in an extensive campaign of numerical tests to quantify the relevance of different design parameters such as incoming wave height and turbine pneumatic damping to characterise the hydrodynamic performance and wave energy conversion chain of the OWC. To capture the flow field inside the OWC in good agreement, additional refinement was required at the field of view together with utilizing either SST or RSM turbulence models rather than k-ɛ. It is found that the applied damping has crucial impacts on the energy conversion process. Also, increasing the wave height can lead to a massive drop in the system efficiency. Furthermore, both power take–off (PTO) damping and wave height play an important role in vortex formation around the upper and lower chamber's lips during the in–flow and out–flow stages.

Resonant Frequency Evaluation on Reradiation Interference from Power Transmission Line Based on the Generalized Resonance

IEEE was not able to give the resonance mechanism of reradiation interference (RRI) above 1.7 MHz from power lines based on research works of electric field. In order to solve this problem, the generalized resonance theory is introduced, and a method based on the electromagnetic (EM) energy balance theory is proposed to predict the RRI resonant frequency. Taking a large-scale space including UHV power lines and antenna arrays as a generalized closed system, the expression of EM open systems' generalized resonance factor is derived based on the complex Poynting theorem. Then the RRI resonant frequency corresponds to the zero point of the generalized resonance factor's imaginary part. Taking the case researched by IEEE as an example, the maximum deviation of the resonant frequency between the values predicted by the generalized resonance theory and the measurement values obtained from scaled model experiments are less than ±0.169 MHz in the frequency band below 1.7 MHz.

Scale Model Experiment of Liquid Water Transport in Gas Diffusion Layer of PEFC and Optimization of the Structure

To improve the performance of a polymer electrolyte fuel cell (PEFC), it is essential to control liquid water behavior in the cell. Gas diffusion layer (GDL) plays an important role for the water transport, and optimization of the structure is one of the major research topics. As the structure of GDL is quite complex and small with the scale order of 200 mm thickness, measurement of liquid water behavior is difficult, and only a few results are reported with X ray measurement. In this study a scale model experiment is proposed to observe the behavior in a model GDL made with a 3D printer in the scale of 300 times of the actual one. The parameters relating to the liquid water motion in a complex fiber structure are Capillary number, Weber number and Bond number. As the pore scale in the GDL is quite small and the speed of the water is very slow, it was assumed that capillary force is the dominant factor for the motion and other effects such as viscosity, inertial and gravity can be ignored. This gives that the behavior in the GDL is organized by Capillary number, Ca = uμ/σ, where, u is velocity, μ is viscosity and σ is interface tension. It represents the ratio of viscous to capillary forces. By using silicone oil as water and water as air, the scale model can be magnified to 300 times of actual size. Gravitational effect can be also removed, as the densities of the two liquids are similar. The scale model was made by 3D printer from the structural data obtained by X ray CT images of actual GDL.Figure 1 shows the GDL made by 3D printer. The length is 25mm ´ 25 mm ´ 45 mm. The bottom of the model faces to a flat plate with a hole assuming a crack of micro porous layer (MPL). Silicone oil representing water is dyed in red. Viscosity ratio of silicone oil to liquid water is 55, which is same as the ratio of air to liquid water. Inter face tension is σ = 3.1´10-2 N/m, equivalent order of water and air. The contact angle of the material and the silicone oil was about 130°, which is the same order with the actual GDL condition. The GDL structure is set in the box made of acrylic and the GDL is immersed in liquid water representing air. Figure 2 shows comparison of liquid water behavior in the scale model and they are compared to the results simulated by Lattice Boltzmann Method (LBM). Length of the simulation area is 80 μm ´ 80 μm ´ 160μm. The interfacial (surface) tension is σ = 7.29´10-2 N/m. Viscosity ratio of liquid phase to gas phase is 55 and the contact angle is set 130° in the simulation. In each case Capillary number, Ca, is adjusted to ~10-2 by inlet velocity. The developments of liquid water in the fibers are quite similar between the scale model and the simulation. Particularly the selection of pores in different scales in the water motion is very similar. Variety of observations in different Ca conditions showed good similarity between the model and the simulation. These results indicate the possibility of the scale modeling. Investigation was made for the water behavior for the wide range of different Capillary numbers. Figure 3 shows pictures with different capillary numbers. In Ca ~10-1 liquid phase immerses small pores in bottom region, whereas the small pores are not filled by the water in Ca less than 10-2. This is due to the fact that viscous and inertial forces become large relative to the capillary force when Capillary number is large, and the capillary force becomes dominant when Capillary number is small. In less than Ca ~10-2, the phenomena were almost same and independent to the Capillary numbers. In this study the characteristics of liquid water behavior was investigated intensively for wide range of Capillary numbers.Using the scale model experiment, optimization of the fiber structures was attempted by comparing the results with LBM simulation. Water motion in the vicinity of libs and channels facing to the GDL was also investigated. Some of the results will be presented to show clues for the optimization of the GDL structure. Figure 1

Aerodynamic Simulation of the MARINTEK Braceless Semisubmersible Wave Tank Tests

Model scale experiments of floating offshore wind turbines are important for both platform design for the industry as well as numerical model validation for the research community. An important consideration in the wave tank testing of offshore wind turbines are scaling effects, especially the tension between accurate scaling of both hydrodynamic and aerodynamic forces. The recent MARINTEK braceless semisubmersible wave tank experiment utilizes a novel aerodynamic force actuator to decouple the scaling of the aerodynamic forces. This actuator consists of an array of motors that pull on cables to provide aerodynamic forces that are calculated by a blade-element momentum code in real time as the experiment is conducted. This type of system has the advantage of supplying realistically scaled aerodynamic forces that include dynamic forces from platform motion, but does not provide the insights into the accuracy of the aerodynamic models that an actual model-scale rotor could provide. The modeling of this system presents an interesting challenge, as there are two ways to simulate the aerodynamics; either by using the turbulent wind fields as inputs to the aerodynamic model of the design code, or by surpassing the aerodynamic model and using the forces applied to the experimental turbine as direct inputs to the simulation. This paper investigates the best practices of modeling this type of novel aerodynamic actuator using a modified wind turbine simulation tool, and demonstrates that bypassing the dynamic aerodynamics solver of design codes can lead to erroneous results.

Scale Model Experiment of Liquid Water Transport in Gas Diffusion Layer of PEFC and Optimization of the Structure

In a polymer electrolyte fuel cell (PEFC), it is important to control water transport in the cell to supply oxygen smoothly to the reaction zone. Produced water in the catalyst layer transports through micro-porous layer (MPL), gas diffusion layer (GDL), and then reaches to the channel. All of the layers are important for the water control, and this study focuses on the water transport behavior in the GDL, which has complex fiber structure. For observation of the motion, a scale model experiment was developed using silicon oil and water to keep Capillary number equivalent to the actual cell. The fiber structure of the GDL was fabricated with a 3D printer. With the scale mode, effects of GDL property such as wettability on the water behavior were investigated, and the results were compared to the numerical simulation with Lattice Boltzmann Method.

Experimental and numerical study of a containership under parametric rolling conditions in waves

A set of scaled model experiments have been conducted at HSVA towing tank to study the occurrence of parametric rolling on a containership in regular and irregular waves. Herein the performed model tests are described and the experimental results are presented. Forced rolling tests were also performed with the ship model in order to investigate its roll damping characteristics. By means of these tests the roll damping coefficients were determined for different maximum roll amplitudes and advance speeds. The experimental data of this containership is compared with results from a non-linear time domain model, where the prediction of maximum roll amplitude under parametric rolling conditions associated with different viscous roll damping models is thoroughly discussed.

Numerical investigation of earth pressure reduction on buried pipes using EPS geofoam compressible inclusions

This paper presents a numerical study performed to investigate the effect of expanded polystyrene (EPS) geofoam panels placed over a buried pipe. It is recognized that EPS geofoam panels as compressible inclusions over a buried pipe are effective in reducing the earth pressure acting on the pipe due to positive arching action. To date, however, there is no systematic methodology that links the earth pressure on a buried pipe with the geometry of EPS panels. To investigate the ‘optimal’ geometry of EPS panels, a two-step numerical modeling approach was employed and calibrated against results of a model-scale experimental study. First, material properties were estimated for each component used in the model-scale tests (i.e., soil, EPS geofoam and steel pipe). Second, the model-scale experiments were simulated using the selected material properties. These simulations resulted in reasonable agreement between model-predicted and measured vertical and lateral earth pressures. Using the calibrated model, additional cases that were not covered in the experimental study were investigated to examine different widths and thicknesses of EPS panels. The numerical analysis provided quantification of the effect of EPS compressible inclusion and a systematic approach to optimizing the design of buried pipes using EPS geofoam panels.

Assessing Anidolic Daylighting System for efficient daylight in open plan office in the tropics

The current study seeks to determine the Anidolic Daylighting System (ADS) variables that are applicable under tropical climate, according to modified duct shapes, duct width, duct length and distributor configuration. Our study involves experimental scale model and Integrated Environmental Solutions 〈Virtual Environment〉 (IES〈VE〉) computer simulation. We use physical scale model (1:10) to validate the simulation tool and to determine the appropriate orientation. Subsequently, the ADS simulation involves different variables of duct shapes, duct width, duct length and distributor configuration in an open plan office. The analysis of results for daylight quantity is based on absolute Work Plan Illuminance (WPI), daylight factor and daylight ratio. The results suggest that the ADS performed well for all orientations, but its performance in the South orientation is better than other orientations. This means that the developed ADS by rectangular duct shape and three meter duct width can transfer daylight as deep as 12.5m and 20m from window wall in overcast and intermediate sky conditions respectively. The study findings can give architects, engineers and built environment scientists some insights into exploring opportunities of using ADS to improve of occupants visual comfort as well as energy saving designs.

Experimental study on longitudinal and transverse temperature distribution of sidewall confined ceiling jet plume

This paper investigates the longitudinal and transverse temperature profiles of a strong plume impinging flow, induced by a turbulent porous gas burner impinging on the sidewall confined ceiling of a long-narrow tunnel-like structure. A series of model scale experiments were conducted for fires against a tunnel sidewall with increasing vertical burner heights (0, 0.17 and 0.35m), 8 different HRRs (heat release rate) from 15.94 to 106.28kW were used. Measurements of the vertical temperature profiles against the sidewall and radial horizontal temperature profiles under the ceiling are presented. Results show that for the strong impingement plume, the temperatures at the impingement point can be well correlated by the three-regime of buoyant plume, intermittent flame and continuous flame. The horizontal temperature profiles under the ceiling show obviously asymmetric. It is confirmed that the characteristic length scale of plume radius at ceiling level is sufficiently applicable for predicting the ceiling excess temperatures of strong plume impingement flow, and the correlations of the ceiling excess temperature in both transverse and longitudinal directions are proposed and validated by comparing them with previous research.

Dynamic internal light shelf for tropical daylighting in high-rise office buildings

Many high-rise offices in tropical regions do not have good quality of daylighting despite having abundance of daylight. Due to large glazed façade without external shading device, the office spaces receive high indoor illuminance with non-uniform distribution and glare problems. Thereby, efforts are needed to look into effective internal shading which is flexible to be installed by office tenants without modifying external façade. Daylighting performance of various internal light shelves was studied using Radiance-based simulation. The simulation results were validated against physical scaled model experiment and the results indicated significant Pearson correlations which ranged from 0.826 to 0.985. This study proved that high-rise office without any shading had poor daylighting quality with average illuminance as high as 11,193 lux and uniformity ratio below 0.1. Light Shelf (LS) 6 and LS 4 exhibited the best performance under intermediate sky, whereas LS 2 was the best under overcast sky. Although there was a decrease in illuminance level when comparing the optimum cases to the Base Case (ranging from −62.0% to −34.1%), the optimum cases showed a significant increase in distribution uniformity which was up to 178.6%. The finding has proposed a dynamic internal light shelf which could provide optimum daylighting performance for different sky conditions, times, months and orientations under tropical sky. Nevertheless, the proposed light shelf did not give significant improvement in Guth Visual Comfort Probability and CIE Glare Index. Thus, further studies are needed to consider the impacts of other types of shading and glazing on glare prevention.

모형실험을 통한 식생형 방음벽의 소음저감 효과 분석

모형실험을 통한 식생형 방음벽의 소음저감 효과 분석

Sedimentation-induced burial of subsea pipelines: Observations from field data and laboratory experiments

Sediment transport-induced changes to the embedment of three 26km long sections of subsea pipeline are analysed and subsequently explained using model scale experiments. Rather than the scour and scour-induced sinking and sagging traditionally thought to dominate post-lay pipeline spanning and embedment change, the change for these pipelines is shown to be caused by sedimentation. The pipelines traverse a range of metocean and soil conditions; the variation in embedment correlates well with the variation in metocean conditions, with most change occurring in an area where multidirectional high-velocity short-duration flows associated with internal waves propagate at near-perpendicular angles to the pipeline. To understand the mechanism driving these changes, a series of model scale tests in O-tube flumes have been completed under flow conditions mimicking those recorded in the field. Good agreement is found between the field and laboratory results, both in terms of the process timescale and the post-sedimentation profile. The consistency of the embedment changes between the pipelines, their correlation with metocean conditions, and the ability to replicate these changes in model scale tests suggests that such changes can be accounted for in more effective pipeline design. Spans are relatively rare along the pipelines but where they do occur fish rather than scour are shown to be the principal agent of span formation.