Scaled-down Models Research Articles

Effect of Barrier Height on the Design of Stepped Spillway Using Smoothed Particle Hydrodynamics and Particle Image Velocimetry

Three-dimensional stepped spillway problems are simulated numerically using smoothed particle hydrodynamics (SPH) to visualize the flow of water along the steps and its flow dynamics. In particular, two distinct scaled-down stepped spillway models were studied with each having barrier heights of 10 mm and 25 mm, respectively. The impact of varying the height of the barrier in the design of the stepped spillway is studied in terms of it flow pattern, flow dynamics, aeration efficiency and oxygenation performances. State-of-the-art particle image velocimetry (PIV) experiment was carried out to affirm the validity of SPH findings and it turns out that both the water flow patterns attained in the SPH and PIV are quantitatively comparable. Further quantitative analysis revealed that the flow velocities in both methodologies are in great consensus. Conclusively, this has demonstrated that the capability and reliability of SPH to precisely approximate the water using finite set of particles to model the flow along the stepped spillway. Both stepped spillway configurations show nappe flow regime as the water descends down the steps. Nonetheless, vigorous hydraulic jump phenomena that is associates with the formation of turbulence and vortices is prominently observed in the configuration with larger barrier height. Decisive SPH data obtained concluded that as the barrier height increases from 10 mm to 25 mm, the water flows down the steps faster at lower pressure value and the overall aeration efficiency is improved from 1.1% to 1.2%. The usage of the higher barrier would promote the occurrence of substantial air entrainment during water swirling that will increase the power dissipation in flow. Subsequently, this while lower the power drawn to achieve the desired aeration effect. Ultimately, this study has justified the critical influence of barrier height dimension on the stepped spillway flow behavior and aeration performance.

A Flow-Through Chromatographic Strategy for Hepatitis C Virus-Like Particles Purification

Biopharmaceuticals are currently becoming one of the fastest growing segments of the global pharmaceutical industry, being used in practically all branches of medicine from disease treatment to prevention. Virus-like particles (VLP) hold tremendous potential as a vaccine candidate due to their anticipated immunogenicity and safety profile when compared to inactivated or live attenuated viral vaccines. Nevertheless, there are several challenges yet to be solved in the development and manufacturing of these products, which ultimately can increase time to market. Suchlike virus-based products, the development of a platform approach is often hindered due to diversity and inherent variability of physicochemical properties of the product. In the present work, a flow-through chromatographic purification strategy for hepatitis C VLP expressed using the baculovirus-insect cell expression system was developed. The impact of operational parameters, such as residence time and ionic strength were studied using scaled-down models and their influence on the purification performance was described. The flow-through strategy herein reported made use of radial-flow chromatography columns packed with an anion exchanger and was compared with a bind and elute approach using the same chromatography media. Overall, by selecting the optimal operational setpoints, we were able to achieve higher VLP recoveries in the flow-through process (66% versus 37%) with higher removal of DNA, baculovirus and host-cell protein (92%, 99% and 50% respectively).

Elastic limit load estimation including similarity approach for different end conditioned conical shells with high semi-vertex angle under axial compression

Abstract This study investigates the stability loss of thin walled conical shell structures under axial loading. More specifically, conical shells with semi-vertex angle greater than 65 ∘ ( β c > 65 ∘ ) and with different bottom edge radial stiffness were studied in order to fill the gap in existing literature. The effects of geometrical parameters of the structure on the load bearing capacity were determined. Conical shell structures with high semi-vertex angle and different boundary conditions display highly non-linear character under axial loading, hence conventional analytical approaches are not adequate to predict the limit load. Therefore, a new method was proposed in this study which can accurately predict the limit load of these structures. The deviation between the proposed method and numerical results was found to be ± 13 % , while it was one order higher (+ ~ 300%) in classical shell theory, based on the configuration. Furthermore, similarity parameters were suggested to increase the range of application of the proposed method. Similarity parameters enable researchers to work with scaled-down models which are capable of simulating the behaviour of real-time-scale models. In addition, the effect of geometrical initial imperfections on the load bearing capacity was investigated and a new reduction coefficient was identified which is much more accurate compared to the overly conservative standard counterpart. A numerical model was developed with COSMOS/M software. This model was validated with experiments, and then was used for the parametric study.

Low energy ultrasonic single beacon localization for testing of scaled model vehicle

Tracking the location (position) of a surface or underwater marine vehicle is important as part of guidance and navigation. While the Global Positioning System (GPS) works well in an open sea environment but its use is limited whenever testing scaled-down models of such vehicles in the laboratory environment. This paper presents the design, development and implementation of a low energy ultrasonic augmented single beacon-based localization technique suitable for such requirements. The strategy consists of applying Extended Kalman Filter (EKF) to achieve location tracking from basic dynamic distance measurements of the moving model from a fixed beacon, while on-board motion sensor measures heading angle and velocity. Iterative application of the Extended Kalman Filter yields x and y co-ordinate positions of the moving model. Tests performed on a free-running ship model in a wave basin facility of dimension 30 m by 30 m by 3 m water depth validate the proposed model. The test results show quick convergence with an error of few centimeters in the estimated position of the ship model. The proposed technique has application in the real field scenario by replacing the ultrasonic sensor with industrial grade long range acoustic modem. As compared with the existing systems such as LBL, SBL, USBL and others localization techniques, the proposed technique can save deployment cost and also cut the cost on number of acoustic modems involved.

Experimental investigation on dynamic response and damage models of circular RC columns subjected to underwater explosions

Reinforced concrete (RC) columns are widely used as supporting structures for high-piled wharfs. The study of damage model of a RC column due to underwater explosion is a critical issue to assess the wharf’s antiknock security. In this study, the dynamic response and damage model of circular RC columns subjected to underwater explosions were investigated by means of scaled-down experiment models. Experiments were carried out in a 10.0 m diameter tank with the water depth of 2.25 m, under different explosive quantities (0.025 kg–1.6 kg), stand-off distances (0.0 m–7.0 m), and detonation depths (0.25 m–2.0 m). The shock wave load and dynamic response of experiment models were measured by configuring sensors of pressure, acceleration, strain, and displacement. Then, the load distribution characteristics, time history of test data, and damage models related to present conditions were obtained and discussed. Three damage models, including bending failure, bending-shear failure and punching failure, were identified. In addition, the experience model of shock wave loads on the surface of a RC column was proposed for engineering application.

Numerical scaling assessment on natural circulation in Core Makeup Tank

To assess the impact of the wall-stored energy on natural circulation in the Core Make-up Tank (CMT) system in advanced PWR design, the Hierarchical Two-Tiered Scaling (H2TS) method was applied to scaling effects in the corresponding transient process. The models were simulated with the Relap5 code under different scales, and the transient scaling distortion for the key parameters and the similarity criteria numbers were evaluated. The results show that the wall-stored energy can affect the natural circulation in CMT, and remarkably delay the dropping of the mass flow rate at the second stage, but does not affect the time for the thermal stratification to penetrate the CMT. As far as the key parameters dominating natural circulation are concerned, the different scaled-down models can simulate the prototype process with acceptable deviations throughout the CMT cooling period. The evolution of the wall-stored energy in the model and the prototype can be in good agreement by selecting appropriate similarity criteria numbers. However, large deviations of some similarity criteria numbers may occur due to the great change of thermophysical properties.

CFD simulation and analysis of reactor integral hydraulic tests

Scaled-down reactor models are widely used to investigate the reactor integral hydraulic characteristics, due to the feasibility and economy. However, no definite conclusion can be drawn from previous researches for the effects of different scaling methods on simulation results. In this paper, in order to analyze the effects of simulation core design parameters and flow flux on core inlet flow distribution, a CFD simulation is conducted based on the hydraulic tests of the 1/4 scale model of 600 MW reactor in Qinshan phase II. The effects of different scaling velocities, core resistance distributions and lateral resistance on flow distribution are investigated. Calculation results reveal that the uniformity of flow distribution increases with test velocity. Ignoring the resistance of fuel assembly would reduce the uniformity of flow distribution. The flow distributions under conditions of uniformly and segmented distributed core resistance are basically the same, indicating that the detailed simulation of axial pressure drop distribution in assemblies is unnecessary for the design of hydraulic simulator of assembly. The lateral resistance could significantly affect the flow distribution and excessive lateral resistance would reduce the uniformity of distribution.

Impact of Thermal Boundary Resistance on the Performance and Scaling of Phase-Change Memory Device

The scaling of RESET current ( $I_{\mathrm{ RESET}}$ ) used for reamorphization in phase-change memory (PCM) devices has been a challenging task to meet the energy-efficient programming. The faithful prediction of $I_{\mathrm{ RESET}}$ of scaled-down devices demands realistic physical models in order to examine low-power, miniaturized device characteristics, and the potential of a highly scalable PCM technology. Therefore, modeling the intrinsic interface effects, thermal boundary resistance (TBR) at the GeSbTe (GST)–metal and GST–oxide interfaces, and electrical interface resistance (EIR) at the GST–metal interface of the nanoscale PCM device is necessary. In this paper, the impact of presence and absence of TBR and EIR on $I_{\mathrm{ RESET}}$ in a mushroom-type PCM device is investigated, and their usefulness on scaling is predicted for diminished devices. Reductions in $I_{\mathrm{ RESET}}$ , 32% in the case of 100 nm contact diameter (CD), 45% for the 40-nm CD and 73% for the 10-nm CD are achieved by taking into account of interface effects, and these results are validated with experimental results published elsewhere. The fitted model suggests $I_{\mathrm{ RESET}}$ scales down linearly with CD and necessitates for the combined effects of TBR and EIR to successfully follow the isotropic scaling in mushroom-type devices. Hence, our simulation results demonstrate the significance of TBR and EIR for a better optimization and a reliable prediction of $I_{\mathrm{ RESET}}$ for low-power programming of PCM devices toward enabling next generation high-speed, high-density nonvolatile memory applications.

Seismic Performance of Precast Shear Wall–Diaphragm Connection: A Comparative Study with Monolithic Connection

The primary objective of the present study is to understand the behaviour of innovative precast shear wall–slab connection subjected to reverse cyclic loading. The response of the precast connection is then compared with that of the similar monolithic connection. One-third scaled-down models were used for the investigation. In the monolithic connection, typically used U-shaped bars were employed for the connectivity between shear wall and slab. In the precast connection, the connectivity was established in two steps. In the first step, the precast slab and a lower half portion of the shear wall were connected through dowel bars and tied with the screed reinforcement. In the second step, the bottom and top panel of the shear walls were connected through the dowel bars. The specimens were subjected to reverse cyclic loading at the slab ends on both sides. The seismic performance regarding strength, load–displacement relationship, crack pattern, energy dissipation, moment–rotation curve, stiffness and ductility were obtained and compared with the monolithic connection. The average ultimate load and moment-carrying capacity of the precast specimen are found to be 28.66% and 21.74% greater than the monolithic specimen. The cumulative energy dissipation and ductility factor of the precast specimen are found to be 128.95% and 74.34% higher than the monolithic specimen. It is concluded that the precast specimen showed better performance concerning the ultimate load, moment, energy dissipation and ductility with reference to the monolithic specimen.

A Similitude Theory for Modeling Traffic Flow Dynamics

Similitude theory, particularly dimension analysis, is a common tool for testing scaled-down engineering models and is widely used in vehicle dynamics and other engineering fields. However, it is barely employed in scaling traffic flow dynamics. In this paper, dimension analysis is adopted to scale car-following dynamics. Under the guidance of the similitude theory, a scaled downvehicle test bed is built where seven cars are running on a circular track at a maximum speed initially and congestion emerges after a period of time. In other words, a phantom traffic jam appears in our similitude test bed without any bottlenecks. The fundamental diagrams drawn from the experimental results show that our test bed has the capability of generating traffic hysteresis that is commonly observed in the field. Therefore, the design of this test bed can be used to simulate traffic dynamics to a certain degree and will pave the way for scaled-down connected and automated vehicle systems development.

Failure conditions for stand-alone cold-frame greenhouse under snow loads

In South Korea, even snowfalls under the design snow loads are frequently known to cause significant deformations or failures of stand-alone cold-frame greenhouses. However, the possible causes of such events are not reflected in the structural design criteria currently used. To estimate the deformations related to structural failures, this study set up possible scenarios to be able to make the structural failures and examined the reasons through scaled-down experiments and nonlinear structural analyses. Hinge boundary conditions of supports and non-uniform snow loads occurred by the repetitive freeze–thaw cycles of the soils surrounding the supports without concrete foundations, and differences between internal and ambient temperatures, respectively, were considered. Two-dimensional scaled-down models of the greenhouses were constructed based on the similarity law. The experimental results were compared with those from nonlinear structural analyses of linear elastic–plastic models. For fixed boundary conditions at both ends and uniform snow loads, the relative errors of displacements between the experimentally obtained values and the results of the finite element analyses were within 6.10%. The results revealed that structural failures occurred in all cases with hinge boundary conditions for the supports at both ends for both uniform and non-uniform snow loads, but the greatest deformation behavior of the structure was observed with a hinge–hinge boundary condition and non-uniform snow loads where the horizontal displacement was similar to the vertical displacement. The temporary installations of diagonal braces in the greenhouses when heavy snowfalls are forecasted are therefore recommended to reduce the side sway.

Experımental Investıgatıon of Performance of a Small Scale Horızontal Axıs Wınd Turbıne Rotor Blade

Experimental testing of a scaled-down rotor blade for a 2kW small scale HAWT is the forefront of the present research work. To facilitate the objectives, a rotor blade for a 2kW HAWT has been analytically designed employing the iterative Blade Element Momentum Theory (BEMT). For the ease of manufacturing, the linearized blade obtained through the BEM theory is fabricated and subsequently, its performance is evaluated at wind velocities V=1-20m/s and TSR=1-20. The performance parameter defined by coefficient of power C p is considered for appraising and comparing the performance of the analytical and the experimental scaled-down versions of the blade. At the design conditions, the coefficient of power C p for the blade was calculated to be C p =0.40. Further, appropriate scaling laws have been incorporated to scale down the original blade to retrofit to an existing wind turbine generator. Performance of the blade was examined at the prescribed wind velocities V and TSR λ. The experimental outcomes depicted a C p trend for the scaled-down model to be similar to the actual model. At design conditions, the experimental results rendered a maximum C P =0.380 for the scaled-down model with an error of around 6%. However, the investigation showed that the C P for the scaled-down model was aligned with the actual model. The error in C p of the analytical and scaled-down models are deemed due to the ignorance of hub losses, 3-Dimensional flow effects and unsteady aerodynamic effects in the study.

Aspects that condition physical modeling in predicting the behavior of structures real geotechnics

The use of scaled-down models to reproduce the behavior of geotechnical structures is the most widely accepted technique today to properly model a geotechnical problem. The most complete methodology to adequately model this type of scenario is the geotechnical centrifuge, which allows assembling models reduced to the necessary scale and induces in the model a gravity field proportional to the selected scale. According to the established scaling laws, different quantities can be extrapolated from the reduced model to a full-scale structure. However, several aspects that must be considered in detail affect the results, so that they must be thoroughly analyzed so that the dispersion of results between the measurements and the expected is as small as possible, or, otherwise, it can be identify with reliability which was the aspect that most influenced the high dispersion of the results. This research describes these effects exactly, so that they are taken into account when this type of prediction analysis is carried out on geotechnical structures.

Development of similarity-based scaling criteria for creep age forming of large/extra-large panels

A scaling method is developed for the creep age forming (CAF) process to downscale manufacturing of large/extra-large panels to lab-scale experimental trials for industrial application. Similarity theory is applied to identify both the geometrical and physical (non-geometrical) similarities between large-size prototypes and scaled-down models in all process stages of CAF, including loading, stress-relaxation and unloading (springback). A constitutive model is incorporated into the theory in order to identify the similarity in the highly non-linear stress-relaxation behaviour for aluminium alloy plates during CAF, and to obtain the effective scaling criteria for the CAFed plates after springback. The method was demonstrated by scaling down CAF manufacturing of both singly curved and doubly curved large plates under both proportional and non-proportional geometrical scaling conditions. The analytical results of the scaling method and numerical results obtained by CAF FE modelling were found to be in good agreement. Scaling diagrams linking the key deformation (springback) and structural (flexural rigidity) variables to scaling ratios under both proportional and non-proportional conditions were generated, and the developed scaling diagrams have been validated by corresponding CAF experiments. The scaling method developed in this study provides guidance on the design of scaled-down CAF experimental trials and will be used in the practical CAF process of large/extra-large panels.

Comparison of Reynolds Averaging Navier-Stokes (RANS) turbulent models in predicting wind pressure on tall buildings

This paper presents a detailed comparison of using Reynolds Averaging Navier-Stokes (RANS) approach in predicting wind pressure on a super-tall 406 m slender tower with circular cross-section. The results obtained from wind tunnel tests using a rigid model approach in a boundary layer wind tunnel (BLWT) were compared to that of Computational Fluid Dynamics (CFD) numerical simulations. The main objective of this study is to critically investigate the possibility of using RANS turbulent model based CFD approach in tall building design. Three different RANS turbulence models were compared with the wind tunnel data in predicting flow characteristics. The detailed wind tunnel experimental procedure and numerical approach are discussed and presented. It was shown that the shear stress transport (SST) variant model, k−ωSST, could predict pressure coefficients comparable to that of the wind tunnel experiments. The influence of flow separation point on flow characterisation and pressure prediction is highlighted. The improvement that can be made in the near-wall region in the finite volume mesh to achieve an accurate separation point is presented. The effects of Reynolds number produced in the wind tunnel and scaled-down numerical models were compared with the anticipated full-scale flow Reynolds number. Hence, it is shown that a correct modelling technique in CFD using RANS turbulence models can be used as an alternative design approach of super-tall structures to estimate wind-induced pressures.

The development of the Scaled Accelerated Loading Simulator facility and transfer functions to the full-scale pavement using theory of similitude by finite element analysis

The purpose of this study is to investigate the relationship of the vertical deformation between the scaled-down pavement test and full-scale pavement structure according to the theory of similitude-based analysis procedure. Finite element analysis used to investigate and establish the relationship between the scaled-down and full-scale models. Four scaled-down models with scaling factors of 0.9, 0.75, 0.6, and 0.45 with two types of constitutive models of asphalt concrete materials, elastic and viscoelastic, are considered. The results show that the vertical deformation in the full-scale model achieved by applying a vertical shift to the vertical deformation in the scaled-down model. The vertical shift factor varies linearly in normal and logarithm scale with the scaling factor from 0.9 to 0.45 for linear elastic and viscoelastic material, respectively. Moreover, this study proposes a systematic analysis procedure to determine the testing temperature in the SALS test at a specific loading speed by using the time–temperature superposition principle. This study contributes considerably to preliminary understanding of the relationship between the scaled-down tester in the laboratory and the full-scale model according to the theory of similitude.

Peculiarities of using hot-air balloons in tests of parachute systems

Some peculiarities of using hot-air balloons in testing parachute systems are described in the paper. The main aim is to reduce expenses while testing parachute systems. Similarity criteria such as Froude number and Newtons number were used to assess the reliability of the results of testing scaled-down models of parachute systems. The issue of expeditious changes in the structure of parachute systems and assessment of their effectiveness in tests is discussed. A conclusion is drawn about the advantages of using hot-air balloons for testing models of parachute systems and prospects of their further use.

An experimental study of Rayleigh waves based on seismoelectric measurements

In laboratory acoustic experiments of Rayleigh waves, spatial resolution often suffers from the size effect of the acoustic receivers, which often cannot be scaled-down by the experimental wavelength used for model scaling due to the limitations of the acoustic technique. Based on scaled-down models with homogeneous and lateral inhomogeneous media, the laboratory experiments of Rayleigh waves are performed using acoustic and seismoelectric measurements, respectively. The measurements and resulting dispersion analysis indicate that the accompanying seismoelectric fields, which are measured by point-like electrodes, can represent the acoustic fields measured in the experiments by wide band acoustic receivers. Moreover, for the lateral inhomogeneous model, seismoelectric signals received by electrodes with a point-like size show more detail in the dispersion features of Rayleigh waves than do acoustic signals measured by acoustic receivers with a size close to that of the wavelength. This verifies that the receiver sizes have a great effect on the spatial resolution of the waves. The experimental results suggest a potential application of the seismoelectric conversion effect to the development of point-like and wide band receivers to improve spatial resolution as well as to meet the requirement of dispersion measurement in acoustic experiments of Rayleigh waves, for the size of electrodes with a broad bandwidth can easily be scaled down by using the same wavelength as that for the scaled-down model with little technical limitation.

Pedestrian-Level Urban Wind Flow Enhancement with Wind Catchers

Dense urban areas restrict air movement, causing airflow in urban street canyons to be much lower than the flow above buildings. Boosting near-ground wind speed can enhance thermal comfort in warm climates by increasing skin convective heat transfer. We explored the potential of a wind catcher to direct atmospheric wind into urban street canyons. We arranged scaled-down models of buildings with a wind catcher prototype in a water channel to simulate flow across two-dimensional urban street canyons. Velocity profiles were measured with Acoustic Doppler Velocimeters. Experiments showed that a wind catcher enhances pedestrian-level wind speed in the target canyon by 2.5 times. The flow enhancement is local to the target canyon with little effect in other canyons. With reversed flow direction, a “reversed wind catcher” has no effect in the target canyon but reduces the flow in the immediate downstream canyon. The reversed wind catcher exhibits a similar blockage effect of a tall building amid an array of lower buildings. Next, we validated Computational Fluid Dynamics (CFD) simulations of all cases with experiments and extended the study to reveal impacts on three-dimensional ensembles of buildings. A wind catcher with closed sidewalls enhances maximum pedestrian-level wind speed in three-dimensional canyons by four times. Our results encourage better designs of wind catchers to increase wind speed in targeted areas.

Bio-inspired cab-roof fairing of heavy vehicles for enhancing drag reduction and driving stability

Cab-roof fairing (CRF) has been developed to reduce the drag exerted on the forebody, thereby promoting fuel saving and environmental pollution control. Conventional CRFs with a 2D streamlined curvature have limitations in enhancing the driving stability and in reducing the drag at the forebody. In this study, new CRFs were designed with flow-guiding structures by mimicking the external forebody shape of sea lions. To evaluate the drag reduction effects of the proposed bio-inspired CRFs, three different types of CRFs (i.e., basic, bio-inspired, and advanced bio-inspired) were installed at scaled-down vehicle models of 15-ton (1:8) and 5-ton (1:6) heavy vehicles. The advanced bio-inspired CRF considerably reduced the drag coefficient of the 15-ton and 5-ton models by ∼20% and 22.4%, respectively. The side force was also reduced by up to 8% and 9% for the 15-ton and 5-ton models with the advanced bio-inspired CRF at a yaw angle of β = 3°, respectively. The flow characteristics around the forebody of the 15-ton model (1:15) with and without CRFs were analyzed by particle image velocimetry to elucidate the drag-reduction mechanism of the proposed CRFs. The bio-inspired CRFs significantly reduced the regions of separated shear flow and turbulent kinetic energy level on the side surfaces of the vehicle models. The findings provide useful information for improving the design of new forebody devices to reduce the drag and enhance the driving stability of heavy vehicles.