Scale Physical Model Research Articles

Modelling and Control Tank Testing Validation for Attenuator Type Wave Energy Converter - Part I: Experiment Setup and Control-Oriented Modelling

Advanced non-causal optimal control strategies have been demonstrated to significantly improve the energy output of a scale physical model of an attenuator type wave energy converter (WEC) by tank testing experiments using FloWave tank facilities in Edinburgh supported by Wave Energy Scotland's control project. The results are reported in a series of three papers, summarizing the tank testing setup, dynamic modelling, and validation of both linear non-causal optimal control (LNOC) and model predictive control (MPC) in regular and irregular waves. Compared with an optimally tuned passive damping control, both LNOC and MPC can significantly improve the energy output, by between 10% to 460%, using irregular waves with low to medium magnitude and peak periods ranging from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$1.7~\mathrm{s}$</tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$2.8~\mathrm{s}$</tex-math></inline-formula> at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$1/20^{th}$</tex-math></inline-formula> scale, as shown in Part II and Part III papers. These controllers also show robust performance in spread waves and side waves which are normally encountered in real sea conditions. Furthermore, the control technologies can be transferred to other types of WECs. The results pave the way for the sea trial testing and full control system validation involving the electricity generation stage and power conditioning stage. This Part I paper will focus on the tank testing setup, the passive damping control experimental results, and the control-oriented models for the WEC. Two state-space models derived respectively from the hydrodynamic model and system identification of experimental data, are validated and compared for use on the controller designs to be presented in Part II and Part III.

An experimental investigation into soil–structure interactions of integral bridge abutments due to cyclic translations

Integral bridges are built without expansion joints to avoid many of the persistent issues with joint degradation and maintenance problems regularly experienced by traditional bridges. In the absence of expansion joints, the cyclic thermal displacements of the integral bridge would be transferred unmitigated by the joints to the abutment resulting in accentuated soil–structure interactions. Previous studies have mainly focussed on the rotational mode of integral abutment movement while the translational mode of movement and backfill deformations have received much less attention. This paper presents the results of laboratory tests conducted on a semiscale (1:2) physical model, which was designed using dimensional analysis to achieve field stress and strain similarity with a full-scale 1.92 m high-prototype integral abutment. The comparative effects from five tests covering low to high cyclic translation amplitude on backfill surface settlement and heave, and lateral earth pressures behind the abutment were investigated over assumed 120 seasonal cycles. Asymptotic settlement depth of the backfill was obtained in each test. Full passive failure surface was observed when the cyclic translation amplitude of the test exceeded the threshold amplitude. The findings also suggest that the settlement depth seemed to be linked to the development of passive failure surface in the following sense—the asymptotic settlement depth in those tests which developed full passive failure surface would attain the same (ultimate) asymptotic depth; conversely, when the passive failure surface had not or only partially developed in that test, the asymptotic settlement depth was dependent on the cyclic translation amplitude, but it was less than the ultimate observed for full passive failure surface. Lateral earth pressure only stabilized to an asymptotic state for the test with the lowest cyclic translation amplitude during the 120 cycles. Shakedown limit state was observed for this case. At larger cyclic translation amplitudes, the lateral earth pressure did not stabilize but continued to evolve with the elapsed cycles, and shakedown limit state was not observed for these cases.

An investigation of a 3D printed micro-wind turbine for residential power production

The wind energy sector is rapidly growing and has become one of the most important sources of renewable power production. New technologies are being developed to increase energy production. This study focuses on developing and evaluating a 3-D printed micro-wind turbine system for residential electricity production. The effectiveness of using Poly Lactic Acid material for model production was assessed using the SolidWorks environment. Then, three–dimensional CFD model was developed to simulate a micro-wind turbine. The CFD model was validated in good agreement against scale physical model experiments performed in a wind tunnel. The results demonstrated that the 5-blade micro-wind turbine design was the most effective under the tested conditions, with a low cut-in speed and the ability to operate under torque up to 70 N.m. Finally, the currently available manufacturing processes for micro-wind turbines have been evaluated. Future work should evaluate the performance of the MWT system under realistic conditions in a site test to determine energy production and total efficiency

Effect of Froude similitude deviation on curved channel simulations: A case study in the Middle Yangtze River

Froude similitude and friction similitude are the two crucial similarity conditions that are often used in physical-scale modeling of rivers. However, models often deviate from Froude similitude when dealing with real-world situations. This study developed several fixed-bed river models with various curvatures to determine the effect of Froude similitude deviation on curved channel modeling. Models were constructed according to the characteristics of the Middle Yangtze River. Differences in longitudinal slope, transverse slope, and main stream line location were measured by varying Froude similitude deviation. The deviations of longitudinal slope and velocity were negligible because friction similitude was accounted for. The transverse slope varied significantly with the Froude similitude deviation, and the main stream line varied with the curvature and Froude similitude deviation. Formulae were derived to estimate the slope deviation. These analyses helped to clarify the feasibility of the method of Froude similitude deviation for curved channels.

Experimental uncertainty analysis of monopile scour protection stability tests

Hydraulic experiments using physical scale models of monopile scour protections typically have high experimental uncertainties and data scattering. These uncertainties may severely affect the accuracy of the experimental results and need to be analysed quantitatively. This paper presents a study on the quantification of experimental uncertainties in monopile scour protection damage tests following the Guide to the expression of Uncertainty in Measurement (GUM) (ISO, 2008). The uncertainty analysis is performed using the three-dimensional damage number S3D and the widely applied STAB number. Through the analysis of the S3D number from individual test and repeated tests, it is found that the uncertainty analysis method for an individual test can be efficiently applied to predict the experimental uncertainty. The wave peak period and the current velocity are identified as the two major sources of uncertainties for the S3D number. The flow turbulence and correlations between input parameters can be neglected when estimating the uncertainty. The uncertainty analysis of the STAB number shows that the experimental uncertainty due to measurement can be up to 5% to 7% of the obtained STAB result. This uncertainty range is wide in comparison with the narrow margin of a dynamic scour protection design in DNV’s recent recommended practice (DNV-RP-0618). The uncertainty of the STAB number is more affected by the armour stone density, wave peak period and significant wave height.

Experimental and Numerical Investigations of RC Frame Stability Failure under a Corner Column Removal Scenario

In recent decades, interest in the resistance of buildings and structures to progressive collapse has been increasingly sparked in research communities. Although several experimental, numerical, and analytical research projects on the robustness of building frames under a column removal scenario have been implemented, some aspects of this problem remain understudied. These aspects encompass failure mechanisms of reinforced concrete frames with slender columns, as well as criteria used to evaluate such failures. This paper focuses on experimental and numerical investigations of the structural behavior and failure of a scale reinforced concrete frame with slender columns under a sudden corner column removal scenario. In addition, we analyze the stability failure mechanism of a reinforced concrete frame with slender columns and the tangent stiffness criterion, which allow for evaluation of the ultimate state of a structure subjected to an accidental impact. A scale physical model of a reinforced concrete frame of a multistory building was designed and tested using the theory of functional similarity. For numerical study purposes, a finite element model was made that exactly the same as the test frame. We validated the findings by comparing simulation results and experimental data. The studies on the behavior of a reinforced concrete frame subjected to quasistatic loading with unequal concentrated loads identified the load transfer between columns through beams. Although these effects were minor in the frame under consideration, they can become more significant in cases of long-term loading. Numerical simulation and physical modeling of an accidental impact allowed for identification of the mechanism of load capacity exhaustion triggered by stability failure. Such failure was fragile. The moment of stability failure of the column of the experimental frame corresponded to the extremum on the force–displacement curve, indicating that zero tangent stiffness was reached. Hence, a criterion of tangent stiffness can be proposed for evaluation of the ultimate state of a structure subjected to an accidental impact.

LSPIV measurements to assess the impact of a bridge on a weakly undulating flow

The modification of the surface velocity field of the weakly undulating flow in a reach of the Suquía River (Córdoba city, Argentina) due to the placement of a bridge was investigated in a physical model. Measurements using Large-Scale Particle Image Velocimetry (LSPIV) allowed evaluating how the hydraulic structure changes the size, shape, wavelength, and relative position to river centerline of the wave train downstream of the first ridge of the weak undular jump. Analysis and discussion of results in terms of the dimensionless parameters reported in the literature (obtained from laboratory studies) are offered. Results show that LSPIV is a reliable, fast low-cost tool to gather valuable information regarding the surficial flow field at the physical model scale in the presence of a weakly undular flow.

Combining numerical tools to determine wave forces on moored ships

Accurate modelling of waves in harbours and the response of moored ships to that type of forcing is of prime importance to determine the safety and workability of ships moored at berths exposed to local wave conditions. This study investigates the combination of a non-hydrostatic wave-flow model (SWASH) and a 3D boundary-integral diffraction model (Harberth) to compute wave forces acting on moored ships. A series of systematic numerical tests has been performed to develop the proposed methodology and gain insight on its limits of application. The approach is validated using physical scale model test data of waves and forces acting on a restrained ship. Results indicate a good performance even for extremely energetic wave conditions, setting the investigated modelling approach as a potential alternative for future applications. • The SWASH and Harberth models are coupled to simulate the interactions between waves and moored ships. • The wave modelling is the main potential source of inaccuracies to the overall approach. • The coupling procedure does not introduce additional requirements to the wave simulations. • The approach is effective for extreme non-linear waves in intermediate/shallow waters and influenced by complex geometry.

Effect of organic substrate thickness on synthetic acid mine drainage (AMD) treatment

A Successive Alkalinity Producing System (SAPS) employing an organic substrate of peat soil and limestone aggregate was investigated for the restoration of synthetic Acid Mine Drainage (AMD). The composition, carbon content, and particle size distribution of the peat soil and limestone were determined by characterisation. Iron sulphate (FeSO4) and sulfuric acid were used to create synthetic AMD (H2SO4). The synthetic AMD was acidic (pH4.0) and had a concentration of iron (Fe) of 100 ppm. A laboratory scale physical model of a tailing pond was created. The synthetic AMD was introduced and filtered through the media. Following that, samples of effluent water were collected and examined to ascertain the pH level. Furthermore, the Fe concentration was determined using a UV-Vis test with a retention duration ranging from 6 to 48 hours. After only 6 hours of retention time, the new technology successfully reduced more than 85% iron concentration and neutralised pH. These findings demonstrated that a combination of peat soil and limestone of adequate thickness might potentially be recommended as an additional treatment media for treating AMD with SAPS.

Numerical and Physical Modeling of Ponte Liscione (Guardialfiera, Molise) Dam Spillways and Stilling Basin

Issues such as the design or reauditing of dams due to the occurrence of extreme events caused by climatic change are mandatory to address to ensure the safety of territories. These topics may be tackled numerically with Computational Fluid Dynamics and experimentally with physical models. This paper describes the 1:60 Froude-scaled numerical model of the Liscione (Guardialfiera, Molise, Italy) dam spillway and the downstream stilling basin. The k-ω SST turbulence model was chosen to close the Reynolds-averaged Navier–Stokes equations (RANS) implemented in the commercial software Ansys Fluent ®. The computation domain was discretized using a grid with hexagonal meshes. Experimental data for model validation were gathered from the 1:60 scale physical model of the Liscione dam spillways and the downstream riverbed of the Biferno river built at the Laboratory of Hydraulic and Maritime Constructions of the Sapienza University of Rome. The model was scaled according to the Froude number and fully developed turbulent flow conditions were reproduced at the model scale (Re &gt; 10,000). From the analysis of the results of both the physical and the numerical models, it is clear that the stilling basin is undersized and therefore insufficient to manage the energy content of the fluid output to the river, with a significant impact on the erodible downstream river bottom in terms of scour depths. Furthermore, the numerical model showed that a less vigorous jet-like flow is obtained by removing one of the sills the dam is supplied with.

Laboratory investigation on short design wave extreme responses for floating hinged-raft wave energy converters

In offshore renewable energy design procedures, accurate predictions of extreme responses are required in order to design for survivability whilst minimising associated costs. At present, the established method for predicting extreme responses is to conduct a large number of long-duration simulations, which is practical only in cases where the structural behaviour is captured by a computationally efficient linear approach. Many applications, however, will require a nonlinear approach, which significantly increases the computational cost, and hence the time required to analyse a problem. Should high-fidelity numerical approaches be the appropriate analysis tool, the long-duration simulations are likely to be impractical and in many cases infeasible. Laboratory testing can be utilised to address this to some extent, but this still time-consuming and expensive from a financial perspective. Consequently, there has been considerable interest in the use of short design waves as an alternative method for speeding up the design process. Currently, standards advise that short design waves can be utilised in the design of fixed offshore structures, but application to floating offshore structures needs verification before it becomes an established procedure. This study considers application of single and constrained short design waves to a floating hinged-raft wave energy converter using a 1:50 scale physical modelling approach, and compares with equivalent irregular sea states. The single wave approaches considered here are “NewWave” and the “Most Likely Extreme Response” wave, which are derived from the frequency content of the wave spectrum and response spectrum, respectively. The constrained approach considered in this study is the “Conditional Random Response Wave,” where the Most Likely Extreme Response wave is embedded within a random short irregular background. Results show that the single wave approaches under-estimate the extreme loading for the hinge-angle and mooring system compared with the irregular and constrained approaches. The discrepancy between single and constrained waves implies that memory effects are non-negligible, and hence it is critical that they are accounted for when utilising short design waves for floating applications.

Using Physical Modeling to Optimize the Aluminium Refining Process.

Concern for the environment and rational management of resources requires the development of recoverable methods of obtaining metallic materials. This also applies to the production of aluminium and its alloys. The quality requirements of the market drive aluminium producers to use effective refining methods, and one of the most commonly used is blowing an inert gas into liquid aluminium via a rotating impeller. The efficiency and cost of this treatment depends largely on the application of the correct ratios between the basic parameters of the process, which are the flow rate of the inert gas, the speed of the rotor and the duration of the process. Determining these ratios in production conditions is expensive and difficult. This article presents the results of research aimed at determining the optimal ratio of the inert gas flow rate to the rotary impeller speed, using physical modeling techniques for the rotor as used in industrial conditions. The tests were carried out for rotary impeller speeds from 150 to 550 rpm and gas flow rates of 12, 17 and 22 dm3/min. The research was carried out on a 1:1 scale physical model, and the results, in the form of visualization of the degree of gas-bubble dispersion, were assessed on the basis of the five typical dispersion patterns. The removal of oxygen from water was carried out analogously to the process of removing hydrogen from aluminium. The curves of the rate of oxygen removal from the model liquid were determined, showing the course of oxygen reduction during refining with the same inert gas flows and rotor speeds mentioned above.

Plausible Differences between the Laboratory and Prototype Behaviors of Spillway Aerator Flows

An aerator, installed to prevent cavitation damages in spillways and outlet works, generates a typical two-phase flow affected by its configuration and flow conditions. The major parameters of concern include air demand, jet trajectory and streamwise changes of air concentration near chute bottom. This study reviews the theoretical basis and deals with several aspects of physical scale modeling, supported exclusively by field measurements. Analyses reveal that the sub-atmospheric pressure generated in the air cavity should also be scaled in physical modeling, which is seldom the case in the laboratory environment. Thus, the conventional approach to upscale the air demand is controversial. With the data from both fields and laboratories, it is demonstrated that a direct conversion of air flow from model to prototype is justified only if the approach flow velocity in the model exceeds 7.0–7.5 m/s or the Reynolds number exceeds 1.58 × 106. Failing to meet this premise would bring about errors for prototype predictions; the error extent depends on both model scale and flow magnitude. In terms of cavity pressure drop, the prototype differs by a factor of less than 10 from its scale model with sufficient air supply. In a model, the air concentration along the chute bottom drops considerably within one to two trajectory lengths. The prototype differs from its model in such a way that the air concentration decay is much slower, with a higher level that is maintained over a longer distance downstream of the impact location. This study is intended to provide insight for laboratory studies and engineering design.

The challenges associated with laboratory scale physical modelling of high-plasticity spoil materials

Characterisation of spoil (surface mine overburden) material is essential when investigating geotechnical issues associated with the spoil, e.g., for investigating the stability of pit lakes formed with spoil or spoil-structure interaction for any structures built on the spoil as part of sustainable developments. A significant proportion of spoils found across European countries are classified predominantly as silty clay with significant plasticity index and low permeability. In this paper, the difficulties associated with laboratory testing of highly plastic spoil materials obtained from different post-mining sites within Europe are discussed. The issues associated with small-scale laboratory testing of field spoil samples, development of an equivalent spoil for performing physical modelling tests, and the difficulties of centrifuge tests with spoil models are discussed in detail.

Leading-Edge Vortex Lift (LEVL) Sample Probe for Venusian Atmosphere

Can a small, lightweight, free-falling sample probe be slowed enough in the Venusian atmosphere to run a 10 min microelectromechanical systems (MEMS) ion gas micro spectrometer, without adding a propulsion systems or explosives and parachutes to the probe mass? To meet this requirement a leading-edge vortex lift (LEVL) autorotating probe design (i.e., maple or sycamore seed shape) has been proposed and evaluated. It has been found that a probe with a total mass of less than 1 kg would allow prolonged flight longer than 15 min. Mathematical modelling and physical scale model testing has been performed to show that this flight time is achievable, allowing MEMS ion gas micro-spectrometer sampling of the Venusian atmosphere.

Numerical Validation of the Hydrodynamic Drag of a Surfaced and Fully Appended Underwater Vehicle

Underwater Vehicles (UV) are required to travel on the surface for periods of time to complete mission requirements. However, knowledge on the drag of a surfaced UV is scarce in the public domain and the knowledge on the behaviour of surface craft is generally not applicable due to substantial differences in hull form. This paper presents a numerical study on the drag coefficient of a surfaced and fully appended BB2 UV in calm water. The results were firstly validated with the available experimental drag data for a range of speeds. Secondly, the free surface elevation along the length of the UV photographed during physical model scale experiments is compared to the free surface elevation predicted by CFD. This research has shown that a multiphase CFD model can accurately predict the drag due to the forward motion of a surfaced UV in calm water.

Effect of Foundation Geometry and Structural Properties of Buildings on Railway-Induced Vibration: An Experimental Modeling

This paper considers the impact of foundation geometry on the vibrations transferred to a building in the vicinity of a railway line from the aspect of choosing an appropriate foundation type. For this purpose, a 1-g scale physical model is developed that includes the main parts containing dry sandy soil, a rigid soil container, and a five-story structure with three types of foundations, i.e., single, strip and mat. Next, the effects of the floor slab frequency associated with the local bending mode, the dominant soil frequency in vertical translation, and foundation geometry on the vibration level in the building are investigated. The experimental results obtained from the impulse loading exciting the frequency range of 0–156 Hz and scaled train axle load show that the vibration level transmitted to the floors in a structure with mat foundation is the smallest. Additionally, the strip and mat foundations reduced the root mean square ratio of vertical velocity on the first floor by, respectively, almost 8% and 53% in comparison with the single foundation, confirming the superior performance of the mat foundation. When the natural frequency of the slab bending mode approaches the dominant frequency of the ground’s vertical motion, resonance amplification becomes an inevitable phenomenon.

Design and analysis of a novel 3T1R four-degree-of-freedom parallel mechanism with infinite rotation capability

A 4-degree-of-freedom (DOF) parallel mechanism with 3 translations and 1 rotation (3T1R) has wide application potential in the industry. However, most of the existing 3T1R parallel mechanisms have limited rotation capacity of the moving platform, which is usually less than ±90°. In this paper, a new type of 3T1R parallel mechanism is designed by configuration deduction method based on the 3T1R parallel mechanism studied at present. The structure of the parallel mechanism is simple and symmetrical, and the motion pairs are all rotating pairs, which have Selective Compliance Assembly Robot Arm motion and complete rotation capability. Firstly, the branch motion spiral system is established by using the screw theory, and then the constraint spiral of each branch to the motion platform is solved, and the constraint spiral system is analyzed, so as to determine the number of DOFs and properties of the mechanism. Secondly, the position, velocity, and singularity of the mechanism are analyzed, and the workspace of the mechanism is analyzed by the positive position solution. Then, the trajectory planning of operation space is completed, and a mathematical model of portal grasping trajectory is established. Thirdly, the kinematic simulation analysis of the mechanism is carried out. Finally, an equal scale physical model was made by 3D printing technology to verify the rationality of the design and the correctness of the theoretical analysis.

Application of Fractals to Evaluate Fractures of Rock Due to Mining

Fractures caused by mining are the main form of water inrush disaster. However, the temporal and spatial development characteristics of fractures of the rock mass due to mining are not clearly understood at present. In this paper, two geometric parameters, namely, fractal dimension and fracture entropy, are proposed to determine the spatial and temporal states of rock mass fractures caused by mining. The spatial and temporal structure characteristics of fractures in the rock mass due to mining are simulated with physical scale model testing based on digital image processing technology. A spatiotemporal model is created to examine the spatial and temporal patterns of hot and cold spots of the fractures based on a Geographic Information System (GIS). Results indicate that the fractal dimensions and entropy of the fractures network in the rock mass increase and decrease with the progression of mining, respectively, which can be examined in three stages. When the fractal dimension of the fractures in rock mass rapidly increases, the conductive fracture zone has a saddle shape. The fracture entropy of fracture has periodic characteristics in the advancing direction of the panel, which reflects the characteristics of periodic weighting. The fractal dimension and fracture entropy of fractures of the rock mass increase with time, and the rock mass system undergoes a process of increasing entropy. When the fractal dimension and fracture entropy of the fractures increase, the spatiotemporal state of fractures in rock mass caused by mining is initiated. When the fractal dimension and fracture entropy of the fractures decrease, the spatiotemporal state of fractures in rock mass is closed.

Analyzing the Effect of Flux Intensification Due to Propeller Shaft and Rudder Upon the 3D Induced Magnetic Signature of Marine Vessels

This study investigates and analyzes the effect of flux intensification due to the propeller shaft and rudder on the 3D mapped induced magnetic signature of marine vessels. The study was designed to extrapolate the 3D induced magnetic signature and to analyze the difference between signature components in two different cases: a vessel without propeller shaft or rudder and a vessel with the propeller shaft and rudder attached. Numerical modeling was conducted using full-scale vessel dimensions and finite-element analysis (FEA) modeling software. Measurements on a 1:100 properly scaled and designed physical scale model (PSM) were conducted in a magnetically clean area. To enrich the analysis, both signature components from the numerical evaluation and experimental measurements were 3D mapped. Both the scaling technique and scaling effect on magnetic signature were investigated. The signature measurements of the scaled vessel model were performed to verify the numerical model. Both the numerical and experimental results are both discussed and shown to be consistent. The extrapolated signature components revealed that the studied effect became prominent as the saliency of the 3D mapped signature components increased. Consequently, this effect increases the magnetic susceptibility of the vessel to detection or destruction. Finally, this study suggests solutions to reduce this effect.