Scale Effects In Models Research Articles

Investigation of Appropriate Scaling of Networks and Images for Convolutional Neural Network-Based Nerve Detection in Ultrasound-Guided Nerve Blocks.

Ultrasound imaging is an essential tool in anesthesiology, particularly for ultrasound-guided peripheral nerve blocks (US-PNBs). However, challenges such as speckle noise, acoustic shadows, and variability in nerve appearance complicate the accurate localization of nerve tissues. To address this issue, this study introduces a deep convolutional neural network (DCNN), specifically Scaled-YOLOv4, and investigates an appropriate network model and input image scaling for nerve detection on ultrasound images. Utilizing two datasets, a public dataset and an original dataset, we evaluated the effects of model scale and input image size on detection performance. Our findings reveal that smaller input images and larger model scales significantly improve detection accuracy. The optimal configuration of model size and input image size not only achieved high detection accuracy but also demonstrated real-time processing capabilities.

Violent breaking-wave impacts. Part 4: A detailed analysis and comparison of field and 1:4 scale measurements on sloping and vertical walls including the influence of air and scale effects

Pressure and aeration measurements obtained under storm conditions on the steep-fronted masonry wall of a rubble-mound breakwater are analysed in detail, and the results compared with those obtained using a 1:4 scale freshwater model of the field test site. New insights are gained into the complex behaviour of the most violent impacts, with particular attention given to aeration and scale effects.The existence in the field of both low-aeration (LA) and high-aeration (HA) impacts is confirmed and new parameters introduced to facilitate further analysis. Maximum pressures (Pmax) up to 771 kPa are categorised and the magnitudes of the resultant impulses found to depend mainly on their durations. The alternate expansion and recompression (ERC) of air following a HA impact is shown to apply significant oscillatory pressures and forces to the wall. Information on the magnitude, period and damping of these oscillations is presented.The model results are initially scaled in accordance with the Froude law. In conditions comparable to those in the field, the highest pressure on the sloping wall is again found to occur in HA impacts with Pmax ≤ 3.17 MPa followed by ERC oscillations. Like those in the field, the oscillations at different elevations tend to come into phase with each other and can subject the wall to oscillatory forces of significant vertical extent. Both the initial excursion and the damping of the oscillations tend be greater in the model than in the field. The maximum forces on the wall also tend to be greater than those on the field breakwater, but the durations of the impulses tend to be shorter. This apparent trade-off between force and duration may indicate that the model is responding differently to the momentum flux of the incoming waves. Pmax ≤ 5.42 MPa are obtained when the model wall is vertical.Because the Froude law does not scale aeration effects correctly, model data are also scaled in accordance with the Bagnold-Mitsuyasu (B-M) law which increases the highest Pmax for the vertical wall to 20.97 MPa. An alternative assessment of the ERC oscillations is also made on the assumption that the trapped-air pockets are geometrically similar to ones that could occur in the field.Likely generic characteristics of violent wave-impacts are identified as are probable model scale-effects. Impact-pressure reduction curves derived from a numerical model are presented to emphasise the influence of entrained air on wave loading. Further work is recommended.

Forced surge motion of a floating bridge pontoon to evaluate the hydrodynamic damping properties

Dedicated model tests were carried out to investigate the hydrodynamic force coefficients in surge for a pontoon that is designed to support a floating bridge. The experiments were carried out by oscillating the pontoon at various Keulegan–Carpenter (KC) numbers and oscillation periods in forced motion. A pontoon designed for the floating bridge in Bjørnarfjorden, Norway, is investigated herein. Several numerical simulations are performed to supplement the experiments. The estimated damping coefficients in surge are of significant importance at the first horizontal resonant mode of the floating bridge, which may be excited due to swell sea in the fjord. The first horizontal resonant mode of the floating bridge is around 15–16 s. The model tests were conducted with and without turbulence triggers. A finding from the model tests were that turbulence triggers did not prove to be necessary to eliminate model scale effects in oscillatory flow.The KC-dependent added mass and damping coefficient in oscillatory flow is investigated. The added mass and damping coefficients are clearly KC-dependent. The wave radiation damping in surge is small at the tested oscillation periods, and the damping in surge is dominated by the damping due to flow separation.Numerical simulations using a hybrid potential flow-CFD solver with linear free-surface conditions, PVC3D, are carried out with both linear and nonlinear body-boundary conditions. The simulations with nonlinear body-boundary conditions predict the hydrodynamic force coefficients with reasonable accuracy, whilst the simulations with linear body-boundary conditions fail to predict the hydrodynamic coefficients with the desired accuracy — both used to investigate the viscous damping which arises due to flow separation along the pontoon body.

Integrating “Neoliberal-Turn” and “Social-Turn” Constructs in Examining Sustainable Development and Happiness and Life Satisfaction: A Global-, Country Cluster-, and Country-Level Study

This study explores several global and country cluster sustainable development (herein SD) models. It jointly examines constructs from the “Neoliberal-turn” ((e.g., Institutional Enhancers (e.g., business freedom, property rights, government integrity, and judicial effectiveness), Financial Enhancers (e.g., government spending and monetary, trade, investment, and financial freedoms), Foreign Direct Investment, Global Competitiveness-institutions, and Global Competitiveness-innovation-sophistication)), the “Social-turn” (five SD pillars (e.g., Planet, People, Peace, Prosperity, and Resources), which synthesize the 17 United Nations SD goals), and Happiness and Life Satisfaction (herein H&LS). This study examines a large and diverse set of relationships encompassing 11 years of data of 108 social, economic, and environmental indicators from 125 countries at the global, country cluster, and country levels. We analyze data using structural equation modeling. Remarkably, Planet, an SD pillar constituted by biophysical variables, is the least of the five SD pillars positively related to the “neoliberal-turn” constructs and H&LS. The results show model configurations and scale effects. Furthermore, the findings reveal both synergies between neoliberal and the five SD pillars, as well as both negative and nonsignificant relationships among them. The diversity of the results calls for further model integration and specificity. The diverse findings entail caution and difficulties in generalizing knowledge. Similarly, the results suggest that it is not advisable, since there may be many different and partly legitimate alternatives, to rely on just one perspective (e.g., giving primacy to economic-based analyses) and/or in analyses at only one scale. The perspective effects and the stakes involved in SD urgently call for more collaborative efforts at all levels.

Spatial Scale Effects in COVID-19 Spread Models

The COVID-19 pandemic has highlighted epidemiological models as important forecasting methods and planning strategies, with studies conducted using a wide variety of analytical and computational techniques. Knowing that more pandemic episodes may occur, it is essential that epidemiological modeling present increasingly credible results. From this perspective, this paper aims to highlight the influence of spatial distribution on an epidemic dynamic, using agent-based modeling. To calibrate the behavioral profile of the population, data was taken on mobility, population pyramid, individual behavior and government policies of a real population during the pandemic. Two different initial spatial distribution scenarios are tested and the robustness of the infection is analyzed. Totalistic rules were designed to assess the influence of infected individuals in the vicinity of an agent, a factor that must not be ignored in modeling respiratory diseases with viruses capable of spreading by aerosols, such as SARS-CoV-2. It is shown that the scenario with nonuniform distribution of agents is much more robust, generating an epidemic process even when uniform distribution, for the same parameters, did not propagate the infection. Our results also suggest that herd immunity is attained in different levels of recovered individuals, showing higher values in denser regions. In conclusion, it is reinforced that the nonuniform feature of the spatial distribution of individuals plays a key role in the infection dynamics and should receive more attention when building epidemiological models.

Discrete element method for simulations of the jack-up foundation penetration

This paper presents the application of a novel discrete element-based method to simulate the continuous penetration process of jack-up foundations in various soil profiles. A special application of the linear contact bond model is proposed to reproduce the strength distributions of offshore clay. The calibrated inter-particle parameters accurately describe the sophisticated soil characteristics. The effects of particle size, boundary size, model scale, and penetration rate are investigated in this study. The established model balances the accuracy of the results and the computational efficiency. The results of the discrete element simulation are verified by comparison with three published examples. The numerical simulation results provide a microscopic perspective to understand the penetration process and show its advantages in coping with large deformation problems in geomechanics.

Medical 3D Printing Dimensional Accuracy for Multi-pathological Anatomical Models 3D Printed Using Material Extrusion.

Medical 3D printing of anatomical models is being increasingly applied in healthcare facilities. The accuracy of such 3D-printed anatomical models is an important aspect of their overall quality control. The purpose of this research was to test whether the accuracy of a variety of anatomical models 3D printed using Material Extrusion (MEX) lies within a reasonable tolerance level, defined as less than 1-mm dimensional error. Six medical models spanning across anatomical regions (musculoskeletal, neurological, abdominal, cardiovascular) and sizes (model volumes ranging from ~ 4 to 203cc) were chosen for the primary study. Three measurement landing blocks were strategically designed within each of the six medical models to allow high-resolution caliper measurements. An 8-cc reference cube was printed as the 7th model in the primary study. In the secondary study, the effect of model rotation and scale was assessed using two of the models from the first study. All models were 3D printed using an Ultimaker 3 printer in triplicates. All absolute measurement errors were found to be less than 1mm with a maximum error of 0.89mm. The maximum relative error was 2.78%. The average absolute error was 0.26mm, and the average relative error was 0.71% in the primary study, and the results were similar in the secondary study with an average absolute error of 0.30mm and an average relative error of 0.60%. The relative errors demonstrated certain patterns in the data, which were explained based on the mechanics of MEX 3D printing. Results indicate that the MEX process, when carefully assessed on a case-by-case basis, could be suitable for the 3D printing of multi-pathological anatomical models for surgical planning if an accuracy level of 1mm is deemed sufficient for the application.

The effect of model scale, acceleration history, and soil condition on closed-ended pipe pile response under coupled static-dynamic loads

This paper analyzes the effect of scaling-up model and acceleration history on seismic response of closed-ended pipe pile using a finite element modeling approach and the findings of 1g shaking table tests of a pile embedded in dry and saturated soils. A number of scaling laws were used to create the numerical modeling according to the data obtained from 1g shake table tests performed in the laboratory. The current study found that the behaviors of the scaled models, in general have similar trends. From numerical modeling on both the dry and saturated sands, the normalized lateral displacement, bending moment, and vertical displacement of piles with scale factors of 2 and 35 are less than those of the pile with a scale factor of 1 and the shaking table test. In general, the pile deformation factor was higher in saturated sand models than the dry sand models. Liquefaction ratios were increased by increasing the seismic intensity; hence the maximum liquefaction ratio was observed with the model of scale 1 under the effect of the Kobe earthquake (0.82g). In another full-scale model, the liquefaction ratio decreased significantly; i.e., it was decreased from 1.64% (λ=1) to 1.04% (λ=35) in the same mentioned model. Pile frictional resistance was numerically investigated and the overall results were compared with previous studies in the literature. In general, the frictional resistance at the pile tip was slightly higher than the frictional resistance around the pile body, and the frictional resistance factor on the ground surface of dry soil models was slightly higher than those of saturated soil models.

Modified couple stress-based nonlinear static bending and transient responses of size-dependent sandwich microplates with graphene nanocomposite and porous layers

This paper investigates the nonlinear static bending and dynamic transient responses of the rectangular and circular sandwich microplates composed of functionally graded graphene nanocomposite (GNC) face sheets and a porous polymeric core layer based on the modified couple stress theory (MCST) within the isogeometric analysis (IGA) framework. The four-variable higher-order shear deformation refined plate theory (RPT) and the von Kármán large deflection assumption are synthetically employed to describe the kinematics of the microplate. The nonlinear governing equations of motion are derived from the Hamilton’s principle. The nonlinear bending problem is solved by the Newton–Raphson technique under a displacement criterion strategy, while the dynamic responses under transient loads are obtained by the Newmark integration scheme in conjunction with Newton–Raphson iterative procedure. Comparisons are carried out to test the accuracy of iteration procedure in present formulation and the reliability in capturing small scale effect of present model. Obtained outcomes reveal that raising the material length scale (MLS) parameter and volume fraction index of graphene nanofillers both leads to reductions in nonlinear static deflections, dynamic amplitudes of deflection and periods of motion. The examples for porosity coefficient show that embedding pores in core layer leads to slight changes in terms of static and dynamic responses and an improvement in weight reduction of the sandwich microplate.

Effect of model scale on helical piles response established from shake table tests

This paper investigates the effect of model scale on seismic response of prototype helical pile (HP) groups employing finite element modelling approach verified by the results of single gravity shaking table models of piles installed in dry and saturated sands. The prototype shaking test configuration was established from model shake table tests by adopting a set of similarity and dimensional laws. The results demonstrated that the scaled models exhibited generally similar responses. The HPs' response in the saturated sand bed was dominated by the rocking behaviour, while the flexural behaviour dominated the response in the dry tests. In addition, the HPs' lateral response followed the lateral soil uniform deformation in the dry tests, while they did not follow the nonuniform soil deformation in the saturated tests. However, the prototype models' axial and lateral responses were different from the results of the shaking table scale. The HP exhibited less scaled lateral deformation, bending moments, and settlement in the prototype models than those at the shaking table scale in the dry and saturated tests. Meanwhile, the prototype helices’ stress was higher than the shaking table helices in the saturated tests and less than them in the dry tests. A set of scaling factors was suggested for extrapolating the soil and HP responses from 1 g shake table model tests. Based on the obtained results, the soil and HP responses may be extrapolated from 1 g shake table model tests employing the following scaling factors: soil displacement increase factor, SDIF = 0.8n in the saturated tests, and SDIF = 0.6n in the dry tests, while the pile displacement increase factor, PDIF = 0.7n in the saturated test and 0.5n in the dry test.

ReaxFF Molecular Dynamics Simulations of Thermal Reactivity of Various Fuels in Pyrolysis and Combustion

The methodology development and applications of ReaxFF molecular dynamics (ReaxFF MD) in unraveling the complex reactions and kinetics for pyrolysis and oxidation of organic systems are reviewed. Particular attention is given to the large-scale ReaxFF MD simulation method of similar to 10,000 atoms and practical simulation strategies to overcome the temporal-spatial limits as much as possible. High-performance computing codes running on CPU cluster/supercomputers and on GPU were overviewed. GPU-enabled code like GMD-Reax is revolutionizing large-scale ReaxFF MD simulations to run mainly on a single GPU. A step-forward for reaction analysis was achieved in the code of VARxMD to reveal detailed reactions based on the identification of bond types and unique species that allows for categorization of reaction species and pathways through structure searching of reaction sites and reactants/products. Efforts for extracting rate constants and kinetics modeling from unperturbed kinetics of ReaxFF MD simulations are reviewed, and challenges remain. The important factors of model scale effects, elevated simulation temperature, and possible validation of ReaxFF MD reaction simulation results theoretically and experimentally are illustrated and discussed. The novel hybrid simulation strategies proposed recently that may expand applications of ReaxFF MD to connect with realistic scenarios of engine combustion and relevant chemical effects on aerospace vehicle materials are briefed. The simulation practices of large-scale ReaxFF MD in understanding the similarities and differences of reactivity and reaction mechanisms in pyrolysis of liquid hydrocarbon fuels, solid fuels (coal, biomass, polymer), and energetic materials of CL-20 and its cocrystals are briefly described, which indicates that large-scale ReaxFF MD simulations are a feasible and straight means to capture the dynamics of an almost entire reaction process and to evaluate reactivity of organic systems computationally. There is still a great deal of work to be done to push the boundaries of ReaxFF MD simulations forward. With the constant improvement of the ReaxFF force field and reaction analysis capability, ReaxFF MD playing a key role in understanding reaction mechanisms and its potential in kinetics modeling of pyrolysis and oxidation of various fuels can be expected.

Urban surface water flood modelling – a comprehensive review of current models and future challenges

Abstract. Urbanisation is an irreversible trend as a result of social and economic development. Urban areas, with high concentration of population, key infrastructure, and businesses, are extremely vulnerable to flooding and may suffer severe socio-economic losses due to climate change. Urban flood modelling tools are in demand to predict surface water inundation caused by intense rainfall and to manage associated flood risks in urban areas. These tools have been rapidly developing in recent decades. In this study, we present a comprehensive review of the advanced urban flood models and emerging approaches for predicting urban surface water flooding driven by intense rainfall. The study explores the advantages and limitations of existing model types, highlights the most recent advances, and identifies major challenges. Issues of model complexities, scale effects, and computational efficiency are also analysed. The results will inform scientists, engineers, and decision-makers of the latest developments and guide the model selection based on desired objectives.

Quantifying the effects of land use and model scale on water partitioning and water ages using tracer-aided ecohydrological models

Abstract. Quantifying how vegetation mediates water partitioning at different spatial and temporal scales in complex, managed catchments is fundamental for long-term sustainable land and water management. Estimations from ecohydrological models conceptualising how vegetation regulates the interrelationships between evapotranspiration losses, catchment water storage dynamics, and recharge and runoff fluxes are needed to assess water availability for a range of ecosystem services and evaluate how these might change under increasing extreme events, such as droughts. Currently, the feedback mechanisms between water and mosaics of different vegetation and land cover are not well understood across spatial scales, and the effects of different scales on the skill of ecohydrological models needs to be clarified. We used the tracer-aided ecohydrological model EcH2O-iso in an intensively monitored 66 km2 mixed land use catchment in northeastern Germany to quantify water flux–storage–age interactions at four model grid resolutions (250, 500, 750, and 1000 m). This used a fusion of field (including precipitation, soil water, groundwater, and stream isotopes) and remote sensing data in the calibration. Multicriteria calibration across the catchment at each resolution revealed some differences in the estimation of fluxes, storages, and water ages. In general, model sensitivity decreased and uncertainty increased with coarser model resolutions. Larger grids were unable to replicate observed streamflow and distributed isotope dynamics in the way smaller pixels could. However, using isotope data in the calibration still helped constrain the estimation of fluxes, storage, and water ages at coarser resolutions. Despite using the same data and parameterisation for calibration at different grid resolutions, the modelled proportion of fluxes differed slightly at each resolution, with coarse models simulating higher evapotranspiration, lower relative transpiration, increased overland flow, and slower groundwater movement. Although the coarser resolutions also revealed higher uncertainty and lower overall model performance, the overall results were broadly similar. The study shows that tracers provide effective calibration constraints on larger resolution ecohydrological modelling and help us understand the influence of grid resolution on the simulation of vegetation–soil interactions. This is essential in interpreting associated uncertainty in estimating land use influence on large-scale “blue” (ground and surface water) and “green” (vegetation and evaporated water) fluxes, particularly for future environmental change.

MODELLING TRANSPORT AND FATE OF WOODY DEBRIS IN COASTAL WATERS

Woody debris is ubiquitous in coastal waters, and on shorelines proximate to forested regions. Logs and driftwood play a vital role in coastal and global ecosystems, and can provide valuable data to support studies of oceanography, geomorphology, ecology, history and archaeology. There is growing interest in the role that woody debris can play in nature-based coastal engineering solutions. However, large quantities of woody debris in coastal waters can pose significant hazards to communities, infrastructure, navigation and ecosystems. Thus, the changing abundance and distribution of coastal driftwood, driven by factors including human activities and climate change, has potential for both positive and negative consequences. A better understanding of coastal driftwood fate and transport processes is needed to inform management practices, uses, and sustainable ecosystem management. To date, research on physical transport of woody debris, has been concentrated on tsunami and inland (riverine) environments, where spatiotemporal scales and driving processes are significantly different from typical climatic or even extreme (storm) conditions in coastal waters. In this paper, we describe a series of scale physical model experiments, conducted to provide insight to debris transport processes in coastal waters under a range of controlled wave and water level conditions. The experiments were conducted in a 50.4-metre by 29.4-metre wave basin, in which a 1/30 scale model of a natural shoreline comprised of a shallow fringing reef, a sandy shoreline, and several small coastal structures (groynes and breakwaters) was constructed. Wooden dowels and tree branches, scaled to replicate the size distribution of woody debris observed on Pacific Northwest shorelines, were released in the model. Despite some limitations (e.g., model scale effects), the experimental test results provided several valuable insights to factors affecting debris mobility in coastal areas. The results will inform the parameterization of important physical processes in a numerical model being developed to predict the fate and transport of woody debris in coastal waters.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/hvBHZVObDhY

Numerical modelling of the hydrodynamics and sediment transport near the water intake of the Cardinal power plant

A three-dimensional numerical model was developed to better understand the hydrodynamics and sediment processes near the water intake of the Cardinal power plant. Sediment is represented with particles that are suspended, deposited or transported as bed load depending on particle size, flow turbulence and local bed shear stress, neglecting morphological changes. Validation against field velocity data indicated that buoyancy forces, originated by temperature gradients, need to be included to predict the observed flow pattern. The existing intake structures do not fully prevent the entrainment of warm water from the plant into the intake, which affects the plant efficiency, flow pattern and sediment deposition. Location of deposited particles and deposition rate predicted with the model compared well against observations in a physical model. However, computations at prototype scale show deviations from the physical model, suggesting that model scale effects in the physical model can be significant.

Efficient and Accurate 3-D Numerical Modelling of Landslide Tsunami

High-speed and accurate simulations of landslide-generated tsunamis are of great importance for the understanding of generation and propagation of water waves and for prediction of these natural disasters. A three-dimensional numerical model, based on Reynolds-averaged Navier–Stokes equations, is developed to simulate the landslide-generated tsunami. Available experiment data is used to validate the numerical model and to investigate the scale effect of numerical model according to the Froude similarity criterion. Based on grid convergence index (GCI) analysis, fourteen cases are arranged to study the sensitivity of numerical results to mesh resolution. Results show that numerical results are more sensitive to mesh resolution in near field than that in the propagation field. Nonuniform meshes can be used to balance the computational efficiency and accuracy. A mesh generation strategy is proposed and validated, achieving an accurate prediction and nearly 22 times reduction of computational cost. Further, this strategy of mesh generation is applied to simulate the Laxiwa Reservoir landslide tsunami. The results of this study provide an important guide for the establishment of a numerical model of the real-world problem of landslide tsunami.

Investigation on the hydrodynamic scaling effect of an OWC type wave energy device using experiment and CFD simulation

This paper presents a study of the effect of model scale on the performance of a fixed Oscillating Water Column (OWC) type Wave Energy Converter (WEC). Tank tests at two different scales, including the effect of scaling of the test tanks to minimise the bias introduced by different wave blockage effects. CFD simulations based on Reynolds Average Navier Stokes (RANS) method were then carried out for both scaled OWCs to investigate whether CFD simulation is able to reproduce the scale effect. Comparison between the tank test results and the CFD simulation results suggests that CFD simulation is capable of reproducing the hydrodynamic scaling effect with a good accuracy. Results also suggest that the hydrodynamic scaling effect is mainly introduced by the Reynolds number effect for cases investigated in the current study.

Use of impulses to determine the reaction force of a hydraulic structure with an overhang due to wave impact

This paper describes a method of determining the reaction forces of a vertical structure with an overhang to impulsive wave impacts. The aim is to develop a method to design a hydraulic structure exposed to the impulsive wave impact. At present, there is a lack of guidelines on the designing and verification with such a purpose. The impulse of the impact is taken as the primary design variable to estimate the impulsive reaction force instead of peak impact forces. By using extreme value analysis (EVA), the characteristic impulse (e.g., Iim,0.1%) can be determined. Then a simple structure model is used for obtaining reaction forces to the characteristic impact impulse. The sum of the impulsive reaction force and the quasi-steady wave force could represent the total reaction force, which can be used as a design load on the structure. The advantage of using the impact impulse could give an approach in which several aspects of the impulsive wave impact force can be incorporated better, like determining the exceedance probability of a certain load, incorporating the flexibility of the structure and correcting possible scale effects in small scale hydraulic models. The proposed method based on the characteristic value of the Iim,0.1% is applied to forces measured in a small scale model of the Afsluitdijk discharge sluice, and compared well to a full-time domain solution. The results indicate the initial assumption that using the impact impulse of the impact as the primary design variable, it is possible to estimate the dynamic response of the structure.

Investigation of the effects of particle size and model scale on the UCS and shear strength of concrete using PFC2D

In this paper, the effects of particle size and model scale of concrete has been investigated on the failure mechanism of PFC2D numerical models under uniaxial compressive test. For this purpose, rectangular models with same particle sizes and different model dimensions, i.e., 3 mmx6 mm, 6 mmx12 mm, 12 mmx24 mm, 25 mmx50 mm and 54 mmx108 mm, were prepared. Also rectangular models with dimension of 54 mmx108 mm and different particle sizes, i.e., 0.27 mm, 0.47 mm, 0.67 mm, 0.87 mm, 1.07 mm, 1.87 mm and 2.27 mm were simulated using PFC2D and tested under uniaxial compressive test. Concurrent with uniaxial test, direct shear test was performed on the numerical models. Dimension of the models were 75x100 mm. Two narrow bands of particles with dimension of 37.5 mmx20 mm were removed from upper and lower of the model to supply the shear test condition. The particle sizes in the models were 0.47 mm, 0.57 mm, 0.67 mm and 0.77 mm. The result shows that failure pattern was affected by model scale and particle size. The uniaxial compressive strength and shear strength were increased by increasing the model scale and particle size.

Performance of a horizontal axis marine current turbine– A comprehensive evaluation using experimental, numerical, and theoretical approaches

This study provides a comprehensive assessment of a 2 bladed horizontal axis marine current turbine using experiments on two scale models, compared to both theoretical and numerical models and previous experiments in other facilities. The experiments were performed in a towing tank and a circulating water channel on rotors of 500 mm and 800 mm diameter. The effect of model scale was investigated together with facility bias. The impact of facility bias on the performance assessment was found to be induced from blockage and the presence of a shear flow velocity profile in the circulating water channel. A BEM model was modified to consider shear velocity profile in the performance calculations. No significant changes were seen in the BEM model results by inserting the shear flow in the code. In addition, the QBlade software was employed as a tool to investigate the effect of Reynolds number. It can provide the performance outcomes for a range in which the results are sensitive to Reynolds number. A RANS CFD model was provided which simulates the turbine in steady flow conditions. The theoretical, numerical and physical models were used to study the effect of scaling. The BEM and CFD model both had good agreement with the experimental results, which provides a strong platform for more detailed study on the HAMCT hydrodynamics.