Scale Model Tests Research Articles

Large-scale model test study of the mechanical characteristics on sprayed ECC layer of highway tunnel under confining pressure

As the geological environment of highway tunnels becomes increasinlgy complex, sprayed engineered cementitious composites (ECC) has broad application prospects in the field of highway tunnel support. This study focuses on the shotcrete layer in the initial support of Wulingtou extra-long highway tunnel, the 1:4 scale model test of sprayed ECC layer under confining pressure was prepared. Its mechanical properties and real-time joint monitoring are determined using strain gauges, distributed optical fibers, and cameras. The results show that the maximum confining pressure of the sprayed ECC layer is 0.975 MPa with the maximum displacement of 15.497 cm, which outperforms ordinary shotcrete. The loading process of steel bars and sprayed ECC can be divided into three stages, with the change rate of these three stages showing an ascending trend. The failure mode is ductile, involving normal section, oblique section compression shear failure and bending shear failure. In addition, based on the similarity theory, the real mechanical characteristics of the sprayed ECC layer at the tunnel site can be predicted according to the experimental model.

Physical Modelling Of Propeller Jet Induced Scour Near Quay Walls

Ship propellers cause high flow velocities near quay walls, jetties, locks and other hydraulic structures which can lead to scour of the bed near these structures and potentially result in instabilities of the construction. Bed protection is commonly applied as a measure to prevent damage and increase the life span of such hydraulic structures. When designing bed protection, the existing guidelines e.g. (PIANC 2015, BAW 2010) may not always result in optimal designs due to simplifications made in jet-flow schematizations and uncertainty of propeller-induced loads. To improve these design guidelines and optimize bed protection, a working group led by CROW and the Dutch Government was formed, and a joint research programme was initiated aiming at developing knowledge on propeller jet-induced scour by combining field measurements (Tukker 2021), scale model tests (Deltares 2023), and numerical modelling. The objective of the presentation during the Coastlab24 conference is to provide an overview of the various measurement techniques applied in the present research.

Experimental design and verification of heat transfer flow in a scaled cabin model under the influence of convective and radiative coupling

With the development of aircraft towards high altitude, high speed, and long endurance, the influence of aerodynamic and radiant heat on the flow and heat transfer in the cabin has increased. To explore the flow conditions in the cabin under the influence of ventilation, convection, and radiation coupling, a scaled model test was conducted for verification and simulation. According to the scaling principle, a small ventilation box with a scale of 1: 5 was designed to simulate the boundary conditions in grid computing methods by building ventilation, heating, and irradiation systems. The CFD results were compared with experimental results for analysis. The results show that the experimental results of the scaled model are comparable to the flow field of the prototype model, and the experimental measurement data can be used as a reference indicator for evaluating the temperature field inside the model cabin. The comparison between the simulation experiment and the simulation results verifies the applicability of numerical calculation methods to simulate the flow field in the passenger compartment and the rationality of the scaled test technical scheme.

Experimental study on monopile-supported offshore wind turbine subjected to long-term wind and wave cyclic loading

Offshore wind energy has recently gained much attention. During its service life, a monopile-supported offshore wind turbine (OWT) is subjected to long-term wind and wave lateral cyclic loads with different cycle characteristics, inducing accumulated deformation of the OWT system to exceed the serviceability limit state and causing safety accidents. In this study, a 1g scaled model test with a similarity ratio of 1:100 was conducted to investigate the lateral response of a monopile-supported OWT in sand under long-term wind and wave cyclic loads. Two sets of centrifugal gear cyclic loading devices applied stable long-term wind and wave cyclic loads and different cyclic load amplitudes and directions were achieved by adjusting the input voltage and counterweight masses. Four groups of long-term cyclic loading tests were conducted for the monopile-supported OWT, considering different wind load simplification methods and various wind-wave load contribution ratios. The lateral displacement and accumulated tilt of the OWT were monitored using two laser displacement transducers installed at different heights. The results show that a simplistic treatment of wind loads as static loads results in an overestimation of the cumulative rotational deformation, and an increase in the wind-wave load contribution ratio decreases the cumulative tilts of the OWT structures.

Multi-freedom effects on a raft-type wave energy convertor- hydrodynamic response and energy absorption

This research delves into the effects of multiple degrees of freedom on a raft-type wave energy converter (WEC), using both experimental and computational methods. The WEC features two interconnected floating bodies linked by a specialized parallelogram joint, allowing for distinct heave, pitch, and surge motions. The power take-off (PTO) system, integrating Coulomb damping, is analysed for its impact on energy absorption. Despite varying damping amplitudes, peak energy absorption is consistent across different wave periods, as shown in scaled model tests. Computational simulations further investigate the multi-freedom effects by imposing constraints on various degrees of freedom, thus elucidating their individual and combined influences on energy absorption. Preliminary results indicate that the addition of degrees of freedom can enhance the WEC's efficiency, especially through coordinated release of the bodies' relative pitch and surge motions. The study also finds that the energy absorption efficiency from pitch motion depends on the release of surge motion. Moreover, the energy distribution among each degree of freedom is significantly affected by the device's multi-freedom characteristics. This research provides valuable insights and practical guidelines for the development of advanced multi-freedom WEC technologies.

Numerical Investigation of Single and Double Steps in Planing Hulls

Incorporating steps into a hull reduces the wetted surface, promoting improved hydrodynamic lift and reduced resistance at high speeds, provided that the step is designed appropriately. Traditional hydrodynamics studies rely on scaled model testing in towing tanks, but numerical tools offer a more efficient alternative. This study focused on investigating the hydrodynamic performance of stepped hulls by modifying the parent hull of the Naples Systematic Series (C1). The Computational Fluid Dynamics (CFD) code SIEMENS PLM STAR CCM+ version 2302 was used for simulations, including four different beam Froude numbers (FrB = 1.13, 2.22, 2.56, and 2.96) and a total of 15 hull configurations with single and double steps. By employing a three-dimensional computational analysis of multiphase flow using Dynamic Fluid–Body Interaction (DFBI) and overset mesh, various performance parameters such as resistance coefficient, dimensionless wetted surface, sinkage, and dynamic trim were analyzed. The accuracy of the CFD results was confirmed through comparison with experimental data and grid uncertainty assessment. The study demonstrated that placing a single step near the transom decreased trim and increased resistance and wetted surface. Conversely, positioning a step in the forward section reduced the trim angle at lower step heights but increased trim at higher step heights in single-stepped hulls. The application of these findings contributes to the design optimization of stepped hulls for enhanced performance in high-speed maritime applications.

Study on the Earth-Covered Magazine Models under the Internal Explosion

The use of earth-covered magazines (ECMs) is increasingly prevalent in protective engineering due to their concealment and cost-effectiveness. To explore the optimal thickness of earth covering for ECMs, scaled model tests were conducted under explosive charges equivalent to 30 kilograms of TNT. The resulting overpressure outside the model in the 180° direction was measured. Subsequently, computational analyses were conducted employing LS-DYNA software to examine these experimental findings. The findings indicate that increasing the thickness of the rear soil can mitigate peak overpressure, delay the air shock wave’s arrival time, and reduce the impulse of the positive phase. The numerical calculations closely align with experimental data, with peak overpressure deviation remaining under 10%. The shock wave initially impacts the top of the model before reaching the rear, with soil scattering more pronounced in the 90° direction compared to the 180° direction. Furthermore, an analysis of soil energy absorption rate variation was conducted based on energy conservation principles. These results provide valuable insights for optimizing the design and construction of ECMs.

Influence of synchronous grouting on surrounding sandy cobbles during shield tunnelling process: Insights from a scaled model test

Substantial soil deformation around tail-grouting activity is frequently observed during the shield tunnelling process in the sandy cobble strata, which is attributed to the convergence and potential collapse of the soils around the tail-void left behind the shield machine. The stability of the underlying strata is significantly impacted by synchronous grouting inside the tail-void. This study examines four-opening synchronous grouting, which is frequently used in shield tunnelling of metro-tunnels, to analyze the grout-spreading mechanism and soil displacement generated by the synchronous grouting in the sandy cobble layer. Laboratory tests are used to determine the characteristics of grouting mortar and soils in accordance with the similarity theory. The model experiment outcomes show that a rise in the GVR (Grouting-Volume Ratio) can cause the settlement at the ground surface. However, as the GVR improves, the pace of settlement growth diminishes. Additionally, the expanding cover depth of the tunnel contributes to the stability of the soil after synchronous grouting. As observed in the model test, when GVR achieves its maximum amplitude (i.e., GVR = 200 %), the grout mortar cannot spread to the crown of the tail-void, necessitating secondary grouting after the synchronous grouting during tunnelling practice. After grout hardening process, it was discovered that grout material above the tunnel waist was concentrated near the upper grout openings, implying a seepage spreading mode of the grout-mortar at these locations. In contrast, grout material below the tunnel waist was evenly distributed along the periphery of the tail void. The model test outcomes may be utilized as a guide for tail-grouting while shield tunneling in sandy cobble strata.

Scale effect on wave planing performance of amphibious aircraft at constant speed

Scaled model testing is commonly recognized as a valuable approach for predicting aircraft performance in the aeronautical applications. However, challenges arise in the case of wave planing events for amphibious aircraft due to difficulties in satisfying the scaling laws of Reynolds number and Froude number simultaneously in a water tank. Therefore, it is important to evaluate the scale effect of regular wave planing process for amphibious aircraft. In this study, by fixing the Froude number, five geosim cases with different scale factors (1/1, 1/2, 1/4, 1/8 and 1/16) are carried out based on the Reynolds-Averaged Navier–Stokes equations (RANS) framework. The hydrodynamic and aerodynamic characteristics at different scales are respectively examined in detail through several physical results, including acceleration, pressure, shear force, velocity and free surface elevation. Comparative analyses among all scaled models reveal that the aerodynamic and hydrodynamic performance both monotonously change with the scale factor, yet the proportion of aerodynamic and hydrodynamic loads remains within a reasonably small range. Furthermore, the results indicate that the scale effect primarily stems from the lack of similarity in Reynolds number, thus resulting in the discrepancies of boundary layer, wave surface elevation and flow separation between the scale model and prototype.

Barrier Lyapunov function-based adaptive optimized control for full-state and input-constrained dynamic positioning of marine vessels with simulation and model-scale tests

For practical marine engineering, ensuring system performance and avoiding violations of safety-related system constraints in various scenarios remains a challenging problem. To tackle this problem, this paper addresses adaptive neural network (NN) optimized control for dynamic positioning (DP) of marine vessels suffering from unknown model uncertainties and control gains, ocean disturbances, and full-state/input constraints. To realize model-free optimized control, the reinforcement learning (RL) with a critic–actor–identifier architecture is constructed on the basis of NN approximation, in which the actor, critic, and identifier NNs are designed to perform control actions, evaluate control performance, and estimate unknown dynamics, respectively. To effectively guarantee the system safety, the critics and actors in the corresponding subsystems are decomposed into a guaranteed safety-related constraint term with respect to the barrier Lyapunov function (BLF) and an unknown dynamic term to be learned. Such a control strategy can ensure that all the state variables are restricted to a predefined safety region, even in the learning control process. From the above logical ideas, the adaptive optimized kinematic and kinetic control laws are presented to guarantee that the whole vessel system is optimized. Moreover, the motion control responses of vessels in various scenarios are realistically simulated through convincing simulations and model-scale tests. The validation results prove the applicability and feasibility of the proposed DP control strategy for practical offshore engineering.

Comparison of frustum confining vessel (FCV) and full-scale testing for helical and expanded piles geotechnical performance

This study focuses on investigating the compression and pullout load-displacement characteristics of various pile types using a frustum confining vessel at Amirkabir University of Technology (FCV-AUT) and full-scale tests. The FCV-AUT provides a versatile platform for physically modeling reduced-scale deep foundations in a laboratory setting, accounting for flexible geometric and stress factors, and the full-scale load tests took place at two research sites situated along the southern coastline of the Caspian Sea. A comprehensive dataset comprising 40 model-scale and 15 full-scale load tests on different pile configurations (including conventional, helical, and expanded piles) installed in sands has been compiled to facilitate a geotechnical performance evaluation. Conventional piles, encompassing cast-in-place drilled shafts, H piles, pipe piles, and box piles, were considered in the analysis. Helical piles with one to three helixes and various expanded piles, including self-expanded, bubble, and wing piles, were also examined. Notably, among the tested piles, those installed through jacking and expanded piles displayed the highest resistance to compression. Conversely, helical piles and expanded piles demonstrated superior pullout performance when compared to conventional piles. Comparisons between physical model-scale tests and full-scale tests validate the suitability of FCV-AUT for assessing the geotechnical performance of diverse pile types in sand under realistic stress conditions.

Analysis of the mechanism of corrugation based on the scale test model

Analysis of the mechanism of corrugation based on the scale test model

A theoretical method for scaling the dynamic response of steel beams subjected to blast loads

Conducting experiments using scaled models is a highly efficient and cost-effective approach to predicting structural dynamic responses to blast loads. However, accurate representation of the prototype in a scaled model is hindered by the strain rate effect of the materials, thus limiting the application of scaled model tests. To address this issue, this paper proposes a theoretical correction method for scaling the dynamic response of steel beams subjected to blast loads. This method allows for direct and quantitative evaluation of the error caused by the strain rate effect on the similarity of the maximum mid-span displacement of the beam without the need to modify the charge mass or stand-off distance. In addition, the proposed method eliminates the need for extensive model tests. The accuracy of the proposed method is verified through numerical simulations. The results demonstrate that the strain rate effect scarcely influences the geometric similarity of the maximum mid-span displacement of the beam in the elastic response stage. However, in the plastic response stage, the maximum mid-span displacement of the beam does not conform to geometric similarity. Accordingly, the similarity of the maximum mid-span displacement of the beam can be expressed as the product of the geometric scale factor and calculated strain rate correction coefficient. These theoretical innovations can significantly enhance the reliability of scaled-model tests, help extrapolate scaled-model test results back to the prototype, and reduce the difficulty and consumption of field blast tests.

Steering and Rising Testing of an Innovative Tourist Submarine

An innovative tourist submarine was studied by scale-model tests in a towing tank to determine its steering capabilities and detect motion instabilities during usual manoeuvres and emergency rising. Motion instabilities are caused by the combination of the submarine motions and the fluid flow, leading to excessive roll and pitch that can cause severe endangerment to passenger safety. The submarine model was built on a scale of 1:9. The model had six thrusters to conduct the tested manoeuvres, i.e., two main thrusters at the stern, two side thrusters, and two vertical thrusters. The thrusters were computer-controlled, so each thruster had a speed controller and could run forwards and backwards. Six different steering tests and four rising tests were conducted, with at least two runs per test. During the tests, the roll and pitch were measured. Lifting the submarine by a crane was also a part of the experimental campaign. In general, the steering capabilities of the submarine were satisfactory and rolling instabilities were absent. Just a few deficiencies in the steering capabilities were detected. The rising tests were performed without any major motion instabilities, but in one case, the final position of the model at the surface was unstable.

Experimental Test and Finite Element Analysis on a Concrete Box Girder of a Cable-Stayed Bridge with W-Shaped Prestressed Concrete Diagonal Braces

This paper presents an experimental study on the box girder of a low-tower cable-stayed railway bridge with a W-shaped section that consists of prestressed concrete diagonal braces. A 1:6 scale test model was designed and constructed for the experiment. The mechanical behavior of the test model was investigated under two loading conditions: a double-track train symmetrical load and a single-track train unsymmetrical load. The experimental results were validated against a finite element model. Furthermore, the torsional performance of the box girder section was analyzed and discussed.

Short-time aerodynamic research for large scale test models in hypersonic wind tunnels

Current research in hypersonic wind tunnel aerodynamic testing predominantly focuses on small-scale and lightweight models, typically limited to scales of 4 m and weights under 1 ton. However, there's an emerging trend in the design of hypersonic vehicles towards larger scales and heavier loads, often surpassing 9 m in length and several tons in weight. This shift poses new challenges as there's a noticeable gap in research specifically addressing the aerodynamic testing needs of these larger-scale models. Firstly, this study aims to fill this gap by conducting an exhaustive analysis of the impact of the strain box-balance floating frame on aerodynamic force transmission characteristics. This analysis is crucial as it offers essential theoretical guidance for designing large-scale strain box-balances in pulse combustion wind tunnels. These designs are uniquely tailored to test large and heavy air-breathing hypersonic vehicles (AHVs), addressing a critical need in the field. Subsequently, this study developed an innovative large-scale strain box-balance, measuring 2.4 m, specifically devised for aerodynamically testing extensive AHVs. Finally, to validate the effectiveness of this new strain box-balance design, the study undertook a series of comprehensive tests. These included static calibration tests, floating frame stiffness tests, and wind tunnel tests. The results from these experiments were remarkable, demonstrating high sensitivity across each test channel of the box-balance. Specifically, the sensitivities were 1.308 kg/10μv in the drag force test channel, 1.464 kg/10μv in the lift force test channel, and 1.104 kg/10μv in the pitching moment test channel. Additionally, the hysteresis levels recorded were exceptionally low, at 0.489 %, 0.0649 %, and 0.0086 % respectively for each channel. These findings not only validate the technical efficacy of the large-scale strain box-balance but also mark a significant stride in hypersonic aerodynamic research, catering to the emergent requirements of larger, heavier hypersonic vehicle models.

Effects of pressure waves on the cooling-fan performance and indoor flow of air-conditioning units on the roof of a high-speed maglev train

Air-conditioning units (ACUs) are important components of trains, and their performance directly affects the thermal environment of train cabins. Their operational performance is affected by the ventilation capacity of its core component, the cooling fan. The compressible unsteady Reynolds-averaged Navier-Stockes (URANS) and the shear-stress transport (SST) k-ω turbulence model were used to simulate the flow field and pressure waves of high-speed maglev trains, both in open air and tunnels with different lengths, at 600 km/h. We validated the numerical method and settings using a scaled model test. The effects of pressure waves on the fan flow of the ACUs and the flow field around them on the roof of the train were analyzed. The results demonstrated reduced cooling-fan flow due to the high-speed flow generated by the train operation, with the flow of the downstream fan affected by the indoor flow from the upstream fan in the same ACU. The pressure waves from trains passing each other in the open air can cause significant fluctuations in the cooling-fan flow and are positively correlated with the pressure wave amplitude. Moreover, the cooling-fan flow of the ACUs was significantly affected by the tunnel pressure wave, particularly that coming from two trains passing each other in the tunnel. The impact of airflow caused by trains exiting the tunnel on the cooling-fan flow was significantly greater than that entering the tunnel, and the amplitude of the sudden change in the cooling-fan flow was closely related to the gradient of the tunnel pressure wave. Some Findings would help improve the cooling-fan performance and the internal construction design of ACUs.

Investigation of Hydraulic Performance and Arrangement Optimization of Non-Prismatic Water Conveyance Tunnel—A Case Study of Project X

The water conveyance tunnel is an important hydraulic structure in water conservancy projects. Typically, it manifests as a non-prismatic tunnel due to variations in the cross-sectional geometry, which give rise to an unpredictable flow pattern that significantly impacts the secure and stable operation of the tunnel. This study takes water conservancy project X as a case and investigates the hydraulic performances of a non-prismatic water conveyance tunnel using a scale model test and numerical simulation; the hydraulic performance, such as flow pattern, discharge, flow velocity, and water depth profile are analyzed for both free flow and submerged flow conditions. The results show that the simulation data fit well with the experimental value observed in the scale model test for free flow; however, a substantial discrepancy emerges under submerged flow conditions. This discrepancy is attributable to the presence of a vacuum in the distortional plan section. Notably, the effect of water entrainment phenomena on flow rate and velocity is diminished in the scale model test, emphasizing the advantage of numerical simulation in predicting hydraulic parameters for the prototype. On this basis, the optimization of the gate shaft arrangement is executed through numerical simulation; the results indicate that the vacuum issues in the contraction section were partially resolved through structure optimization. The simulation values are close to the experimental results, and the modified design of the tunnel can be used in a water conveyance project.

Ice channel breakout performance of a double-acting vessel

The capability of an icegoing ship to break out from an ice channel is a main index of its manoeuvrability in ice. Breakout is necessary if a ship needs to change its course when sailing in an ice channel. Breakout can also be used as an evasive action to avoid collision with the leading ship in emergencies during escort and convoy. Although the ice channel breakout test is documented in ITTC guidelines as a standard manoeuvring test, little data is available on the performance of icegoing ships in this context. This paper presents model-scale tests carried out at Aalto Ice Tank with a double-acting vessel with podded propulsion. Parameters including ice thickness and strength, ice channel width, initial speed and propulsive settings are varied between the tests to examine their influence on the capability and distance to break out from ice channels. In addition, stopping tests by reversing propeller revolution were conducted in ice channels to benchmark the breakout operation as an option to avoid collision. The test results reveal the influence of multiple factors on the ship's channel-breakout capability, including channel width, shaft power, initial speed, as well as thickness and strength of ice. With additional complementary numerical simulations at high speeds, it is found that for collision avoidance braking is more efficient at low speed and breakout at high speed. Recommendations on breakout test in model scale are given based on the lessons and experience learnt from the experiments.

Multi-objective optimization of a pipe energy pile with heat exchanger pipes subjected to chaotic advection

Shallow geothermal energy extraction through an energy pile system relies on the constant temperature available below the earth's surface at shallow depths. The energy pile system transfers the heat stored in the earth to a place of utility for space heating and cooling through fluid circulation, thus extracting geothermal energy. In this study, a 3D energy pile model comprising a helical heat exchanger pipe (HHEP) was developed and validated with the existing experimental data using a FEM-based software package. Further, it was hypothesized that replacing HHEP with a chaotic configured helical heat exchanger pipe (CHEP) would enhance thermal performance. The numerical analyses supported the hypothesis, where there was about a 15 % increase in heat release rate for energy piles containing CHEP. The above results form a basis for exploring the simulation results through laboratory scale model tests. Thus, an experimental setup was fabricated to conduct geothermal energy tests on a scaled pipe energy pile (PEP) model. The investigation was carried out by considering three design-input parameters: flow rate, pitch, and inlet temperature at three different levels with water and ethylene glycol as heat exchanger fluid (HEF) in a 4:1 ratio. The heat release rate of the PEP (Qp), heat flux per unit length of HEP (qpl), soil excess temperature (θs), total thermal resistance (TTR), and energy consumed (EC) were analyzed. Furthermore, multi-objective optimization using the MO-Jaya algorithm and multiple attribute decision-making (MADM) R-method were used to predict an optimal set of design-input parameters. Finally, a confirmation test was conducted to test the competence of the predicted parameters. The percentage variation between the predicted design input parameters and the experimental values was below 10 %.