Scale Model Tests Research Articles

Effects of outer-layer porous cover sheet parameters on wind loads of double-layer flat roof systems

The double-layer roof system with porous cover sheets (DRSPCS) is widely used in large-scale projects, but existing literature and standards for determining wind loads on the DRSPCS are insufficient. This study conducts wind pressure measurements of the DRSPCS in flat roof buildings with three typical porosities (ϕ = 6.8%, 21.8%, and 36.8%) of the outer-layer porous cover sheets and cavity depths (H = 5, 15, and 25 mm) between the cover sheets and the inner-layer roof by wind tunnel tests. The effects of volume distortion in the scale model, ϕ and H on the wind loads of both outer-layer cover sheets and inner-layer roof are investigated. The results indicate that volume distortion minimally impacts the mean and standard deviation wind pressure coefficients, allowing it to be disregarded in wind tunnel scale model tests for the DRSPCS. Internal pressures within the cavity reduce the mean and peak net wind loads on the outer-layer cover sheets, and increasing H or decreasing ϕ reduces peak wind loads on the inner-layer roof but increases peak net wind loads on the outer-layer cover sheets. In various parameter scenarios of the DRSPCS, the most critical upward wind loads on the outer-layer cover sheets and inner-layer roof are approximately 0.15–0.50 and 0.70–0.95 of those on a single-layer roof with the same dimensions, respectively. Reduction and conversion factors are proposed for estimating wind loads on the DRSPCS based on similar single-layer roofs.

Shear properties of jointed dual-pylon of the cable-stayed bridge with separated unequal-width decks under asymmetric load

The significant load disparity between the two decks of a cable-stayed bridge with separated unequal-width decks results in complex asymmetric static effects in the jointed dual-pylon. To investigate the structural behaviour and reliability of the jointed dual-pylon under asymmetric loads, a 1:30 scaled model test and numerical simulation were conducted based on the world's first road-railway same-level cable-stayed bridge with jointed pylons. The test results indicate when the unbalanced horizontal force of the jointed dual-pylon structure reaches its maximum during the service phase, the stress at the dual-pylon connectivity node remains relatively low, indicating good shear resistance of the dual-pylon connectivity node. Structural failure occurs when the load reaches 1.82 times the maximum shear stress at the tower column merging section, and the railway beam will experience severe cracking and stiffness degradation, ultimately leading to loss of bearing capacity. The calculation results further reveal that under the combined action of dead load, full-span moving load, and lateral wind load, the minimum calculated nonlinear stability coefficient of the dual-pylon connectivity node is 1.65. Moving load and longitudinal wind load have minimal impact on the nonlinear stability coefficient, and the dead load and lateral wind load primarily govern the failure of the dual-pylon connectivity node.

Steady and dynamic load measurements over a generic submarine hull form with various appendage configurations

Experimental studies for the steady and dynamic loads over a generic submarine hull form ( SUBOFF) with various appendage configurations in submerged motion was investigated through scaled model tests in the High Speed Towing Tank facility at Naval Science & Technological Laboratory, India. Steady load measurements were performed for a range of angles of incidence in angle of attack (± 35°) and drift (0° to 35°) including control surface deflections (± 20°). Measurements for dynamic loads were performed in both vertical and horizontal plane of motion for oscillating frequencies ranging from 0.21 to 0.55 Hz. The studies were carried out for four different configurations of SUBOFF comprising of bare hull, bare hull with sail, bare hull with control fins and fully appended hull. The aim of the present study for the load measurements is to gather steady and dynamic force/moment data, estimate hydrodynamic coefficients, validate and extend such data over a wide range of operation scenarios experienced by a submarine including high angle of incidence. The particulars of the SUBOFF model, experimental facility and measurement technique, test results for load measurements and estimated hydrodynamic coefficients are highlighted in the paper. The measurements data generated from the above studies will greatly complement the current research on hydrodynamic load characteristics for submerged bodies both computationally and experimentally.

Excavating trajectory planning of electric shovel based on dynamic excavating volume prediction

Mining electric shovels are one of the core equipments for open-pit mining, and are currently moving towards intelligent and unmanned transformation, with intelligent mining instead of traditional manual operation. In the excavation operation process, due to the complexity and changeability of the material surfaces, different excavation strategies should be adopted to achieve the optimal excavation trajectory. It is an important research direction to realize the unmanned excavation of electric shovels by studying a trajectory planning method that is not limited to fixed resting angle surface, can comprehensively consider the type of material surfaces and aim at the minimum excavation energy consumption per unit volume. Therefore, an electric shovel excavation trajectory planning method based on material surface perception is proposed, which firstly obtains the point cloud data of the material surface through laser radar to perceive the excavation environment, and then carries out horizontal calibration and filtering processing on the point cloud data, and adopts Delaunay triangulation rule to realize the calculation of the dynamic excavation volume of the material. Then, the trajectory model of the dipper tooth tip is established by using the 6th polynomial interpolation method, and the minimum excavation energy consumption per unit volume is taken as the optimization objective, and the whale optimization algorithm is used to plan the excavation trajectories for four kinds of complex stacking surfaces (concave, convex, convex–concave and stepped stacking surfaces). Finally, an electric shovel scaled model test bench is built to experimentally verify the trajectory planning results of the simulation. The correlation coefficient R2 values between the test results and the simulation results are both greater than 0.85, and the deviation between the material amount in the bucket and the planned excavation volume is about 5%, which verifies the reliability of the trajectory optimization model and the accuracy of dynamic modeling.

Numerical and Experimental Investigation of Magnetohydrodynamic Effects on Radiative Heating During Superorbital Earth Reentry

Numerical predictions of radiative heat flux were performed on a representative Mars return (Earth reentry upon return from Mars) condition with a flight equivalent velocity of [Formula: see text], produced by the University of Queensland’s X2 expansion tube. The primary goal was to numerically evaluate the effect of an externally applied magnetic field on radiative heat flux to a scaled test model based on NASA’s Stardust vehicle. Numerical simulations used the Eilmer4 computational fluid dynamics (CFD) code coupled with NASA’s NEQAIR code for radiation calculations. A two-dimensional, axisymmetric magnetohydrodynamic (MHD) model was implemented in order to model MHD effects. The numerical results predicted a significant increase of 54% to stagnation point radiative heat flux when the magnet was used, and a smaller increase of 8% to afterbody radiative heat flux. An attempt was made to compare the numerical predictions to experimental measurements. A spherical permanent magnet fitted into the test model provided a stagnation point magnetic flux density of 0.68 T. A radiation gauge was developed consisting of a thin-film heat flux gauge placed behind an optical window, enabling isolation of the radiative heat flux component. Several challenges were encountered, including the absorbance calibration of the radiation gauges, chemical contamination of the test flow, and noisy measurements when the magnet was on. These prevented firm conclusions to be made and warrant further experiments to validate the CFD results.

Comparison of 1g and centrifuge modelling of drag anchors with subsurface wireless tracking

The kinematic behaviour of drag embedment anchors has become a recent research focus due to the increase in offshore renewable energy devices. This is due to their potential use as an anchoring system for future floating wind applications, in addition to the need to understand their penetration behaviour as a part of the Cable Burial Risk Assessment. Studies on the behaviour of anchors typically consist of field scale or model centrifuge tests, where such facilities are not readily available to all and can result in significant cost. In addition to this, measuring the load–penetration behaviour of an anchor has proven to be a significant challenge, as any contact-based methods are likely to influence the penetration behaviour of the anchor. In this paper, a novel wireless method of recording the inclination of the anchor and calculating the penetration depth is presented. A comparison of the penetration behaviour of a Class F (AC-14) anchor has been made in sand using centrifuge and 1g model scale testing. The results indicate that the 1g testing can match the behaviour of the anchor testing in the centrifuge in terms of both the position of the anchor and its orientation during the dragging event.

Study on static performance of the steel-concrete joint in a high-speed railway hybrid girder low tower cable-stayed bridge

The steel-concrete joint (SCJ) of mixed beam bridge plays a key role in connecting concrete box girder and steel box girder, but its complex structure makes its mechanical properties unclear. Compared with traditional mixed beam cable-stayed Bridges, mixed beam low tower cable-stayed Bridges show stronger competitiveness. However, there is still a lack of published literature on the study of SCJ of mixed beam low tower cable-stayed Bridges for high-speed railway. In order to study its mechanical properties, a scale model test with similar ratio of 1:5 was carried out under the background of Yongjiang River mega-bridge. The results show that under the action of 5.0 times maximum axial force and maximum negative bending moment, the components of the test model are still in the elastic state, the vertical deformation of the model is continuous and smooth, and the slip between steel and concrete is small, which indicates that the model has good bearing capacity and safety. At the same time, the force transfer mechanism of steel-hybrid section under axial compression is discussed by finite element analysis(FEA). The numerical results show that the rear bearing plate is the main force transfer member of the SCJ, while the front bearing plate transmits a small proportion of axial force. Improving the strength of concrete has limited effect on the transmission path, but can enhance the overall stiffness. The increase of the thickness of the rear pressure plate and the T-rib with variable section mainly affects the force transfer ratio of the rear bearing plate, but has little effect on other force transfer indexes and the overall stiffness. The increase of the stiffness of the shear connectors significantly affects the force transfer proportion and the force transfer uniformity of the bearing plate, but its increase is far more than the change of the force transfer index, and the influence on the overall stiffness of the joint section can be ignored. The results can provide reference for the subsequent research and design of similar structures.

Model scale tests on the behaviour of single piles in cohesive soils under combined loads

ABSTRACT Model scale tests were conducted to study the influence of combined loads (uplift + compressive, uplift + lateral, lateral + compressive and lateral + uplift) on stress distribution, ultimate capacities and deformations of single piles in Indian black cotton soils, in comparison to pure uplift and lateral loads. Numerical analysis was performed in Plaxis 3D to examine the effect of pile slenderness ratio (L p /d = 15, 20 and 25) on ultimate capacity and pile head displacements. The test results showed that uplift capacity and pile head displacements increased by 35–49% and 30–50% with an increase in staged compressive loads, respectively. Therefore, piles subjected to combined uplift and compressive loads should be designed for pile head displacements rather than uplift capacity. The compressive loads did not affect the stress distribution along the pile–soil interface. However, lateral loads altered stress distribution, resulting in a curved failure plane and a substantial increase of 80–150% in the uplift capacity of piles under combined uplift + lateral loads. The lateral load–deflection curve for 60% and 80% of staged uplift loads showed an elastic response, indicating that the pile and surrounding soil did not yield under the applied lateral loads.

A study on the effect of cylindrical shell scaled model size on ESCM prediction accuracy

Abstract Current research on similitude theory has introduced numerous methods to address the distortion similitude model. However, these methods still encounter some challenges in guiding the design of scale models, such as insufficient accuracy and a limited range of design sizes. In this paper, the Energy Similitude Correction Method (ESCM) is used to analyze the effect of size design on the accuracy of cylindrical shell-scaled models, taking into account distortion factors such as wall thickness and thermal environment. The research shows that the closer the model size is to the prototype size, the higher the prediction accuracy is. Additionally, larger size combinations are more reliable for predicting the prototype frequency in scaled model tests. The research results provide a basis for the reasonable design of the size of the scaled model group and make a positive contribution to improving the prediction accuracy of the scaled model.

Detection Method for Asteroid Interior Structure Verified by Scale Model

Abstract We have developed a radar scheme for detecting the asteroid interior structure. Using the auto rotation of an asteroid, radar system can hover at a fix distance from the asteroid, and continuously measure the internal structure echoes at different spin angles, which can be processed to obtain the internal structure profile image. Through simulation and scale model test, we have verified the internal structure imaging results and conformed the effectiveness of the hovering radar method. The proposed radar scheme was selected as the science payload for internal structure in China’s asteroid exploration program aiming at Asteroid 2016HO3.

On the design of a scaled rotor for a tethered tidal converter to deploy at sea

Abstract Model scale testing is vital for developing technologies like tidal turbines. Reduced-scale tests follow numerical design and are cost-effective in controlled environments, allowing parameter adjustments. However, controlled tests face drawbacks, such as blockage effects and the inability to replicate real sea conditions. Sea trials, conducted in actual marine environments, offer realistic data and continuous collection, potentially being cost-effective despite environmental variability and complex data processing. This work aims to measure real sea effects, such as marine growth and stream turbulence, on fixed and moving parts, of a scaled model of GEMSTAR tidal stream energy converter, a twin rotors submerged tethered device, designed to tap tidal current energy. The planned model installation site is at the Renewable Marine Energy Laboratory, a natural facility located on the East coast of the Strait of Messina (southern Italy), characterized by tidal currents with a maximum speed of about 1.25 m/s. Due to the low stream speed, in order to get significant data, an up-scaling of the existing model rotor diameter has been necessary, and a specific new blade design has been performed, in order to lower the cut-in speed, increasing in this way the useful power production time of the model. The paper illustrates the different phases of model scale design.

Research on Coordinated Relationship Between Deformation and Force in Shaft Foundation Pit Support Structures

In order to investigate the coordinated relationship between lateral deformation of the diaphragm wall and axial force of the internal strut, this paper first carried out a scaled model test on the mechanical features of a foundation pit support system based on a novel axial force servo device. Then, a finite element model was established to simulate the scaled model test, and the correctness of the finite element modeling approach was validated by comparing test results. After that, the same finite element modeling method was used to analyze the coordinated relationship between axial force and lateral deformation in the prototype foundation pit support structure. The results show that the axial force of the inner strut is negatively correlated with the lateral deformation in the diaphragm wall. The initial maximum lateral deformation in the diaphragm wall of the shaft foundation pit occurs at the bottom of the foundation pit, so changing the length of bottom strut simultaneously is the most effective way to adjust the mechanical behavior of the support structure. Under various support conditions, the maximum lateral deformation of the diaphragm wall in the prototype project is 0.59~0.66‰ of the total excavation depth of the foundation pit, and the maximum axial force of internal support is 11~30% of the yield load of a single steel strut.

Evaluation of the powering extrapolation of a ship with a gate rudder system, including ageing and fouling effects

This paper is based on the evaluation results of the calm water powering extrapolation of a 90-m general cargo vessel, originally built with a conventional rudder system (CRS) and later retrofitted with an innovative energy-saving device (ESD) known as the Gate Rudder System® (GRS), as part of the EU H2020 Project GATERS. The power estimation of the vessel was conducted using an adapted extrapolation procedure based on the scaled model tests of the vessel in a towing tank, validated by the three sets of sea trials. The first sea trial was performed when the ship was new, while the latter two were conducted during the project timeline, before and after the GRS retrofit. This paper aims to adapt the ITTC-78 power extrapolation method to predict the power performance of a ship retrofitted with the GRS for the first time in the maritime industry. Within this framework, the specific objectives of the paper are to describe and validate the proposed method using relevant power-speed data of the GATERS project target vessel (M/V ERGE) initially equipped with the CRS and later replaced by the retrofit GRS to achieve the project objective. Due to the real-world circumstances of retrofitting a 13-year-old ship with a novel energy-saving device, investigating the effects of ageing, hull roughness, and fouling has also become one of the key objectives of the paper. The findings demonstrate the ageing effect on the target ship's powering performance after retrofitting with GRS, highlighting the need for special consideration of power extrapolation alongside the hull fouling effects. The paper also demonstrates that the GRS is an emerging ESD, as a retrofit beside newly built ships with GRS, which improved the powering performance of the project target vessel, achieving a remarkable 25% power saving based on the comparative full-scale sea trials.

Scaled model tests on pile types influencing the stability of stiffened deep mixed pile-supported embankment over soft clay

Scaled model tests on pile types influencing the stability of stiffened deep mixed pile-supported embankment over soft clay

Intelligent vibration control of tensile cable based on deep reinforcement learning

Vibration of tensile cables commonly occurs in the engineering structures such as cable-stayed bridges, which may have negative effect on the driving comfort and safety, and further lead to the fatigue problems of the structure. This paper proposes a semi-active control strategy based on deep reinforcement learning and magneto-rheological (MR) damper, for the vibration control of tensile cables, and the corresponding algorithm have been developed. Through the interaction with the cable-damper system, the intelligent agent can evaluate every possible control parameter and achieve an effective control policy. Then, according to the real-time vibration state, the agent would determine an action current for the MR damper and thus change the damping coefficient of the damper, further make influences on the vibrating cable. Basically, the proposed strategy realizes the model-free semi-active control of cable vibrations. To validate the effectiveness of the proposed semi-active control strategy, a scale model test has been conducted, where the test cases of passive and semi-active control strategies are carried out and compared. Results show that, the semi-active control shows a prior performance in vibration reduction compared to the passive control strategy, with regard to the vibration profile, the vibration energy, as well as the energy dissipation of MR damper.

Experimental and numerical study on dynamic responses of a TLP-type modular floating structure system

This paper explores a proposed TLP-type modular floating structure system, incorporating both central TLP modules and peripheral floating artificial reef modules. The outermost floating artificial reef module can function as a floating breakwater, and also serving as a habitat for surrounding marine organisms. To assess the system's multi-body coupling dynamics under various wave conditions, both scale model tests (1:80) and time-domain numerical simulations were performed. The simulations accounted for hydrodynamic interactions among the bodies and the mechanical coupling effects. During the scale model test, a survival strategy has been proposed to prevent collision risks between reef modules and adjacent TLP modules, which involving a hinge connector with additional linear spring. A preliminary stiffness recommendation was suggested by a trade-off between the pitch of the reef module and the spring force. Numerical and experimental results have been widely compared and discussed, including the multi-body motion responses and the tension leg loads. A good agreement has been achieved, although responses are slightly overestimated by numerical simulation due to the neglect of the viscous damping effect. In addition, the responses of the proposed system, connected with and without the outermost floating artificial reef module, have been compared and analyzed. The results suggest that the connection of the reef module can significantly reduce the system's surge response and enhance its survivability under severe sea conditions. The validated numerical model can serve as a valuable reference for subsequent system optimization and further engineering applications.

A procedure for estimating mitigation effect of air injection on ship underwater radiated noise

Increasing evidence exists that underwater radiated noise (URN) from ships has a negative impact on marine ecosystems. This has led to numerous initiatives aimed at monitoring and mitigating ambient sound levels generated by shipping. Within the European Union, noise abatement is being addressed by a wide range of stakeholders, with activities focused on developing procedures and thresholds for evaluating noise impact as well as knowledge on the effectiveness of a range of mitigation measures. In the SATURN project, MARIN is studying air injection systems for mitigation of both propeller cavitation and machinery noise; the so-called "Prairie" and "Masker" systems. Model-scale tests have been performed in order to quantify performance in terms of sound level reductions for a range of test conditions. In this paper we elaborate a procedure for applying the processed measurement data to ship-scale URN predictions for assessing mitigation potential during the early design stage. Data reduction of the model test results is explained, leading to a model for estimating the mitigation effect and power requirement of the two systems. We subsequently apply the model to a number of test cases, covering both measured and calculated source levels. Limitations of the approach will also be discussed.

Lateral capacity of group helical piles in sand: an experimental and numerical study for sustainable infrastructures

ABSTRACT Helical piles are integral to support resilient infrastructures subjected to axial and lateral loads. This study explored model-scale testing of group helical piles in cohesionless soil in a rigid box. Initially, a total load of 5000 N is applied to the pile raft model, followed by a lateral load of 1600 N. Nine model tests are performed with a configuration of four, six, and nine, having conventional, single helical, and double helical piles. The data logger facilitated data collection using MATLAB software, and the load was increased at rate of approximately 4.9N/sec. The computed average reduction in the displacement of Single and Double Helical Pile Rafts is observed as 36.43% and 55.71%, respectively, compared to Conventional Pile Rafts. The addition of a second helix further reduced lateral displacement by 19.27%. Numerical analysis on Plaxis-3d showed that the experimental and numerical results are in good agreement.

Experimental investigation on damage development and failure mechanism of shield tunnel lining under internal blast considering stratum-structure interaction

With the expansion of international terrorism and the potential threat of attacks against civil infrastructure, the dynamic response and failure modes of underground tunnels under explosive loads have become a prominent research topic. The high cost and inherent danger associated with explosion experiments have limited current research on tunnel internal explosions, particularly in the context of scaled model tests of shield tunnels. This study presents a series of scaled model tests under 1g-condition simulating internal blast events within a shield tunnel based on the prototype of the Shantou Bay Tunnel, considering the influences of surrounding stratum and equivalent explosive yield. Three different TNT explosive yields are considered in the model tests, namely 0.2, 0.4, and 1.0 kg. The model tests focus on the damage behavior and collapse modes of the shield tunnel lining under internal explosive loads. The model tests reveal that the shield tunnel is prone to damage at the joints of the tunnel crown and shoulder when subjected to internal explosive loads, with the upper half of the tunnel lining experiencing segment collapse, while the lower half remains largely undamaged. As the TNT equivalent increases, the damage area at the tunnel joints expands, and the number of segment failures in the upper half of the tunnel rises, transitioning from a damaged state to a collapsed state. The influence of “stratum-structure” interaction is investigated by comparing two models, one with overburden soil and the other positioned at the ground surface. The model tests reveal that the presence of soil pressure and confinement can significantly enhance the tunnel resistance to internal blast loads. Based on the observation of the model tests, five different damage modes of segment joints under internal explosion are proposed in this study.

Study on the Optimized Perception of Structural Behavior in Shield Tunneling by Fiber Grating Layouts

Shield tunnels’ structural stability is challenged due to the fact that they are often built under rivers, lakes, and oceans. It is crucial to execute the structural deformation perception of the shield tunnel. Fiber Bragg grating (FBG) sensing technology is sensitive to deformation information, making it one of the greatest options for shield tunnels to perceive structural deformation. In this study, a 1:20 scale model test was carried out to investigate the deformation perception of the shield tunnel structure under three different layouts of surface-mounted FBG sensors. The deformation law of the tunnel is discussed, under the condition of two-factor cross fusion and especially under the condition of constant water pressure and soil pressure change. The results indicate that, under the combined action of water and soil pressure, the uniform water pressure of 0.33 MPa has a stabilizing effect on the segment strain under the vertical load of 0.4 MPa. The traditional four-point layout and the 18° uniform layout are more effective in detecting changes in local tunnel curvature and strain, respectively, compared to the 36° uniform layout mode. It is advised that the traditional four-point layout be used to collect information for other sections’ monitoring and that the 18° uniform layout is for harsh terrain conditions.