Experimental Model Tests Research Articles

Experimental Test of the Cooperative Free Volume Rate Model under 1D Confinement: The Interplay of Free Volume, Temperature, and Polymer Film Thickness in Driving Segmental Mobility.

We show that the Cooperative Free Volume (CFV) rate model, successful at modeling pressure-dependent dynamics, can be employed to describe the temperature and thickness dependence of the segmental time of polymers confined in thin films (1D confinement). The CFV model is based on an activation free energy that increases with the number of cooperating segments, which is determined by the system's free volume. Here, we apply the CFV model to new experimental results on the segmental relaxation of 1D confined poly(4-chlorostyrene), P4ClS, and find remarkable agreement over the whole temperature and thickness ranges investigated. This work further validates the robustness of the CFV model, which relates the effects of confinement on dynamics to pressure changes in the bulk, and supports the idea that confinement effects originate from local perturbations in density.

Numerical and experimental analysis of a diffuser-augmented micro-hydro turbine

In the current work, a micro-horizontal axis diffuser-augmented turbine (MHDT) system for renewable energy applications of marine or river stream systems is designed and analyzed through computational fluid dynamics (CFD) and experiment. A bare and diffuser-augmented turbines were applied to MHDT through full-scale experimental model tests, showing agreement with numerical results (the average deviation did not exceed a value of 6%) and verifying the reliability of the numerical method. Several diffuser-augmented turbines with varied camber (f) and angle of attack (α) were analyzed using ANSYS-Fluent. It is found that both f and α have a great impact on the hydrodynamic performance of a diffuser-augmented turbine, which can significantly enhance power and axial force levels and which affects the variation of the power coefficient curve. Additionally, diffuser performance is not only directly linked to its shape design but also to its interactions with the rotor. Critical interaction factors ac (the axial induction factor when a bare turbine and a diffuser-augmented turbine has the same CP at a tip speed ratio) based on the CFD results are proposed to offer a clearer explanation of the energy extraction performance of a diffuser-augmented turbine.

Validation of a distributed simulation of ship replenishment at sea with model tests

A simulation of ship motions during replenishment at sea was validated using dedicated model test data. Motions of the supply ship and receiving ship are influenced by hydrodynamic forces and forces from replenishment gear used to transfer payloads. Simulated entities include rudders and propellers, with associated controllers. The composite simulation was implemented as a distributed simulation using the high-level architecture. An experimental model test program was developed for a tanker and destroyer conducting replenishment in head seas at a speed of 15 knots. The simulation gives generally good agreement with the model tests for heave, roll, and pitch motions, with some noted exceptions. For dynamic positioning of the destroyer relative to the tanker, there is very good agreement for mean values but underprediction of lower frequency sway and yaw motions. The variation of heave and roll motion accuracy is likely due to the hydrodynamic force prediction method using the frequency domain Green function for zero forward speed, thus not accurately modelling the propagation of radiated and diffracted waves between vessels. Prediction of viscous roll forces using semi-empirical methods likely contributed to differences between simulated and model test roll motions. The underprediction of lower frequency sway and yaw motions for the destroyer in waves could be caused by the ship motion predictions not including second-order wave drift forces.

Numerical study of hybrid GFRP-steel reinforced concrete shear walls and SFRC walls

Experimental results show that concrete shear walls reinforced with a hybrid scheme of steel and fiber-reinforced polymer (FRP) bars are able to achieve similar strength, stiffness and ductility to the walls constructed of conventional steel-reinforced concrete (RC). The elastic response of the FRP bars provides self-centering capacity to the system and mitigates the post-yield strength deterioration observed in the typical hysteretic response of RC walls, while the steel reinforcement provides ductility and energy dissipation capacity. Evidently, adoption of this innovative type of wall in construction requires a better understanding of performance of the hybrid system at the material and system levels, both through experimental testing and development of reliable numerical models. In this study, the finite-element analysis model developed by the authors is used to conduct a comprehensive parametric study on hybrid GFRP-steel reinforced shear walls. First, the validated model is used to address some other design aspects of tested specimens such as presence of axial load and arrangement of GFRP bars. Next, the reliability of the section analysis based on CSA A23.3-14 code for design of conventional and hybrid squat walls are investigated. The self-centering and economic aspects of design of hybrid GFRP-steel reinforced walls are also addressed. Using the analysis model, a promising structural application of SFRC (steel fiber-reinforced concrete) shear walls is also proposed. Findings of this study can assist practitioners with a more reliable and convenient shear wall design.

An experimental test of the mutation-selection balance model for the maintenance of genetic variance in fitness components.

Despite decades of research, the factors that maintain genetic variation for fitness are poorly understood. It is unclear what fraction of the variance in a typical fitness component can be explained by mutation-selection balance (MSB) and whether fitness components differ in this respect. In theory, the level of standing variance in fitness due to MSB can be predicted using the rate of fitness decline under mutation accumulation, and this prediction can be directly compared to the standing variance observed. This approach allows for controlled statistical tests of the sufficiency of the MSB model, and could be used to identify traits or populations where genetic variance is maintained by other factors. For example, some traits may be influenced by sexually antagonistic balancing selection, resulting in an excess of standing variance beyond that generated by deleterious mutations. We describe the underlying theory and use it to test the MSB model for three traits in Drosophila melanogaster We find evidence for differences among traits, with MSB being sufficient to explain genetic variance in larval viability but not male mating success or female fecundity. Our results are consistent with balancing selection on sexual fitness components, and demonstrate the feasibility of rigorous statistical tests of the MSB model.

Experimental Testing of Scattering Polarization Models

Abstract We realized a laboratory experiment to study the scattering polarization of the Na i D-doublet at 589.0 and 589.6 nm in the presence of a magnetic field. This work was stimulated by solar observations of that doublet, which have proven particularly challenging to explain through available models of polarized line formation, even to the point of casting doubts on our very understanding of the underlying physics. The purpose of the experiment was to test a quantum theory for the polarized scattering of spectrally flat incident radiation, on which much of the current magnetic diagnostics of stellar atmospheres is based. The experiment has confirmed the predictions of that theory, and its adequacy for the modeling of scattering polarization under flat-spectrum illumination.

Variation in lateral load capacity of pile embedded near slope with ground inclination and edge distance

ABSTRACT There are many circumstances in which piles have to be provided on slopes. Experimental model tests in the laboratory have been undertaken to investigate the lateral pile response in sloping ground. The paper discusses about the investigation in a series of 22 laboratory tests in dense sand at 72% relative density. The main motive of the study was to examine the effect of slope angle and edge distance on the pile response. Ground slope was varied as 1V:1.5H, 1V:1.75H and 1V:2H for sloping ground condition. Pile response was obtained for seven different positions of pile from the crest of the slope for a specified relative density. Then pile response for horizontal ground condition was obtained for quantification of effect of sloping ground. Displacement and bending moments in the pile increased significantly when the ground surface changes from horizontal to slope. An increase in the edge distance from the slope crest causes reduction in the pile displacement and maximum bending moment.

Behavioural analysis of vertical and batter pile groups under vertical and lateral loading in sand

Laboratory model tests were carried out to study the behaviour of vertical piles and batter pile groups under vertical and lateral load. The model pile groups were made up of mild steel rod of 8-mm diameter. Parameters such as degree of batter and different length to diameter ratios of 7.50, 15.00 and 22.50 were considered in this study. The size of the model tank was 1000 mm × 1000mm × 800 mm. Experiments were performed on 3 × 3 model pile groups with a row of batter piles both positive and negative in addition to vertical pile groups with batter angle 0° in sandy soil subject to vertical and lateral loads. It was observed that the behaviour of vertical pile groups and group of piles with batter piles were similar but it showed substantial variation in the capacity of pile groups. Results indicated that the load–settlement relationships were non-linear for all model pile groups both under vertical and lateral loading. Numerical FEM analysis using ABAQUS/CAE 6.11 was also used to compare and validate the load carrying capacity of pile groups obtained from the experimental model tests.

Effect of particle size distribution of cohesionless soils on the ultimate carrying capacity of open ended pipe piles under different saturation conditions

This research is performed to study the effect of grain size distribution of cohesionless soils (i.e., fine, medium, and coarse sand) on the ultimate carrying capacity of open-ended pipe pile models of different diameters under different saturation conditions (i.e., fully and partially saturated). Poorly graded clean sand of rounded particles was used as natural soil in the present study. The soil is sieved on standard sieves to obtain fine-, medium-, and coarse-graded soil according to (ASTM D 422-02). Experimental model tests were performed on four open-ended steel pipe piles models with diameters of (25, 30, 35, and 40 mm) embedded within different grain size distribution of sand prepared under fully and partially saturated conditions with specified relative density of 65%. The unsaturated states was achieved by lowering of water table according to matric suction values of soil. The relationship between matric suction and depth of ground water table was measured in suction profile set by using three Tensiometers. The soil water characteristic curve (SWCC) was estimated by applying fitting methods through the program (SoilVision). The results show that the ultimate load carrying capacity of pipe pile under unsaturated conditions is higher than those of saturated condition and increases with increasing of matric suction values. On the other hand, the fine sand shows an increase in ultimate load carrying capacity more than the other grain size distributions under unsaturated conditions for all different types of pipe pile diameters. However, the coarse sand gives a lower resistance at different saturation conditions.

Coordination and evolutionary dynamics: When are evolutionary models reliable?

This study reports a continuous-time experimental test of evolutionary models in coordinated attacker–defender games. It implements three experimental treatment conditions: one with strong coordination incentives, one with weak coordination incentives, and one with zero coordination incentives. Each treatment exhibits identical equilibrium predictions but distinct evolutionary predictions. Observed behavior was tightly clustered around equilibrium under both the zero coordination treatment and the weak coordination treatment but widely dispersed from equilibrium under the strong coordination treatment. This result was anticipated by explicitly dynamic models but not by conventional stability criteria. In contrast to the widely maintained assumption of sign-preservation, subjects frequently switched to lower earning strategies, suggesting that non-sign-preserving evolutionary models may provide a more accurate characterization of human behavior.

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Slope stability analysis based on real-time displacement measurements

This paper proposes an effective and convenient method to analyze slope stability in real time, which is based on fiber Bragg grating (FBG) sensors. First, a new type of FBG inclinometer is designed to capture the internal slope displacement variation considering temperature compensation, and an optimum displacement algorithm is selected by an experiment. Once the monitoring work is prepared, the potential slope slip surface is determined by monitored displacement in an optimization model based on the maximum displacement increment of the objective function. Finally, integral processing is used with the Bishop method to simplify the calculation, and a safety factor is estimated by the integral method. An experimental model test of homogeneous soil is conducted to verify the feasibility and reliability of the proposed analytical method and the FBG monitoring technique.

Theoretical and experimental comparative analyse on the hydrodynamic resistance of a racing sailboat

The large appendages have a very important influence on the hydrodynamic resistance of the sailboats. In this paper, a comparative analyse of the theoretical and experimental results was performed, related to the hydrodynamic resistance of a racing sailboat having an overall length of 12.8 m. The theoretical approach was performed based on the method proposed by Larson and Eliasson. In order to compute the residuary resistance it was used the formulations based on Delft systematic yacht series. The estimation of the resistance components, including the keel, rudder and additional weight influence was carried out based on a computer code in Java language. The experimental model tests have been carried out in the Towing Tank of the Naval Architecture Faculty of “Dunărea de Jos” University of Galati. A 1/10 scaled model with appendages was used for experimental investigations. The level of accuracy of the theoretical prediction was evaluated based on comparative theoretical/experimental diagrams. It was found that the influence of the large appendages is very important and an optimisation procedure becomes mandatory. Moreover, the theoretical methods specific to the preliminary design stage must be improved in order to increase the level of accuracy of hydrodynamic resistance predictions.

Dynamical evolution properties of debris flows controlled by different mesh-sized flexible net barriers

Because the flexible net barrier is a gradually developed open-type debris-flow counter-measure, there are still uncertainties in its design criterion. By using several small-scale experimental flume model tests, the dynamical evolution properties of debris flows controlled by large and small mesh-sized (equal to D90 and D50, respectively) flexible net barriers are studied, including the debris flow behaviors, segregation, and permeability of sediments, as well as the energy absorption rates and potential overtopping occurring when debris flows impact the small mesh-sized one. Experimental results reveal that (a) two sediment deposition patterns are observed depending on variations in debris flow textures and mesh sizes; (b) the aggregation against flexible net barriers is dominated by flow dynamics; (c) the segregation and permeable functions of the barrier are determined by the mesh size, concentration, and flow dynamics; and (d) the smaller mesh-sized flexible net barrier tends to be more efficient in restraining more turbulent debris flows and can absorb greater rate of kinematic energy, and finally, the great kinematic energy dissipation that occurs when secondary debris flows interact with the post-deposits in front of the small mesh-sized flexible net barrier is believed to cause the failure of overtopping phenomenon. The mesh size is concluded to be the decisive parameter that should be associated with debris flow textures to design the control functions of flexible net barriers.

Response of Skirted Foundations Resting on Dry Medium Dense Sand

Experimental model tests were carried out to study the response of skirted foundation resting on dry sand. The experiments were performed in a large soil container (1000 1000 mm in cross section and 800 mm in height). Skirts with three different lengths (L) varied from 0.5D to 1.5D was attached to the edge of shallow circular foundations having three different diameters (D=60, 90 and 120 mm). Different parameters have been studied; these parameters involve skirt length, foundation size and skirt conditions. Skirts with open end and closed end were used. The relative density was kept constant and equals to 60%. The case of foundation without skirt (L=0) was initially tested and set as a reference for comparison purpose. From the results of experimental tests, it was found that the skirt modifies the load-settlement behaviour, increasing the load carrying capacity and reducing the foundation settlement. The results also indicate that load carrying capacity of skirted foundation increases with increase skirt length as well as foundation size. The results show that using skirt with closed end brought a considerable increase in load carrying capacity than that of open end.

Physical model testing and numerical simulation for temperature distribution of mass concrete freezing shaft lining in deep alluvium

In this study, we conducted an experimental model test and numerical thermal analysis to determine the temperature distribution and thermal gradients of mass concrete freezing shaft lining under the influence of low-temperature frozen soil wall. A non-scaled-down model was built with embedded thermocouple sensors to monitor the temperature distribution of the shaft lining and the frozen soil wall. Transient heat transfer analysis was conducted using ANSYS finite element software to validate the monitoring results of the model test. The temperature distribution at different points along the radial direction in the shaft lining and frozen soil wall are evaluated and compared by using finite element method and experimental work. The results are in good agreement and thus validated.

Analysis and experiment of a bio-inspired flyable micro flapping wing rotor

Inspired by insect flapping wings, a novel flapping wing rotor (FWR) has been developed for micro aerial vehicle (MAV) application. The FWR combines flapping with rotary kinematics of motions to achieve high agility and efficiency of flight. To demonstrate the feasibility of FWR flight and its potential MAV application, an extensive and comprehensive study has been performed. The study includes design, analysis, manufacture, experimental and flight test of a flyable micro FWR model of only 2.6 g weight. By experiment, the FWR kinematic motion and aerodynamic lift were measured using high speed camera and load cells. Within a range of input power, the difference between the measured aerodynamic force and the analytical results by a quasi-steady model was found to be within 3.1%–15.7%. It is noted that the FWR aeroelastic effect plays a significant role to obtain an ideal large angle of attack especially in up-stroke and enhance the FWR performance. Further analysis of the unsteady aerodynamic characteristics has been carried out based on the detailed airflow field of the FWR in a flapping cycle by CFD method. A successful vertical take-off and short hovering flight of the micro FWR model has been achieved for the first time in the research field. The flight test demonstrates the FWR feasibility and its unique feature of flight dynamics and stability for the first time. These characteristics have also been simulated by using ADAMS software interfaced with the aerodynamic model.

Motions and safety of a floating liquefied natural gas and shuttle tanker during side-by-side offloading operations

In recent years, the use of natural gas has remarkably increased due to growth in energy demands and concerns about the environment. Generally, pipelines are used for liquefied natural gas transportation; however, there are technical problems and cost increases in constructing liquefied natural gas pipelines in the deep sea. For this reason, floating liquefied natural gas system has attracted the attention of the industries, governments and academia. One of the major issues to be overcome in realisation of floating liquefied natural gas is the motion prediction of close-proximity floating bodies including the gap resonance between the two bodies. In this article, three steps were carried out in order to understand the ship motions and the gap resonance and their effects to the side-by-side offloading operations. First, the two-dimensional gap resonance between the two bodies was investigated using a viscous flow numerical method. Second, the three-dimensional gap resonance and the floating body motions were studied using a potential flow method and validated by the experimental model test. Finally, the limits of environmental conditions for the side-by-side offloading operations were examined by the results of numerical calculation.

SUITABLE LOCATION OF SHEET PILE UNDER DAM RESTING ON SANDY SOIL WITH CAVITY

This research describes the seepage characteristics of experimental model test of dam with cutoff located at different region (at dam heel, at mid floor of dam, and at dam toe). It is resting on sandy soil with cavity at different locations in X and Y directions (such as in Al-Najaf soil city). Thirty three model tests are performed in laboratory by using steel box to estimate the quantity of the seepage and flow lines direction. It was concluded that the best location of the cutoff wall is at the dam toe for model test with cavity ( Xc/B= 0 and 0.5), but for model test with cavity ( Xc/B≥1), the best location of the sheet pile wall becomes at the dam heel. For negative location of the cavity, the best location of the sheet pile wall is at the middle of the floor dam.

Molecular probes reveal deviations from Amontons\u2019 law in multi-asperity frictional contacts

Amontons’ law defines the friction coefficient as the ratio between friction force and normal force, and assumes that both these forces depend linearly on the real contact area between the two sliding surfaces. However, experimental testing of frictional contact models has proven difficult, because few in situ experiments are able to resolve this real contact area. Here, we present a contact detection method with molecular-level sensitivity. We find that while the friction force is proportional to the real contact area, the real contact area does not increase linearly with normal force. Contact simulations show that this is due to both elastic interactions between asperities on the surface and contact plasticity of the asperities. We reproduce the contact area and fine details of the measured contact geometry by including plastic hardening into the simulations. These new insights will pave the way for a quantitative microscopic understanding of contact mechanics and tribology.