Conducting Model Tests Research Articles

Propeller cavitation noise investigations of a research vessel using medium size cavitation tunnel tests and full-scale trials

The rising environmental awareness of various adverse emissions by commercial shipping has recently targeted Underwater Radiated Noise (URN) due to its potential impact on marine mammals. Amongst the various sources on-board a commercial ship, cavitation is the dominating one following its inception. In order to ensure acceptable noise levels for sustainable shipping, accurate prediction of the noise signature is vital. Within this framework, a widely utilized method for full-scale noise prediction is to conduct model tests in cavitation tunnels and to extrapolate to full-scale.The aim of this paper is to provide invaluable URN data of a full-scale vessel and its prediction using cavitation tests from a medium-sized tunnel to evaluate the prediction methodology. Extrapolated URN data based on the tunnel tests was compared with the data obtained from the full-scale trials with The Princess Royal in order to assess the prediction methodology. The comparisons indicate that, whilst the ideal experimental approach is to conduct such involving tests with a full-hull model in large cavitation tunnels, the medium size facilities using dummy-hull models with wake screens, can still provide a very useful means for the URN investigations with a rapid turn around and an economical way of conducting such tests.

Comparative Model Tests of SDP and CFA Pile Groups in Non-Cohesive Soil

Abstract The research topic relates to the subject of deep foundations supported on continuous flight auger (CFA) piles and screw displacement piles (SDP). The authors have decided to conduct model tests of foundations supported on the group of piles mentioned above and also the tests of the same piles working as a single. The tests are ongoing in Geotechnical Laboratory of Gdaňsk University of Technology. The description of test procedure, interpretation and analysis of the preliminary testing series results are presented in the paper.

Identification of mastication organ muscle forces in the biocybernetic perspective.

Purpose of the Paper. This paper is an attempt to mathematically describe the mastication organ muscle functioning, taking into consideration the impact of the central nervous system. Material. To conduct model tests, three types of craniums were prepared: short, normal, and long. The necessary numeric data, required to prepare the final calculation models of different craniofacial types, were used to identify muscle and occlusion forces generated by muscles in the area of incisors and molars. The mandible in model tests was treated as a nondeformable stiff form. Methods. The formal basis for the formulated research problem was reached using the laws and principles of mechanics and control theory. The proposed method treats muscles as “black boxes,” whose properties automatically adapt to the nature of the occlusion load. The identified values of occlusion forces referred to measurements made in clinical conditions. Results. The conducted verification demonstrated a very good consistency of model and clinical tests' results. The proposed method is an alternative approach to the so far applied methods of muscle force identification. Identification of muscle forces without taking into account the impact of the nervous system does not fully reflect the conditions of mastication organ muscle functioning.

Experimental estimate of Nγ values and corresponding settlements for square footings on finite layer of sand

Any structure constructed on the earth is supported by the underlying soil. Foundation is an interfacing element between superstructure and the underlying soil that transmits the loads supported by the foundation including its self weight. Foundation design requires evaluation of safe bearing capacity along with both immediate and long term settlements. Weak and compressible soils are subjected to problems related to bearing capacity and settlement. The conventional method of design of footing requires sufficient safety against failure and the settlement must be kept within the allowable limit. These requirements are dependent on the bearing capacity of soil. Thus, the estimation of load carrying capacity of footing is the most important step in the design of foundation. A number of theoretical approaches, in-situ tests and laboratory model tests are available to find out the bearing capacity of footings. The reliability of any theory can be demonstrated by comparing it with the experimental results. Results from laboratory model tests on square footings resting on sand are presented in this paper. The variation of bearing capacity of sand below a model plate footing of square shape with variation in size, depth and the effect of permissible settlement are evaluated. A steel tank of size <TEX>$900mm{\times}1200mm{\times}1000mm$</TEX> is used for conducting model tests. Bearing capacity factor <TEX>$N_{\gamma}$</TEX> is evaluated and is compared with Terzaghi, Meyerhof, Hansen and Vesic's <TEX>$N_{\gamma}$</TEX> values. From the experimental investigations it is found that, as the depth of sand cushion below the footing (<TEX>$D_{sc}$</TEX>) increases, ultimate bearing capacity and settlement values show an increasing trend up to a certain depth of sand cushion.

Model Tests of Regolith Packaging Mechanism

A robot construction method is developed for burying a lunar outpost. With this method, sandbags are made and piled up on the lunar surface to build a sandbag stack around an outpost and bury it. This method makes it possible to build a lunar base efficiently while minimizing risky manned space operations. In this study, we focused on the “sandbag,” which is the most critical element in a burying mission using a sandbag stacking robot, made a basic design based on soil pressure analysis, and evaluated the validity of design by conducting model tests. We confirmed the validity of the basic design of the sandbag stacking robot from these studies.

An experimental study on the load settlement behavior of a fiber-reinforced sand bed

The ultimate bearing capacity of a strip footing resting on sand reinforced with randomly distributed fibers overlying poorly graded sand has been investigated. In this study, sand was reinforced with 1% randomly distributed synthetic fibers of 6 mm length and the top reinforced layer was separated from bottom unreinforced layer with the help of jute fabric. The effect on pressure-settlement characteristics were plotted for a footing under plain strain conditions resting on sand reinforced up to 0.5 <i>B</i>, 1.0 <i>B</i>, 1.5 <i>B</i> and 2.0 <i>B</i> depths below the base of the footing of width <i>B</i>. Numerical modeling of the results was carried out using a finite element based software GEO STUDIO - SIGMA/W. Pressure-settlement characteristics were studied by conducting model tests on 0.10 m wide footing under plain strain conditions and it was concluded that reinforcing the top layer with 1% randomly distributed fibers increases the bearing capacity and reduces the settlement. Model tests results show that there is up to five times increase in bearing capacity of footing, resting on sand, if the top layer of sand is reinforced up to 1 <i>B</i> depth and up to eight to nine times increase in bearing capacity if top layer is reinforced up to 2 <i>B</i> depths. Experimentally, the values of settlement for virgin soil decrease up to 77% and analytically these decrease up to 69% when soil is reinforced down to a depth of 2 <i>B</i>. For a footing of size of 1 m, resting on the same sand as has been used for model tests; analytical results show an increase in allowable bearing capacity of 2.7 times that of unreinforced sand after reinforcing the top 1m (1 <i>B</i>) soil with randomly distributed fibers.

Tribological performance of thin overlays for journal bearings

This paper describes the analysis of overlay materials used in journal bearings. We conducted model tests using ring-on-disc test configuration and component tests on bearing test rigs. Appropriate test strategies were designed for investigating the running-in, stable operating, emergency running and break-down behaviour. We investigated three different types of overlays: PbSn18Cu2 galvanic, polymeric overlay (PAI matrix with MoS 2-lamellae and graphite), PVD-coated AlSn20Cu-Sputter. Main results are: PbSn18Cu2 improves emergency running conditions. Polymeric overlay shows high need for running-in, where a particle structured surface is formed. AlSn20Cu-Sputter exhibits lowest wear and highest load capacity in component tests, but requires optimum running conditions.

On composite foundation with different vertical reinforcing elements under vertical loading: a physical model testing study

A physical model facility was designed, built, and setup for conducting model tests on a composite foundation in a soil ground. The model tests were carried out on a composite foundation with different combinations of vertical reinforcement elements in the same soil ground. Via the analysis of the collected data the characteristics of the composite foundation with different reinforcing elements were obtained, including the characteristics of load-settlement curves, column stresses, stresses of the inter-column soil, pile-soil stress ratio, and load-sharing ratios of columns and soil. Results from the model tests reveal the mechanism of a composite foundation with different reinforcing elements quantitatively. It is concluded that both a composite foundation with a combination of steel pipe pile and sand column and that with a combination of concrete pile and lime column have a higher bearing capacity than the composite foundation with only sand columns with the same conditions of soil ground and loading. A composite foundation with lime column and sand column embodies no much better performance than that with sand columns only.

Dimensionless Numbers in Phase-Change Thermosyphon and Heat-Pipe Heat Exchangers

Heat pipes and thermosyphons can be very effective heat transport devices for transferring the thermal energy of the Next Generation Nuclear Plant to a hydrogen production plant and/or other process heat applications. These devices operate nearly isothermally, transporting large amounts of thermal energy with little or no temperature drop. A dimensional analysis of the thermosyphon and the heat pipe is presented in this paper. Dimensional analysis is a valuable mathematical technique useful in research work for design and conducting model tests. This analysis yielded two terms - Er and EM - particular to the operation of these devices in addition to those commonly used in many heat transfer applications. The Er term relates the latent heat of vaporization to the pressure drop across the device, while the EM term relates the latent heat of vaporization to the capillary pressure. The significance of these two terms is discussed. The universal nature of these numbers should be useful in increasing the fundamental understanding of both the thermosyphon and the heat pipe.

Discussion of Sharma, R., Chen, Q., Abu-Farsakh, M., and Yoon, S. (2009) “Analytical modeling of geogrid reinforced soil foundation” Geotextiles and Geomembranes, vol. 27, pp. 63–72

The discusser appreciates the authors’ effort in conductingmodel tests and in deriving an analytical model for the bearingcapacity of footings on reinforced soil foundations. The discusseralso acknowledges the authors used the analytical model of Huangand Menq (1997) to interpret their results. The disagreementbetween the values of bearing capacity ratio (BCR) calculated usingHuang and Menq’s model and the test results obtained by theauthorshighlightssomeaspectswhichmighthavebeenignoredbythe authors.(1) The cohesion intercept (c) of the moist soils (sand and siltyclay) used by the authors may account for the generally lowvaluesofBCRobtainedbytheauthors.Ingeneral,experimentalvalues of BCR were lower than 1.5 in author’s study, whileabout 2–2.5 times larger values of experimental BCR werereported by previous studies (Huang and Tatsuoka, 1990;Takemura et al., 1992; Khing et al., 1992) based on similarreinforcing conditions for dry sands. The existence of thecohesion intercept also accounts for the discrepancy betweenthe test results and those calculated using Huang and Menq’smodel which was originally derived for cohessionless (c¼0)soil.(2) The ‘mode 3’ failure mechanism was used to simulate the testresults for silty clay foundations; the ‘mode 4’ failure mecha-nism was used to simulate the test results for sandy founda-tions. This contradicts the principle of mechanics which statesthat the failure is always controlled by the critical mechanism,instead of one based on subjective judgments.(3) Some important parameters were introduced in the authors’analytical model, such as the cohesion intercept (c), elasticmodulus (E

Bearing capacity of square footings on geosynthetic reinforced sand

The results from laboratory model tests and numerical simulations on square footings resting on sand are presented. Bearing capacity of footings on geosynthetic reinforced sand is evaluated and the effect of various reinforcement parameters like the type and tensile strength of geosynthetic material, amount of reinforcement, layout and configuration of geosynthetic layers below the footing on the bearing capacity improvement of the footings is studied through systematic model studies. A steel tank of size 900 × 900 × 600 mm is used for conducting model tests. Four types of grids, namely strong biaxial geogrid, weak biaxial geogrid, uniaxial geogrid and a geonet, each with different tensile strength, are used in the tests. Geosynthetic reinforcement is provided in the form of planar layers, varying the depth of reinforced zone below the footing, number of geosynthetic layers within the reinforced zone and the width of geosynthetic layers in different tests. Influence of all these parameters on the bearing capacity improvement of square footing and its settlement is studied by comparing with the test on unreinforced sand. Results show that the effective depth of reinforcement is twice the width of the footing and optimum spacing of geosynthetic layers is half the width of the footing. It is observed that the layout and configuration of reinforcement play a vital role in bearing capacity improvement rather than the tensile strength of the geosynthetic material. Experimental observations are supported by the findings from numerical analyses.

Factor Structure of PTSD in a Community Sample of Sexual Assault Survivors

ABSTRACT Recent factor analytic research on posttraumatic stress disorder (PTSD) has questioned the 3-factor structure of the diagnosis as codified in the Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM–IV), proposing that a 4-factor model may more accurately reflect the phenomenology of the disorder. Confirmatory factor analyses of the Posttraumatic Stress Diagnostic Scale (E. B. Foa, 1995) were used to conduct model tests of the structure of PTSD in a large sample (N = 967) of adult female sexual assault survivors. A model specifying 4 correlated factors of reexperiencing, effortful avoidance, dysphoria, and hyperarousal provided the best fit to the data, although no model fits were excellent (including that of the traditional DSM–IV 3-factor model). Tests of measurement invariance across race and education suggest that differences may exist in the underlying factor structure of PTSD.

Bulk Models of the Sheared Convective Boundary Layer: Evaluation through Large Eddy Simulations

Abstract A set of first-order model (FOM) equations, describing the sheared convective boundary layer (CBL) evolution, is derived. The model output is compared with predictions of the zero-order bulk model (ZOM) for the same CBL type. Large eddy simulation (LES) data are employed to test both models. The results show an advantage of the FOM over the ZOM in the prediction of entrainment, but in many CBL cases, the predictions by the two models are fairly close. Despite its relative simplicity, the ZOM is able to quantify the effects of shear production and dissipation in an integral sense—as long as the constants describing the integral dissipation of shear- and buoyancy-produced turbulence kinetic energy (TKE) are prescribed appropriately and the shear is weak enough that the denominator of the ZOM entrainment equation does not approach zero, causing a numerical instability in the solutions. Overall, the FOM better predicts the entrainment rate due to its ability to avoid this instability. Also, the FOM in a more physically consistent manner reproduces the sheared CBL entrainment zone, whose depth is controlled by a balance among shear generation, buoyancy consumption, and dissipation of TKE. Such balance is manifested by nearly constant values of Richardson numbers observed in the entrainment zone of simulated sheared CBLs. Conducted model tests support the conclusion that the surface shear generation of TKE and its corresponding dissipation, as well as the nonstationary terms, can be omitted from the integral TKE balance equation.

Experimental investigation of a fast monohull in forced harmonic motions

The paper presents the results of an experimental investigation of added masses and damping coefficients of a model of a fast monohull. A model of 4.5 m length between perpendiculars was constructed of fiber glass reinforced plastic (FRP) with four segments connected by a backbone. The backbone was instrumented with load cells at the positions of the cuts. This configuration, combined with load cells measuring the force exerted by the forced motion actuators, made it possible to obtain the hydrodynamic coefficients for each of the four hull segments. The investigation focused on the vertical motions. Thus, the experimental program included forced harmonic heave and pitch motions in calm water (no incident waves). Subtracting inertial and restoring forces from total measured forces, one obtained the hydrodynamic component, which then resulted in the hydrodynamic coefficients. The effects of steady forward speed on the radiation forces were investigated by conducting model tests at four forward speeds. Finally, nonlinear effects were assessed by conducting model tests for three amplitudes of forced heave and forced pitch motions.

Dynamics of contained liquids: A personal odyssey

Dynamics of contained liquids: A personal odyssey

On the flexural strength of DUT-1 synthetic model ice

Based on the statistical values of Bohai ice physical and mechanical parameters—such as density, compressive strength, flexural strength, shear strength, elastic modulus and friction coefficient—an ideal synthetic model ice was designed following the scale of 1:10–1:30. A model ice prescription and making art were found and called DUT-1 Ice. In order to know the flexural strength of DUT-1 Ice in detail, two stages of experiment were arranged. During the first stage, over 500 samples for a series of systematic tests were done. It is found that ductile bending occurs below 350–400 kPa/s in three-point bend test and 60–65 kPa/s in cantilever bend test. Their corresponding failure time are in the range of 0.03–0.38 s and 0.5–0.76 s, respectively, which is in the range of flexural failure time of simulated natural ice. Comparison of flexural strength of downward and upward loading cantilever tests gives the affirmation of isotropy of the model ice because of its granular structure. After 1 h wetting, the peak flexural strength of three-point specimens becomes steady and maintains this state for more than 4 h. This period gives us enough time to conduct model tests of ice behaviors or ice interactions with structures. In the second stage, another 500 specimens was tested. The effects of cement content and curing period were obtained, and the selection method of suitable peak flexural strength for different ices and test scale can be done based on the effects. Similar with natural ice, DUT-1 Ice flexural strength increases with increased wetted density. The ratio of elastic modulus and flexural strength over 2000 indicated that DUT-1 Ice is capable of physical simulations of ice bending failures with inclined structures, with waves, ice pile-up and ice jam processes.

ELASTIC BUCKLING OF EXTERNALLY-PRESSURIZED IMPERFECT TOROIDAL SHELLS

This paper summarizes the results of numerical studies into the effects of initial geometric imperfections on the elastic buckling behaviour of steel circular and elliptic toroidal shells subjected to follower-type external pressure. The types of initial imperfection studied are (a) axisymmetric localized ones and (b) sinusoidal buckling modes. The principal localized imperfections studied are (i) circular increased-radius "flat spots" and (ii) smooth dimples. The buckling pressures pcr of circular toroidal shells were not very sensitive to initial imperfections. With elliptic toroids, whether the shell was sensitive to initial imperfections or not depended on the ratio k(≡ a/b) of major to minor radii of the section. The shells on the ascending part of the pcr versus k curve behaved like circular toroidal shells, i.e. they were not sensitive to initial imperfections. However, the behaviour of elliptic toroids on the descending part of the versus k curve was very different. The numerical results quoted in the paper are for limited ranges of the geometric parameters. It would be useful to extend these ranges, to explore the effects of plasticity and to conduct model tests on imperfect steel models to verify the conclusions of the numerical studies.

Rotorcraft Aeroelastic Testing in the Langley Transonic Dynamics Tunnel

Wind-tunnel testing of a properly scaled aeroelastic model helicopter rotor is considered a necessary phase in the design and development of new rotor systems. For this reason, extensive testing of aeroelastically scaled model rotors is done in the Transonic Dynamics Tunnel (TDT) located at the Langley Research Center. A unique capability of this facility, which enables proper dynamic scaling, is the use of diflourodichloromethane, or Refrigerant-12 (R-12) as a test medium. The paper presents a description of the TDT and a discussion of the benefits of using R-12 as a test medium. A description of the system used to conduct model tests is provided and examples of recent rotor tests are cited to illustrate the types of aeroelastic model rotor tests conducted in the TDT.

Model Testing in Multidirectional Waves

Capabilities for generating waves in model basins have advanced from unidirectional regular waves to unidirectional random waves and recently in several facilities to multidirectional regular and random waves. The history of this development is reviewed briefly. The motivation for conducting model tests in multidirectional waves is discussed along with some sample applications. The principle for generating multidirectional waves is outlined and the facilities for performing this function at Offshore Technology Corporation are described.

Model-Prototype Comparision of Free Surface Vortices

A Comparison between model and prototype observations of vortex intensity is used to investigate potential scale effects of modeling free surface vortices. Due to the inherent difficulty with field observations, a reasonably large number of such comparisons are needed prior to reaching conclusions. To this end, a survey of available model-prototype data is made and presented in summary form for a variety of intake types. Based on this comparison summary, and referring to previously published research on this subject, some scale effects may exist when modeling air core vortices, and some increase in model flow may compensate for such effects. Little or no scale effect is evident for weak vortices or dimples. Recommendations are made for conducting model tests.