3D Tank Research Articles

Numerical Investigation Baffle Position in Rectangular Tank to Reduce Sloshing Interface between Liquid and Gas Phase

Objectives: In this study, sloshing interface in the 2D and 3D tanks were investigated by Open FOAM software Methods/ Statistical Analysis: The obtained results were in good agreement with experimental results. 2D and 3D results that were based on the first natural frequency excitement and ratio of A⁄L<0.1 (stimulation amplitude relative to the length of tank) were very close together. Findings: Rectangular tank with two phase such as gas and liquid was simulated with and without baffle under horizontal excitement in first natural frequency. The torque on the baffle, the height of the liquid in the FS and pressure on the wall of tank for different height of the baffle (installed at the bottom of the tank) were studied. Baffle was mounted in the bottom of the tank, height equal to half the initial height of the liquid. In Previous studies, baffles have been mounted at the liquid part on bottom of tank. In this study, in order to increase efficiency of baffles and reduce the torque exerted on it, baffles were installed in gas part on top wall and only tangent to the surface of liquid in first time. Installing baffles in the roof of tank reduce sloshing, because less torque entered on it in comparison with baffle on bottom of the tank. Application/Improvement: Installed baffles in top of the tank relative to optimum baffle in bottom decreased wave amplitude about 34 percent and exerted torque became half.

Simulation of Sloshing in Rigid Rectangular Tank and a Typical Aircraft Drop Tank

In this research, the liquid sloshing behavior in a 3D rectangular tank was simulated and validated by applying peak acceleration load using computational fluid dynamics technique. The application of this sloshing phenomenon was carried out on a typical Aircraft Drop tank with and without baffle plates for 7 g peak acceleration. The structural integrity of the drop tank has been taken into consideration during the cruise flight condition. Further, an optimized design of a drop tank has been modeled. The comparison of computed results for 3D rectangular tank case with experimental results showed that the numerical technique is capable of simulating hydrostatic pressure loads exerted on tank walls. Similarly, the necessary sloshing loads in the form of hydrodynamic pressure generated on the tank walls have been estimated for different cases of a typical aircraft drop tank. The kinematic profiles of liquids were observed at different instances for various cases. Computational results indicated that there is a reduction in the peak pressure on aft side of the tank with the use of baffle plates.

MO-FG-202-03: Efficient Data Collection of Continuous 2D and Discrete Relative Dosimetric Data for Annual LINAC QA Using TrueBeam Developer Mode and a 1D Scanning Tank

Purpose: To develop a method to exploit real-time dynamic machine and couch parameter control during linear accelerator (LINAC) beam delivery to facilitate efficient performance of TG-142 suggested, Annual LINAC QA tests. Methods: Varian's TrueBeam Developer Mode (Varian Medical Systems, Palo Alto, CA) facilitates control of Varian's TrueBeam LINAC via instructions provided in Extensible Markup Language (XML) files. This allows machine and couch parameters to be varied dynamically, in real-time, during beam delivery. Custom XML files were created to allow for the collection of (1) continuous Tissue Maximum Ratios (TMRs), (2) beam profiles, and (3) continuous output factors using a 1D-scanning tank. TMRs were acquired by orienting an ionization chamber (IC) at isocenter (depth=25cm) and synchronizing a depth scan towards the water surface while lowering the couch at 1mm/s. For beam profiles, the couch was driven laterally and longitudinally while logging IC electrometer readings. Output factors (OFs) where collected by continually varying field sizes (4×4 to 30×30-cm2) at a constant speed of 6.66 mm/s. To validate measurements, comparisons were made to data collected using traditional methods (e.g. 1D or 3D tank). Results: All data collecting using the proposed methods agreed with traditionally collected data (TMRs within 1%, OFs within 0.5% and beam profile agreement within 1% / 1mm) while taking less time to collect (factor of approximately 1/10) and with a finer sample resolution. Conclusion: TrueBeam developer mode facilitates collection of continuous data with the same accuracy as traditionally collected data with a finer resolution in less time. Results demonstrate an order of magnitude increase in sampled resolution and an order of magnitude reduction in collection time compared to traditional acquisition methods (e.g. 3D scanning tank). We are currently extending this approach to perform other TG-142 tasks.

Base Aspect Ratio Effects on Resonant Fluid Sloshing in a Rectangular Tank

A PSME model is used to study the base aspect ratio effect on resonant fluid sloshing in a 3D tank. Three different depth classes (shallow water, intermediate depth and finite depth) and three base aspect ratios (very long base, half width base and square base) are considered. Longitudinal and diagonal excitations are applied to all cases. Results show that sloshing in lower depth tank strongly depends on the base aspect ratio. Keywords: PSME method; Nonlinear sloshing waves; Base aspect ratio effect.

SU‐F‐E‐06: Dosimetric Characterization of Small Photons Beams of a Novel Linear Accelerator

Purpose:The aim of the present contribution was to measure the main dosimetric quantities of small fields produced by UNIQUE and evaluate its matching with the corresponding dosimetric data of one 21EX conventional linear accelerator (Varian) in operation at the same center. The second step was to evaluate comparative performance of the EDGE diode detector and the PinPoint micro‐ionization chamber for dosimetry of small fields.Methods:UNIQUE is configured with MLC (120 leaves with 0.5 cm leaf width) and a single low photon energy of 6 MV. Beam data were measured with scanning EDGE diode detector (volume of 0.019 mm3), a PinPoint micro‐ionization chamber (PTW) and for larger fields (≥ 4×4cm2) a PTW Semi flex chamber (0.125 cm3) was used. The scanning system used was the 3D cylindrical tank manufactured by Sun Nuclear, Inc. The measurement of PDD and profiles were done at 100 cm SSD and 1.5 depth; the relative output factors were measured at 10 cm depth.Results:PDD and the profile data showed less than 1% variation between the two linear accelerators for fields size between 2×2 cm2 and 5×5cm2. Output factor differences was less than 1% for field sizes between 3×3 cm2 and 10×10 cm2 and less of 1.5 % for fields of 1.5×1.5 cm2 and 2×2 cm2 respectively. The dmax value of the EDGE diode detector, measured from the PDD, was 8.347 mm for 0.5×0,5cm2 for UNIQUE. The performance of EDGE diode detector was comparable for all measurements in small fields.Conclusion:UNIQUE linear accelerator show similar dosimetrics characteristics as conventional 21EX Varian linear accelerator for small, medium and large field sizes.EDGE detector show good performance by measuring dosimetrics quantities in small fields typically used in IMRT and radiosurgery treatments.

SU‐F‐T‐162: Comparison of Beam Data for Two Varian ProBeam Pencil Beam Scanning Proton Systems

Purpose:To compare the beam data for proton spot scanning beams for the first two Varian ProBeam sites in the US at the Maryland Proton Treatment Center (MPTC) and Scripps Proton Therapy Center (Scripps). To investigate how well beams can be matched between rooms.Method:Beam data were acquired with independent dosimetry systems and compared for two sites. Integrated depth dose curves (IDDs) were acquired with large volume PTW Bragg peak chambers in a 3D water tank for pencil beams at both sites. Spot profiles were acquired at different distances from the isocenter at a gantry angle of 0 degrees as well as function of gantry angle.Results:IDDs for the two Varian ProBeam proton sites are similar, except in the plateau region were the Scripps data is on average 4.5% higher relative to each other, but only 1.5% relative to the maximum at the Bragg Peak. This increase in the plateau region decrease as energy increase and for energies larger than 180 MeV there is no marked difference. Range in water coincide for all energies within 0.5mm. The sigma of the spot profiles in air are within 10% of each other at isocenter. This difference increase as the detector distance from the isocenter is increased.Conclusion:Beam data of the Varian ProBeam proton spot scanning beams for two sites are very well matched. Differences will not be clinically relevant.

SU-G-TeP1-10: Predicting Photon Percentage Depth Dose From Profile Due to Changes in Beam Quality

Purpose: To predict photon percentage depth dose (PDD) from profile due to a change in flattened (FF) and flattening-filter-free (FFF) beam quality. Methods: 6MV photon beam PDDs and profiles in a 3D water tank (3DW) and profiles in an ionization chamber array (ICP) were collected for different field sizes and depths with FF and FFF beams in a Versa HD (Elekta Ltd.). The energy was adjusted by changing the bending magnet current (BMC) ±15% from the clinical beam (6MV) in 5% increments. For baseline establishment, PDDs(depth≥3cm) were parameterized with bi-exponential functions and the PDD 20 to 10cm ratios (PDD20,10) were calculated. Then, the FF profile at 10cm from the central axis (Pr10) and the slope of the FFF central linear region (SFFF) were calculated. Calibration curves were established: (1) change in Pr10 and SFFF as functions of the change in PDD20,10 and (2) change in PDD(depth=3, 15 and 30cm) as function of the change in PDD20,10. The differences between Pr10 and SFFF from baseline were calculated and, from calibration curves, changes in PDD20,10 and PDD(depth=3, 15 and 30cm) were obtained. Then, absolute PDD(depth=3, 15 and 30cm) values were input into a least-square-optimization algorithm to calculate the bi-exponential function's optimal coefficients and generate the PDD(depths≥3cm). Results: The change in PDD20,10 relative to baseline increased (<±4%) with BMC. Pr10 increased (±6%) and SFFF decreased (±11%) with BMC. Relative differences between measured and calculated (i.e. PDD calculation from Pr10 and SFFF) PDDs were less than 1%. Results apply to FF and FFF beams measured in 3DW and ICP. Conclusion: Pr10 and SFFF are more sensitive than PDD to changes in beam energy and PDD information can be accurately generated from them. With known 3DW and ICP profile relationship, ICP can be used to obtain PDD for current photon beam.

A Sensitivity Dosimetry Study of the Setup Uncertainties during Machine Commissioning and Annual QA

This study is to investigate three common potential setup uncertainties during Linac commissioning and annual QA and to evaluate how these uncertainties propagate into the quality of beam profiles and patient dosimetry using gamma analysis. Three uncertainty scenarios were purposely introduced for gantry position tilted from 0&ring; - 3&ring; (scenario 1), isocenter position misaligned from 0 - 6 mm (scenario 2) and SAD changed from 99.5 - 103 cm (scenario 3). A 60 × 60 × 60 cm3 water phantom cube was created to replicate a 3D water tank in VarianEclipse (V.11) treatment planning system (Varian Medical Systems, Palo Alto, CA). For each scenario, beam data profiles (crossline and diagonal) and PDD curves were calculated at different field sizes and depths for three energies: 6 MV, 6 MV-FFF and 10 MV-FFF. Gamma analysis method was used to compare a total of 263 profiles to baseline using a 1%/1mm parameter with 90% gamma passing rate criteria. For scenario 1, a ≥90% gamma passing rate and ≤1% dose difference were seen on both crossline and diagonal profiles, and PDD curves for gantry tilted up to 2&ring;. For 3&ring; degree tilt, the gamma passing rate decreased to ≤90% at depth of ≥20 cm for 6MV/6MV-FFF and depth of ≥12 cm for 10MV-FFF. For scenario 2, a ≤90% gamma passing rate and ≥1% dose difference were seen at depths from dmax to 20 cm for all energies. For depths ≥20 cm, mostly ≥90% gamma passing rate and ≤1% dose difference were seen. For scenario 3, a ≥90% gamma passing rate and ≤1% dose difference were seen on ≤4 mm isocenter misalignments for all energies. In summary, gamma analysis of the beam profiles is a very sensitive test for SAD deviation scenarios and can reveal issues of sub millimeter setup uncertainty. However, it is not as sensitive for isocenter misalignment scenarios. The test is also more sensitive for FFF beams than flattening filter beams.

Dynamics of vortex evolution in a 2D baffled tank

A finite difference method with coordinate transformation and fictitious cell approach were used to analyze the vortex generation and shedding phenomenon for sloshing liquid in 2D tanks with baffles. The detailed description of the dynamics of vortex evolution for sloshing fluid in a tank with baffles is seldom seen in the literatures and is firstly reported in this study. The exploration of liquid sloshing in a 2D tank with vertically bottom-mounted baffles is demonstrated. The benchmark tests of a tuned liquid damper (TLD) solved by the present numerical scheme show good agreements with the reported results. The experimental measurement is also carried out in this study and the present numerical simulation has excellent accuracy according to the comparison between the computational results and experimental measurement. The evolution of vortices inside a baffled tank in terms of vortex generation, vortex shedding and the trajectories of vortices are analyzed. Four phases of interaction processes of vortices are categorized in this work. The comprehensive discussions include the evolution of vortices and vortex shedding around the baffle tip, the vortex size generated in the vicinity of the baffle tip, the shedding frequency of the vortices, and the interaction of vortices inside the tank with various heights of the baffles and liquid depths. The vortex shedding phenomenon in the vicinity of the baffle tip is tightly correlated with the strength of the vertical jet along the baffle walls and the excitation frequency of the tank. Vortex size is closely correlated with the baffle height. When the baffle height is small (db≤0.2d0), the vortex size mainly grows in the horizontal direction. Instead, the vortex size dominantly develops in the vertical direction as db≥0.3d0. The period of the generation and shedding of vortices near the baffle tip is nearly about one half of the excitation period of the tank. The dynamics of vortex evolution is closely related to the growth and the hydrodynamic interaction of the vortices and sensitively depends on the baffle height, liquid depth, excitation frequency, and excitation displacement of the tank.

Effects of geologic heterogeneity on migration of gaseous CO2 using laboratory and modeling investigations

There is a concern that underground stored CO2 may potentially escape and intrude shallow aquifers that may lead to degradation of the water quality and possible mobilization of metals. Moreover migrating CO2 gas may invade buildings causing lethal conditions for humans. A better understanding of gaseous CO2 migration in heterogeneous aquifer systems at low pressure will help in risk assessment of Carbon Capture and Storage (CCS). We performed complementary 1D column and 2D tank experiments by injecting gaseous CO2 at three different rates into constructed heterogeneous porous media in laboratory setups. Soil moisture sensors were installed in the test systems to monitor the movement of the gaseous phase. The generated experimental data was analyzed using the numerical multiphase modeling code T2VOC. The results confirmed that large-scale heterogeneity controls overall gaseous CO2 migration in porous media while processes occurring at smaller scale are of significance for gas saturations. Monitoring the exact gaseous movement and concentrations is difficult even in a constructed heterogeneous medium and point measurements are not always capturing the full dynamics of the system. The numerical model provided good estimates of the general flow of the gaseous phase around larger heterogeneous features and estimated the total amount of gaseous CO2 in the test system to a good approximation. However, the numerical model was not able to adequately describe the processes occurring at smaller scale including unstable gaseous movement at low flow rates and dissolution of CO2.

Transparent Aquabeads to Model LNAPL Ganglia Migration Through Surfactant Flushing

Light nonaqueous phase liquids (LNAPLs) represent potential long-term sources for continuing groundwater contamination. Their movement in the subsurface is controlled by several complex multiphase conditions because of soil heterogeneity and fluid saturations. The first part of this paper reviews previous experimental studies on LNAPL transport. For developing numerical models and remediation technologies, these studies reproduce the transport parameters, such as density, viscosity, capillary pressure, saturation and residual saturation, and relative permeability found in the subsurface environment. The second part presents 2D tank experiments of LNAPL ganglia migration using transparent synthetic soils. The main contribution of this part is to demonstrate the possibility for the transparent Aquabeads model for better simulation of macroscopic flow properties of natural soils. Transparent synthetic soil can visualize flow problems in the subsurface environment by an optical system and digital image processing. A water-based transparent material called Aquabeads is suitable for modeling flow properties of natural soils. Advantages of Aquabeads over available transparent synthetic soils include such features as their being a water-based material, having similar macroscopic hydraulic characteristics to natural soils, and compatibility with water- and oil-selected surfactants/alcohols used for simulating multiphase flow. Therefore, this transparent material is suitable for visualizing 2D flow and soil-contamination problems. Surfactant-flushing tests were conducted to model LNAPL ganglia transport through a multilayer Aquabeads model. This model visualized the concentration profile and upward migration of motor oil ganglia during surfactant flushing. The results showed the feasibility of surfactant flushing on multilayer soils using the Aquabeads model.

Effect of ullage gas on sloshing, Part I: Global effects of gas–liquid density ratio

Previous analytical, numerical, and experimental studies have proved that properties of ullage gas influence sloshing wave impacts and induced pressures. One of those properties is ullage gas density (ρg), also considered in dimensionless form as gas–liquid density ratio (DR). Previous studies intended to study the effects of DR sometimes mixed DR effects with gas compressibility and ullage gas pressure effects and attributed them only to DR. This study is based on experiments and is meant to focus only on the effects of DR far from impact zones which will be addressed as global effects. Effects of DR near impact zones and before detection of any compressibility effects are addressed as local effects and will be treated in part II. Quantitative and statistical comparisons will be presented in part III.Test setup consisted of two 2D tanks as transverse slices of tank 2 of a membrane LNG carrier with total capacity of 152000 m3 at scales 1:20 and 1:40 at 20% fill level. Using two liquids of water and sodium polytungstate (SPT) and different ullage gases of helium (He), air, two mixtures of sulfur hexafluoride (SF6) and nitrogen (N2), and pure SF6, all at atmospheric pressure, provided a range of DRs from 0.0002 to 0.0060.For the tested range of DR, the global effects of DR on sloshing geometry (free surface) are small when comparing at the same scale or at two different scales. Small discrepancies exist even between two exact repetitions with the same DR at the same scale. Global flow keeps the same phase regardless of tested DRs which implies that all breaking wave impacts take place at the exact same time instants, considering a small time window (usually smaller than 100 ms). This was confirmed by verifying the recorded impact times.Based on this, scaling in sloshing model tests as well as the effect of changing the ullage gas can be investigated impact by impact as opposed to the solely statistical approaches adopted so far. It also helps to track down impacts measured at full-scale (on board the ship) and to further verify whether sloshing model tests are representative for them or not. The stochastic nature of sloshing can be studied more in depth also with the help of high-speed video recordings for corresponding wave impacts. Reevaluations of the current statistical sloshing assessment methodologies can be envisaged.

Effects of the flexibility of the structure on sloshing waves in 3D elastic tanks

The flexible walls of the liquid container will deform under the sloshing loads. The deformation has a significant influence on the hydrodynamic behavior of the sloshing in the tank. A model test is conducted to study the hydro-elastic effect on the sloshing waves in the elastic square tank. The experimental liquid depth h / L is 0.167. The model tanks are exited in 1D harmonic longitudinal motion and the excitation frequency is close to the lowest natural frequency of the liquid. Due to the influence of the fluid-structure interaction, the lowest natural frequency of the liquid in the elastic tank slightly deviates from that in the rigid tank of the same size. The wave shapes and amplitudes in the rigid and elastic square tanks are classified and analyzed under the 1D harmonic longitudinal excitation with different excitation frequencies. Corresponding to the different wave regimes of the two-dimensional traveling waves, transition state, three-dimensional resonance and the secondary resonance, the free surface elevations are compared between the rigid tank and the elastic tank to investigate the effect of fluid-structure interaction.

Time-domain simulation of large-amplitude wave–structure interactions by a 3D numerical tank approach

A time-domain 3D Rankine panel method based on a simplified variant of the mixed Eulerian–Lagrangian scheme under certain approximations is developed for studying steep nonlinear waves interacting with practical ship and offshore configurations at zero speed. Appropriate techniques have been developed that enable the method to produce very long-duration simulation results. Two levels of time-domain computations are performed: (1) a fully linear formulation where all external forces are computed on the mean wetted surface, and (2) an approximate nonlinear computation where the hydrodynamics interaction forces (diffraction and radiation forces) are determined on the mean surface and the forces arising from the incident steep waves and hydrostatic restoring forces are determined based upon the exact wetted surface under the nonlinear incident wave. Numerical computations for three practical marine structures, the barge, the S175 hull, and the semisubmersible are presented. The linear computations for which very long-duration simulations are achievable from the present method are validated against results from other available methods. As the method is developed for stationary floating bodies undergoing oscillation about their mean location, it cannot be applied for a fully unrestrained body which can freely drift. In absence of physical restraints, the approximate nonlinear calculation requires imposition of artificial constraints partially or fully restraining the horizontal motions. Very long-duration simulations under the influence of steep nonlinear large-amplitude waves for all the three structures considered could be achieved. Comparative studies between different force and motion components in large-amplitude waves from linear and the approximate nonlinear computations are made to bring out the influence of the incident wave nonlinearities on these structures. It is found that the nonlinearities of the forces and motions are strongly dependent on the above water hull geometry. Compared to a small water-plane area hull (the semisubmersible), or a wall-sided hull (the barge), a flared hull (S175) results in pronounced nonlinear features in the forces and motion time-histories.

Experimental Study on the Dissipation Characteristics of Curtain-Type Flexible Floating Breakwater

ABSTRACT Wang, H.; Xu, H.; Liu, P.; Duan, J.; Chen, H., and Wang, B., 2015. Experimental study on the dissipation characteristics of curtain-type flexible floating breakwater. This paper presents the wave dissipation efficacy of the new curtain-type flexible floating breakwater (CFFB) with the implementation of 3D tank tests. It evaluates the influence of the presence of the upper plate, the incident wave height, wave period and other factors on the wave dissipation property of CFFB. The main structure of CFFB is united body which consists of wave dissipation blocks and flexible cables. It has been found that this new CFFB has superior characteristics of hydrodynamic and wave attenuation.

Numerical investigation of the influence of texture, surface drip emitter discharge rate and initial soil moisture condition on wetting pattern size

Knowledge of the dimensions of the wetted zone formed under point source surface drip irrigation is essential to the design of cost-effective and efficient irrigation systems. Numerical simulations were carried out with Hydrus-2D/3D to investigate the influence of emitter discharge rates and initial soil moisture conditions on the wetting pattern dimensions of a series of soils with varying textures. Numerical simulations of simple 2D soil tank irrigation experiments were also conducted on two soil types. Based on the simulation results, the parameters of the Schwartzman and Zur model were refined. The results showed a small influence of discharge rates >1 L h−1 on the size of the wetting pattern. The only major difference was observed for the rates lower than 0.5 L h−1, where the largest wetting patterns were observed. Higher initial soil water content caused larger wetting pattern sizes in all directions. When compared to the 2D tank experimental results, Hydrus-2D/3D predicted the wetting pattern dimensions with a relatively small root mean square error not exceeding 2.6 cm. The numerical data obtained for a wide range of textures provided the opportunity to refine the parameters of the Schwartzman and Zur model, which, when compared to experimental data from the literature, provided good estimates of wetting pattern dimensions. This suggests that this simple model, for which the only soil parameter required is the saturated hydraulic conductivity, could provide a valuable and practical tool for irrigation design.

SU‐E‐T‐297: Small Field Dosimetry for Superficial Lesions

Purpose:Kilo‐voltage (kV) photons and low megavoltage (MeV) electrons are the most common options for treating small superficial lesions, but they present complex dosimetry. Using a tertiary lead shield may protect the surrounding critical structures. Our goal was to quantitatively evaluate the dosimetric impact resulting from applying tertiary shields on superficial lesions.Method:We directly compared the beam characteristics of 80 kV (0.8 mm Al) photon setup abutting the water phantom surface and 6 MeV electron setup at 100 cm SSD. Profiles and depth doses were acquired using a 3D scanning water tank and an ion chamber (active volume 0.01 cm^3). Beam profiles were scanned at Dmax. Three lead sheets (2 mm thickness) with 2.7, 2.2, and 1.6, cm diameter circular cutouts were fabricated and placed at the water surface for both photon and electron fields.Results:The penumbra (80% – 20%) of the open 4×4 cm^2 electron insert was 10.7 mm, compared to an average of 7.2 mm with the tertiary cutouts. The penumbra of the open kV photon beam was 2.8 mm compared to an average of 1.8 mm with the tertiary cutouts. For field widths 2.7, 2.2, and 1.6 cm, the flatness of the electron beams was 16%, 17.3%, and 21%, respectively, and for the kV photon beams was 1.4%, 2.3%, 3.3%, respectively. The electron depth dose (PDD) shifted shallower and the photon PDD shifted deeper as the field size became smaller.Conclusion:The penumbra of small electron fields can be improved by adding tertiary lead shields. Both modalities are clinically feasible; however, kV photons still offer sharper penumbra and better flatness than that of 6 MeV electrons with tertiary shielding. Thus, kV photons may still be a superior option for small superficial lesions.

Hydroelastic slamming response in the evolution of a flip-through event during shallow-liquid sloshing

The evolution of a flip-through event [6] upon a vertical, deformable wall during shallow-water sloshing in a 2D tank is analyzed, with specific focus on the role of hydroelasticity. An aluminium plate, whose dimensions are Froude-scaled in order to reproduce the first wet natural frequency associated with the typical structural panel of a Mark III containment system, is used. (Mark III Containment System is a membrane-type tank used in the Liquefied Natural Gas (LNG) carrier to contain the LNG. A typical structural panel is composed by two metallic membranes and two independent thermal insulation layers. The first membrane contains the LNG, the second one ensures redundancy in case of leakage.) Such a system is clamped to a fully rigid vertical wall of the tank at the vertical ends while being kept free on its lateral sides. Hence, in a 2D flow approximation the system can be suitably modelled, as a double-clamped Euler beam, with the Euler beam theory. The hydroelastic effects are assessed by cross-analyzing the experimental data based both on the images recorded by a fast camera, and on the strain measurements along the deformable panel and on the pressure measurements on the rigid wall below the elastic plate. The same experiments are also carried out by substituting the deformable plate with a fully stiff panel. The pressure transducers are mounted at the same positions of the strain gauges used for the deformable plate. The comparison between the results of rigid and elastic case allows to better define the role of hydroelasticity. The analysis has identified three different regimes characterizing the hydroelastic evolution: a quasi-static deformation of the beam (regime I) precedes a strongly hydroelastic behavior (regime II), for which the added mass effects are relevant; finally, the free-vibration phase (regime III) occurs. A hybrid method, combining numerical modelling and experimental data from the tests with fully rigid plate is proposed to examine the hydroelastic effects. Within this approach, the measurements provide the experimental loads acting on the rigid plate, while the numerical solution enables a more detailed analysis, by giving additional information not available from the experimental tests. More in detail, an Euler beam equation is used to model numerically the plate with the added-mass contribution estimated in time. In this way the resulting hybrid method accounts for the variation of the added mass associated with the instantaneous wetted length of the beam, estimated from the experimental images. Moreover, the forcing hydrodynamic load is prescribed by using the experimental pressure distribution measured in the rigid case. The experimental data for the elastic beam are compared with the numerical results of the hybrid model and with those of the standard methods used at the design stage. The comparison against the experimental data shows an overall satisfactory prediction of the hybrid model. The maximum peak pressure predicted by the standard methods agrees with the result of the hybrid model only when the added mass effect is considered. However, the standard methods are not able to properly estimate the temporal evolution of the plate deformation.

規則波中における後ろ曲げダクトブイ型波力発電装置の一次変換性能に関する実験的研究

A primary conversion efficiency of a floating OWC-type wave energy converter Backward Bent Duct Buoy (BBDB) in regular waves is investigated in 2D and 3D wave tank tests. Firstly, the amplitude and phase difference between the internal wave height and motions are investigated. In a 3D tank test, surge, heave and pitch become in-phase at efficiency become maximum. The phase of internal wave height is close to motion. Secondary, the efficiency of duct-extended buoy is investigated in 2D test. Efficiency is reduced because the pitch becomes small by duct extension. Thirdly, the effect of a moment of inertia is investigated. In case of total mass and draft is constant, frequency band of high-efficiency increases as the moment of inertia become large. Fourthly, the effect of the shape of the air chamber is also investigated.

Comparison of Sloshing Pressures in 2D and 3D Tanks

This paper introduces the experimental results of sloshing model tests carried out at Seoul National University. Two 1/50-scale tanks, i.e., 2D and 3D models with the same shape, were manufactured for the comparative study. Particular interest was taken in the differences in impact pressures between the 2D and 3D models. Regular motion tests were conducted for different filling depths. For each filling depth, 500 cycles of regular excitation were imposed at each frequency. To observe the characteristics and severity of sloshing from the acquired pressure data, statistical analyses were performed, not only for the peak pressure, but also for the area-concept indices, which represented the amount of impulse.