66 research outputs found
Repeatability and Two-Dimensionality of Model Scale Sloshing Impacts
No full textCanonical test cases for sloshing wave impact problems are pre-sented and discussed. In these cases the experimental setup has been simpli?ed seeking the highest feasible repeatability; a rectangular tank subjected to harmonic roll motion has been the tested con?guration. Both lateral and roof impacts have been studied, since both cases are relevant in sloshing assessment and show speci?c dynamics. An analysis of the impact pressure of the ?rst four impact events is provided in all cases. It has been found that not in all cases a Gaussian ?tting of each individual peak is feasible. The tests have been conducted with both water and oil in order to obtain high and moderate Reynolds number data; the latter may be useful as simpler test cases to assess the capabilities of CFD codes in simulating sloshing impacts. The re-peatability of impact pressure values increases dramatically when using oil. In addition, a study of the two-dimensionality of the problem using a tank con?guration that can be adjusted to 4 di?erent thicknesses has been carried out. Though the kinemat-ics of the free surface does not change signi cantly in some of the cases, the impact pressure values of the ?rst impact events changes substantially from the small to the large aspect ratios thus meaning that attention has to be paid to this issue when reference data is used for validation of 2D and 3D CFD codes
Experimental sloshing pressure impacts in ensemble domain: Transient and stationary statistical characteristics
No full textThe present paper focuses on the analysis of impact pressure registrations from repeated model scale sloshing experiments under harmonic rotational excitation. A series of more than 100 experiments, each one encompassing more than 100 impact events, has been conducted seeking the highest feasible repeatability. Different excitation periods, that cover the main features of the impact dynamics, have been considered in a preliminary screening, describing the main features of the impact dynamics. Since, even under a nominally deterministic excitation, the pressure at each impact is characterized by a high variability, a statistical approach is used treating the impact pressure as a stochastic process. For one selected excitation period, the statistical analysis focuses on the ensemble distribution of the maximum pressure during each impact event. Particular attention is given to the evolution of such distributions, in order to detect the variations in the statistical characteristics of the process. This is achieved by, first, identifying the presence and the length of the transient phase and, second, by characterizing the process at stationary state. The statistics of impact pressure for different peaks are discussed mostly in the ensemble domain. Linking the latter with the time domain analysis is made by checking that the problem can be considered “practically ergodic.” The “practical ergodicity” of the process is dealt with by checking to what extent steady state ensemble statistical information can be obtained from a single long run experiment. Statistical checks for correlation and independence of maximum impact pressures are also carried out to test the hypothesis of independent identically distributed random variables. The method of analysis presented in this paper through the considered example case is general in nature and is considered to be highly portable. In particular, it is considered to allow for a more thorough understanding of non-deterministic events such as those considered herein, by looking at them from a sound statistical perspective. The thorough description of the whole experimental setup makes the presented data suitable for comparison purposes and for validation of theoretical/numerical approaches
Smoothed particle hydrodynamics (SPH) simulation of a tuned liquid damper(TLD) with angular motion.
No full textThe roll motion response of a single degree of freedom (SDOF) structural system to which a rigid rectangular partially filled liquid tank has been attached is considered. The SDOF structural system with the empty tank is first described with a mathematical model and this model is validated by performing decay experiments as well as experiments in which periodic excitations are applied to the system. The responses are accurately predicted by the model. The accuracy of these predictions allows us to study both experimentally and numerically, with weakly compressible SPH, the performance of the partially filled tank as a tuned liquid damper (TLD). The sloshing flows inside the tank comprise the onset of breaking waves which make the TLDs devices extremely difficult to model, especially for the potential flow multimodal approaches commonly used to simulate these sorts of coupled systems. In order to characterise the wave breaking effects on the response curves, tests have been performed with liquids of different viscosity, the increasing viscosity preventing the onset of breaking waves. The capabilities of SPH to treat this coupling problem are assessed and the results show that SPH is able to capture a substantial part of the physics involved in the addressed phenomena but further work remains still to be done relating to a more accurate treatment of the laminar viscosity and turbulence effects
A set of canonical problems in sloshing. Part 2: Influence of tank width on impact pressure statistics in regular forced angular motion
No full textContinuing along the path of previous papers in this series, the present paper addresses, experimentally, sloshing in a rectangular tank under harmonic angular forcing. Since lateral and roof impacts are relevant in sloshing assessment and present distinct dynamics, these have been studied. Water and oil have been used in order to obtain data for high and moderate Reynolds numbers. With the aim of addressing effects induced by the three-dimensionality of the flow, a study of the influence of the tank width on pressure statistics has also been conducted. For this purpose, a tank which can be adjusted to 4 different widths by replacing the side plates was built. For each combination of fluid, tank width and filling level, a total of 120 experiments, each comprising 120 peaks, have been conducted, allowing an analysis in time and ensemble domains to be performed. Impact pressure statistics are presented including mean values, percentiles, and exceedance probability graphs
Three SPH Novel Benchmark Test Cases for free surface flows
No full textAbstract—Benchmark Test Cases have been used by SPHERIC interest group members for the validation of SPH models and their corresponding computer implementations. Since the use of SPHERIC benchmark test cases as validation reference for SPH implementations has slightly declined in the most recent editions,
we think it might be interesting to document three novel test cases with the aim of enriching the database with complementary validation data. The first proposed test case is a wave impact problem in a rectangular tank. The time history of the motion
of the tank and the pressure of the first instances of lateral and roof impacts for both water and oil are provided. An analysis of the two-dimensionality and repeatability of the pressure peaks is provided. The second proposed test case treats the coupling
of the angular motion of a sloshing tank and a single degree of freedom structural system. Finally, the third proposed test case, is a canonical fluid structure interaction problem consisting in the interaction between a free surface sloshing flow and an elastic body. As both SPH practitioners and experimentalists, regardless of the discussion provided in this paper, we are committed to improving these test cases for future use. We hope to increase our experimental skills and capabilities not only in light of experience from our own simulations but mainly by receiving a feedback
from the SPH community
Strategies for avoiding preference profiling in agent-based e-commerce environments
No full textAgent-based electronic commerce is known to offer many advantages to users. However, very few studies have been devoted to deal with privacy issues in this domain. Nowadays, privacy is of great concern and preserving users' privacy plays a crucial role to promote their trust in agent-based technologies. In this paper, we focus on preference profiling, which is a well-known threat to users' privacy. Specifically, we review strategies for customers' agents to prevent seller agents from obtaining accurate preference proles of the former group by using data mining techniques. We experimentally show the efficacy of each of these strategies and discuss their suitability in different situations. Our experimental results show that customers can improve their privacy notably with these strategies
Hydrodynamic coefficients from forced and decay heave motion tests of a scaled model of a column of a floating wind turbine equipped with a heave plate
No full textThis paper describes the results of an experimental campaign aimed at the determination of heave hydrodynamic coefficients for a column of a floating wind turbine platform, equipped with a solid heave plate. The tests are carried out with an experimental system that allows performing both heave forced oscillation tests and heave decay tests. A specific characteristic of the system is the reduced mechanical friction, thanks to the use of air bushings. A series of forced oscillation and decay experiments have been carried out with such a model, and the hydrodynamic coefficients obtained in both types of tests are compared. Results show correlation between both methods if the mean of the peaks of the decay process is chosen to represent its Keulegan–Carpenter number (KC), with a fair matching of the results in the KC range where both methods are applicable. With the objective of conducting an uncertainty assessment which can be relevant for the full-scale extrapolation of results, non-dimensional added mass and damping coefficients are proposed. They incorporate the primitive relevant variables and are shown to lead to a notable collapse of the various results in the form of curves with small differences among them. With these coefficients, an uncertainty assessment is carried out, propagating to those coefficients the uncertainties of the primitive variables in place. Such non-dimensional coefficients are useful to develop simple models to estimate the dimensional ones to be used in numerical simulations of the full scale system. The estimated uncertainties can serve to define design safety margins for the values of such coefficients
Repeatability and Practical Ergodicity of 2D Sloshing Experiments
No full textThe present paper focuses on the statistical analysis of impact pressure peaks registers in 2-D harmonic motion model scale sloshing experiments. A series of 100 experiments each comprising about 100 impact events has been conducted, seeking the highest feasible repeatability. The statistical analysis focuses on the ensemble distribution of the maximum pressure during these impact events. Particular attention is given to the time domain evolution of such distributions, in order to separate stochastic transient from stochastic steady state. Statistical characteristics of impact pressure for different peaks are discussed in the ensemble domain. Particular attention is given to the connection between the characteristics of the ensemble distribution of impact pressure and the process of CFD validation. Finally, the (practical) ergodicity of the process is dealt with by checking to what extent steady state ensemble statistical information can be obtained from a single long run experiment
A combined Experimental and SPH Approach to Sloshing and Ship Roll Motions
No full textPassive anti-roll tanks have been used for a long time in ships to damp their roll motion. The coupled roll motion response of a single degree of freedom (SDOF) system to which a passive anti-roll tank has been attached is considered in the present paper. The performance of the anti-roll tank has been studied both experimentally and numerically, with weakly compressible SPH. The sloshing flows inside the tank comprise the onset of breaking waves. In order to characterise the wave breaking effects on the response curves, tests have been performed with liquids of different viscosity, the increasing viscosity preventing the onset of breaking waves. The capabilities of SPH to treat this coupling problem are assessed and the results show that SPH is able to capture a part of the physics involved in the addressed phenomena but further work remains still to be done
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