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A N Timokha - One of the best experts on this subject based on the ideXlab platform.

  • analytical modeling of liquid sloshing in a two dimensional Rectangular Tank with a slat screen
    Journal of Engineering Mathematics, 2011
    Co-Authors: Odd M Faltinsen, Reza Firoozkoohi, A N Timokha
    Abstract:

    Potential-flow theory is employed with linear free-surface conditions, multimodal method, and a screen-averaged pressure-drop condition to derive an analytical modal model describing the two-dimensional resonant liquid motions in a Rectangular Tank with a vertical slat-type screen in the Tank middle. The Tank is horizontally excited in a frequency range covering the two lowest natural sloshing frequencies. The model consists of a system of linear ordinary differential [modal] equations responsible for liquid sloshing in compartments, as well as a nonlinear ordinary differential equation describing the liquid flow between the compartments. New experimental model tests on steady-state wave elevations near the Tank wall are reported for the solidity ratios 0.328 ≤ Sn ≤ 0.963 where Sn is the ratio between the solid area and the full area of the screen. The experiments generally support the applicability of the model. The discrepancy can be explained by the free-surface nonlinearity. The screen acts as a damping mechanism for low and intermediate solidity ratios, but it causes an increase in the lowest resonant sloshing frequency at higher solidity ratios as if the screen had been replaced by an unperforated wall.

  • effect of central slotted screen with a high solidity ratio on the secondary resonance phenomenon for liquid sloshing in a Rectangular Tank
    Physics of Fluids, 2011
    Co-Authors: Odd M Faltinsen, Reza Firoozkoohi, A N Timokha
    Abstract:

    Mounting a screen with a high solidity ratio (0.5 ≲ Sn < 1) at the center of a Rectangular Tank qualitatively changes the secondary resonance phenomenon for liquid sloshing. In contrast to the clean Tank, the steady-state sloshing due to lateral excitation is then characterized by multi-peak response curves in a neighborhood of the primary resonance frequency. The present paper revises the adaptive nonlinear multimodal method to study the secondary resonance phenomenon for the screen-affected resonant sloshing with a finite liquid depth and, thereby, clarify earlier experimental results of the authors.

  • steady state liquid sloshing in a Rectangular Tank with a slat type screen in the middle quasilinear modal analysis and experiments
    Physics of Fluids, 2011
    Co-Authors: Odd M Faltinsen, Reza Firoozkoohi, A N Timokha
    Abstract:

    Two-dimensional resonant liquid sloshing in a Rectangular Tank equipped with a central slat-type screen is studied theoretically and experimentally with focus on nonsmall solidity ratios of the screen (0.5≲Sn≲0.95), nonlarge number of slots (N≲50), and steady-state conditions. The Tank is horizontally and harmonically excited with frequencies in a range covering the two lowest primary-excited natural sloshing resonance frequencies in the corresponding clean Tank. The liquid depth is finite. Theoretical analysis is based on the multimodal method with linear free-surface conditions and a quadratic pressure drop condition at the screen expressing an “integral” effect of the screen-induced cross-flow separation (or jet flow). New experimental data on the maximum wave elevations at the wall are compared with the theoretical predictions. Very good agreement is shown for the smallest forcing amplitudes (the forcing amplitude-to-Tank width ratio is ≈0.001). Increasing the nondimensional forcing amplitude to ≈0.01...

  • natural sloshing frequencies and modes in a Rectangular Tank with a slat type screen
    Journal of Sound and Vibration, 2011
    Co-Authors: Odd M Faltinsen, A N Timokha
    Abstract:

    Being installed in Tanks, screens play the role of slosh-suppressing devices which may strongly change resonant sloshing frequencies and yield an extra nonlinear damping due to cross-flow resulting in either flow separation or jet flow. Employing the linear sloshing theory and domain decomposition method, we construct an accurate analytical approximation of the natural sloshing modes in a Rectangular Tank with a slat-type screen at the Tank middle. Two-dimensional irrotational flow of an ideal incompressible liquid is assumed. Because the considered flow model does not account for flow separation and jet flow at the screen, the velocity field is locally singular at the sharp edges. The constructed solution captures this singularity. Analyzing this solution establishes a complex dependence of the natural sloshing frequencies on the solidity ratio, the number of submerged screen gaps, the liquid depth, and the position of perforated openings relative to the mean free surface. Results are compared with experimental data. Natural surface wave profiles are discussed in the context of a jump of the velocity potential at the screen and the local inflow component to the screen.

  • modal modelling of the nonlinear resonant fluid sloshing in a Rectangular Tank ii secondary resonance
    Mathematical Models and Methods in Applied Sciences, 2008
    Co-Authors: Martin Hermann, A N Timokha
    Abstract:

    In Part I of this work [Math. Mod. Meth. Appl. Sci.15 (2005) 1431–1458], we studied periodic (steady-state) solutions of an asymptotic nonlinear modal system which describes two-dimensional resonant sloshing in a Rectangular Tank. The system was derived by Faltinsen et al. (2000) under the assumption that the primary excited (lowest) natural mode gives the largest contribution to the wave patterns. We found that this assumption is not true in a certain frequency domain due to internal (secondary) resonance leading to an amplification of the second mode. This frequency domain can also be identified for the critical depth-to-breath ratio h = 0.3368 … which was discussed in Part I. In Part II, this secondary resonance is modelled by a double-dominant modal system by Faltinsen and Timokha (2001). A comparative analysis with the results from Part I is presented. The emphasis is placed on the case of the mentioned critical ratio when a double turning point arises in the branching diagram. The appearance of the double turning point explains why classical laboratory experiments by Fultz (1962) underestimate the value of the critical depth.

Odd M Faltinsen - One of the best experts on this subject based on the ideXlab platform.

  • analytical modeling of liquid sloshing in a two dimensional Rectangular Tank with a slat screen
    Journal of Engineering Mathematics, 2011
    Co-Authors: Odd M Faltinsen, Reza Firoozkoohi, A N Timokha
    Abstract:

    Potential-flow theory is employed with linear free-surface conditions, multimodal method, and a screen-averaged pressure-drop condition to derive an analytical modal model describing the two-dimensional resonant liquid motions in a Rectangular Tank with a vertical slat-type screen in the Tank middle. The Tank is horizontally excited in a frequency range covering the two lowest natural sloshing frequencies. The model consists of a system of linear ordinary differential [modal] equations responsible for liquid sloshing in compartments, as well as a nonlinear ordinary differential equation describing the liquid flow between the compartments. New experimental model tests on steady-state wave elevations near the Tank wall are reported for the solidity ratios 0.328 ≤ Sn ≤ 0.963 where Sn is the ratio between the solid area and the full area of the screen. The experiments generally support the applicability of the model. The discrepancy can be explained by the free-surface nonlinearity. The screen acts as a damping mechanism for low and intermediate solidity ratios, but it causes an increase in the lowest resonant sloshing frequency at higher solidity ratios as if the screen had been replaced by an unperforated wall.

  • effect of central slotted screen with a high solidity ratio on the secondary resonance phenomenon for liquid sloshing in a Rectangular Tank
    Physics of Fluids, 2011
    Co-Authors: Odd M Faltinsen, Reza Firoozkoohi, A N Timokha
    Abstract:

    Mounting a screen with a high solidity ratio (0.5 ≲ Sn < 1) at the center of a Rectangular Tank qualitatively changes the secondary resonance phenomenon for liquid sloshing. In contrast to the clean Tank, the steady-state sloshing due to lateral excitation is then characterized by multi-peak response curves in a neighborhood of the primary resonance frequency. The present paper revises the adaptive nonlinear multimodal method to study the secondary resonance phenomenon for the screen-affected resonant sloshing with a finite liquid depth and, thereby, clarify earlier experimental results of the authors.

  • steady state liquid sloshing in a Rectangular Tank with a slat type screen in the middle quasilinear modal analysis and experiments
    Physics of Fluids, 2011
    Co-Authors: Odd M Faltinsen, Reza Firoozkoohi, A N Timokha
    Abstract:

    Two-dimensional resonant liquid sloshing in a Rectangular Tank equipped with a central slat-type screen is studied theoretically and experimentally with focus on nonsmall solidity ratios of the screen (0.5≲Sn≲0.95), nonlarge number of slots (N≲50), and steady-state conditions. The Tank is horizontally and harmonically excited with frequencies in a range covering the two lowest primary-excited natural sloshing resonance frequencies in the corresponding clean Tank. The liquid depth is finite. Theoretical analysis is based on the multimodal method with linear free-surface conditions and a quadratic pressure drop condition at the screen expressing an “integral” effect of the screen-induced cross-flow separation (or jet flow). New experimental data on the maximum wave elevations at the wall are compared with the theoretical predictions. Very good agreement is shown for the smallest forcing amplitudes (the forcing amplitude-to-Tank width ratio is ≈0.001). Increasing the nondimensional forcing amplitude to ≈0.01...

  • natural sloshing frequencies and modes in a Rectangular Tank with a slat type screen
    Journal of Sound and Vibration, 2011
    Co-Authors: Odd M Faltinsen, A N Timokha
    Abstract:

    Being installed in Tanks, screens play the role of slosh-suppressing devices which may strongly change resonant sloshing frequencies and yield an extra nonlinear damping due to cross-flow resulting in either flow separation or jet flow. Employing the linear sloshing theory and domain decomposition method, we construct an accurate analytical approximation of the natural sloshing modes in a Rectangular Tank with a slat-type screen at the Tank middle. Two-dimensional irrotational flow of an ideal incompressible liquid is assumed. Because the considered flow model does not account for flow separation and jet flow at the screen, the velocity field is locally singular at the sharp edges. The constructed solution captures this singularity. Analyzing this solution establishes a complex dependence of the natural sloshing frequencies on the solidity ratio, the number of submerged screen gaps, the liquid depth, and the position of perforated openings relative to the mean free surface. Results are compared with experimental data. Natural surface wave profiles are discussed in the context of a jump of the velocity potential at the screen and the local inflow component to the screen.

  • an adaptive multimodal approach to nonlinear sloshing in a Rectangular Tank
    Journal of Fluid Mechanics, 2001
    Co-Authors: Odd M Faltinsen, A N Timokha
    Abstract:

    Two-dimensional nonlinear sloshing of an incompressible fluid with irrotational flow in a Rectangular Tank is analysed by a modal theory. Innite Tank roof height and no overturning waves are assumed. The modal theory is based on an innite-dimensional system of nonlinear ordinary dierential equations coupling generalized coordinates of the free surface and fluid motion associated with the amplitude response of natural modes. This modal system is asymptotically reduced to an innite-dimensional system of ordinary dierential equations with fth-order polynomial nonlinearity by assuming suciently small fluid motion relative to fluid depth and Tank breadth. When introducing inter-modal ordering, the system can be detuned and truncated to describe resonant sloshing in dierent domains of the excitation period. Resonant sloshing due to surge and pitch sinusoidal excitation of the primary mode is considered. By assuming that each mode has only one main harmonic an adaptive procedure is proposed to describe direct and secondary resonant responses when Moiseyev-like relations do not agree with experiments, i.e. when the excitation amplitude is not very small, and the fluid depth is close to the critical depth or small. Adaptive procedures have been established for a wide range of excitation periods as long as the mean fluid depth h is larger than 0.24 times the Tank breadth l. Steady-state results for wave elevation, horizontal force and pitch moment are experimentally validated except when heavy roof impact occurs. The analysis of small depth requires that many modes have primary order and that each mode may have more than one main harmonic. This is illustrated by an example for h=l =0 :173, where the previous model by Faltinsen et al. (2000) failed. The new model agrees well with experiments.

Il-hyoung Cho - One of the best experts on this subject based on the ideXlab platform.

  • Anti-sloshing effects of a vertical porous baffle in a rolling Rectangular Tank
    Ocean Engineering, 2020
    Co-Authors: Arun George, Il-hyoung Cho
    Abstract:

    Abstract The anti-sloshing effects of a vertical porous baffle placed at the center of a rolling Rectangular Tank have been investigated rigorously. The potential-based analytical solutions were developed using the matched eigenfunction expansion method (MEEM) with an equivalent linearized quadratic loss model. For this, the empirical formula of the drag coefficient was obtained through the curve-fitting with the CFD results for the channel flow with a circular void hole. In parallel with the analytical model, a 3D implicit turbulent model based on incompressible unsteady Reynolds-averaged Navier–Stokes (RANS) equations was used with the volume of fluid (VOF) multiphase model. To validate the analytical and numerical model, experiments were conducted in a rolling Rectangular Tank with a fully/partially submerged porous baffle of different porosities. The acceptability and limitation of the present analytical model was quantified and qualified using experimental and numerical approach. The presented analytical and 3D turbulent numerical model will provide a mutually complementary tool for the understanding of the energy dissipation mechanism and efficient design of the porous baffle as an anti-sloshing device.

  • liquid sloshing in a Rectangular Tank with vertical slotted porous screen based on analytical numerical and experimental approach
    Ocean Engineering, 2019
    Co-Authors: Sunny Kumar Poguluri, Il-hyoung Cho
    Abstract:

    Abstract The performance of a porous screen placed in the center of a Rectangular Tank has been investigated based on an analytical, numerical, and experimental approach for the lateral excitation of the Tank. The two-dimensional potential model was solved analytically with the Galerkin method by adding the frictional damping coefficient at the free surface condition and considering the energy dissipation across the porous screen. The comparison of the analytical solution with the experimental results shows a good agreement for the frictional damping coefficient of 0.3. The main physical parameters are the surface elevation, pressure at the Tank walls, including hydrodynamic forces on the wall, and the horizontal load on the porous screen for different submergence depths and porosities that were investigated. The presence of screen shifts the sloshing Tank natural periods slightly, especially in the lowest mode. The unrevealed phenomena accompanied with linear potential theory, the nonlinear wave profile and screen associated effects were also investigated based on an experimental and numerical method. The results show that the numerical prediction with STAR-CCM+ was in good agreement with the experimental results up to second-harmonics. It was found that the porous slotted screen can be an effective device for the suppression of sloshing motion if properly designed.

  • Effect of dual vertical porous baffles on sloshing reduction in a swaying Rectangular Tank
    Ocean Engineering, 2016
    Co-Authors: Il-hyoung Cho, Moo-hyun Kim
    Abstract:

    Abstract Liquid sloshing inside Tanks of a vessel may result in increased/decreased vessel motions or structural damages. The resonant sloshing motions can be suppressed by using baffles inside a Tank. Especially, more energy dissipation is possible by using porous baffles. Here, the effect of dual vertical porous baffles on the sloshing reduction inside a Rectangular Tank is investigated both theoretically and experimentally. The matched eigenfunction expansion method is applied to obtain the analytic solutions in the context of linear potential theory with porous boundary conditions. The porosity effect is included through inertial and quadratic-drag terms. The theoretical prediction is then compared with a series of experiments conducted by authors with harmonically oscillated Rectangular Tank at various frequencies and baffle parameters. The measured data reasonably correlate with the predicted values. It is found that the dual vertical porous baffles can significantly suppress sloshing motions when properly designed by selecting optimal porosity, submergence depth, and installation position.

Reza Firoozkoohi - One of the best experts on this subject based on the ideXlab platform.

  • analytical modeling of liquid sloshing in a two dimensional Rectangular Tank with a slat screen
    Journal of Engineering Mathematics, 2011
    Co-Authors: Odd M Faltinsen, Reza Firoozkoohi, A N Timokha
    Abstract:

    Potential-flow theory is employed with linear free-surface conditions, multimodal method, and a screen-averaged pressure-drop condition to derive an analytical modal model describing the two-dimensional resonant liquid motions in a Rectangular Tank with a vertical slat-type screen in the Tank middle. The Tank is horizontally excited in a frequency range covering the two lowest natural sloshing frequencies. The model consists of a system of linear ordinary differential [modal] equations responsible for liquid sloshing in compartments, as well as a nonlinear ordinary differential equation describing the liquid flow between the compartments. New experimental model tests on steady-state wave elevations near the Tank wall are reported for the solidity ratios 0.328 ≤ Sn ≤ 0.963 where Sn is the ratio between the solid area and the full area of the screen. The experiments generally support the applicability of the model. The discrepancy can be explained by the free-surface nonlinearity. The screen acts as a damping mechanism for low and intermediate solidity ratios, but it causes an increase in the lowest resonant sloshing frequency at higher solidity ratios as if the screen had been replaced by an unperforated wall.

  • effect of central slotted screen with a high solidity ratio on the secondary resonance phenomenon for liquid sloshing in a Rectangular Tank
    Physics of Fluids, 2011
    Co-Authors: Odd M Faltinsen, Reza Firoozkoohi, A N Timokha
    Abstract:

    Mounting a screen with a high solidity ratio (0.5 ≲ Sn < 1) at the center of a Rectangular Tank qualitatively changes the secondary resonance phenomenon for liquid sloshing. In contrast to the clean Tank, the steady-state sloshing due to lateral excitation is then characterized by multi-peak response curves in a neighborhood of the primary resonance frequency. The present paper revises the adaptive nonlinear multimodal method to study the secondary resonance phenomenon for the screen-affected resonant sloshing with a finite liquid depth and, thereby, clarify earlier experimental results of the authors.

  • steady state liquid sloshing in a Rectangular Tank with a slat type screen in the middle quasilinear modal analysis and experiments
    Physics of Fluids, 2011
    Co-Authors: Odd M Faltinsen, Reza Firoozkoohi, A N Timokha
    Abstract:

    Two-dimensional resonant liquid sloshing in a Rectangular Tank equipped with a central slat-type screen is studied theoretically and experimentally with focus on nonsmall solidity ratios of the screen (0.5≲Sn≲0.95), nonlarge number of slots (N≲50), and steady-state conditions. The Tank is horizontally and harmonically excited with frequencies in a range covering the two lowest primary-excited natural sloshing resonance frequencies in the corresponding clean Tank. The liquid depth is finite. Theoretical analysis is based on the multimodal method with linear free-surface conditions and a quadratic pressure drop condition at the screen expressing an “integral” effect of the screen-induced cross-flow separation (or jet flow). New experimental data on the maximum wave elevations at the wall are compared with the theoretical predictions. Very good agreement is shown for the smallest forcing amplitudes (the forcing amplitude-to-Tank width ratio is ≈0.001). Increasing the nondimensional forcing amplitude to ≈0.01...

Kamila Kotrasova - One of the best experts on this subject based on the ideXlab platform.

  • Vibration Analysis of Simply Supported Rectangular Tank Partially Filled with Water
    MATEC Web of Conferences, 2018
    Co-Authors: Kamila Kotrasova
    Abstract:

    Ground-supported Tanks are used as fluid storage. One of the phenomena associated with the seismic response of liquid-filled Tanks is the fluid motion occurring that causes “sloshing” at the top of free surface. This paper presents the theoretical of fluid response of Rectangular Tank due to horizontal acceleration of Tank bottom, the impulsive and convective (sloshing) pressure and the fluid natural frequencies. The vibration analysis of fluid filled Rectangular container was monitored and was evaluated in experiment for purpose to evaluation of the first frequency mode and vibration response of fluid were analysed by using FEM.

  • Sloshing of Liquid in Rectangular Tank
    Advanced Materials Research, 2014
    Co-Authors: Kamila Kotrasova
    Abstract:

    Ground-supported Tanks are used to store a variety of liquids. During earthquake activity the liquid exerts impulsive and convective pressures (sloshing) on the walls and bottom of the Rectangular Tank. This paper provides theoretical background for analytical calculating of circular frequencies and hydrodynamic pressures developed during an earthquake in Rectangular container. Analytical results of first natural frequency are compared with experiment.