Performance Evaluation of Vertical Porous Screen In A Sloshing Tank By Analytical and Experimental Investigation

Abstract

Liquid participation in the vessels or tanks is called as sloshing. The sloshing dynamics in the tank is a complicated phenomenon. Dynamics of sloshing mainly include transient motion of liquid, resonant condition, linear and nonlinear motion, frequency shift phenomenon etc. Therefore, it attracts many researcher and scantiest to study the dynamics of liquid motion in the tanks. Due to its complex and significant phenomenon that has many engineering applications. Stability of sloshing tank and stability of moving vehicles or/and structures coupled with sloshing tank are most concern. In view of fact of sloshing in the tank for many engineering application, it is important to control and/or reduce the liquid participation in the sloshing tank and achieve a required level damping. The damping in tank include viscous effect of liquid in the tank, wave- tank interaction, and wave motion in the baffled tank. For this purpose, one such system is the liquid (water) tank with flow damping device. Many researchers have investigated the sloshing dynamics in the tank with solid and porous baffles in order to control and/or reduce the wave elevations in the sloshing tank. The varying types solid baffles in the sloshing tanks are used to reduce the hydrodynamic action (force and pressure) on tank walls and reduce the weight penalty and cost. Similar to the solid baffles, the porous baffles with varying porosities are also being used in the sloshing tank not only to control hydrodynamics action but also used to enhance the required level damping in the tank. The perforation in the baffles generally include slat type configuration with horizontal and vertical arrangement with respect flow direction. In the porous baffled tank, the dynamic of sloshing includes wave-baffle interaction associated with linear and nonlinear phenomenon. The wave- structures (baffles) interaction is dependent in tank geometry, liquid fill level, type of excitation, flow through baffles, and most importantly drag, loss, and inertia coefficients. The tank with varying porous baffled with optimum liquid fill level in the tank are mainly designed as a Tuned Liquid Damper (TLD) to reduce the structural vibrations. In this regard, many researchers have been working on sloshing dynamics in the tanks to construct the damping in the tank with porous baffles and appropriate liquid fill level. And, the screen drag coefficient is an important parameter to consider to study the dynamic of liquid sloshing the porous baffled tank, iThe liquid free surface in most important, where the wave energy is concentrated during liquid motion and first resonant mode of sloshing in the tank is an important factor for structure-TLD interaction problems. On this basis, using fully extended porous baffles from tank bottom may result in increased wave baffles interaction inducing larger sloshing attenuation near the resonant modes. Hence, the concept of using circular hole perforation in the baffle is comprehended for the advancement of porous baffles in the sloshing tank. In the present study, free surface elevations, sloshing force, and energy dissipation of the porous baffle in the rectangular sloshing tank are examined by both analytical and experimental program. The three varying porosity is adopted for porous baffles in the sloshing study. To concerns of first resonant mode in the sloshing tank, the porosity of 4.4%, 6.8%, and 9.2% are adopted for the baffles. Initially, the gravitational flow test is planned and conducted to study the flow phenomena through porous baffles, and documented the drag coefficient variation for all porous baffles based on the Reynold numbers. Secondly, the linear second-order ordinary differential equations for sloshing dynamics in the rectangular tank were solved using Newmark’s beta method and obtained the analytical solutions for liquid sloshing with and without baffles in the tank following the procedure similar to Warnitchai and Pinkaew (1998) and Tait (2008). The porous baffle loss coefficient is an important parameter to study the baffle’s performance in the tanks. Hence, the two analytical models based on porous baffle loss coefficients were formulated for rectangular sloshing tanks with porous baffles. The analytical model-1 includes both Reynold’s number and porosity dependent loss coefficient, whereas model-2 includes porosity dependent and independent of Reynold’s number. The model's test results were validated with a series of shake table experiments under sway motion at different excitation frequencies which cover up to the first four sloshing resonant modes. In the third stage, experiment shake table tests are performed to validate analytical model results. Initially the test includes rectangular clean tank with varying liquid fill level to study the effect of liquid fill level in the sloshing tank. Considered small, medium, high, and liquid fill in the tank based on tank height (H) which include iiaspect ratio (ratio of static liquid depth to tank length) of 0.163, 0.325, and 0.488 respectively. In the experiment test series, the sloshing with varying fill level subjected to seventeen different excitation frequencies which are include first five resonant mode of liquid sloshing in the tank and the tank driven by sway amplitude (A/L) of 0.0075. Further, the shake table tests are performed for porous baffled tank. In the test series, initially the tank with two baffle condition were considered. In the tank the two baffles are positioned at 0.33 distance of tank length from both end walls. And tank with single baffle case, the baffle positioned at centre of the tank length. The response of free surface elevation and sloshing force variations in the tank analytical models were compared with the experiment's test results. In the two porous baffled sloshing tank under the range of sway excitations, the response of wave motion and sloshing force by both analytical and experimental tests results exhibit the resonant frequency shift phenomenon which is provoked by the low-level porosity of screens (4.4% and 6.8%) in all three fill levels. As porosity of baffle increases (9.2%), the secondary peak start appearing near the first resonant mode along with secondary peak at third resonant mode of sloshing tank. The analytical results matched with shake table test results with a quantitative difference near the first resonant frequency. It is found that Reynolds number dependent porous baffles in the sloshing tank significantly reduce the sloshing elevations in the tank compared to Reynolds number independent one. As a result, Reynold’s number and porosity dependent loss coefficient for porous baffles was found to be more effective. In the case of tank with single porous baffle condition, the analytical model fails to exhibits the exact resonant phenomenon near the secondary resonant excitation mode. but, experiment rest results show the exact resonant frequency shift phenomenon in the tank with centrally positioned porous baffle.