Now showing 1 - 10 of 136
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    Regular wave measurements on a submerged semicircular breakwater
    (01-08-2010)
    Dhinakaran, G.
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    Graw, K. U.
    The submerged semicircular breakwater (SBW) is mainly adopted to prevent beach erosion and to reduce the incident wave energy on its leeside, if it is used in front of a vertical breakwater. In addition, it facilitates the premature wave breaking, which in turn causes the reduction in wave energy. The dynamic pressures and forces exerted on the submerged SBW with 7%, 11%, and 17% of the exposed surface area with perforations on its seaside due to regular waves were measured. The hydrodynamic characteristics such as variations in the dimensionless pressures and forces, reflection and transmission coefficients on the semicircular caisson as a function of scattering parameter for three different water depths are presented and an optimum depth of submergence is arrived. The results on the above stated variables for seaside perforated SBWs are compared with the results of an impermeable SBW to study the effect of perforations. Copyright © 2010 by ASME.
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    Diffraction-radiation of multiple floating structures in directional waves
    The dynamics of multiple floating structures have been studied using the finite element method. The emphasis is on the hydrodynamic behaviour of multiple bodies under a multi-directional wave field. A two-dimensional numerical model has been adopted to evaluate hydrodynamic coefficients and forces in an oblique wave field. The responses in sway, heave and roll modes are reported. The linear filter technique is then used to extrapolate the responses under directional waves. The effect of mean wave direction and directional homogeneity on the hydrodynamic behaviour of the structure is studied. Based on the present study, it is found that the two-dimensional model is applicable to investigate the wave-structure interaction problems of the type herein considered. (C) 2000 Elsevier Science Ltd. All rights reserved.
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    Ocean space utilization using very large floating semi-submersible
    (01-12-2013)
    Srinivasan, Nagan
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    Very Large Floating Structures (VLFS) are highly specialized floating structures with variety of applications in the civil engineering of ocean. Their economic design is based on their hydro-elastic behavior due to wave environmental forces. VLFS are extra large in size and mostly extra long in span in the design feature for their applications. For that reason they are mostly modularized into several smaller structures and joined together in the site. The critical problem is the longitudinal bending moment of the long floating vessel in severe wave environment. With the result of that the present available VLFS designs become not economical for applications in hostile-ocean. This paper presents ocean space utilization using an innovative VLFS with truss pontoon concept. The concept uses a strong deck with strong longitudinal beams to take care of the needed bending moment of the vessel for the survival, standby and operational conditions of the ocean environment. At the submerged bottom just above the keel-tank top, a simple open-frame truss-structure is used instead of a heavy shell type pontoon. The truss-pontoon provides the necessary flow transparency for the reduction of the wave exciting forces and consequently reduces heave amplitude of motions and the vertical acceleration. Each individual columns of the truss pontoon semi-submersible is tuned to have heave-period over 22 sec, independently, such that minimum hydrodynamic-motions are obtained for the overall structure. The VLFS is designed with minimum heave for the extreme storms unlike the conventional column stabilized semi-submersible unit with conventional pontoon. The paper proposes a new VLFS concept which is feasible for applications in harsh environment. Most importantly cost effective VLFS is achieved. This paper presents the details of the VLFS design, stability, motion, and experimental verification from the physical wave-tank with the scaled-down model. At the end of the paper, a few comprehensive example applications are illustrated. Copyright © 2013 by ASME.
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    Vibration study due to controlled trial blasting for rock dredging and berth dismantling
    (01-01-2019)
    John, J. M.
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    Saha, N.
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    Modi, S. K.
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    Murthy, V. M.S.R.
    The existing old ports have to be renovated to accommodate vessels with higher drafts, and if necessary, the aged berths have to be dismantled, and new berths are constructed. In the case discussed, the old berth has turned unserviceable with age, and there is a lack of minimum draft available to shelter new vessels. It is decided to make berths suitable for boarding vessels with a draft up to 14 m. The old berths were made of 22 vertical caissons, constructed partially using rubble masonry and partially using RCC masonry. It is decided that the old berths have to be demolished and the draft has to be brought to −16.1 m. The vibrations and peak particle velocities were measured at the location were found to be within the desirable limits set by Indian standards. A graph is plotted between peak particle velocity and scaled distance, and a correlation is drawn between ground vibration, distance and explosive charge. The desirable maximum explosive charge per delay for blasting with varying radial distance keeping the existing structures in vicinity safe and sound can be obtained using the derived correlation.
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    Innovative harsh environment dry-tree support semi-submersible for ultra deepwater applications
    (01-12-2009)
    Srinivasan, Nagan
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    Selvakumar, R.
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    Kanotra, Rahul
    Natural heave period exceeding over 21 sec is not the only important design criteria for the design of an ultra deepwater semi-submersible for dry-tree support application. The key design features that would enhance the applications of the semi-submersible design for ultra deepwater are vessel motion characteristic, heave natural period, high air-gap, large deck-area, large deck payload, reduced mooring load, large riser pull-down load, feasible for dynamic positioning, feasible for dry-tow, feasible for wet- tow, feasible for self-installation, feasible for quay-side top side integration, feasible for float-over installation. This paper presents the design innovations of the semi-submersible that has reached the above listed desired key factors. The designed vessel supports dry-tree with large riser loads resulted from ultra deepwater which is decoupled and is also independent of the designed top side pay load. The design is streamlined to withstand harsh environment. The vessel is designed to favor both options with quay-side deck integration or float-over deck installation. Extreme low accelerations in extreme wave environment on top of the above desired features make this semi-submersible suitable for harsh environment and ultra deepwater applications. A brief summary of hydrodynamic response of the vessel is added in this paper. Copyright © 2009 by ASME.
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    Wave runup on a concentric perforated circular cylinder system
    (24-03-2006)
    Vijayalakshmi, K.
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    Neelamani, S.
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    The regular wave interaction with a double concentric porous circular cylinder system consisting of an inner impermeable cylinder and an outer perforated cylinder was studied through physical model study. The experiments were carried out on the the double cylinder model in a wave flume to study the runup and rundown at the leading and trailing edges of the perforated cylinder. It was found that the maximum wave runup on the perforated cylinder is almost the same as the incident wave height. The predictive formulae were also developed for the wave runup and rundown on the perforated cylinder, which can be easily used for design applications.
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    Experimental investigation of wave runup on offshore intake wells in a random wave environment
    (01-01-2019)
    Kumar, V. Prabu
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    The seawater intake system is one of the essential operational units in many industries located in the coastal regions. The selection of the type of intake system to a specific sector depends on the total volume required and the quality of the sea water. The offshore seawater intake wells are a suitable option to meet the large volume water requirement and desired water quality. Sometimes two or more intake wells are installed to supply the large volume of the sea water. Since the increase in spacing between the wells leads to an increase in capital cost, it is predominant important to find the optimum distance between the wells. The present study focuses on the external and internal hydrodynamics of two caisson type offshore intake wells situated in random wave environment. Two wells are fabricated in 1:20 model scale and installed in the shallow wave basin and exposed to the random waves. The outer to outer face distance between two wells changed by concerning the outer diameter (D) of the well such that 1D, 1.5D and 2D. The wave run-up, diffraction wave height and free surface water oscillations inside the wells are measured. The distance between the two intake wells has a significant role in wave runup and free surface oscillation inside the well. Besides, the H/d have a substantial influence on the wave run-up on the seaward face compared to the side and shoreward face in all three cases. Also, the diffraction wave height is minimum when the wells are separated by 1.5D distance. Moreover, wave run-up and free surface water oscillation are optimum when the separation distance between the wells is 1.5D.
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    Experimental study on wave-structure interaction of an offshore intake well with a curtain wall
    (01-01-2020)
    kumar, V. Prabu
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    The present study focus on the wave-structure interaction of a caisson type offshore intake well with the regular waves. A 1:20 scale model is experimentally investigated with and without curtain wall in the shallow wave basin for its hydrodynamic responses like wave run-up, rundown, and free surface water oscillation inside the well. The wave run-up and rundown on all the faces record maximum when the scattering parameter (ka) is minimum. Moreover, the increase in relative wave height (H/d) results in an increase in the run-up on the seaward and shoreward faces. Besides, the free surface oscillation at the inlet and pumping chambers measures maximum when ka is minimum, and the influence of H/d keeps on reducing when the ka approaches the maximum value. The insertion of the curtain wall reduces the free surface oscillation at the pumping chamber when the relative water depth (d/L) ranges from 0.21 to 0.36.
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    Physical model study on geo-tube with gabion boxes for the application of coastal protection
    (01-03-2019)
    Nishold, Selvaraj Sherlin Prem
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    Saha, Nilanjan
    Shoreline erosion takes place due to the movement of sand by tides, wave actions, and wave-induced currents. The conventional techniques used for coastal protection such as artificial armor units and rubble mound are costly, and transportation is difficult in remote areas. Moreover, they may not be suitable for poor soil conditions. In this paper, the detailed physical experimental studies were carried out for a geo-tube saline embankment with ten geo-tubes in a four-layer configuration in a wave flume. This soft engineering solution may be particularly viable since the location is remote with poor soil strata. The studies include a scaled model (1:10) of geo-tube embankment with and without gabion boxes to check its possible utilization for coastal protection. The model is tested in the deep wave flume equipped with a piston type wave maker. The embankment is studied for two different water depths of 0.4 m and 0.5 m. The chosen 0.4-m water depth characterizes the high tide condition, while the 0.5-m water depth reproduces the combined high tide and storm surge conditions. The regular wave heights are varied in the range of 2 to 16 cm with a corresponding wave period of 1.5 to 2.2 s. Three probe methods are used to obtain the hydrodynamic parameters, based on which a geo-tube embankment protected with gabion box as armor is designed and constructed along the coast of Pentha (Odisha, India).
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    Experimental investigations on a non-ship shaped FPSO vessel
    (01-12-2008)
    Vijayalakshmi, R.
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    Panneerselvam, R.
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    Nagan Srinavasan, R.
    Off late, nontraditional structures and concepts are being explored for use in offshore industry. Experiments were carried out on a 1:45 non-ship shaped FPSO model. The main objective of the model test was to study the response of the vessel (heave and pitch) under regular and random waves. The vessel was tested for three different mooring configurations. Tests were also conducted on models with and without damping plates. In the present paper, the effect of mooring configurations in the heave response of the FPSO and the effect of damping plates in the heave and pitch responses of the FPSO under regular waves have been presented. Salient features of the details of the experiments carried out are also included. Copyright © 2008 by The International Society of Offshore and Polar Engineers.