Nonlinear response of tension leg platform subjected to wave, current and wind forces

Tension leg platform (TLP) superstructure and submerged areas are being subjected to wind and wave forces during their lifetime, yet the magnitude of each respective energy density affects the TLP response. The present work aims to study the influence of possible load combinations on the response of the TLP. In order to achieve this objective, the Joint North Sea Wave Project (JONSWAP) spectrum and Simiu and Leigh wind spectrum were used for the computation of wave and wind spectral densities. Airy wave theory and Morison equation were adopted for the calculation of wave kinematics and forces on the platform. The variable submergence, drag force in the Morison equation, tension fluctuation from large displacement were the sources of nonlinearities considered. Subsequently, mathematical formulation for the dynamic analysis of intact and a tether-missing TLP was developed in FORTRAN software. The nonlinear equation of motion was solved using Newmark-Beta scheme coded in the software. From our findings, the sea state with high significant wave height and wave period suppressed the effect of current and wind loads on the TLP motion response as compared to the sea state with low sea state parameters. The effect of wind drag force increases the surge and heave responses, but the overall influence of the current drag depends on the magnitude of the wave energy spectrum. There was no abrupt behaviour when a tether was missing although the loss of tether’s stiffness slightly affects the TLP motion and tension variation.</p

Nonlinear dynamic response of tension leg platform under environmental loads

This paper investigated the platform motion and tether tension of tension leg platform subjected to eight sea states ranging from extreme to moderate states. The mass, stiffness and damping force matrices were formulated for the platform and the tethers were considered as non-linear springs. The surface elevation and wave kinematics were calculated by small wave amplitude theory. On the other hand, the force vector was calculated by integrating over the entire length of the hull members using Morison equation. The various degree of non-linearity considered include the drag force, the variable added mass, large displacement as well as variations in tether tension. A finite element numerical research program was developed for solution of the nonlinear problem. The statistical response parameters for the degrees of freedom show that as we move towards the less severe sea states, all the responses were decreasing. Response comparison of one tether missing and an intact tendon of tension leg platform show an increase in surge and tether tension but heave response decreased due to reduction in stiffness against vertical movement. Dynamic analysis of the platform under the combined action of wave, current and wind is recommended so as to know true platform behaviours.</p

Physio-chemical and microstructural characteristics of selected pozzolanic materials for possible utilization in the cement and concrete production

Abundant aquatic animal by-products are available in Nigeria which includes Clam, Oyster, Rock Snail and Periwinkle shells. These are usually dumped on open lands without any economic value after fleshy parts of these animals had been consumed by humans, hence, result into environmental problems. In the agricultural sector, Rice husk and Palm oil fuel ashes are by-products from rice and palm oil industries after the husks have been used as source of fuel. Disposal of these wastes are always a major issue as they constitute nuisance to the environment. This research has collected and characterized these wastes in the laboratory to ascertain their suitability as supplementary cementitious materials. With this study, physical properties such as particle size, specific gravity, specific surface area and morphology are conducted by Scanning Electron Morphology, SEM; chemical analysis are carried out with the aid of X-ray Fluorescence (XRF), for microstructure examination, X-ray Diffraction (XRD) machine is used for detecting minerals in the materials while Field Emission Scanning Electron Microscopy and Energy-Dispersive X-ray analysis (FESEM-EDX) are used for image and element detection. The results of these analyses will help in the future work of pozzolanic and geopolymer construction in Nigeria. The results are further compared with previous literature to see their compatibility and discrepancy