Stochastic response of intact and a removed tendon tension leg platform to random wave and current forces

This work analysed the dynamic response of intact and a removed tendon tension leg platform (TLP) in simultaneous action of random wave and current loads in normal and less severe environments. Two different sea states of extreme severe sea state but less probable and less severe state and most probable are considered in this study. The artificial random wave is simulated by Monte Carlo simulation using Pierson–Moskowitz spectrum. Wave diffraction effect is not considered since the ratio of characteristic dimension to wavelength is less than limit. The coupling in all degree of freedoms and various degrees of nonlinear effects is considered. The inertia, mass, damping matrices of equation of motion and hydrodynamic force vector are formulated and solved numerically using Newmark integration scheme. The statistical results show that removal of one tendon increases surge and tendon tension values, while heave and pitch are not adversely affected in both environments. The response values of the TLP in extreme severe sea state are quite higher compared to less severe sea state. The percentage increase in all degree of freedoms and tendon tension is <5 % when one tendon is removed as compared to intact tendon TLP. It could be concluded that maximum and minimum tension in tendon constraints is equally passed by the TLP tendons

Dynamic behaviour of tension leg platform in short-crested directional seas

The representation of the sea condition has great influence on the behaviour of the Tension Leg Platform, (TLP). A real sea condition is a random directional field that varies both in space and time. The aim of this study is to compare responses of the TLP when the ocean surface is simulated as either unidirectional or directional sea. A stochastic sea surface elevation was assumed and simulated using linear wave superposition method for both unidirectional and directional seas. Joint North Sea Wave Project, (JONSWAP) spectrum was used to simulate wave frequency and quantify the energy density. A numerical code was developed in FORTRAN software for solving non-linear uncoupled dynamic analysis. The nonlinearity considered includes relative velocity square drag force in Morison, large displacement, variable submergence and tension fluctuation in the tendon. It was inferred that unidirectional sea simulation overestimates motion responses when compared to directional sea.</p

Prediction of optimum compressive strength of light-weight concrete containing Nigerian palm kernel shells

Palm kernel shells (PKS) are vast agricultural by-products that possess silica and alumina minerals in Nigeria. The use of PKS as aggregates has not been standardized for public use, hence, there is need for the prediction and optimization through trial mixes. A target mix was calculated based on American Concrete Institute, ACI code using PKS laboratory properties. Subsequently, factorial design was used to refine mix proportions with additional fourteen mix designs through the means of central composite design. This study employed response surface methodology to design constituent mix proportions and afterward predicted respective values of their compressive strength. The effect of each mix proportion was investigated for fresh and hardened properties of light-weight palm kernel shell concrete (LWPKSC). In addition, the optimal compressive strength of concrete was predicted at 22.24 MPa and realized experimentally at 21.10 MPa. The mix proportion ratio was found to be 1:3.33:1:27 at water-cement ratio of 0.50 with an oven-dry density less than 2000 kg/m 3 . Finally, analysis of variance, (ANOVA) of the results showed that optimum compressive strength of the concrete could be predicted and reliable. </p

Investigation of tendon dynamics effects on tension leg platform response in random seas

This study investigated tendon dynamics effects of tension leg platform models with tendons modelled by finite element spring and beam elements for uncoupled and coupled tension leg platform in random waves and current environment. The purpose of the study is to proffering numerical solution of single mathematical equation of motion for fully integrated-coupled tension leg platform floater with tendons model. Structural modelling of complete tension leg platform is achieved with the help of ABAQUS/Standard finite element tools which is incorporated with ABAQUS/Aqua module for the application of hydrodynamic loadings on the partially submerged tension leg platform hull and fully submerged platform tendons. For the uncoupled tension leg platform model, weight, inertia, hydrodynamic force and damping forces are ignored on the tendons modelled with springs, while the stiffness of the tendons is considered as a static restoring force. The coupled tension leg platform model had all the forces applied on the tendons modelled with beam elements. Conclusively, modelling and analysis of the tension leg platform as uncoupled and coupled models have expanded our understanding to know that surge motion response is fairly predicted by the two models, however, heave and pitch motions, and variations in tendon tension differ significantly; hence, coupled tension leg platform model is recommended. The influence of a removed tendon due to accident or maintenance on the tension leg platform motions is also reported. © IMechE 2018