Conceptual Design and Hydrodynamic Performance of a Modular Hybrid Floating Foundation

The comprehensive utilization of offshore renewable energies is an effective way to solve the intermittency and variability of power supply. This paper aims to present a hybrid floating system (HFS) based on a modular buoyancy-distributed floating foundation (BDFF) that can be equipped with a horizontal-axis wind turbine, solar panels, and wave energy converters (WEC). A simplified test model with a Froude scale ratio of 1/10 is employed to perform the experiments in a deep-water basin to validate the numerical results computed from the code program ANSYS AQWA based on the potential flow theory. The Response Amplitude Operators (RAOs) under regular waves are compared to evaluate the hydrodynamic performance. There is a good agreement in the surge, pitch, and heave RAOs for experiments and the numerical simulation, with a maximum of 6.45 degrees per meter for the pitch motion. Furthermore, the mooring tensions in the time domain are analyzed under different wave conditions.The tension RAOs from simulations are slightly higher than those from measurements with a maximum value at the period of 3.416 s. The mooring line on the windward side has a more considerable mooring tension that is far less than the allowable tensile strength, especially under the wave height of 2 m and the wave period of 2.873 s. The influence of loaded weight representing solar panels is weak, and the impact of winds is acceptable, as the platform deviates 1.3 degrees from the equilibrium state under the test wind speed. Eventually, the effect of irregular waves on the HFS is presented with the critical parameters of mooring tension and pitch motion. The results show that the HFS has a good motion performance.

Study of Motion Performance of a Floating System With Four Moonpools and a VAWT

In this paper the hydrodynamic performance of a barge-type floating foundation installed with four moonpools and a VAWT was investigated through model tests and theoretical calculations. The characteristics of wave-induced motion responses and tether tensions and the effects of turbine rotations were examined. Physical model tests were conducted in a wave tank using regular waves with the wave period ranging from 0.6 to 1.6 seconds and 0.01 or 0.02 meters in amplitude. A 2-MW-class VAWT was modelled with a scale ratio of 1/100 in the experiments. By varying the mass and the rotational speed of the turbine, gyroscopic moment effects were studied. In addition, numerical calculations based on the linear potential theory and Green function method were carried out to estimate motion responses and tether tensions. The present results indicate that the gyroscopic effect due to turbine rotations can be profound. It was found that the first-order motions of the floating system were substantially reduced by the gyroscopic effect, while the second-order motions and tether tensions may be significantly increased. Moreover, the viscous damping of water motions in moonpools was found not negligible. As a result, theoretical models based on linear potential theory should be used with care in hydrodynamic analysis with regard to the floating systems with VAWT rotations. In addition, the present in-house program code was validated against WAMIT through comparing hydrodynamic predictions of a floating foundation with four moonpools, with reasonable agreement.

Model Comparison of The Floating Foundations for The Development of Floating Houses at Coastal Areas

ABSTRACT Floating house is a building, which stands or floats on water by relying itself on the weight and the area sunk as the load parameter compatible to the structure. This house can float or be placed on the seashore on the water. This research was conducted by comparing the magnitude of the floating force (Fa) of the three foundation materials of the houses, namely plastic drum, Styrofoam and bamboo. The materials were calculated based on the total load of the house (G), with the safety number of 1.5. .The research result is the total load of the floating house structure (G) is 364.585,5 Newton (down), the floating force (Fa) magnitude of plastic drum as the foundation material is 549,814 Newton (upward), Styrofoam as the foundation material is 552,720 Newton (upward), and Bamboo as the foundation material is 540,883 Newton (upward). The amounts of the foundation materials for plastic drum are 232 pieces, for Styrofoam are 56 sheets, and for bamboo are 3900 sticks. Keywords: Floating house, floating foundation, floating force, plastic drum, Styrofoam, bamboo

Offshore Wind Turbine Coupled Motion in Regular Waves

This study aims to accurately predict the hydrodynamic performance and motion responses of offshore wind turbines on the basis of computational fluid dynamics (CFD) theory. Continuous and Navier-Stokes (N-S) equations are employed as control equations, and the k-ε model is used as a turbulence model. The finite difference method is utilized to discretize the equation. The Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) algorithm is applied to solve the control equation, and the volume-of-fluid (VOF) method is used to capture the free surface. The numerical wave tank of irregular wave is also established. The hydrodynamic performances and motion responses of the offshore wind turbines under regular waves are studied. First, we assume a floating foundation without the influence of a rotational fan and examine its motion responses and wave force in three typical sea conditions, namely, Levels 5, 6, and 7. Thereafter, we use a series of force and torque acting on the rotating center of the offshore to substitute for the influence of the rotational fan on the floating foundation. Then, we study the hydrodynamic performance influenced by blade rotation of the floating foundation in various sea conditions and three wind speeds, namely, 5, 8, and 11 m/s. Research results can provide usable theoretical principle and technical support for the investigation of the hydrodynamic performance and motion responses of similar offshore wind turbines.

PLANNING OF FLOATING FOUNDATION FOR SOFT SOIL IN GLAGAH AGUNG, BANYUWANGI CITY

Soft soil in construction often creates a problem. Soft soil which has the characteristics of low bearing capacity and high shrinkage properties becomes a problem for construction. One of the efforts to overcome these problems is by planning building foundations that are following soft soil characters. A floating foundation is planned that adopts the concept of lightweight concrete. The lightweight concrete used is an innovative concrete that uses styrofoam as a substitute for coarse aggregate. So that this concrete does not require broken stone or gravel as a concrete filler. Initial planning for floating foundations was carried out in the Purwoharjo area. Soil samples are taken and analyzed their characteristics to get the soil parameters. Then the dimensions of the foundation are planned by using the terzaghi formula for shallow foundations. The decrease or settlement of the soil was analyzed using the help of PLAXIS 2D software. Tanah lunak dalam konstruksi seringkali menjadi sebuah kendala. Tanah lunak yang memiliki karakteristik daya dukung rendah dan sifat kembang susut tinggi menjadi sebuah permasalahan dalam mendirikan bangunan di atasnya. Salah satu upaya untuk mengatasi permasalahan tersebut adalah dengan merencanakan pondasi bangunan yang sesuai dengan karakter tanah lunak. Direncanakan sebuah pondasi apung yang mengadopsi konsep beton ringan. Beton ringan yang digunakan merupakan beton inovasi yang menggunakan styrofoam sebagai pengganti agregat kasarnya. Sehingga beton ini tidak memerlukan batu pecah atau kerikil sebagai bahan pengisi beton. Perencanaan awal untuk pondasi apung, dilakukan di daerah Purwoharjo. Sample tanah diambil dan dianalisis karakteristiknya untuk mendapatkan parameter-parameter tanahnya. Kemudian direncanakan dimensi pondasi dengan menggunakan rumus terzaghi untuk pondasi dangkal. Penurunan atau settlement tanah dianalisis menggunakan bantuan software PLAXIS 2D.