Journal of Marine Science and Engineering

Research

13 pages, 7592 KiB

Open AccessArticle

The Effect of the Second-Order Wave Loads on Drift Motion of a Semi-Submersible Floating Offshore Wind Turbine

by Thanh-Dam Pham and Hyunkyoung Shin

J. Mar. Sci. Eng. 2020, 8(11), 859; https://doi.org/10.3390/jmse8110859 - 30 Oct 2020

Cited by 11 | Viewed by 4209

Floating offshore wind turbines (FOWTs) have been installed in Europe and Japan with relatively modern technology. The installation of floating wind farms in deep water is recommended because the wind speed is stronger and more stable. The design of the FOWT must ensure [...] Read more.

Floating offshore wind turbines (FOWTs) have been installed in Europe and Japan with relatively modern technology. The installation of floating wind farms in deep water is recommended because the wind speed is stronger and more stable. The design of the FOWT must ensure it is able to withstand complex environmental conditions including wind, wave, current, and performance of the wind turbine. It needs simulation tools with fully integrated hydrodynamic-servo-elastic modeling capabilities for the floating offshore wind turbines. Most of the numerical simulation approaches consider only first-order hydrodynamic loads; however, the second-order hydrodynamic loads have an effect on a floating platform which is moored by a catenary mooring system. At the difference-frequencies of the incident wave components, the drift motion of a FOWT system is able to have large oscillation around its natural frequency. This paper presents the effects of second-order wave loads to the drift motion of a semi-submersible type. This work also aimed to validate the hydrodynamic model of Ulsan University (UOU) in-house codes through numerical simulations and model tests. The NREL FAST code was used for the fully coupled simulation, and in-house codes of UOU generates hydrodynamic coefficients as the input for the FAST code. The model test was performed in the water tank of UOU. Full article

(This article belongs to the Special Issue Analysis and Design of Offshore Wind Turbine Support Structures)

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25 pages, 9636 KiB

Open AccessArticle

Simplified Numerical Models to Simulate Hollow Monopile Wind Turbine Foundations

by Susana Lopez-Querol, Michail Spyridis, Pedro J. M. Moreta and Juana Arias-Trujillo

J. Mar. Sci. Eng. 2020, 8(11), 837; https://doi.org/10.3390/jmse8110837 - 24 Oct 2020

Cited by 3 | Viewed by 2883

Abstract

The majority of wind turbine foundations consist of hollow monopiles inserted in the soil, requiring high computational effort to be numerically simulated. Alternative simplified models are very often employed instead. Three-dimensional solid models, in which the hollow structure and pile are substituted by [...] Read more.

The majority of wind turbine foundations consist of hollow monopiles inserted in the soil, requiring high computational effort to be numerically simulated. Alternative simplified models are very often employed instead. Three-dimensional solid models, in which the hollow structure and pile are substituted by solid cylinders with equivalent properties, are the most extended simplifications. Very few 2D models can be found in the literature due to the challenge of finding suitable equivalent properties and loads to fully represent the 3D nature of the problem. So far, very limited attention has been devoted to the accuracy of both 3D and 2D simplified models under dynamic and even static actions. Thus, in this paper, simplified 3D and 2D solid models are proposed and justified. An elasto-plastic constitutive model with accumulative degradation is used to simulate the soil behaviour, and frictional contact elements are implemented between the soil and pile to model their interaction. These simplified approaches are compared with the full 3D hollow model, under static and cyclic loads. The results demonstrate that the proposed simplified approaches are a reasonable alternative to the 3D hollow model, which allows researchers and designers to drastically reduce the computational effort in the simulations under long term conditions. Full article

(This article belongs to the Special Issue Analysis and Design of Offshore Wind Turbine Support Structures)

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26 pages, 3996 KiB

Open AccessArticle

Platform Optimization and Cost Analysis in a Floating Offshore Wind Farm

by Alberto Ghigo, Lorenzo Cottura, Riccardo Caradonna, Giovanni Bracco and Giuliana Mattiazzo

J. Mar. Sci. Eng. 2020, 8(11), 835; https://doi.org/10.3390/jmse8110835 - 23 Oct 2020

Cited by 55 | Viewed by 9473

Abstract

Floating offshore wind represents a new frontier of renewable energies. The absence of a fixed structure allows exploiting wind potential in deep seas, like the Atlantic Ocean and Mediterranean Sea, characterized by high availability and wind potential. However, a floating offshore wind system, [...] Read more.

Floating offshore wind represents a new frontier of renewable energies. The absence of a fixed structure allows exploiting wind potential in deep seas, like the Atlantic Ocean and Mediterranean Sea, characterized by high availability and wind potential. However, a floating offshore wind system, which includes an offshore turbine, floating platform, moorings, anchors, and electrical system, requires very high capital investments: one of the most relevant cost items is the floating substructure. This work focuses on the choice of a floating platform that minimizes the global weight, in order to reduce the material cost, but ensuring buoyancy and static stability. Subsequently, the optimized platform is used to define a wind farm located near the island of Pantelleria, Italy in order to meet the island’s electricity needs. A sensitivity analysis to estimate the Levelized Cost Of Energy is presented, analyzing the parameters that influence it most, like Capacity Factor, Weighted Average Capital Cost (WACC) and number of wind turbines. Full article

(This article belongs to the Special Issue Analysis and Design of Offshore Wind Turbine Support Structures)

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24 pages, 5978 KiB

Open AccessArticle

Improving the Computational Efficiency for Optimization of Offshore Wind Turbine Jacket Substructure by Hybrid Algorithms

by Ding-Peng Liu, Tsung-Yueh Lin and Hsin-Haou Huang

J. Mar. Sci. Eng. 2020, 8(8), 548; https://doi.org/10.3390/jmse8080548 - 22 Jul 2020

Cited by 2 | Viewed by 2559

Abstract

When solving real-world problems with complex simulations, utilizing stochastic algorithms integrated with a simulation model appears inefficient. In this study, we compare several hybrid algorithms for optimizing an offshore jacket substructure (JSS). Moreover, we propose a novel hybrid algorithm called the divisional model [...] Read more.

When solving real-world problems with complex simulations, utilizing stochastic algorithms integrated with a simulation model appears inefficient. In this study, we compare several hybrid algorithms for optimizing an offshore jacket substructure (JSS). Moreover, we propose a novel hybrid algorithm called the divisional model genetic algorithm (DMGA) to improve efficiency. By adding different methods, namely particle swarm optimization (PSO), pattern search (PS) and targeted mutation (TM) in three subpopulations to become “divisions,” each division has unique functionalities. With the collaboration of these three divisions, this method is considerably more efficient in solving multiple benchmark problems compared with other hybrid algorithms. These results reveal the superiority of DMGA in solving structural optimization problems. Full article

(This article belongs to the Special Issue Analysis and Design of Offshore Wind Turbine Support Structures)

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9 pages, 4249 KiB

Open AccessArticle

Model Test and Numerical Simulation of Grouted Connections for Offshore Wind Turbine Under Static Axial Load

by Weiqiu Zhong, Wuxu Li, Tao Yang, Deming Liu and Lintao Li

J. Mar. Sci. Eng. 2020, 8(7), 543; https://doi.org/10.3390/jmse8070543 - 21 Jul 2020

Viewed by 2057

Abstract

The bearing capacity of the grouted connections is investigated through the model test and numerical simulation with two rates (low and high) and four kinds of specimens: shorter without shear keys, shorter with shear keys, longer with shear keys, and conical with shear [...] Read more.

The bearing capacity of the grouted connections is investigated through the model test and numerical simulation with two rates (low and high) and four kinds of specimens: shorter without shear keys, shorter with shear keys, longer with shear keys, and conical with shear keys. It reveals that the bearing characteristics of the specimen of longer with shear keys is worse than the specimen of conical with shear keys, but better than the specimen of shorter with shear keys. Moreover, the bearing characteristics of the specimen of shorter without shear keys is the worst one. Full article

(This article belongs to the Special Issue Analysis and Design of Offshore Wind Turbine Support Structures)

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14 pages, 2660 KiB

Open AccessArticle

Analytical Solution for Estimating Bearing Capacity of a Closed Soil Plug: Verification Using An On-Site Static Pile Test

by Suchun Yang, Junwei Liu, Ankit Garg and Mingyi Zhang

J. Mar. Sci. Eng. 2020, 8(7), 490; https://doi.org/10.3390/jmse8070490 - 3 Jul 2020

Cited by 8 | Viewed by 2222

Abstract

When the open-ended pile penetrates the soil layer, the resistance generated by the soil plug cannot be ignored. A pile with a full-size pressure sensor installed at pile tip can detect resistance more accurately than a microsensor when the pile penetrates into the [...] Read more.

When the open-ended pile penetrates the soil layer, the resistance generated by the soil plug cannot be ignored. A pile with a full-size pressure sensor installed at pile tip can detect resistance more accurately than a microsensor when the pile penetrates into the soil. In this paper, the pile installed full-size pressure sensor was used for penetration test and the relationship between formation parameters and pile tip force is obtained. Using the solution of the Kelvin problem in infinite space and the plane stress distribution function, the analytical solution of the bearing capacity of the soil plug is derived under the condition that the displacements of the bottom of the pile and the soil plug are consistent. The results show that the ultimate stress of the soil plug is closely related to the pile diameter and pipe thickness. The bearing capacity of the soil plug is closely related to the properties of the soil layer. The analytical solution of the bearing capacity of the soil plug has a linear relationship with the formation parameters SPT and CPT. The analytical solution of the ultimate bearing capacity of the soil plug has been verified by field test data and has a good match with the geometric dimensions of the pile tip and the formation parameters. Full article

(This article belongs to the Special Issue Analysis and Design of Offshore Wind Turbine Support Structures)

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26 pages, 8098 KiB

Open AccessFeature PaperArticle

Suction Bucket Pile–Soil–Structure Interactions of Offshore Wind Turbine Jacket Foundations Using Coupled Dynamic Analysis

by Pasin Plodpradit, Osoon Kwon, Van Nguyen Dinh, Jimmy Murphy and Ki-Du Kim

J. Mar. Sci. Eng. 2020, 8(6), 416; https://doi.org/10.3390/jmse8060416 - 8 Jun 2020

Cited by 16 | Viewed by 5993

Abstract

This paper presents a procedure for the coupled dynamic analysis of offshore wind turbine–jacket foundation-suction bucket piles and compares the American Petroleum Institute (API) standard method and Jeanjean’s methods used to model the piles. Nonlinear springs were used to represent soil lateral, axial, [...] Read more.

This paper presents a procedure for the coupled dynamic analysis of offshore wind turbine–jacket foundation-suction bucket piles and compares the American Petroleum Institute (API) standard method and Jeanjean’s methods used to model the piles. Nonlinear springs were used to represent soil lateral, axial, and tip resistances through the P–Y, T–Z, and Q–Z curves obtained by either API’s or Jeanjean’s methods. Rotational springs with a stiffness equated to the tangent or secant modulus characterized soil resistance to acentric loads. The procedure was implemented in X-SEA program. Analyses of a laterally loaded single pile in a soft clay soil performed in both the X-SEA and Structural Analysis Computer System (SACS) programs showed good agreements. The behaviors of a five MW offshore wind turbine system in South Korea were examined by considering waves, current, wind effects, and marine growth. In a free vibration analysis done with soil stiffness through the API method, the piles were found to bend in their first mode and to twist in the second and third modes, whereas the first three modes using Jeanjean’s method were all found to twist. The natural frequencies resulting from Jeanjean’s method were higher than those from the API method. In a forced vibration analysis, the system responses were significantly influenced by soil spring stiffness type. The procedure was found to be computationally expensive due to spring nonlinearities introduced. Full article

(This article belongs to the Special Issue Analysis and Design of Offshore Wind Turbine Support Structures)

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17 pages, 5239 KiB

Open AccessArticle

Soil Interaction and Grout Behavior for the NREL Reference Monopile Offshore Wind Turbine

by Mário Vieira, Miguel Viana, Elsa Henriques and Luís Reis

J. Mar. Sci. Eng. 2020, 8(4), 298; https://doi.org/10.3390/jmse8040298 - 24 Apr 2020

Cited by 7 | Viewed by 3375

Abstract

Monopiles for offshore wind are the most used foundations by farm operators due to their low production costs, when compared to other bottom-fixed or floating foundations. In this research, a monopile foundation for offshore wind power was evaluated for its soil interaction and [...] Read more.

Monopiles for offshore wind are the most used foundations by farm operators due to their low production costs, when compared to other bottom-fixed or floating foundations. In this research, a monopile foundation for offshore wind power was evaluated for its soil interaction and grout behavior, and an appropriate numerical model for the structural analysis of the foundation and tower was developed. FAST 8, an aero-hydro-servo-elastic numerical code developed by NREL, was used to obtain the loads applied on the supporting structures. These loads were pre-processed before they were inputted on the finite element model, developed using the finite element software ANSYS. The considered conical grout connection, which connects the monopile to the transition piece through friction, was modeled under a changing-status nonlinearity condition. To model the soil–pile interaction, a p-y model was applied using the ANSYS APDL commands. Static, modal, and transient structural analyses were produced to study the structure suitability for its use on offshore environments. Different soil interactions were modeled, and their results were then compared within the transient and modal analysis, indicating that the angle of the grout connection strongly affects the loading conditions on the grout. Moreover, scouring affects the dynamic behavior of the overall supporting structures, thus protection against this phenomenon is suggested. Full article

(This article belongs to the Special Issue Analysis and Design of Offshore Wind Turbine Support Structures)

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