Xuefeng Wang

Bio: Xuefeng Wang is an academic researcher from Shanghai Jiao Tong University. The author has contributed to research in topics: Mooring & Dynamic positioning. The author has an hindex of 8, co-authored 45 publications receiving 186 citations.

Uncertainties related to predictions of loads and responses for ocean and offshore structures

Abstract: This paper discusses uncertainties related to the prediction of loads and responses for ocean and offshore structures in accordance with the findings by the Ocean Engineering Committee of the International Towing Tank Conference (ITTC) The parameters that may cause uncertainties in ocean engineering model tests, full-scale tests and numerical simulations are presented in terms of physical properties of the fluid, initial conditions, model definition, environment, scaling, instrumentation and human factors Emphasis is given to the uncertainty sources in model tests involving deepwater mooring lines, risers and dynamic positioning systems and the need for quantifying them A methodology for uncertainty analysis is described according to the International Organization for Standardization (ISO) Guidance for Uncertainties in Measurement (GUM) As an example of application, the combined and expanded uncertainties in the model tests of a moored semi-submersible platform were assessed and quantified in terms of motion responses, air gap and mooring line tensions It is concluded that the quantification of uncertainties may be challenging in model tests and numerical simulations of ocean and offshore structures It is particularly challenging in extrapolating model test results to full scale and utilizing complex numerical models, especially if the effects of hydrodynamic nonlinearities are significant

A simplified method to estimate the hydroelastic responses of VLFS in the inhomogeneous waves

Abstract: For the very large floating structure (VLFS) which is deployed near seashore, islands and reefs, the encounter wave conditions will become extremely complex. The influences of the inhomogeneous incident waves (multi-directions, different wave height) should be taken into account, particularly in extreme typhoon wave environment. Therefore, the traditional methods with homogeneous wave inputs cannot be applied in this type of hydroelasticity analysis of VLFS. A simplified method and its corresponding software THAFTS-IHIW were established to estimate the hydroelastic responses of VLFS in the inhomogeneous waves. The accuracy of the simplified method was verified by model test results, and an application of this simplified method for the hydroelastic analysis of the 8-module VLFS in the Typhoon ‘Kalmaegi’ was presented in this paper. Some useful conclusions are obtained, which can provide a reference for the analysis of dynamic responses, design and construction of the floating bodies near seashores and islands.

Penetration depth of torpedo anchor in cohesive soil by free fall

Abstract: Developing deep sea technologies, many marine novel facilities have been introduced; and mooring systems, however, have become more expensive, complex, and hard cooperative in deep-water marine industry. The torpedo anchor is regarded as a modern technology benefits from easy installation, cost efficiency, and high level of anchor force. In this study, the penetration depth of a free falling torpedo anchor into cohesive soil has been laboratory investigated. 128 Sets of tests have been conducted with nine different torpedo anchors not only in shape, but also in size. Three anchor aspect ratios and three different types of muds were tested while mud rheological properties such as the yield stress and flow curves were also measured. Finally, a formula calculating the penetration depth of the anchor, regardless of soil separation has been proposed based on energy conservation principle and experimental measurements. Results indicate that the predicted penetration depth has a good conformity with the measured penetration depths in laboratory and field tests. Static undrained shear strength values should be reduced in formula when the impact velocity exceeds a critical value. Soil separation occurs depending on the anchor nose angle and surface roughness, and also soil properties. Nevertheless, the critical impact velocity resulting into soil separation and its degree require further study in the future.

A fuzzy rule-based PID controller for dynamic positioning of vessels in variable environmental disturbances

Abstract: Conventional dynamic positioning systems are based on PID controllers and an extended Kalman filter or a nonlinear state observer. However, it is nontrivial to tune the control parameters, and the station-keeping performance varies with environmental or loading conditions since the dynamics of the vessel are essentially nonlinear. To overcome these difficulties, a fuzzy rule-based PID controller is evaluated, which takes the estimated positioning error and low-frequency velocity as inputs, and outputs the time-varying PD control coefficients through fuzzy inference, while the integral control parameters are kept constant. The performance of the proposed controller is evaluated numerically through a time domain simulation of a dynamically positioned semi-submersible platform operating in variable environmental disturbances. Simulation results are compared with the conventional fixed gain PID controller, and the comparison results show that the proposed fuzzy PID controller can automatically tune the PD control coefficients according to the positioning accuracy and significantly improve the performance of the dynamic positioning system.

Vertical holding capacity of torpedo anchors in underwater cohesive soils

Abstract: Torpedo anchors are regarded as one of the most efficient mooring solutions for taut mooring systems and can withstand vertical loads. The estimation of the undrained pullout capacity of the anchors is vital for the design of offshore floating facilities. There have been some achievements obtained for the calculation of the holding capacity of a torpedo anchor via field tests, conventional model tests under one gravity, centrifuge tests with a high value of gravity acceleration and numerical tests. However, a simple and reliable formula is still required to calculate the holding capacity of a torpedo anchor. In this study, 240 sets of laboratory tests were performed, and 11 differently shaped model anchors, vertically embedded in a soft sedimentary bed, were pulled out vertically from different types of cohesive soils and different embedment depths. The characteristics of the loading curves were analyzed, and the relationship between the pullout capacities and properties of the anchors and types of soils were investigated. Based on force analysis and the laboratory data, a formula was proposed for the calculation of the undrained monotonic holding capacity of a torpedo anchor, which mainly depends on the embedded depth of the anchor, net weight, geometry, and in situ soil properties. The calculated vertical holding capacities were consistent with the laboratory and field data obtained by the authors and other scientists.

Guidance And Control Of Ocean Vehicles

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Review of mooring design for floating wave energy converters

Abstract: A review of some representative floating wave energy converter (WEC) projects in the world, including the wave energy capturing technology, development history, main dimensions and tested sea sites is presented. The design essentials of WEC mooring system are discussed and a mooring system design procedure for WEC is proposed, which includes the introduction of related design codes and mooring analysis methods. In the last part, a comprehensive review of mooring system design in the current WECs projects is conducted. Different mooring systems and mooring materials are introduced and discussed. Based on the discussions, recommendations are made for the suitable mooring design according to the WEC's dimensions and working principles. It is shown that the elastic synthetic rope has great potential in the application of WEC mooring system, and the hybrid mooring system could be a good solution for WEC station keeping problem.

Real-Time Hybrid Model Testing of a Braceless Semi-Submersible Wind Turbine: Part I — The Hybrid Approach

Abstract: This article presents a method for performing Real-Time Hybrid Model testing (ReaTHM testing) of a floating wind turbine (FWT). The advantage of this method compared to the physical modelling of the wind in an ocean basin, is that it solves the Froude-Reynolds scaling conflict, which is a key issue in FWT testing. ReaTHM testing allows for more accurate testing also in transient conditions, or degraded conditions, which are not feasible yet with physical wind. The originality of the presented method lies in the fact that all aerodynamic load components of importance for the structure were identified and applied on the physical model, while in previous similar projects, only the aerodynamic thrust force was applied on the physical model. The way of applying the loads is also new. The article starts with a short review (mostly references) of ReaTHM testing when applied to other fields than marine technology. It then describes the design of the hybrid setup, its qualification, and discusses possible error sources and their quantification. The second part of the article [1] focuses on the performance of a braceless semisubmersible FWT, tested with the developed method. The third part [2] describes how the experimental data was used to calibrate a numerical model of the FWT. ∗Corresponding author (thomas.sauder@marintek.sintef.no)

Wave energy converter and large floating platform integration: A review

Abstract: Extracting wave energy is a promising solution for renewable energy production because of the high energy intensity of ocean waves when compared to other renewable energy resources. On another front of ocean utilization, large floating platforms are an effective solution for creating artificial space on the sea for various purposes such as airports, seaports, aquaculture platforms, and recreation and residential areas. Integrating wave energy converters with large floating platforms brings many benefits owing to space-sharing, cost-sharing, and multiple functions of the integrated system. This paper presents a literature review of wave energy converter and large floating platform integration. Overviews of wave energy and large floating platform technologies are first presented. This is followed by a review of various integrated systems between wave energy converters and large floating platforms, a brief on hydrodynamic analysis of the integrated systems and some recommendations for future studies.

Structural health management utilization for lifetime prognosis and advanced control strategy deployment of wind turbines: An overview and outlook concerning actual methods, tools, and obtained results

Abstract: In this contribution, Structural Health Monitoring (SHM) systems applied to wind turbines (WTs) are considered. Challenges resulting from contradictions between requirements related to efficient operation with respect to energy production costs and those related to lifetime and maintenance are discussed. Especially pronounced in larger WT systems, structural loads contribute to lifetime shortening due to damage accumulation and damage-caused effects influencing subsystems of the wind turbine. Continuous monitoring of the WT system concerning State-of-Health is necessitated to provide information about the condition of the system guaranteeing reliable and efficient operation, as well as efficient energy extraction. In recent years, structural health monitoring of WT systems is significantly improved through automated on-line fault detection and health or condition monitoring (CM) system integration. In this contribution the focus is given to hardware components (mainly sensor technologies) and methods used for change evaluation, damage detection, and damage accumulation estimation. Accordingly, this contribution comprises recent knowledge about methods and approaches of handling structural loads with emphasis on offshore wind turbine systems and applied sensing technologies (especially with respect to wind turbine blades, gearboxes, and bearings) and partly hardware. Moreover, a brief sketch of an advanced concept is developed concerning structural load examination affected by operating conditions. Key idea of the introduced approach is to use the operating conditions to control and especially to extend system׳s lifetime. The review presents an actual state-of-the-art and overview related to the use and application of SHM-related technologies and methods. Especially in combination with the briefly introduced lifetime extension concept, the contribution gives comprehensive and detailed overview in combination with an outlook to upcoming technological options.