Unsteady aerodynamics of offshore floating wind turbines using free vortex wake model

Among the offshore floating wind turbine software packs, the blade element momentum theory (BEM) and generalized dynamic wake (GDW) model are widely used. A free vortex wake model has been coupled to FAST v7 to do a comparative dynamic analysis between using the BEM theory and GDW method on offshore floating wind turbine. The verification test on the free-wake model has been performed according to the NREL VI experiment in steady and yaw conditions. To analyze the unsteady aerodynamics of floating wind turbine, the OC3 spar type wind turbine has been used to do simulations. The global performances on both the rotor and the platform and their interactions are shown and discussed

Analysis on the hull girder ultimate strength of a bulk carrier using simplified method based on an incremental-iterative approach

The hull girder ultimate strength of a typical bulk carrier is analyzed using a simplified method based on an incremental-iterative approach. First, vertical bending moment is examined by seven different methods. The moment versus curvature curves and the values of the ultimate longitudinal moments at collapse states are determined for both hogging and sagging cases. Second, the ultimate strength under coupled vertical and horizontal bending moment is accounted. An interaction curve is obtained, which corresponds to the results of series of calculation for the ship hull subject to bending conditions with different angles of curvature. It is found that the interaction curve is asymmetrical because the hull cross section is not symmetrical with respect to the horizontal axis and the structural response of the elements under compression is different from that under tension due to nonlinearity caused by buckling. The angles of the resultant bending moment vector and that of the curvature vector are different in investigated cases. The interaction design equations proposed by other researches are also addressed to discuss the results presented by this study

Methodology for Designing Fault-Protection Software

A document describes a methodology for designing fault-protection (FP) software for autonomous spacecraft. The methodology embodies and extends established engineering practices in the technical discipline of Fault Detection, Diagnosis, Mitigation, and Recovery; and has been successfully implemented in the Deep Impact Spacecraft, a NASA Discovery mission. Based on established concepts of Fault Monitors and Responses, this FP methodology extends the notion of Opinion, Symptom, Alarm (aka Fault), and Response with numerous new notions, sub-notions, software constructs, and logic and timing gates. For example, Monitor generates a RawOpinion, which graduates into Opinion, categorized into no-opinion, acceptable, or unacceptable opinion. RaiseSymptom, ForceSymptom, and ClearSymptom govern the establishment and then mapping to an Alarm (aka Fault). Local Response is distinguished from FP System Response. A 1-to-n and n-to- 1 mapping is established among Monitors, Symptoms, and Responses. Responses are categorized by device versus by function. Responses operate in tiers, where the early tiers attempt to resolve the Fault in a localized step-by-step fashion, relegating more system-level response to later tier(s). Recovery actions are gated by epoch recovery timing, enabling strategy, urgency, MaxRetry gate, hardware availability, hazardous versus ordinary fault, and many other priority gates. This methodology is systematic, logical, and uses multiple linked tables, parameter files, and recovery command sequences. The credibility of the FP design is proven via a fault-tree analysis "top-down" approach, and a functional fault-mode-effects-and-analysis via "bottoms-up" approach. Via this process, the mitigation and recovery strategy(s) per Fault Containment Region scope (width versus depth) the FP architecture

A review of nondestructive examination methods for new-building ships undergoing classification society survey

Classification societies require ship manufacturers to perform nondestructive examination (NDE) of ship weldments to ensure the welding quality of new-building ships. Ships can contain hundreds of kilometers of weld lines and 100% inspection of all welded connections is not feasible. Hence, a limited number of weldments are specified by rules of classification societies to be inspected on a sampling basis. There is a variation between the rules and guidelines used by different classification societies in terms of both philosophy and implementation which results in significant discrepancy in the prescribed checkpoints, numbers, and their locations. In this article, relevant sections of the rules of mainstream International Association of Classification Societies members are studied and potential ways of improving them are discussed. The authors have endeavored to make this study as comprehensive as much as possible. However, given the challenges of covering every single aspect and variable related to NDE in the classification societies’ rules and guidelines reviewed here, the authors can only attempt to cover the key features

Optimising Structural Loading and Power Production for Floating Wave Energy Converters

This is the author accepted manuscript. The final version is available from EWTEC via the link in this record.This paper investigates the design trade-off between power production and structural loading for Wave Energy Converters (WECs), based on tank test results for the Albatern 12S floating wave energy array. This work feeds into the design development process, which is currently in the concept design and testing phase. The paper focuses on two methods for reducing structural loading: limiting the power take off (PTO) torque generation capacity (for operational loads), and controlling the PTO damping (for extreme loads). The torque that can be generated by the primary PTO mechanism affects the size (and cost) of the structural components within the device. Increased torque results in a potentially greater power capture, but also greater structural loading. It is therefore important to highlight the target torque limit early in the design process. The aim of this work is to identify the optimum torque limit to refine the design towards the lowest overall Levelised Cost of Energy (LCoE). In addition, a high-level investigation of the impact of PTO damping on extreme loading has been carried out, to help to identify appropriate “operational” and “survival” sea states for the device. The paper calculates an optimum torque limit for the device at the West Harris site and quantifies the trade-off between Annual Energy Production and structural cost, using the LCoE as an optimisation criteria. The approach is in principle applicable to other technologies, if the design drivers are adjusted to the technology’s working principle.Tank testing was funded by Wave Energy Scotland (WES) as part of the Novel Wave Energy Converter Stage 1 (NWEC1) programme. This work has been carried out as part of the IDCORE programme, funded by the Energy Technology Institute and RCUK Energy programme (grant no. EP/J500847/1

An intelligent system for vessels structural reliability evaluation

An intelligent system is proposed within INCASS (Inspection Capabilities for Enhanced Ship Safety) project for evaluating ship structural reliability and assisting in fatigue damage and structure response assessment. The system combines hydrodynamic, finite element and structural reliability models.. The hydrodynamic analysis model is not discussed in this paper. The finite element model input is a mesh for the mid-ship part of the vessel. Finally, the in-house structural reliability model input is the calculated output of the previous model as well as models for estimating crack development and propagation, corrosion growth and fatigue loading. The output includes the probability of failure for all the investigated components versus time which can be used to assess safe operation through the developed decision support software. The database can receive information from various sources including inspection and robotic systems data. The case study of a capsize bulk carrier the presents structural evaluation process

Steel-concrete connections for floating wave energy converters

In order to make wave power technologies competitive within the overall energy market, there needs to be significant reductions in the levelised cost of energy (LCoE). One area for potential cost reduction is the use of cheaper materials that are suitable for use in the harsh marine environment, such as reinforced concrete, which gives good corrosion and fatigue properties while providing excellent strength and stiffness at low unit cost. Concrete has the potential to be used for a wide range of wave energy device configurations, however in general use has been limited to nearshore fixed bottom wave energy converters. To date, no dynamic floating wave energy devices have successfully utilised reinforced concrete as structural material, mainly due to the uncertainty surrounding the behaviour of critical dynamic connections between concrete sections and other materials. This paper explores the main issues surrounding steel-concrete connections for floating wave energy converters, providing a review of available design options and standards and assessing the applicability of these to WECs. A methodology is proposed for the evaluation of connection options, and a case study of the Squid 12S floating WEC (developed by Albatern) is presented.This work has been carried out as part of the IDCORE programme, funded by the Energy Technology Institute and RCUK Energy programme (grant no. EP/J500847/1

How to determine the principal dimensions of FPSO vessel

The evaluation of the principal dimensions of the Floating Production, Storage and Offloading (FPSO) system is one of the most critical tasks at the initial design stage of the vessel. It is therefore important to get this right from the onset. This paper presents a simple method of determining the optimal principal dimensions of FPSO vessels of any specified oil storage capacity. An interactive programme, the Principal Dimensions Programme (PDP) has therefore been designed to accurately evaluate them based on the required cubic number (L× B × D) and the needed oil storage capacity (as the modern segregated vessels are volume-limited). The prediction of these dimensions has been given to ensure a safe operation and optimal performance of the vessels with regards to their motion responses in deep sea waves