The Royal Institution of Naval Architects Design & Operation of Wind Farm Support Vessels 29-30 March 2017, London, UK A SUMMARY OF THE ENGINEERING PROCESS AND THE MODELLING TOOLS USED IN THE DESIGN OF A NEXT GENERATION WFSV INCORPORATING A SUSPENSION BASED RIDE CONTROL SYSTEM PROVIDING IMPROVED TRANSIT AND TRANSFER PERFORMANCE Author - M J Longman, Chief Engineer, Nauti-Craft Pty Ltd Presenter K N Johnsen, Managing Director, Nauti-Craft Pty Ltd
OFF TOPIC, BUT A GREAT PICTURE
INTRODUCTION The Task To design and build a 24m WFSV incorporating a revolutionary suspension based ride control system to deliver: improved safety and comfort in transit safe technician transfer in seas up to 2.5m Hs classification society approval The Team Client Strategic Marine Pte Ltd (Singapore) Designer Southerly Designs (Dongara, West Australia) Ride Control Nauti-Craft Pty Ltd (Dunsborough, West Australia)
BACKGROUND Nauti-Craft s suspension system has been developed with the support of The Carbon Trust s Offshore Wind Acceleration program A 1/3 rd scale of a 24m vessel used as the development platform and model validation Independent Pitch and Roll circuits are hydraulically coupled to provide passive reactive pitch and roll control Active inputs can be used to control roll-in on turns and deck attitude when slow moving or docking
MODEL DEVELOPMENT MSC ADAMS (Automated Dynamic Analysis of Mechanical Systems) used to model the entire dynamic system by incorporating the following elements : Hydraulic System Structural Components Compression and Rebound Stops Hull Water Interface Wave Input Based on known inputs (sea conditions, vessel weight and operating envelope) the model is used to determine the dynamic loads so the hydraulic and structural elements of the vessel can be designed to meet operational and Class requirements.
MODEL ELEMENTS Hydraulic Systems Model Pitch Circuit & Roll Circuit Modal damping model (op7onal) Simulates controls used to vary vessel opera7ng mode Structural Model Real data input for vessel and component masses, CoG and rota7onal iner7as Joints and bushings incorporated into model Compression and Rebound Stops Modelled as a spring with progressive soc stop and high s7ffness hard stop
MODEL ELEMENTS Hull Water Interface Each hull (and corresponding water segment) divided into 25 segments (from CAD) Water height and buoyancy spline determines buoyancy force at each segment Relative velocity is multiplied by a damping factor and buoyancy force Hull acceleration is calculated and multiplied by a mass effects factor and buoyancy force. A true vertical force is calculated for each segment The impact of planing is ignored (for this vessel)
MODEL ELEMENTS Wave Model JONSWAP wave spectrum used (representative of North Sea) Wave Period (T1) to Wave Height (Hs) relationship derived from Dogger Bank Linear fit derived for one month of data Wave spectrum calculated from 0.5/T1 to 4.0/T1 Wave speed at each frequency combined with forward velocity and a wave height is derived at each segment of the hull. Hull Water Interface Model Testing/Calibration Buoyance correlates well with Maxsurf data Added Mass factors were evaluated. Water damping vertical acceleration from ADAMS correlates well with DNV-GL code
MODEL ELEMENTS Simulations of both transit and transfer in various conditions Confirms design intent for safe transfer in a 2.5 Hs sea state Demonstrate much reduced peak vertical accelerations in transit Definition of an operating profile
MODEL OUTPUTS Hydraulic and Mechanical Hard Points Cylinder, valve and pipe sizing Mechanical control arm sizes and geometry Load spectrum produced enables Complete Finite Element Analysis of suspension related components and supports Comprehensive bearing design and life calculations Full fatigue analysis of highly stressed elements
Wave Height Range Hs m 0.0 to 0.5 0.5 to 1.0 1.0 to 1.5 1.5 to 2.0 2.0 to 2.5 2.2 to 3.0 Mid- Wave Height HS m (for analysis) % of life cycle Sta7onary 0.25 2.6 0.75 13.7 1.25 17.3 1.75 14.9 2.25 9.1 2.75 5.4 Transit Slow < 10 knots 0.0 to 0.5 0.25 0.5 to 1.0 0.75 1.0 5.0 LOADINGS AND LOAD LIMITS Load Production In field (North Sea) data from a comparable WFSV gave indicative usage profile Hs and usage analysis yields 18 life test cases 1,000 sec of dynamic data for each of 18 cases Load Limits Longitudinal in operation 0.29g collision 4.5g Lateral 0.53g High Speed Determined from operating envelope (1g max) Post Processing and Data Reduction Simulation accuracy increased to remove unrealistic data spikes DNV-GL guidance led to a factor being applied to all load cases to generate factored design loads Peak loads generated for analysis of suspension components and bearings DNV-GL has issued Approval In Principle for this design method
STRUCURAL DESIGN Aim to minimize weight while maintaining minimum factors of safety Clevis, Pin and Tang sizing - code ASME BTH used Plain spherical bearings - 18 load cases applied to SKF life calcs Design life 5 years at 3000 hours per annum Arm design Solidworks design transferred to NX NASTRAN Finite Elements Analysis Fatigue life determined by applying 18 load cases to 600,000 elements
3D views SCALE (no change)
CONCLUSION A modelling method was developed in order to design and construct a 24m WFSV designed to: Achieve 2.5m Hs safe transfer Much improved crew/technician comfort in transit DNV-GL have approved in principal the engineering method 18 load cases were used to design ride control and vessel structures An extended operating profile (compared to standard vessel) was developed Acceptable bearing and fatigue life achieved without significant weight penalty Resultant design is expected to deliver tangible safety and economic benefits to the offshore wind industry.