2,398 research outputs found
A RANS Modelling Approach for Predicting Powering Performance of Ships in Waves
No full textIn this paper, a modelling technique for simulating selfpropelled ships in waves is presented. The flow is modelledusing a RANS solver coupled with an actuator diskmodel for the propeller. The motion of the ship is takeninto consideration in the definition of the actuator disk region as well as the advance ratio of the propeller. TheRPM of the propeller is controlled using a PID-controllerwith constraints added on the maximum permissible RPMincrease rate. Results are presented for a freely surgingmodel in regular waves with different constraints put onthe PID-controller. The described method shows promisingresults and allows for the studying of several factorsrelating to self propulsion. However, more validation datais needed to judge the accuracy of the model
Numerical study of resistance and form factor of high-speed catamarans
No full textSince the prediction of resistance of the full-scale ship mainly relies on extrapolation of form factor of the model, it is important to determine the form factor precisely. Nowadays, the computer performance has been developed, commercial CFD code with Reynolds-averaged Navier-Stokes Equations (RANS), which is widely accepted and used by many researchers is capable of determining resistance components. This paper presents the development and procedures for the prediction resistance components and form factor of displacement catamarans by using commercial CFD code, STAR CCM+, with SST k-ω turbulence model. The Wigley catamarans with three hull configurations including S/L = 0.2, 0.3 and 0.4 are investigated at Froude number between 0.2 and 0.8. Resistance components, which are total (CT), skin friction (CF), viscous (CV), residual (CR) and wave (CW) resistance, form factor (1+k), form resistance interference factor (β), wave resistance interference factor (τ) and wave elevation along the hull are estimated and validated against experiment retrieved from Insel (1992). The results show that CFD code with RANS equations is capable of estimating resistance components and demonstrates that form factor increases with speed (Fn)
Is wave height necessary to determine ship performance in calm water from measurements?
No full textIn order to monitor the performance of a vessel in calm seas it is important to ensure that the operational parameters are not biased by weather conditions. This paper makes a comparison between the relationship of true wind speeds obtained from on-board anemometer measurements and hindcast MetOcean data with the wave heights obtained from the MetOcean data. The insights obtained from the correlations between wind and waves is used to make a comparison calm water model derived from ‘wind-wave’ filtering and data filtered using only the wind speed. Finally, the increase in shaft power with respect to wind speed and wave heights for discrete intervals is presented. The results presented indicate that an average decrease of 4-5% in shaft power is seen when including an additional wave filter in the calm water model. However, this discrepancy improves when a stricter wind speed filtering is used
Blockage effects on resistance prediction of high-speed catamarans
No full textModel experiment is the most reliable method to estimate ship resistance; however, price and complexities are the most disadvantage factors. Another aspect that affects the precision of the results are blockage effects due to tank dimension and model size. Some correction procedures introduced by ITTC are widely used. However only resistance components that can be corrected while flow field and wave elevation cannot be justified using the blockage correction procedures. To demonstrate how the blockage affects the flow around catamaran, this study focuses on resistance prediction and flow characteristics around high-speed catamarans using CFD code with RANS equations. Two Southampton University towing tanks – Solent and Boldrewood – are compared. The NPL 5b model is used as it is widely investigated and used in the commercial applications. Four Froude numbers (Fn = 0.273, 0.433, 0.70 and 0.90) are investigated. CFD results show that resistance components measured from the higher blockage towing tank are higher than the bigger tank. Wave contour plots and wave cut show that the higher blockage towing tank causes the higher wave elevation due to the reflection of the wall which results in differences for the wave resistance prediction between the two towing tanks
Design of high speed craft: The human factor
No full textDesign procedures for high speed craft are currently centred on performance and structural considerations. Dramatic improvements in craft performance in recent years have led to crew injury, fatigue or performance loss becoming the limiting factor for high speed operation, particularly offshore. This has resulted in the re-evaluation of the primary design considerations to centre the design process on human capabilities.In this paper a systematic procedure is developed to enable direct correlation between numerical, or model-scale, motion data and human responses in the full scale craft. The nature of different modes of motion and their specific effects on the performance of a vessel’s crew are analysed in both a quantitative and qualitative manner. This investigation has identified the factors most detrimental to crew endurance and their performance post-transit. A procedure for measuring human responses to full scale vessel motion, enabling real time measurements of crew reactions to be made, is described. Data acquired for a high speed rigid inflatable boat, including measurements of sea state, vessel motions, seat motions and human responses are discussed together with associated towing tank results and predictions of vessel motion from a numerical method. An overview of the computational techniques used for predicting motions of high speed craft is given concentrating on recent improvements to them. Such an approach, combining simulation with full scale data, allows direct correlation between crew physiological and psychological responses and the sea conditions for different craft designs. This in turn enables the human response to vessel operations to be considered when the craft are being designed.<br/
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