MULTI-DIMENSIONAL SURROGATE BASED AFT FORM OPTIMIZATION OF SHIPS USING HIGH FIDELITY SOLVERS

Surrogate (metamodel) based optimization has numerous potential applications in the field of naval architecture. It is aimed here to establish a methodology for the aft form optimization for minimum viscous resistance, thus the present study is focused on the aft form where the viscous effects become dominant. It is necessary to solve this problem within acceptable time span from practical naval architectural point of view which requires metamodeling techniques currently under investigation. Accordingly, the present paper investigates the metamodeling ability of the Kriging interpolation and attempts to explore its capabilities and limitations in the aft form optimization from viscous resistance point of view. As metamodeling techniques become more widely used, their constraints are more apparent. Especially in highly nonlinear design spaces, the effect of dimensionality should be taken into consideration. Taking all those factors into account, the present paper is to examine the capabilities of Kriging and to establish the learning performance in terms of RMS error, correlation coefficient and required number of training points according to selected optimization algorithm for multidimensional ship design problem. The results show that, at least 5% reduction in viscous pressure drag can be attained by the present optimization methodology

An automated methodology for optimisation with respect to vessel manoeuvring

Over the past two decades the marine industry has been facing ever more stringent and radical environmental aims. These are not only been defined by the International Maritime Organisation (IMO), but also by individual countries defining limitations to greenhouse gases emitted by vessels. To combat this the industry has turned towards the use of more complex fluid analysis tools, both model scale tests and computational simulations. This analysis has not only focused on hull design, but also on hull roughness, hull propeller rudder interaction and the marine environment. The focus of this PhD research is to develop methodologies that can be utilised within the industry to optimise vessel performance. With this research optimisation aimed towards improving vessel manoeuvring, with focus away from the traditional nondimensional methodologies. To do so, this research aims to lean heavily on the utilisation of Reynolds Averaged Navier Stokes (RANS) method within Computational Fluid Dynamics (CFD). Towing tests have been considered the primary means of evaluating designs, not only for resistance but also for vessel motions. This includes the analysis forces and motions from both waves and manoeuvring tests. These tests however can be time consuming and financially costly. Therefore, the industry has begun to utilise CFD analysis at the early design stage as a low-cost and fast alternative. Not only this, but in recent years CFD has begun to achieve a level of accuracy matching towing tank tests. Due to these factors this research has a focus on the use of such computational means to improve vessel performance, with extensive validation against multiple towing tank tests. The research has a focus on developing and understanding that can be used to quickly evaluate a potential ship design’s manoeuvring characteristics. The methodology for simulating a captive harmonic test is presented, which has been validated against towing tank data conducted for the SIMMAN 2014 conference. This methodology is used in conjunction with a fully parametric hull form, developed within this research, to create and evolve equations used for ranking the hull forms manoeuvring performance. These unique equations are used in two optimisations cycles, one on the NPL hull and a further one on a custom hull to improve the vessels performance and efficiency. The optimum NPL hull forms are evaluated through a virtual turning circle manoeuvring simulation in CFD to quantify the improvements made through optimisation. This research developed a novel methodology for ranking manoeuvring characteristics that significantly reduced the overall optimisation time, as well as producing manoeuvring gains over 20% when evaluated in a simulated turning circle manoeuvre. In addition, the research has also presented best practice approaches for developing such a scheme and how to create a parametric setup that enables quick and accurate CFD simulations for complex manoeuvring simulations. This has been extensively validated against benchmark studies of the DTMB hull form from the SIMMAN 14 towing tank data.Over the past two decades the marine industry has been facing ever more stringent and radical environmental aims. These are not only been defined by the International Maritime Organisation (IMO), but also by individual countries defining limitations to greenhouse gases emitted by vessels. To combat this the industry has turned towards the use of more complex fluid analysis tools, both model scale tests and computational simulations. This analysis has not only focused on hull design, but also on hull roughness, hull propeller rudder interaction and the marine environment. The focus of this PhD research is to develop methodologies that can be utilised within the industry to optimise vessel performance. With this research optimisation aimed towards improving vessel manoeuvring, with focus away from the traditional nondimensional methodologies. To do so, this research aims to lean heavily on the utilisation of Reynolds Averaged Navier Stokes (RANS) method within Computational Fluid Dynamics (CFD). Towing tests have been considered the primary means of evaluating designs, not only for resistance but also for vessel motions. This includes the analysis forces and motions from both waves and manoeuvring tests. These tests however can be time consuming and financially costly. Therefore, the industry has begun to utilise CFD analysis at the early design stage as a low-cost and fast alternative. Not only this, but in recent years CFD has begun to achieve a level of accuracy matching towing tank tests. Due to these factors this research has a focus on the use of such computational means to improve vessel performance, with extensive validation against multiple towing tank tests. The research has a focus on developing and understanding that can be used to quickly evaluate a potential ship design’s manoeuvring characteristics. The methodology for simulating a captive harmonic test is presented, which has been validated against towing tank data conducted for the SIMMAN 2014 conference. This methodology is used in conjunction with a fully parametric hull form, developed within this research, to create and evolve equations used for ranking the hull forms manoeuvring performance. These unique equations are used in two optimisations cycles, one on the NPL hull and a further one on a custom hull to improve the vessels performance and efficiency. The optimum NPL hull forms are evaluated through a virtual turning circle manoeuvring simulation in CFD to quantify the improvements made through optimisation. This research developed a novel methodology for ranking manoeuvring characteristics that significantly reduced the overall optimisation time, as well as producing manoeuvring gains over 20% when evaluated in a simulated turning circle manoeuvre. In addition, the research has also presented best practice approaches for developing such a scheme and how to create a parametric setup that enables quick and accurate CFD simulations for complex manoeuvring simulations. This has been extensively validated against benchmark studies of the DTMB hull form from the SIMMAN 14 towing tank data

Fishing the waves: comparing GAMs and random forest to evaluate the effect of changing marine conditions on the energy performance of vessels

The optimization of consumption and the reduction of gas emissions in fisheries rely on a thorough examination of all factors affecting the energy balance of fishing vessels. Engines, propellers, or the hydrodynamic characteristics of vessels and gears are unquestionably the primary factors affecting this balance, and an improvement in energy efficiency based on these factors is typically attained through technical modifications to existing technologies. Behavioral modifications, such as a reduction in operational speeds or the selection of closer fishing grounds, are another option. There may still be room for improvement in behavioral responses, for instance by adapting fishing strategies in response to changing weather and sea conditions. As far as the authors are aware, the influence of varying sea state and wind conditions on the energy expenditure of fishing vessels has not yet been investigated and is the focus of this research. In this study, wind and wave actions were associated with the observed activity of three fishing vessels operating in the northern Adriatic Sea: an OTB, a PTM, and a TBB trawler. The analysis made use of a comparison between two different approaches, generalized additive models (GAMs) and random forest, in order to quantify the significance of each variable on the response and generate consumption forecasts. In our analysis, the observed influence of predictors was significant albeit occasionally ambiguous. Wave height had the most obvious impact on energy expenditure, with the towing and gear handling phases being the most affected by wave action. Conversely, navigation seemed to be mostly unaffected by significant wave heights up to 1.5 meters, with unclear effects on consumption estimated above this threshold. The relationship between winds and fuel consumption was found to be nonlinear and ambiguous; hence, its significance should be investigated further

Cumulative index to NASA Tech Briefs, 1986-1990, volumes 10-14

Tech Briefs are short announcements of new technology derived from the R&D activities of the National Aeronautics and Space Administration. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This cumulative index of Tech Briefs contains abstracts and four indexes (subject, personal author, originating center, and Tech Brief number) and covers the period 1986 to 1990. The abstract section is organized by the following subject categories: electronic components and circuits, electronic systems, physical sciences, materials, computer programs, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences