Journal of Offshore Mechanics and Arctic Engineering-transactions of The Asme 

About: Journal of Offshore Mechanics and Arctic Engineering-transactions of The Asme is an academic journal published by ASM International. The journal publishes majorly in the area(s): Finite element method & Nonlinear system. It has an ISSN identifier of 0892-7219. Over the lifetime, 1929 publications have been published receiving 24991 citations. The journal is also known as: JOMAE & Offshore mechanics and Arctic engineering.

VIVACE (Vortex Induced Vibration Aquatic Clean Energy): A New Concept in Generation of Clean and Renewable Energy From Fluid Flow

Abstract: Any device aiming to harness the abundant clean and renewable energy from ocean and other water resources must have high energy density, be unobtrusive, have low maintenance, be robust, meet life cycle cost targets, and have a 10-20 year life. The vortex induced vibration aquatic clean energy (VIVACE) converter-invented by Bernitsas and Raghavan, patent pending through the University of Michigan-satisfies those criteria. It converts ocean/river current hydrokinetic energy to a usable form of energy such as electricity using VIV successfully and efficiently for the first time. VIVACE is based on the idea of maximizing rather than spoiling vortex shedding and exploiting rather than suppressing VIV. It introduces optimal damping for energy conversion while maintaining VIV over a broad range of vortex shedding synchronization. VIV occurs over very broad ranges of Reynolds (Re) number Only three transition regions suppress VIV. Thus, even from currents as slow as 0.25 m/s, VIVACE can extract energy with high power conversion ratio making ocean/river current energy a more accessible and economically viable resource. In this paper, the underlying concepts of the VIVACE converter are discussed. The designs of the physical model and laboratory prototype are presented. A mathematical model is developed, and design particulars for a wide range of application scales are calculated. Experimental measurements on the laboratory prototype are reported in the sequel paper and used here for preliminary benchmarking.

Constrained Optimal Control of a Heaving Buoy Wave-Energy Converter

Abstract: Current prognoses are that, unless counteracted by very strong political measures, the world will meet both energy shortage and climate crisis within a horizon of a few decades, both of which are strongly related to our dependence on fossil fuels. Renewable energy sources may be harvested sustainably, and developing technology for their exploitation therefore forms an obvious part of strategies to reduce emissions and secure energy supply. Wave energy is a resource with relatively high power density, readily available along the coasts, and thus coinciding with the areas where industry and people tend to be accumulated. In some regions this resource is large enough to form a significant part of the energy mix. The technology for harnessing the power of ocean waves is today still on the research and development stage. The challenge is to make a design where the costs of investment, operation and maintenance (in terms of money, resources and energy) can be justified by the availability and potential earnings. This thesis focuses on two aspects of systems for wave energy conversion: How to model such systems, which is important for understanding and design, and how to control their motion, which is crucial for the primary power conversion – the inevitable step that forms the basis for revenues and energy output from such a device. The dissertation is based on articles published in scientific conferences and journals, as well as an account for background of the undertaken research and the methods used. The bond graph modelling language has been chosen as a promising aid for the modelling of the power converter dynamics. It enables a systematic and transparent approach to the path from drawing board to mathematical equations. Examples show how energy conversion systems may be modelled and simulated within this framework. These include heave-motion models for a semi-submerged sphere, a platform/buoy two-body system and a smallscale oscillating water column (OWC), as well as wave-to-wire models of two made-up systems. The OWC model was also studied by laboratory experiments. A range of control strategies has been studied and compared by numerical simulation, and in one case also by laboratory experiments. These strategies include phase control by latching and by clutching, approximations to complex-conjugate control, and model predictive control (MPC). Constraint handling and real-time parameter tuning are discussed, too. The constrained optimal power absorption is investigated, and for the example of a semi-submerged heaving sphere in irregular waves it is found that MPC in combination with a Kalman filter predictor is able to provide an absorbed power in excess of 90% as compared to the non-causal (and hence not completely realisable) constrained optimum. Other causal controller implementations gives an absorbed power ranging from 10 to 90% of that achieved with MPC. The best performing control strategies, however, involve a large flow of reactive power through the machinery, which in normal irregular-wave operation may give peak-to-average power ratio as high as 25 and above. This represents a challenge to the design of machinery and controller. An interesting observation from the numerical simulations is the possibility of increased absorbed power in irregular waves as compared to regular waves having about the same wavelength characteristics and the same wave power level. An explanation is suggested for this phenomenon.

Hydrodynamic damping. flow-induced oscillations, and biharmonic response

Abstract: A brief review of damping is followed by a comparison of three sets of lift-force data for circular cylinders, subjected only to transverse oscillation. Then the significance of two-dimensional or biharmonic oscillations (in both the in-line and transverse directions) is discussed in light of experiments undertaken for that purpose, to simulate more closely the true nature of flow-induced oscillations.

A Comparison of Selected Strategies for Adaptive Control of Wave Energy Converters

Abstract: Current prognoses are that, unless counteracted by very strong political measures, the world will meet both energy shortage and climate crisis within a horizon of a few decades, both of which are strongly related to our dependence on fossil fuels. Renewable energy sources may be harvested sustainably, and developing technology for their exploitation therefore forms an obvious part of strategies to reduce emissions and secure energy supply. Wave energy is a resource with relatively high power density, readily available along the coasts, and thus coinciding with the areas where industry and people tend to be accumulated. In some regions this resource is large enough to form a significant part of the energy mix. The technology for harnessing the power of ocean waves is today still on the research and development stage. The challenge is to make a design where the costs of investment, operation and maintenance (in terms of money, resources and energy) can be justified by the availability and potential earnings. This thesis focuses on two aspects of systems for wave energy conversion: How to model such systems, which is important for understanding and design, and how to control their motion, which is crucial for the primary power conversion – the inevitable step that forms the basis for revenues and energy output from such a device. The dissertation is based on articles published in scientific conferences and journals, as well as an account for background of the undertaken research and the methods used. The bond graph modelling language has been chosen as a promising aid for the modelling of the power converter dynamics. It enables a systematic and transparent approach to the path from drawing board to mathematical equations. Examples show how energy conversion systems may be modelled and simulated within this framework. These include heave-motion models for a semi-submerged sphere, a platform/buoy two-body system and a smallscale oscillating water column (OWC), as well as wave-to-wire models of two made-up systems. The OWC model was also studied by laboratory experiments. A range of control strategies has been studied and compared by numerical simulation, and in one case also by laboratory experiments. These strategies include phase control by latching and by clutching, approximations to complex-conjugate control, and model predictive control (MPC). Constraint handling and real-time parameter tuning are discussed, too. The constrained optimal power absorption is investigated, and for the example of a semi-submerged heaving sphere in irregular waves it is found that MPC in combination with a Kalman filter predictor is able to provide an absorbed power in excess of 90% as compared to the non-causal (and hence not completely realisable) constrained optimum. Other causal controller implementations gives an absorbed power ranging from 10 to 90% of that achieved with MPC. The best performing control strategies, however, involve a large flow of reactive power through the machinery, which in normal irregular-wave operation may give peak-to-average power ratio as high as 25 and above. This represents a challenge to the design of machinery and controller. An interesting observation from the numerical simulations is the possibility of increased absorbed power in irregular waves as compared to regular waves having about the same wavelength characteristics and the same wave power level. An explanation is suggested for this phenomenon.