Much has been written about theory and practice in the law, and the tension between practitioners and theorists. Judges do not cite theoretical articles often; they rarely "apply" theories to particular cases. These arguments are not revisited. Instead the Essay explores the working and interaction of theory and practice, practitioners and theorists. The Essay starts with a story about solving a legal issue using our intellectual tools - theory, practice, and their progenies: experience and "gut." Next the Essay elaborates on the nature of theory, practice, experience and "gut." The third part of the Essay discusses theories that are helpful to practitioners and those that are less helpful. The Essay concludes that practitioners theorize, and theorists practice. They use these intellectual tools differently because the goals and orientations of theorists and practitioners, and the constraints under which they act, differ. Theory, practice, experience and "gut" help us think, remember, decide and create. They complement each other like the two sides of the same coin: distinct but inseparable.

Of Theory and Practice

Hydraulics in Civil and Environmental Engineering

Every geothermal site has its own unique set of characteristics and operating conditions. For example, the fluid produced from a geothermal well can be steam, brine, or a mixture of the two; and the temperature and pressure of the resource can vary substantially from site to site. The chemical composition of the resource can contain dissolved minerals, gases, and other hard-to-manage substances. Geothermal power plants are designed to optimize power generation by taking these site-specific conditions into account.

Energy Conversion ～水車～

Uses of ErrorLessons learnt

In a time span of over 3,000 years, the function of harbor breakwaters has remained the same (i.e., the energy dissipation), with differences depending on the general breakwater configurat...

Review of Innovative Harbor Breakwaters for Wave-Energy Conversion

Oscillating Water Column (OWC)-based power take-off systems are one of the potential solutions to the current energy problems arising from the use of nuclear fission and the consumption of fossil fuels. This kind of energy converter turns wave energy into electric power by means of three different stages: firstly wave energy is transformed into pneumatic energy in the OWC chamber, and then a turbine turns it into mechanical energy and finally the turbogenerator module attached to the turbine creates electric power from the rotational mechanical energy. To date, capture chambers have been the least studied part. In this context, this paper presents an analytical model describing the dynamic behavior of the capture chamber, encompassing the wave motion and its interaction with the OWC structure and turbogenerator module. The model is tested for the case of the Mutriku wave power plant by means of experimental results. For this purpose, representative case studies are selected from wave and pressure drop input-output data. The results show an excellent matching rate between the values predicted by the model and the experimental measured data with a small bounded error in all cases, so that the validity of the proposed model is proven.

/pdf/mathematical-modeling-of-oscillating-water-columns-wave-1qj9ix1p1i.pdf

Mathematical Modeling of Oscillating Water Columns Wave-Structure Interaction in Ocean Energy Plants

After the 2015 United Nations Climate Change Conference (COP21) the interest for clean and renewable energy is high priority in global energy policy. In this sense, the ocean offers a great potential for energy harnessing. However, in the path to commercialization, conversion systems still lack maturity. Oscillating water column (OWC) power plants are among the most promising cost-effective and ecologically compatible technologies. The NEREIDA MOWC wave power plant, located on the Basque coast of Mutriku, is a clear example of this principle. In addition, the maximum power point tracking (MPPT) strategy, which has already been used successfully in other renewable energy systems, stands out as one of the most useful schemes. In this context, this paper focuses on the implementation of a novel MPPT control approach for the OWC systems in order to optimize the power delivered to the grid. For this purpose, a full wave-to-wire plant model is introduced, and a new MPPT-based control scheme is presented. The controller continuously adjusts the energy conversion of the doubly fed induction generator according to an established MPPT curve so as to optimize the power generated. In order to demonstrate the goodness and feasibility of the proposed control scheme, its behavior is tested and compared in two representative case studies of both uncontrolled and controlled plants. In the first case, an air valve control is employed, and in the second case, an MPPT-based control strategy has been implemented. Results show that the proposed MPPT-based control successfully matches the optimum rotational speed, allowing maximum active power generation.

Rotational Speed Optimization in Oscillating Water Column Wave Power Plants Based on Maximum Power Point Tracking

Oceans, and particularly waves, offer a huge potential for energy harnessing all over the world. Nevertheless, the performance of current energy converters does not yet allow us to use the wave energy efficiently. However, new control techniques can improve the efficiency of energy converters. In this sense, the plant sensors play a key role within the control scheme, as necessary tools for parameter measuring and monitoring that are then used as control input variables to the feedback loop. Therefore, the aim of this work is to manage the rotational speed control loop in order to optimize the output power. With the help of outward looking sensors, a Maximum Power Point Tracking (MPPT) technique is employed to maximize the system efficiency. Then, the control decisions are based on the pressure drop measured by pressure sensors located along the turbine. A complete wave-to-wire model is developed so as to validate the performance of the proposed control method. For this purpose, a novel sensor-based flow controller is implemented based on the different measured signals. Thus, the performance of the proposed controller has been analyzed and compared with a case of uncontrolled plant. The simulations demonstrate that the flow control-based MPPT strategy is able to increase the output power, and they confirm both the viability and goodness.

https://www.mdpi.com/1424-8220/18/2/535/pdf

Flow Control in Wells Turbines for Harnessing Maximum Wave Power

This article covers research into cost reduction pathways for wave energy. The primary focus is the development and test of reliable and controllable power take-off (PTO) technology for oscillating water column converters (OWC). This is highly relevant to the ocean energy challenge. Extensive testing via data of the NEREIDA MOWC demonstration project, a breakwater wave plant located in the Basque location of Mutriku, using Wells turbines and Doubly Fed Induction (DFIG) generators is proposed to advance wave energy converter (WEC) devices. The control tests involve the integration of the PTO technology within a new variable controller for OWC wave power generation plants. Due to the nature of the control law, it allows monitoring faults caused by parametrical errors or system disturbances. The reliability tests by means of analysing the electrical signals have been conceived as conditioning monitoring, detection of mechanical faults and hardware damaging also fulfil a secondary aim for the reduction of maintenance cost and unscheduled downtime during operation of OWC plants.

Oscillating water column control and monitoring

Within the different types of on-shore wave-based ocean energy devices, Oscillating Water Column (OWC) converters are one of the widely used ones. This work deals with the modeling and simulation of OWC on-shore wave power plants. The study is particularized for the case of the Mutriku's MOWC power plant. The model for the wave, chamber and turbo-generator module is implemented using a Characteristic Curve Tracking Control and then validated by means of experimental data. Results show an excellent matching between the values predicted by the model and measured data.

Jon Lekube

Papers

Mathematical Modeling of Oscillating Water Columns Wave-Structure Interaction in Ocean Energy Plants

Rotational Speed Optimization in Oscillating Water Column Wave Power Plants Based on Maximum Power Point Tracking

Flow Control in Wells Turbines for Harnessing Maximum Wave Power

Oscillating water column control and monitoring

Modeling of Oscillating Water Column wave energy systems