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Cross-flow turbine performance and flow fields exhibit cycle-to-cycle variations, though this is often implicitly neglected through time- and phase-averaging. This variability could potentially arise from a variety of mechanisms—inflow fluctuations, the stochastic nature of dynamic stall, and cycle-to-cycle hysteresis—each of which have different implications for our understanding of cross-flow turbine dynamics. In this work, the extent and sources of cycle-to-cycle variability for both the flow fields and performance are explored experimentally under two, contrasting operational conditions. Flow fields, obtained through two-dimensional planar particle image velocimetry inside the turbine swept area, are examined in concert with simultaneously measured performance. Correlations between flow-field and performance variability are established by an unsupervised hierarchical flow-field clustering pipeline. This features a principal component analysis pre-processor that allows for clustering based on all the dynamics present in the high-dimensional flow-field data in an interpretable, low-dimensional subspace that is weighted by contribution to overall velocity variance. We find that the flow-field clusters and their associated performance are correlated primarily with inflow fluctuations, despite relatively low turbulence intensity, that drive variations in the timing of the dynamic stall process. Further, we find no evidence of substantial cycle-to-cycle hysteresis. Cycle-to-cycle performance variability occurs earlier in the cycle than flow-field variability, indicating the limits of co-temporal correlation between performance and flow fields, but clustering reveals persistent ties between performance and flow-field variability during the upstream portion of the turbine rotation. The approach employed here provides a more comprehensive picture of cross-flow turbine flow fields and performance than aggregate, statistical representations. [ABSTRACT FROM AUTHOR]

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In this study, the computational and experimental examination of the hydraulic cross-flow turbine (CFT) is presented. The experimental studies are conducted at the turbine laboratory of Gebze Technical University. The commercial Computational Fluid Dynamics (CFD) software, Star CCM+, is employed to calculate three-dimensional, incompressible, steady Reynolds-Averaged Navier–Stokes (RANS) equations for the flow inside the CFT. In the numerical model, the rotational motion of the blades is modeled by means of the moving reference frame approach. The correlation between the turbulent viscosity and the velocities is acquired using the standard k-ɛ turbulence model. The computational results are obtained in terms of the torque, power, and efficiency of the turbine. The outcome of this research reveals that the CFD software used in this study can reliably be used to predict experiments since the numerical model can accurately estimate the experimental values of the torque, power, and efficiency of the CFT. [ABSTRACT FROM AUTHOR]

Copyright of BHM Berg- und Hüttenmännische Monatshefte is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A cross-flow wind turbine has a high torque coefficient at a low tip speed ratio; therefore, it is a good candidate for a self-starting turbine. This study aims to investigate the best configuration between guide vanes and cross-flow vertical axis wind turbine. The experiment test was carried out to determine the turbine with the highest power coefficient. The cross-flow turbine has 14, 18, and 22 blades with using 6,10 and 14 blades of guide vane (GV) was developed in this study, employing 15°, 25°, 35°, 45°, 55°, 65°, and 75° of tilt angles in fifth different wind speed conditions 4 m/s, 6 m/s, 7.5 m/s, 9.20 m/s, and 11 m/s. The turbine has 22 blades with 14 GV blades at 55° of tilt angle blades producing more remarkable turbine performance improvement than other blades. The highest power coefficient (CP) of cross-flow using 14 GV blades at 55° was 0.0162 at 0.289 TSR, which increased around 59% of the turbine's performance using GV. [ABSTRACT FROM AUTHOR]

The development of microchannels with open flow for use in irrigation and rainy areas is challenged by electricity generation via hydrokinetic devices in shallow and low velocity flows. Conventional hydrokinetic turbines are known to be highly dependent on current speed and water depth. Another drawback of conventional turbines is their low efficiency. These shortcomings lead to the need to accelerate the flow in the channel system to enhance the extracted power. The method of deploying a novel turbine configuration in irrigation channels can help overcome the low performance of conventional hydrokinetic turbines. Therefore, this study experimentally presents a bidirectional diffuser-augmented channel that includes dual cross flow/Banki turbines. Results show that the maximum efficiency of the overall system with two turbines is nearly 55.7%. The efficiency is low relative to that of hydraulic turbines. Nevertheless, the result can be considered satisfactory given the low head of the present system. The use of this system will contribute to a highly efficient utilization of flows in rivers and channels for electrical energy generation in rural areas. [ABSTRACT FROM AUTHOR]

Abstract  The development of a three-hole pressure probe with back-flushing combined with a conductivity probe, used for measuring simultaneously the magnitude and direction of the velocity vector in complex air–water flows, is described in this paper. The air–water flows envisaged in the current work are typically those occurring around the rotors of impulse hydraulic turbines (like the Pelton and Cross-Flow turbines), where the flow direction is not known prior to the data acquisition. The calibration of both the conductivity and three-hole pressure components of the combined probe in a rig built for the purpose, where the probe was placed in a position similar to that adopted for the flow measurements, will be reported. After concluding the calibration procedure, the probe was utilized in the outside region of a Cross-Flow turbine rotor. The experimental results obtained in the present study illustrate the satisfactory performance of the combined probe, and are encouraging toward its use for characterizing the velocity field of other complex air–water flows. [ABSTRACT FROM AUTHOR]

The urban landscape water areas are vulnerable to cyanobacterial blooms. However, current cyanobacteria removal equipment is unsuitable for urban landscape water due to its large size, high energy consumption, and complex operation. Therefore, the present study aims to design and optimize a novel cyanobacterial control system for urban water areas using FLUENT simulation software, as well as to construct the cyanobacterial removal module and assess its effectiveness based on the optimized parameters. The results showed increases in the velocity distribution uniformity index (γv) and the cyanobacterial concentration distribution uniformity index (γm) by 30% and 52.9%, respectively, following the addition of the water distributor. In addition, the γv and γm values were first decreased and then increased with increasing the diversion bin lengths, reaching an optimal value at a diversion bin length of 160 mm. On the other hand, the lowest distortion parameter (K) value was observed using the 300-mesh filter bag, indicating the best uniformity of the filter surface. The optimized parameter-based removal module can effectively remove different cyanobacteria bloom levels. Indeed, the removal efficiency was proportional to the severity of the cyanobacteria bloom. Furthermore, the removal rate was increased by increasing the rotation speed of the removal module, resulting in a shorter operation time. The cyanobacterial control system can be applied to control cyanobacterial blooms in urban landscape water areas. [ABSTRACT FROM AUTHOR]

Bangladesh has a huge potential for utilizing renewable energy with the availability of sources for solar, wind, hydro, and biogas. This paper provides a comprehensive analysis of the potential for renewable energy sources and predicts optimal sites for renewable plant implementation in Bangladesh. A country-wise mapping approach is followed by validation of prediction using multi-criteria decision analysis (MCDA) known as the analytical hierarchy process (AHP) which will aid in the planning and execution of Bangladesh's upcoming expansion of renewable farms and will also be a useful tool for policymakers. Moreover, an economic analysis for 50 MW solar and wind power plant has been presented to estimate the levelized cost of electricity (LCoE) of the system and society. This work predicts the enormous potential for the expansion of renewable energy by assessing the appropriate future sites, economic viability, and provides several suggestions on the basis of the analysis from Bangladesh's perspective. [ABSTRACT FROM AUTHOR]

Reconstruction of unsteady vortical flow fields from limited sensor measurements is challenging. We develop machine learning methods to reconstruct flow features from sparse sensor measurements during transient vortex–airfoil wake interaction using only a limited amount of training data. The present machine learning models accurately reconstruct the aerodynamic force coefficients, pressure distributions over airfoil surface, and two-dimensional vorticity field for a variety of untrained cases. Multi-layer perceptron is used for estimating aerodynamic forces and pressure profiles over the surface, establishing a nonlinear model between the pressure sensor measurements and the output variables. A combination of multi-layer perceptron with convolutional neural network is utilized to reconstruct the vortical wake. Furthermore, the use of transfer learning and long short-term memory algorithm combined in the training models greatly improves the reconstruction of transient wakes by embedding the dynamics. The present machine-learning methods are able to estimate the transient flow features while exhibiting robustness against noisy sensor measurements. Finally, appropriate sensor locations over different time periods are assessed for accurately estimating the wakes. The present study offers insights into the dynamics of vortex–airfoil interaction and the development of data-driven flow estimation. [ABSTRACT FROM AUTHOR]

Structured-light-based profilometry techniques provide a simple and suitable tool to characterize experimentally the dynamics of the interaction between fluid and structure. The study implements a method based on the analysis of a sinusoidal fringe pattern. This method allows the retrieval of a three dimensional surface shape from a two dimensional video recording of the deformation of fringes projected on the surface. A detailed description of the method and the implementation is provided which will facilitate its adaption to and utilization in custom FSI applications (the code is published under open-source license). An application example is presented in the form of an experiment. A hyperflexible hydrofoil is set under forced rotational oscillation in a closed water tunnel to mimic the characteristics of a vertical-axis hydrokinetic cross-flow turbine. The flexible structures encounter large deformations which are linked to corresponding hydrodynamic forces. To capture this interdependence, the deformations were recorded in sync with forces registered with a six-axis load cell. A validation of the method is presented and shows good accuracy in the deformation measurements of a hyperflexible hydrofoil. A benefit compared to other common techniques like Laser-interferometer measurements is the simplicity and modest hardware requirements of the method with the possibility to acquire height fields with good spatial and temporal resolution, which allows a spectral analysis of the surface deformation. The hydrodynamic forces are presented together with the corresponding deformation of the structure, and spectral analyses are performed which demonstrates the possibilities of the proposed method. In summary, the presented method allows the analysis of fluid–structure interactions using a simple assembly consisting of a projector and a high-speed camera. [ABSTRACT FROM AUTHOR]

Globally abundant wave energy for power generation attracts ever increasing attention. Because of non-linear dynamics and potential uncertainties in ocean energy conversion systems, generation productivity needs to be increased by applying robust control algorithms. This paper focuses on control strategies for a small ocean energy conversion system based on a direct driven permanent magnet synchronous generator (PMSG). It evaluates the performance of two kinds of control strategies, i.e., traditional field-oriented control (FOC) and robust adaptive control. The proposed adaptive control successfully achieves maximum velocity and stable power production, with reduced speed tracking error and system response time. The adaptive control also guarantees global system stability and its superiority over FOC by using a non-linear back-stepping control technique offering a better optimization solution. The robustness of the ocean energy conversion system is further enhanced by investigating the Lyapunov method and the use of a DC-DC boost converter. To overcome system complexity, turbine-generator based power take-off (PTO) is considered. A Matlab/Simulink study verifies the advantages of a non-linear control strategy for an Oscillating Water Column (OWC) based power generation system. [ABSTRACT FROM AUTHOR]

Hydrokinetic turbine proximity to deformable free surface in shallow open surface flume has significant impacts on flow hydrodynamics around the turbine, affecting the hydrodynamic performance of the hydrokinetic turbine. Also, the free surface deformation extent depends on the flow restriction created by the turbine, which works as a barrier to the fluid flow. This phenomenon is called solid blockage or formally the blockage. The present investigation aims to assess the effects of blockage and free surface deformation on flow hydrodynamics around a flapping-blade vertical-axis hydrokinetic turbine called "Hunter turbine." A 1:20 Hunter turbine model was fabricated and experimentally investigated in a laboratory altogether with transient CFD simulations. The simulation was carried out for both rigid lid surfaces and free surface assumptions, while k–ω SST turbulence model was used for both cases, and the volume-of-fluid method was employed for the free surface model. Simulations results were verified by empirical data, showing a good agreement. The power coefficient reached 0.23 in the best-case scenario, and the maximum power coefficient occurs at a flow coefficient between 0.39 and 0.43 for all investigated flows. CFD results demonstrated that the flow deformation blockage ratio increment leads to greater exerted torque on the turbine blades. While the mean torque coefficient for the rigid lid is bounded up to 0.18, the mean torque coefficient in the presence of the free surface reaches 0.4 at the same blockage. Also, the power coefficient is increased by 10%. Furthermore, rigid lid surface simulation shows that increasing the blockage ratio also increases power coefficient such that the power coefficient at blockage ratio 0.32 is approximately three times larger than the power coefficient at blockage ratio 0.2. [ABSTRACT FROM AUTHOR]

Predicting the velocity distribution of double horizontal axis tidal turbines (DHATTs) is significant for the effective development of tidal streams. This current research gives an account on double turbine wake theory and flow structure of DHATT connected to single support by using the joint axial momentum theory and computational fluid dynamics (CFD) method. Characteristics of single turbine wake were previously studied with two theoretical equations predicting the initial upstream velocity closer to the turbine, and it's lateral distributions along the downstream of the turbine. This current works agreed with the previous wake equations, which was used for predicting the velocity region along the downstream of the turbines. Flow field separating the two turbines is complicated in nature due to the indirect disturbance of turbines and no report was found on this central region. The Central region in the downstream flow is initially suppressed due to the blockage effects with a high velocity close to the free stream. Lateral expansion of two turbine wakes penetrated the central region with velocity reduction and followed by the flow recovery further downstream. This work provides more understandings of the wake and its central mixing region for double turbines with a proposed theoretical model. [ABSTRACT FROM AUTHOR]

The characteristics of the fluid–structure interaction on the flexible blades of a horizontal-axis water turbine are studied; this bioinspired technology features mechanical simplicity, performance and lifetime improvement, and low fish impact risk, all characteristics of a truly sustainable renewable energy exploitation. A surface-tracking method synchronized with force measurements was applied on a surrogate model of single-bladed, vertical-axis water turbine in a water channel. This allows for the characterization of the structural deformations and their link to the hydrodynamic forces, over a large range of turbine designs and operating points. It is shown that the phase angles of the maxima in blade deformation coincide with those of the load maxima on a rigid blade in identical flow conditions. The influence of the turbine's tip/speed ratio on the blade deformation and blade load is investigated. With the chosen blade design, hydrofoil deformation is found to be maximum in the operating points where the performance improvement is maximized ( k o = 0.3 ). With lower values of reduced frequency (corresponding to lower rotation speed), fluid-induced forces dominate the fluid–structure interaction. Conversely, at higher frequencies, structural inertia dominates the interaction, and blade deformation is again reduced. Results suggest that the optimal blade rigidity may depend on the operating point; nevertheless the potential of the flexible-blade design is demonstrated through clear linking of fluid-induced forces and blade deformation in the complex flow conditions of the Darrieus water turbine. [ABSTRACT FROM AUTHOR]

A marine current turbine (MCT) that extracts energy from ocean currents should be hydrodynamically and structurally stable to generate uninterrupted power. This can be achieved through the shape optimization of MCT blades. In this work, a horizontal axis MCT of 0.8 m diameter was optimized through multi-fidelity numerical approach. The design parameters such as blade pitch angle (θ) and the number of rotor blades (NR) were modified to increase the power coefficient (CP) and to reduce the von-Mises stress (σv) using multi-objective optimization technique. A coupled fluid–structure interaction method is used for fluid and structural analysis of MCT. Also, an analysis for identifying the cavitation inception is incorporated. A surrogate-based optimization code was used to produce a Pareto optimal front. The MCT with CP = 0.451 encountered σv = 125.83 MPa and a high total deformation (TD) = 20.259 mm near the blade tip. The TD of the same MCT blade was later reduced to 1/3rd of its actual value by identifying an alternate turbine material. The losses due to vortices, wake generation, and cavitation study are discussed in the present work. [ABSTRACT FROM AUTHOR]

The aerodynamic characteristics of Darrieus vertical axis wind turbines (VAWTs) are affected by several geometrical parameters. Airfoil shape is one of the important factors which have not been received enough attention in the past, compared to other parameters such as solidity, number of blades, chord length, rotor diameter, pitch angle and aspect ratio. In this paper, four airfoils with varying maximum thickness (12%, 15%, 18% and 21%) are investigated by calculating the aerodynamic characteristics of Darrieus VAWTs using computational fluid dynamics technology. The power and torque characteristics, as well as their flow field characteristics, are analyzed. The results indicate that the power coefficient follows a trend of CP_NACA 0018 > CP_NACA 0015 > CP_NACA 0021 > CP_NACA 0012 below an optimum TSR, while it increases with the decrease in airfoil maximum thickness beyond the optimum TSR. The optimum TSR and operational zone also increase with the decrease in airfoil maximum thickness. An optimized airfoil thickness is determined to be between 15 and 18% for a relatively high power coefficient and appropriate optimum TSR, as well as a wider operational zone and a high efficiency band. Moreover, the airfoil maximum thickness influences the strength and region of the vorticity, as well as the interactions between blades and shed vortex, being the main reason for the observed differences in instantaneous torque coefficient. The vorticity of NACA 0015 model is weaker and smaller than that of NACA 0021 model when TSR is 2.0. [ABSTRACT FROM AUTHOR]

Wind energy, together with other renewable energy sources, are expected to grow substantially in the coming decades and play a key role in mitigating climate change and achieving energy sustainability. One of the main challenges in optimizing the design, operation, control, and grid integration of wind farms is the prediction of their performance, owing to the complex multiscale two-way interactions between wind farms and the turbulent atmospheric boundary layer (ABL). From a fluid mechanical perspective, these interactions are complicated by the high Reynolds number of the ABL flow, its inherent unsteadiness due to the diurnal cycle and synoptic-forcing variability, the ubiquitous nature of thermal effects, and the heterogeneity of the terrain. Particularly important is the effect of ABL turbulence on wind-turbine wake flows and their superposition, as they are responsible for considerable turbine power losses and fatigue loads in wind farms. These flow interactions affect, in turn, the structure of the ABL and the turbulent fluxes of momentum and scalars. This review summarizes recent experimental, computational, and theoretical research efforts that have contributed to improving our understanding and ability to predict the interactions of ABL flow with wind turbines and wind farms. [ABSTRACT FROM AUTHOR]

In the present study, the effect of the turbine solidity on the performance of helical cross-flow hydrokinetic turbines is numerically investigated under different flow conditions. Four turbines, with different solidities of 0.15, 0.2, 0.25 and 0.3, were investigated in five dissimilar flow conditions with Froude numbers of 0.0714, 0.143, 0.214, 0.286 and 0.357. The devices employed in the analyses were three-bladed with the diameter of 1 m and length of 1.5 m. They were positioned horizontally in a rectangular-shaped channel with a perpendicular alignment to the flow direction. Symmetrical NACA0018 hydrofoils, which are twisted with an angle of 120°, were used in the blade design. The investigation results have shown that the turbines with the solidity values 0.15 and 0.2 are more efficient than the other two cases. Considering all five flow conditions, the models have displayed the worst performance at a tip speed ratio of 4.0. [ABSTRACT FROM AUTHOR]

The complex structure at trailing edge reduces the manufacturing precision, which results in an error in the size of the trailing edge structure. In this study, the performance of a stage high-pressure turbine (HP turbine) is calculated out in three dimensions. In the HP turbine guide vane, the trailing edge cutback configuration is adopted. Through three-dimensional simulation, the complex flow around the trailing edge with cutback cooling configuration is presented in this study, and the manufacturing precision reduction due to the complex structure at trailing edge is considered. Furthermore, the effect of trailing edge lip thickness and deflection of the stator on the turbine performance is discussed. Overall, as the press-side lip thickness increasing, the turbine efficiency and turbine inlet flow are reduced. However, the changes in the turbine work output are relatively complex. On the other hand, as the spacing between suction-side lip and press-side lip increases, turbine performance becomes worse. Both of the turbine efficiency and the turbine work output become smaller, while the turbine inlet flow becomes bigger. The effect of the spacing between suction-side lip and press-side lip is obviously greater than that of the press-side lip thickness. The change of the press-side lip thickness has little effect on the relation between the turbine performance and the spacing between suction-side lip and press-side lip. However, when the spacing between suction-side lip and press-side lip deviates from the baseline value, the effect law of the press-side lip thickness on the turbine performance will be affected. As the press-side lip thickness increases, it leads to an increase in the low-velocity zone at both of the pressure-side and suction-side trailing edge. And more main stream is affected or mixed into the wake flow. When the spacing between suction-side lip and press-side lip becomes smaller, the low-velocity zone at the trailing edge is smaller, and the change of vortex with the press-side lip thickness is affected. With a bigger spacing between suction-side lip and press-side lip, the variation is contrary. [ABSTRACT FROM AUTHOR]

Benzo[a]pyrene is a carcinogen often present in diesel. For pervaporative removal of benzo[a]pyrene from n-tetradecane, representing a model diesel composition, both conventional as well as statistically designed experimental methods have been carried out. The effect of membrane composition, thickness, the effect of membrane pretreatment time and operating temperature on pervaporative separation have been investigated by response surface methodology, RSM for efficient permeation of target compound. The suitable membrane has been further used to study the effect of different physico-chemical parameters on permeation conventionally. RSM has also been applied to optimize the operational conditions of pervaporation process to maximize the response, i.e., the pervaporation separation index. With the design of experiments, the quadratic response surface models have been developed to link the response with input variables via mathematical relationships. The maximum value of Pervaporation Separation Index obtained is 1.9654 kg m−2 h−1. The optimized process condition’s run time is 10.79 h, the feed PAH concentration is 166.34 ppm with a permeate side pressure of 0.73 mmHg and an operating temperature of 451.25 K. [ABSTRACT FROM AUTHOR]

The assessment of climate change and its impacts on hydropower generation is a complex issue. This paper evaluates the application of representative concentration pathways (RCPs, 2.6, 4.5, and 8.5) with the change factor (CF) method and the statistical downscaling method (SDSM) to generate six climatic scenarios of monthly temperature and rainfall over the period 2020-2049 in the Karkheh basin, Iran. The identification of unit hydrographs and component flows from rainfall, evaporation and streamflow data (IHACRES) model was employed to simulate runoff for the purpose of designing a run-of-river hydropower plant in the Karkheh basin. The non-dominated sorting genetic algorithm (NSGA)-II was employed to maximize yearly energy generation and the plant factor, simultaneously. Results indicate the runoff scenarios associated with the SDSM lead to higher run-of-river hydropower generation in 2020-2049 compared to the CF results. [ABSTRACT FROM AUTHOR]

The aim of the review is to assess the value of model experimental studies for the development of classical rotor aerodynamics as well as to describe the most significant recent results stimulated by intense development of wind power. [ABSTRACT FROM AUTHOR]

The development of offshore wind farms in deep water favors floating wind turbine designs, but floating horizontal axis wind turbines are facing the challenge of high cost of energy (CoE). The development of innovative designs to reduce the CoE is thus desirable, such as floating vertical axis wind turbines (VAWTs). This study demonstrates the characteristics of aerodynamic loads and load effects of a two-bladed floating VAWT supported by a semi-submersible platform. Fully coupled simulations are performed using the time-domain aero-hydro-servo-elastic code SIMO-RIFLEX-AC. It is found that thrust, lateral force, and aerodynamic torque vary considerably and periodically with the rotor azimuth angle. However, the variation in the generator torque can be alleviated to some extent by the control strategy applied. Moreover, the variations of platform motions and tensions in the mooring lines are strongly influenced by turbulent winds, whereas those of tower-base bending moments are not. The tower-base bending moments exhibit notable two-per-revolution (2P) response characteristics. [ABSTRACT FROM AUTHOR]

Recently, small hydroelectric generators have gained attention as a further development in water turbine technology for ultra low head drops in open channels. The authors have evaluated the application of cross-flow water turbines in open channels as an undershot type after removing the casings and guide vanes to substantially simplify these water turbines. However, because undershot cross-flow water turbines are designed on the basis of cross-flow water turbine runners used in typical pipelines, it remains unclear whether the number of blades has an effect on the performance or flow fields. Thus, in this research, experiments and numerical analyses are employed to study the performance and flow fields of undershot cross-flow water turbines with varying number of blades. The findings show that the turbine output and torque are lower, the fluctuation is significantly higher, and the turbine efficiency is higher for runners with 8 blades as opposed to those with 24 blades. [ABSTRACT FROM AUTHOR]

In order to meet the growing demand for energy, the development of hydropower leads to an increase of the river exploitation by human activities. Thereby, water management has become a major issue in the energy transition. A better definition of the flow release rules is now required to improve the Minimal Flow Requirement (MFR) concept, which has long been used in spite of its environmental inconsistency. In this work, we present a class of non-proportional redistribution rules that broadens the spectrum of dynamic flow releases based on proportional redistribution for run-of-the-river power plants. We adapt the mathematical form of the Fermi-Dirac statistical distribution to engineer a novel class of redistribution functions. In particular, such functions are used to define the fraction of water allocated to the environment depending on the inflow at the intake. The theoretical background as well as the economic interpretation is presented, and the ability to generate variable flow releases carefully discussed. MFR, proportional and non-proportional distribution policies are then applied to a real case study and their respective economic and environmental efficiencies quantitatively compared. We show that non-proportional distribution policies allow for operating conditions actually close to the Pareto frontier, which improve both efficiencies with respect to those obtained from some traditional MFR and proportional policies. [ABSTRACT FROM AUTHOR]

The Maine Tidal Power Initiative (MTPI), an interdisciplinary team of engineers, marine scientists, oceanographers, and social scientists, is using a transdisciplinary sustainability science approach to collect biophysical and social data necessary for understanding interactions between human and natural systems in the context of tidal power development in Maine. MTPI offers a unique opportunity to better understand how group structure and process influence outcomes in transdisciplinary sustainability science research. Through extensive participant observation and semi-structured interviews we: (1) describe MTPI's organizational structure; (2) examine MTPI's research approach and engagement with stakeholders from different sectors of society (i.e., industry, government, and the local community); and (3) identify challenges and opportunities for involving different disciplinary expertise and diverse stakeholders in transformational sustainability science research. We found that MTPI's holistic mission, non-hierarchical structure, and iterative stakeholder engagement process led to important benefits and significant challenges. Positive outcomes include knowledge development, a transferable research framework, shared resources, personal reward, and a greater understanding of the local environment and community. Challenges identified include balancing diverse interests and priorities, maintaining engagement, managing stakeholder relationships, and limited resources. Lessons learned from the process of integrative collaborative research in Maine can offer guidance on what should be considered when carrying out similar transdisciplinary sustainability science projects in other research contexts. [ABSTRACT FROM AUTHOR]

Fish are a key part of the marine ecosystem likely to be affected by hydrokinetic tidal turbines, but little is known about their behavior around such obstacles in the natural environment. In September 2010, two DIDSON acoustic cameras were used to observe fish interactions with a commercial-scale turbine in Cobscook Bay, Maine. Twenty-two hours (nearly two tidal cycles) of footage were collected. Behaviors of individual fish and schools were classified (e.g., entering, avoiding, passing, or remaining in the wake of the turbine). We analyzed the effects of turbine motion (rotating or not rotating), diel condition (day or night), and fish size (small, ≤10 cm; large, >10 cm) on individual fish behaviors, and compared behaviors of individual fish to schools of fish. When the turbine was rotating, the probability of fish entering the turbine decreased by over 35 % from when it was not. The probability that fish would enter the turbine was higher at night than during the day, and this difference was greater for small fish than for large fish (probability of small fish entering = 0.147 day, 0.513 night; large fish = 0.043 day, 0.333 night). Fish were almost always present in the wake of the turbine. Schools of fish had a 56 % lower probability of entering the turbine than individual fish, and reacted at greater distances from the turbine (median distance of 2.5 m for schools, 1.7 m for individuals). This study indicates that fish behavior in response to tidal turbines appears to be similar to responses to obstacles such as trawls, and highlights the importance of environmental context in determining the effects of a tidal turbine on fish. [ABSTRACT FROM AUTHOR]

Barotrauma caused by rapid decompression during hydroturbine (turbine) passage may occur as fish move through the low pressure region below the turbine runner. This scenario is of particular concern in North American rivers with populations of ESA-listed salmon. The US Army Corps of Engineers (USACE) and the Pacific Northwest National Laboratory released Sensor Fish into lower Snake and Columbia River turbines to determine the magnitude and rate of pressure change fish might experience. Recorded pressures were applied to simulated turbine passage (STP) in laboratory studies to determine the effect of rapid decompression on juvenile Chinook salmon. These STP studies have increased our understanding of how pressure effects fish passing through turbines and suggest that the ratio of pressure change [acclimation pressure (the depth upstream of the dam where fish are neutrally buoyant) divided by nadir pressure (lowest pressure)] is highly predictive in determining the effect on smolt survival. However, uncertainty remains in smolt acclimation depth prior to entering turbine intakes at hydroelectric facilities. The USACE continues to make progress on salmon survival and recovery efforts through continued research and by applying pressure study results to turbine design. Designing new turbines with higher nadir pressure criteria is likely to provide safer fish passage for all salmonid species experiencing turbine passage. [ABSTRACT FROM AUTHOR]