scholarly journals Vertical wake deflection for floating wind turbines by differential ballast control

2021 ◽  
Author(s):  
Emmanouil M. Nanos ◽  
Carlo L. Bottasso ◽  
Dimitris I. Manolas ◽  
Vasilis A. Riziotis
Keyword(s):  
Structural Analysis ◽  
Water Surface ◽  
Water Movement ◽  
Turbine Rotor ◽  
Sea Surface ◽  
Feasibility Analysis ◽  
Ambient Conditions ◽  
Power Capture ◽  
Rotor Disk ◽  
Floating Turbines

Abstract. This paper presents a feasibility analysis of vertical wake steering for floating turbines by differential ballast control. This new concept is based on the idea of pitching the floater with respect to the water surface, thereby achieving a desired tilt of the turbine rotor disk. The pitch attitude is controlled by moving water ballast among the columns of the floater. This study considers the application of differential ballast control to a conceptual 10 MW wind turbine installed on two platforms, differing in size, weight and geometry. The analysis considers: a) the aerodynamic effects caused by rotor tilt on the power capture of the wake-steering turbine and at various downstream distances in its wake; b) the effects of tilting on fatigue and ultimate loads, limitedly to one of the two turbine-platform layouts; and c) for both configurations, the necessary amount of water movement, the time to achieve a desired attitude and the associated energy expenditure. Results indicate that – in accordance with previous research – steering the wake towards the sea surface leads to larger power gains than steering it towards the sky. Limitedly to the structural analysis conducted on one of the turbine-platform configurations, it appears that these gains can be obtained with only minor effects on loads, assuming a cautious application of vertical steering only in benign ambient conditions. Additionally, it is found that rotor tilt can be achieved in the order of minutes for the lighter of the two configurations, with reasonable water ballast movements. Although the analysis is preliminary and limited to the specific cases considered here, results seem to suggest that the concept is not unrealistic, and should be further investigated as a possible means to achieve variable tilt control for vertical wake steering in floating turbines.

scholarly journals Rapid coral mortality following unusually calm and hot conditions on Iriomote, Japan

F1000Research ◽  
2018 ◽  
Vol 6 ◽  
pp. 1728 ◽  
Author(s):  
Andrew H Baird ◽  
Sally A. Keith ◽  
Erika Woolsey ◽  
Ryuta Yoshida ◽  
Tohru Naruse
Keyword(s):  
Water Movement ◽  
Sea Surface ◽  
Bleaching Event ◽  
Coral Mortality ◽  
Average Wind Speed ◽  
Common Cause ◽  
Wind Speeds ◽  
Average Wind ◽  
The Mean ◽  
Low Wind Speeds

Coral bleaching can be induced by many different stressors, however, the most common cause of mass bleaching in the field is higher than average sea surface temperatures (SST). Here, we describe an unusual bleaching event that followed very calm sea conditions combined with higher than average SST. Patterns of mortality differed from typical bleaching in four ways: 1) mortality was very rapid; 2) a different suite of species were most affected; 3) tissue mortality in Acropora spp. was often restricted to the center of the colony; 4) the event occurred early in summer. The two weeks prior to the event included 8 days where the average wind speed was less than 3 ms-1. In addition, SSTs in the weeks preceding and during the event were 1.0-1.5°C higher than the mean for the last 30 years. We hypothesize that this unusual bleaching event was caused by anoxia resulting from a lack of water movement induced by low wind speeds combined with high SST.

Wind effects on the water in a narrow two-layered lake. Part I. Theoretical analysis. Part II. Analysis of observations from Windermere. Part III. Application of the theory to Windermere

1966 ◽  
Vol 259 (1102) ◽  
pp. 391-430 ◽  
Keyword(s):  
Wind Stress ◽  
Water Surface ◽  
Water Movement ◽  
Lower Layer ◽  
Longitudinal Section ◽  
Bottom Friction ◽  
Bottom Current ◽  
Numerical Application ◽  
Warm Surface Water ◽  
Temperature Observations

This paper presents a theoretical study of water movement in a long narrow lake subject to wind action during the summer season of thermal stratification. A model basin of uniform depth and width, consisting of two homogeneous layers of slightly different density, is considered. The motion of the water is assumed to be two dimensional in the vertical longitudinal section; geostrophic effects are ignored. The top and bottom layers in the model respectively represent the relatively warm surface water and the colder bottom water in the natural lake. Hydrodynamical equations are formulated in terms of the currents in the upper and lower layers, the elevation of the interface between the layers, and the elevation of the water surface. Solutions are sought to determine the dynamic response of the basin to an instantaneous rise in the wind stress applied tangentially over the surface. Three cases are considered corresponding to different frictional conditions at the bottom of the basin: (i) bottom friction zero, (ii) bottom friction proportional to the depth mean of the horizontal current in the lower layer, (iii) bottom current zero. It is assumed that internal friction is zero at the interface between the layers (this interface corresponds to the thermocline boundary in reality). Results obtained show that in the motion of the water there are ordinary and internal seiches characteristic of the two-layered model, together with a wind-driven circulation in the top layer. The theory is applied to determine vertical oscillations of the thermocline in an actual lake (Windermere) at one station, in response to a succession of wind pulses representing actual wind conditions over the lake. The oscillations thus obtained from theory compare satisfactorily with those derived from temperature observations taken in the lake. Depth-mean currents in the lake are deduced from theory, but there are no current measurements against which these values may be tested. The paper is divided into three parts. Part I deals with the development of the theory. Part II gives an account of actual physical conditions in Windermere, describing the analysis of temperature observations taken in the lake (yielding thermocline movements) and the analysis of wind records (yielding corresponding values of wind stress over the water surface). Part III is concerned with the numerical application of the theory to Windermere (under conditions described in part II), and gives general conclusions resulting from the entire work.

scholarly journals Result of modeling temperature anomalies on the water surface of the research basin of the institute of hydromechanics NAS of Ukraine

2018 ◽  
pp. 40-45
Author(s):  
Oleksandr Fedorovsky ◽  
Vitalii Filimonov ◽  
Iryna Piestova ◽  
Stanislav Dugin ◽  
Vladyslav Yakymchuk ◽  
...  
Keyword(s):  
Water Surface ◽  
Water Layer ◽  
Sea Surface ◽  
National Academy Of Sciences ◽  
Near Surface ◽  
Aerial Photos ◽  
Temperature Anomalies ◽  
Structural And Textural Parameters ◽  
The Difference ◽  
Hydrocarbon Deposits

The results of the research and physical modeling of temperature anomalies of natural or man-made origin on the water surface are presented.  The information for the research was obtained from the experimental basin of the Institute of Hydromechanics of the National Academy of Sciences of Ukraine from the self-propelled model as the generator of hydrodynamic processes. The information obtained after image processing allowed to significantly expand the existing ideas about the mechanism of formation of anomalies on the open surface with the hydrodynamic disturbances from hydrocarbon deposits and moving submerged object. The interaction of the emerging hydrodynamic disturbances with the near-surface water layer and the occurrence of unmasking temperature anomalies on the open sea surface have a lot in common between the hydrocarbon deposits and the moving submerged object. The application of the difference of the above structural and textural parameters by calculating the value of "entropy" has been proposed as the informative feature for decoding the images of the water surface with the presence of hydrocarbon deposits or moving immersed objects. The decoding of temperature anomalies consists of two stages: learning and proper decoding. The first stage is the supervised learning, during which the system is being researched using the existing set of images, in which only the background and no hydrocarbon deposits or moving submerged object. Training is carried out in order to determine the signs of belonging to the background or hydrocarbon deposits, moving submerged object. It was determined that the background has minimal entropy values, and with the appearance of an anomaly, the entropy grows to the maximum value, after which, as the temperature trace dissipates, it begins to fall to background values. This confirms the informativity of the entropy feature for decoding the optical anomalies of man-made and natural origin on the sea surface from aerial photos.

scholarly journals Vertical Motions Damping Model Test of a Lifeboat Lowered Onto a Flat Sea Surface

2018 ◽  
Vol 25 (s1) ◽  
pp. 51-55
Author(s):  
Aleksander Kniat ◽  
Paweł Dymarski
Keyword(s):  
Mathematical Model ◽  
Model Test ◽  
Water Surface ◽  
Vertical Motion ◽  
Sea Surface ◽  
Damping Factor ◽  
Initial Speed ◽  
The Mathematical Model ◽  
Damping Model

Abstract The article presents the experiment’s results of the lifeboat model lowered with an initial speed and then released to fall onto a flat water surface. The purpose of the research is to determine the trajectory of the vertical boat motion and describe it with a mathematical model. This is closely related to determining the damping factor since the vertical motion is damped and the lifeboat gets balanced and stops moving after some time. The procedure of selecting parameters in the mathematical model to adjust to the results of the experiment was described in details. The summary describes the imperfections of the presented damping model and their probable causes.

On the Cushioning of Water Impact by Entrapped Air

1968 ◽  
Vol 12 (02) ◽  
pp. 116-130 ◽  
Author(s):  
Grant Lewison ◽  
W. M. Maclean
Keyword(s):  
Free Surface ◽  
Flat Plate ◽  
Water Surface ◽  
Peak Pressure ◽  
Water Movement ◽  
Theoretical Work ◽  
Two Dimensional ◽  
Water Impact ◽  
Entrapped Air

Impact between a rigid flat plate and the free surface of water has been investigated experimentally and theoretically. Under two-dimensional conditions, the experiments give values of peak pressure of the same order as those recorded on ships slamming at sea, but very much smaller than would be expected from existing theories. New theoretical work is presented which takes account of the air trapped between the model and the water surface, and of both compressible and incompressible water movement. This shows good general agreement with the experiments, though further work is needed to confirm some of the assumptions made.

Probabilistic Analysis of Turbine Disc SCC Incubation and Propagation

2002 ◽  
Author(s):  
Tony C. T. Lam ◽  
Robert Dewey
Keyword(s):  
Growth Rate ◽  
Incubation Time ◽  
Chromium Content ◽  
Probabilistic Approach ◽  
Turbine Rotor ◽  
Time Data ◽  
Weld Repair ◽  
Low Pressure Turbine ◽  
Turbine Disc ◽  
Rotor Disk

Stress corrosion cracking (SCC) is a common problem found on aging low-pressure turbine (LP) rotors that operate in a wet/dry stream environment. While much has been published on the growth rate of SCC in turbine rotor-disk materials, incubation time is rarely addressed. Since no effective way has been demonstrated to prevent disk rim SCC from occurring other than to replace the damaged rim with a weld repair of higher chromium content, a better understanding of incubation time could provide operators with a means to treat SCC before cracks are large enough to start to grow. This paper discusses the critical mechanisms involved in the SCC incubation, process and describes a probabilistic approach to make meaningful assessments of incubation time. Data published for General Electric turbine rotors is used to test the model.

Doppler Spectra of Microwave Backscatter From Water Surface

2004 ◽  
Author(s):  
Chang-Kyu Rheem ◽  
Hidetaka Kobayashi ◽  
Kazuomi Yamanishi
Keyword(s):  
Water Surface ◽  
Microwave Remote Sensing ◽  
Close Relation ◽  
Global Scale ◽  
Experimental Results ◽  
Sea Surface ◽  
Surface Measurement ◽  
Doppler Spectrum ◽  
Microwave Scattering ◽  
The Mean

This paper describes the experimental results of microwave backscattering at water surfaces. Active microwave remote sensing is one of the useful techniques for sea surface measurement. For example, it enables us to know the wind vector on global scale. A principle of measurement is that the microwave backscattering depends on the wind speed. Therefore understanding of the phenomena of microwave scattering at sea surface in detail is indispensable for improvement of measuring accuracy. The purpose of the research is to investigate the characteristics of microwave scattering at various water surface conditions. Water surface was generated by wind and currents, microwave backscattering at that surface was measured by X and C-band microwave scatterometer. The experimental results were summarized in scattering coefficients and Doppler spectra. X-band microwave was more sensitive at wind wave surface than C-band. The mean frequency of Doppler spectrum of backscattering microwave was corresponded to the phase velocity of the mean water surface wave and the bandwidth of Doppler spectrum had close relation to the orbital velocity of the mean wave. A current had no effect on the scattering coefficient, but the Doppler spectrum was shifted to the side corresponding to current direction.

Numerical Modeling of the Oil Spill Trajectory and Real-Time Tracking Using Intelligent Swarm Robots

2013 ◽  
Vol 446-447 ◽  
pp. 1261-1265 ◽  
Author(s):  
Mohsen Pashna ◽  
Rubiyah Yusof ◽  
Zool H. Ismail
Keyword(s):  
Numerical Modeling ◽  
Numerical Model ◽  
Crude Oil ◽  
Oil Spill ◽  
Water Surface ◽  
Sea Surface ◽  
Sea Waves ◽  
Robot Locomotion ◽  
Swarm Robots ◽  
Real Time Tracking

An oil spill is discharge of fluid petroleum such as crude oil or its by-product derivations such as diesel and gasoline on the water surface. In this paper, a numerical model of the oil spill has been introduced as a simulation of releasing oil on the sea surface. Meantime, the influence of sea waves and wind has been considered and shown. Moreover, a swarm of robots is engaged in order to track the spreading boundaries of the slicked oil, so that a novel schedule of robot locomotion is presented, based on the online sharing information in the flock network. Therefore, the swarm of robots tracks the oil spill margins intelligently and successfully.

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