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1
Moore, Ian F. "Inertial response from wind turbines." Thesis, Cardiff University, 2012. http://orca.cf.ac.uk/42939/.
Повний текст джерелаАнотація:
Wind power is an essential part of the strategy to address challenges facing the energy sector. Operation of the electricity network in 2020 will require higher levels of response and reserve from generation. The provision of inertial response from wind turbines was investigated. A model was developed for the simulation of frequency on the mainland UK system, including a simplified model for a synchronous generator to represent Full Power Converter turbines. Two different methods of inertia response, the step method and the inertia coupling method, were modelled and introduced into the turbine torque speed control. Simulations illustrated the effects on primary frequency control for a high penetration of wind turbines. Results are shown for different demand levels with generation losses of 1320GW and 1800GW. A comparison of the inertia functions is included and the effect of wind speed and the constant speed region of the maximum power extraction curve. For the scenarios modelled only a small change in turbine output was required for inertia response (0.02p.u). Without inertia response a large increase in synchronous plant response was needed. A test rig was constructed consisting of a Full Power Converter bridge and a synchronous generator driven by a dc machine. Power converters were designed and constructed by the candidate. Vector control of both the generator converter and grid converter was implemented on a dedicated control platform. The inertia coupling function was implemented and a test frequency deviation injected to represent a load generation imbalance. Results compared closely to those from the model and demonstrated the capability to closely couple turbine speed to system frequency with adjustment of the response via a filter if desired. The experimental work confirmed the adequacy of the simplified generator model and further confirmed the possibility of using inertia response. The inertia coupling function was considered suitable for use for the UK system.
2
Song, Qingtao. "Surface wind response to oceanic fronts /." View online ; access limited to URI, 2006. http://0-wwwlib.umi.com.helin.uri.edu/dissertations/dlnow/3225330.
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3
Rousseau, Guillaume 1982. "Wind-induced dynamic response of bridges." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/29416.
Повний текст джерелаАнотація:
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2004.Includes bibliographical references (leaves 52-54).
Wind loading has long played a significant role in bridge design. Some spectacular failures, such as the Tay Bridge (Scotland, 1879), or the Tacoma Narrows Bridge (Washington State, 1940) acted as a painful reminder to engineers in case they had forgotten the importance of wind loading. Today, a constant drive for longer spans in suspension or cable-stayed bridges forces designers to give even more care to wind load. The Golden Gate Bridge (1280 m, San Francisco, built in 1937), which held the record for the longest span for 27 years, is now a distant 7th to the Akashi-Kaikyo (1991 m, Japan, 1998). Different in many ways, the current hunger of Japan and China for new infrastructure leads a renewal of innovation in bridge design and wind engineering. A few projects in Europe or the United States, like the Great Belt Bridge (1624 m, Denmark, 1998), or the Messina Bridge project (3300 m, Italy, not built) are part of the same trend. The design of such a structure is a real challenge for the designer. A good example is given by the Messina Bridge in Veneziano and Van Dyck, 1998. Wind loading in different directions, determination of the reference wind speed, earthquake load, numerous cases of traffic loading ... are investigated thoroughly. The intent of this thesis is to present the essentially dynamic behavior of bridges submitted to wind. The main phenomenon involved will be exposed, as well a method to evaluate the maximum response for given wind conditions. Theories and methods developed by A.G. Davenport and R.H. Scanlan support most of the developments in this text.
(cont.) This thesis will not deal with specific design issues, the analysis of the response being already quite an extensive topic. Rather, its purpose is to give the reader a better understanding of wind engineering, in the belief that good design is a complete thinking process based on understanding of the underlying behavior, and not the application of straightforward recipes. This is particularly true when dealing with those high-performance structures mentioned above.
by Guillaume Rousseau.
M.Eng.
4
Lee, Kwang Hyun. "Responses of floating wind turbines to wind and wave excitation." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/33564.
Повний текст джерелаАнотація:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 2005.Includes bibliographical references (leaf 55).
The use of wind power has recently emerged as a promising alternative to conventional electricity generation. However, space requirements and public pressure to place unsightly wind turbines out of visual range make it desirable to move large wind farms offshore and into deeper coastal waters. A necessary step for the deployment of wind turbines into deeper waters is the development of floating platform systems. This thesis will present a general technical description of two concept designs for floating wind turbine systems, and make a preliminary evaluation of their performance in wind and waves. A new approach to computing the nonlinear wave excitation is also presented.
by Kwang Hyun Lee.
S.M.
5
Giumelli, Matteo. "Wind Response of The New Svinesund Bridge." Thesis, KTH, Bro- och stålbyggnad, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-36800.
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6
Iannuzzi, A. "Response of guyed masts to simulated wind." Thesis, University of Westminster, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.378340.
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7
Singh, A. K. "Geomagnetic response of solar wind-magnetosphere coupling." Thesis, Indian Institute of Geomagnetism, Mumbai, 2012. http://localhost:8080/xmlui/handle/123456789/213.
Повний текст джерелаАнотація:
A thesis submitted to the university of Mumbai for the Ph. D.(Science) degree in Physics under the guidance of Prof. B.M.Pathan.A brief summary of the important new findings is given below: • The data adaptive filtering technique singular spectrum analysis identifies and extracts trend and period modes of around 27-day, 13-day and 9-day in various solar wind and geomagnetic parameters. The response of the magnetosphere to the solar wind forcing is found to be the most prominent during the declining phases of the solar cycles. However, oscillations of these modes have considerable amplitudes during the entire sunspot cycle.Multi-frequency structures in substorm associated magnetic fluctuations are extracted by the SSA. The study throws light on several features of various modes thus detected, for example, poleward propagation of modes at high latitudes, dip equatorial enhancement. • Geomagnetic substorms, which may have considerably high magnetic disturbance (up to ∼-500 nT) at stations poleward of standard auroral oval, are occasionally missed out in the standard AE indices. However, their low latitude signatures like positive bays, Pi2 bursts are often evident. Signature and strength of such substorms have significant asymmetry in the opposite hemispheres. • This study clearly brings out 24-hour periodicity in the ring current asymmetry during magnetic storms. The asymmetry is observed maximum near dusk hours, whereas it is minimum near dawn hours. This periodicity is attributed to changing local time due to rotation of the Earth. For the first time, we also report clear westward and eastward propagating modes around the globe using ground-based magnetic data. These propagation characteristics are associated with the westward and eastward drifts of energetic ions and electrons, respectively in the ring current region. • This thesis reports various new aspects of substorm associated auroral and low latitude indices. (1) The AU index (supposedly positive), which is expected to represent the maximum intensity of the eastward electrojet during a substorm, turns negative under the conditions when entire auroral oval is dominated by westward electrojet. Such negative AU values result in underestimation of strength of substorm in the AE index (AE = AU − AL). Our study supports the finding of Kamide and Ros toker [2004] that use of AE index should be avoided for identification of a substorm.Rather AL index gives better representation of substorms. (2) Intense and prolonged solar flares generate asymmetric magnetic field at low latitudes. This asymmetry significantly alters non-substorm and substorm time ASY indices. (3) Low latitude ASY indices, often used in relation to substorm activities, are affected by prompt penetration of interplanetary electric field to lower latitudes.
8
Gavhed, Désirée. "Human responses to cold and wind /." Stockholm, 2003. http://diss.kib.ki.se/2003/91-7045-669-0/.
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9
Konstantinou, Nikolaos. "Ocean mixed layer response to gap wind scenarios." Thesis, Monterey, Calif. : Naval Postgraduate School, 2006. http://bosun.nps.edu/uhtbin/hyperion.exe/06Dec%5FKonstantinou.pdf.
Повний текст джерелаАнотація:
Thesis (M.S. in Meteorology)--Naval Postgraduate School, December 2006.Thesis Advisor(s): Qing Wang, Roland W. Garwood. "December 2006." Includes bibliographical references (p. 61-62). Also available in print.
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Li, Yu. "Dynamic Response Analysis of an Offshore Wind Turbine." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-15786.
Повний текст джерелаАнотація:
The offshore wind power is an attractive renewable energy resource. To improve the wind power generation capacity, there is a strong desire for offshore wind turbine to go to deep waters. For offshore fixed wind turbine, stronger foundation like jacket structure has a good applicability for deeper water depth. A 70-meters jacket substructure for offshore wind turbine is designed. This thesis focuses on the dynamic structural response analysis of this jacket substructure, with a particular focus on hot spot stress of critical points on tubular joints. Three types of models are applied for analyses in this thesis. For eigen-value analysis the entire modal including the wind turbine, tubular tower and jacket supporting structure is used in the program USFOS-VPOne. For hydrodynamic analysis the refined substructure model with complete jacket structure and tubular tower is applied in USFOS. The equivalent monopile model is constructed in HAWC2 to predict wind loads. Eigen value analysis is performed to check the validity of decoupled method for dynamic response analysis. The first eigen period is about 2.9s, far less than the main wave input periods, which implies the wave loads are mainly quasi-static, therefore the simplified decoupled analysis method can be applied. The global modes, the blade modes and the modes related to jacket braces are identified. Hydrodynamic analysis is performed to compare wave loads with different regular wave theories, including: Extrapolated Airy theory, Stretched Wave theory, Stoke’s 5th order wave theory and Stream Function theory. It is proved that for extreme wave conditions, higher order wave theories such as Stoke’s 5thorder wave theory and Stream Function theory should be applied since linear wave theories will under-estimate the structural reactions. Dynamic structural response analysis is performed in time domain with decoupled analysis method. The effect of misalignment of wind and wave on hot spot stress at joints is studied. It is observed that wave propagation directions has more significant effects on structural response than wind directions, while wind force has more significant influence on dynamic structural response rather than wave forces no matter in which directions they are propagating.
11
Bernardini, Sara. "Earthquake and Wind Response of Plan-Asymmetric Buildings." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amslaurea.unibo.it/2328/.
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12
Jones, Scott Alan. "Effect of pruning type, pruning dose, and wind speed on tree response to wind load." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0013321.
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13
Buckiewicz-Smith, Alexander. "Methods for measuring the acoustic response of wind instruments." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=18800.
Повний текст джерелаАнотація:
This thesis studies methods to take acoustical measurements of wind instrument bodies and mouthpieces. Acoustic responses and existing measurement methods are reviewed. Multiple- and single-microphone measurement techniques are compared with a discussion of object-length limitations and frequency response. Impulse response measurements using a complex input signal are discussed and signals used for measuring room acoustics are reviewed. Construction and deconvolution methods for several types of signals are specified and the effects of signal degradation on measurements are discussed. A novel pulse reflectometry technique that can use these signals as stimulus is presented. The signals are used in a waveguide model which simulates adverse measurement scenarios and calculated impedances are compared. Model measurements are then compared with actual reflection function measurements of two fabricated test objects to show the limitations of pulse reflectometry when calculating the impedance of long objects. Viscothermal losses and open-end radiation characteristics measured using a pulse reflectometry setup are then compared with their theoretically predicted values. Finally, the input impedance calculated from several saxophone mouthpieces are presented and a novel method for measuring the reed resonance frequency of a mouthpiece is shown.Cette thèse étudie des méthodes pour prendre des mesures acoustiques des corps et embouchures d'instruments à vent. Les réponses acoustiques et les méthodes existantes de mesure sont passées en revue. Mesures de multiples pressions et pression unique sont contrastées par un discussion des limitations sur la longueur de l'objet et la réponse en fréquences. Les mesures de réponse d'impulsion employant un signal d'entrée complexe sont discutée et des signaux utilisés pour mesurer l'acoustique de salles sont passés en revue. Les méthodes de construction et de déconvolution pour plusieurs types de signaux sont spécifiés et les façons dont la dégradation des signaux affecte les mesures sont discutées. Une nouvelle technique de réflectométrie d'impulsion qui peut employer ces signaux comme stimulus est présentée. Les signaux sont employés dans un modèle de guide d'ondes qui simule les scénarios défavorables de mesures et calculent les impédances. Des mesures de modèles sont alors comparées aux mesures réelles de fonction de réflexion de deux prototypes fabriqués pour montrer les limitations de la réflectométrie d'impulsion lors de calculs de l'impédance de longs objets. Les pertes viscothermiques et les caractéristiques de rayonnement d'extrémité ouverte mesurées en utilisant une installation de réflectométrie d'impulsion sont alors comparées à leurs valeurs théoriques prévues. En conclusion, l'impédance d'entrée calculée à partir de plusieurs embouchures de saxophones sont présentées ainsi qu'une nouvelle méthode pour mesurer la fréquence tubulaire de résonance d'une embouchure.
14
Pietrzak, J. D. "Low frequency response of coastal waters to wind forcing." Thesis, Swansea University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638531.
Повний текст джерелаАнотація:
The low frequency flow dynamics of the N.W. Aegean Sea, are investigated using a barotropic shelf circulation model, and by analysis of data from current meters deployed in Thermaikos Gulf. The performance of Groves (1955) and Lanczos-cosine filters is assessed to provide optimal low-pass filtering for the current meter records. The Lanczos-cosine filter is found to be the most effective in the present study. Time series and spectral analysis are applied to the filtered current meter records and to concurrent meteorological data. The results of these analyses show significant inputs of low frequency energy at periods of 2-4 days, 6-8 days and 20-26 days. An anomalous energy band exists that is uncorrelated with the wind and which is absent from one current meter record. The results from a depth-integrated momentum balance suggest that these bands are related to direct meteorological forcing. The 2-4 day band is related to 3-dimensional coastal water processes. The 6-8 day band is described in terms of internal Kelvin waves and the 20-26 day band is related to continental shelf waves. The anomalous band with 11-13 day period is associated with freshwater forcing from rivers. The low frequency shelf circulation of the Aegean Sea is modelled analytically. Solutions to the two-dimensional vorticity equation written in terms of stream functions are sought within a circular basin with exponential cross-shelf topography. The dispersion relations for the propagation of free waves is given. Introduction of the ageostrophic approximation allows solution to the wind-forced vorticity equation wherein, parameter separation leads to a wave equation soluble by the method of characteristics. The separation parameter is determined from the associated Sturm-Liouville equation. The damped wave problem is also solved. The model predicts the propagation of continental shelf waves, with periods of 20-26 days around the Aegean Sea.
15
Whitney, Claudia S. "Modeling the tropical ocean response to westerly wind forcing." Thesis, Monterey, California. Naval Postgraduate School, 1992. http://hdl.handle.net/10945/23969.
Повний текст джерелаАнотація:
Approved for public release; distribution is unlimitedA primitive equation ocean general circulation model, with mixed layer physics, has been developed and applied to an investigation of the equatorial ocean. The major physical problem addressed with this model is the response of the upper ocean to westerly wind events, such as those that occur during tropical cyclones and during El Nino events. In the model development phase, several configurations of the mixed layer physics, domain size, and wind stress were tested. The best overall simulations were produced when both Richardson number dependent mixing and a bulk mixed layer model were included. Small model domains were found to be especially sensitive to the prescribed lateral boundary conditions and wind stress. Smaller domains required more realistic wind stress fields in order to achieve reasonable current structures. In addition, the off-equatorial currents were particularly responsive to changes in the zonal gradient of the wind stress. The final configuration of the model produces realistic simulations of climatological threedimensional temperature and current structures in the equatorial ocean. In the model application phase, synoptically varying winds for the tropical Pacific were used to force the model. The winds came from the Navy's Operational Global Atmospheric Prediction System's (NOGAPS) daily analyses for the 1991-92 El Nino, which included several strong westerly wind events. The strong temporal and spatial variability in these winds produced complex fluctuations of the model's temperatures, currents, and internal waves, including reversals of the South Equatorial Current and equatorially trapped Kelvin waves. Model verification was performed by comparison with an observational study of in situ equatorial Pacific buoy data. This comparison showed that synoptic scale variations in the wind stress are needed to simulate the ocean's strong responses to westerly wind events.
16
Littler, John David. "The response of a tall building to wind loading." Thesis, University College London (University of London), 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367955.
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Rudge, Daniel, and Chen-Yang Fei. "Response of structural members to wind-induced vortex shedding." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/12836.
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18
Proskovics, Roberts. "Dynamic response of spar-type offshore floating wind turbines." Thesis, University of Strathclyde, 2015. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=26017.
Повний текст джерелаАнотація:
In recent years there has been a significant increase in the interest in floating offshore wind turbines from the wind energy industry, governments and academia. Partially driven by the recent nuclear disaster in Japan, but also by the lack or complete absence of shallow waters in various countries around the globe (making fixed offshore wind turbines infeasible), multiple different topology floating offshore wind turbines have been proposed and, in some cases, prototypes built and installed offshore. The most well-known of these is Hywind by Statoil, which has been operational off the coast of Norway since the end of 2009. While small scale prototypes had been installed even before Hywind, for example Blue-H in 2007, no guidelines have yet emerged that would give recommendations and guiding principles in designing new floating offshore wind turbines. The aim of this thesis is to provide some knowledge base for future design of floating offshore wind turbines by looking at what simplifications could be made and what effect these would have on the preliminary designs of new floating offshore wind turbines. This thesis starts by comparing different topology floating offshore wind turbines and choosing one, deemed the most promising, as the base case scenario for use in the subsequent analysis and calculations. This thesis also looks at the importance of unsteady representations of the aerodynamics compared with quasi-steady when designing a new floating offshore wind turbine, by comparing quasi-steady aerodynamic loads first with fully-attached unsteady loads and later with fully-unsteady (fully-attached, separated and dynamic stall). A chapter is allocated to identifying which degree-of-freedom of loading is the most damaging to the system, as floating offshore wind turbines operate in very harsh and unstable environments. Once identified, this knowledge can be used to further improve floating offshore wind turbines, hence making them even more feasible. Finally, the wind turbine previously chosen as a base case has its floating support shortened and four different draft designs proposed that would allow it to be deployed in medium-to-deep waters, in which fixed supports for wind turbines are not economical.
19
Banham-Hall, Dominic. "Active power control response from large offshore wind farms." Thesis, Brunel University, 2012. http://bura.brunel.ac.uk/handle/2438/11051.
Повний текст джерелаАнотація:
The GB power system will see huge growth in transmission connected wind farms over the next decade, driven by European clean energy targets. The majority of the UK’s wind development is likely to be offshore and many of these wind farms will be interfaced to the grid through power converters. This will lead to a loss of intrinsic inertia and an increasing challenge for the system operator to keep grid frequency stable. Given this challenge, there is increasing interest in understanding the capabilities of converter control systems to provide a synthesised response to grid transients. It is interesting to consider whether this response should be demanded of wind turbines, with a consequential reduction in their output, or if advanced energy storage can provide a viable solution. In order to investigate how large offshore wind farms could contribute to securing the power system, wind turbine and wind farm models have been developed. These have been used to design a patented method of protecting permanent magnet generator’s converters under grid faults. Furthermore, these models have enabled investigation of methods by which a wind turbine can provide inertial and frequency response. Conventionally inertial response relies on the derivative of a filtered measurement of system frequency; this introduces either noise, delay or both. This research proposes alternative methods, without these shortcomings, which are shown to have fast response. Overall, wind farms are shown to be technically capable of providing both high and low frequency response; however, holding reserves for low frequency response inevitably requires spilling wind. Wind’s intermittency and full output operation are in tension with the need of the power system for reliable frequency response reserves. This means that whilst wind farms can meet the technical requirements to hold reserves, they bid uncompetitive prices in the market. This research shows that frequency response market prices are likely to rise in future suggesting that the Vanadium Redox Flow Battery is one technology which could enter this market and also complement wind power. Novel control incorporating fuzzy logic to manage the battery is developed to allow a hybrid wind and storage system to aggregate the benefits of frequency response and daily price arbitrage. However, the research finds that the costs of smoothing wind power output are a burden on the store’s revenue, leading to a method of optimising the combined response from an energy store and generator that is the subject of a patent application. Furthermore, whilst positive present value may be derived from this application, the long payback periods do not represent attractive investments without a small storage subsidy.
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Creekmore, Cathy E., and J. L. Stroehlein. "Phosphorus Response in Wine Grapes." College of Agriculture, University of Arizona (Tucson, AZ), 1990. http://hdl.handle.net/10150/215732.
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21
Moore, Alan James. "Dynamic Characteristics and Wind-induced Response of a Tall Building." Thesis, The University of Sydney, 2016. http://hdl.handle.net/2123/16810.
Повний текст джерелаАнотація:
The design of tall buildings requires an accurate understanding of the expected wind loads and the resulting responses. The techniques used to estimate the wind-induced response are subject to uncertainty, which can result in unsatisfactory building performance or an over-designed structure. Altering the structure to rectify unsatisfactory performance can be extremely difficult and prohibitively expensive, while an over-designed structure represents unnecessary cost to the owner. This implies that accurate estimates of wind loads and responses are crucial to tall building design. Two aspects of tall building wind-induced response estimation are investigated: the estimation of natural frequencies and damping ratios; and the understanding of mechanisms causing wind-induced responses. This was primarily conducted via full-scale testing of a tall building. The building used for full-scale measurements is Latitude tower, an office tower located in the Sydney central business district, with a height of 187m above ground and 28m of underground levels. The building has a composite design including a reinforced concrete core, and reinforced concrete floor slabs supported by steel beams spanning between the core and perimeter columns. Outriggers linking the core and perimeter columns, as well as offset outriggers at the facade, are located at mid-height. The full-scale testing was conducted in two parts: vibration testing during construction; and a two year monitoring programme commenced after construction completion. Vibration testing during construction was conducted to determine the natural frequencies and damping ratios as the structure changed. Forced vibration testing and ambient vibration testing techniques were used. The Frequency Domain Decomposition and Stochastic Subspace Identification techniques were used to estimate the natural frequencies and damping ratios from the ambient vibration test outputs. The natural frequencies and damping ratios from the forced and ambient vibration tests differed by less than 5% and 30% respectively. Changes in the fundamental natural frequencies during construction were discussed in conjunction with the structural changes to further the understanding of how changes in the stiffness and mass of a tall building influence the natural frequencies. The measured natural frequencies during the early stages of construction were used to update a finite element model representing the structure at the time of testing. The material properties and floor beams were the primary focus of the model updating. The knowledge gained from partial structure updating was applied to a model of the completed structure, and the natural frequency estimate errors improved from 17% to 7%. The fundamental mode damping ratios measured during construction changed by less than 15% between the first test, conducted when 38% of the tower height was reached, and the final test at construction completion. The wind-induced monitoring programme included the measurement of wind velocities, accelerations, and displacements at the top of the building. The peak events for southerly and westerly wind directions were discussed. It was found that the acceleration response was dominated by the fundamental vibration mode. For southerly winds this corresponded to an along-wind response, but for westerly winds this corresponds to a cross-wind response. The probability distributions of upcrossings for along-wind and cross-wind responses where not significantly different to a Gaussian distribution for both southerly and westerly winds. The slope of the linear least squares fit was greater than two in all cases, which suggested intermittent characteristics were present in the responses. The standard deviation resonant acceleration responses from a high frequency base balance wind tunnel test were within 29% of the measured values.
22
Revuz, Julia. "Numerical simulation of the wind flow around a tall building and its dynamic response to wind excitation." Thesis, University of Nottingham, 2011. http://eprints.nottingham.ac.uk/13151/.
Повний текст джерелаАнотація:
Wind action is particularly important for tall buildings, both in providing a significant contribution to the dynamic overall loading on the structure and by affecting its serviceability. Whereas low and medium-rise buildings are fairly rigid, tall structures are characterized by a greater flexibility and a lower natural frequency, which is more likely to be in the frequency range of wind gusts. In addition, wake effects, such as vortex shedding, can become a significant problem for flexible structures when the vortex shedding frequency is close to the natural frequency of the building. The aim of the present thesis is to assess the validity of commercial CFD codes for modelling the wind flow around a high-rise building, including the consideration of the coupled dynamic response of the building to turbulent wind loading. Three intermediate objectives are set. The first is to develop a tool to couple fluid and structure in a sequential manner. The equations for the air flow are solved using the commercial CFD program ANSYS-Fluent. The response of the structure is found from solving the structural response with a modal approach, the response in each vibration mode being treated as a SDOF problem. This fluid-structure interaction tool is applied to model a 180 m building, allowed to move in the across wind direction. The second objective is to investigate and find a method to generate fully turbulent inflow for LES in order to reproduce an accurate wind spectrum. The chosen method is tested and validated in an empty fetch. Ultimately, both tools are brought together and applied to model a 180 m building, which is allowed to bend in the along wind and across wind directions. Finally, the third intermediate objective brings together the tools developed in the first and second intermediate objective to model the dynamic response of a 180 m building to dynamic wind loading, within a turbulent inflow, using LES.
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Lygren, Jon Erik Lønøy. "Dynamic response analysis of a tension-leg floating wind turbine." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-15502.
Повний текст джерелаАнотація:
Offshore wind energy has a significant potential and for increasing water depths it may be most cost effective to exploit this potential by using floating wind turbines. Many concepts have been suggested but it is not yet possible to decide which type of concept is the best. This report investigates a tension-leg platform (TLP) type of concept. A computer model has been established and time domain simulations have been performed using the computer codes GeniE, HydroD (WADAM) and DeepC (SIMO, RIFLEX, TDHMILL3D). Wind and wave forces are included in the analysis and some theory on how these forces are calculated is given. How the computer model was established is also explained. The mooring system is modeled as a finite element model. The water depth is 200m. TLPs have a stiff mooring system and high heave, roll and pitch natural frequencies. The second-order sum-frequency wave forces are calculated to see how sensitive the TLP considered is to these forces (springing). This is done using HydroD with a finite element model of the free surface. A simple sensitivity study is performed to investigate how small the element size and how large the radius of the free surface have to be in order to give reliable results. The effect of including the sum-frequency forces in the time domain simulations is seen to be small and the rest of the simulations are performed with only first-order and slowly varying forces included. The effect of having a control system designed to prevent negative damping contributions from the wind turbine at wind speeds above rated is also investigated. Without the control system (simple notch filter) activated, the pitch response of the TLP is actually unstable due to a large negative damping contribution when the wind speed is close to rated. For wind speeds not very close to the rated speed the unstable behavior is not a problem, and the effect of having the filter is smaller. The effect of reducing the water depth from 200 m to 120 m is investigated. The TLP performs better at the reduced water depth. The TLP is also compared with a spar buoy and a semi-submersible concept designed to support the same 5.2 MW wind turbine as the TLP. The TLP has the smallest dynamic heave, roll and pitch motions. The semi-sub has the smallest nacelle accelerations and the spar seems to have the best mooring line characteristics. The comparison given in this study is not extensive enough to decide on which concept is the best. More work is needed in the future.
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Solberg, Thomas. "Dynamic Response Analysis of a Spar Type Floating Wind Turbine." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-16215.
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Wind power is a large natural source for renewable energy, and many countries have shown interest in establishing floating offshore wind parks. There are many advantages with floating offshore wind turbines, but also many challenges connected to them. This report focuses on establishing a model for wave-wind induced loading on a Spar type floating wind turbine named OC3-Hywind. The OC3-Hywind is a modified version of an original design developed by Statoil. Two fellow MSc students have developed models for a tension leg platform (TLP) and a semi-submersible, and a comparison between the three concepts have been done. The model has been constructed by the use of the well known software tools HydroD and DeepC. In addition, a DLL extension, TDHMILL3d, was used to obtain thrust force. HydroD was used in calculations of the hydrodynamic coefficients of the floater. DeepC was used to run coupled floater and mooring analysis in time domain. Important parameters like hydrodynamic coefficients and natural frequencies compare well to data from the literature. Simulations showed that the Spar is mostly influenced by wind loads in the operational conditions. At rated wind speed of 11.4 m/s the pitch motions of the Spar was showed to be large. To reduce these motions a simple filter was used to extend the turbine control system. In situations where wind and waves have different directions, the Spar experiences large yaw motions. Several factors that may contribute to these motions have studied. To achieve good accuracy in statistical parameters, 10 or more simulations with different seeds were needed.The original depth of 320 m was changed to 160 m. Only minor changes to the mooring system were needed to obtain similar performance as the base case. In the comparison part typical trends of the different floaters was studied. Based on these trends, positive and negative response characteristics were discovered. The semi-submersible had the largest pitch and surge motions, while the TLP had the largest accelerations below rated. This may result in difficulties in maintenance operations. Only the Spar showed sign of excessive yaw motions. The semi-submersible had the lowest nacelle accelerations and STD for all load cases. In addition, the semi-submersible is the most versatile when it comes to water depth.
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Blackburn, G. R. A. "The growth and mechanical response of trees to wind loading." Thesis, University of Manchester, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.506075.
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Krakowska, Teresa L. "Wind loading and dynamic response of air-supported roof structures." Thesis, City University London, 1989. http://openaccess.city.ac.uk/7408/.
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This thesis is concerned with defining, theoretically, approximate values of wind loading and predicting dynamic response of air-supported structures subject to suddenly applied loads. Wind loading on air-supported structures is a phenomenon involving significant mutual interaction between inertial, elastic and aerodynamic forces. The aerodynamic forces described by fluid mechanics equations are examined in the first part of the thesis, Chapters 2 to 6. Chapter 2 contains a brief discussion of wind as a flow of air around rigid bodies. This review is followed by an introduction to modern wind engineering, and then by discussion on the theoretical and/or experimental methods to assess wind response of flexible structures. Under the simplifying assumption of three-dimensional potential flow of an incompressible, inviscid, steady air flow, the three-dimensional pressure coefficient distribution on an open-sided paraboloid shallow shell roof is examined in Chapter 5, employing three versions of a vortex-lattice method. The modified Hedman method with horseshoe vortices in the plane z=0, and a boundary condition of tangential flow applied on the body of the shell yielded the best results. In the Appendix to Chapter 5 a real flow solution based on the 'SIMPLE' algorithm is investigated for a numerical example of a thin shell submerged in steady flow - a two-dimensional approximation of the section employed in Chapter 5. For a 3D structure which cannot be adequately represented by 2D model a simple 3D potential flow solution is likely to yield more accurate pressure distributions than a sophisticated 2D real flow analysis. The wind tunnel tests described in Chapter 6 were conducted on a thin, rigid eliptic paraboloid subject to two flow conditions: uniform flow, and in the thick turbulent boundary layer. The theoretical results predicted fairly well the mean pressure distribution on the shell in uniform flow, except on the rearmost part of the model, where separation occurred. In the case of the turbulent boundary layer flow, discrepancies in mean pressure coefficient distributions are of the same order as for uniform flow. However, as the turbulent boundary layer flow is a much more complicated phenomenon than the theoretical description of potential flow, the above conclusion cannot be generalized without further work. The vortex-lattice method, due to its simplicity, can be easily incorporated into any structurefluid interactive scheme accounting for both static and quasi-dynamic behaviour, and an assessment of dynamic response is essential for the design of large air-supported structures. The second part of the thesis, Chapters 7 to 12, is concerned with the structural response of air-supported structures; with special emphasis on the dynamic response following sudden release of a loading system. Chapter 7 gives a review of methods of analysis for pneumatic structures; those experiencing strong geometric nonlinearities are especially focused. The dynamic relaxation method with kinetic damping is discussed in Chapter 8 with respect to the static analysis of pneumatic structures; structural idealization depending on the fabric patterning, type of loading and kind of membrane material being used. Two series of model tests are described; both employing fairly large scale pneumatic domes. The first test model constructed using an orthotropic woven fabric is subject to centrally placed suddenly applied loading. The second test model constructed with very lightweight polythene is subject to suddenly released loading, both central and asymmetric. For this case the internal air and added mass effects become dominant. Explicit dynamic analysis using a centred finite difference scheme is employed in Chapter 9 to analyse the response of pneumatic structures; and in particular to assess the response of the test structures. The influence of surrounding air is included as far as internal air stiffening is considered. For the suddenly unloaded dome, a revised, more efficient numerical scheme is developed, where checking for buckling is carried out at each time step, but creep strains, updated stiffness matrices and unit pressure vectors are calculated at less frequent intervals. In Chapter 10 the tests on the impulsively loaded and unloaded pneumatic domes are described. Dome membrane properties are established from static and dynamic tests on specimens. For dynamic tests a new procedure is devised, to model more closely the state of stresses, by including twodimensional stresses in the testing area of the specimen. Still and movie cameras were used in the static and dynamic tests on the pneumatic domes to record deflection. The results were analysed by means of photogrammetric techniques. The static results compare very well with theoretical predictions. The theoretical dynamic trace for the apex nodal deflection of the impulsively centrally loaded dome differs only slightly from experimental results. The heavy central load influences greatly the response. Discrepancies between theoretical and experimental dynamic responses of the very lightweight and suddenly unloaded dome are however large. The main area of error is caused by improper modelling behaviour of the surrounding air which should be treated as an intrinsic part of the structure. A coupled fluid-structure explicit dynamic analysis, including membrane and air modelling, is presented in Chapter 11. The behaviour of irrotational, inviscid, compressible fluid is described from a Lagrangian point of view. Although only the simplest axisymmetric case is considered, the amount of computing is enormous, hence the procedure cannot, at present, be advocated for use in practice. In Chapter 12 the added mass effect due to vibrating air is discussed. A method to account for virtual mass in shallow pneumatic structures, based on potential incompressible flow and discrete source distributions, is presented and included in the numerical explicit dynamic procedure. The results for the centrally unloaded dome show a great improvement in terms of frequencies, with only a small increase in computing time compared with the numerical scheme of Chapter 9. The discrete source distribution method to calculate added mass effects can be easily extended to any shape of pneumatic structure, and when combined with an explicit dynamic analysis can provide a useful scheme for calculating frequencies and the approximate dynamic response of air-supported structures.
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Hamidi, Vandad. "Domestic demand response to increase the value of wind power." Thesis, University of Bath, 2009. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.519917.
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This thesis describes a new method to evaluate the value of wind power combined with domestic demand response. The thesis gives a brief overview of current domestic demand management programmes, and highlights the demand response and its current application. Such technology has conventionally been used for different purposes, such as frequency regulation, and to minimize the spot electricity prices in the market. The aim is to show whether such technology may become useful to make the renewables, and in particular wind power more interesting for investors. An assessment framework based on generation scheduling is developed to quantify the value of wind power. A further important aspect of value of wind power is the impact of intermittency on overall reliability of the system. This necessitates increasing the spinning reserve level which will increase the production cost. The changes in the spinning reserve level has been investigated in this thesis and it has been shown that how different forecasting errors may change the overall value of a windfarm over its lifetime. One of the most important aspects of a system containing demand response, is the availability of demand response. A load modelling package is developed to show the potential for demand response in a real system from domestic sector. With every increasing the concerns with regard to future of generation mix in Britain, this work has proposed over 72 scenarios for the future of generation mix in Britain and the impact of demand response to increase the value of wind power in 2020 has been investigated. The assessment framework is enhanced by showing that how the value of wind power combined with domestic demand response may change by changes in emission price, and cost of demand response. This will show the degree of feasibility of such system in which demand response is treated like a commodity.
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Lee, Sungho Ph D. Massachusetts Institute of Technology. "Dynamic response analysis of spar buoy floating wind turbine systems." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/46545.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references (leaves 83-84).
The importance of alternative energy development has been dramatically increased by the dwindling supplies of oil and gas, and our growing efforts to protect our environment. A variety of meaningful steps have been taken in order to come up with cleaner, healthier and more affordable energy alternatives. Wind energy is one of the most reliable energy alternatives for countries that have sufficiently large wind sources. Due to the presence of steady and strong winds, and the distance from coastline residential, the offshore wind farm has become highly attractive as an ideal energy crisis solution. Floating wind turbine systems are being considered as a key solution to make the offshore wind farm feasible from an economic viewpoint, and viable as an energy resource. This paper presents the design of a synthetic mooring system for spar buoy floating wind turbines functioning in shallow water depths. Nacelle acceleration, static and dynamic tensions on catenaries, the maximum tension acting on the anchors are considered as design performances, and a stochastic analysis method has been used to evaluate those quantities based on sea state spectral density functions. The performance at a 100-year hurricane condition is being defined as a limiting case, and a linear wave theory has been the most fundamental theory applied for the present analysis.
by Sungho Lee.
S.M.
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Goodman, Joseph Neal. "Performance measures for residential PV structural response to wind effects." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54910.
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This thesis applies structural reliability measures for the performance based design of residential PV system structures. These measures are intended to support designers in delivering systems with quantified and consistent reliability. Existing codified practices prescribe global factors (allowable stress design) and partial factors (load and resistance factor design) intended to provide an acceptable level of reliability as defined by historical practice. When applied to residential PV systems this prescriptive approach has two flaws, (1) calibration efforts needed to ensure consistency across structural system types have not kept up with the commercially available system types and (2) the actual expected reliability is not quantified and available to support decisions. The proposed reliability measures include probability of failure conditioned to wind speed in a fragility curve and the reliability index β, both of which are commonly used in performance based design. The approach is demonstrated through the application of the reliability measures to code compliant designs. Diverse system types are utilized to demonstrate how the existing code prescribed approach may lead to non-uniform structural performance. For each of the system types on which the reliability measures are demonstrated, a code compliant design is developed for three roof slopes, wind tunnel testing is conducted to provide an experimental measure of wind pressure coefficients, system specific fragility curves are generated to quantify the probability of failure conditioned to a set of wind speeds, and then, a site specific wind model is applied to produce a probability of failure and reliability index β. Through the performance based approach proposed in this thesis, two key outputs show non-uniform and unanticipated structural performance of PV systems designed according to the prescriptive code method. The two key outputs which illustrate this finding are fragility curves which illustrate the probability of failure over a range of wind speeds and reliability index, β values which couple the structural and wind distributions for a single measure of reliability.
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Elsen, Ronald. "Global modeling of the average response of the magnetosphere to varying solar wind conditions /." Thesis, Connect to this title online; UW restricted, 1996. http://hdl.handle.net/1773/6802.
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Mohammadi, Alireza. "Wind Performance Based Design for High-Rise Buildings." FIU Digital Commons, 2016. http://digitalcommons.fiu.edu/etd/3032.
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The rapid growth of high-rise high-density urban areas in coastal and near coastal, hurricane-prone cities has been observed globally and in the United States in recent decades. Favored by modern urban growth and planning policies, this trend is expected to accelerate in future. Recent climate change studies suggest a significant increase in the destructiveness of hurricanes in past 30 years by both increases in lifetime and intensity of hurricanes. Current prescriptive wind design approach does not provide transparent methods and criteria to reliably quantify the performance of buildings as well as the functional requirements necessary to accommodate large populations during extreme wind. Since this approach primarily intends to keep the structural system essentially elastic, the more efficient design may be achievable by allowing controlled inelasticity in structural components. All these facts put a great emphasis on using a reliable wind design and assessment approach evidently describing the performance of high-rise building to wind loads beyond the current design wind loads.
This dissertation presents the development of a wind performance-based engineering approach and its practical implementation for three, 47-, 40- and 30-story steel moment frame high-rise buildings. In this study, the nonlinear dynamic responses of the buildings to different wind hazard levels were evaluated by developing 3D nonlinear finite element models and utilizing a wind incremental dynamic analysis (IDA) approach. The wind loading for the 47-story building was measured by conducting wind pressure testing on a scaled rigid model at the Wall of Wind (WOW) facility at Florida International University. For two other buildings wind loads were acquired using TPU Aerodynamic Database. Using the IDA results and adopting available wind performance criteria, a wind performance assessment approach was developed representing the estimated performance levels as a function of the basic wind speed. Three types of wind performance were evaluated: structural component performance; cladding performance to wind-induced shear deformation; and serviceability motion comfort performance. This evaluation indicated remarkable lateral capacity associated with allowing controlled structural nonlinearity, in contrast to considerations required to assure acceptable serviceability and non-structural (e.g. cladding) performances.
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Wu, Xiaoxiao M. Eng Massachusetts Institute of Technology. "Wind-induced dynamic responses of structures with outrigger systems." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/99621.
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Thesis: M. Eng., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (page 55).
A multi-degree of freedom lumped mass model with rotational springs was built to investigate the influence of outrigger system on the natural periods and mode shapes of a structure. The presence of outrigger system was found to significantly stiffen the structure, reducing the natural periods and distorting the mode shapes. The influences of outrigger system on the modal properties of a structure vary with the change of its number, locations and rotational stiffness. Wind-induced along-wind and across-wind responses of structures with and without outrigger system were analyzed, compared and discussed. It was found that the outrigger system can effectively decrease the along-wind responses (peak displacements and accelerations) and its influence is the most significant when it's located at the middle of the structural height. For across-wind responses, the outrigger system(s) could help with the prevention of vortex-induced resonance, if its location(s) is(are) appropriately chosen, by shifting the natural periods of the original structure without outrigger away from the frequency of vortex shedding. Two methodologies were proposed for the design of outrigger systems in two different scenarios, one with the number and locations of outrigger(s) preset and the other not. For the first scenario, the corresponding methodology is a checking process and for the second, it is a designing process. Both methodologies are aimed at preventing vortex-induced resonance and minimizing along-wind peak displacements and accelerations, satisfying related human comfort criteria for motions and lateral drifts requirements.
by Xiaoxiao Wu.
M. Eng.
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Walach, Maria-Theresia. "Ionospheric convection and auroral responses to solar wind driving." Thesis, University of Leicester, 2017. http://hdl.handle.net/2381/39717.
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This thesis studies the large-scale dynamics in the Earth's magnetosphere due to solar wind driving. When the interplanetary magnetic field (IMF) is orientated southward, reconnection on the dayside magnetopause opens magnetic flux, which eventually reconnects in the magnetotail. When dayside reconnection is dominant, the polar cap, the area where open magnetic flux meets the Earth's surface, increases. Similarly, when nightside reconnection is dominant, the polar cap decreases in size. This framework is known as the expanding and contracting polar cap paradigm (ECPC). Part of this thesis considers the ionospheric flows, a part of the ECPC, which relates global auroral imagery of the size of the polar cap through a physics-based model of the ECPC, and compares the calculated ionospheric flow velocities to satellite, and ground-based measurements of plasma drift. The comparison also discusses the known limitations of the model and the observations. In the following chapters, specific events within the ECPC, or magnetospheric modes, are put into the context of solar wind driving and the auroral response. Substorms are a sporadic magnetospheric response mode, where the polar cap expands at first, followed by a distinct nightside brightening of the aurora and a decrease in polar cap flux. Steady magnetospheric convection events (SMCs) are times when the day and nightside reconnection rates are balanced, such that the polar cap flux stays constant. By considering dayside reconnection rates and the magnetospheric response during these events, it is established that the majority of SMCs are part of the substorm cycle. Sawtooth events (SEs) appear as a quasi-periodic version of substorms, but occur under more extreme solar wind driving. It is shown that the aurora behaves according to the ECPC in terms of latitudinal expansions and contractions, but the temporal behaviour is significantly different from substorms.
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Forni, Fabio. "Investigating the axial response of pile foundations for offshore wind turbines." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.
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I crescenti problemi legati ai cambiamenti climatici rendono l'impiego delle energie rinnovabili sempre più interessante.
In questa ottica, in Germania si sta pianificando di aumentare la produzione di energia pulita attraverso lo sfruttamento dell’energia eolica. Nuovi impianti di turbine eoliche sono previsti nel Mare del Nord in acque medio profonde (25-45m) dove la parte immersa della struttura della turbina eolica (chiamata sottostruttura) è spesso costituita da una struttura jacket (traliccio) o tripod (a treppiedi). Questo tipo di sottostrutture trasmettono principalmente carichi assiali alle fondazioni (in genere fondazioni su palo), e il carico a trazione è la forza che maggiormente ne influenza il dimensionamento.
Molte compagnie energetiche tedesche sono interessate a migliorare l’efficienza e i costi dei loro impianti eolici e, per questo, incaricano università ed istituti di ricerca (come il Fraunhofer IWES) per indagarne gli aspetti, come ad esempio il comportamento delle fondazioni offshore.
All’autore di questa tesi è stata data l’opportunità di studiare e lavorare al Fraunhofer IWES e perciò questa tesi tratterà del compramento di pali caricati assialmente e staticamente pensati per sottostrutture jacket o tripod per turbine eoliche.
Nello studio effettuato per questa tesi, i dati seprimentali, ottenuti da una campagna sperimentale condotta (in larga scala 1:10 1:5) su pali infissi in terreno sabbioso, sono confrontati attraverso l’impiego delle load-transfer curves (funzioni che descrivono il comportamento d’interfaccia palosuolo) usando sia un’approccio classico (fornito dal metodo di calcolo API Main Text) sia approcci più recenti (dati dai metodi di calcolo CPT).
Uno script Matlab creato appositamente dall’autore di questa tesi riesce ad implementare 11 diversi tipi di load-transfer curves. Il lavoro di tesi si conclude con un esempio pratico in grado di fornire un’idea di come questo script può essere usato nella progettazione.
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Polonichko, Vadim Dmitri. "Response of the upper ocean to wind, wave and buoyancy forcing." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0019/NQ34283.pdf.
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Pedersen, Eja. "Human response to wind turbine noise : perception, annoyance and moderating factors." Doctoral thesis, Göteborg : Occupational and Environmental Medicine, Department of Public Health and Community Medicine, Institute of Medicine, The Sahlgrenska Academy, Göteborg University, 2007. http://hdl.handle.net/2077/4431.
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Imam, Yehya Emad. "Modal decomposition of the baroclinic response to wind in elongated lakes." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/39953.
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The baroclinic response to wind is examined in narrow elongated lakes. The main objective is to link the excitation and modulation of baroclinic modes to lake bathymetry and stratification, temporal and spatial characteristics of wind forcing, and damping. Three lake bathymetries are examined which represent 1) variable-depth single basins with straight thalweg, 2) two-basin lakes with straight thalweg, and 3) two-basin lakes with arms at which the thalweg bends sharply. The bathymetries are examined using idealized lake forms as well as data from two Canadian lakes. Modal analysis and a three-dimensional hydrodynamic numerical model are used to analyze the baroclinic response. Also, a modal-based forced model is developed to simulate the decoupled modal responses to wind and provide a direct link between lake and forcing characteristics and modal composition of the response.
This study shows that coupling between wind-forcing spatial structure and bathymetry determines which modes are excited, while wind-forcing temporal patterns modulate the magnitude of excited modes. It is found that, when wind is near-uniform, the first horizontal mode, H1, dominates the response regardless of bathymetry, because the near-uniform wind couples with the spatial distribution of layer flow for H1. In sub-basins separated by geometric constrictions (sills and contractions) or sharp bends in the thalweg relative to wind direction, the wind induces local metalimnetic tilts that are superimposed on the domain-wide H1 tilt. The sub-basin tilts are attributable to higher horizontal modes which are equivalent to the H1 modes of the decoupled sub-basins.
Furthermore, this study demonstrates the following: 1) interbasin exchange due to H1 shifts from two to more layers due to interaction of vertical modes, 2) geometric constrictions result in strong damping of H1 which causes high forcing-response coherence and broadens the resonance bandwidth, and 3) along-thalweg depth variability in single basins increases the number of excited modes and localizes the interface shear for asymmetric basins and causes the opposite effects for symmetric basins. The findings of this study contribute to understanding the baroclinic response to wind in lakes of complex bathymetry.
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Strachan, Nicholas P. W. "Investigation of dynamics, control, power quality and fault response of a MW-size wind generator with integrated storage." Thesis, University of Aberdeen, 2010. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=103113.
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a control, power quality and stability perspective. This is chiefly due to the future influence on power system behaviour resulting from the rapid cumulative growth of grid integrated wind power, and the improved control characteristics afforded by modern variable speed wind power generators. There is consequently strong motivation to enhance the inherent control robustness, power quality and fault-ride-through characteristics of modern wind power generators. By so doing, the attributes essential for power system operation regarding security of supply, reliability, and power quality can be assured. The work presented in this thesis employs a two-fold methodology in order to improve the inherent control, power quality and fault tolerance characteristics of a modern wind power generator based on a 2MW medium-voltage directly-driven permanently-excited architecture employing full-scale power conversion. Firstly, due to the complexity of modern wind power generators, accurate and complementary detailed non-linear (circuit orientated) and linear analytical (state-space based) wind generator models are developed. Collectively, these facilitate a wide range of detailed transient and smallsignal, control, stability and fault analysis studies. Ultimately, this facilitates the means by which advanced AC voltage controls are developed that significantly extend the wind power generator stable operating range for grid strength variations (grid impedance variation). Secondly, a supercapacitor based electrical energy storage system is designed and integrated within the developed wind generator models in order to facilitate the means by which fault-ridethrough characteristics and power quality can be improved. Fault-ride-through characteristics are ultimately improved by absorbing a proportion of generated power in the integrated storage system during grid-side faults. Power quality is ultimately improved by effectively buffering wind speed fluctuations in the integrated storage system so that a ‘smoothed’ version of the generated power results at the wind generator terminals.
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Schachterle, Gregory Dallin. "Improved Analysis Techniques for Scatterometer Wind Estimation." BYU ScholarsArchive, 2020. https://scholarsarchive.byu.edu/etd/9218.
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In this thesis, three improved analysis techniques for scatterometer wind estimation are presented. These techniques build upon previous methods that help validate scatterometer data. This thesis examines the theory connecting the 1D and 2D kinetic energy spectra and uses QuikSCAT data to measure the 2D kinetic energy spectrum of ocean winds. The measured 2D kinetic energy spectrum is compared to the traditional 1D kinetic energy spectrum. The relationship between the 2D kinetic energy spectra and the 1D kinetic energy spectra confirms findings from previous studies that ocean winds modeled in 2D are isotropic and nondivergent. The 1D and 2D kinetic energy spectra also confirm the known conclusion that the zonal and meridional components of ocean winds are uncorrelated. Through simulation, the wind response function (WRF) is calculated for three different QuikSCAT processing algorithms. The WRF quantifies the contribution that the wind at each point of the surface makes to a given wind estimate. The spatial resolution of the different processing algorithms is estimated by their WRFs. The WRFs imply that the spatial resolution of ultrahigh resolution (UHR) processing is finer than the spatial resolution of conventional drop-in-the-bucket (DIB) processing; the spatial resolution of UHR processing is ~5-10 km while the spatial resolution of DIB slice processing is ~12-15 km and the spatial resolution of coarse resolution DIB egg processing is ~30 km. Simulation is used to analyze the effectiveness of various wind retrieval and ambiguity selection algorithms. To assist in the simulation, synthetic wind fields are created through extrapolating the 2D Fourier transform of a numerical weather prediction wind field. These synthetic wind fields are sufficiently realistic to evaluate ambiguity selection algorithms. The simulation employs the synthetic wind fields to compare wind estimation with and without direction interval retrieval (DIR) applied. Both UHR and DIB wind estimation processes are performed in the simulation and UHR winds are shown to resolve finer resolution wind features than DIB winds at the cost of being slightly noisier. DIR added to standard QuikSCAT UHR wind estimation drops the wind direction root-mean-squared error by ~10° to ~24.74° in the swath sweet spot.
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Vittal, Eknath. "A static analysis of maximum wind penetration in Iowa and a dynamic assessment of frequency response in wind turbine types." [Ames, Iowa : Iowa State University], 2008.
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Pauw, Marina. "Chitin synthesis in response to environmental stress." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/86435.
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Thesis (MSc)--Stellenbosch University, 2014.ENGLISH ABSTRACT: Previous studies have indicated that fermentation with yeast strains whose cell walls contain higher chitin levels may lead to reduced wine haze formation. In order to adjust cell wall chitin levels, more information on the regulation of chitin synthesis in wine-relevant yeast is required. Yeast cells are known to increase chitin levels when subjected to certain environmental changes such as an increase in temperature. The main aim of this project was to investigate chitin accumulation and synthesis in wine yeast strains when exposed to environmental change. This was achieved by subjecting the strains to various environmental conditions and comparing chitin levels. The information gained may aid future selection and/or manipulation of yeast strains for the production of higher chitin levels. Three Saccharomyces cerevisiae strains and two Saccharomyces paradoxus strains were subjected to conditions that had been linked to a change in chitin synthesis in past studies in laboratory yeast strains. Of the conditions used in this study, the addition of calcium to a rich media led to the highest cell wall chitin levels. The data also show that chitin synthesis is largely strain dependant. Two conditions which resulted in increased chitin deposition were chosen for gene expression analyses, using strains with strongly diverging average chitin levels. Results showed that an increase in chitin levels correlates with an increase in expression of GFA1, the gene encoding for the first enzyme of the chitin synthesis pathway. Overall, this study provides novel insights into chitin synthesis in Saccharomyces cerevisiae wine yeast strains as well as Saccharomyces paradoxus strains, with possible future implications on haze prevention studies.
AFRIKAANSE OPSOMMING: Vorige studies het aangetoon dat fermentasie met gisrasse waarvan die selwande hoë chitienvlakke bevat, kan lei tot verminderde wynwaasvorming. Om selwandchitienvlakke aan te pas, word daar meer inligting rakende die regulering van chitienvlakke in wyn gisrasse verlang. Dit is bekend dat gisselle chitienvlakke verhoog wanneer die selle onderwerp word aan sekere veranderinge in die omgewing soos ’n verhoging in temperatuur. Die hoofdoel van hierdie projek was om die chitienopbou en -sintese in wyngisrasse te ondersoek waar gis blootgestel word aan omgewingsveranderinge. Dit is bereik deur die selle aan verskeie omgewingstoestande bloot te stel en chitienvlakke met mekaar te vergelyk. Die inligting hieruit verkry kan toekomstige gisraskeuses asook die manipulering van gisrasse met die oog op hoër vlakke van chitienproduksie vergemaklik. Drie Saccharomyces cerevisiae rasse en twee Saccharomyces paradoxus rasse is onderwerp aan toestande wat in vorige studies gekoppel is aan ’n verandering in chitienvorming in laboratorium-gisrasse. Van die toestande toegepas in hierdie studie, het die toevoeging van kalsium tot ’n nutrientryke medium gelei tot die hoogste chitienvlakke in selwande. Die data toon ook aan dat chitiensintese hoofsaaklik rasverwant is. Twee toestande wat gelei het tot verhoogde chitienafsetting is gekies vir geen-uitdrukkingsanalise, terwyl rasse gebruik is met gemiddelde chitienvlakke wat wyd uiteenlopend is. Die resultate het getoon dat ’n verhoging in chitienvlakke ooreenstem met ’n verhoging in die uitdrukkingsvlakke van GFA1, die geen wat kodeer vir die eerste ensiem in die chitiensintesebaan. Oor die algemeen verskaf hierdie studie nuwe insigte oor chitiensintese in Saccharomyces cerevisiae wyngisrasse en Saccharomyces paradoxus rasse en verskaf dit belangrike inligting vir moontlike toekomstige studies oor waasvoorkoming.
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Zhu, Q. "Frequency supporting of smart grid with wind power via demand side response." Thesis, University of Liverpool, 2017. http://livrepository.liverpool.ac.uk/3005582/.
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EL, Itani Samer. "Short-term frequency support utilizing inertial response of variable-speed wind plants." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=104853.
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In regions with increasing penetration of variable-speed wind generators, grid operators are concerned about frequency security as system inertia is decreasing. The partial replacement of conventional plants with modern wind plants may cause system frequency regulation to fall below acceptable levels, especially in isolated power systems. This study investigates the contribution of variable-speed wind generators to short-term frequency support. This contribution is obtained by transiently releasing part of the stored kinetic energy in the turbine blades, namely the inertial response. Some inertial response schemes have been researched to be incorporated as auxiliary loops in the controllers of wind generators. First, we compare the performance of these earlier implementations and identify their shortcomings. Then, we quantify the extractable inertial power from a modern wind turbine, given its power characteristic, equivalent inertia, and prevailing wind condition. From this understanding, a new controller, based on the asynchronous release of kinetic energy, is proposed to achieve a superior, more controllable performance. The controller is composed of a 'detection and triggering' scheme that detects the frequency event, a 'power shaping' function that decides the duration and amount of inertial power released, and a 'rotor speed recovery' scheme that brings the turbine back to its optimal speed which corresponds to maximum power tracking. Time-domain simulations were performed to examine the performance of this controller. Based on its impact on system frequency and wind farm operation, the new controller was compared to earlier implementations of wind plant inertial response. The results show that the proposed controller is capable of bringing together the advantages of the different earlier implementations for better grid integration of wind turbine generators. Its effectiveness in reducing the initial frequency fall after a load-generation mismatch promises significant contribution to system inertia. Its controllable, predictable nature is a distinct advantage that enables grid operators to understand, forecast and quantify the impact of incorporating this controller into grid-connected wind generators.Dans les régions à forte pénétration d'éoliennes à vitesse variable, les opérateurs de réseau sont concernés par la sécurité de la fréquence lorsque l'inertie du système décroît. La substitution partielle d'usines conventionnelles par des usines éoliennes modernes pourrait causer le réglage de la fréquence du système à chuter sous des niveaux acceptables, surtout dans le cas de systèmes d'alimentation isolés. Cette étude se penche sur comment les éoliennes à vitesse variable peuvent contribuer au support de la fréquence à court terme. Cette contribution est obtenue grâce au relâchement transitoire d'une partie de l'énergie cinétique contenue dans les aubes de turbine, plus spécifiquement la réponse transitoire. Quelque programmes de réponse inertielle ont été étudiés afin d'être incorporés comme boucle auxiliaire dans les contrôles des génératrices à vent. En premier lieu, on compare la performance d'implémentations préexistantes entre-elles afin d'en identifier les défauts respectifs. En second lieu, on quantifie la puissance inertielle capable d'être extraite d'une génératrice à vent moderne tout en prenant en considération les caractéristiques de puissance, son inertie équivalente ainsi que les conditions de vent dominantes. Avec cette notion, un nouveau régulateur qui est basé sur un relâchement non-synchronisé d'énergie cinétique est proposé afin d'obtenir une performance supérieure et plus contrôlable. Le contrôleur est composé d'un programme de «détection et déclenchement» qui détecte la variation de la fréquence, d'une fonction «formatrice de puissance» qui calcule la durée ainsi que la quantité de puissance cinétique relâchée, et d'un programme de «récupération de vitesse du rotor» qui ramène la turbine à sa vitesse optimale qui correspond au suivi de la vitesse maximale. Des simulations dans le domaine du temps ont été effectuées afin d'examiner la performance du régulateur. À partir de son impact sur la fréquence du système et l'opération de plants éolien, le nouveau contrôleur a été comparé aux implémentations antérieures de réponse inertielle d'usines de vent. Les résultats démontrent que le contrôleur proposé est capable d'unifier les avantages des implémentations précédentes afin d'avoir une meilleure intégration des éoliennes. Sa capacité de réduire la chute de fréquence initiale qui suit un décalage au niveau de la génération de charge promet une contribution significative sur l'inertie du système. En fait, sa nature contrôlable et prévisible lui donne un avantage distinct qui permet aux opérateurs de réseau de pouvoir comprendre, prédire et quantifier l'impact potentiel de l'implémentation de ce régulateur dans des génératrices à vent connectées au réseau.
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Kucherera, Grant Tarwirei. "Stability behaviour and dynamic response of cooling towers subjected to wind loading." Master's thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/24305.
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In this study, a linear eigenvalue buckling parametric analysis is presented for various cooling tower shell geometries. The shells are subjected to increasing wind pressures (speeds) to observe the trends in the critical buckling pressures/speeds at which the shell first buckles and the corresponding buckling modes. The cooling tower's geometry is changed in a systematic manner to obtain the relationship between critical wind speeds associated with the first mode of buckling and the cooling tower's geometry. Geometrical parameter ratios of the cooling tower's dimensions are considered in order to cover a wider spectrum of the cooling tower's geometry. The critical wind speed versus height curve is observed to be similar to the Euler buckling curve. There appears to be a certain optimum throat height to total height ratio of about 0.75 for any cooling tower at which the critical wind speed is maximum. The critical wind speed varies linearly with the cooling tower thickness and non-linearly with all diameter ratios. A linear eigenvalue vibration parametric analysis is presented for various cooling tower shell geometries to observe trends in the free vibration response (natural frequencies and mode shapes). The forced response of the cooling tower to various forcing frequencies of wind gusts is analysed using the mode superposition method. The shells are subjected to increasing wind gust periods of the same speed to obtain the trends in the forced vibration response (response frequencies and modes). The cooling tower's geometry is changed in a systematic manner to obtain the free and forced vibration behaviour. The natural frequencies and their corresponding bandwidths for the first ten different modes reduce with increasing height. They are generally invariant with the height to top diameter ratio, but the bandwidth increases with increasing height to top diameter ratio. The response frequencies and their corresponding bandwidths generally decrease with increasing height as well as the height to top diameter ratios. The response frequency generally decreases with decreasing forcing frequency, but not for all the cooling tower geometries. The findings can be used as a basis for further research and establishment of conceptual design guidelines when considering stability, free and forced vibration cooling tower behaviour.
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Xia, Jun. "Future power system dynamic frequency response under high penetration levels of wind." Thesis, University of Strathclyde, 2015. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=24851.
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Due to environmental concerns, offshore wind plant will play an important role in next decades for meeting the requirement of carbon emission and renewable energy target. The variable speed wind turbine will not have a load-frequency response similar with traditional synchronous generator which may cause the inertia less problems in the system. The UK National Grid has developed scenarios where high wind power penetration levels are considered which are likely to change the patterns of UK transmission network operation and dynamic performance. Therefore, it is necessary to develop an analytical capability which can assess the system dynamic performance ahead of the anticipated changes. Although some work has been reported in this area, the studies are either based on very simple network representations or involve very complex proprietary network modelling not publically available and with results which are often difficult to interpret. This thesis aims to develop appropriate ways of deriving a representative dynamic system model using UK transmission system as a benchmark. The methodology "Individual channel analysis and design (ICAD)" is utilized to realise the trade-off between plant dynamical requirements (feedback design) and the limitations (coupling effects) on achieving such requirements in multivariable system. A representative 21 bus dynamic model of the entire UK transmission system based on Ten Year Statement has been developed and implemented in Power System Simulator (PSS/E). A few recent system-wide events, captured by the existing Phasor Measurement Units (PMU), have been used to validate the frequency response of the model. Moreover, the General Electric (GE) type DFIG models are added for the purpose of analysing the future system performance with the increasing penetration levels of wind energy. The case study reveals that improvements are to be had by transmission line reinforcements under appropriate wind energy distribution scenarios with system transient stability largely improved. The impact of key influencing factors such as the size of the largest generating unit for n-1 contingency, amount of primary system response, frequency dependency of load, and others are presented. The study concludes that none of the individual factors can provide a complete solution and that careful cost benefit analysis is needed to determine the proper mix of services and reinforcements needed in the future.
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Zhang, Shuyang. "Two impacts of wind penetration transient frequency response and load following requirements /." [Ames, Iowa : Iowa State University], 2008.
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Tse, Kam Tim. "Cost and benefits of response mitigation techniques for wind-excited tall buildings /." View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202009%20TSE.
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Matus, Manuel A. Mr. "Experimental Investigation of Wind-induced Response of Span-wire Traffic Signal Systems." FIU Digital Commons, 2018. https://digitalcommons.fiu.edu/etd/3655.
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The purpose of this investigation was to identify key design parameters that might significantly affect the response of span wire traffic light systems during extreme wind events. The performance of these systems was assessed through physical testing in an effort to quantify the effect of sag ratio, wire tension and wire clearance. The Wall of Wind experimental facility at Florida International University was utilized for testing the systems at different wind speeds and wind directions.
The findings showed that, at all tested wind directions, lift, drag and tension forces increased with increasing wind speeds. On the contrary, increasing the wind speed resulted in higher inclination on the traffic lights, lower drag coefficients and higher lift coefficients. Overall, when the wind was approaching from the rear face of the traffic signals, increased drag coefficients were recorded. When the sag was set at 7% lower drag coefficients were observed.
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Bitaraf, Hamideh. "Mitigating Impacts of High Wind Energy Penetration through Energy Storage and Demand Response." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/70864.
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High renewable energy penetration is a goal for many countries to increase energy security and reduce carbon emissions from conventional power plants. Wind energy is one of leading sources among different renewable resources. However, high wind energy penetration in the system brings new challenges to the electric power system due to its variable and stochastic nature, and non-correlation between wind and load profiles. The term non-correlation is used in this research refers to the fact that wind or any other renewable generation, which is nature driven, does not follow the load like conventional power plants.
Wind spill is a challenge to utilities with high wind energy penetration levels. This occurs from situations mentioned above and the fact that wind generation sometimes exceeds the servable load minus must-run generation. In these cases there is no option but to curtail non-usable wind generation. This dissertation presents grid-scale energy storage and demand response options as an optimization problem to minimize spilled wind energy. Even after managing this spilled wind energy, there is still a challenge in a system with high wind energy penetration coming from wind power forecast error.
Wind power forecast error is handled by having more back-up energy and spilling the non-usable wind power. This research offers a way to use the grid-scale energy storage units to mitigate impacts of wind power forecast error by. A signal processing method is proposed to decompose the fluctuating wind power forecast error signal, based on the fact that each energy storage or conventional unit is more efficient to operate within specific cycling regimes. Finally, an algorithm is proposed schedule energy storage for mitigating both impacts.Ph. D.
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Chapman, Timothy Peter. "Morphological and neural modelling of the orthopteran escape response." Thesis, University of Stirling, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391494.
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