112 research outputs found
Manage Your Career 10 Keys to Survival and Success When Interviewing and on the Job, Second Edition
No full textProfessor Sathe is a great gift, a passionate teacher who cares deeply about the life arc of each individual student. In his vibrant classroom, he translates strategic management into a personal discipline—and here in these pages, he brings to you and me the bene ts of his wise mentorship. —Jim Collins, author of Good to Great
This book gives the reader the keys to survival and success as his or her career progresses from one job to the next in the same, or a different, organization—be
it for-pro t, nonpro t, government, or volunteer. It is designed to help the reader avoid the many traps and pitfalls encountered along his or her career path and to
help facilitate increased personal effectiveness during all three stages of the job cycle—interviewing, new hire, and long-term employment. Whether preparing to enter the workforce for the first time or in early, middle, or later career stages, this book will show the reader how to avoid jobs and organizations that are not a good fit. It will also go beyond survival and show how to achieve success by doing the job well and making other contributions to the organization in ways that improve job performance, satisfaction, happiness, and personal and professional growth. The keys this book provides will work whether the reader is an independent contributor, a manager
responsible for the work of others, or an executive responsible for the enterprise. Organizational leaders, human resource professionals, career coaches, and mentors can
also utilize this book to educate and train employees to be more productive at work and happy in their worklife
Monin-Obukhov similarity theory applied to offshore wind data - validation of models to estimate the offshore wind speed profile in the north sea
No full textThe offshore wind energy is gaining more and more importance in the scenario of the European renewable energies. Due to high costs of installation and maintenance, it is important to have a good assessment of the wind speed profile. The wind speed at the turbine hub level is used for energy yield evaluations and the knowledge of the wind shear helps estimating turbine structure loads. The wind speed profile in a marine environment is investigated using the data provided from the German offshore research platform FINO-1, the meteorological mast of the Dutch offshore wind park Egmond aan Zee and the weather forecast model COSMO-EU of the Deutscher Wetterdienst DWD. The data are compared to the Monin-Obukhov Similarity Theory using the Richardson Bulk Method, the Richardson Gradient Method and the Profile Methods. The results show that the models do not predict the wind speed profile well and large scatter is present. The weather forecast model COSMO-EU for offshore wind energy purposes is validated using FINO-1 measurements and the results are promising.AEWE - WindenergyAerospace Engineerin
On the possibility of using site data for offshore wind turbine design
No full textAerospace Engineerin
Influence of wind conditions on wind turbine loads and measurement of turbulence using lidars
No full textVariations in wind conditions influence the loads on wind turbines significantly. In order to determine these loads it is important that the external conditions are well understood. Wind lidars are well developed nowadays to measure wind profiles upwards from the surface. But how turbulence can be measured using lidars has not yet been investigated. This PhD thesis deals with the influence of variations in wind conditions on the wind turbine loads as well as with the determination of wind conditions using wind lidars. Part I of the thesis focuses on analysis of diabatic wind profiles, turbulence, and their influence on wind turbine loads. The diabatic wind profiles are analyzed using the measurements from two offshore sites, one in the Dutch North Sea, and the other in the Danish North Sea. Two wind profile models are compared, one that is strictly valid in the atmospheric surface layer, and the other that is valid for the entire boundary layer. The second model is much more complicated in comparison to the first. It is demonstrated that at heights more than 50 m above the surface, where modern wind turbines usually operate, it is advisable to use a wind profile model that is valid in the entire boundary layer. The influence of diabatic wind profiles under steady winds on the fatigue damage at the blade root is also demonstrated using the aero-elastic simulation tool Bladed. Furthermore, detailed analysis of the combined influence of diabatic wind profile and turbulence on the blade root flap-wise and edge-wise moments, tower base fore-aft moment, and the rotor bending moments at the hub is carried out using the aero-elastic simulation tool HAWC2. It is found that the tower base fore-aft moment is influenced by diabatic turbulence and a rotor bending moment at the hub is influenced by diabatic wind profiles. The blade root loads are influenced by diabatic wind profiles and turbulence, which results in averaging of the loads, i.e. the calculated blade loads using diabatic wind conditions and those calculated using neutral wind conditions are approximately the same. The importance of obtaining a site-specific wind speed and stability distribution is also emphasized since it has a direct influence on wind turbine loads. In comparison with the IEC standards, which generalize the wind conditions according to certain classes of wind speeds, the site-specific wind conditions are demonstrated to give significantly lower fatigue loads. There is thus a potential in reducing wind turbine costs if site-specific wind conditions are obtained. In this regard we then are faced with measurement challenges. The current industry standard for the measurement of wind speed is either the cup or the sonic anemometer. Both instruments require a meteorological mast to be mounted at the measurement site. For measuring the wind profile the instruments need to be mounted at several heights on the mast. To install a mast and set up these instruments is quite expensive, especially at offshore sites, where the cost of foundation increases significantly. Besides, there are problems with the flow distortion that have to be taken care of. In order to overcome these problems it would be ideal to have a remote sensing instrument that measures wind speed. Wind lidars are capable of doing that albeit with a price. Part II of the thesis deals with detailed investigations of the ability of wind lidars to perform turulence measurements. Modelling of the systematic errors in turbulence measurements is carried out using basic principles. Two mechanisms are identified that cause these systematic errors. One is the averaging effect due to the large sample volume in which lidars measure wind speeds, and the other is the contribution of all components of the Reynolds stress tensor. Modelling of turbulence spectra as measured by a scanning pulsed wind lidar is also carried out. We now understand in detail the distribution of turbulent energy at various wavenumbers, when a pulsed wind lidar measures turbulence. The lidar turbulence models have been verified with the measurements at different heights and under different atmospheric stabilities. Finally, a new method is investigated that in principle makes turbulence measurements by lidars possible. The so-called six beam method uses six lidar beams to avoid the contamination by all components of the Reynolds stress tensor. The theoretical calculations carried out demonstrates the potential of this method. In order to avoid averaging due to volume sampling, a different analysis method is required, which has not been investigated in this thesis. To summarize the entire thesis, it can be said that more work is required to ascertain the influence of atmospheric stability on wind turbine loads. In particular, comparing with the load measurements will go a long way in consolidating the understanding gained from the analysis in this thesis. If lidars are able to measure turbulence, there is a tremendous potential for performing site-specific wind turbine design and making the class based design of the IEC standards obsolete.Wind EnergyAerospace Engineerin
Atmospheric stability and wind profile climatology over the North Sea: Case study at Egmond aan Zee
No full textThe statistics of atmospheric stability and non-dimensional wind profiles are studied using the standard surface-layer theory at Egmond aan Zee in the North Sea. Measurements at 21, 70 and 116 m are used to validate the theoretical profiles. Charnock’s relation is used to estimate the sea surface roughness. Bulk Richardson number is used to estimate the Obukhov length. The measured sea water temperature has a positive bias of 0.82?C resulting in the dominance of unstable conditions and a poor agreement of the theoretical wind profiles with the measurements. The conditions at Egmond aan Zee are dominated by unstable and neutral stabilities. The theoretical wind profiles agree very well with the measurements in the unstable and neutral conditions. In stable conditions, the wind profiles are over-predicted significantly as the height increases. The scaling of the wind profile with respect to the boundary layer height is necessary under stable conditions and the addition of another length scale parameter is preferred.Aerodynamics, Wind Energy & PropulsionAerospace Engineerin
Influence of different wind profiles due to varying atmospheric stability on the fatigue life of wind turbines
No full textAerospace Engineerin
Lattice dynamic study of nickel ferrite nanoparticles using high pressure Raman spectroscopy
No full text
Measurement of turbulence spectra using scanning pulsed wind lidars
No full textTurbulent velocity spectra, as measured by a scanning pulsed wind lidar (WindCube), are analyzed. The relationship between ordinary velocity spectra and lidar derived spectra is mathematically very complex, and deployment of the three-dimensional spectral velocity tensor is necessary. The resulting scanning lidar spectra depend on beam angles, line-of-sight averaging, sampling rate, and the full three-dimensional structure of the turbulence being measured, in a convoluted way. The model captures the attenuation and redistribution of the spectral energy at high and low wave numbers very well. The model and measured spectra are in good agreement at two analyzed heights for the u and w components of the velocity field. An interference phenomenon is observed, both in the model and the measurements, when the diameter of the scanning circle divided by the mean wind speed is a multiple of the time between the beam measurements. For the v spectrum, the model and the measurements agree well at both heights, except at very low wave numbers, k1 <0.005 m−1. In this region, where the spectral tensor model has not been verified, the model overestimates the spectral energy measured by the lidar. The theoretical understanding of the shape of turbulent velocity spectra measured by scanning pulsed wind lidar is given a firm foundation
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