Modal testing of a simplified wind turbine blade

Abstract: This paper examines the modal analysis techniques applied in experiments using a uniform and a stepped beam. These simplified shapes are representative of the a wind turbine blade. Natural frequencies have been identified, therefore designers can ensure those natural frequencies will not be close to the frequency of the main excitation forces (1P or NbP with Nb being the number of rotor blades) in order to avoid resonance. The turbine blade is approximated by a cantilever, therefore, it is fully constrained where attached to a turbine shaft/hub. Flap-wise, edge-wise and torsional natural frequencies are calculated. The results found have been compared to numerical results and the exact solution of an Euler-Bernoulli beam. Concurrence is found for the frequency range of interest. Although, some discrepancies exist at higher frequencies (above 500 Hz), finite element analysis proves to be reliable for calculating natural frequencies

Analysis of vibration of a variable blade length wind turbine

Abstract: In this paper, both flap-wise and edge-wise natural frequencies of vibration of a variable blade length wind turbine are calculated. A stepped beam with two portions has been used to approximate the blade. The two portions of the blade have been approximated by a hollow beam and a solid beam with rectangular cross section. As the outboard portion of the blade can be slid in and out of the inboard portion, ten different configurations of the stepped beam have been investigated. A MATLAB program has been developed for a finite element analysis of a one dimensional model of the stepped beam. Subsequently a three dimensional model of the stepped beam has been developed in the finite element program Unigraphics NX4. The results found using the MATLAB program have been compared with those found with NX4 and satisfactory agreement between these results has been found. Additionally, the influence of varying the blade length on the natural frequencies has been investigated

Vibration analysis of a variable length blade wind turbine

Abstract: In this paper, Flap-wise, edge-wise and torsional natural frequencies of a variable length blade have been identified. Therefore designers can ensure that natural frequencies will not be close to the frequency of the main excitation forces in order to avoid resonance. The fixed portion and moveable portion of the variable length blade are approximated respectively by a hollow and a solid beam which can be slid in and out. Ten different configurations of the variable length blade, representing ten different positions of the moveable portion are investigated. A MATLAB program was developed to predict natural frequencies. Similarly three-dimensional models of the variable length blade have been developed in the finite element program Unigraphics NX5. Concurrence between MATLAB and Unigraphics NX5 results has been found for the frequency range of interest. This means that an effective method to compute natural frequencies of a variable length blade was developed

Chain Deformation for a Polymer Melt under Shear

We used a Couette cell placed within an NMR microscopy apparatus to examine molecular alignment in polydimethylsiloxane melts under shear. 1H dipolar interactions are used to examine main chain ordering while 2H NMR quadrupole splittings are measured in a deuterated oligomer probe, in each case selectively observing different alignment orientations with respect to the flow field. While the main chain results are consistent with the alignment tensor as measured by birefringence, the oligomer senses a uniaxial environment whose director is normal to the velocity-vorticity plane. In the light of these results we propose supramolecular ordering involving polymer stratification

The effects of oil price shocks on U.S. inflation

During the 1970’s the United States experienced several periods of high inflation that have been at least partially attributed to positive oil price shocks. The effectiveness of the Organization of Petroleum Exporting Countries at controlling the price of oil has varied over time, as well as the responsiveness of U.S. inflation to an oil price shock. Current economic theory, supported by empirical data, suggest that oil price shocks can lead to short run changes in inflation. Since the GDP deflator can be considered the average price of final goods produced in an economy, the effects from an input price change can be quite different on the GDP deflator from the Consumers Price Index which measures the average price of consumption. As the price of oil rises, nominal value added falls while domestic real value added remains constant, creating a short run deflation in value added measures such as the GDP deflator. The CPI experiences rising inflation because the consumer’s goods basket has now become more expensive from the rising price of oil. In the long run, inflation is not affected by an oil price shock because it is controlled by monetary policy

Atlas of radiographic features of osteoarthritis of the ankle and hindfoot

To develop a radiographic atlas of osteoarthritis (OA) for use as a template and guide for standardized scoring of radiographic features of OA of the ankle and hindfoot joints

SWAMI: Searching the Web Using Agents with Mobility and Intelligence

Abstract. The rapid growth of the World Wide Web has complicated the process of web browsing by providing an overwhelming wealth of choices for the end user. To alleviate this burden, intelligent tools can do much of the drudge-work. This paper describes the SWAMI system. It combines multiple aspects of adaptive web technologies into a framework for an intelligent web browsing system. It uses a multi-agent system to represent the interests of the user dynamically and takes advantage of the active nature of agents to provide a platform for parallel look-ahead evaluation, page searching, and cooperative link recommendation swapping. The collection of agents reflects the user’s interests by self-organizing into a hierarchicy according to the evidence of apparent interest demonstrated by the user. Example results of the functioning prototype are presented, demonstrating its ability to infer and react to a user’s interests.