Horizontal-axis tidal turbine blade loading for multi-frequency oscillatory motion

This paper presents results from an experimental study which analysed the hydrodynamic response of the out-of-plane blade root bending moment for a horizontal-axis turbine exposed to multi-frequency oscillatory motion. Estimates of the amplitude and phase agree well with those for single frequency oscillatory motion, which suggests that a model based on the principles of linear superposition is applicable. When minor flow separation is experienced, linear superposition is likely to offer conservative estimates. The findings are likely to be of interest to designers of turbines deployed in tidal streams, rivers or canals, and who are seeking low computational approaches for assessing the dynamic blade loads

Tidal turbine blade load experiments for oscillatory motion

This paper presents blade root bending moment measurements of a horizontal-axis tidal turbine for planar oscillatory motion, conducted in a stationary water towing tank. By comparing the measurements with quasi-steady reconstructions for both single and multiple frequency oscillatory motion, the bending moment was shown to be sensitive to both frequency and amplitude, as well as to the mean tip-speed ratio. The unsteady loads associated with the separation of the flow and dynamic stall are shown to be of considerably greater importance than those which are already present for attached flow, such as added mass and dynamic inflow. A linear model fit to the unsteady bending moment also indicates that the inertia contribution is relatively small. For cases where attached flow exists over the majority of the load cycle, these reconstruction methods are likely to be sufficient to obtain a reasonable prediction of the root out-of-plane bending moment. However, turbines whose blades are likely to operate near stall are likely to require more complex models for accurate load predictions to mitigate the risk of fatigue failure

The characterisation of the hydrodynamic loads on tidal turbines due to turbulence

An improved characterisation of the hydrodynamic blade loads due to onset turbulence is essential in order to mitigate premature failures, reduce excessive levels of conservativeness and ultimately ensure the commercial viability of tidal turbines. The literature focussing on the turbulence in fast flowing tidal streams and of the unsteady loads that are subsequently imparted to rotors has previously been very limited. However, increased activity in the tidal energy community has led to new investigations and insights which are reported in this paper. It has been found that through the use of acoustic Doppler-based sensors, the streamwise turbulence intensities generally tend to a value of approximately 6–8% at the mid-depth of proposed tidal energy sites. Evidence that the anisotropic structure and scales of the turbulence are more consistent with open-channel-based models than atmospheric-based correlations has also been found. Rapid distortion theory has been applied to estimate that the standard deviation of the streamwise turbulent velocity fluctuations in the onset free-stream flow may be amplified significantly by 15% due to the presence of a turbine. The turbulent fluctuations have also been predicted to remain well correlated over the outer span of the blades at the rotational frequency of the rotor. Recent model-scale experiments have enabled the unsteady hydrodynamic loading to be isolated from the steady-flow loading. For cases where the boundary layer remains primarily attached across the blades, this has enabled linear transfer functions to be developed and applied to model the response to a multi-frequency forcing. It has also been found that phenomena consistent with delayed separation and dynamic stall can result in a blade root bending moment that exceeds the steady value by 25%, and this needs to be taken into account in design to reduce the probability of failure

cDNA-AFLP analysis of cold-acclimated wheat plants reveals unique transcript profiles in crown tissues

Non-Peer ReviewedLow temperature (LT) adversely affects the productivity of plants. Hence, improving the cold hardiness of crop plants is an important goal in agriculture. However, further understanding of LT tolerance mechanisms in plants is required to achieve this objective. In wheat, survival of crown tissues after exposure to below freezing temperatures during the winter determines successful crop stand establishment at the onset of spring season. Therefore, identification of differentially expressed genes in crown tissues of cold acclimated wheat plants is important as it can allow dissection of molecular mechanisms and biochemical pathways within these tissues. In this study, cDNA-AFLP global transcriptomic profiles of crown tissues cold acclimated at 6oC for 0, 2, 14, 21, 35, 42, 56 and 70 days were compared among a cold hardy winter (vrn-A1) cv. Norstar, a tender spring habit (Vrn-A1) cv. Manitou and two reciprocal near-isogenic lines derived from these two parents differing at the vernalization locus. A total of 2061 differentially expressed transcript-derived fragments (TDFs) were identified using 37 pairs of standard AFLP primer combinations, 30 of which were considered unique due to their genotypic and temporal presence or absence. The remaining TDFs showed differential expression patterns in the four genotypes. Cluster analysis of the unique TDFs revealed influence of the genetic background on expression of these TDFs. BLAST searches of 240 sequenced TDFs showed that 87% of the TDFs had similarity to genes coding for products involved in known functions such as signal transduction, RNA processing and translation, transcription, flowering, cell wall synthesis, metabolism, and protein folding. Thirty-two TDFs did not show similarity to any known genes. Quantitative real-time PCR (QPCR) analyses of these unknown TDFs validated their differential expression patterns. Characterization of their biological function will contribute to an understanding of the role of these novel genes in LT tolerance in wheat. These results suggest that crown tissues undergo a complex adaptive process by changing the expression levels of several genes that determine the level of LT tolerance

Expression analysis of low temperature-induced genes in wheat

Non-Peer ReviewedWheat (Triticum aestivum L.) is a widely adapted, economically important crop exhibiting winter, spring and intermediate growth habits. Winter wheat is seeded in the fall, over-winters, resumes growth in spring and is harvested in early summer. It also requires a period of low temperature (LT) exposure, experienced during the fall, to switch from the vegetative to reproductive phase in spring, a process known as vernalization. Low temperature also allows the wheat plant to cold-acclimate to withstand freezing winter temperatures. There has always been an interest to grow winter wheat because of its yield advantage over spring wheat. However, LT tolerance needs to be improved to prevent winter kill and maximize its yield potential. To achieve this more detailed understanding of molecular mechanisms underlying LT tolerance is required. Thus, objectives of this study were to determine the expression of a LT-induced gene and cDNA-AFLP profile in leaf and crown tissues of LT-exposed wheat plants. Survival of crown tissues after exposure to sub-zero temperatures is an indication of the level of LT tolerance of a cultivar. Thus, pattern and levels of expression of LT-induced genes and identification of LT-induced transcripts in this tissue will add to understanding of LT tolerance. Genotypes used in this study included a winter hardy cultivar, Norstar, a tender spring cultivar, Manitou and two-near-isogenic lines with the Vrn-A1 (spring Norstar) and vrn-A1 (winter Manitou) alleles of Manitou and Norstar, respectively. The dominant Vrn-A1 locus confers spring habit and therefore no requirement for vernalization. Quantitative real-time polymerase chain reaction (QPCR) for the cold-regulated gene, Wcor410, indicated that in leaf tissue the Vrn-A1 locus determined level of expression, being higher in the lines having the recessive vrn-A1 allele compared to the dominant Vrn-A1 allele lines. In the crown tissue, the Norstar genetic background led to the higher level of expression than in the Manitou background. cDNA-AFLP analysis also exhibited variable profiles between the two tissues

Blade loads on tidal turbines in planar oscillatory flow

Characterisation of the unsteady hydrodynamic loads is essential for accurate predictions of the fatigue life and ultimate loads of tidal turbine blades. This paper analyses a set of experimental tests of the hydrodynamic blade root out-of-plane bending moment response to planar oscillatory motion, chosen as an idealised representation of the unsteadiness imparted by waves and turbulence. Phenomena associated with dynamic stall are observed which are sensitive to the oscillatory frequency and velocity amplitude. Flow separation is shown to result in loads significantly greater in magnitude than that for steady flow. Following flow reattachment, the load cycles compare relatively well with Theodorsen’s theory for a two-dimensional foil oscillating in heave, suggesting that circulation due to the shed wake dominates the unsteadiness in phase with acceleration, over added mass effects. For attached flow, the effect of unsteadiness is comparatively much smaller. At low frequencies a phase lead over the velocity is observed, compared to a lag at higher frequencies. Multiple frequency oscillations are also briefly considered. Reconstruction of the multi-frequency response using both the steady flow measurements, and the single frequency measured response, is shown to offer a relatively good fit when the flow is attached, for lower frequency combination

Shell Corrections of Superheavy Nuclei in Self-Consistent Calculations

Shell corrections to the nuclear binding energy as a measure of shell effects in superheavy nuclei are studied within the self-consistent Skyrme-Hartree-Fock and Relativistic Mean-Field theories. Due to the presence of low-lying proton continuum resulting in a free particle gas, special attention is paid to the treatment of single-particle level density. To cure the pathological behavior of shell correction around the particle threshold, the method based on the Green's function approach has been adopted. It is demonstrated that for the vast majority of Skyrme interactions commonly employed in nuclear structure calculations, the strongest shell stabilization appears for Z=124, and 126, and for N=184. On the other hand, in the relativistic approaches the strongest spherical shell effect appears systematically for Z=120 and N=172. This difference has probably its roots in the spin-orbit potential. We have also shown that, in contrast to shell corrections which are fairly independent on the force, macroscopic energies extracted from self-consistent calculations strongly depend on the actual force parametrisation used. That is, the A and Z dependence of mass surface when extrapolating to unknown superheavy nuclei is prone to significant theoretical uncertainties.Comment: 14 pages REVTeX, 8 eps figures, submitted to Phys. Rev.

The STAR Photon Multiplicity Detector

Details concerning the design, fabrication and performance of STAR Photon Multiplicity Detector (PMD) are presented. The PMD will cover the forward region, within the pseudorapidity range 2.3--3.5, behind the forward time projection chamber. It will measure the spatial distribution of photons in order to study collective flow, fluctuation and chiral symmetry restoration.Comment: 15 pages, including 11 figures; to appear in a special NIM volume dedicated to the accelerator and detectors at RHI

Colloidally-induced fines release in porous media

A critical value of the total ionic strength (CTIS) has been found to exist for mixed salt solutions flowing in porous media. If the ionic strength drops below this value, significant amounts of fines are released in-situ due to colloidal forces, causing drastic formation damage. For a NaCl/CaCl2 system, the CTIS is strongly dependent on the relative amount of CaCl2 present in the solution. The concept of a critical salt concentration (CSC) and the analysis based on DLVO theory has been extended to mixed salt systems to estimate the CTIS. The difference between critical flocculation concentration (CFC), and the present definition of CTIS has been pointed out. Predictions of this analysis are consistent with experimental observations.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28497/1/0000294.pd