A multi-objective framework for the optimisation of life-cycle costs of wind turbines

Peer reviewedPublisher PD

Investigation of the influence coefficient method for balancing of flexible rotors systems

Abstract Several sophisticated procedures for balancing flexible rotors have been developed during the past two decades. For a variety of reasons, none of these methods has gained general acceptance by practicing balancing engineers. Some of these balancing techniques require a great deal of expertise from the operator. This thesis is dedicated to the research of flexible rotor balancing techniques, and aims to apply some advanced techniques to the field of high-speed rotor balancing. Significant progress in balancing methods for flexible rotors can be achieved by the improvement and optimization of existing balancing techniques. Experimental tests were conducted to demonstrate the ability of the influence coefficient method to achieve precise balance of flexible rotors. Various practical aspects of flexible- rotor balancing were investigated. Tests were made on a laboratory quality test rig having a 3.6 m long rotor representing a High Pressure Turbine (H.P.T) (10.1 kg)(43.767 cm), a Low Pressure Turbine (L.P.T) (43.922 kg) (113.698 cm) and a Generator Rotor (G. Rotor) (71.611kg) (146.413 cm) and covering a speed range up to 6000 rpm. A specific data acquisition system has been developed for use in a high-speed rotor balance facility. Special measurement requirements for this facility include order-tracked vibration measurements and phase angle data. The data acquisition system utilizes dual high-speed computer systems to share the tasks of measurement data processing, and results display. A study of balancing errors is systematically discussed in detail from the view point of increasing the balancing precision. The methods for controlling and reducing these errors are also discussed. Both the qualitative and quantitative analyses of balancing errors are performed as the guide to reduce the error and improve the balancing quality. The thesis also presents the theoretical background and the techniques necessary to the procedure to balance the flexible rotor. A trim balancing method was developed to expand the implementation of flexible rotor balancing. A computer program has been written which generates influence coefficient from measured motions and goes on to predict the correction mass. The vibration has been measured at several locations and speeds and the results have been used to (a) ensure that the vibration levels were not excessive as the rotor speed increased and (b) to calculate the balance correction weights using the traditional influence coefficient method and a least squares influence coefficient method. The procedure developed was verified using an experimental rotor rig. The successful application of the procedure to the balancing of this rotor demonstrates that balancing using Singular Value Decomposition, QR Factorization, and QR Factorization combined with SVD and new trim balancing method is not only a theoretical but also a practical possibility. The Moore-Penrose generalized inverse has been employed to solve the problem. The dynamic characteristics of the rotor rig, however, were somewhat limited and did not cover all the possibilities considered during the project. Therefore, a more complete numerical example was also successfully solved using the computer model of a rotor with characteristics similar to those of a real turbine by using a finite element software package called ANSYS. Ph.D. Thesis Rotor unbalance and shaft misalignment are the two main sources of vibration in rotating machinery. The vibration caused by unbalance and misalignment may destroy critical parts of the machine, such as bearings, seals, gears and couplings. Experimental studies were performed on a system test apparatus to verify the correlation between shaft misalignment and rotor unbalance of multi-rotor multi-bearing systems. The rotor shaft displacements were measured under different misalignment and unbalance conditions. New equipment was installed using a laser alignment system and based upon vibration measuremen..

Aggressive Victims, Passive Victims, and Bullies: Developmental Continuity or Developmental Change?

We evaluated the extent to which aggressive victims show unique developmental pathways that are different from those of passive victims, bullies, and uninvolved children. A total of 1,722 children were followed from 4th grade to 6th grade, and the prevalence and stability of each group were assessed. Aggressive victims became less prevalent and passive victims and bullies became more prevalent with age. Although it was common for aggressive victims and bullies to move from one group to the other across time, there was little overlap with the passive victim group. Stability estimates were higher for the bully and aggressive victim groups than for the passive victim group, and patterns of stability were influenced by peer rejection and exposure to violence

Cosmic clocks: A Tight Radius - Velocity Relationship for HI-Selected Galaxies

HI-Selected galaxies obey a linear relationship between their maximum detected radius Rmax and rotational velocity. This result covers measurements in the optical, ultraviolet, and HI emission in galaxies spanning a factor of 30 in size and velocity, from small dwarf irregulars to the largest spirals. Hence, galaxies behave as clocks, rotating once a Gyr at the very outskirts of their discs. Observations of a large optically-selected sample are consistent, implying this relationship is generic to disc galaxies in the low redshift Universe. A linear RV relationship is expected from simple models of galaxy formation and evolution. The total mass within Rmax has collapsed by a factor of 37 compared to the present mean density of the Universe. Adopting standard assumptions we find a mean halo spin parameter lambda in the range 0.020 to 0.035. The dispersion in lambda, 0.16 dex, is smaller than expected from simulations. This may be due to the biases in our selection of disc galaxies rather than all halos. The estimated mass densities of stars and atomic gas at Rmax are similar (~0.5 Msun/pc^2) indicating outer discs are highly evolved. The gas consumption and stellar population build time-scales are hundreds of Gyr, hence star formation is not driving the current evolution of outer discs. The estimated ratio between Rmax and disc scale length is consistent with long-standing predictions from monolithic collapse models. Hence, it remains unclear whether disc extent results from continual accretion, a rapid initial collapse, secular evolution or a combination thereof.Comment: 14 pages, 7 figures, 3 in colour. Published in MNRAS. This v2 corrects wrong journal in the references section (all instances of "Astrophysics and Space Sciences" should have been ApJ). The Posti+2017 has also been updated. An erratum has been submitted to MNRA

Choirs, H I galaxy groups: catalogue and detection of star-forming dwarf group members

Hα observations centred on galaxies selected from the H i Parkes All-Sky Survey (HiPASS) typically show one and sometimes two star-forming galaxies within the ∼15 arcmin beam of the Parkes 64 m H i detections. In our Survey for Ionization in Neutral Gas Galaxies (SINGG) we found 15 cases of HiPASS sources containing four or more emission line galaxies (ELGs). We name these fields Choir groups. In the most extreme case, we found a field with at least nine ELGs. In this paper, we present a catalogue of Choir group members in the context of the wider SINGG sample. The dwarf galaxies in the Choir groups would not be individually detectable in HiPASS at the observed distances if they were isolated, but are detected in SINGG narrow-band imaging due to their membership of groups with sufficiently large total H i mass. The ELGs in these groups are similar to the wider SINGG sample in terms of size, Hα equivalent width and surface brightness. Eight of these groups have two large spiral galaxies with several dwarf galaxies and may be thought of as morphological analogues of the Local Group. However, on average our groups are not significantly H i deficient, suggesting that they are at an early stage of assembly, and more like the M81 group. The Choir groups are very compact at typically only 190 kpc in projected distance between the two brightest members. They are very similar to SINGG fields in terms of star formation efficiency (SFE; the ratio of star formation rate to H i mass), showing an increasing trend in SFE with stellar mass

The HI - Star Formation Connection: Open Questions

We show data from the Survey of Ionization in Neutral Gas Galaxies (SINGG) and Survey of Ultraviolet emission in Neutral Gas Galaxies (SUNGG) which survey the star formation properties of HI selected galaxies as traced by H-alpha and ultraviolet emission, respectively. The correlations found demonstrate a strong relationship between the neutral ISM, young massive stars, and the evolved stellar populations. For example the correlation between R band surface brightness and the HI cycling time is tighter than the Kennicutt-Schmidt Star Formation Law. Other scaling relations from SINGG give strong direct confirmation of the downsizing scenario: low mass galaxies are more gaseous and less evolved into stars than high mass galaxies. There are strong variations in the H-alpha to UV flux ratios within and between galaxies. The only plausible explanations for this result are that either the escape fraction of ionizing photons or the upper end of the IMF varies with galaxy mass. We argue for the latter interpretation, although either result has major implications for astrophysics. A detailed dissection of the massive star content in the extended HI disk of NGC2915 provides a consistent picture of continuing star formation with a truncated or steep IMF, while other GALEX results indicate that star formation edges seen in Halpha are not always apparent in the UV. These and other recent results settle some old questions but open many new questions about star formation and its relation to the ISM.Comment: To appear in AIP Conference Proceedings, "The Evolution of Galaxies through the Neutral Hydrogen Window", Feb 1-3 2008, Arecibo, Puerto Rico, eds. R. Minchin & E. Momjian. 7 page

UVUDF: Ultraviolet Through Near-infrared Catalog and Photometric Redshifts of Galaxies in the Hubble Ultra Deep Field

We present photometry and derived redshifts from up to eleven bandpasses for 9927 galaxies in the Hubble Ultra Deep field (UDF), covering an observed wavelength range from the near-ultraviolet (NUV) to the near-infrared (NIR) with Hubble Space Telescope observations. Our Wide Field Camera 3 (WFC3)/UV F225W, F275W, and F336W image mosaics from the ultra-violet UDF (UVUDF) imaging campaign are newly calibrated to correct for charge transfer inefficiency, and use new dark calibrations to minimize background gradients and pattern noise. Our NIR WFC3/IR image mosaics combine the imaging from the UDF09 and UDF12 campaigns with CANDELS data to provide NIR coverage for the entire UDF field of view. We use aperture-matched point-spread function corrected photometry to measure photometric redshifts in the UDF, sampling both the Lyman break and Balmer break of galaxies at z ~ 0.8-3.4, and one of the breaks over the rest of the redshift range. Our comparison of these results with a compilation of robust spectroscopic redshifts shows an improvement in the galaxy photometric redshifts by a factor of two in scatter and a factor three in outlier fraction (OLF) over previous UDF catalogs. The inclusion of the new NUV data is responsible for a factor of two decrease in the OLF compared to redshifts determined from only the optical and NIR data, and improves the scatter at z 2. The panchromatic coverage of the UDF from the NUV through the NIR yields robust photometric redshifts of the UDF, with the lowest OLF available

A Multiwavelength Study on the Fate of Ionizing Radiation in Local Starbursts

The fate of ionizing radiation is vital for understanding cosmic ionization, energy budgets in the interstellar and intergalactic medium, and star formation rate indicators. The low observed escape fractions of ionizing radiation have not been adequately explained, and there is evidence that some starbursts have high escape fractions. We examine the spectral energy distributions of a sample of local star-forming galaxies, containing thirteen local starburst galaxies and ten of their ordinary star-forming counterparts, to determine if there exist significant differences in the fate of ionizing radiation in these galaxies. We find that the galaxy-to-galaxy variations in the SEDs is much larger than any systematic differences between starbursts and non-starbursts. For example, we find no significant differences in the total absorption of ionizing radiation by dust, traced by the 24um, 70um, and 160um MIPS bands of the Spitzer Space Telescope, although the dust in starburst galaxies appears to be hotter than that of non-starburst galaxies. We also observe no excess ultraviolet flux in the GALEX bands that could indicate a high escape fraction of ionizing photons in starburst galaxies. The small H-alpha fractions of the diffuse, warm ionized medium in starburst galaxies are apparently due to temporarily boosted H-alpha luminosity within the star-forming regions themselves, with an independent, constant WIM luminosity. This independence of the WIM and starburst luminosities contrasts with WIM behavior in non-starburst galaxies and underscores our poor understanding of radiation transfer in both ordinary and starburst galaxies.Comment: 10 pages, 8 figures, accepted to ApJ 10/11/1

The Next 50 Years: Considering Gender as a Context for Understanding Young Children’s Peer Relationships

The study of children’s peer relationships has been well represented within the pages of Merrill-Palmer Quarterly. Particularly over the last decade, the pace of publishing studies on peer relationships has increased. Despite this upswing in interest in peer relationships, significant gaps remain. In this article, we focus on a particularly overlooked and significant area of peer relationships, namely, the role of sex-segregated peer interactions and how these relate to development in early childhood. We review why this topic is important for researchers to consider and highlight promising directions for research that we hope will appear in future volumes of Merrill-Palmer Quarterly

The Wyoming Survey for H-alpha. III. H-alpha Luminosity Functions at z ~ 0.16, 0.24, 0.32, and 0.40

The Wyoming Survey for H-alpha, or WySH, is a large-area, ground-based imaging survey for H-alpha-emitting galaxies at redshifts of z ~ 0.16, 0.24, 0.32, and 0.40. The survey spans up to four square degrees in a set of fields of low Galactic cirrus emission, using twin narrowband filters at each epoch for improved stellar continuum subtraction. H-alpha luminosity functions are presented for each Delta(z) ~ 0.02 epoch based on a total of nearly 1200 galaxies. These data clearly show an evolution with lookback time in the volume-averaged cosmic star formation rate. Integrals of Schechter fits to the incompleteness- and extinction-corrected H-alpha luminosity functions indicate star formation rates per co-moving volume of 0.010, 0.013, 0.020, 0.022 h_70 M_sun yr^{-1} Mpc^{-3} at z ~ 0.16, 0.24, 0.32, and 0.40, respectively. Statistical and systematic measurement uncertainties combined are on the order of 25% while the effects of cosmic variance are at the 20% level. The bulk of this evolution is driven by changes in the characteristic luminosity L_* of the H-alpha luminosity functions, with L_* for the earlier two epochs being a factor of two larger than L_* at the latter two epochs; it is more difficult with this data set to decipher systematic evolutionary differences in the luminosity function amplitude and faint-end slope. Coupling these results with a comprehensive compilation of results from the literature on emission line surveys, the evolution in the cosmic star formation rate density over 0 < z < 1.5 is measured to be rho_dot_SFR(z) = rho_dot_SFR(0) (1+z)^{3.4+/-0.4}.Comment: Accepted for publication in ApJ Letter