169,730 research outputs found
Large-scale experiments on wave downfall pressures
No full textMany exposed vertical or steep-fronted coastal structures experience large horizontal impact pressures generated by breaking waves. Breaking and non-breaking waves can however also generate a large uprush of water at the structure, in some cases reaching heights of 70 m and more. This uprush is often carried over the structure, leading to overtopping. It has only recently been shown in small-scale model tests that the downfalling water mass can also generate significant vertical impact loadings on the deck of a breakwater. Within an ongoing research project, large-scale measurements of wave impact and downfall generated pressures on vertical and steeply-faced seawalls and breakwaters were conducted in the Large Wave Channel (GWK) at the Coastal Research Centre (FZK) in Hanover, Germany. The downfall pressures were found to consist of very short pressure peaks (durations down to 0.5 ms) of up to 220 kPa magnitude (corresponding to 12 rho gH(i)). The highest downfall pressures occurred for near-breaking waves; non-breaking and breaking waves generated smaller pressures of 20-70 kPa (corresponding to 2-6 rho gH(i)). The magnitude of the observed downfall pressures is in the range of horizontal wave impact pressures and suggests that this type of loading, for which no guidance exists, should be considered in the design of coastal structures
Scour at a seawall – field measurements and physical modelling
No full textThis comprehensive volume contains 432 papers presented at the 30th International Conference on Coastal Engineering, held in San Diego, California, USA, 3-8 September 2006. It is divided into five parts: Waves; Long Waves, Nearshore Currents, and Swash; Sediment Transport and Morphology; Coastal Management, Beach Nourishment, and Dredging; and Coastal Structures. The papers cover a broad range of topics including theory, numerical and physical modeling, field measurements, case studies, design, and management. "Coastal Engineering 2006" provides coastal engineers, scientists, and planners state-of-the-art information on coastal engineering and coastal processes
Field and large scale model tests of wave impact pressure propagation into crack
No full textWithin a large & full scale study on wave impact induced pressures on coastal structures (BWIMCOST) an investigation of impact pressure propagation into structure cracks and fissures was carried out. The mechanism, which is held responsible for localized damage to existing blockwork breakwaters, had previously been verified in small scale model tests and a numerical model had been developed. The current investigation is the first which describes the effect at full scale, with recorded pressures of up to 199 kPa found within the cracks. The experimental results are related to their possible impact on coastal structural integrity
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Failure mechanisms of shingle barrier beaches
No full textPhysical model tests were undertaken at HR Wallingford to address gaps in the knowledge of the failure process of shingle barrier beaches. During these tests, numerous factors were considered such as sediment characteristics, the type of waves (storm or swell), and beach crest geometry (height, width, back slope). This technical note summarises the test procedures, the experimental set-up, the test conditions and the data obtainedFloodsit
Thermal Stratification and Turbulent Wind Loading on Floating Wind Turbines
No full textPhD thesis in Offshore technologyOffshore wind is a promising clean energy alternative to fossil fuels. The wind resource at sea is considerably stronger than on land, and the offshore wind turbines (OWTs) tend to be larger. Currently, more than 160 commercial offshore wind farms (OWFs) are in operation worldwide, of which 2% are floating wind farms (FWFs). Bottom-fixed OWTs are mainly installed close to shore and in shallow water, where operation, maintenance and substructure costs are lower than for floating solutions. However, some countries have deep water close to the coast, which makes the development of floating offshore wind turbines (FOWTs) an attractive alternative (e.g. in Japan, Norway, and the west coast of the USA). The floating offshore wind industry is expected to continue to reduce costs, making it competitive with bottom-fixed developments in the near future.
The atmospheric inflow to wind turbines includes mesoscale and microscale processes. For a FOWT, the floater introduces additional degrees of freedom compared to a bottom-fixed foundation, thus extending the dynamic response of FOWTs to a wider frequency interval. The natural frequencies of the floaters are in the range of the microturbulence frequencies influenced by the thermal stratification of the atmosphere (atmospheric stability). The design standards for wind turbines do not usually take atmospheric stability into account. However, atmospheric stability should be considered in the design of state-of-the-art FOWTs to improve estimates of the wind loads, structural response and power production.
This thesis investigates the impact of atmospheric stability on the FOWT response and fatigue loads through numerical simulations. The two study cases include the 5MW OC3-Hywind spar wind turbine (WT) and the 5MW OC4 DeepCwind semi-submersible WT. The wind inflow is generated using different turbulence spectral models: Davenport-Kaimal, Uniform Shear, Pointed-Blunt, and Højstrup Spectral Model with Daven port co-coherence. The variable atmospheric stability is simulated using the Pointed-Blunt Model and the Højstrup Spectral Model with Davenport co-coherence. The effects of single-point and two-point spectra on the two WTs are assessed separately and then jointly. A single wave loading scenario with a fixed significant wave height and peak period is adopted.
In both study cases, the simulated fatigue damage associated with the tower top twisting and the side-side bending moment is found to increase in an unstable atmosphere compared to a near-neutral atmosphere, as is the yaw and sway of the floaters. In a near-neutral atmosphere, the difference in the spatial turbulence characteristics (co-coherence) in the two spectral models (Uniform Shear Model and the Davenport-Kaimal Model) is also seen to affect the response of the OC3-Hywind and the OC4 DeepCwind. For example, the tower side-side bending moment is found to be greater by up to 27% in a less coherent turbulent flow. This emphasises the need to base the design of FOWT on lateral co-coherence models derived from offshore field measurements at separations relevant to FOWTs, which are currently scarce.
The simulated response of the OC3-Hywind to atmospheric stability using the Pointed-Blunt Model is compared to the observed response from the full-scale measurements of a 6MW spar WT at Hywind Scotland. The simulated floater pitch and yaw are found to be consistent with the measured responses. This highlights the importance of incorporating atmospheric stability into the design of FOWTs.
In addition, analyses of wind measurements at a coastal site, Vindeby, are carried out with a focus on turbulence characteristics. These characteristics are then compared with measurements from an offshore platform, FINO1, from which the Pointed-Blunt model is derived. The spectral turbulence characteristics observed at Vindeby (≤ 45m above sea level (asl)) show a reasonable agreement with the characteristics observed at FINO1 (≤ 81.5m asl).
This thesis recommends the inclusion of atmospheric stability in the design of state-of-the-art FOWTs, to obtain representative wind loading. Future wind measurements to include heights above 100m asl, and measurements to obtain information on lateral co-coherence are encouraged to provide relevant design data. Lateral co-coherence, which is representative of offshore sites with relevant separation distances for modern FOWTs, has been partially addressed in the COTUR (COherence of TURbulence with lidars) project. However, lateral co-coherence in the MABL remains a topic for further study.
Keywords: Floating wind turbine, Atmospheric stability, Turbulence model, Spectral turbulence characteristics, Co-coherence, Floater response, Fatigue loa
Mitomycin C in highly myopic eyes - Author reply
No full textOphthalmology. 2005 Feb;112(2):208-18; discussion 219.
Mitomycin C modulation of corneal wound healing after photorefractive keratectomy in highly myopic eyes.
Gambato C, Ghirlando A, Moretto E, Busato F, Midena E.
SourceRefractive Surgery Service and Antimetabolite Therapy Research Unit, Department of Ophthalmology, University of Padova, Padova, Italy.
Abstract
PURPOSE: To evaluate the role of topical mitomycin C in corneal wound healing (CWH) after photorefractive keratectomy (PRK) in highly myopic eyes.
DESIGN: Prospective, double-masked, randomized clinical trial.
PARTICIPANTS: Seventy-two eyes of 36 patients affected by high (>7 diopters) myopia.
METHODS: In each patient, one eye was randomly assigned to PRK with intraoperative topical 0.02% mitomycin C application, and the fellow eye was treated with a placebo. Postoperatively, mitomycin C-treated eyes received artificial tears (3 times daily, tapered in 3 months), whereas the fellow eye was treated with fluorometholone sodium 2% and artificial tears (3 times daily, tapered in 3 months).
MAIN OUTCOME MEASURES: Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA), contrast sensitivity, manifest refraction, and biomicroscopy. Contrast sensitivity was determined using the Pelli-Robson chart. Corneal confocal microscopy documented CWH.
RESULTS: Mean follow-up was 18 months (range, 12-36). No side effects or toxic effects were documented. At 12-month follow-up examination, UCVAs (logarithm of the minimum angle of resolution) were 0.4+/-0.48 and 0.5+/-0.53 (P = .03) in mitomycin C-treated eyes and corticosteroid-treated eyes, respectively. At 1 year, corneal haze developed in 20% of corticosteroid-treated eyes, versus 0% of mitomycin C-treated eyes. At 12, 24, and 36 months, corneal confocal microscopy showed activated keratocytes and extracellular matrix significantly more evident in untreated eyes (Ps = 0.004, 0.024, and 0.046, respectively).
CONCLUSION: Topical intraoperative application of 0.02% mitomycin C can reduce haze formation in highly myopic eyes undergoing PRK.
Comment in
Ophthalmology. 2006 Feb;113(2):357; author reply 357-8
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
A Multi-Language Comparison of Influences on Author Verification using Character N-Grams
No full textWe create a new multi-language corpus for author verification based on Wikipedia talkpages, and evaluate the influence that differences in topic and time have on character n-gram author profiles. Topic alignment between two texts is found to increase author verification precision, and an authors writing style is found to change over time, but not more significantly after 3 years than after 1 year.Information ArchitectureWISElectrical Engineering, Mathematics and Computer Scienc
A 0.12mm<sup>2</sup> Wien-Bridge Temperature Sensor with 0.1°C (3σ) Inaccuracy from -40°C to 180°C
No full text Resistor-based temperature sensors can achieve much higher resolution and energy efficiency than conventional BJT-based sensors [1], but they typically occupy more area (> 0.25 mm 2 ) and have lower operating temperatures (le 125 {circ} {C}) [2]-[4]. This work describes a 0.12mm 2 resistor-based sensor that uses a Wien-bridge (WB) filter to achieve 0.1 {circ} {C} (3 sigma) inaccuracy from - 40 {circ} {C} to 180 {circ} {C}. Compared to a state-of-the-art WB sensor [4], it occupies 6 × less area and achieves comparable relative accuracy over a 76% wider operating range. Session 10.3 Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic InstrumentationMicroelectronic
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