Bottom Structures Research Articles

Directional effects on the reliability of non-axisymmetric support structures for offshore wind turbines under extreme wind and wave loadings

In comparison with monopile support structures commonly used for offshore wind turbines (OWTs) in shallow water, fixed bottom support structures for deeper water such as jackets tend to lack axisymmetry and have different capacities when loaded in different directions. Design of such a structure may therefore benefit from consideration of the directional characteristics of loading. This paper focuses on a rational and efficient approach to assess the structural safety of jacket type OWTs under directionally dependent extreme environmental loads. The Incremental Wind–Wave Analysis (IWWA) framework is reviewed and used to assess capacity of jacket-type OWTs under directional environmental wind–wave conditions. The approach uses static pushover analysis of OWT jackets subject to combined wind and wave load patterns corresponding to increasing mean return periods (MRPs). The wind and wave conditions are calculated independently and assumed to occur simultaneously. The loading direction and jacket orientation are both included in the analysis. To illustrate the approach, metocean conditions at different sites along the U.S. Atlantic coast are obtained from the historical database of the National Oceanic and Atmospheric Administration (NOAA) Data Buoy Center. Two models are introduced for estimating the occurrence probability of wave direction, one of which directly uses the frequency of wave directions and the other uses a Gaussian kernel to represent the range of wave directions represented by given directional spectra. For each combination of wind–wave direction and structural orientation, an IWWA analysis gives the capacity in terms of the MRP conditions leading to formation of a fully developed plastic mechanism in the jacket. Those capacities, convolved with MRP models for loading intensity, yield direction-dependent structural reliabilities, and when those reliabilities are convolved with the probability density function for load direction, a total failure probability is obtained that accounts for wave directionality. Example analyses are conducted for an OWT supported by a four-leg jacket adapted from a design published as part of the European Union UpWind Project. Effects of extreme load directionality, structural orientation, structural geometry and site specification on the ultimate capacity of the jacket are carefully discussed.

Bottom-up silicon nanowire-based thermoelectric microgenerators

In this work, bottom-up intrinsic crystalline Si nanowire arrays in combination with top-down microfabrication techniques and a vertical device architecture have been proposed to develop an all-silicon nanostructured thermoelectric generator. To fabricate this device, a suitable vertical integration of Si NWs on patterned microstructures, which define the thermoelectric legs of the generator, has been achieved by bonding top and bottom silicon structures through nanowires. The process has been proven to be a feasible approach that employs a regrowth process of the nanowires for bonding purposes.

On the Performance Degradation of Poly(3-Hexylthiophene) Field-Effect Transistors

Polymeric transistor degradation was investigated on bottom and top gate structures. Shelf-lifetime studies in both kinds of devices demonstrate an accelerated increase in effective charge carrier mobility, threshold voltage, and off current in modulus when poly(3-hexylthiophene) (P3HT) is exposed to atmospheric gases. Although P3HT is underneath PMMA dielectric and gold gate electrode films, electrical parameters degradation can be only delayed by 100 h. Therefore, only glass encapsulation of the active area is capable of effectively preventing current modulation decrease after exposure to atmospheric gases. Differently from their bottom-gate counterparts, capped top-gate TFTs clearly present negative threshold voltage and positive hysteresis. An interface with reduced deep traps concentration and electrical characterization influence on shallow traps filling are believed to play a significant role in these top-gate P3HT/PMMA transistors under operating conditions. Alternating gate voltage stress along 3000 cycles provides evidence of electrical sweep as a cause of performance degradation. Similarly, dc gate bias stress monitored for 127 min can impair current modulation and shifts threshold voltage depending on its sign. Finally, reversibility of both kinds of stress points that shallow traps are the major problem in these capped devices.

Frequency response of rectangular plate structures in contact with fluid subjected to harmonic point excitation force

Numerical procedure for the forced vibration analysis of bottom and vertical rectangular plate structures in contact with fluid, subjected to internal point harmonic excitation force is developed. The procedure is based on the assumed mode method for free vibration calculation and mode superposition method for forced vibration analysis. Structural model covers Mindlin rectangular plates and stiffened panels. Lagrange's equation of motion is utilized to formulate the eigenvalue problem taking into account potential and kinetic energies of a plate and reinforcements, and fluid kinetic energy which is calculated according to potential flow theory, respectively. From the boundary conditions for the fluid and structure the fluid velocity potential is derived and it is utilized for the calculation of added mass using the assumed modes. The developed theoretical model and in-house code are verified with extensive numerical examples related to forced vibration of bare plates and stiffened panels in contact with different fluid domains. Comparisons of the results with those obtained by a general purpose finite element (FE) software confirmed high accuracy of the presented numerical procedure.

Metallic Nanoparticles and Nanostructure for Light Trapping

One major challenge for photovolatics solar cell is to improve its light-to-electrical efficiency while reducing its cost and weight. Thin film solar cells satisfy the demand of the high efficiency, low cost, and low weight. The hydrogenated alloy of amorphous silicon (a-Si:H) has high optical absorption than many other materials, a-Si:H thin film solar cells are able to improve the absorption efficiency, since the minority carrier diffusion length is less than or around 300nm for amorphous silicon. However, there is a limitation in all thin film solar cell technologies, the limitation is that red spectrum absorbance is too low. Excitation of surface plasmons via scattering from noble metal nanostructures was proposed to overcome the limitation, to enhance light-trapping efficiency, and to increase light absorption in red spectrum. We investigated a sandwich-like solar cell: a-Si:H thin film between a top layer of nano-particles and a bottom layer of metallic structures. We studied the optical absorption efficiency of the a-si:H thin film with nano-metallic particles, and investigate the size and shape of these nano-particles. Our investigations show that for a 100nm thick a-Si:H thin film, deposit an array of nano-metallic cubes or cylinders will increase the optical absorption in the red light (e.g. 650nm) dramatically. We also see the strong light trapping effect of the bottom metallic nano structures as a back reflector.

Culvert replacements: improvement of stream biotic integrity?

Roads and associated stream crossings can modify and degrade natural hydrology of a system and alter organism movement. Culvert replacement and stream crossing improvements are extremely common and often done with the intent to improve biotic integrity of a system. We evaluated 3 sites where poor road‐stream crossings were improved by replacing improper culverts with full‐span natural bottom structures. We used a before‐after‐control‐impact paired series (BACIPS) design to determine if there was evidence of associated improvement in biotic integrity of the stream communities. Biotic integrity indices developed for coldwater fish and macroinvertebrates in the Northern Lakes and Forests Ecoregion were used to estimate responses of the biotic communities adjacent to culvert replacements. With poor to fair fish and macroinvertebrate communities prior to culvert replacement, we predicted communities would show improvement into the good range of the indices. With 2–4 years of pre‐data and 3–5 years of postdata, we were not able to detect improvements in overall biotic integrity utilizing fish or macroinvertebrate index scores. Road crossing improvements may synergistically restore stream ecosystems, restore natural sediment dynamics, and improve passage; however, in these cases local biotic integrity scores were not significantly improved. Culvert replacements are often developed based on the potential, or the perception, that they will restore ecological integrity and biological communities or fisheries; however, as restoration practitioners, researchers, and managers, assessing these claims and learning from prior restoration attempts is necessary.

Interpreting Echo Statistics of Three Distinct Clutter Classes Measured With a Midfrequency Active Sonar: Accounting for Number of Scatterers, Scattering Statistics, and Beampattern Effects

A recently developed published approach to predict echo statistics is applied to clutter data that were collected with a midfrequency sonar and published in a separate independent study. This method explicitly accounts for the (finite) number of unresolved scatterers, the statistics associated with the arbitrary scattering properties of the individual scatterers [but assumed to have identical echo probability density functions (pdfs) in this application], and beampattern effects which significantly affect the echo statistics due to each scatterer being randomly located in the sonar beam. The data had been categorized according to whether they were associated with bottom structures, diffuse compact clutter, and compact nonstationary (moving) clutter. In this paper, the recently developed method is incorporated in a two-component mixed pdf (mixed with a Rayleigh distribution to account for the diffuse background) to model the statistics of the three classes of clutter. This is the first such application of the model which had principally been validated only numerically. The degree to which the data are non-Rayleigh (heavy tailed) is reasonably predicted by the model and the number of scatterers per resolution cell is inferred for each type of clutter.

Natural vibration analysis of rectangular bottom plate structures in contact with fluid

A simple and effective procedure for the natural vibration analysis of rectangular bottom plate structures in contact with fluid is presented. Structural part of the coupled hydroelastic problem covers thin and thick rectangular plates and stiffened panels with different framing types. The eigenvalue problem is formulated using Lagrange׳s equation of motion and taking into account potential and kinetic energies of a plate structure and fluid kinetic energy, respectively. Natural frequencies and modes are obtained applying the assumed mode method using the characteristic polynomials of a Timoshenko beam. Potential flow theory assumptions are adopted for the fluid and the effect of free surface waves is ignored. From the boundary conditions for the fluid and structure the fluid velocity potential is derived and it is utilized for the calculation of added mass using the assumed modes. The developed theoretical model is verified with several numerical examples dealing with the natural vibration of bare plates and stiffened panels in contact with different fluid domains. A comparison of the results with those obtained by a general purpose FEA software showed very good agreement, especially for the lowest natural frequencies that are actually most relevant for the structural design from the viewpoint of vibration.

Газогидраты в структурах дна континентальних окраин Антарктики (по результатам геофизических исследований)

Газогидраты в структурах дна континентальних окраин Антарктики (по результатам геофизических исследований)

Electrode metal penetration of amorphous indium gallium zinc oxide semiconductor thin film transistors

Penetration effects of various electrode materials, namely Al, Au, and Cu, on the physical and electrical characteristics of amorphous oxide semiconductor thin film transistors (TFTs) were investigated. Amorphous indium gallium zinc oxide (a-IGZO) TFTs were fabricated with conventional staggered bottom gate structures on a p-type Si substrate. X-ray photoemission spectroscopy (XPS) analysis under the electrode deposition area revealed variations in the oxygen bonding states and material compositions of the a-IGZO layer. Field-emission scanning electron microscopy (FE-SEM) with the line scan of energy dispersive spectroscopy (EDS) showed lateral penetration by the electrode metal. To compare the electrical characteristics of the tested TFTs, the initial current–voltage (I–V) transfer characteristics were examined. In addition, the tested TFTs fabricated using various electrode materials were tested under bias stress to verify the correlations between variations in TFT characteristics and both the metal work function and penetration-induced oxygen vacancies in the channel around the contact area.

The electrified benthic frame trawl (EBFT): A new approach for sampling benthic fish species in a large river – The experiences of the Joint Danube Survey 3

Event Abstract Back to Event The electrified benthic frame trawl (EBFT): A new approach for sampling benthic fish species in a large river – The experiences of the Joint Danube Survey 3 Ágnes I. György1*, András Weiperth1, Vinzenz Bammer2, Michael Schabuss3, Horst Zornig3, Luchezar Pehlivanov4 and Zoltán Szalóky1 1 MTA Centre for Ecological Research, Danube Research Institute, Hungary 2 Federal Agency for Water Management, Institute for Water Ecology, Fisheries and Lake Research, Austria 3 Pro Fisch OG., Austria 4 Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences, Bulgaria In large rivers, such as the Danube, standardized and representative sampling of fish is still problematic. Until now, night time shoreline electrofishing proved to be the most comprehensive fish assessment method, however, it is not suitable for detecting sterlet (Acipenser ruthenus), the only native sturgeon species still present in the upper and middle Danube. Besides, other rather rare native bottom dwelling fish species (e.g. Zingel streber) are also usually underrepresented in shoreline catches. Hence, we have developed in 2010 the electrified benthic frame trawl (EBFT) which, due to its robust frame, can overcome bottom structures and can give important results on offshore benthic fish species (i.e. presence-absence, distribution, spawning habitats, etc.). In 2013, this method was adopted by the fish Core Team of the Joint Danube Survey 3, providing an opportunity to test the equipment in diverse conditions along the whole river for the first time. Data were collected parallel with standard electrofishing at 22 sites from river km 2214 (Austria) to river km 15 in the Sulina arm (Romania) sampling 500 m long stretches parallel to the riverbank. We found that offshore areas were intensively used by a variety of species. Most abundant and most frequently occurring were the highly invasive round goby (Neogobius melanostomus, 9 ind/500 m) and the whitefin gudgeon (Romanogobio vladykovi, 4 ind/500 m). The number of Z. strebers caught (138 individuals from 16 sites) was much higher in the EBFT samples than in the shoreline catches (34 individuals from only 6 sites). The EBFT was also successful in catching sterlets but only 9 individuals were caught and only below the inflow of Tisa River. The survey proved the relevance of using the EBFT during large river fish assessments, and it also revealed the alarmingly low abundance of sturgeons. Based on the results further development (e.g. lifting device) and optimization possibilities of the EBFT may be also considered. Acknowledgements We are very grateful for the support of the ICPDR and our team comrades, Björn Deutschmann, Sándor Sipos and our captain, Otto Bohdal. Keywords: trawling, Electrofishing, Fish assemblages, Deep water, Danube River, sturgeon, Zingel spp., Gobies Conference: XV European Congress of Ichthyology, Porto, Portugal, 7 Sep - 11 Sep, 2015. Presentation Type: Poster Presentation Topic: Ecology, Conservation and Invasive Species Citation: György ÁI, Weiperth A, Bammer V, Schabuss M, Zornig H, Pehlivanov L and Szalóky Z (2015). The electrified benthic frame trawl (EBFT): A new approach for sampling benthic fish species in a large river – The experiences of the Joint Danube Survey 3. Front. Mar. Sci. Conference Abstract: XV European Congress of Ichthyology. doi: 10.3389/conf.FMARS.2015.03.00148 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 23 Nov 2015; Published Online: 27 Nov 2015. * Correspondence: PhD. Ágnes I György, MTA Centre for Ecological Research, Danube Research Institute, Budapest, Hungary, gyorgyagi@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract Supplemental Data The Authors in Frontiers Ágnes I György András Weiperth Vinzenz Bammer Michael Schabuss Horst Zornig Luchezar Pehlivanov Zoltán Szalóky Google Ágnes I György András Weiperth Vinzenz Bammer Michael Schabuss Horst Zornig Luchezar Pehlivanov Zoltán Szalóky Google Scholar Ágnes I György András Weiperth Vinzenz Bammer Michael Schabuss Horst Zornig Luchezar Pehlivanov Zoltán Szalóky PubMed Ágnes I György András Weiperth Vinzenz Bammer Michael Schabuss Horst Zornig Luchezar Pehlivanov Zoltán Szalóky Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Investigation and Preliminary Analysis of Rural and Town Building Damages of Yunnan Ludian Ms6.5 Earthquake

The "8.03" Ms6.5 Ludian earthquake in Yunnan province is the largest earthquake of the area in recorded history. The PGA of epicenter (Longtoushan town) reaches 948gal and the intensity of meizoseismal area arrives to IX degree. The earthquake has caused severe casualties and huge property losses. Based on the earthquake damage investigation, it is found that structure types of affected towns mainly include mud-wood, brick-wood, masonry, frame, bottom frame and composite structures. In the IX degree area, most of the mud-wood, brick-wood, unfortified masonry and composite structures turn into severely damaged or destroyed. Most bottom frame structures obtain inclined shear cracks on bottom walls. Part of the masonry structures built after 2008, which are set with ring beams, construction columns, cast-in-place floors and roofs, show well earthquake performances and suffer slight damage. What’s more, most filler walls and other non-structural components of frame structures in the meizoseismal area are severely damaged, part of their column ends or beam-column joints fall into failure, which doesn’t achieve "strong column-weak beam" yielding mechanism of the seismic design code expectation. The ending of this paper summarizes a number of recommendations for post-earthquake recovery and reconstruction work according to local conditions.

Impact of source and drain contact thickness on the performance of organic thin film transistors

This paper analyzes the impact of source (ts) and drain (td) contact thicknesses on top contact (TC) and bottom contact (BC) organic thin film transistors (OTFTs) with a gate in the bottom, using a benchmarked industry standard Atlas 2-D numerical device simulator. The parameters including drive current (Ids), mobility (μ), threshold voltage (Vt) and current on-off ratio (ION/IOFF) are analyzed from the device physics point of view on different electrode thicknesses, ranging from infinitesimal to 50 nm, for both top and bottom contact structures. Observations demonstrate that the performance of the BC structure is more affected by scaling of ts/d in comparison to its counterpart. In the linear region, the mobility is almost constant at all the values of ts/d for both structures. However, an increment of 18% and 83% in saturation region mobility is found for TC and BC structures, respectively with scaling down ts/d from 50–0 nm. Besides this, the current on-off ratio increases more sharply in the BC structure. This analysis simplifies a number of issues related to the design and fabrication of organic material based devices and circuits.

Switchable wavelength-selective and diffuse metamaterial absorber/emitter with a phase transition spacer layer

We numerically demonstrate a switchable metamaterial absorber/emitter by thermally turning on or off the excitation of magnetic resonance upon the phase transition of vanadium dioxide (VO2). Perfect absorption peak exists around the wavelength of 5 μm when the excitation of magnetic resonance is supported with the insulating VO2 spacer layer. The wavelength-selective absorption is switched off when the magnetic resonance is disabled with metallic VO2 that shorts the top and bottom metallic structures. The resonance wavelength can be tuned with different geometry, and the switchable metamaterial exhibits diffuse behaviors at oblique angles. The results would facilitate the design of switchable metamaterials for active control in energy and sensing applications.

Fabrication of ballistic suspended graphene with local-gating

Herein we discuss the fabrication of ballistic suspended graphene nanostructures supplemented with local gating. Using in situ current annealing, we show that exceptional high mobilities can be obtained in these devices. A detailed description is given of the fabrication of bottom and different top-gate structures, which enable the realization of complex graphene structures. We have studied the basic building block, the p-n junction in detail, where a striking oscillating pattern was observed, which can be traced back to Fabry–Perot oscillations that are localized in the electronic cavities formed by the local gates. Finally we show some examples how the method can be extended to incorporate multi-terminal junctions or shaped graphene. The structures discussed here enable the access to electron-optics experiments in ballistic graphene.

Foraminiferal biostratigraphy and sequence stratigraphy of peritidal carbonates at the Triassic–Jurassic boundary (Karaburun Peninsula, Western Turkey)

Continuous shallow marine carbonates spanning the Triassic–Jurassic boundary are exposed in the Karaburun Peninsula, Western Turkey. The studied section (Tahtaiskele section) consists of Upper Triassic cyclic shallow marine carbonates intercalated with clastics overlain by Lower Liassic carbonates. Based on the microfacies stacking patterns, three main types of shallowing-upward cycles have been recognized. Cycles are mostly composed of subtidal facies at the bottom, intertidal/supratidal facies and/or subaerial exposure structures at the top. The duration of the cycles suggests that cycles were driven by the precessional Milankovitch rhytmicity. In the sequence stratigraphic frame of the Tahtaiskele section 4 sequence boundaries were detected and globally correlated. The first sequence boundary is located at the Alaunian–Sevatian boundary nearly coinciding with the first appearance of Triasina hantkeni. The second falls in the Rhaetian corresponding to a major sea level fall which led to the invasion of forced regressive siliciclastic deposits over the peritidal carbonates. The third occurs close to the T/J boundary and the fourth lies slightly above the base of the Jurassic. In the studied section, extinction, survival and recovery intervals have been recognized based on the stratigraphic occurrence patterns of benthic foraminifera and algae. Foraminifers became nearly totally extinct in the inner carbonate shelves at the Triassic–Jurassic boundary and an interval of approximately 0.5my passed before the begining of the recovery of Jurassic foraminifera.

Influence of Diverse Post-Trench Processes on the Electrical Performance of 4H-SiC MOS Structures

This paper focuses on the evaluation of subsequent process steps (post-trench processes, PTPs) after 4H silicon carbide (4H-SiC) trench etching with respect to the electrical performance of trenched gate metal oxide semiconductor field effect transistors (Trench-MOSFETs). Two different types of PTP were applied after 4H-SiC trench formation, a high temperature post-trench anneal (PTA) [1] and a sacrificial oxidation (SacOx) [2]. We found significantly improved electrical properties of Planar-MOS structures using a SacOx as PTP, prior to gate oxide deposition. Besides excellent quasi-static capacitance-voltage (QSCV) behavior even at T = 250 °C, charge-to-breakdown (QBD) results up to 8.8 C/cm2 at T = 200 °C are shown to be similar on trenched surfaces as well as on untrenched surfaces of SacOx-treated Planar-MOS structures. Moreover, dielectric breakdown field strengths up to 12 MV/cm have been measured on Planar-MOS structures. However, thick bottom oxide Trench-MOS structures indicate best dielectric breakdown field strengths of 9.5 MV/cm when using a trench shape rounding PTA as the PTP.

Design of Light Trapping Structures for Ultrathin Solar Cells

The conversion efficiency of thin film silicon solar cell is still much below that of wafer silicon solar cell due to low optical absorption. Light trapping techniques can enhance the optical absorption in solar cells. Here, we design light trapping structures of double-side grating for ultrathin silicon solar cells based on a rigorous coupled-wave analysis method. The role of each grating was identified by analyzing the absorption spectra of ultrathin solar cell from 350 nm to 1100 nm wavelength at normal incidence, which shows use of top and bottom light trapping structures can achieve large optical absorption in different wave regimes. Inspired by this observation, the dual dielectric/dielectric and dielectric/ metallic grating structures were proposed and optimized to obtain broadband optical absorption close to the theoretic limit.

An atmospheric air gas-liquid diffuse discharge excited by bipolar nanosecond pulse in quartz container used for water sterilization

In this Letter, we report that the air gas-liquid diffuse discharge plasma excited by bipolar nanosecond pulse in quartz container with different bottom structures at atmospheric pressure. Optical diagnostic measurements show that bountiful chemically and biologically active species, which are beneficial for effective sterilization in some areas, are produced. Such diffuse plasmas are then used to treat drinking water containing the common microorganisms (Candida albicans and Escherichia coli). It is found that these plasmas can sterilize the microorganisms efficiently.

Lagrangian transport in a microtidal coastal area: the Bay of Palma, island of Mallorca, Spain

Abstract. Coastal transport in the Bay of Palma, a small region in the island of Mallorca, Spain, is characterized in terms of Lagrangian descriptors. The data sets used for this study are the output for two months (one in autumn and one in summer) of a high resolution numerical model, ROMS (Regional Ocean Model System), forced atmospherically and with a spatial resolution of 300 m. The two months were selected because of their different wind regime, which is the main driver of the sea dynamics in this area. Finite-size Lyapunov exponents (FSLEs) were used to locate semi-persistent Lagrangian coherent structures (LCS) and to understand the different flow regimes in the bay. The different wind directions and regularity in the two months have a clear impact on the surface bay dynamics, whereas only topographic features appear clearly in the bottom structures. The fluid interchange between the bay and the open ocean was studied by computing particle trajectories and residence time (RT) maps. The escape rate of particles out of the bay is qualitatively different, with a 32% greater escape rate of particles to the ocean in October than in July, owing to the different geometric characteristics of the flow. We show that LCSs separate regions with different transport properties by displaying spatial distributions of residence times on synoptic Lagrangian maps together with the location of the LCSs. Correlations between the time-dependent behavior of FSLE and RT are also investigated, showing a negative dependence when the stirring characterized by FSLE values moves particles in the direction of escape.