284 research outputs found
Updatable Probabilistic Evaluation of Failure Rates of Mechanical Components in Power Take-Off Systems of Tidal Stream Turbines
Full text linkThis paper presents a method for the probabilistic evaluation of the failure rates of mechanical components in a typical power take-off (PTO) system of a horizontal-axis tidal stream turbine (HATT). The method is based on a modification of the method of the influence factors, when base failure rates, relevant influence factors and, subsequently, resulting failure rates are treated as random variables. The prior (i.e., initial) probabilistic distribution of the failure rates of a HATT component is generated using data for similar components from other industries, while taking into account actual characteristics of the component and site-specific operating and environmental conditions of the HATT. A posterior distribution of the failure rate is estimated numerically based on a Bayesian approach as new information about the component performance in an operating HATT becomes available. The posterior distribution is then employed to obtain the updated mean and lower and upper confidence limits of the failure rate. The proposed method is illustrated by applying it to the evaluation of the failure rates of two key components of the PTO system of a typical HATT—main seal and main bearing. In particular, it is shown that uncertainty associated with the method itself has a major influence on the failure rate evaluation. The proposed method is useful for the reliability assessment of both PTO designs of new HATTs and PTO systems of operating HATTs
Resilience of Critical Infrastructure Systems to Floods:A Coupled Probabilistic Network Flow and LISFLOOD-FP Model
No full textIn this paper, a network-flow model was constructed to simulate the performance of interdependent critical infrastructure systems during flood hazards, when there is shortage of commodities such as electrical power and water. The model enabled us to control the distribution of commodities among different consumers whose demand cannot be fully met. Incorporating time-variance in the model allowed for evaluating the time evolution of the functional level of the infrastructure systems and quantifying their resilience. As a demonstration of the model’s capability, the network model was coupled with a raster-based hydraulic flooding model in the way of Monte Carlo simulations. It was then used to investigate the cascading effects of flood-related failures of individual infrastructure assets on the performance of the critical infrastructure systems of a coastal community under different flooding scenarios and future climate impacts. The coupled modelling framework is essential for correctly assessing the interdependences and cascading effects in the infrastructure systems in the case of flood hazards. While in the considered example, the extent of inundation becomes less severe with a changing climate, the risk to infrastructure does not recede because of the cascading effects. This behaviour could not be captured by the flood model alone
Moving toward resilience and sustainability in the built environment
No full textDeveloping and managing infrastructure requires considering the system's physical performance and operational, financial, social, environmental, and managerial aspects. These aspects interact in a dynamic environment that evolves and changes continuously. Changes in demand, socio-economic pressures, and the increasing frequency and intensity of natural events – exacerbated by climate change – make resilience and sustainability essential for the built environment's current and future performance. Sustainable infrastructures add value to society and maintain social equity and justice through time. To achieve this, it is necessary to consider socio-economic as well as environmental aspects. On the other hand, resilience focuses on recovery in case of a damaging event, a critical property that minimizes functionality disruptions. This paper presents a conceptual discussion about the role of resilience and sustainability in relationship with infrastructure and the built environment's design and operation. It provides insight into risk-informed decision-making for evolving infrastructure systems, and change based on a systems-thinking approach. These concepts are central to the built environment's safe and responsible evolution and growth. In the end, the paper identifies challenges and proposes future research paths.</p
Global optimisation approach for designing high-efficiency piezoelectric beam-based energy harvesting devices
Full text linkThe paper proposes a novel methodology for developing high-power energy harvesting gravity-based devices using an array of piezoelectric beams for wind energy applications. The methodology incorporates a global multidimensional constrained optimisation algorithm, which accounts for the physical size of the device, the physical, geometrical and electrical properties of the piezoelectric beams, and the power management circuit to increase the device's efficiency. As the beams are plucked sequentially, they vibrate out-of-phase, which consequently leads to charge cancellation issues. The paper proposes and incorporates an electrical circuit design to avoid such problems, being able to further increase the efficiency of the device by 35% when compared against the output from the standard energy harvesting (SEH) circuit with independent rectifiers. The proposed optimisation methodology is applied to the devices utilising flexible polyvinylidene fluoride beams. The developed dynamic numerical model of the beams’ vibration is validated using the experimental results and the results of a Finite Element Analysis. To study the electro-mechanical coupling of the beams, an electric circuit and the power management circuit are created and modelled in Matlab/Simulink software. The optimised device delivers 6 to 17 times higher energy output compared to the unoptimised device. The performance of this device was also compared to that of the device with much stiffer LiNbO 3 beams (Clementi et al., 2021, [1]) to demonstrate the direct applicability of such devices to power sensors and transmitter units for structural monitoring of wind turbine blades. It has been demonstrated that the LiNbO 3-beam device yields an energy output with one order of magnitude higher. The applied optimisation methodology enabled a 0.057 × 0.017 × 2 m 3 dimension device to produce a power output in the range from 0.5 to 1 W depending on the blades’ speed, resulting in 1.06 mW/cm 3 power density of the device. </p
The Role of Contracts in the Organic Supply Chain: 2004 and 2007
Full text linkOrganic food products are excellent candidates for contract production and marketing because they are produced using a distinct process and are in high demand. This report summarizes survey data on contracting in the organic sector, addressing the extent of contracting, the rationale for using contracts, and contract design for select commodities. The central survey data were collected from certified organic handlers (intermediaries)in the United States who marketed and procured organic products in 2004 and 2007. Contracting is widespread in the organic sector, and, in 2007, firms used contracts most frequently to secure organic products essential to their business and to source products in short supply. Large firms were more likely to use contracts for procurement, and these firms contracted for a larger share of their procurement needs. Nearly all contracts required suppliers to provide evidence of organic certification. Firms using contracts rarely assisted suppliers with obtaining organic certification or the transition to organic. Most contracts include provisions regarding quality, and quality verification was an essential component of these contracts. Prices were determined in a variety of ways and, in some cases, depended on delivered quality.Organic supply chain, contracts, organic marketing, organic procurement, intermediaries, certified organic handlers, contract design, certified organic, Agribusiness, Marketing,
Singular perturbations of Volterra equations with periodic nonlinearities: Stability and oscillatory properties
No full textSingularly perturbed integro-differential Volterra equations with MIMO periodic nonlinearities are considered, which describe synchronization circuits (such as phase- and frequency-locked loops) and many other “pendulum-like” systems. Similar to the usual pendulum equation, such systems are typically featured by infinite sequences of equilibria points, and none of which can be globally asymptotically stable. A natural extension of the global asymptotic stability is the gradient-like behavior, that is, convergence of any solution to one of the equilibria. In this paper, we offer an efficient frequency-domain criterion for gradientlike behavior. This criterion is not only applicable to a broad class of infinite-dimensional systems with periodic nonlinearities, but in fact ensures the equilibria set stability under singular perturbation. In particular, the proposed criterion guarantees the absence of periodic solutions that are considered to be undesirable in synchronization systems. In this paper we also discuss a relaxed version of this criterion, which guarantees the absence of “high-frequency” periodic solutions, whose frequencies lie beyond a certain bounded interval.Accepted Author ManuscriptTeam Tamas Keviczk
Uncertainty and the price for crude oil reserves
Full text linkInnovations in futures, options, and derivative instruments permit active trading, speculating and hedging - linking markets for physical petroleum products with financial markets. These derivative markets continuously value petroleum delivered today and for future dates, providing a market price for inventories. Underground petroleum reserves are also an inventory defined by exploration surveys and development drilling. Thus, observable market information can be used to value these reserves. Option - valuation models can be used to price reserves using observable markets, but are dependent on unexplained convenience yields revealed by the term structure of futures prices. The authors apply a general inventory pricing model to petroleum inventories and generate an empirical model of the returns to storage for petroleum markets. They examine the determinants of the crude oil convenience yield using a stochastic control model. They specify optimal production and inventory conditions using a third-order cost function and estimate them using monthly observations. Their inventory arbitrage condition embodies the Hotelling principle and Kaldor's convenience yield, and includes a premium on the dispersion in crude oil prices. The empirical results suggest that returns to storage contain both a cost-reducing component and often sizable premiums associated with the dispersion of petroleum prices. Their findings suggest that crude oil markets differentiated by quality and location provide similar premiums. The premiums associated with the dispersion of petroleum prices may account for persistent backwardation in crude oil prices. This finding may also explain the wide discrepancies between Hotelling values and transaction prices found in previous studies.Economic Theory&Research,Environmental Economics&Policies,Markets and Market Access,Labor Policies,Payment Systems&Infrastructure,Oil Refining&Gas Industry,Environmental Economics&Policies,Access to Markets,Markets and Market Access,Economic Theory&Research
Reliability of Marine Energy Converters
No full textThe oceans cover 71% of Earth’s surface and are an enormous source of renewable energy which comes from tides, waves, ocean currents, and salinity and temperature differences [...
"Asset Poverty in The United States: Its Persistence in an Expansionary Economy"
Full text linkFrom this paper's Preface, by Dr. Dimitri B. Papadimitriou, President: Economic growth and a rising stock market in the 1990s gave the impression that everyone was accumulating wealth and asset poverty rates were declining. The impression was supported by the official, income-based poverty measure, which exhibited a sharp decline. According to Senior Scholar Edward N. Wolff and Research Scholar Asena Caner, poverty measures should include wealth as well as income. Their study of asset poverty in the United States between 1984 and 1999 focuses on the lower end of the wealth distribution and shows that asset poverty rates did not decline during the period studied, and that the severity of poverty increased. It also shows that asset poverty is much more persistent than income poverty.
Ballet Fairy-Tale. Sketches by Dimitri Bouchène for Serge Lifar’s Productions
No full textThe article is dedicated to set designs and sketches for costumes, performed by Russian-French
artist Dimitri Bouchène (1893–1993) for ballets choreographed by Serge Lifar. Bouchèn emigrated
from the Soviet Union in 1925. In Europe he successfully worked in different styles
and genres: as a painter, book illustrator and graphic artist, designer for fashion and interiors.
Bouchène is known primarily as a set designer. He was the author of set designs and sketches
for costumes for more than 30 productions: dramatic performances, operas, ballets, and individual
dances. In the 1940s–1960s, he made stage designs for 6 ballets staged by Serge Lifar in
France (Paris, Grand Opera), Sweden (Göteborg, Stora Theater) and Portugal (Lisbon, Tivoli
Theater). The article is the first to summarize this material, touching on each performance
and known designs for them in detail. Its aim is to identify the place and role of these works
in developing the artistic manner of Bouchène and draw attention to the successfully formed
creative and friendly tandem of the artist and choreographer. In the drawings made for Lifar’s
ballets, the artist demonstrates a bold and broad stroke, active work of colour, inherent
in his mature manner. Bouchène’s decoration designs are ornamental, full of expression and
dynamics; they are distinguished by brilliance, play of saturated colour spots and temperamental
manner. Creating sketches for costumes, Bouchène uses colour intensity, possibilities
of various textures and the ability to combine them, accented with decorations to enhance and
emphasize the characters and images
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