6 research outputs found
Optimal allocation of airplanes to routes
No full textIn this paper, we introduce a model that can assist airline planners in deploying their fleets as efficiently as possible. Specifically, we outline an optimization model that assigns a fleet of aircraft of different types to routes to maximize profits. An algorithm for solving nonlinear transportation problem is suggested. It is based on the use of Lagrange multipliers. We define and illustrate the use of the loss function, the cost structure of which is piecewise linear. The necessary and sufficient conditions for optimality are given. To illustrate the proposed approach, a numerical example is given.
First Published Online: 14 Oct 201
Numerical study of gas turbine nozzle guide vane external heat transfer and showerhead film cooling effectiveness by means of hybrid RANS-LES CFD modelling
No full textAn accurate estimation of gas turbine nozzle guide vane metal temperature locally on its surface is crucial for predicting vane lifetime. The stagnation region at the vane leading edge is, typically, exposed to the highest thermal load, thus, the showerhead configuration of film cooling is often applied on the leading edge. Widely used lean-burn combustors implement swirlers, leading to a complex flow field over the nozzle guide vane as the swirling profile is often preserved at the inlet of the guide vane. The nozzle guide vane external heat transfer coefficient in the industry is often computed either with boundary layer codes or RANS methods. However, higher accuracy hybrid RANSLES models are of interest since such models are becoming more and more available due to improved capabilities to facilitate the increase of computational resource demands. This study aims at introducing hybrid RANS-LES modelling to investigate swirling inflow effects on showerhead film cooling performance.The implemented methodology and various turbulence models are first validated by replicating an experimental case of a linear cascade of blades. The uncooled blade external heat transfer coefficient distribution is compared to the experimental data for cases with turbulence intensities of Tu =1% and Tu =8%. The SST k − ω and lag elliptic blending k − ε turbulence models successfully replicated the HTC distribution but the γ − Reθ transition model was required to capture transition on the suction side for cases with Tu =1%. The showerhead film cooling effectiveness is investigated with both RANS and hybrid RANS-LES models for a configuration of three rows of staggered cooling holes and blowing ratios of 1.4 and 1.9. Uniform inflow and two profiles of swirling inflow are analysed, with the strongest swirl being coupled with a radial temperature profile. Results indicate that the RANS-LES hybrid model is promising in capturing the unsteadiness of the horseshoe vortex. Mixing between mainstream and coolant jets, and the inherent unsteadiness of the mixing shear layers can only be captured with a scale resolving simulation. The swirling inflow lead to an altered stagnation line and imposed a radial pressure distribution close to the leading edge, which interfered with the coolant distribution on theleading edge. The coolant jet contact with the vane surface area is found to be the most important parameter affecting the cooling effectiveness since a coolant liftoff led to a significant reduction in cooling effectiveness. A liftoff was often observed in areas where the swirling velocity component misaligned to the mainstream flow direction. A positive contribution to cooling effectiveness was recorded in regions where the swirl component aligned to the mainstream flow direction. The increase in cooling effectiveness was observed due to locally increased momentum of the main flow that aids coolant staying attached to the surface. The benefits of hybrid RANS-LES modelling are established, and theresults signify the importance of accounting for an unsteady stagnation line during the design of the showerhead film cooling.Aerospace Engineerin
Optimal airline seat inventory control for multi‐leg flights
No full textAirline seat inventory control is about “selling the right seats to the right people at the right time”. In this paper, the problem of determining optimal booking policy for multiple fare classes in a pool of identical seats for multi‐leg flights is considered. During the time prior to departure of a multi‐leg flight, decisions must be made concerning the allocation of reserved seats to passengers requesting space on the full or partial spans of the flight. It will be noted that in the case of multi‐leg flights the long‐haul passengers are often unable to obtain seats because the shorter‐haul passengers block them. For large commercial airlines, efficiently setting and updating seat allocation targets for each passenger category on each multi‐leg flight is an extremely difficult problem. This paper presents static and dynamic models of airline seat inventory control for multi‐leg flights with multiple fare classes, which allow one to maximize the expected contribution to profit. The dynamic model uses the most recent demand and capacity information and allows one to allocate seats dynamically and anticipatorily over time.
First Published Online: 14 Oct 201
Electrical measurements of charge density wave nanomaterials at cryogenic temperatures
No full textLādiņa blīvuma viļņi ir parādība, kuras rezultātā kādu materiālu veidojošie joni maina savas līdzsvara pozīcijas, kā rezultātā arī elektroni no vienmērīga sadalījuma pāriet nevienmērīgā jeb viļņu sadalījumā. Šo fāzu pāreju dēļ mainās arī materiāla elektriskās īpašības, kuras var izmantot elektrisko ierīču - fotodetektoru, slēdžu, u.c. veidošanā. Darbā pārbaudītajiem N bSe3 un T aS3 materiāliem lādiņa blīvuma viļņu parādību var novērot tikai kriogēnās temperatūrās, kādēļ bija nepieciešams izveidot atbilstošu elektrisko mērījumu sistēmu. Autors izgatavoja pētāmo paraugu stiprinājumus kriostata kamerai, kas nodrošina gan labu termisko, gan elektrisko kontaktu, izstrādāja mēriekārtu datorvadības programmatūru, veica pārbaudes mērījumus un analizēja iegūtos rezultātus. Tika novērots, ka T aS3 nanovadu paraugam lādiņa blīvuma viļņu fāzu pārejas notiek pie aptuveni 210 K un 130 K temperatūras, bet N bSe3 pie aptuveni 144 K.Charge density waves affect the distribution of electrons in some given material, which in turn also affect the electrical characteristics. Due to such phase transitions, charge density wave materials can be used for electrical devices, such as photodetectors, switches and other applications. Due to N bSe3 and T aS3 displaying charge density wave properties only at cryogenic temperatures, it was necessary to create an experimental set up for performing electrical measurements at such temperatures. The author created a way to secure the experimental device in the cryostat chamber in such a way that it provides both a good thermal an electrical contact, created and tested a Python program for controling measurement devices, performed measurements and analyzed the results. It was observed that T aS3 phase changes occur at around 210 K and 130 K temperature, but for N bSe3 at around 144 K
Energy substrate metabolism and mitochondrial oxidative stress in cardiac ischemia/reperfusion injury
No full textFunding Information: This article is based upon work from COST Action EU‐CARDIOPROTECTION CA16225 supported by COST ( European Cooperation in Science and Technology ). C.J.Z. was supported by a grant from European Foundation of the Study of Diabetes and from Boehringer –Ingelheim to investigate the cardiac working mechanism of empagliflozin. V.B. received funding from the European Social Fund (project No 09.3.3-LMT-K-712-01-0131) under grant agreement with the Research Council of Lithuania . E.L. research is supported by funding from the Latvian Council of Science , project TRILYSOX, grant No. LZP-2018/1–0082. Publisher Copyright: © 2021 The Author(s)The heart is the most metabolically flexible organ with respect to the use of substrates available in different states of energy metabolism. Cardiac mitochondria sense substrate availability and ensure the efficiency of oxidative phosphorylation and heart function. Mitochondria also play a critical role in cardiac ischemia/reperfusion injury, during which they are directly involved in ROS-producing pathophysiological mechanisms. This review explores the mechanisms of ROS production within the energy metabolism pathways and focuses on the impact of different substrates. We describe the main metabolites accumulating during ischemia in the glucose, fatty acid, and Krebs cycle pathways. Hyperglycemia, often present in the acute stress condition of ischemia/reperfusion, increases cytosolic ROS concentrations through the activation of NADPH oxidase 2 and increases mitochondrial ROS through the metabolic overloading and decreased binding of hexokinase II to mitochondria. Fatty acid-linked ROS production is related to the increased fatty acid flux and corresponding accumulation of long-chain acylcarnitines. Succinate that accumulates during anoxia/ischemia is suggested to be the main source of ROS, and the role of itaconate as an inhibitor of succinate dehydrogenase is emerging. We discuss the strategies to modulate and counteract the accumulation of substrates that yield ROS and the therapeutic implications of this concept.Peer reviewe
