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Electronic Power Converters in Wind Turbines and Solar Photovoltaic Systems
Published in Muhammad H. Rashid, Ahmad Hemami, Electricity and Electronics for Renewable Energy Technology, 2017
Rotor is the rotating part of a turbine; it consists of (mostly) three blades and the central part that the blades are attached to, the hub. A turbine does not necessarily have to have three blades; it can have two, four, or another number of blades. But the three-blade rotor has the best efficiency and other advantages. Blades are not solid; they are hollow and are made of composite material to be light and strong. The trend is to make them larger (for more power), lighter, and stronger. The blades have the form of an airfoil (same as the wings of an airplane) to be aerodynamic. As well, they are not flat and have a twist between their root and their tip. The blades can rotate up to 90° about their axes. This motion is called blade pitch. The function of the hub is to hold the blades and make it possible for them to rotate with respect to the rest of the turbine body.
Trailerable Boats–Hubs and Hitches, Trailering, Boat Ramps, Launching, Recovery, and Anchoring
Published in George A. Maul, The Oceanographer's Companion, 2017
Modern boat trailers are made with metal frames, either galvanized steel or aluminum, and are fitted with a spare tire, towing lights, and a license plate bracket. Usually, a cross frame box beam is connected to the frame by leaf springs, which are held in place with U-bolts. The solid wheel hub axles, which are about 10″ in length, are welded into the box-beam. The hubs turn on bearings fitted to the axle, and must be maintained regularly by packing them with waterproof grease. Nothing can be quite so disconcerting when towing than for a bearing to burn out or freeze at 55 mph; salt water has a nasty way of infiltrating seals and hubs. Maintaining the leaf springs too is essential as they are, of necessity, ferrous materials. Figure 10.1 shows an assembled wheel hub, and Figure 10.2 shows the disassembled unit.
Wind technology design and reverse osmosis systems for off-grid and grid-connected applications
Published in Hacene Mahmoudi, Noreddine Ghaffour, Mattheus Goosen, Jochen Bundschuh, Renewable Energy Technologies for Water Desalination, 2017
Eftihia Tzen, Kyriakos Rossis, Jaime González, Pedro Cabrera, Baltasar Peñate, Vicente Subiela
The hub of the wind turbine is the component that connects the blades to the main shaft and ultimately to the rest of the drivetrain. Hubs are generally made of steel, either welded or cast. The hub transmits energy and must withstand all the loads generated by the blades. The amount of energy which the wind transfers to the rotor through the blades depends on the density of the air, the rotor area and the wind speed. In a typical wind turbine, the kinetic energy of the wind is converted to rotational motion by the rotor. Wind speed is an important factor for the amount of energy a wind turbine can convert to electricity. This is indicated by the power curve and the terms cut-in and cut-out speed, typical technical characteristics of a wind turbine.
A two-stage robust hub location problem with accelerated Benders decomposition algorithm
Published in International Journal of Production Research, 2022
Reza Rahmati, Mahdi Bashiri, Erfaneh Nikzad, Ali Siadat
Direct shipments of commodities that flow between origin-destination nodes increase total transportation costs. In other words, vehicles that transport commodities may not be completely full, or may be totally empty on the way back. Appropriate hub location can reduce transportation costs by using intermediate centres (hub facilities). In this case, flows are gathered in hub facilities and distributed to destinations, and economies of scale occur. It is obvious that hub location problems can be considered in a variety of applications, including airport and aviation industries (Karimi and Setak 2018; Masaeli, Alumur, and Bookbinder 2018; Madani, Shahandeh Nookabadi, and Hejazi 2018), supply chain management, and logistics (Wang and Cheng 2010; Ishfaq and Sox 2010) and transportation systems (Lin and Lee 2010; Gelareh and Pisinger 2011). Hub location problems have been used abundantly in the design of transportation and distribution systems, including postal delivery, air freight and passenger travel, trucking, express package delivery, and rapid transit systems. Uncertainty is part of reality in the real world, and exists in some parameters. For example, consumer behaviour affects the volume and supply of demand. While in some cases there is a lower degree of uncertainty (such as demand cancellation by customers), a higher degree of uncertainty may also occur. For example, the COVID-19 pandemic can be considered one of major sources of such uncertainty.
Strategic airline network design problem in a duopolistic market
Published in Transportation Planning and Technology, 2020
Ta-Hui Yang, Ching-Hui Tang, Hung-Chun Hsiao
The objective function (2) is to maximize the leader’s total profit. Constraint (3) is used to determine the path type (i.e. non-stop, one-hub-stop, or two-hub-stop path) for each OD pair. Only one of the three path types is selected for each OD pair. Constraint (4) indicates that if airport k is not a hub, then one-hub-stop and two-hub-stop paths are prevented for airport k. Constraint (5) indicates that if either the origin or destination station is a hub, then the two-hub-stop path is prevented, and the one-hub-stop or non-stop path is preferred. Constraint (6) denotes that if both the origin and destination stations are hubs, then only the non-stop path can be used for this OD pair. Constraint (7) is used to calculate the flight distance for each OD pair. Constraint (8) indicates that if airport k is set to be a hub, then there must be flow transshipment at airport k. Constraint (9) is used to draft the ticket price. Constraint (10) is the market share function which is used to estimate the attracted demand for each OD pair for the leader. Constraints (11) to (16) define the variables in the model.
Optimal design of hub-and-spoke networks with access to regional hub airports: a case for the Chinese regional airport system
Published in Transportmetrica A: Transport Science, 2018
Weiwei Wu, Haoyu Zhang, Wenbin Wei
As the regional hub airport is introduced in the current network, the objective function (11) represents two total costs: (1) the total cost of the original transit traffic that have transferred through hub airports and (2) a new total cost generated by traffic that has been diverted to regional hubs. is the new generated cost of traffic on route i–j, where there must be one regional hub airport as the transfer hub. Since a regional hub can collect traffic as well as distribute traffic, Cimtj=χCim+αCmt+δCtj is the unit cost on path i–m–t–j. In the objective function (11), represents the current congestion cost in the hub airport k, where is the extra traffic that exceeds its capacity in the improved network, and β denotes the congestion coefficient. Based on the idea of traffic sharing by a regional hub, it is expected that the current traffic at a hub k will be reduced, and consequently reduce the congestion cost. The final two expressions of Equation (11) represent the total airport charge for passengers transferred at the hub airport and the regional hub airport. Generally, charges at a regional hub are less than that at a hub airport due to subsidies from the government and other factors such as lower classification of runway by the International Civil Aviation Organization (ICAO).