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Energy Storage
Published in Mukund R. Patel, Omid Beik, Wind and Solar Power Systems, 2021
In a fast-discharge application, such as for starting a heavily loaded motor, the battery may be required to deliver the maximum possible power for a short time. The peak power it can deliver is derived using the maximum power transfer theorem in electrical circuits. It states that the maximum power can be transferred from the source to the load when the internal impedance of the source equals the conjugate of the load impedance. The battery can deliver the maximum power to a DC load when RL = Ri. This gives the following: Pmax=Ei24Ri
Lexicon
Published in Samuel C. Sugarman, HVAC Fundamentals, 2020
power factor: (Electrical) The ratio of real power to apparent power or watts divided by volt-amperes, expressed as a decimal or percentage. In an electric power system, a load with a low power factor draws more current than a load with a high power factor for the same amount of useful power transferred. The higher currents increase the energy lost in the distribution system and require larger wires and other equipment. Because of the cost of larger equipment and wasted energy, electrical utilities will usually charge a higher cost to industrial or commercial customers where there is a low power factor. Power factors are usually stated as “leading” or “lagging” For energy management purposes the power factor on motors is generally read at the motor control center or at the disconnect box using a portable clamp-on digital or analog power factor meter. The power factor is measured on only one phase of a single-phase system and on each phase of a three-phase induction system. The power factor should be 0.85 or greater. See lagging power factor and leading power factor. Another definition of power factor is the ratio of the average (or active) power to the apparent power (root-mean-square voltage times root-mean-square current) of an alternating-current circuit. Aka phase factor.
Principles of Energy Conversion
Published in Hamid A. Toliyat, Gerald B. Kliman, Handbook of Electric Motors, 2018
Hamid A. Toliyat, Gerald B. Kliman
The efficiency is the ratio of output power to input power under specified conditions. On small machines, these can be measured directly. On larger equipment where the mechanical power cannot be measured accurately, a conventional efficiency, based on segregated losses, is used. The losses to be considered are: Armature I2R loss (corrected to a specified temperature)Field I2R loss (corrected to a specified temperature)Friction and windage lossCore loss (on an open circuit)Stray-load loss (on a short circuit)
Contribution of segmental kinetic energy to forward propulsion of the centre of mass: Analysis of sprint acceleration
Published in Journal of Sports Sciences, 2022
Jean Slawinski, Nicolas Houel, Camille Moreau, Alexia Mahlig, Daniel Dinu
In physics, power is the rate, with respect to time, at which work is done; thus power is the time derivative of work. As such, several studies have evaluated external work (Wext), defined as the sum of the potential and kinetic energy (KE) variations measured at the CoM level, in order to identify the overall mechanical determinants of sprinting. A recent study of 12 young, male athletes performing a maximal 60 m sprint (Matsuo et al., 2019) showed that performance mainly depended on horizontal anterior–posterior Wext during the propulsion phase. In other words, the greater the mechanical work produced, the higher the sprint performance. Indeed, the use of the KE of the body segments, because it take into account mass and velocity of each segment, supplies useful information concerning the upper and lower limbs’ contributions to the translation of the body in the forward direction during rapid movement (Hubley & Wells, 1983; J Slawinski et al., 2010).
RESNA position on the application of dynamic seating
Published in Assistive Technology, 2021
Michelle L. Lange, Barbara Crane, Frederick J. Diamond, Suzanne Eason, Jessica Presperin Pedersen, Greg Peek
Dynamic, in the context of physics, is defined as “of or relating to physical force or power” and “marked by usually continuous and productive activity or change” (Merriamwebster.com, 2019). Force is a vector, embodied by magnitude and direction. A wheelchair user exerts force onto a dynamic component in a specific direction or directions at a certain magnitude. Work results from forces acting upon an object and can either cause or hinder motion. Within dynamic seating, the individual is imparting “work” on the dynamic component, resulting in its displacement or movement. Power is the rate of performing work and is represented by work/time. A person provides more power when displacing the dynamic component rapidly rather than slowly. The dynamic motion imparts kinetic energy into the system. As the dynamic components displace, the kinetic energy is stored as potential energy, typically by displacing springs or polymers. This potential energy allows the dynamic component to return to its original position when the force is removed.
Ship hull wake effect on the hydrodynamic performance of a heave–pitch combined oscillating fin
Published in Ships and Offshore Structures, 2021
Anties K. Martin, P. Anathakrishanan, P. Krishnankutty
Figure 17(a) shows the comparison of foil thrust in behind ship and open water conditions. The thrust force variations are not significant up to St = 0.15. After that, the thrust force in behind ship condition picks up and become higher than that of the open water condition. Figure 18 shows the velocity contour around the foil at St = 0.4. In behind ship condition, the inflow velocity is 1.789 m/s which is the design speed of the model but the velocity at the vicinity of the foil is higher than the inlet velocity given which is around 2 m/s. Flow at the leading edge joined at the trailing edge and formed the velocity of jet formation of water and an increase in the reactionary thrust force in the direction of propagation of the vehicle. Figure 17(b) compares the power required in open water and in behind ship conditions. The power required for the oscillating foil increases with the oscillation frequency. The power required is higher in behind ship condition compared to the open water condition which is due to the higher normal force and pitch moment in the behind condition. Efficiency is defined as the ratio of output power to input power. Figure 17(c) shows that the higher range of efficiency is obtained in behind ship condition compared to that of the open water condition. The thrust generated in behind ship condition is more compared to the open water condition resulting in high efficiency for behind ship condition.