Phase Delay Angle Research Articles

Multiobjective Design Study of a Flapping Wing Power Generator

Abstract In conventional windmills, the high tip speed creates aerodynamic noise, and when they are used at very low Reynolds numbers, their performance deteriorates due to laminar separation. These are important issues in modern windmills. Present study deals with a new windmill concept, the “flapping wing power generator,” which would solve such problems. The concept is to extract energy via the flutter phenomena and the concept has been developed by some researchers. In 2003, Isogai et al. 2003, “Design Study of Elastically Supported Flapping Wing Power Generator,” International Forum on Aeroelasticity and Structural Dynamics, Amsterdam) proposed a new system. The system utilizes dynamic stall vortices efficiently and generates high power. The dynamic stall vortex is something that should be avoided in conventional windmills. They optimized the system to maximize the efficiency and obtained the set of design parameters, which achieved best efficiency. The system works at low frequencies and it enables high efficiency. To realize the system, it is necessary to consider the power and the efficiency. Thus, the present study optimized the system to maximize both the power and the efficiency. To obtain nondominated solutions, which are widely distributed in the design space, adaptive neighboring search, which is one of evolutionary algorithms, has been extended to handle multiple objectives and was used in the present study. Self-organizing map was used for the data mining. The trade-off between the power and the efficiency has been visualized. The trade-off curve was shaped by the constraints on the reduced frequency and the phase delay angle, which were imposed so that the dynamic stall phenomenon gives favorable effects on the power generation. The heaving amplitude was a parameter correlated to the objective functions. The reduced frequency and the phase delay angle change to control the heaving amplitude. Consequently, when the power is emphasized, the system undergoes a large heaving motion with a low frequency. On the other hand, when the efficiency is emphasized, the system undergoes a small heaving motion with a high frequency. Multiobjective optimization and data mining revealed the trade-off of the objective functions and the parameters correlated to the objective functions. The power obtained was comparable to that of present windmills at low tip-speed ratio region.

High-pulse conversion techniques for HVDC transmission systems

A high-pulse conversion technique for high voltage and high power applications such as HVDC transmission system is proposed. The proposed technique, based on the DC current reinjection, further decreases the number of components in the auxiliary circuit to achieve the same pulse number. An optimised control strategy over the whole range of phase delay angle is provided along with sophisticated input current and output voltage analysis. With the pulse multiplication strategy the proposed schemes demonstrate 24-pulse, 36-pulse and 48-pulse characteristics both in the input current and in the output voltage. Experimental results from a 3 KVA laboratory prototype verify the proposed concept.

Designing and testing low-resistance grounding systems

Induction motors have good efficiencies when operating at full load. At lower than rated loads, however, efficiency is greatly re - duced. This letter describes using fuzzy logic to optimize the efficiency of an induction motor drive while keeping good dynamic response. The proposed fuzzy controller adjusts the magnetizing current component with respect to the torque current component to give the minimum total copper and iron losses. Nomenclature: VV sr () : stator (rotor) voltage II sr () : stator (rotor) current ϕ: stator current and voltage phase delay angle ω s : stator frequency ω : mechanical frequency µ: magnetization subscript o: nominal value subscript Introduction: Electrical machines normally operate at rated flux in a variable frequency drive to get the best transient response. Most of the

THEORETICAL EVALUATION OF NEW PHASE DELAY METHODS FOR MEASURING LOCAL HEAT TRANSFER COEFFICIENTS

A one-dimensional analytical solution has been derived for unsteady heat conduction within a semi infinite body, of high thermal resistance, that is subject to a surface heat flux that varies periodically with time. The heat flux is assumed to be generated within a thin isothermal coating. The model predicts that a phase delay will develop between the heat flux and the coating thermal response. This phase delay is independent upon the material properties of the substrate and coating, on the heat flux driving frequency, and on the local heat transfer, coefficient. With the exception of this last quantity the other parameters are known a priori, hence if the phase delay can be measured experimentally it can then be used to determine the local heat transfer coefficient. Absolute values of the local coating temperature and local heat flux are not required. Hence calibration of the devices for measuring these quantities should not be required. In contrast to the overall surface temperature, it is predicted that the phase delay angle will attain a steady-state value within a few heat flux cycles, thus reducing the time required obtaining a measurement. Furthermore, the one-dimensional mathematical model that has been developed reduces to those used in previous experimentally validated techniques, when appropriate constants in the boundary condition are used.

音響信号の位相遅れを利用したひずみ円形状の測定

In this paper, we discuss the development of a new noncontact method for determining cylinder configurations using sound phase delay. In order to improve the accuracy of the measurements, the effect of the cavity in which the cylinder is placed has been studied. When the cylinder is placed near a side wall of the cavity, the phase delay angle increases, particularly for cylinders with odd periodic deflection. Thus, by varying the gap between the cylinder and the side wall, it is possible to determine the cylinder configuration even if the deflections are small. We propose a new method, in which the influence of noise is avoided by measuring the noise interference using a pair of microphones in the cavity.

Formation and Propagation of Tidal Bore

In a tidal river, the peak value of the discharge occurs earlier than the peak value of the tidal elevation. The high water level of a tidal wave moves faster than the low water level, and as a result the slope of the wave-surface profile, in the direction of propagation, increases from high water to low and decreases from low water to high. This differential slope causes retention of tidal flux during ebb, which in turn elevates the low water level and introduces a delay in the occurrence of the low water phase. This delay causes the flood discharge, at the transition of flow from ebb to flood, to start with an initial value. During the passage of tides of large amplitudes, the delay angle and consequently the initial value of the flood discharge at the transition of flow from ebb to flood becomes large and generates a surge. This surge discharge, at the transition of flow from ebb to flood, generates the bore. This is possible only in rivers where the summation of the phase lead and delay angles exceeds π/2. The veracity of these computations is checked from observed data.

Current and voltage controlled capacitor charging schemes

Future naval shipboard power systems for electrothermal chemical guns will require power conditioning to charge capacitors from a rectified generator source. This paper describes results of laboratory testing involving two low voltage capacitor charging schemes. These experiments demonstrate the power conditioning equipment's voltage and current control characteristics. The first sequence of tests utilized a phase-controlled rectifier to control the current. A series of constant phase delay angles and a predetermined phase delay angle profile were tested to produce a constant current charge on the capacitors. The second sequence utilized generator field control to ramp the charge voltage through a diode bridge to charge the capacitors. Using the results of each configuration, an optimum design of simultaneous current and voltage control can be developed. The control aspects of using combined generator field control and rectifier current control is addressed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Atmospheric pressure torque and axial rotation of Venus

The influence upon the axial spin rate of Venus of a ground pressure of atmospheric origin is investigated. This semi-diurnal sectorial pressure distribution leads to a deformation of the solid planet (pressure bulge). In addition to the classical (braking) torque due to the solar solid tide, other kinds of torques can possibly occur: the tidal torque upon the pressure bulge (braking), the pressure torque upon the pressure bulge itself (braking) and the pressure torque upon the tidal bulge (accelerating). The torque budget is estimated and shows that, for usual values of the phase delay angles of thermal origin or caused by internal friction, the main effect is to slow down the axial rotation of the planet.

A proposed high-frequency high-power silicon-silicide multilayered device

A new, integrated device, comprised of a series of metal and semiconductor films, is proposed for use as a high-frequency high-power source. The new metal-semiconductor device provides the excess carrier generation and the drift phase angle delay required to accomplish the negative resistance. The metal acts as a reservoir to collect the excess generated carriers from both sides of the semiconductor and to isolate the performance of each element of the integrated device. Following simple scaling rules, the area of an integrated device having n elements is n times larger than the area of each element; and the power output is about n2times the output of a single element at the same operation frequency, if the heat dissipation is not a limiting factor. The device can be fabricated-by using the silicon-silicide epitaxial process with MBE.

Effective value of direct-voltage ripple

Rectifiers produce a ripple of the direct-voltage output. Because it has many different shapes, it is hard to describe in simple terms except by the effective (root-mean-square) value of the ripple voltage, giving only one number to designate its magnitude. Within the limitations given in the paper, all ripples depend only on voltage magnitude, repetition rate, overlap (time of current commutation), and phase delay angles. Calculation of the magnitude is attempted by various methods; the most straightforward one uses two normalized functions of overlap and repetition rate (expressed as per-unit values). Figures in the paper give these functions within the range of validity and examples show how to use the method and interpret the results. Without phase control the resulting relative ripple magnitude (ripple voltage over direct voltage) is plotted against both repetition rate and overlap.

Transit-Time Effects in Ultra-High-Frequency Class-C Operation

Transit-time effects in ultra-high-frequency triodes and tetrodes used in class-C operation are analyzed. Effects discussed are electron-transit reactance; electron-transit phase-delay angle; cathode back-heating; use of a screen grid to improve efficiency; changes in optimum shunt impedance; secondary emission; and anode back-heating by secondary electrons. It is pointed out that by increasing voltage and current density simultaneously the frequency and power can be raised without sacrificing efficiency or bandwidth. An equivalent circuit is described which takes account of certain important transit-time effects.