Average Power Flow Research Articles

Effects of Hormonal Contraception and the Menstrual Cycle on Fatigability and Recovery From an Anaerobic Exercise Test.

Cabre, HE, Ladan, AN, Moore, SR, Joniak, KE, Blue, MNM, Pietrosimone, BG, Hackney, AC, and Smith-Ryan, AE. Effects of hormonal contraception and the menstrual cycle on fatigability and recovery from an anaerobic exercise test. J Strength Cond Res 38(7): 1256-1265, 2024-This study sought to evaluate the effects of oral contraceptive (OC) and hormonal intrauterine device (H-IUD) use, compared with a eumenorrheic (EUM) cycle, on fatigability and recovery between hormone the phases. Peak power (PP), average power (AP), fatigue index (FI), blood lactate, vessel diameter, and blood flow (BF) were measured from a repeated sprint cycle test (10 × 6 seconds) in 60, healthy, active women (mean ± SD ; age: 26.5 ± 7.0 years, BMI: 22.5 ± 3.7 kg·m -2 ) who used monophasic OC (≥6 months; n = 21), had a H-IUD (≥6 months; n = 20), or had regular naturally occurring menstrual cycle (≥3 months) or had a nonhormonal IUD (EUM; n = 19). Subjects were randomly assigned to begin in either the low-hormone phase (LHP) or high-hormone phase (HHP) and were tested once in each phase. Separate univariate analyses of covariances assessed the change from HHP to LHP between the groups, covaried for progesterone, with significance set at p ≤ 0.05. All groups demonstrated similar changes in PP, AP, FI, blood lactate, vessel diameter, and BF between the phases ( p > 0.05). Although not significant, AP was higher in LHP for OC (Δ -248.2 ± 1,301.4 W) and EUM (Δ -19.5 ± 977.7 W) and higher in HHP for H-IUD (Δ 369.3 ± 1,123.0 W). Oral contraceptive group exhibited a higher FI (Δ 2.0%) and reduced blood lactate clearance (Δ 2.5%) in HHP. In recreationally active women, hormonal contraception and hormone phases may minimally impact fatigue and recovery. Individual elite female athletes may benefit from understanding hormonal contraception type as performance and recovery may slightly vary across the cycle.

Relation between Mass Sensitivity and Complex Power Flow in Love Wave Sensors.

In this paper, we investigate the connection between average power flows in Love wave waveguides with the mass sensitivity of Love wave sensors. In fact, loading with a Newtonian liquid gives rise to two extra power flows, in the transverse direction towards the loading Newtonian liquid. The first is an active power flow feeding viscous losses in the Newtonian liquid and the second is a reactive power flow that is responsible for the phase delay of the Love wave and consequently for the changes in phase velocity of the Love wave. Since loading with a lossless mass also leads to changes in the phase velocity, we assert that mass sensitivity of Love wave sensors is connected to the average reactive power flow, in the transverse direction , bouncing back and forth, between the interior of the waveguide and the loading Newtonian liquid. Subsequently, we found the thickness of the effective surface layer of mass that is equivalent to loading with a semi-infinite Newtonian liquid. The analytical formulas developed in this paper are illustrated by the results of numerical calculations performed for an exemplary Love wave waveguide composed of a PMMA surface layer deposited on an ST-Quartz substrate.

Study of power flow mechanism of capacitive power transfer system based on Poynting vector analysis

In this paper, the power flow mechanism of a typical Capacitive Power Transfer (CPT) system is studied by analysing the electric field, magnetic field, and Poynting vector, to determine the power distribution as well as the average power flow to the load. It is found that the average power from the source flows along the wires on the transmitting side and passes the external areas of the coupling plates mainly along the channel between the two coupling pairs (instead of going through the air gaps in between), then converges along the wires before reaching the load. The average power calculated by integrating the real part of the Poynting vector across a defined power flow plane at the receiving end is consistent with CST (Computer Simulation Technology) simulation, circuit analysis, and practical measurements of the CPT system. Although the power density described by Poynting vector changes with the separation distance between the two coupling pairs, the total average power keeps approximately constant because the power flow area changes accordingly. Compared to the traditional lumped circuit analysis, the Poynting vector analysis shows the power distribution around the coupling plates in relation to their physical configuration. This research reveals the power flow mechanism and distribution in a CPT system from field point of view, which is useful to gain deeper understanding of the CPT system beyond the traditional circuit theory and would also be helpful to improve practical system design in the future.

Sinusoidally Modulated AC-Link Microinverter Based on Dual-Active-Bridge Topology

In this article, a bidirectional single-stage ac-link microinverter is proposed with a novel sine pulsewidth modulation. The proposed microinverter operates on the principles of dual-active-bridge converter modulation and thus allows seamless bidirectional power flow with soft switching. Contrary to the traditional two-stage microinverter interfacing a variable input voltage source, the proposed converter integrates dc–dc and dc–ac into a single stage, retaining functionality over a wide input-to-output voltage ratio. The synthesis of the sinusoidal output is achieved by applying a new composite modulation scheme that utilizes phase-shift modulation schemes used in the dual-active-bridge converter. Different parameters of the phase-shift modulation (namely, triple-phase-shift modulation) affect the overall composite modulation in terms of its ability to achieve soft switching and the average power flow. The mode analysis was carried out to demonstrate different modulation segments and its overall effect on the output power, efficiency, total harmonic distortion, etc. Previous works on a similar topology requires computationally intensive optimal modulation methods, which update every switching cycle. However, the proposed modulation parameters are analytically determined; hence, the controller only updates every line cycle, which is a significant reduction of control complexity. The proposed converter modulation scheme is designed and simulated in PSIM environment, which supports the theoretical analysis. A prototype was built for an experimental study. Results verifying the modulation scheme and the working principles of the converter are presented.

Improving the MVA-km Method for Transmission Cost Allocation Using Counter-Flow Approaches

Today with restructuring in power systems and the emergence of competitive electricity markets, operation of the power system have been many changes one of the challenges facing the electricity markets, is transmission pricing. transmission pricing has great impact on the network return on investment, competition and attracting new investors. In this paper, transfer pricing is performed by combination of Zbus and MVA-km methods. The Zbus method is used to determine the contribution of participant of lines transmission power and MVA-km method is used to determine the cost of participant transmission. Lines average apparent power flow is used in MVA-km method. three approaches to using MVA-km is defined in order to investigate the effect of reverse power of lines and how to calculate costs is presented by each approach. Simulation of the proposed method on the test network of 12 Bass is done. and the results of MW-km is compared with MVA-km. also, the results of these three approaches of MVA-km method were compared together and analysis their advantages and disadvantages.

Dispersion Equations of a Rectangular Tape Helix Slow-Wave Structure

A rectangular tape helix slow-wave structure with infinitesimal thickness and finite width in free space is investigated. With the expansion of surface currents in the helix and the applications of the modified Marcatili's method, as well as average power flow matching method at the boundaries, the dispersion properties and the interaction impedance for transverse antisymmetric modes in a rectangular tape helix immersed in free space are obtained. It is shown that, compared with the results of the simplified sheath model by previous researchers, higher accuracy has been obtained between the calculation results of the present theory and the data obtained from HFSS, and the validity of the present theory is further demonstrated by comparison with experiments. The improved characteristic equations hold scientific and practical significance in the design and performance evaluation of such plane slow-wave structure in the application of compact traveling-wave tubes. The distribution characteristics on the cross section of the longitudinal electric field fundamental component are also discussed based on this theory.

Hierarchical Spectral Clustering of Power Grids

A power transmission system can be represented by a network with nodes and links representing buses and electrical transmission lines, respectively. Each line can be given a weight, representing some electrical property of the line, such as line admittance or average power flow at a given time. We use a hierarchical spectral clustering methodology to reveal the internal connectivity structure of such a network. Spectral clustering uses the eigenvalues and eigenvectors of a matrix associated to the network, it is computationally very efficient, and it works for any choice of weights. When using line admittances, it reveals the static internal connectivity structure of the underlying network, while using power flows highlights islands with minimal power flow disruption, and thus it naturally relates to controlled islanding. Our methodology goes beyond the standard k-means algorithm by instead representing the complete network substructure as a dendrogram. We provide a thorough theoretical justification of the use of spectral clustering in power systems, and we include the results of our methodology for several test systems of small, medium and large size, including a model of the Great Britain transmission network.

Study on the Tunneling Mode in a Sub-Wavelength Open-Cavity Resonator Consisting of Single Negative Materials

We have investigated the process which establishes the tunneling mode in a conjugately matched pair consisting of ε-negative (ENG) and μ-negative (MNG) materials in theory and experiment. The one-dimensional conjugately matched pairs is realized by two L-C loaded transmission lines and the dynamical behavior of the transmitted signal along the pair is measured and recorded on an oscilloscope. It is found that the field does not decay to zero in a finite length single negative material and the average power flow is a constant since the phase difference between electric field and magnetic field varies with the position. While for a conjugately matched ENG/MNG pair, the incident field attenuates in ENG material in the first instance and then the fields are rapidly enhanced at the ENG-MNG interface and reach the steady state due to the resonating effect of the structure. It is revealed that there is a combination of travelling wave and reactive standing wave inside the bilayer with the ratio between them varying with the position. It is also proved that the bilayer can also be treated as an open resonator, in which the charging up characteristic time is in proportion to the Q factor of the structure.

Effect of Structural and Import Parameters on Solar Energy Regenerator Performance

In view of characteristics of working medium and villages buildings, the paper took pebble as material to store collected solar energy and studied the regenerator performance by numerical simulation (Matlab Programming) and experimental research. To comprehensively consider heat-exchange performance and operating cost, average regenerative power and air flow resistance were taken as target functions. Research results showed that the larger cross section velocity and length of pebble bed, the larger average heat storage power and air flow resistance. However, it's different for pebble diameter. The smaller pebble diameter, the larger average heat storage power and air flow resistance. So, pebble diameter was suggested to be 0.04∼0.08m. The determination of cross section velocity and length of pebble bed would need to take into account volume flow and regenerator structure.

Vibration transfer analysis of component interfaces by a power flow mode approach

A method has been developed to dynamically characterize complex structures’ interfaces at low frequencies. The aim is to optimize vibration isolation of a main structure subjected at its junctions to forces generated by connected substructures. An eigenvalue problem is formulated by minimizing the average dissipated power flow of the system. Hence, the derived eigenvalues and eigenvectors describe the energy pattern at each given frequency. It is then possible to characterize the real interface forces and, for example, to control them by determining the appropriated external forces to apply to the structure. This method has been studied on an academic system and applied to a simple coupled structure.

Vibration transfer analysis of component interfaces by a power flow mode approach

A method has been developed to dynamically characterize complex structures’ interfaces at low frequencies. The aim is to optimize vibration isolation of a main structure subjected at its junctions to forces generated by connected substructures. An eigenvalue problem is formulated by minimizing the average dissipated power flow of the system. Hence, the derived eigenvalues and eigenvectors describe the energy pattern at each given frequency. It is then possible to characterize the real interface forces and, for example, to control them by determining the appropriated external forces to apply to the structure. This method has been studied on an academic system and applied to a simple coupled structure.

New approach in back-to-back m -level diode-clamped multilevel converter modelling and direct current bus voltages balancing

Multilevel power converter structures have been introduced as the solution for high-power high-voltage applications and also for grid interface connection of renewable energy sources systems, where they have several advantages, namely low distortion voltages and currents and low switching losses resulting in higher efficiency. As a consequence of increasing interest on the multilevel converter applications, accurate models of these power converters are essential to be used in computer simulation studies. This study presents a new systematic modelling approach suitable to obtain global generalised models for back-to-back m-level diode-clamped multilevel converters connecting AC loads. Using the proposed converter modelling, an advantageous generalised method to balance the (m−1) DC bus capacitors, based on the DC bus average power flow is also presented. The generalised proposed model is particularised to the back-to-back multilevel structure for m=5. This back-to-back converter is studied working with bidirectional power flow, connecting an induction machine (in motor or self-excited generator mode) to the power grid as a flexible AC transmission system.

Electricity transmission pricing: Tracing based point-of-connection tariff

Point-of-connection (POC) scheme of transmission pricing in decentralized markets charges the participants a single rate per MW depending on their point-of-connection. Use of grossly aggregated postage stamp rates as POC charges fails to provide appropriate price signals. The POC tariff based on distribution of network sunk costs by employing conventional tracing assures recovery of sunk costs based on extent of use of network by participants. However, the POC tariff by this method does not accommodate economically efficient price signals which correspond to marginal costs. On the other hand, the POC tariff, if made proportional to marginal costs alone, fails to account for sunk costs and extent of use of network. This paper overcomes these lacunae by combining the above stated desired objectives under the recently proposed optimal tracing framework. Since, real power tracing problem is amenable to multiple solutions, it is formulated as linearly constrained optimization problem. By employing this methodology, consideration of extent of network use and sunk cost recovery are guaranteed, while objective function is designed such that the spatial pattern of price signals closely follows the pattern of scaled locational marginal prices. The methodology is tested on IEEE 30 bus system, wherein average power flow pattern is established by running various simulation states on congested and un-congested network conditions.

Construction of symmetrical and asymmetrical notches from elementary steps in isotropic plates

The interactions of the fundamental Lamb modes with discontinuities in an isotropic structure will be presented and analyzed in a simple and a fast way. The key point is to decompose the symmetrical or asymmetrical notch into two elementary steps. The fundamental antisymmetrical and symmetrical Lamb modes contributions are separated by means of the simple arithmetic operations of addition and subtraction. The power reflection and transmission coefficients are then computed with the well-known average power flow equation described in a previous work [NDT&E international, Vol. 41, p.1-9 (2008)]. Using these coefficients, the symmetrical notch can be constructed from one elementary symmetrical step while the asymmetrical notch is constructed from the superposition of asymmetrical down- and up-steps. Mode conversions phenomena are observed and analyzed for the asymmetrical steps and notches case. Finally, an experimental device is realized to test aluminum plates with different notch depths. Good agreement is found between experimental and numerical results.

Study of the fundamental Lamb modes interaction with asymmetrical discontinuities

The interaction of the fundamental Lamb modes with asymmetrical discontinuities in isotropic plates is studied numerically and experimentally. Three kinds of discontinuities that enable mode conversions are considered: steps down, steps up and asymmetrical notches. The anti-symmetrical and symmetrical Lamb modes contributions are separated by means of the simple arithmetic operations of addition and subtraction. The power reflection and transmission coefficients are then computed with the well-known average power flow equation described in a previous work. Furthermore, the asymmetrical notch is reconstructed from the superposition of a step down and a step up. It is shown that it allows directly the determination of all power coefficients of the reflected, the transmitted and the multiple converted Lamb modes contrarily to the finite element model. Finally, an experimental device is realized to test aluminum plates with different notch depths. Good agreement is found between experimental and numerical results.

Orthogonality of 3D guided waves in viscoelastic laminates and far field evaluation to a local acoustic source

The fundamental properties of guided waves in a laminate with any homogeneous boundary conditions on its faces are considered. As shown, the waves satisfy orthogonality relations whose physical meaning is related to the additivity of the average power flow. The applications of this orthogonality for solving some particular boundary value problems are discussed. A method for exact calculation of the far field caused by an acoustic source of a finite size is suggested. The only restriction is that the distance required must exceed the longitudinal radius of the source. The obtained results can be used for evaluating the fields radiated by ultrasonic transducers of arbitrary aperture and by other realistic sources.

Study of the fundamental Lamb modes interaction with symmetrical notches

The aim of this work is to predict the propagation of the fundamental Lamb modes in an isotropic structure containing discontinuities in a simple and a fast way. The key point is to decompose the symmetrical notch into two elementary abrupt changes in the plate section. The power reflection and transmission coefficients are computed, using two techniques, with the help of the finite element and the well-known average power flow equation. In the first technique, the through-thickness displacements and stresses are used while in the second technique only the normal or tangential displacement at a given location on the plate surface is used. An equality relation between the direct and the inverse abrupt changes of the plate section is given, which allows computing the power reflection and transmission coefficients for a symmetrical notch from those obtained from one elementary damage. Finally, aluminum plates with different notches depths are tested. Experimental and numerical results are in good agreement.

Characterisation of a dissipative assembly using structural intensity measurements and energy conservation equation

It is possible to get from complex velocity maps obtained by optical measurements (holographic interferometry, laser doppler vibrometry, etc.) and wavenumber processing, useful quantities to study energy flows in structures such as intensity, power flow, forces, localisation of sources and sinks of energy. In this paper, scanning laser vibrometer measurements on two-plate assembly are used to determine the dissipating power by the joints from the above-mentioned energetic quantities. The average power flow over lines parallel to the junction is computed using the proposed method in order to check a one-dimensional model of power flow distribution along the other dimension. An approximate energy conservation law of flexural vibration which gives good results on beam structures and measurement data are used to determine the dissipation characteristic of joints.

Power Flow Structures in Two Dimensional Electromagnetic Fields

Qualitative behaviour of time average power flow in electromagnetic fields can be studied by observing the critical points of the Poynting vector field, S. In order to analyze the behaviour of the flow lines of a plane Poynting vector field in the neighbourhood of a critical point, the S field is expanded in a Taylor series. Using this expansion, critical points can be classified according to their order and degeneracy. A formula for the index of rotation of the S field at a critical point is derived. The behaviour of the transverse electric or magnetic field component in the neighbourhood of the critical point is also studied. Lowest order critical points are always nondegenerate and they have interesting properties with regards to polarization and energy distribution. Examples involving linearly polarized system of interfering plane and/or cylindrical waves are given to show the critical points. The behaviour of flow lines is illustrated in these examples.

Power Flow in Linear, Active Vibration Isolation Systems

Power flow and net energy transfer are examined for actively controlled, vibration isolation dynamics. Fundamental concepts of active damping systems are studied by examining the average power flow in the controlled and passive actuators subject to harmonic inputs. Expressions for energies delivered and absorbed by the actuators per cycle are derived for one and two degree-of-freedom vibration models. Sensitivity to system parameters on power flow in the passive and active components is examined. This analysis tool can be useful in the design of low-power active and regenerative systems.