•Applies analytic vortex model to generate encounter signatures.•Examines solution space constraints from data and fitting accuracies.•Demonstrates model with new high-quality terrestrial field ...data.•Considers optimal camera views for InSight mission.
A physically-realistic migrating vortex model is developed and applied to generate pressure and wind speed and direction histories for dust devil passage. The asymmetric character of wind histories is noted, and we examine how these combined data constrain the solution space of dust devil parameters (migration velocity, diameter and intensity), ambient wind, and miss distance. These histories are compared with a new terrestrial field dataset of high-time resolution pressure and wind measurements of over twenty dust devil encounters in New Mexico. This new dataset is made available electronically and it is found that model fits can be typically achieved with simultaneous root-mean-square errors of ∼0.05hPa (∼5–10% of the peak pressure signature), ∼20°of wind azimuth, and ∼2m/s windspeed. The fits are not unique, however, and some heuristic aspects of resolving the intrinsic degeneracies of the problem and nonideal features of real encounters are discussed. The application of this approach to the InSight lander is noted, offering the possibility of defining the context for any possible detections of electromagnetic and seismic signatures of dust devils on Mars.
This paper presents robustness evaluation of deadbeat-direct torque and flux control (DB-DTFC) of interior permanent-magnet synchronous machine (IPMSM) drives with respect to machine parameter ...variation. For performance comparison, current vector control (CVC), one of the most widely used control methods, is also implemented under identical operating conditions as DB-DTFC. As the metrics to evaluate dynamic performance of DB-DTFC and CVC IPMSM drives, command tracking is used to investigate torque command tracking performance and dynamics stiffness is used to evaluate disturbance rejection performance. In addition, the torque estimation accuracy of DB-DTFC and CVC is investigated with respect to parameter variation. Simulation and experimental results of robustness evaluation of DB-DTFC and CVC are presented in this paper.
This paper presents a design approach for interior permanent-magnet (IPM) machines with variable-flux characteristics using low-coercive-force magnets for improved efficiency and extended operating ...speed range. A flux-intensifying IPM type with is used in the design due to positive Id operation and reduced loaded Iq effects. Design considerations of machine structures and variable-flux machine attributes are discussed. In addition, leakage flux in a rotor is particularly designed to also obtain another flux-varying capability. Evaluation of the designed machine is provided by finite-element analysis simulations and experiments on a proof-of-principle machine. The designed machine shows benefits in increasing efficiency and speed range in a low-torque region when variable magnetization control of the low-coercive-force magnets or the design of the leakage flux proposed in this paper is implemented.
This handbook provides you with the best, state-of-the-art coverage for every aspect of petroleum and natural gas engineering. With thousands of illustrations and 1,600 information-packed pages, this ...handbook is a handy and valuable reference. Written by dozens of leading industry experts and academics, the book provides the best, most comprehensive source of petroleum engineering information available. Now in an easy-to-use single volume format, this classic is one of the true "must haves" in any petroleum or natural gas engineer's library. A classic for over 65 years, this book is the most comprehensive source for the newest developments, advances, and procedures in the oil and gas industry. New to this edition are materials covering everything from drilling and production to the economics of the oil patch.
Although 60-W wireless power transfer (WPT) was demonstrated in 2007, still there is no equivalent circuit model for a submeter air-gap, hundreds of watts, and high-efficiency wireless system. A ...design-oriented circuit model is needed for this technology to evolve. This paper proposes an equivalent circuit model for the wireless system and analyzes the system based on the proposed model. The proposed model and its analysis are validated by means of finite-element analysis (FEA) and experimental results. Furthermore, as a viable solution for high-power (multikilowatt) applications, losses in the WPT system are investigated in the following section. Because of the high operating frequency (in megahertz), skin and proximity effects were shown to be dominant. A new spatial layout of a coil is proposed that significantly reduces losses caused by skin and proximity effects. With the new spatial layout, i.e., the surface spiral layout, the efficiency and size of WPT system can be improved significantly in high-power applications. The proposed coil design is evaluated by means of FEA.
•Reviews near-surface wind measurements from Venus probes.•Develops analytic (Weibull) probability distribution of wind speeds.•Implies frequent motion of surface particulates.•Critical input for ...landing safety assessment on future missions.
A surface wind specification is needed for future landed missions to Venus. While sparse, there exist enough data from the limited surface and near-surface measurements to date to define a probability density function that guides expectations of winds for rational design of landing systems. Following a review of all available data (mostly from the Venera missions), a Weibull function, used previously for Mars and Titan, and widely used in terrestrial engineering applications, is proposed. Best-estimate wind measurements are reasonably described by P(>V)=exp−(V/c)k, with c=0.8m/s, k=1.9: this function yields a 95% chance of winds <1.4m/s and 99% <1.8m/s. A worst-case function, allowing the high end of Venera measurement uncertainties to force the fit, has slightly higher values (c=0.9m/s, k=1.7; 95% wind 1.7m/s; 99%, 2.2m/s). The data suggest that winds strong enough to move dust and sand on Venus are rather common (more so than is typical for Mars, Earth or Titan), a prediction testable with radar interferometry on future orbital missions and/or from landed observations. More elaborate analyses should take site-specific factors such as slope or time of day into account, but cannot be meaningfully constrained by present data.
Junction temperature sensing for high-bandwidth power MOSFET junction temperature protection is usually achieved on the power converter's high power side, by directly monitoring the power switches ...with additional temperature detectors. This requires special considerations for high voltage, high current, high temperature, and EMI protection. This paper presents a new method applied on the power converter's low power side (MOSFET gate drive) so that junction temperature sensing can be integrated into MOSFET gate drive. For the purpose of demonstrating MOSFET junction temperature sensing, a push-pull gate drive is applied to a switching current divider circuit. The gate drive turn-on current transient waveform is used for MOSFET junction temperature estimation. A "gate drive-MOSFET" switching dynamic model is implemented indicating the mechanisms of MOSFET gate drive output dynamics. Modeling includes gate-drive push-pull output, gate drive output parasitics, power MOSFET intrinsic parameters, PCB parasitics, and load parasitics. LTSpice simulation of this model is studied and compared with experimental results.
The most recent Cassini RADAR images of Titan show widespread regions (up to 1500 kilometers by 200 kilometers) of near-parallel radar-dark linear features that appear to be seas of longitudinal ...dunes similar to those seen in the Namib desert on Earth. The Ku-band (2.17-centimeter wavelength) images show ~100-meter ridges consistent with duneforms and reveal flow interactions with underlying hills. The distribution and orientation of the dunes support a model of fluctuating surface winds of ~0.5 meter per second resulting from the combination of an eastward flow with a variable tidal wind. The existence of dunes also requires geological processes that create sand-sized (100- to 300-micrometer) particulates and a lack of persistent equatorial surface liquids to act as sand traps.
Variable flux permanent magnet synchronous machines (VF-PMSMs) have recently been proposed to reduce driving cycle losses in electric vehicle traction motors via magnetization state (MS) ...manipulation. This paper presents a closed-loop MS control method to enable reliable loss minimization control of VF-PMSMs. The MS is estimated at every sample instant and is used as a feedback for closed-loop control. Under most circumstances, the proposed method maintains precise torque control even during the MS manipulation transient by using a deadbeat-direct torque and flux control (DB-DTFC) framework. The state-of-the-art high-speed flux trajectory generation method for MS manipulation is integrated in the new closed-loop method to allow MS manipulation up to the maximum speed within the inverter voltage limit. The effectiveness of the proposed methods, in terms of driving cycle loss reduction capability and its thermal impact, is evaluated experimentally by emulating the road load using the dynamometer load motor.
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