Maximum Performance In Terms Research Articles

Analysis of DC–DC power supply systems for pulsed loads from green electronics perspective

Discontinuous loads frequently compromise the performance of their power source and electronics. They cause the voltage and current ripple at the source and load, and introduce electromagnetic interferences. Also, they affect the efficiency of the power source. The aforementioned issues are particularly relevant in battery powered electronics. In order to minimise these unwanted effects, it is necessary to introduce a power supply architecture between the load and the source that should filter and/or regulate the currents and voltages. This architecture could be made solely of passive components or could use DC–DC regulators. The present work classifies and characterises the most relevant architectures available. A novel switched power supply architecture for pulsed loads with adaptive input current is also introduced. A mathematical analysis of the conditions and characteristics that the regulated architectures should fulfil to obtain the maximum performance in terms of efficiency and green electronics is provided. The simulation and experimental results shown in this study demonstrate the theoretical analysis.

Effect of consolidation pressure on volumetric composition and stiffness of unidirectional flax fibre composites

Unidirectional flax/polyethylene terephthalate composites are manufactured by filament winding, followed by compression moulding with low and high consolidation pressure, and with variable flax fibre content. The experimental data of volumetric composition and tensile stiffness are analysed with analytical models, and the composite microstructure is assessed by microscopy. The higher consolidation pressure (4.10 vs. 1.67 MPa) leads to composites with a higher maximum attainable fibre volume fraction (0.597 vs. 0.530), which is shown to be well correlated with the compaction behaviour of flax yarn assemblies. A characteristic microstructural feature is observed near the transition stage, the so-called local structural porosity, which is caused by the locally fully compacted fibres. At the transition fibre weight fraction, which determines the best possible combination of high fibre volume fraction and low porosity, the high pressure composites show a higher maximum performance in terms of tensile stiffness (40 vs. 35 GPa). The good agreement with the model calculations (fibre compaction behaviour, and composite volumetric composition and mechanical properties), allows the making of a property diagram showing stiffness of unidirectional flax fibre composites as a function of fibre weight fraction for consolidation pressures in the range 0–10 MPa.

Vibration control of a flexible space manipulator during on orbit operations

Space manipulators are complex systems, composed by robotic arms accommodated on an orbiting platform. They can be used to perform a variety of tasks: launch of satellites, retrieval of spacecraft for inspection, maintenance and repair, movement of cargo and so on. All these missions require extreme precision. However, in order to respect the mass at launch requirements, manipulators arms are usually very light and flexible, and their motion involves significant structural vibrations, especially after a grasping maneuver. In order to fulfill the maneuvers of space robotic systems it is hence necessary to properly model the forces acting on the space robot, from the main terms, such as the orbital motion, to the second order perturbations, like the gravity gradient and the orbital perturbations; also flexible excitation of the links and of the joints can be of great importance in the manipulators dynamics. The case is furthermore complicated by the fact that the manipulator, together with its supporting spacecraft, is an unconstrained body. Therefore the motion of any of its parts affects the entire system configuration. The governing equations of the dynamics of such robotic systems are highly nonlinear and fully coupled. The present paper aims at designing and studying active damping strategies and relevant devices that could be used to reduce the structural vibrations of a space manipulator with flexible links during its on orbit operations. In particular an optimized adaptive vibration control via piezoelectric devices is proposed. The number of piezoelectric devices, their placement and operational mode should be correctly chosen in order to obtain maximum performance in terms of elastic oscillations reduction and power consumption. Even though an optimal placement cannot have a universal validity, since it depends on the type of maneuver and on the overall inertial and geometrical characteristics, an approach to solve the problem is proposed.

High thickness Ti/TiN multilayer thin coatings for wear resistant applications

Hard coatings like titanium nitride (TiN) normally contain a high degree of internal stress (usually compressive in-plane parallel with the surface) owing to growth defects developed during the deposition process and thermal mismatch effects after final cooling; it is, therefore, difficult to produce single-layer TiN coatings thicker than 6–7 μm, without adhesion problems. In the present study, thick coatings (i.e. >10 μm) have been achieved by alternate multilayering of TiN with Ti interlayers, leading to a tougher and less-stressed film. However, having a constant distribution of titanium interlayer thickness is not necessarily the best solution to achieve maximum performance in terms of wear resistance and hardness. The residual stress distribution along the thickness is unlikely to be constant with the inner layers being more stressed due to a greater amount of thermal differential strain. Following this guideline, a series of numerical simulations was performed in order to calculate the residual stress through thickness distribution due to the deposition process. Three sets of multilayered Ti/TiN coatings having both constant and variable Ti interlayer thickness were modelled and deposited, using a reactive arc PVD process. Mechanical and tribological properties were characterized using static and depth sensing Vickers micro-hardness indentation tests, rotating wheel (dimpling grinder) abrasive wear tests and Rockwell C adhesion tests. Coating interface characterizations were made by SEM-EDS. Results showed that adhesion can be significantly improved by adopting a titanium through thickness quantity increasing towards the interface: an optimized distribution allows also higher hardness and wear resistance to be obtained, as it requires a lower total amount of titanium to obtain good adhesion properties.

Methane steam reforming and ethanol steam reforming using a Ni(II)-Al(III) catalyst prepared from lamellar double hydroxides

Abstract In this work the methane steam reforming (MSR) and the ethanol steam reforming (ESR) on Ni(II)-Al(III) catalyst prepared from lamellar double hydroxides (LDHs) as precursor are studied. A comprehensive analysis of the kinetics results obtained at different water/methane and water/ethanol feed ratio and its correlation with the structural characteristic and redox behavior of the catalyst is carried out. The results show evidence that the catalyst behavior is related with the presence of only one type of active site in the Ni/Al 2 O 3 catalyst. The competition for the active sites between reactants is verified for MSR. This behavior is also observed in ethanol steam reforming since methane steam reforming determines the products distribution in the exit stream. There would be an optimum inlet water concentration that gives a maximum performance in terms of H 2 and CO 2 selectivity and, simultaneously, a minimum CO selectivity. This is a promissory result taking into account that the hydrogen flow entering a PEM fuel-cell requires a CO concentration lower than 20 ppm.

System Performance and Thermodynamic Cycle Analysis of Airbreathing Pulse Detonation Engines

A modular approach to the study of system performance and thermodynamic cycle efficiency of airbreathing pulse detonation engines (PDEs) is described. Each module represents a specific component of the engine, and its dynamic behavior is formulated using conservation laws in either one or two spatial dimensions. A framework is established for assessing quantitatively the influence of all known processes on engine dynamics. Various loss mechanisms limiting the PDE performance are identified. As a specific example, a supersonic PDE for high-altitude applications is studied comprehensively. The effects of chamber configuration and operating sequence on the engine propulsive efficiency are examined. The results demonstrate the existence of an optimum cycle frequency and valve close-up time for achieving maximum performance in terms of thrust and specific impulse. Furthermore, a choked convergent-divergent nozzle is required to render the PDE competitive with other airbreathing propulsion systems, such as gas-turbine and ramjet engines.

Optimisation of the hyphenation between solid-phase microextraction, capillary gas chromatography and inductively coupled plasma atomic emission spectrometry for the routine speciation of organotin compounds in the environment

The hyphenation between solid-phase microextraction, gas chromatography and inductively coupled plasma atomic emission spectrometry (SPME-GC-ICP-AES) has been developed for the speciation of butyl- and phenyltin compounds in sediment and water samples. Factors determining the GC-ICP-AES analysis were optimised by an experimental design approach to evaluate critical parameters influencing the overall analytical performance system. Quasi-dry plasma conditions and a high helium carrier gas flow rate were required to obtain maximum performance in terms of sensitivity. The use of SPME to preconcentrate the analytes allowed detection limits within 1 to 42 ng (Sn) l−1 to be obtained for water samples. Validation of the technique was performed by the analysis of certified reference sediment (PACS 2) and a wastewater sample.

Uncured and cured state properties of fly ash filled unsaturated polyester composites

Physical properties of fly ash filled unsaturated polyester composites in both uncured and cured states have been studied with special reference to the effect of degree of loading, nature of filler surface, and surface treatment of filler. The effect of filler surface on curing and oil absorption characteristics of filler were also examined. In the uncured state, sedimentation rate test and viscosity measurement for fly ash reinforced composites were performed. For cured fly ash filled unsaturated polyester composites, tensile properties decreased with the addition of fly ash particles whereas surface treatment led to improved mechanical properties and resistance to swelling. In terms of dynamic mechanical thermal analysis, effects of both filler and surface treatment on loss factor (tan δ) were discussed. Tan δ value and damping temperature range increased to the 15% fly ash addition. The composite having 15% unsilanized fly ash was found to have the highest tan δ and damping temperature range together with maximum performance in terms of tensile properties and swelling behavior. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1128–1136, 2000

Modeling the software architecture of a prototype parallel machine

A high-level Petri net model of the software architecture of an experimental MIMD multiprocessor system for Artificial Intelligence applications is derived by direct translation of the code corresponding to the assumed workload. Hardware architectural constraints are then easily added, and formal reduction rules are used to simplify the model, which is then further approximated to obtain a performance model of the system based on generalized stochastic Petri nets. From the latter model it is possible to estimate the optimal multiprogramming level of each processor so as to achieve the maximum performance in terms of overall throughput (number of tasks completed per unit time).

Rotating Machinery Utilizing Superconductors

The properties of superconducting materials appropriate for a discussion of their application in rotating machines are cited. The electrical, mechanical, and thermal losses that will occur in superconducting rotating machines are defined and estimated. The requirements for maintaining the cryogenic environment are given in terms of refrigerant use and in terms of refrigeration. Some estimates are given of refrigerator size and efficiency. The results of a circuit analysis of an alternator are given to define the maximum performance in terms of circuit parameters. The results of an electromagnetic field analysis are used to relate circuit parameters to geometry and material properties. On the basis of these analyses some estimates are made of the specific mass of alternators with superconducting armatures and with ambient temperature armatures. These results are combined with the results of the loss analysis to obtain the overall specific mass and efficiency of each alternator system. Finally, a proposed system is presented for a 1000 kVA turboalternator having a specific mass of 1.85 pounds per kilowatt including the gas turbine, and refrigerator.

Rotating Machinery Utilizing Superconductors

The properties of superconducting materials appropriate for a discussion of their application in rotating machines are cited. The electrical, mechanical, and thermal losses that will occur in superconducting rotating machines are defined and estimated. The requirements for maintaining the cryogenic environment are given in terms of refrigerant use and in terms of refrigeration. Some estimates are given of refrigerator size and efficiency. The results of a circuit analysis of an alternator are given to define the maximum performance in terms of circuit parameters. The results of an electromagnetic field analysis are used to relate circuit parameters to geometry and material properties. On the basis of these analyses some estimates are made of the specific mass of alternators with superconducting armatures and with ambient temperature armatures. These results are combined with the results of the loss analysis to obtain the overall specific mass and efficiency of each alternator system. Finally, a proposed system is presented for a 1000 kVA turboalternator having a specific mass of 1.85 pounds per kilowatt including the gas turbine, and refrigerator.

Maximum Utilization of Narrow-Band Data Links for Interplanetary Communications

Our ability to communicate with vehicles in space continues to be limited by the amount of received energy required to transmit a unit of information to earth. We have available, in practical hardware, radio-communication systems which provide us with theoretical maximum performance in terms of data bandwidth and distortion for a given transmission range and power output. The development and refinement of transmission, receiving, and powersupply techniques will extend the range of communication or increase the data bandwidth at a given range; but any significant extension of our capacity to communicate in space must come from advances in the state-of-the-art of telemetry data handling. New and advanced means for data processing and encoding prior to transmission should be investigated. The discussion which follows defines some technical areas which merit investigation, presents an outline for one approach to such an investigation and contemplates the evaluation of findings.