716 research outputs found
High reliability megawatt transformer/rectifier
The goal of the two phase program is to develop the technology and design and fabricate ultralightweight high reliability DC to DC converters for space power applications. The converters will operate from a 5000 V dc source and deliver 1 MW of power at 100 kV dc. The power weight density goal is 0.1 kg/kW. The cycle to cycle voltage stability goals was + or - 1 percent RMS. The converter is to operate at an ambient temperature of -40 C with 16 minute power pulses and one hour off time. The uniqueness of the design in Phase 1 resided in the dc switching array which operates the converter at 20 kHz using Hollotron plasma switches along with a specially designed low loss, low leakage inductance and a light weight high voltage transformer. This approach reduced considerably the number of components in the converter thereby increasing the system reliability. To achieve an optimum transformer for this application, the design uses four 25 kV secondary windings to produce the 100 kV dc output, thus reducing the transformer leakage inductance, and the ac voltage stresses. A specially designed insulation system improves the high voltage dielectric withstanding ability and reduces the insulation path thickness thereby reducing the component weight. Tradeoff studies and tests conducted on scaled-down model circuits and using representative coil insulation paths have verified the calculated transformer wave shape parameters and the insulation system safety. In Phase 1 of the program a converter design approach was developed and a preliminary transformer design was completed. A fault control circuit was designed and a thermal profile of the converter was also developed
Developing vanadium redox flow technology on a 9-kW 26-kWh industrial scale test facility: Design review and early experiments
Redox Flow Batteries (RFBs) have a strong potential for future stationary storage, in view of the rapid expansion of renewable energy sources and smart grids. Their development and future success largely depend on the research on new materials, namely electrolytic solutions, membranes and electrodes, which is typically conduced on small single cells. A vast literature on these topics already exists. However, also the technological development plays a fundamental role in view of the successful application of RFBs in large plants. Despite that, very little research is reported in literature on the technology of large RFB systems. This paper presents the design, construction and early operation of a vanadium redox flow battery test facility of industrial size, dubbed IS-VRFB, where such technologies are developed and tested. In early experiments a peak power of 8.9 kW has been achieved with a stack specific power of 77Wkg−1. The maximum tested current density of 635 mA cm−2 has been reached with a cell voltage of 0.5 V, indicating that higher values can be obtained. The test facility is ready to be complemented with advanced diagnostic devices, including multichannel electrochemical impedance spectroscopy for studying aging and discrepancies in the cell behaviors
Hybrid performance modelling of opportunistic networks
We demonstrate the modelling of opportunistic networks using the process
algebra stochastic HYPE. Network traffic is modelled as continuous flows,
contact between nodes in the network is modelled stochastically, and
instantaneous decisions are modelled as discrete events. Our model describes a
network of stationary video sensors with a mobile ferry which collects data
from the sensors and delivers it to the base station. We consider different
mobility models and different buffer sizes for the ferries. This case study
illustrates the flexibility and expressive power of stochastic HYPE. We also
discuss the software that enables us to describe stochastic HYPE models and
simulate them.Comment: In Proceedings QAPL 2012, arXiv:1207.055
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Interlaminar Toughening of Fiber Reinforced Polymers
Modification in the resin-rich region between plies, also known as the interlaminar region, was investigated to increase the toughness of laminate composites structures. To achieve suitable modifications, the complexities of the physical and chemical processes during the resin curing procedure must be studied. This includes analyses of the interactions among the co-dependent microstructure, process parameters, and material responses. This dissertation seeks to investigate these interactions via a series of experimental and numerical analyses of the geometric- and temperature-based effects on locally interleaving toughening methods and further interlaminar synergistic toughening without interleaf.
Two major weaknesses in composite materials are the brittle resin-rich interlaminar region which forms between the fiber plies after resin infusion, and the ply dropoff region which introduces stress concentration under loads. To address these weaknesses and increase the delamination resistance of the composite specimens, a dual bonding process was explored to alleviate the dropoff effect and toughen the interlaminar region. Hot melt bonding was investigated by applying clamping pressure to ductile thermoplastic interleaf and fiber fabric at an elevated temperature, while diffusion bonding between thermoplastic interleaf and thermoset resin is performed during the resin infusion. This method increased the fracture energy level and thus delamination resistance in the interlaminar region because of deep interleaf penetration into fiber bundles which helped confining crack propagation in the toughened area.
The diffusion and precipitation between thermosets and thermoplastics also improved the delamination resistance by forming a semi-interpenetration networks. This phenomenon was investigated in concoctions of low-concentration polystyrene additive modified epoxy system, which facilitates diffusion and precipitation without increasing the viscosity of the system. Additionally, chemical reaction induced phase separation, concentration of polystyrene, and various curing temperatures are used to evaluate their effects on diffusion and precipitation. These effects were directly investigated by performing attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). The diffusivity and curing kinetics experiments are performed to quantify the diffusivity coefficient of epoxy, hardener and thermoplastics, as well as the reaction rate constant of curing epoxy at various temperatures. Finally, mechanical testing and fracture surface imaging were used to quantify the improvements and characterize the toughening mechanism.
Further improvement on delamination resistance was studied through the synergistic effect of combining different modification methods without the interleaf. Polysulfone molecules are end-capped with epoxide groups. Fiber surface is functionalized with amino groups to generate micro-mechanical interlocks. The interaction between two individual modifications chemically links the modified semi-interpenetration networks to the improved interfacial strength between fiber and epoxy to. The impact of the additive on the crosslinking density was examined through glass transition temperatures, and the chemical modification was characterized by Raman spectroscopy. Mode I and II fracture tests were performed to quantify the improvement of delamination resistance under pure opening and shear loads. The mechanism of synergistic effect was explained based on the fracture surface morphology and the interactions between the modification methods
Composite Materials in Design Processes
The use of composite materials in the design process allows one to tailer a component’s mechanical properties, thus reducing its overall weight. On the one hand, the possible combinations of matrices, reinforcements, and technologies provides more options to the designer. On the other hand, it increases the fields that need to be investigated in order to obtain all the information requested for a safe design. This Applied Sciences Special Issue, “Composite Materials in Design Processes”, collects recent advances in the design methods for components made of composites and composite material properties at a laminate level or using a multi-scale approach
Nondestructive Evaluation (NDE) Methods and Capabilities Handbook - Volume II Appendices - Appendix A - Appendix D
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06241 Abstracts Collection -- Human Motion - Understanding, Modeling, Capture and Animation. 13th Workshop
From 11.06.06 to 16.06.06, the Dagstuhl Seminar 06241 ``Human Motion - Understanding, Modeling, Capture and Animation. 13th Workshop "Theoretical Foundations of Computer Vision"\u27\u27 was held
in the International Conference and Research Center (IBFI),
Schloss Dagstuhl.
During the seminar, several participants presented their current
research, and ongoing work and open problems were discussed. Abstracts of
the presentations given during the seminar as well as abstracts of
seminar results and ideas are put together in this paper. The first section
describes the seminar topics and goals in general
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