FETI‐DP: a dual–primal unified FETI method—part I: A faster alternative to the two‐level FETI method

The FETI method and its two‐level extension (FETI‐2) are two numerically scalable domain decomposition methods with Lagrange multipliers for the iterative solution of second‐order solid mechanics and fourth‐order beam, plate and shell structural problems, respectively.The FETI‐2 method distinguishes itself from the basic or one‐level FETI method by a second set of Lagrange multipliers that are introduced at the subdomain cross‐points to enforce at each iteration the exact continuity of a subset of the displacement field at these specific locations. In this paper, we present a dual–primal formulation of the FETI‐2 concept that eliminates the need for that second set of Lagrange multipliers, and unifies all previously developed one‐level and two‐level FETI algorithms into a single dual–primal FETI‐DP method. We show that this new FETI‐DP method is numerically scalable for both second‐order and fourth‐order problems. We also show that it is more robust and more computationally efficient than existing FETI solvers, particularly when the number of subdomains and/or processors is very large. Copyright © 2001 John Wiley & Sons, Ltd.     

The effects of Ni3Al binder content on the electrochemical response of melt-infiltration processed TiC–Ni3Al cermets

TiC–Ni₃Al samples were successfully fabricated with varying amounts of the Ni₃Al intermetallic binder (alloy IC-50), ranging from 10 to 40?wt-%, through a simple melt-infiltration method. Each sample was then tested to determine the degree of resistance of that composition to electrochemical corrosion in an aqueous solution containing 3.5?wt-% NaCl, using a range of testing procedures including open-circuit potential, potentiodynamic polarisation and cyclic polarisation. Results indicate that the lowest binder content results in greater potential to resist corrosion. It is demonstrated that the Ni₃Al binder undergoes dissolution for the examined conditions, which was confirmed through the high amount of Al and Ni in the electrolyte solutions following testing. It was also confirmed from the electrochemical experiments and the SEM that localised corrosion was visible.     

Cathodic titania nanotube arrays as anode material for lithium-ion batteries

The titanium dioxide nanotube arrays (TNAs) have been synthesized at cathode and anode via standard electrochemical method for their subsequent use as anode material for lithium-ion batteries (LIBs). The TNAs fabricated at cathode have higher Ti³⁺ in comparison to TNAs at anode, which was confirmed using X-ray photoelectron spectroscopy and Raman spectrometry. Moreover, the lattice parameters of cathodic TNAs are estimated via Rietveld refinement of X-ray diffraction, which also conform to Ti³⁺ doping and insertion of protons (H⁺). The electrochemical impedance spectroscopy hints an increment in the electronic conductivity of TNAs fabricated at cathode. As a result, high reversible areal–specific capacity (~385.5 µAh cm^?2 at 100 µA cm^?2) with excellent rate capability is acquired by utilizing TNAs fabricated at cathode as anode material in LIBs.     

Comminution limit (CL) of particles and possible implications for pumped storage reservoirs

Comminution (fragmentation) of solid particles is important in a range of technologies. An interesting effect is the so-called comminution limit (CL), which is effectively a brittle/ductile transition. Above the CL particles fail by fracture. However, as particle size decreases the amount of stored energy in the particle also decreases and eventually there is no longer sufficient stored energy in the particle to propagate a crack and the particle flows plastically. The CL depends on the hardness, H, and the toughness, K _Ic. In mountainous countries, two-reservoir systems are used to generate and store power. When power is needed, water runs through the turbines to the lower reservoir. If there is excess power, water is pumped to the upper reservoir. This recycling of liquid through the turbines can break up entrained particles. Previous work in this area has been primarily concerned with sedimentation of the particles. The research reported in this paper uses the CL to calculate the particle sizes produced for different materials including different rock types. Interestingly, the particle sizes predicted mainly fall in the range where they sediment near the upper water surface. In such cases, the surface layers become opaque to sunlight and plant and animal life will be affected. It is suggested that the CL provides additional information which would assist research in this area. Where H and K _Ic are not known for a particular rock type they should be measured.     

Performance evaluation of a thermodynamic solar power plant: fifteen years of operation history

The thermodynamic solar power plant of the National Institute for Scientific Research in Tunisia has been in operation since 1984. The plant served as a pilot unit for exploring the technical reliability and evaluating the economic feasibility of the process of converting solar thermal energy into electricity. This paper consists of a close evaluation and analysis of the long-term performance of the system and a review of 15 years of successful operation. The aim of this study was to go over the main problems and technical difficulties encountered and pinpoint the major factors affecting the plant operation in order to identify the optimal operating policies toward the enhancement of the plant efficiency. Even though the thermal performance of the plant was relatively low, the impact of such a plant on the energy sector of the country was significant in terms of energy saving and environmental protection. In regions with high solar radiation such as Tunisia with a daily mean insolation of 4.8 kWh m⁻², the use of solar power plants — similar to this one — essentially for heat production prove to be a good alternative especially for remote and rural areas.     

Catalytic coprocessing of coal and petroleum residues with waste plastics to produce transportation fuels

Coprocessing reactions with waste plastics, petroleum residues and coal were performed to determine the individual and blended behavior of these materials using lower pressure and cheaper catalysts. The plastic used in this study was polypropylene. The thermodegradative behavior of polypropylene (PP) and PP/petroleum residues/coal blends were investigated in the presence of solid hydrocracking (HC) catalysts. A comparison among various catalysts has been performed on the basis of observed temperatures. The higher temperatures of initial weight loss of PP shifted to lower values by the addition of petroleum residues and coal. The catalysts were also tested in a fixed-bed micro reactor for the pyrolysis of polypropylene, petroleum residues and coal, alone and blended together in nitrogen and hydrogen atmosphere. High yields of liquid fuels in the boiling range 100-480 °C and gases were obtained along with a small amount of heavy oils and insoluble material such as gums and coke. The results obtained on the coprocessing of polypropylene with coal and petroleum residues are very encouraging as this method appears to be quite feasible to convert plastic materials into liquefied coal products and to upgrade the petroleum residues and waste plastics.