Zulfiqar Ahmad Khan

Bio: Zulfiqar Ahmad Khan is an academic researcher from Bournemouth University. The author has contributed to research in topics: Corrosion & Coating. The author has an hindex of 25, co-authored 121 publications receiving 2154 citations. Previous affiliations of Zulfiqar Ahmad Khan include University of Toledo & Johnson Controls.

Wireless connector with a hollow telescopic waveguide

Abstract: Wireless connectors and communication systems are described including a first communication device configured to emit a modulated signal, a second communication device configured to receive the emitted modulated signal and a waveguide disposed between the first and second communication devices and configured to wirelessly receive the emitted modulated signal from a first end of the waveguide, guide the received signal from the first end to an opposite second end of the waveguide, and wirelessly transmit the guided signal from the second end to the second communication device. In some embodiments, the telescopic waveguide includes a plurality of guiding sections, each guiding section being configured to slide within or over an adjacent guiding section inwardly to reduce a length of the telescopic waveguide and outwardly to increase the length of the telescopic waveguide.

Current tidal power technologies and their suitability for applications in coastal and marine areas

Abstract: A considerable body of research is currently being performed to quantify available tidal energy resources and to develop efficient devices with which to harness them. This work is naturally focussed on maximising power generation from the most promising sites, and a review of the literature suggests that the potential for smaller scale, local tidal power generation from shallow near-shore sites has not yet been investigated. If such generation is feasible, it could have the potential to provide sustainable electricity for coastal homes and communities as part of a distributed generation strategy, and would benefit from easier installation and maintenance, lower cabling and infrastructure requirements and reduced capital costs when compared with larger scale projects. This article reviews tidal barrages and lagoons, tidal turbines, oscillating hydrofoils and tidal kites to assess their suitability for smaller scale electricity generation in the shallower waters of coastal areas at the design stage. This is achieved by discussing the power density, scalability, durability, maintainability, economic potential and environmental impacts of each concept. The discussion suggests that tidal kites and range devices are not well suited toward small-scale shallow water applications due to depth and size requirements, respectively. Cross-flow turbines appear to be the most suitable technology, as they have high power densities and a maximum size that is not constrained by water depth. Oscillating hydrofoils would also be appropriate, provided comparable levels of efficiency can be achieved.

Ceramic rolling elements with ring crack defects—A residual stress approach

Abstract: Experimental results of rolling contact fatigue on ceramic bearing elements with refrigerant lubrication are presented. Residual stress measurements located on the contact path and other locations on the surface are described. An X-ray method was employed. Residual stress measurements are helpful in predicting rolling contact fatigue life. In addition, analysing the relationship of residual stress with rolling contact fatigue is an important study, which will provide guidelines on the design, process and manufacturing of these elements. During this research, ring crack defects were induced in ceramic rolling contact bearing elements. A compressive residual stress value of −73 MPa near the ring crack and a comparatively lower value of −12 MPa on the contact indicate sub-surface crack initiation and propagation. The average fatigue spall ranges from 100 to 148 μm in depth. Within the spall area residual stress measurements suggest that compressive residual stress is relieved much faster in the region of sub-surface damage.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

VALIDITY OF CUBIC LAW FOR FLUID FLOW IN A DEFORMABLE ROCK FRACTURE - eScholarship

Abstract: The validity of the cubic law for laminar flow of fluids through open fractures consisting of parallel planar plates has been established by others over a wide range of conditions with apertures ranging down to a minimum of 0.2 µm. The law may be given in simplified form by Q/Δh = C(2b)3, where Q is the flow rate, Δh is the difference in hydraulic head, C is a constant that depends on the flow geometry and fluid properties, and 2b is the fracture aperture. The validity of this law for flow in a closed fracture where the surfaces are in contact and the aperture is being decreased under stress has been investigated at room temperature by using homogeneous samples of granite, basalt, and marble. Tension fractures were artificially induced, and the laboratory setup used radial as well as straight flow geometries. Apertures ranged from 250 down to 4µm, which was the minimum size that could be attained under a normal stress of 20 MPa. The cubic law was found to be valid whether the fracture surfaces were held open or were being closed under stress, and the results are not dependent on rock type. Permeability was uniquely defined by fracture aperture and was independent of the stress history used in these investigations. The effects of deviations from the ideal parallel plate concept only cause an apparent reduction in flow and may be incorporated into the cubic law by replacing C by C/ƒ. The factor ƒ varied from 1.04 to 1.65 in these investigations. The model of a fracture that is being closed under normal stress is visualized as being controlled by the strength of the asperities that are in contact. These contact areas are able to withstand significant stresses while maintaining space for fluids to continue to flow as the fracture aperture decreases. The controlling factor is the magnitude of the aperture, and since flow depends on (2b)3, a slight change in aperture evidently can easily dominate any other change in the geometry of the flow field. Thus one does not see any noticeable shift in the correlations of our experimental results in passing from a condition where the fracture surfaces were held open to one where the surfaces were being closed under stress.

Review on thermal conductivity enhancement, thermal properties and applications of phase change materials in thermal energy storage

Abstract: In recent years, energy conservation and environmental protection have become most important issues for humanity. Phase change materials (PCMs) for thermal energy storage can solve the issues of energy and environment to a certain extent, as PCMs can increase the efficiency and sustainability of energy. PCMs possess large latent heat, and they store and release energy at a constant temperature during the phase change process. Thereby PCMs have gained a wide range of applications in various fields, such as buildings, solar energy systems, power systems and military industry. However, low thermal conductivity of PCMs leads to low heat transfer rate, thus, numerous studies have been carried out to improve thermal conductivity of PCMs. The main purpose of this paper is to review the methods for enhancing thermal conductivity of PCMs, which include adding additives with high thermal conductivity and encapsulating phase change materials. It is found that addition of thermal conductivity enhancement fillers is a more effective method to improve thermal conductivity of PCMs, where carbon-based material additives possess a more promising application prospect. Finally, the applications of PCMs in solar energy system, buildings, cooling system, textiles and heat recovery system are also analyzed.