Beschreibung: In order to study the impact of an expanding conjunction (with a divergent conjunction or with an abruptly expanding conjunction) between a stilling basin and the downstream channel on the height after jump, systematic experimental studies were carried out with different divergent angles and different abrupt expansion ratios at the conjunction. The link between the conjunction type and the height after jump is explored. The height after jump without an expanding conjunction is larger than that with a divergent conjunction, while the height after a jump without an expanding conjunction is larger than that with the abrupt expanding conjunction. Furthermore, with a larger divergent angle or larger expansion ratio, the impact on the height after jump becomes more variable. It is proposed that the existing formula which is used to calculate the height after jump in a straight channel is not appropriate for a jump with an expanding conjunction. This paper proposes a corrected formula to calculate the height after jump with an expanding conjunction, which is suggested for application in the engineering design process.

Beschreibung: In the oil and gas industry, crude oil is frequently transported and centrifugal pumps are used extensively. The pump impeller works under both design and off-design conditions in the applications, and the flow pattern deviates from the ideal case because of viscosity and density changes. An experimental as well as a numerical study was conducted to study the performance of a pump delivering water and light crude oil under design and off-design conditions. A 3D steady incompressible flow in the centrifugal pump was simulated by solving the Reynolds-averaged Navier–Stokes equations and SST turbulence model. At a low flow rate, extensive reverse flow occurs at the inlet of the impeller in the case of water, whereas the opposite was found for light crude oil. Recirculation was observed in the impeller flow passage for both water and the crude oil, but this diminished at higher flow rates.

Beschreibung: Externally bonded method would be the most potential technique for optimal shear strengthening of deficient reinforced concrete (RC) beam subjected to eliminate premature debonding failure. The main aim of this research was to eliminate debonding failure of steel plate using embedded connector systems for optimal shear strengthening of RC beam. Dimensions of steel plates were optimized based on the proposed design guideline in accordance with EC2. The strengthened beams with connectors were then compared with those of U-jacketing system. Bond strength enhancements of steel plate using connectors were experimentally investigated through pullout test of prisms. The beam specimens were fabricated and tested to investigate the effects of embedded connectors. Result showed that steel bar and adhesive embedded connectors significantly increased the bond strength of externally bonded plates. The connectors completely prevented premature debonding failure of steel plates and allowed the beams to fail by flexure with full ductility and strength, whereas U-jacket showed the premature debonding of plates. The embedded connectors optimized/reduced the dimension of the externally bonded steel plate by 60% as compared to those of arbitrarily strengthened beam. The experimental results satisfactorily verified the proposed design guideline.

Beschreibung: Current manufacturing trend adopts newer technology that can reduce both the design and manufacturing lead time in order to face the challenging demands of the customer in an effective manner. In this regard, rapid prototyping technology, among all newly developed technologies, is reliable one because it is capable of manufacturing accurate and durable parts with 3D complex geometry within a stipulated time with less material waste. In this research work, effect of six relevant controllable input parameters (contour number or external perimeter, layer thickness, raster width, part orientation, air gap and raster angle) on flexural strength of the fused deposition modelling (FDM) build parts is analysed. Experimentation has been carried out using face-centred central composite design to reduce the number of experimentation. Contour number appears to be more influencing parameter because it helps to move the stress concentration zone from outer edge to the centre avoiding premature failure of the specimen. The study develops a statistically valid empirical model relating flexural strength with process parameters to ease prediction of flexural strength by tool engineers. Scanning electron microscope micrographs are used to explain the microstructure behaviour of FDM build parts when subjected to three point bend test. Finally, one nature-inspired metaheuristic approach known as Firefly algorithm is adopted to obtain optimal parameter setting for improving the flexural strength.

Beschreibung: In order to improve the tribological properties of titanium alloys at high temperature, the possibility of producing Ti \(_{3}\) Al intermetallic with the addition of ceramic (cBN) coatings on titanium substrate using laser technique cladding was investigated. cBN is generally known for its high hot hardness, wear resistance and chemical stability. Laser cladding is an emerging material processing technique which is an efficient and cost-effective technique for improving the surface properties of general metallic materials. This paper presents the effects of laser cladding on the phase combination, microstructure, hardness and wear resistance of titanium aluminide/cBN IMC composites at different variations in quantity of cBN in the composite. Optical microscopy, X-ray diffraction and scanning electron microscopy with EDX were used for characterising the microstructure of the coating. In addition, the composite coating was subjected to wear testing using the ball-on-disc, friction and wear apparatus. The XRD results revealed phases with small cBN, \(\hbox {Ti}_{2}\hbox {N}\) and \(\hbox {TiB}_{2}\) peaks in addition to the rich \(\gamma \) -Ti, \(\alpha 2\hbox {-Ti}_{3}\hbox {Al}\) and TiAl intermetallics phases in the coatings after cladding process, whereas the microstructure of the cBN cladded layer contained partially melted cBN grains evenly dispersed within the laths of alpha Widmanstätten phase in the form of dendrites, precipitate of \(\alpha _{2}\hbox {-Ti}_{3}\hbox {Al}\) and spherical-shaped pure titanium. The effect of the addition of cBN into \(\hbox {Ti}_{3}\hbox {Al}\) alloy at increasing weight percentages showed an improvement in the hardness and wear resistance of the coatings. The increase is attributed to reacted boron nitrides particles with titanium, being distributed uniformly in the intermetallic matrix.

Beschreibung: A one-dimensional fluid model has been developed and used to investigate a capacitively coupled discharge operating on a pure water vapor and on a mixture of water with helium. These models incorporate 29 main species and 81 dominant reaction channels. The effects of gas pressure and gap distance on the production of some species are discussed. The simulation results reveal that the plasma ignition in a pure water vapor can only be reached at low pressure when all dominant reactions are included in the model. The main mechanism by which the plasma ignition is suppressed may be attributed to the high rate of electron cooling. It is worth indicating that the creation rates of the vibrationally and rotationally excited states in water vapor compared to ionization are much more higher than they are in noble gases, such as argon or helium. As a result, this might be the main reason why the ignition of He plasma is easier when applying the same operating parameters. Therefore, two approaches are suggested to overcome this difficulty. The first one lies in decreasing the gas pressure to around \(10^3\) Pa, and the gap distance to 0.5 mm. And the second one is by adding a small fraction (5%) of \(\mathrm{H}_2\mathrm{O}\) to (95%) of helium and keeping the gap distance at 1 mm. The input parameters for plasma ignition have been identified, and the density profiles of the main species are reported and discussed.

Beschreibung: Gansu province wind energy potential in China is around 237 GW. According to the schedule, 20 GW wind energy is connected to the grid by 2020. However, there is a chance of instability in the presence of big intermittency. To integrate this huge generated wind power, a reliable control strategy is required. The proposed portable power plant (PPP) energy storage system is fully compatible with a smart grid and mitigates the dispatching complexity and provides better designing and implementation of Gansu wind farm in China. In a two-way power flow, when the generation is bigger than the load demand, the additional power is stored in the PPP for future use, and when the demand is higher than the total generation, the stored power is applied to feed the grid. Also the PPP can charge the grid during peak demand periods or when the local network is stressed. An intelligent controller is linked with PPP to monitor the power flow. The stator flux-oriented vector method is used for modeling the system. Then, a fuzzy controller is applied to adjust the modulation index of PWM inverter and also uses energy storage units to stabilize the output of the power plant. Real field data of the Gansu wind farm with 24-h horizon have been applied on the proposed system. The results show the high performance of the fuzzy-based PPP system in the presence of fluctuations and increase the efficiency of the power system by storing energy through PPP. With a large-scale plan for application of smart grid and renewable energy sources in China, this paper introduces an essential step of this vision to provide a feasible framework for future large-scale smart grid projects in China as well as stable operation of Gansu wind farm as the biggest wind farm in mainland when it is completed.

Beschreibung: The coagulant chitosan and poly(diallyldimethylammonium chloride) (PDDA) were proven effective to aid the sedimentation of microalgal cells through electrostatic patch flocculation. A total amount of 30 mg/L chitosan and PDDA can achieve cell separation efficiency of \(96.7 \pm 0.7\) and \(98.4 \pm 1.0\) %, respectively. The chitosan outperformed PDDA and promoted 4.4 times faster rate of cell sedimentation than the self-sedimentation rate of cells. The chitosan employed the mechanism of charge neutralization to form larger flocs, while the PDDA that favored the formation of loops and tails protruding away from cell surface employed the bridging mechanism to form flocs. The rate of cell sedimentation induced by chitosan was the highest at pH 7, 8 (control) and 9 compared to that of PDDA, where the cell flocculation by using chitosan was dominated by charge neutralization mechanism at pH 7 and 8 (control), while the cell flocculation was mainly driven by bridging mechanism at pH 9. This result shows that the chitosan is feasible in the harvesting of freshwater microalgae without the need of pH adjustment. Therefore, the chitosan was proven more reliable and time effective than the PDDA in harvesting the freshwater Chlorella sp. without the need of pH adjustment.

Beschreibung: Cloud computing providers have to deal with the energy-performance trade-off: minimizing energy consumption, while meeting service level agreement (SLA) requirements. This paper proposes a new heuristic approach for the dynamic consolidation of virtual machines (VMs) in cloud data centers. The fast best-fit decreasing (FBFD) algorithm for intelligent VMs allocating into hosts and dynamic utilization rate (DUR) algorithm for utilization space and VM migration are successfully proposed. We performed simulations using PlanetLab and GWDG data center workloads to compare our approach against the existing models. It has been observed that the FBFD heuristic algorithm produces better results compared to modified BFD algorithm in terms of energy consumption and SLA violation. Additionally, the time complexity of FBFD algorithm is significantly improved from the order of O( \(m\,*\,n\) ) to O( \(m\,*\,\log _2{n}\) ). Furthermore, leaving some rates of capacity in the physical machines by the proposed DUR algorithm for VMs to be extended reduces the number of migrations which in turn improves the energy consumption and SLA violation. Our heuristic approach is evaluated using CloudSim and the results show that it performs better than the current state-of-the-art approaches.

Beschreibung: Class cohesion has an immediate impact on maintainability, modifiability and understandability of the software. Here, a new metric of cohesion based on complex networks (CBCN) for measuring connectivity of class members was developed mainly relying on calculating class average clustering coefficient from graphs representing connectivity patterns of the various class members. In addition, the CBCN metric was assessed with theoretical validation according to four properties (nonnegativity and normalization, null and maximum values, monotonicity, cohesive modules) of the class cohesion theory. Based on data comparison with existing seventeen typical class cohesion metrics of class cohesion for a system, the CBCN metric was superior to others. Applying the CBCN metric to three open source software systems to calculate class average clustering coefficients, we found that understanding, modification and maintenance of classes in an open software system could be likely less difficult compared with those of others. Three open software systems have power-law distributions for the class average clustering coefficient, which makes possible the further understanding of the cohesion metric based on complex networks.