Multi-Objective Flexible Job Shop Scheduling Using Genetic Algorithms

Flexible Job Shop Scheduling is an important problem in the fields of combinatorial optimization and production management. This research addresses multi-objective flexible job shop scheduling problem with the objective of simultaneous minimization of: (1) makespan, (2) workload of the most loaded machine, and (3) total workload. A general-purpose, domain independent genetic algorithm implemented in a spreadsheet environment is proposed for the flexible job shop. Spreadsheet functions are used to develop the shop model. Performance of the proposed algorithm is compared with heuristic algorithms already reported in the literature. Simulation experiments demonstrated that the proposed methodology can achieve solutions that are comparable to previous approaches in terms of solution quality and computational time. Flexible job shop models presented herein are easily customizable to cater for different objective functions without changing the basic genetic algorithm routine or the spreadsheet model. Experimental analysis demonstrates the robustness, simplicity, and general-purpose nature of the proposed approach

Effect of a Support Tower on the Performance and Wake of a Tidal Current Turbine

Tidal energy is one of the major sources of renewable energy. To accelerate the development of tidal energy, improved designs of Tidal Current Turbine (TCT) are necessary. The effect of tower on performance and wake of TCT is investigated using Computational Fluid Dynamics (CFD) simulations. Transient analysis with transient rotor stator frame change model and shear stress transport turbulence model are utilized in ANSYS CFX. An experimentally validated numerical model with full scale tidal turbine with a blockage ratio of 14.27% and Tip Speed Ratio (TSR) 4.87 is used to simulate the effect of different tower diameters on performance and wake. The effect of different tower diameters is quantified in terms of coefficient of performance (CP). Coefficient of performance for a 3.5 m tower diameter is 0.472 which is followed by 3, 2.5 and 2 m with coefficients of performance of 0.476, 0.478 and 0.476 respectively. Similarly, the coefficient of thrust (CT) on the rotor for 3.5 m tower diameter is 0.902, for 3 m diameter 0.906 and for 2.5 and 2 m diameters are 0.908 and 0.906 respectively

Characterization of PTFE Film on 316L Stainless Steel Deposited through Spin Coating and Its Anticorrosion Performance in Multi Acidic Mediums

Polytetrafluoroethylene (PTFE) was coated on 316L stainless steel (SS) substrate through a spin coating technique to enhance its corrosion resistance properties in hydrochloric acid (HCl) and nitric acid (HNO3) medium. Scanning electron microscopy (SEM) revealed the morphology of the coated and uncoated substrates and showed a uniform and crack-free PTFE coating on 316L SS substrate, while a damaged surface with thick corrosive layers was observed after the electrochemical test on the uncoated sample. However, an increased concentration of HCl and HNO3 slightly affected the surface morphology by covering the corrosive pits. An atomic force microscope (AFM) showed that the average surface roughness on 316L SS and PTFE coating was 26.3 nm and 24.1 nm, respectively. Energy dispersive X-ray spectroscopy (EDS) was used for the compositional analysis, which confirmed the presence of PTFE coating. The micro Vickers hardness test was used to estimate the hardness of 316L SS and PTFE-coated substrate, while the scratch test was used to study the adhesion properties of PTFE coating on 316L SS. The anticorrosion measurements of 316L SS and PTFE-coated substrates were made in various HCl and HNO3 solutions by using the electrochemical corrosion test. A comparison of the corrosion performance of PTFE-coated substrate with that of bare 316L SS substrate in HCl medium showed a protection efficiency (PE) of 96.7%, and in the case of HNO3 medium, the PE was 99.02%, by slightly shifting the corrosion potential of the coated sample towards the anodic direction

Mechanism of Fatigue Crack Growth in Biomedical Alloy Ti-27Nb

Implants are widely used in the human body for the replacement of affected bones. Fatigue failure is one of the serious concerns for implants. Therefore, understanding of the underlying mechanism leading to fatigue failure is important for the longevity of biomaterial implants. In this paper, the fracture toughness and fatigue crack growth of titanium alloy biomaterial Ti-27Nb has been experimentally investigated. The Ti-27Nb material is tested for fatigue crack growth in different environmental conditions representing the ambient and in vitro environments for 504 hours and 816 hours, respectively. Fractography of the tested specimen is conducted using Scanning Electron Microscope (SEM). The results of the fatigue crack growth propagation of the ambient and in vitro samples are similar in the Paris crack growth region. However, in the threshold region, the crack growth rate is higher for the Simulated Body Fluid (SBF) treated specimen. The fracture surface morphology of in vitro samples shows brittle fracture as compared to ambient specimens with significant plasticity and striations marks. It is proposed that a similar investigation may be conducted with specimens treated in SBF for prolonged periods to further ascertain the findings of this study