Sahar Noor

Hybrid Genetic Algorithm (GA) for job shop scheduling problems and its sensitivity analysis

The Job Shop Scheduling Problem (JSSP) is a hard combinatorial optimisation problem. This paper presents a heuristic-based Genetic Algorithm (GA) or Hybrid Genetic Algorithm (HGA) with the aim of overcoming the GA deficiency of fine tuning of solution around the optimum, and to achieve optimal or near optimal solutions for benchmark JSSP. The paper also presents a detail GA parameter analysis (also called sensitivity analysis) for a wide range of benchmark problems from JSSP. The findings from the sensitivity analysis or best possible parameter combination are then used in the proposed HGA for optimal or near optimal solutions. The experimental results of the HGA for several benchmark problems are encouraging and show that HGA has achieved optimal solutions for more than 90% of the benchmark problems considered in this paper. The presented results will provide a reference for selection of GA parameters for heuristic-based GAs for JSSP.

PARAMETRIC ANALYSIS OF VARIOUS CONTROL ALGORITHMS FOR SEMI-ACTIVE SUSPENSION SYSTEM

The research paper involves modeling of passive and semi-active suspension systems using quarter car model. Different systems incorporating control strategies of groundhook, skyhook and hybrid are modeled on the basis of fuzzy logic control. A novel optimized control system is also developed that utilizes relative displacement and relative velocity across the masses as inputs to the fuzzy logic controller resulting in the output of modulating damping coefficient. A comparison of all the designed systems is carried out with the passive system for ascertaining ride comfort and road handling characteristics. The optimized system outperforms all other systems in both the parameters based on the rapid stabilizing time and minimum percentage overshoot. The optimized system comprises three membership functions for each of the inputs resulting in only nine rules thus enabling faster processing of the controller besides improved performance. The results manifest successful designing of an optimized fuzzy logic based control strategy for semi-active suspensions.

IMPLEMENTATION OF KANBAN SYSTEM AT THE SHOP FLOOR OF A MULTINATIONAL COMPANY

Streamlining and managing flow of material in high volume production lines reduce the cost in terms of reduction of Work-In-Progress (WIP). Kanban system, which acts as a nerve of JIT production, is being used worldwide due to its simplicity and ability to reduce inventories and production lead times. This paper presents a case study of a successful attempt of implementation of Kanban System (KS) at shop floor of a Multi National Tobacco Factory (MNTF). A traditional Push system was replaced by Pull system with the objectives to reduce filter rods and quantity of raw material at workstations. The conversion from PUSH lo KS simplifies the material issuing procedure and benefits the company by reducing lead-time, Work-In-Process and inventory of finished items. The reduction of WIP is estimated about 59% which resulted in 42.99 million Pakistani Rupees (PKR) savings for the company.

DEVELOPMENT OF TAR-BONDED DOLOMITE BRICKS FOR STEEL LADLES

Steel ladles at Pakistan Steel have been lined with fireclay bricks and the ladle life remained around 8-9 heats. Steel produced remained dirty due to Alumino-silicate bricks and high tapping temperature. Also production was affected due to non-availability of ladles. In order to de-bottleneck and enhance production with quality it was decided to introduce the concept of using dolomite bricks in the steel ladles. initial hit and trial results showed improvement of campaign life from 8-9 heats to 21-25 heats. Work is undertaken to investigate scientifically total process starting from raw dolomite, calcinations/dead burning, to produce dolomite sinter/crushing, milling, mixing with tar, pressing into brick shape for lining of steel ladles. The level of performance improvement with the dolomite lining over alumino-silicate material is also dependent on steel making and pouring condition such as tapping temperature, ferocity of impact, slag basicity/chemistry and finally the total residence time. it is expected that the ladle life should increase up to 40-50 heats, once the factors adversely affecting the campaign life, are controlled.

CASTING ANALYSIS AND QUALITY IMPROVEMENT OF STEEL GRADES WR-67 AND WR-62

Two steel grades WR-67 and WR-62 cast at Pakistan Steel were analysed for variation in properties of the same grade and heat. Homogenization status of liquid steel and macro segregation aspect during solidification with different continuous casting parameters were focused and it was found that non-homogenization of liquid steel in ladle leads the steel grades to exhibit non-uniform properties of the same grade and was no axial ( centreline ) segregation bot in billet and bloom. Increasing trend of porosity from surface to centre was observed. Increased purging time and installation of electromagnetic stirrer at mould were recommended for elimination of segregation, achieving good cast structure of bloom and billet and having uniform properties.