THE DESIGN AND OPERATION OF Flexible Job-Shop FOR MAKESPAN MINIMIZATION

M.Sc. student - Oshrat Lalush Yechiel

Abstract

Nowadays, firms are facing competitive and dynamic environments, where it is required to customize products while providing high service level and utilization of resources. Flexibility is an important tool to achieve those goals, as operations can be routed to multiple machines that were configured to perform various tasks. As a result, machine utilization is improved and jobs completion times might be shortened. In this talk, we address the problem of simultaneously determining the machine flexibility and job scheduling in a job-shop environment. The problem is combined of two inter-related well studied problems which so far were examined separately. The first involves selecting a process flexibility configuration, while the second consists of assigning and scheduling job operations to machines, given the chosen flexibility. The solution to each of these problems has a major impact on the other, therefore it is important to examine them simultaneously. Our work first investigates the symmetric case, for which an optimal analytical solution with an interesting structure is detected. When generalizing the problem to asymmetric cases, we show that some of them can still be solved to optimality by the same procedure, while others are shown to be NP-Hard. For an important class of asymmetric cases, a heuristic is developed, which is shown to perform very well.

This work was performed under the supervision of Prof. Yossi Bukchin and Prof. Michal Tzur.

ההרצאה תתקיים ביום חמישי 4/12/14, בשעה 12:00 בחדר 206, בנין וולפסון הנדסה, הפקולטה להנדסה, אוניברסיטת תל-אביב.

School of Mechanical Engineering Seminar
Wednesday, December 24, 2014 at 15:00
Wolfson Building of Mechanical Engineering, Room 206

Natural Convection in Non-Uniformly Heated Open-Ended Channels

Prof. Victoria Timchenko

MSc/PhD Student of Prof. Supervisor

School of Mechanical and Manufacturing Engineering,

  University of New South Wales, Sydney, Australia.

To improve understanding of the flow and heat transfer phenomena in narrow, open-ended, channel formed by the double skin façade numerical and experimental investigations have been undertaken. Non-uniform heating configurations in which heat sources alternated with unheated zones on both walls were studied to simulate opaque PV arrays and glazed panes/windows of the building. Heat transfer and flow measurements were obtained for periodicity 1/15 of heated/unheated zones and heat input, 220 W/m² as well as large-eddy simulation has been utilized to capture the flow behaviour and possible transition to turbulence in similar non-uniform heating configuration. Several kinds of flow structures have been identified both experimentally and numerically. Intermittent flow structures are observed disrupting the thermal boundary layer allowing to increase heat transfer and to induce high levels of mixing. Vortices in corners of the channel promote horizontal heat transfer from the panels to the lateral walls. Recirculation zone caused by unheated area at the channel entrance contributes to the periodicity of flow within the channel and lower average temperatures. It has been shown that disturbances introduced at the system inlet improve mixing and heat transfer. In comparison to uniformly heating configuration, non-uniformly heating configuration enhances both convective heat transfer and chimney effect. This enhancement may reach 34% in the heat transfer and 12% in mass flow rate. Concerning the physical mechanisms involved, the results show that the flow does not necessarily undergo transition to turbulence but two walls non-uniformly heated arrangement induces better mixing and higher turbulence production in the channel.

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