Recent Results on Stability Analysis of an Optimal Assembly Line Balance

Two assembly line balancing problems are addressed. The first problem (called SALBP-1) is to minimize number of linearly ordered stations for processing n partially ordered operations V = {1, 2, ..., n} within the fixed cycle time c. The second problem (called SALBP-2) is to minimize cycle time for processing partially ordered operations V on the fixed set of m linearly ordered stations. The processing time ti of each operation i ∈V is known before solving problems SALBP-1 and SALBP-2. However, during the life cycle of the assembly line the values ti are definitely fixed only for the subset of automated operations V\V . Another subset V ⊆ V includes manual operations, for which it is impossible to fix exact processing times during the whole life cycle of the assembly line. If j ∈V , then operation times tj can differ for different cycles of the production process. For the optimal line balance b of the assembly line with operation times t1, t2, ..., tn, we investigate stability of its optimality with respect to possible variations of the processing times tj of the manual operations j ∈ V

Self-assembling multiblock amphiphiles: Molecular design, supramolecular structure, and mechanical properties

We perform off-lattice, canonical ensemble molecular dynamics simulations of the self-assembly of long segmented copolymers consisting of alternating, tunably attractive and hydrophobic {\em binder} domains, connected by hydrophilic {\em linker} chains whose length may be separately controlled. In such systems, the molecular design of the molecule directly determines the balance between energetic and entropic tendencies. We determine the structural phase diagram of this system, which shows collapsed states (dominated by the attractive linkers' energies), swollen states (dominated by the random coil linkers' entropies) as well as intermediate network hydrogel phases, where the long molecules exhibit partial collapse to a {\em single molecule network} state. We present an analysis of the connectivity and spatial structure of this network phase, and relate its basic topology to mechanical properties, using a modified rubber elasticity model. The mechanical properties are further characterized in a direct computational implementation of oscillatory rheology measurements. We find that it is possible to optimize the mechanical performance by an appropriate choice of molecular design, which may point the way to novel synthetics that make optimal mechanical use of constituent polymers

Dynamic conversion of solar generated heat to electricity

The effort undertaken during this program led to the selection of the water-superheated steam (850 psig/900 F) crescent central receiver as the preferred concept from among 11 candidate systems across the technological spectrum of the dynamic conversion of solar generated heat to electricity. The solar power plant designs were investigated in the range of plant capacities from 100 to 1000 Mw(e). The investigations considered the impacts of plant size, collector design, feed-water temperature ratio, heat rejection equipment, ground cover, and location on solar power technical and economic feasibility. For the distributed receiver systems, the optimization studies showed that plant capacities less than 100 Mw(e) may be best. Although the size of central receiver concepts was not parametrically investigated, all indications are that the optimal plant capacity for central receiver systems will be in the range from 50 to 200 Mw(e). Solar thermal power plant site selection criteria and methodology were also established and used to evaluate potentially suitable sites. The result of this effort was to identify a site south of Inyokern, California, as typically suitable for a solar thermal power plant. The criteria used in the selection process included insolation and climatological characteristics, topography, and seismic history as well as water availability

Optimal design of the tractor-front-mounted sugarcane grab loader

Abstract: The percent of sugarcane mechanical sugarcane loading (in Egypt) has not been exceeded 10% because of the poor finance-ability of the farmers to by the imported self-propelled loaders.  The local workshops have been attempting to fabricate a sugarcane loader attached to the farm tractors as a cheap alternative.  Farmers did not accept the tractor-mounted loaders fabricated locally because of the problems concerning poor efficiency and poor balance of the tractor-mounted loader while operation.  The main objective was to overcome the problems concerning precise fabrication of the tractor-front-mounted loader and to develop an efficient dynamically balanced machine.  Fabricating a sugarcane grab loader for the tractor faces difficulties due to the variation of the farm tractor types and sizes.  Reference to the size of the transport vehicles was supposed to be loaded, the medium size tractors 70-90 hp was considered to be equipped with the sugarcane loader.  The most important specifications of the prevailing medium size farm tractors found in the sugarcane production area were recorded through field survey.  Important tractor parameters related to the loader design were specified.  For the prevailing medium size tractors of power range 70-90 hp, wheel base within 2.4 m.  Total tractor weight about three tons, distributes as two thirds on the rear axle and one third on the front axle.  The tractor operator is supposed to have clear view over the boom lowered for pilling, so that the height of steering wheel is important parameter determined as 1.9 m for the medium size tractors.  Important dimensions such as the tractor chassis dimensions and other dimensions related to the sugarcane loader were identified.  A chain of measurements and computations were conducted to facilitate optimizing the design of a tractor mounted sugarcane grab loader dynamically balanced with no need for counterbalance weights.   Considering the data of the medium size tractor, the dimension of the loader components computed in accordance.  A general formula relates the loader size to the tractor on which the loader supposed to be mounted was developed to facilitate fabricating the balanced loader for any size of the farm tractors.   The loader was fabricated and tested in the field.  The loader proved high dynamical stability and economical operation efficiency.   The field test results show operating the loader for loading sugarcane transport vehicles, loading cycle time was about 1.7 min, loading rate up to 14 ton/h and operation efficiency was over 90%.   Keywords: sugarcane grab loader, tractor-front-mounted-loader, loader design, loader balanc

Stability measure for a generalized assembly line balancing problem

AbstractA generalized formulation for assembly line balancing problem (GALBP) is considered, where several workplaces are associated with each workstation. Thus, all tasks assigned to the same workstation have to be partitioned into blocks: each block regroups all tasks to be performed at the same workplace. The product items visit all workplaces sequentially, therefore, all blocks are proceeded in a sequential way. However, the tasks grouped into the same block are executed simultaneously. As a consequence, the execution of a block takes only the time of its longest task. This parallel execution modifies the manner to take into account the cycle time constraint. Precedence and exclusion constraints also exist for workstations and their workplaces. The objective is to assign all given tasks to workstations and workplaces while minimizing the line cost estimated as a weighted sum of the number of workstations and workplaces. The goal of this article is to propose a stability measure for feasible and optimal solutions of this problem with regard to possible variations of the processing time of certain tasks. A heuristic procedure providing a compromise between the objective function and the suggested stability measure is developed and evaluated on benchmark data sets

Extreme ultraviolet and X-ray spectroheliograph for OSO-H

A complex scientific instrument was designed, fabricated, tested, and calibrated for launch onboard OSO-H. This instrument consisted of four spectroheliographs and an X-ray polarimeter. The instrument is designed to study solar radiation at selected wavelengths in the X-ray and the extreme ultraviolet ranges, make observations at the H-alpha wavelength, and measure the degree of polarization of X-ray emissions

A contra-rotating marine current turbine on a flexible mooring : development of a scaled prototype

The contra-rotating marine current turbine concept developed by the Energy Systems Research Unit at the University of Strathclyde is aimed at extracting energy in a wide range of water depths by 'flying' a neutrally-buoyant device from a flexible, tensioned mooring. After successful proof of concept turbine trials, the development programme has moved on to investigate the performance of a scaled prototype of the complete system incorporating the turbine, submersible contra-rotating generator and mooring. The turbine/generator assembly has been tested in a towing tank, and the entire system is now undergoing sea trials. An investigation into turbine wake development (an area in which it is hoped that the contra-rotating turbine will have uniquely beneficial properties) has recently begun. Small single-rotor model turbines have been deployed in a flume. Trends observed so far are in accordance with those observed by other researchers