34 research outputs found

    Graph reduction for the planar Travelling Salesman Problem:An application in order picking

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    Multi-objective vehicle routing and loading with time window constraints:a real-life application

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    Motivated by a real-life application, this research considers the multi-objective vehicle routing and loading problem with time window constraints which is a variant of the Capacitated Vehicle Routing Problem with Time Windows with one/two-dimensional loading constraints. The problem consists of routing a number of vehicles to serve a set of customers and determining the best way of loading the goods ordered by the customers onto the vehicles used for transportation. The three objectives pertaining to minimisation of total travel distance, number of routes to use and total number of mixed orders in the same pallet are, more often than not, conflicting. To achieve a solution with no preferential information known in advance from the decision maker, the problem is formulated as a Mixed Integer Linear Programming (MILP) model with one objective—minimising the total cost, where the three original objectives are incorporated as parts of the total cost function. A Generalised Variable Neighbourhood Search (GVNS) algorithm is designed as the search engine to relieve the computational burden inherent to the application of the MILP model. To evaluate the effectiveness of the GVNS algorithm, a real instance case study is generated and solved by both the GVNS algorithm and the software provided by our industrial partner. The results show that the suggested approach provides solutions with better overall values than those found by the software provided by our industrial partner

    Optimisation of picking process in manual warehouses

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    Skladiščni sistemi so postavljeni pred širok spekter izzivov pri zagotavljanju kakovostnih storitev za stranko. Med vsemi procesi, ki se izvajajo v skladišču, je proces nabiranja časovno najzahtevnejši, zato je ključno, da je izveden čim bolj optimalno. V okviru magistrske naloge smo se zato lotili optimizacije nabiralnega procesa v ročnem skladišču. Predlagali smo hierarhični logični model skladišča, ki s svojo strukturo zmanjša število lokacij, ki jih morajo pregledati implementirani algoritmi za iskanje najkrajše nabiralne poti. Hkrati nam tovrstni model omogoča, da podrobno deljenje lokacij ne vpliva na izvajanje algoritma. Pripravili smo modul za optimizacijo nabiralne poti, ki glede na velikost in tip problema izbere enega od treh implementiranih algoritmov. Prenovili smo procese, povezane z uporabo polavtomatskih viličarjev, in razvili grafični spletni vmesnik za pregled pogostosti nabiranja.Warehouse operators and warehouse management systems encounter a broad spectrum of challenges to ensure the shortest possible shipping times to their customers and maintain their position on the market. The picking process is the most time-demanding among all core warehouse processes. Optimisation of picking is crucial for effective warehouse operation, since it represents the majority of warehousing costs. In this thesis we analyzed, proposed and implemented optimisations of the picking process in the manual warehouse. We prepared a logical model of the warehouse, which is based on a hierarchical representation of the warehouse locations. Using this model we reduced the number of locations, which have to be considered during the computation of the shortest picking path in the implemented algorithms. We developed a module for picking path optimisation, which selects one of three implemented algorithms based on the problem size and the warehouse type. To further improve the picking process we introduced changes to the semi-automatic forklift operations and developed a graphical web interface for the warehouse picking heatmap

    Cuckoo search algorithm for construction site layout planning

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    A novel metaheuristic optimization algorithm based on cuckoo search algorithm (CSA) is presented to solve the construction site layout planning problem (CSLP). CSLP is a complex optimization problem with various applications, such as plant layout, construction site layout, and computer chip layout. Many researchers have investigated the CSLP by applying many algorithms in an exact or heuristic approach. Although both methods yield a promising result, technically, nature-inspired algorithms demonstrate high achievement in successful percentage. In the last two decades, researchers have been developing a new nature-inspired algorithm for solving different types of optimization problems. The CSA has gained popularity in resolving large and complex issues with promising results compared with other nature-inspired algorithms. However, for solving CSLP, the algorithm based on CSA is still minor. Thus, this study proposed CSA with additional modification in the algorithm mechanism, where the algorithm shows a promising result and can solve CSLP cases.publishedVersionPeer reviewe

    Bead geometry modeling on uneven base metal surface by fuzzy systems for multi-pass welding

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    This paper presents a modeling method of weld bead profiles deposited on uneven base metal surfaces and its application in multi-pass welding. The robotized multi-pass tungsten inert gas welding requires precise positioning of the weld beads to avoid welding defects and achieve the desirable welding join since the weld bead shapes depend on the surface of the previously deposited beads. The proposed model consists of fuzzy systems to estimate the coefficients of the profile function. The characteristic points of the trapezoidal membership functions in the rule bases are tuned by the Bacterial Memetic Algorithm during supervised training. The fuzzy systems are structured as multiple-input-single-output systems, where the inputs are the welding process variables and the coefficients of the shape functions of the segments underlying the modeled bead; the outputs are the coefficients of the bead shape function. Each segment surface is approximated by a second-order polynomial function defined in the weld bead’s local coordinate system. The model is developed from empirical data collected from single and multi-pass welding. The performance of the proposed model is compared with a multiple linear regression model. During the experimental validation, first, the individual beads are evaluated by comparing the estimated coefficients of the profile function and other bead characteristics (bead area, width, contact angles, and position of the toe points) with the measurements, and the estimations of a multiple linear regression model. Second, the sequential placement of the weld beads is evaluated while filling a straight Vgroove by comparing the estimated bead characteristics with the measurements and calculating the accumulated error of the filled groove cross-section. The results show that the proposed model provides a good estimation of the bead shapes during deposition on uneven base metal surfaces and outperforms the regression model with low error in both validation cases. Furthermore, it is experimentally validated that the derived bead characteristics provide a suitable measure to identify locations sensitive to welding defects

    Evolutionary computing for routing and scheduling applications

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    Ph.DDOCTOR OF PHILOSOPH

    Evolutionary multi-objective optimization in scheduling problems

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    Ph.DDOCTOR OF PHILOSOPH
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