Browsing by Author "Oosthuizen, Nita-Mare"

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    A decision support framework towards a simulation model for the risk-constrained vehicle routing problem
    (Stellenbosch : Stellenbosch University, 2018-12) Oosthuizen, Nita-Mare; Lotter, Daniel Petrus; Stellenbosch University. Faculty of Engineering. Dept. of Industrial Engineering.
    ENGLISH SUMMARY: The vehicle routing problem is a well-researched problem in the operations research literature that typically involves the delivery of commodities to customers in a transportation network. One particular aspect thereof, however, that has not received as much attention is the security associated with the transportation of valuable commodities. Customers typically rely on companies within the cash-in-transit industry to transport valuable goods between various locations. Due to the high value of these transported goods, the vehicles are constantly exposed to large amounts of risk and the entire cash-in-transit process is therefore susceptible to crime. In this thesis, a decision support system (DSS) framework is put forward for mitigating risk along cash-in-transit routes. The risk along these routes is directly proportional to the amount of valuable goods on board a vehicle and the distance travelled by the vehicle. The proposed routes should, therefore, minimise the risk of the routes and facilitate e ective trade-o s between a variety of decision criteria that are con gurable by a user. Furthermore, it is envisioned that the DSS framework may be used as a basis for implementing a simulation model in the future. The DSS contains three main components, namely a model base, a database and a user interface. The model base forms the heart of the DSS and is responsible for housing two algorithms that are both based on the Clarke-Wright savings algorithm. The rst algorithm is for solving the capacitated vehicle routing problem, is based directly on the original Clarke-Wright algorithm, and does not include any risk constraint, while the second algorithm is for solving a risk-constrained variation on the vehicle routing problem and is based on a modi cation of the Clarke-Wright algorithm. The risk constraint adopted in this thesis involves the speci cation of a risk threshold to which each route must adhere. Furthermore, the user is able to provide speci c input and parameter information through the user interface so as to con gure constraints in order to customise the problem according to his or her preference. After a problem instance has been solved, the user interface provides a visual output to the user, which the user may analyse to draw certain conclusions. The DSS is tested and validated using two di erent methods. The rst method is a trace validation and the second method is a sensitivity analysis. The sensitivity analysis is performed in two parts, with the rst part being based on test data from a benchmark library in the vehicle routing literature and the second part involves parameter variation. The results obtained during these tests are analysed, con rming that the DSS functions correctly. The DSS is implemented in a modelling environment capable of solving both the capacitated vehicle routing problem and its risk-constrained counterpart. The system may be used to observe the e ect of varying the risk threshold associated with a set of vehicle routes. It is found that the DSS produces good results when compared with results obtained from benchmark problems in the literature.