## 4 Review of Literature
### Supply and Delivery in Routing Optimisation Problems
#### 4.1.3 Heuristics and Local Search in Supply and Delivery VRPs
An Emergency Supply using the Heterogeneous Fleet (ESHF) problem is addressed by [61], where a multiple supply point with limited inventories is used to supply relief aid to multiple delivery points through a multi-trip operation. The problem is similar to the VRPPD with a split delivery, but with an improved representation of the problem addressed. The total operational time that includes the travel time, loading time, as well as the unloading time is reduced as the objective of the model, and the problem is modelled through a MIP formulation. All of the proposed constraints are based on the routing constraints, capacity constraints, timing constraints, and other constraints. The heuristic approach is applied to solve the problem for realistic instance. A case study that is based on the forest fire in the Province of Teruel, Spain was used, through which an efficient plan is obtained when applying the proposed heuristic. More recently, ref. [62], in their work, addressed a drought scenario. A Multi-Depot VRP (MDVRP) is considered to reflect multiple water sources where water is to be delivered to nodes with demands. The objective is to minimise the total travel time, given the unloading time of the water supply at each demand point that is assumed to be the same. In order to solve the problem, ref. [62] first allocated each vehicle a water source with a set of their unique demand points. Subsequently, the Clarke and Wright algorithm with 2-Opt moves is applied to solve the CVRP with single depot for each vehicle. A case study on the Brazilian scenario showed potential for improvement for practical planning in terms of management and financial. Ref. [63] planned for helicopter routing, as opposed to ground transport, due to the disrupted road and bridges during a disaster event. Five stages of planning for relief distribution and transportation of personnel in operation are specified where the first stage is to reassess the transport network, followed by the estimation of requirement based on the demands. Meanwhile the air transport is reassessed based on capacity, stability and limitation. Subsequently, the number of helicopters is estimated for the operation. The first operation was a combined distribution for demands which exceed the capacities of the helicopters. The subsequent operation is then optimised based on CVRP with time window where the total time of operation is minimised. The problem is solved using the Clark and Wright algorithm with 2-Opt improvement. The proposed model is applied to the 2011 flood in Serrana Mountain Region, Rio de Janeiro, Brazil for validation. In [64], a 2-echelon VRP is proposed, where a two-delivery level via drones is addressed during the time of a disaster as a PDVRP. Delivery is made to various first aid locations by the same drone. The model that is based on the mathematical formulation from [65] is solved through a fast constructive heuristic based on a biased randomised algorithm. Interestingly, parallel computing is utilised to fulfil the requirement of fast delivery, which made agile optimisation possible. The node addition process in the constructive phase is improved through biased randomisation, instead of depending on a pure greedy mechanism and local search is applied in order to improve the quality of the solution. Instances from [65] are applied to validate the proposed model, where the commercial problem instances are converted into HL operation instances. Increased performance is observed through parallel computation.