| China is a big producer of fruit and vegetable products(FVP),according to the National Bureau of Statistics,the total productions of main fruits and vegetables reached 28351.09 ton and 79779.71 ton,respectively.On the other hand,there is serious waste of FVP.The Ministry of Agricultural and Rural Affairs data says that the perishable FVP amounts to more than 100 million ton each year in China,the total direct economic loss of which amounts to nearly 100 billion CNY.In recent years,the internet media often report that the farmers throughout China suffer huge losses due to unmarketable fruit or vegetable products.There are many reasons causing this problem,but when analyzing it from the perspective of a manager,e.g.,a farmer,wholesaler or retailer,the root causes are the unique product features and the demand features of FVP.First is the product features of the FVP.Different from the regular products or industrially produced foods,FVP are normally got from natural environment and their productions usually observe obvious seasonal characteristic.In addition,even derived from the same farmland,the products show big variations in quality,and their quality decreases over time,i.e.,the perishable feature of the FVP.Another feature of the FVP is that their market prices are highly volatile,which are affected by the harvest,the supply-demand condition,the quality and festival/holiday,among other factors.The demand features of the FVP are also different from that of the regular products.The FVP act as important food and directly affect people's health,therefore,people pay more attention on the products'quality.However,due to different education and income levels,the degree of how much one person cares about"the quality can be very different,i.e.,heterogeneous quality preference,which is reflected by its willingness to pay for quality.Although people have different quality preference,since the FVP are life necessities,they would choose to buy the substitutable products if their first choices are out of stock,i.e.,demand substitution.Besides,based on the past buying experience,people can often make reasonable decisions when facing fluctuating prices.For example,they can take the history prices as references,i.e.,the price referring behavior.As a FVP manager,if it fails to deal with the product or demand features of the FVP,the resulting wrong decision will make it pay a heavy price.For example,the seasonal characteristic restricts the manager's replenishment strategy.It will face the situation of serious out-of-stock if it does not purchase enough products in the harvest season.And it has to dispose many unsold products,the salvage value of which can be very low when the next harvest season comes,if it purchases too many products in the harvest season.The perishable feature of the FVP also requires the manager to skillfully make the inventory and sales strategies,otherwise,the quality of many products can be too low to sell due to long-time inventory.On the other hand,however,these unique features bring new business opportunities to the manager.For example,when facing the fluctuating market prices,it can flexibly"withhold"or"sell"the inventories base on its estimation on the market.Since people have heterogeneous quality preference,it can sort the products into different quality grades before selling them.Besides,some raw FVP can be processed into the coproducts that have more values or are less perishable.Therefore,it can process the raw FVP before sales to gain more revenues.Based on the above analysis,this dissertation studies three problems as follows:(1)The optimal inventory and sales strategies considering the seasonal and perishable features.Because of the two features of the FVP,the wholesaler purchases the products from farmers in the harvest season,and then store them in the well-controlled environment to slow down their perishable process.After that,it gradually sells the products throughout the selling horizon to maximize its total profit.The wholesaler needs to decide the optimal purchase quantity of the products in the harvest season and the inventory rationing quantities in each selling period.When making these decisions,it has to consider the cost factors(e.g.,inventory cost,overstocking cost,.perishable cost),price fluctuations and the uncertain demand which is affected by the customers'price referring behaviors.By constructing a finite-period dynamic program,the objective of which is to maximize the wholesaler's expected profit,this dissertation characterizes the optimal purchase strategy and proves that the wholesaler's optimal sales strategy is the sell-down-to policy.Moreover,sensitivity studies for different parameters are given and two approximate policies are provided to instruct the wholesaler to make the decisions.Finally,a case study of a pear wholesaler from Zhao County is conducted,the results show that:the optimal strategies derived in this dissertation can help the pear wholesaler increase its profit by 22.4 percent in 2014 and reduce its loss by 10.2 percent in 2015.(2)The optimal production and inventory strategies in fixed-proportions co-production system.The fixed-proportions co-production technology are one of the most widely utilized technologies in agricultural production.The FVP manufacturer purchases the raw FVP from the wholesaler or farmer,and then produces them into two coproducts using the fixed-proportions co-production technology to satisfy their demands.Over the processing horizon,the manufacturer has to decide the quantity of the raw FVP processed in each period based on the inventory and demand conditions to maximize its total profit.This dissertation studies both of the cases where the leadtime is zero or positive and the case where the time horizon is infinite,and shows that the produce-up-to policy is optimal for the three cases by using dynamic programs.In addition,this dissertation studies the case where the raw FVP is seasonal and proves that the optimal production strategy is the produce-down-to policy.Finally,two groups of numerical studies are conducted to investigate the impacts of supply-demand relations and price fluctuations on the manufacturer's optimal strategies.(3)The optimal inventory and sales strategies considering consumers' quality preference and demand substitution.After purchasing the FVP from upper supplies,e.g.,the farmer,wholesaler and manufacturer,the FVP retailer faces the customers that have different willingness-to-pay for quality and it has two sales strategies to choose:(a)the unsorted sales strategy(US),i.e.,the retailer does not sort the products and directly sells them at one price;(b)the sorted sales strategy(SS),i.e.,the retailer sorts the products into different grades by quality and sell them at different prices.If the SS is adopted,the retailer has to consider the following factors:the uncertain sorting results,the customers'uncertain quality preferences and the demand substitution.To this end,the retailer has to decide the sales strategy and the corresponding purchase quantity to maximize its profit.This dissertation specifies the conditions under which the US or SS strategy is optimal and calculates the optimal purchase quantity.The analysis states that the optimal sales strategy is decided by two cost factors:the marginal purchase and sorting cost and the fixed investment cost.Finally,numerical studies based on real-world data of agricultural product markets in Beijing are conducted to investigate the impacts of different parameters on the optimal strategies. |
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