现代供应链的复杂性和全球化趋势增大了企业生产运营中的扰动风险。原材料价格上涨、劳动力成本上升、能源短缺、自然灾害、国际贸易摩擦及监管政策等因素变化，会增加企业的生产成本，影响生产力水平，导致延迟交付时间甚至造成频繁缺货。长期的生产扰动会影响企业的竞争力，改变供应链的竞争格局。为减弱上游供给扰动造成的不利影响，生产决策者采取了供应链多元化布局战略，通过多元化采购、分散生产基地等方式，降低采购和生产风险。本论文研究了生产扰动对存在竞争的多层供应链网络的影响，并利用原理和实证案例分析了供应链多元化战略在实践中的利弊。 首先，本论文建立了多层供应网络的竞争模型，提出了不对称竞争中特定均衡点结构稳定的限定条件和识别方法。在该均衡结构下，本论文推导出扰动对供给均衡影响的显式表达式，刻画了竞争企业间的策略性替代和策略性补充互动关系，并利用改进的Pseudoflow算法，对容量非单调变化的网络产出和瓶颈进行参数分析。本论文分析了成本结构为二次函数以及随机产出模型下，竞争均衡和预期缺货的变化及原因，进一步拓展了多层竞争模型的适用范围和情景。其次，本论文将现有的单层网络柔性指标拓展为多层网络柔性指标，并提出了新的基于竞争网络的柔性指标，利用这些指标评估了不同结构供应链网络（长链、短链、指定生产计划网络等）在出现生产扰动和需求波动下的运作效率。最后，本文利用模型在国际头孢霉菌素原料药供应链的真实数据集上进行了仿真实验，评估了当前供应链的效率及薄弱环节，分析了供应链分散化布局、灵活采购等策略在防范供给风险方面的效果，并探讨了这些策略的适用性和潜在问题。 本论文的研究结果显示，一方面，适度的竞争行为有利于减少扰动对产出造成的损失，柔性的供给-采购结构有利于提升网络在应对扰动风险时的效率；另一方面，供应链网络的建设成本和扰动发生频率和分布的不对称性，可能降低过于分散的竞争网络的经济效益，特别是对于中小生产者，上游生产者在产能不足时的选择性供应可能降低其利润。因此，对生产企业而言，适度竞争、平衡的供应链和灵活采购有利于减少生产扰动对其产出造成的负面影响，决策者应根据其在竞争格局中的位置和下游市场分布，制定适当的多元化采购策略。
The complexity and globalization of modern supply chain have increased the disturbance risk faced by manufacturing firms. Inflation, rising wages, energy shortages, natural hazards, trade conflicts and regulatory activities may increase firms‘ production costs, decrease their productivity levels, causing longer lead time and frequent shortfalls. The persistence of disturbing factors may alter the competitive advantages of firms and ultimately transform the structure of supply chain competition. To hedge against disturbance risk, decision makers deploy diversification strategies (e.g. multiple sourcing, manufacturing site diversification) to reduce their procurement and production risks. This dissertation investigates the impact of disturbance on the multitier supply network under competition, and evaluates the trade-offs behind supply chain diversification strategies through theoretical and empirical analysis. First, this dissertation establishes the competition model for the multitier supply chain and underlines the conditions to ensure the stability of the equilibrium structure. The impact of disturbance is explicitly characterized on each supply path, and its interactions with the strategic substitutability and strategic complementarity among firms‘ decisions are analyzed. A parametric analysis based on an adapted pseudoflow algorithm is performed to examine the changes in expected shortfall and bottlenecks when arc capacities change nonmonotonically in the shock level. The model is expanded to account for quadratic production costs and random yield, with discussions on the results and implications. Second, this dissertation extends the existing single-tier network flexibility indices into multitier network flexibility indices and proposes a novel flexibility index which considers the dual effects of adding flexibility under a competitive environment. The flexibility indices are used to evaluate the performance and efficiency of supply chain networks under various configurations (long chain, short chain, dedicated networks, etc.) in the presence of disturbance and demand volatility. Finally, the competition model is applied to the real-world, global cephalosporin supply chain dataset to evaluate the efficiency and vulnerability of the current supply chain and to analyze the effectiveness of diversification and flexible sourcing under disturbance. Practical issues and potential risks behind these diversification strategies are discussed based on the simulation results. The implications of this dissertation are manifold. On the one hand, competition at a moderate level is conducive to reducing disturbance loss, and networks with flexible supply-procurement configurations are proven to be efficient in diversifying disturbance impacts. On the other hand, the costs of enhancing flexibility and the unpredictable occurrence of disturbance may diminish the economic benefits of diversification strategies. In particular, the profit margins of medium and smaller manufacturers may be “squeezed" when large, global suppliers direct most of their products to larger manufacturers under limited capacities. Thus, a balanced supply chain configuration that promotes moderate competitiveness is the most favorable environment for firms to thrive. Decision makers should give thorough consideration of their positions in the competition structure when making their sourcing strategies.
