1、 1 外文翻译 原文 An integrated approach to inventory and flexible capacity management subject to fixed costs and non-stationary stochastic demand Material Source: http:/ Author: Tarkan Tan Osman Alp A crucial problem that manufacturing companies face is how to cope with volatility in demand. For make-to-s
2、tock environments, holding safety stocksis the traditional remedy for handling the variability in demand. If demand is non-stationary, as it is in seasonal business environments, then adjusting production capacity dynamically is another possible tool. While there is an extensive amount of literature
3、 on both of these measures, our aim is to contributeto the relatively limited research that considers both at the same time, whichmay be necessary especially if the demand is both non-stationary and stochastic. Consequently, in this paper we consider a periodic review make-to-stockproduction environ
4、ment under non-stationary stochastic demand. In most of the traditional production/inventory literature, either an infinite production capacity is assumed or a given finite capacity is considered as aconstraint rather than as a decision variable. We relax this assumption in thesense that the flexibl
5、e capacity level in each period is to be optimized, as well as the amount of production. Capacity can be defined as the total productive capability of all productive resources such as workforce and machinery. These productive resources can be permanent or contingent. We define permanent capacity as
6、the maximum amount of production possible in regular worktime by utilizing internal resources of the company, such as existing workforce level on the steady payroll or the machinery owned or leased by the company. Total capacity can be increased temporarily by acquiring contingent resources, which c
7、an be internal or external, such as hiring temporary workers from external labor supply agencies, subcontracting, authorizing overtime production, renting work stations, and so on. We refer to this additional capacity acquired temporarily as the contingent capacity. Flexible capacity management 2 re
8、fers to adjusting the total production capacity in any period with the optionof utilizing contingent resources in addition to the permanent ones. Capacity decisions can occur in all hierarchies of decision making: strategic, tactical, and operational. Examples of each type of decision are determinin
9、g how many production facilities to operate, determining the permanent capacity of a facility, and making contingent capacity adjustments. Our focus is on the operational level. For ease of exposition, we refer to the workforce capacity setting in general. More specifically, we use the temporary (co
10、ntingent) labor jargon to refer to capacity flexibility. Consequently, the problem we consider can be viewed as one where the production is mostly determined by the workforce size, permanent and contingent. Temporary workers can be hired in any period and they are paid only for the periods they work
11、, whereas permanent workers are on a payroll. According to our experience, the lead time of acquiring temporary workers is generally short for jobs that do not require high skill levels. It takes as little as 1or 2 days to acquire temporary workers from the external labor supply agencies, whereas in
12、 some cases temporary labor acquisition is actually practicallyimmediate. In some developing countries, abundant temporary workers that are looking for a job and the companies that are in need of temporary labor gather in some venues early in the morning and the companies hire workers that they are
13、going to make use of that very day. Changing the level of permanent capacity as a means of coping with demand fluctuations, such as hiring and/or firing permanent workers frequently, is not only very costly in general, but it may also have many negative impacts on the company. In case of labor capac
14、ity, the social and motivational effects of frequent hiring and firing makes this tool even less attractive. Utilizing flexible capacity, such as hiring temporary workers from external labor supply agencies, is a means of overcoming these issues, and we consider this asone of the two main operationa
15、l tools of coping with fluctuating demand, along with holding inventory. Nevertheless, long-term changes in the state of the world can make permanent capacity changes unavoidable. Consequently, weconsider the determination of the permanent capacity level as a tactical decision that is made at the be
16、ginning of a finite planning horizon and not changed until the end of the horizon. This decision is kept out of the scope of thi3 s study since we focus only on the operational decisions. We refer the readerto Alp and Tan (2008) for the problem of determining the optimal permanent capacity level. Wh
17、ile flexibility provides many benefits, it comes at a cost. The nominalvariable cost of the flexible resources are likely to be higher than that of the permanent ones. In the workforce context, the productivity of temporary workers is probably less than that of permanent workers. Finally, there may
18、be fixed costs associated with ordering contingent capacity, such as the costs of contacting external labor supply agencies and training costs. Another type of fixed costs in the problem environment that we introduce might be the costs associated with initiating production in each period, such as se
19、tup costs, overhead costs, and the like. In many environments, it is possible that the contingent capacity that canbe acquired in any period is limited, which is the case whenfor exampleovertime production is the only tool for temporarily increasing production capacity, due to reasons such as unavai
20、lability of temporary workers or specialskill requirements. Such environments also fall within our setting, as we allow for an upper bound in the amount of contingent capacity that can be acquired in any period. In the context of overtime production, overtime workers would correspond to contingent c
21、apacity, and initiating an overtime production would correspond to ordering contingent capacity subject to a fixed cost associated with facilities, managerial overhead, and the like. Our contributions is this paper can be summarized as follows: We show the equivalence of the problem that we consider
22、 with the classical capacitated production/inventory problem which has a piecewise-linear production cost function. We characterize the optimal ordering policy when the setup costs are negligible. When the setup costs are positive, we derive the optimal policy for the single period problem. For the
23、multi-period problem, we discuss some properties of the optimal solution through numerical studies. Finally, we build several managerial insights as to the use and value of capacity flexibility. The rest of the paper is organized as follows. We present a review of relevant literature in Sect. 2 and
24、present our dynamic programming model in Sect. 3. The optimal policy for the integrated problem is discussed in Sect. 4 4, and the value of utilizing flexible capacity is analyzed in Sect. 5. We summarize our conclusions and suggest some possible extensions in Sect. The problem that we deal with has
25、 interactions with a number of related fields: (i) integrated production/capacity management, (ii) workforce planning and flexibility, and (iii) capacitated production/inventory models. Instead of providing a detailed literature survey on each of these fields, we cite examples of related work from e
26、ach of them and discuss some of the similarities anddifferences between those problems and the one that we consider. An excellent survey of strategic capacity management problems focusingmainly on the capacity expansion decisions is presented by Van Mieghem (2003). The author discusses prominent iss
27、ues in formulating and solving various capacity management problems. Atamtrk and Hochbaum (2001) deal with an integrated capacity and inventory management problem under a finite planning horizon and deterministic demand, where trade-offs between capacity expansions, subcontracting, production, and i
28、nventory holding are exploited. Angelus and Porteus (2002) also deal with an integrated problem for a short-life-cycle product where the demand has a stochastically increasing and then decreasing structure. Authors showthat the optimal capacity level follows a target interval policy. In anotherwork
29、that dealswith integrated problems, Dellaert and De Kok (2004) show that integrated capacity and inventory management approaches outperform decoupled approaches. Hu jin tao. (2004) deal with an environment similar to ours: There is afixed permanent production capacity, but it can be increased tempor
30、arily by using contingent capacity. Unlike ours, those problems are modeled on a continuous-time framework with a demand rate that is Markov-modulated, and nofixed costs are considered. Tan and Gershwin (2004) also deal with a similar problem. The differences are the existence of several subcontract
31、ing opportunities with different cost and capacity structures and the demand being dependent on the lead time distribution during out-of-stock periods. Yang et al. (2005) deal with a production/inventory system under uncertain capacity levels and the existence of outsourcing opportunities. In their
32、model, there is no fixed cost of production but a fixed cost is associated with outsourcing. The decision epochs of producing with internal resources and determining the quantityof outsourcing are distinguished in such a way that the outsourcing decision5 is made only after the capacity is observed,
33、 production is materialized, and the demand is observed. By using this model, the authors characterize the optimal outsourcing policy under certain conditions and elaborate on the optimal policy of production with internal resources. In the workforce planning and flexibility field, Holt et al. (1960
34、) in their seminal work present models that exploit the trade-off between keeping large permanent workforce levels capable of satisfying peak season demands andfrequent adjustment of the workforce level to cope with fluctuations. Indeed,this very idea of aggregate production planning problem constit
35、utes the essence of our problem too; nevertheless, we consider non-stationary stochastic demand, unlike the deterministic demand assumption of aggregate production planning models. Wild and Schneeweiss (1993) analyze and compare four “instruments” to cope with fluctuating demand when the capacity is
36、 defined in terms of work force level: variation of monthly working time, use of overtime, employment of temporary workers, and use of leased work force. A hierarchical model based on dynamic programming is presented for making rational decisions on the selective use of these instruments. Milner and
37、 Pinker (2001) deal with the design of contracts between firms and external labor supply agencies for hiring long-term and temporary workers under supply and demand uncertainty in a single period environment. In arelated work, Pinker and Larson (2003) consider the problem of managing permanent and c
38、ontingent workforce levels under uncertain demand in a finite planning horizon where inventory holding is not allowed. The sizes of regularand temporary labor are decision variables that are fixed throughout the planning horizon, but the capacity level may be adjusted by setting the number of shifts
39、 for each class of workers. The papers by Federgruen and Zipkin (1986) and Kapuscinski and Tayur(1998) are two examples of the research stream on capacitated production/inventory problems with stochastic demand, where no fixed costs of productionexist. In this case, it is shown that base-stock type
40、policies are optimal. Gallego and Scheller-Wolf (2000) consider the fixed cost of production under a similar environment and partially characterize the optimal policy. Our model is an extension and a generalization of this stream of research, in which we provide the explicit solution of a single per
41、iod problem. Finally, the special case of the problem that we consider with no fixed 6 costs is shown in Sect. 3 to translate into the classical capacitated production/inventory problem with a piecewise-linear, convex production cost. When the capacity constraint is neglected, Karlin (1958) characte
42、rizes the optimal policyfor the case of a strictly convex production cost function as state-dependent order-up-to type. For the single-period problem with a piecewise-linear (hencenon-strict) convex production cost and infinite capacity, Porteus (1990) discusses that the optimal policy is of order-u
43、p-to type, where the order-up-to level is piecewise-linear increasing in initial inventory level. 译文 一种综合的方法来管理受固定费用和非平稳随机需求影响的库存 资料来源： http:/ 作者： Tarkan Tan Osman Alp 制造业企业面临 的 一个关键问题是如何应付需求的波动。按库存环境，持有安全库存是处理需求变化 的 祖传秘方。如 果需求 是 不平稳的， 那是 因为它是在季节性的商业环境中，动态调整产能是另一种可能的工具。虽然 文献上有太大的量在这两种措施上 ， 我们 认为在同一时
44、间，这可能是必要 的，但 我们的目标是促进相对有限的研究 。 因此，在本文中，我们考虑的按库存生产环境下的非平稳随机需求定期审查。 在最传统的生产 中 ，要么是假定生产能力或在有限的容量是作为约束，而不是作为一个决策变量考虑。我们 在 放松这个假设的意义上，在每个时期灵活的容量水平，以及生产量 、 容量可以被定义为如劳动力和机械的所有生产资源的生产能力。这些生产资源可以是永久性的。我们定义利用 公司内部资源，如现有员工薪资或对稳定该公司拥有或租用的机械水平，生产的正常工作时间内的最大金额的永久能力。总容量可提高队伍暂时获得资源，这可以是内部或外部，如聘请外部劳动力供应机构，分包，授权加班生产，
45、租赁站的临时工工作，等等。灵活的容量管理是指在任何调整与利用，除了常设的队伍资源的选择期总生产能力。 7 能力决定可以发生在所有层次的决策：战略，战术和运作。各决策类型的例子有很多 ： 生产设施决定如何操作，确定永久设施的能力，使队伍的能力调整。我们的重点是在业务层面。为了论述方便，我们指的是劳动力的能力。更具体地说 ，我们使用临时（特遣队）劳动能力行话指的灵活性。因此，我们认为这个问题可以被看作是其中的生产主要是由劳动力规模的，永久的和队伍的决定。 雇用临时工可以在任何时期，他们只对他们的工作时间，而固定工在工资支付。根据我们的经验，取得临时工的筹备时间一般为作业，不需要高技能水平的短。它以
46、小为 1 或 2 天的收购外部劳动力供应机构临时工，而在某些情况下，临时劳工收购实际上是几乎立竿见影。更改永久能力作为应对需求波动，如聘请和 /或解雇工人永久频繁，手段的水平，不仅是非常普遍昂贵，但它也可能对公司的一些负面影响。在劳动能力的情 况下，雇用和解雇频繁的社会和激励作用，使这个工具更具有吸引力。如利用从外部劳动力供给雇用临时工灵活的机构能力，是克服这些问题的手段 。 然而，在世界国家的长期变化可以永久能力的变化是不可避免的。因此，我们认为作为一个战术决定，是由在一个有限的计划开始，直到结束改变常设能力水平的测定。这一决定是保留了这项研究的范围，因为我们专注于经营决策。我们指为确定最佳
47、的长期能力层次的问题向 ALP 和谭（ 2008）的读者。 虽然灵活性提供了许多好处，但它是有代价的。名义变动成本可能会比永久的为高。在劳动力方面，可能是暂时的工人的 生产力比长期工少。最后，还有可能是固定的排序和队伍的能力，如接触外部劳动力供应机构的费用和培训费用，相关费用。另一个问题环境中，我们引进可能与启动了在每个这样的设置成本，间接费用期间，生产相关的成本，如固定费用类型。 在许多环境中，可能是队伍的能力，可以在任何时期获得的是有限的，例如，加班生产是暂时增加生产能力的唯一工具，如因暂时不可用道理劳工或特殊技能要求。这样的环境也属于我们的设置，在我们的队伍的容量，可在任何时期获得允许的
48、上限。在生产方面的加班，加班的工人将符合队伍的能力，并发起一个加班生产将符合订货 队伍的能力受到一个固定的成本与设施，相关管理费用等等。 我们本文的贡献可归纳如下： 我们表明了该问题的等价性，我们考虑容量限制生产 /库存问题，有一个分段线性生产成本函数。 当安装成本可以忽略不计 时 刻画了最优订货策略。当安装成本是积极的，我们推导出了单期问题的最优政策。对于多周期的问题，我们通过数值研究，讨论了一些最优解的性质。 8 最后，我们建立了以能力的使用和管理灵活性的价值见解。 本文的其余部分组织如下。我们提出了相关文献中的教派 ： 1，目前我们在派动态规划模型 ； 2， 对于综合问题的最优政策是讨论
49、第二节 ； 3，利用灵活的容量值分析了节 ； 4， 我们总结的结论和建议在派一些可能的扩展。 我们处理了一些相关领域的相互关系：综合生产 /能力管理，劳动力规划和灵活性，以及有限产能生产 /库存模型。我们从他们举出各种相关的工作的例子，讨论了这些问题之间的异同和我们认为的一些差异。 一个优秀的战略能力管理问题的调查集中在产能扩张的决定主要是由 Van Mieghem提出（ 2003 年）。笔者讨论了制定和管理上的问题解决各种突出问题的能力。 Atamtrk 和 Hochbaum（ 2001 年）处理能力和集成在一个有限的计划和确定的需求，其 中贸易之间的产能扩张，分包，生产，库存持有下岗是利用库存管理问题。安格卢斯和波特斯（ 2002）也 是 具有很短的生命周期的产品，就是一个随机的需求增加，然后减少结构的综合处理问题。作者证明了如下的最佳能力水
