2.1 

The fluid model of product flow

产品流动的流体模型

The “supply chain” is the sequence of processes through which product moves from its origin toward the customer. In our metaphor of fluid flow we may say that warehouses represent storage tanks along the pipeline.

供应链是指产品从原产地流向客户的一系列过程。在我们关于流体流动的比喻中，我们可以说仓库代表沿着管道的储存罐。

The analogy with fluid flows can also convey more substantial insight. For example, consider a set of pipe segments of different diameters that have been joined in one long run. We know from elementary fluid dynamics that an incompressible fluid will flow faster in the narrower segments of pipe than in the wider segments. This has meaning for the flow of product: The wider segments of pipe may be imagined to be parts of the supply chain with large amounts of inventory. On average then, an item will move more slowly through the region with large inventory than it will through a region with little inventory.

流体流动的比喻也能传达更实质性的见解。例如，考虑将一组不同直径的管段在一个长时间内连接在一起。从基本流体动力学中我们知道，不可压缩流体在较窄的管段中比在较宽的管段中流动得更快。这也能说明产品的流动：宽管道可以想象为供应链中有大量长尾库存的那部分。平均而言，一件商品在存储着大量长尾库存区域的流通速度要更慢。

The fluid model immediately suggests other general guidelines to warehouse design and operation, such as:

流体模型为仓库的设计和运营提供了其他通用的指导原则：

• Keep the product moving; avoid starts and stops, which mean extra handling and additional space requirements.

保持产品流动。避免中转——这意味着额外的搬运和额外的空间需求。

• Avoid layouts that impede smooth flow.

避免妨碍顺畅流通的布局。

• Identify and resolve bottlenecks to flow.

识别并解决作业流的瓶颈。

Later we shall rely on the fluid model to reveal more profound insights.

稍后我们将依靠流体模型来揭示更深刻的见解。

    It is worth remarking that the movement to “just-in-time” logistics is roughly equivalent to reducing the diameter of the pipe, which means product flows more quickly and so flow time and in-transit inventory are reduced (Figure 2.1).

值得注意的是，向准时制物流的发展大致相当于减少管道的直径，这意味着产品流动更快，因此流动时间和在途库存减少。

图2.1 如果两根管子流速相同，较窄的管子容纳的流体较少。同样的道理，存货流动越快，库存就越少，库存成本也就越低。