Flexsim离散系统仿真时间推进机制

Flexsim离散系统仿真时间推进机制.mp33:01来自LearningYard学苑

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离散系统仿真软件要釆用某种机制来推进模型的仿真时间向前运行，以便在运行过程 中修改系统状态，釆集性能统计数据。绝大多数通用离散系统仿真软件采用的时间推进机 制是下次事件时间推进（next-event time advance）机制（Law,2009）,其控制流程的伪代码 如下所示。

Discrete system simulation software should adopt some mechanism to promote the model simulation time forward to the operation, so as to modify the system state during the operation process, and collect the performance statistical data. The time propulsion mechanism used by the most general simulation software is the next event time propulsion (next-event time advance) mechanism (Law, 2009), and the pseudo code of the control process is shown below.

//开始

初始化仿真钟为0；

初始化系统状态变量和统计计数器；

初始化事件列表；

//While 循环

While （仿真未结束）Do

设置仿真钟为下次事件时间；

更新系统状态和统计计数器；

生成未来事件并加入事件列表；

End While

//仿真结束时生成统计 表

生成统计 表；

//仿真结束

在上面的代码中，仿真钟（simulation clock）是一个记录当前仿真时间的变量，与实际时 间不同，仿真钟并不是连续推进、均匀取值的.而是从当前事件的发生时间跳跃到下一个事 件的发生时间（也就是仿真钟变量的取值是跳跃变化的）。因为相继两个事件之间系统状态 没有发生变化，所有也就没有必要让仿真钟遍历这两个事件间的时间。

事件列表（event list）是一个记录事件信息的列表数据结构，它按时间顺序记录了未来 要发生的各种事件（包括事件发生时间、事件类型等信息）。

In the above code, the simulation clock (simulation clock) is a variable that records the current simulation time. Unlike the actual time, the simulation clock is not continuously advanced and evenly valued. Instead, it jumps from the time of the current event to the time of the next event (that is, the value of the simulation clock variable is used for jumps to change). Because the system state does not change between two successive events, all of it is not necessary to let the simulation clock go through the time between the two events.

Event List (event list) is a list data structure that records event information, which records a variety of future events (including event time, event type, and so on).

仿真钟和事件列表协同工作，在仿真初始化完成后，会从事件列表中移出顶端记录（即 下一个要发生的事件），然后将仿真钟推进到该事件的发生时间（该时间值是事件列表记录 的数据项之一），所移出的记录中的信息（包括事件发生时间、事件类型等）则用于处理该事 件，如何处理取决于该事件的类型和系统当时所处的状态，但一般来说可以包括更新状态变 量和统计累加器、改变实体属性，事件处理完后，生成新事件插入事件列表，开始新一轮 循环。

有时，有些事件会同时发生，但仿真软件仍然要为它们的执行安排一个先后顺序，这时, 建模人员应该特别注意这种顺序对结果有何影响。仿真软件一般都提供事件查看器查看事 件列表信息，可以观察同时发生的事件被安排的顺序。

在现代仿真软件中（包括Flexsim）,事件的生成和管理以及仿真钟的推进都由仿真软 件自动完成用户不必手工处理，这就大大简化了用户的建模工作。

Simulation clock and event lists work together, After the simulation initialization is complete, The top record (the next event) is removed from the event list, The simulation clock is then advanced to the occurrence time of the event (which is one of the data items recorded in the event list), The information in the removed record (including the event occurrence time, event type, etc.) is used to process the event, How this works depends on the type of event and the state of the system at the time, But generally, it can include updating state variables and statistical accumulators, changing entity properties, After the event is handled, Generate a new event insert event list, Start a new cycle.

Sometimes, some events occur simultaneously, but the simulation software still arranges a sequence for their execution, and the modeler should pay special attention to how this order affects the results. Simulation software generally provides the event viewer to view the event list information, which can observe the order of simultaneous events are arranged.

In modern simulation software (including Flexsim), the generation and management of events and the promotion of simulation clocks are automatically completed by the simulation software for the user without having to manually process, which greatly simplifies the user’s modeling work.

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参考资料：《实用系统仿真建模与分析》

翻译：金山词霸

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文案 | 邓粤慧

排版 | 邓粤慧