问题描述
是否可以使用时变变量的先前值
Is it possible to use the previous value of the time varying variable
例如:假设我的管道入口温度为 298K，具有指定的均匀质量流量(m_flow)，现在假设我使用 100 瓦的加热器加热管道.出口温度将达到假设 302K 的更高温度，现在如果我必须使用这个出口温度作为我的入口温度(在我循环水的意义上)，我会怎么做?
for eg:Suppose I have pipe whose inlet temperature is 298K with a specified uniform mass flow(m_flow), now suppose i am heating the pipe using a heater of 100 watts. The outlet temperature will be attain a higher temperature of suppose 302K, now if i have to use this outlet temperature as my inlet temperature (in the sense i am recircuilating the water), how would i be doing it?
是否可以根据前一时间步的出口温度更新入口温度的值?这样在下一次迭代中，入口温度将与前一次迭代中的出口温度相同(换句话说，流体将进行再循环).
is it possible to update the value of the inlet temperature based on the outlet temperature at the previous timestep? so that for the next iteration the inlet temperature will be the same as the oulet temperature in the previous iteration (in other words the fluid would be recirculating).
谢谢
推荐答案
timestep 根本不进入.使用时间步长信息的模型是错误的.自然不知道也不关心积分时间步长，模型应该反映这一点.
The timestep does not enter into it at all. A model that uses information about timestep is just wrong. Nature doesn't know or care about integration time steps, the model should reflect that.
在我看来，您想要捕获的是传输延迟.传输延迟是由分子、电子等通过系统所需的时间引入的延迟.因此，大概您希望建模的是入口流体到达出口所需的时间.同样，这与积分时间步长无关，而是与流体的速度及其必须行进的距离有关.一旦您知道这需要多长时间(通过系统的先验知识或通过查看模拟结果本身)，您就可以遵循 Marco 使用延迟算子的建议.
It seems to me what you want to capture is transport delay. Transport delay is the delay introduced by the time it takes for molecules, electrons, etc. through the system. So presumably what you wish to model is the time it takes the inlet fluid to reach the exit. Again, this has nothing to do with the integration timestep but rather the velocity of the fluid and the distance it must travel. Once you know how long that takes (by either a priori knowledge of the system of by looking at the simulation results themselves), you can follow Marco's suggestion of using the delay operator.
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