This lesson introduces most of FlexSim's Fluid Objects. You will learn how they interact with each other and how to include them in a model with the Discrete Objects. Building a model with the Fluid Objects is more involved and requires more attention to detail than a model with the Discrete Objects. For that reason, it is recommended that you feel comfortable building models with the other objects before you begin to learn about the Fluid Objects.

What You Will Learn

- How to model fluid material with FlexSim
- How to convert flowitems into fluid material
- How to transfer and store fluid material
- How to use level marks on a tank to control material flow
- How to mix fluid materials together
- How to convert fluid material into flowitems

New Objects

In this lesson you will be introduced to the FluidTicker, ItemToFluid, FluidPipe, FluidTank, FluidMixer, FluidProcessor and FluidToItem objects.

Approximate Time to Complete this Lesson

This lesson should take about 45-60 minutes to complete.

Fluid Model Overview

In our fluid model we will have an operator carry boxes of two different types of material into the model. These boxes will be converted into two fluids which will be transported by Pipes to two Tanks. From the Tanks the material is sent to a single Mixer which will mix the two products into a new product. That product is sent through a FluidProcessor, and then converted into flowitems which are carried by a Conveyor to a Sink. The fluid in this model will be measured in gallons, and the time will be in seconds.

### Figure 4-1 Fluid Model diagram

#### Fluid Model Data

Flowitem arrival rate: exponential(0,10) seconds

Maximum Content of ItemToFluid: 20 gallons

Fluid Units per Discrete Unit (ItemToFluid): 10 gallons per flowitem

Maximum Content of Pipe leading to Tank: 20 gallons

Transfer Rate (ItemToFluid to Tank): 2 gallons per second

Tank Low Mark: 1 gallon

Tank High Mark: 45 gallons

Maximum Content of Pipe leading to Mixer: 10 gallons

Transfer Rate (Tank to FluidToItem): 1 gallon per second

Mixer Steps:

Step 1: Material1, no delay time

Step 2: Material2, 10 second delay

Mixer Recipe:

Material1: 10 gallons, step 1

Material2: 20 gallons, step 2

Maximum Content of FluidToItem: 10 gallons

Fluid Units per Discrete Unit (FluidToItem): 10 gallons per flowitem

#### New Concepts

FlexSim Terminology

Before you start this model it will be helpful to understand some of the basic terminology of FlexSim's fluid system.

Fluid: Any material that is not easily or efficiently modeled with discrete flowitems. Typically, material that is measured by weight or volume is hard to model with flowitems. This is because frequently part of a unit (for example, half a gallon) can be moved by itself. There is no easy mechanism for moving half of a flowitem. Fluid material can also represent objects that are so numerous that flowitems are impractical. For example, thousands of bottles in a filling line will slow down a model that uses a flowitem for each bottle. Instead, the Fluid Objects can be used to model these bottles without the overhead that comes with the flowitems.

Fluid Objects: The eleven objects that are designed to handle fluid material. Nine of them cannot interact with FlexSim's Discrete objects, but two of them are designed to work as an interface between the Fluid Objects and the Discrete Objects. More information can be found here.

Tick: The Fluid Objects send and receive material at set intervals. These intervals are called "ticks". At the end of each tick, the Fluid Objects calculate how much material they sent and received during that time period.

Tick time: The length of each tick. The modeler can set this value to some value that is appropriate for their model. A shorter tick time may make the model more accurate, but it may also make it slower. A longer value will be a faster model, but the cost is a loss in accuracy. It is up to each modeler to decide the optimal trade-off of speed and accuracy for their model.

Rate: The maximum speed at which material enters or leaves an object. Generally, the Fluid objects have both an input rate and an output rate that are separate from each other. In a few objects, the rate at which material enters will affect the rate at which it leaves. For these objects, the modeler is not given the opportunity to edit the output rate. The actual rate at which material enters or leaves is based on several factors: the output rate of the upstream object, the input rate of the downstream object, the amount of material available to send and the amount of space available in the downstream object.

Object Rate: This is the maximum rate at which material can enter or leave an object through all input or output ports combined. The objects typically have a separate rate for the input ports and the output ports. If, at the end of any tick, the object calculates that the amount of material it has sent or received has reached the maximum object rate, no more material will be sent or received for that tick, even if there are ports that have not yet sent or received material.

Port Rate: This is the maximum rate at which material can enter or leave any single port on the object. The objects typically have different port rates for input and output ports. This single value applies to all of the input or output ports. It cannot be changed to affect individual ports.

Port Scale Factor: This is a number that is used to change the port rate for each individual port. There is one scale factor available for every input and output port. The value for each port is multiplied by the maximum port rate to find the actual maximum rate for that port.

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