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DualSPHysics & DesignSPHysics common concepts

In this section you will find a series of concepts and explanations for several DualSPHysics and DesignSPHysics concepts.

This section is aimed to new users of each the GUI and the solver package, and covers the usage of things like MK values or order of object creation.

MK Values (MKBound and MKFluid)

MK values are values associated with each object (or group of objects), similar as a 'tag'.

MK values serve this purposes, among others:

  • Organizing and visualizing: Assigning different MK's to different objects makes it easy to organize them and visualizating them in other modes in external software like ParaView.
  • Group objects to apply properties: Some properties like floating apply to an MK, not to an object.

Some use cases are:

  1. Easily viewing the mixing of 2 fluids: Setting different MK to different fluids can help to see how each fluid is situated, viewing the VTK exported particles colored by MK. This way, each fluid would have each color, making it easy to differenciate.
  2. Applying the same properties to several objects: Imagine you want 100 different boxes, but all of them with the same float properties. Setting the same MK to all of them ensures the float properties apply to all of them equally, so you don't have to redefine the float property values for each object. This also applies to movement for boundaries or initial velocity for fluids.

DP (or Inter-particle Distance)

DP is a value set for each case that specify the distance between each particle in the final result. For the same case, setting a higher DP will result in less total particles, as the distance between each one increases.

Setting a lower DP for the same case, though, will result in more total particles.

Mind that setting a higher DP and having less particles will result in a inaccurate simulation. Try to set the particle count to a balance between simulation time and the wanted fidelity.

Object order in a case

Defining objects in a particular order is important in the solver.

In DesignSPHysics you can change the order of object creation with the table placed in the main dock.

Order in objects is useful to slicing and substitution of different objects. Lets put a visual example:

We want to generate the following case.

Let's see the result with 2 different object orders. The first one would be this order:

  1. Obstacle
  2. Water
  3. Container

And the result will be something like this:

As you can see, the obstacle is only above the water. This happens because the creation order specifies that first the obstacle will be created. This way, when water is going to be created, it will fill its volume with particles, substituting the ones already created by the obstacle.

To fix this, the order of particles must be:

  1. Water
  2. Obstacle
  3. Container

This is the result:

The obstacle can now be seen through the water, achieving what we wanted.

This explains easily why object order matters in a case. The particle creation is incremental and substitutes all the possible places that a particle could be (based on DP) with the volume of the current object, in strict order.