How to use the Spatial Search Algorithm

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(An Exemple Configure File)
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Intersection cell and objects: If we do not have this function a simple return true is enougth.  
Intersection cell and objects: If we do not have this function a simple return true is enougth.  
== Calling the Contructor ==
*  Munjiza. Ante,  ''The Combined Finite-Discrete Element Method'',  John Wiley & Sons, Ltd. 2004
*  Munjiza. Ante,  ''The Combined Finite-Discrete Element Method'',  John Wiley & Sons, Ltd. 2004

Revision as of 15:01, 4 May 2012


Using the Spatial Search Algorithm

Large-scale in Finite Element Methods, Discrete Element Method and Combined Finite-Discrete Element Method simulations involve contact of a large number of separate bodies. Processing contact interaction for all possible contacts would involve a total number of operations proportional to N^2, where N is the total number of separates bodies comprising the problem.

This would be very CPU intensive, and would limit the application that use and need to evaluate the contact forces ,comprising a very small number (a few thousand) of separates bodies. To reduce CPU requirements of processing contact interaction, it is necessary to eliminate couples of discrete elements that are far from each other and are not in contact. A set procedures designed to detect bodies that are close to each other is usually called a contact detection algorithm, or sometimes a contact search algorithm.

With this purpose was created in Kratos Program a contact search algorithm based on spatial decomposition, so it can be used for any application and is unique in that it was implemented in a generic way. Therefore it requires a contact search algorithm having the following characteristics:

  • Robust,
  • CPU efficient,
  • RAM efficient

The User Configure File

It say that is the main file created by the user, which defines the types, and operations contenerdores necessary to make the spatial decomposition and the search for contacts. Is then the parameter that defines Bins.

This consists of four parts:

  • Definition of the types and their containers.
  • Function that calculates bounding box
  • Function of intersection between objects
  • Function of intercession between the object and cells.

An Exemple Configure File

Suppose that we have a set of discrete elements like a spheres. In our file called "discrete_configure_file.h" need to create the class, types and methods before mentioned. Is useful to create this file using the template of Kratos found in kratos/templates directory. Only we need to do is changes the default names and directives by the name of our file. Normally this file is stored in the custom_utilities directory of the application.

  • Change the name of directives
  • Change the name of class
 ///@name Kratos Classes
 template <std::size_t TDimension>
 class DiscreteParticleConfigure{
  • Typing the typenames, objects and container of the particle
     ///@name Type Definitions
     typedef  Point<Dimension, double>                        PointType;
     typedef  std::vector<double>::iterator                   DistanceIteratorType;
     typedef  ModelPart::ElementsContainerType::ContainerType ContainerType;
     typedef  ContainerType::value_type                       PointerType;
     typedef  ContainerType::iterator                         IteratorType; 
     typedef  ModelPart::ElementsContainerType::ContainerType ResultContainerType;
     typedef  ResultContainerType::value_type                 ResultPointerType;
     typedef  ResultContainerType::iterator                   ResultIteratorType; 
     typedef  ContactPair<PointerType>                        ContactPairType;
     typedef  std::vector<ContactPairType>                    ContainerContactType; 
     typedef  ContainerContactType::iterator                  IteratorContactType; 
     typedef  ContainerContactType::value_type                PointerContactType; 
     typedef  std::vector<PointerType>::iterator              PointerTypeIterator;

Warn_icon.gif Note:

Another types and container different to the model part can be used.

  • Computing the bounding box
    static inline void CalculateBoundingBox(const PointerType& rObject, PointType& rLowPoint, PointType& rHighPoint)
        rHighPoint = rLowPoint  = rObject->GetGeometry().GetPoint(0);

double radius = rObject->GetGeometry()(0)->GetSolutionStepValue(RADIUS);

        for(std::size_t i = 0; i < 3; i++){
           rLowPoint[i]  += -radius;
           rHighPoint[i] += radius;

Warn_icon.gif Note:

It is necessary the name static inline void CalculateBoundingBox is well type, beacause the function is called by the bins.

  • The Intersection function between objects.
    static inline bool Intersection(const PointerType& rObj_1, const PointerType& rObj_2){
       array_1d<double, 3> rObj_2_to_rObj_1 = rObj_1->GetGeometry().GetPoint(0) - rObj_2->GetGeometry().GetPoint(0);
       double distance_2 = inner_prod(rObj_2_to_rObj_1, rObj_2_to_rObj_1);
       const double& radius_1 = rObj_1->GetGeometry()(0)->GetSolutionStepValue(RADIUS);
       const double& radius_2 = rObj_2->GetGeometry()(0)->GetSolutionStepValue(RADIUS);
       double radius_sum      = radius_1 + radius_2;
       bool intersect         = (distance_2 - radius_sum * radius_sum) <= 0;
       return intersect;

  • Intersection cell and objects
    static inline bool  IntersectionBox(const PointerType& rObject,  const PointType& rLowPoint, const PointType& rHighPoint){
       array_1d<double, 3> center_of_particle = rObject->GetGeometry().GetPoint(0);
       const double& radius = rObject->GetGeometry()(0)->GetSolutionStepValue(RADIUS);
       bool intersect = (rLowPoint[0] - radius <= center_of_particle[0] && rLowPoint[1] - radius <= center_of_particle[1] &&   rLowPoint[2] - radius <= center_of_particle[2] &&
           rHighPoint[0] + radius >= center_of_particle[0] && rHighPoint[1] + radius >= center_of_particle[1] && rHighPoint[2] + radius >= center_of_particle[2]);
       return  intersect;

Warn_icon.gif Note:

Intersection cell and objects: If we do not have this function a simple return true is enougth.

Calling the Contructor


  •  Munjiza. Ante, The Combined Finite-Discrete Element Method, John Wiley & Sons, Ltd. 2004
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