Accurate determination of particle positioned on free surface in particle method

A method for determining whether or not a selected particle belongs to free surface particles, in a calculation process of a particle method in which a continuum subjected to calculation analysis is collectively modeled with a free surface by a plurality of particles, the method comprising steps of:

• determining a near free surface identification information for a selected particle based on whether or not a particle belonging to the free surface exists within a predetermined range of the selected particle by referencing free surface identification information stored in a memory in a previous time step in the calculation process;
• storing in the memory the near free surface identification information for the selected particle which is set one way when the particle belonging to the free surface exists and which is set another way when the particle belonging to the free surface does not exist;
• performing a first stage of a time step of the calculation process using the determined near free surface identification information of the selected particle, wherein a position and flow velocity are calculated for the selected particle due to an external force in the first stage;
• determining a free surface identification information for the selected particle after the first stage when the near free surface identification information for the selected particle indicates that the particle belonging to the free surface exists prior to the first stage and based on a particle number density for the selected particle after the first stage;
• storing the determined free surface identification information in the memory;
• and
• performing a second stage of the time step of the calculation process using the determined free surface identification information of the selected particle, wherein the second stage corrects the position and flow velocity of the selected particle for a force generated by a pressure gradient.