particle forward, and accelerates and decelerates the particle. The acceleration of the particle located in x is given by Eq. (1): ¸ ¹ · ¨ © § ' dt dx V x dt d x D 2 2 (1) where D is known as the sensitivity, x' is the interparticle distance, and V x' is known as the OV function. V x' is given by Eq. (2): ¸¸ ¹ · ¨¨ © § ¸ ¹ · ¨ © § ¸ ¹ · ¨ © §' ' w d w x d v V x tanh tanh 2 max (2) where max v is the maximum velocity, and d w, are the parameters. In this paper we choose 0.47, 0.45 d w . Next, we explain DEM [7]. DEM is a technique for not handling the structure as a continuum, but discretely analyzing it by modeling as individual particle elements. In DEM, the acceleration of the particle is calculated by using a different method, and velocity dx dt and position x are given in Eqs. (3) and (4): t dt d x dt dx dt dx t t t t t ' ' ' 2 2 (3) t dt dx x x t t t t t ' ' ' (4) In this way, as the acceleration at new time t t ' is integrated, displacement and the velocity at time t t ' are obtained. The movement tracks of the particle are computable by repeating this calculation by time step t' . In primary DEM, when the particle comes in contact with something, the contact force is calculated by using the Voigt model and the acceleration is given. However, it is necessary to calculate the acceleration of the particle in the noncontact state in the DEM-base traffic model. Then, the accelerometer calculation is done by using the above OV model in the traffic model. The obstacle-avoiding algorithm by the DEM-base traffic model is described. This algorithm defines view area and affected area [5]. View area distinguishes the obstacle particle with the possibility of jamming in for the target direction of particle i . Affected area judges the particle to be actually influenced by the deceleration vector ov & in the area of view. Fig. 1 shows the view area and the affected area. ir is radius of particle i in the figure. : affected area : area of field of view ir4 d6 d3 $ 30 i Target direction Fig. 1 View area and affected area When the center of obstacle particle j doesn't exist in the view area, i doesn't receive influence from surrounding particles, and give maximum velocity max iv in the target direction of i . On the other hand, when the center of particle j exists in the view area, velocities nj nj ni ni v v T T , cos cos & & of the direction from i to j at t are obtained respectively (Fig. 2). 232
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