$$$$ DREXUS NOTICE CHAT 11/09/12 21:15:56 7124 DATE 11/09/12 Procedure DREXUS Voir aussi : ----------------- Notice : _______ 'DREXUS' ETAB ; input table : ETAB . 'MODELE' : model object ETAB . 'CARACTERISTIQUES' : field of material and geometrical (when necessary) characteristics ETAB . 'LIAISONS' : blockading matrice ETAB . 'CHARGEMENT' : definition of the loading in (created by the CHAR operator) ETAB . 'VITESSE_INITIALE' : initial velocity ETAB . 'GRANDES_DEFORMATIONS' : logical for a large strains calculation. ETAB . 'TEMPS_SORTIE' : values of the evolution for which results are recorded. ETAB . 'FREQUENCE_SORTIE' : frequency of records (integer) ETAB . 'TEMPS_INITIAL' : initial time (real 0. by def.) ETAB . 'COEFF_STABILITE' : option : coeff * t_step (0.5 dy def.) ETAB . 'PAS_TEMPS' : option : time step fixed ( real ) ETAB . 'NPASMAX' : maximal number of time step ETAB . 'FREQ_MENAGE' : frequency at which 'MENA' is launched (50 by def.) ETAB . 'AMORTISSEMENT' : option : damping matrix ETAB . 'IMPACT'. 'MAITRE' : master line (SEG2 type) only in 2D ETAB . 'IMPACT'. 'ESCLAVE' : slave line (SEG2 type) only in 2D ETAB . 'IMPACT' . 'NEZ' : slave nose poi1 (plat,cone,hemi) ETAB . 'IMPACT' . 'LARGEUR' : width or radius of the nose (with poi1) ETAB . 'IMPACT' . 'ANGLE' : angle of the nose (with poi1 cone) ETAB . 'IMPACT' . 'VECTEUR' : axis of the projectile (with poi1) ETAB . 'IMPACT' . 'MASSE' : mass of the slave poi1 output : Outputs are stored in the argument table. They are stored in tables whose indices are intergers (0 1 2 .... N) corresponding to the number of the results saving. 0 defined as the initial time. ETAB . 'NPAS' . N : No of step (integer) ETAB . 'TEMPS' . N : time (reel) ETAB . 'DEPLACEMENTS' . N : champoint of displacement ETAB . 'VITESSES' . N : champoint of speed ETAB . 'ACCELERATIONS' . N : champoint of accelerations ETAB . 'FORCES_EXTERIEURES' . N : champoint of external forces ETAB . 'CONTRAINTES' . N : chamelem of stress ETAB . 'VARIABLES_INTERNES' . N : chamelem of internal variables ETAB . 'DEFORMATIONS_INELASTIQUE' . N : chamelem of inelastic strain (chamelem : field by element , champoint : field by points) The Drexus procedur enables to perform a fast dynamic mechanical computation using a Lagrangian description. Is uses an explicit algorithm : the central differences. -The material behavior might be non linear according to the model object. -Large deformations are possible. An hypoelastic model is the used along with the Truesdell objective rate of cauchy stress. -Impact can be modelled in 2D. To the extent one must define two line of contact : a master and a slave (see IMPO IMPA) -To impose non zero displacement the second derivative with respect to time of the seond member of the relationship must be provided in the chargement object ('CHARGEMENT' index) The computation is performed with a fixed time step until either the maximal time step or the maximal number of steps is reached. Outputs are stored according to a list of instants. The time algorithm si summarized below 0- Displacement Un | Speed Vn |- konwn a time n Acceleration An | 1- Compute displacement at time n+1/2 Un+1 = Un + dt.Vn + (dt.dt/2).An 2- Compute external and internal forces at time (n+1) Fn+1 = Fn+1(ext) - div(Sigma(n+1)) - Fdamping(Vn+1/2) 3- Compute accelerations at time (n+1) taking into account the boundary conditions and possible impacts. M.An+1 = Fn+1 4- Compute the speed a time n+1 Vn+1 = vn + dt/2.(An + An+1) $$$$
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