Practical Numerical Model Research Articles

Numerical study of parameters influencing the response of flexible retaining walls

A practical numerical model is described for analysis of flexible retaining walls. In terms of capabilities, the model fits between traditional limit equilibrium methods and full finite element approaches; it overcomes many of the limitations associated with the former but is not equipped with the versatility offered by the latter. Using an approach similar to that adopted in boundary-element based models, the wall stiffness is represented by a series of elastic beam elements whose stiffness is combined with that of the prestressed struts and the soil to form, the overall stiffness matrix. The stiffness matrix of the soil is obtained by inversion of flexibility matrices generated by interpolation and sealing of flexibility matrices calculated for a simplified soil model using finite element methods. The soil behaves linearly elastically, as long as the pressures correspond to stress levels lying between the limits. Where the lateral displacement of the wall corresponds to a pressure outside of these allowable limits, correction forces are added until the resulting pressures are within the active or passive pressures. Arching is permitted by considering the forces acting on the wall compared with the forces consistent with possible failure surfaces within the soil. Other features that can be accomodated by the model include struts, variations in water table, and the effects of surcharges. The proposed model has been shown to capture the displacement, anchor loads, and lateral stresses for several field problems. Based on these studies and other field applications of the model a number of points have been observed that are of practical interest; these points are separately listed. Key words: numerical analysis, retaining wall, anchor, arching, soil–structure interaction, deflection.

Numerical model for pellet-dispersion igniter systems

A fairly comprehensive practical numerical model for the description of ignition transient flow behavior of pellet-dispersion igniter systems is presented. The model was specifically developed for the study of conventional bag and cartridge igniters employed for small-diameter, composite-propellant rocket motors, but the model in its general form may be adapted for the study of a multitude of ignition transient problems. An extensively modified algorithm based on the random-choice method is applied to obtain the solution of the one-dimensional hydrodynamic equations governing the two-phase core flow behavior within the motor chamber and nozzle, in conjunction with pressure-dependent and crossflow-dependent burning rate equations for the solid propellant and igniter pellets. Good agreement is obtained between experimental firing data and predictions from the model for head-end pressure-time profiles.