In this paper, we present a systematic approach for characterization and reconstruction of statistically optimal representative unit cells of polydisperse particulate composites. Microtomography is used to gather rich three-dimensional data of a packed glass bead system. First-, second-, and third-order probability functions are used to characterize the morphology of the material, and the parallel augmented simulated annealing algorithm is employed for reconstruction of the statistically equivalent medium. Both the fully resolved probability spectrum and the geometrically exact particle shapes are considered in this study, rendering the optimization problem multidimensional with a highly complex objective function. A ten-phase particulate composite composed of packed glass beads in a cylindrical specimen is investigated, and a unit cell is reconstructed on massively parallel computers. Further, rigorous error analysis of the statistical descriptors (probability functions) is presented and a detailed comparison between statistics of the voxel-derived pack and the representative cell is made.
Revolutionary developments in the way aircraft are managed and maintained while in service are needed to enable the U.S. Air Force to reduce its maintenance burden and increase aircraft availability while still ensuring airworthiness and safety. The Airframe Digital Twin (ADT) is envisioned to be an ultra-realistic, cradle-to-grave computer model of an aircraft structure that is used to assess the aircraft's ability to meet mission requirements. The ADT will virtually fly each flight that the physical aircraft flies in order to determine loading and subsequent damage. This paper presents results of a study to assess the current state of the art of performing such a virtual flight. A simplistic ADT was "flown" through a Touch-and-Go practice using the flight parameters recorded during the flight. Technical gaps preventing the full realization of the ADT vision were identified along with alternative approaches that are possible with current technology.
Nomenclatureg's g = gravitational acceleration constant, ft/sec 2 p = roll rate, rad/sec q = pitch rate, rad/sec r = yaw rate, rad/sec u = velocity in the x-direction, ft/sec v = velocity in the y-direction, ft/sec w = velocity in the z-direction, ft/sec φ = roll Euler angle θ = pitch Euler angle ψ = yaw Euler angle ω i = angular velocity about the i-axis, rad/sec ̇ = derivative of x with respect to time
We describe and present results from GEN2, the second-generation three-dimensional solid rocket motor simulation package developed at CSAR. The internal gas dynamics, propellant combustion, and structural response are fully coupled. In addition to several test cases, we simulate propellant slumping at a joint slot due to uneven gas pressure loads in the Titan IV SRMU. We also study the motion of a flexible inhibitor and its effect on the gas flow near a joint slot in a section of a typical large solid rocket motor.
IntroductionDetailed 3-D simulation of solid rocket motors requires solving a very complex, tightly coupled multiphysics problem that includes a wide range of length and time scales. Obtaining accurate numerical solutions for relatively simple geometries, physical models, and even fairly short burn times, requires enormous computational resources that are available today only at major supercomputing centers. Each physics module (gas dynamics, structural mechanics, etc.) must run efficiently in parallel on many processors and data must be exchanged frequently between modules in order to solve the tightly coupled system.
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