Conditions for collisional growth of a grain aggregate     

Sin-iti Sirono 《Icarus》2004,167(2):431-452

Collisional growth of grain aggregates is a critical process in the early stage of planet formation. A collision between grain aggregates is numerically simulated by means of a smoothed particle hydrodynamic code, treating a grain aggregate as a continuum media. A model for mechanical response of a grain aggregate is developed based on published experimental data. Free parameters of the model are the bulk modulus, compressive, shear, and tensile strengths of a grain aggregate, and impact velocity. I have determined three conditions for the growth of an aggregate within the mechanical response model. (1) Compressive strength is the smallest among the three components of strengths. (2) Impact velocity is as low as 4% of the sound speed of an aggregate. (3) Effective restoration of the strengths is necessary due to reconnection between grains followed by compaction of an aggregate. Possibilities of these conditions in the solar nebula are discussed.  相似文献   

Numerical simulation of heat conduction in a random ballistic deposited grain aggregate     

Sin‐iti Sirono 《Meteoritics & planetary science》2014,49(1):109-116

A numerical simulation of heat conduction in a grain aggregate is carried out to determine the packing fraction (the spatial fraction occupied by grains or 1‐porosity) dependence of the thermal conductivity of the aggregate. Arrangements of grains are given by random ballistic deposition. It is found that the packing fraction dependence is well approximated by an exponential function. The number of contacts between grains is the crucial quantity in the conduction, and its packing fraction dependence is exponential. Heat conduction is found to be anisotropic, where the conduction along the deposition direction is more efficient than that perpendicular to the deposition direction.  相似文献