Spiral structures in the disk galaxies have been extensively studied by many theoretical papers, but conventional steady-state models are not consistent with what we observe in time-dependent, multi-dimensional numerical simulations and also in real galaxies. Here we review recent progress in numerical modeling of stellar and gas spirals in disk galaxies. The spiral arms excited in a stellar disk can last for 10 Gyrs without the ISM, but each spiral arm is short-lived and is recurrently formed. The stellar spirals are not waves propagating with a single pattern speed. The ISM is concentrated in local potential minima, which roughly follow the galactic rotation together with the stellar arms, therefore galactic dust lanes are not the classic ‘galactic shocks’.

This paper is devoted to the description of a new full MLS SPH modelisation of rupture of thin shell filled with fluid and the prediction on consecutive fluid loss though the fracture. The paper first presents an efficient and controlled model for elastoplastic rupture of thin shells by a single layer of SPH balls. The proposed model controls as well static and dynamic instabilities using two basic ingredients: additional stress points to control the hourglass like instabilities and extend the Monhagan viscosity control method to shear and bending components of the generalized efforts. The fluid is modeled using standard SPH fluid model. The interaction is modeled using pin-balls method which is very natural in this type of formulation. Application examples are presented.