The analysis of combustion models of the main components of condensed combustion products (CCP) of boron-containing solid propellants (boron, boron carbide, boron nitride, and carbon) is carried out. Using the available experimental data, the parameters of the combustion model of boron carbide and boron nitride particles are determined. Using the combustion models of boron, B<sub>4</sub>C, BN, and carbon particles, parametric calculations of the combustion of both individual indicated particles and their mixtures, which simulates the composition of the CCP of boron-containing solid propellant, have been carried out. A comparative analysis of the combustion of particles of boron, B<sub>4</sub>C, BN, and carbon in proportions characteristic of the CCP of boron-containing solid propellants showed that combustion of BN has the least effect on the completeness of combustion of CCP. This is due to its low calorific value and low content in CCP. Ceteris paribus, carbon particles burn the fastest, but their contribution to the completeness of CCP combustion is less than that of boron and boron carbide due to their lower calorific value.

Molybdenum disulfide (MoS2) has gained significant attention due to its exceptional properties, which include a low friction coefficient, high wear resistance, and excellent thermal stability, contingent upon specific conditions. This review paper offers a thorough analysis of the literature with a focus on space applications, emphasizing the vital significance of solid lubrication and the rise of MoS2 as the most exceptional lubricant. Various deposition methods, such as burnishing, bonded coatings, and sputtering (PVD) have been thoroughly explored to fabricate high-quality MoS2 coatings with enhanced properties, such as improved elastic modulus, hardness, adhesion, and density. The paper further delves into experimental and computational modelling techniques, which have been effectively employed to gain profound insights into the fundamental mechanisms governing the mechanical and tribological behaviour of MoS2 coatings. Theoretical models pertaining to indentation, friction, and wear have been analysed in detail, contributing to a comprehensive understanding of the coating performance. This review comprehensively discusses the different doping elements and nano-composites which play an important role in enhancing the MoS2 properties in space applications, especially in humid conditions. A detailed discussion regarding the change in structural morphology, due to the addition of alloying elements which in turn influence the mechanical and tribological behaviour of MoS2 coatings, has been incorporated. The valuable insights offered in this review provide practical guidance for the design and fabrication of high-performance coatings that exhibit improved reliability and longevity in the demanding space environments. Therefore, this comprehensive review consolidates the knowledge on MoS2 as an exceptional solid lubricant for aerospace applications.

The standard formulation of the upper bound theorem is incompatible with the Coulomb friction law. However, this law is widely used in metal forming processes analysis. An alternative formulation based on non-kinematically admissible velocity fields can evaluate the load required to deform the material. The present paper adopts this formulation for evaluating the compression force in solid and hollow cylinder compression processes. The trial velocity fields are continuous. The field for the solid cylinder involves no parameter for minimization, and the field for the hollow cylinder involves one parameter. Parametric analyses of the solutions are provided. The compression forces found are compared to available results at small friction coefficients. The solution is also in agreement with physical expectations. In particular, the solution for the hollow cylinder compression predicts that the radial velocity is everywhere positive in the friction coefficient is small enough. For larger friction coefficients, the radius where the radial velocity vanishes propagates from the inner radius as the friction coefficient increases. The final result can be used in conjunction with standard procedures for evaluating the friction coefficient.

The stability of the vertical flow that occurs when gas displaces oil from a reservoir is investigated. It is assumed that the oil and gas areas are separated by a layer saturated with water. This method of oil displacement, called water-alternating-gas injection, improves the oil recovery process. We consider the linear stability of two boundaries that are flat at the initial moment, separating, respectively, the areas of gas and water, as well as water and oil. The instability of the interfaces can result in gas and water fingers penetrating into the oil-saturated area and causing residual oil. Two cases of perturbation evolution are considered. In the first case, only the gas–water interface is perturbed at the initial moment, and in the second case, small perturbations of the same amplitude are present on both surfaces. It is shown that the interaction of perturbations at interfaces depends on the thickness of the water-saturated layer, perturbation wavelength, oil viscosity, pressure gradient and formation thickness. Calculations show that perturbations at the oil–water boundary grow much slower than perturbations at the gas–water boundary. It was found that, with other parameters fixed, there is a critical (or threshold) value of the thickness of the water-saturated layer, above which the development of perturbations at the gas–water boundary does not affect the development of perturbations at the water–oil boundary.

The cell motility problem has been investigated for a long time. Today, many biologists, physicists, and mathematicians are looking for new research instruments for this process. A simple 2D model of a free-boundary cell moving on a homogeneous isotropic surface is presented in the paper. It describes the dynamics of the complex actomyosin liquid, whose special properties influence the boundary dynamics and cell motility. The model consists of a system of equations with the free boundary domain and contains a non-local term. In this work, we present a numerical solution of this problem.

The transverse impact of a pulsed water microjet on individual cylindrical fibers is studied. The stages of ejection, breakup, and collision of the microjet were recorded by high-speed photography. A significant deceleration of the microjet by the fiber and its splitting into two parts were revealed. The mechanisms of the observed phenomena and the influence of various factors are discussed.