---

Abstract
Conflict is defined as a situation in which one human group is at involvement with another owing to aims that are incompatible. Due to their features and capacities, the Islamic Republic of Iran and Saudi Arabia are two decisive and significant countries in the area. The Islamic Revolution of Iran has created a field of rivalry and conflict between two countries, which has impacted other surrounding areas. Yemen is one of the most important areas in the sector, owing to variables such as closeness to Saudi Arabia, the Arab Spring, a large Shiite population, the emergence of Shiite organizations and movements, geostrategic location, and so on. The two regional powers' geopolitical interests are located. The purpose of this descriptive-analytical research is to learn more about the nature of the war in Yemen between Iran and Saudi Arabia. What reasons have contributed to the emergence of conflict and rivalry between Iran and Saudi Arabia in Yemen? That is the major subject of the study. The study's results suggest that the war in Yemen is rooted in geopolitical and ideological cases.
 
 
 
 
 
Key Words: Iran, Saudi Arabia, Conflict, Geopolitic, Yemen.

---

A theoretical nonlinear droplet deformation model with an accurate estimation of aerodynamic force, which is appropriate for Lagrangian droplet tracking schemes, is presented and validated. The modeling is based on keeping track only of the fundamental oscillation mode. This conventional approach has been used in many deformation-based breakup models including Taylor Analogy Breakup, Droplet Deformation and Breakup, and Nonlinear Taylor Analogy Breakup. However, these models have some shortcomings such as the use of several calibration coefficient, two-dimensional analysis, and rough approximation of aerodynamic forces in large deformations. This paper is intended to amend these defects. The formulation is based on mechanical energy equation. The pressure distribution profile around the deformed droplet is approximated using a piecewise sinusoidal function which depends on Reynolds number and droplet deformation. The final kinetic equation is numerically solved using a fourth-order Runge-Kutta method and the results are compared with those of other models, experiments, and a Volume of Fluid simulation. Numerical results show that the present model predicts slightly greater deformations in comparison with other models for the unsteady case, which is more consistent with the experimental data. Considering the steady case, the results of present model stand between that of Taylor Analogy Breakup and Nonlinear Taylor Analogy Breakup model, and provide satisfactory predictions. The stream lines obtained from simulation match those of calculated analytically suggesting the appropriateness of the assumptions used in the modeling. Overall, the present model is found to be appropriate for the estimation of droplet deformation.

---

Applications of hollow spherical particles in industry and in thermal spraying process have been developed in recent years. Despite dense droplets, in hollow droplets, the volume changes of the gas play an important role in the dynamics of impact and the shape of the formed splats. In plasma thermal spraying, impact velocities of particles to the surface is in the range of 50 m/s-300 m/s, therefore, changes in pressure and volume of the trapped gas, is important. In this research, impact of hollow droplet on a flat surface and its solidification has been simulated. Volume of fluid model for compressible flows at real thermal spraying condition is used while the impact velocities in the range of 50 m/s-300 is considered. In a few moments after the impact of droplet on the surface, a pressure wave is formed in the air. This wave, increase the vorticity in vicinity of interface of two fluid, which has a great effect on shaping the formed splats. Simulations showed that shape of formed splats vary with velocities in the range of 50 m/s-300 m/s. In higher velocities, the surface of the formed splat is more porous.

---

In this research, the impact of a completely molten hollow droplet and a semi-molten hollow droplet on a surface is simulated numerically. At first, the production process of hollow particles from the agglomerated particles is addressed analytically. By this model, one can predict the particle diameter, solid core diameter and shell thicknesses of produced particle. The results of this section show that hollow particle may hardly develop at small initial porosity values (p=0.2). Then, the collected data from analytical model is used as input data for numerical simulation. In the numerical model, the central solid core was assumed to be a fluid with high viscosity. Due to high impact velocity, volume and density changes of the trapped gas inside droplet are important. Therefore the compressible form of governing equations is used. The results show that the hydrodynamic and solidification behavior of a completely molten droplet and a semi-molten droplet during impact process are different. In the semi-molten state, the central solid core prevents the formation of a counter jet. For this reason, a hollow semi-molten droplet is solidified faster than a completely molten hollow droplet. The overall time of solidification in the completely molten state is 35 μs and the corresponding time for semi-molten state, is 12 μs. Moreover the splat of a semi-molten hollow droplet is more continues compared with a completely molten droplet