Vladimír Horák

Study of phase behavior of carbon dioxide as the power gas for gas guns

The article is focused on the examination of the phase behavior of carbon dioxide (CO2) utilized as the source of energy to propel the projectile in gas guns technology. The objective is to develop an equilibrium discharge mathematical model for carbon dioxide tanks in order to assume thermodynamic equilibrium states at every point in time throughout discharging under ambient temperature conditions. The speed of sound in a two-phase saturation is taken into consideration for the calculation algorithm. The presented model is solved using the MATLAB environment. An experimental setup has been established for the purpose of verifying the results of solution.

DYNAMICS OF KNOCK-OPEN VALVE FOR GAS GUNS POWERED BY CARBON DIOXIDE

The paper is focused on the dynamics of knock-open valve used to control the mass flow from a carbon dioxide (CO2) reservoir. The objective is to formulate the mathematical model simulating dynamics of the knock-open valve system for the gas guns powered by carbon dioxide. The equilibrium discharge mathematical model is overviewed, modified and evaluated to obtain the thermodynamic equilibrium states taking place within the reservoir. The problem is solved using MATLAB environment and results of theoretical solution are verified experimentally. Influence of changes in some design parameters of the knock-open valve system to the mass discharge of CO2 within the reservoir is comprehensively examined.

EXPERIMENTAL MECHANICAL DEVICE FOR RECOIL SIMUALTION

The paper deals with the development and testing of the experimental, spring powered mechanical device for the simulation of the gun’s recoil and further for the obtaining the experimental data for the purpose of research and development of the device for gun’s recoil simulation. Several kinds of the present firearm recoil simulation systems and principles of their function are closely described and explained. Measured force diagrams for the experimental mechanical device and for the real assault rifle are presented.

FORECASTING THE BEHAVIOR OF FRACTAL TIME SERIES: HURST EXPONENT AS A MEASURE OF PREDICTABILITY

The Hurst exponent (H) is a statistical measure used to classify time series. H = 0.5 indicates a random series while H > 0.5 indicates a trend reinforcing series. The larger the H value is the stronger trend. In this paper we investigate the use of the Hurst exponent to classify series of financial data representing different periods of time. In this paper we show that series with large values of the Hurst exponent can be predicted more accurately than those series with H value close to 0.5. Thus the Hurst exponent provides a measure for predictability.

CFD simulation of flow over the dimpled sphere

The paper deals with problems of CFD simulating airflow over a dimpled spherical surface and its validation by the wind tunnel testing. The low-cost simulation approach was applied to be run on a common PC using the commercial software ANSYS CFX. The wind tunnel testing has been performed in the laboratory of aerodynamics at the Department of Air Force and Aircraft Technology of the University of Defence. Measured results of the drag coefficient versus the Reynolds number for smooth and dimpled spheres were compared and discussed. Presented simulation corresponds adequately to the experimental results. It can be stated that the CFD simulation is suitable for simulating the flow over the dimpled surface and for the evaluation of the drag coefficient for smooth and dimpled spheres.

The internal ballistics of airguns

The paper is focused on the development of a thermodynamic mathematical model describing the internal ballistic phenomena, taking place within working chambers of an airgun. The objective is to derive a governing equation modeling the change of gas temperature in a control volume subsuming several incoming and outgoing mass airflow rates. A novel algorithm for solving internal ballistics of all types of airguns is also developed and applied for the case of spring-piston airgun. The mathematical model and solving algorithm are validated and verified experimentally.

DYNAMICS OF RECOIL SIMULATION DEVICE POWERED BY CARBON DIOXIDE

The paper is focused on the dynamics of the recoil simulation device powered by the carbon dioxide (CO2). The objective is to formulate a mathematical model simulating the cylinder pressurization, and the displacement of the recoil simulation device moving part. The CO2 is considered as the real gas. The speed of sound in a two-phase saturation is taken into account for the determination of the critical gas flow rate from the CO2 pressure tank into the cylinder. The problem is solved using the MATLAB environment and results of the theoretical solution are verified experimentally.

Application of fractional calculus to modeling transient combustion of solid propellants

It was Zel’dovich, who first considered the transient combustion problem of solid propellants. Some more detailed models of that process have been developed afterwards. However, until today, numerical methods remain the prevailing tool for modeling unsteady combustion processes. In this work, it has been demonstrated that at least one of the problems of the unsteady combustion theory, which previously investigated numerically, can be treated analytically by means of fractional calculus. The solution for the unsteady speed of combustion thus derived is then compared with the solution obtained by numerical means in previous studies. The comparison shows a good agreement between those results, especially for small values of time.It was Zel’dovich, who first considered the transient combustion problem of solid propellants. Some more detailed models of that process have been developed afterwards. However, until today, numerical methods remain the prevailing tool for modeling unsteady combustion processes. In this work, it has been demonstrated that at least one of the problems of the unsteady combustion theory, which previously investigated numerically, can be treated analytically by means of fractional calculus. The solution for the unsteady speed of combustion thus derived is then compared with the solution obtained by numerical means in previous studies. The comparison shows a good agreement between those results, especially for small values of time.

On the possibility to develop an advanced non-equilibrium model of depressurisation in two-phase fluids

Carbon dioxide is widely used as the power gas in the gas guns community due to its ease of handling, storability at room temperature, and high vapor pressure depending only upon temperature, but not a tank size, as long as some liquid carbon dioxide remains in the tank. This high vapor pressure can be used as the pressurant, making it what is referred to as a self-pressurising propellant. However, as a two-phase substance, carbon dioxide does have its drawbacks: (1) vaporization of liquefied CO2 inside a tank when shooting rapidly or a lot causes the tank to get cool, resulting in pressure fluctuations that makes the gun’s performance and accuracy worse, (2) solid carbon dioxide that is also known as dry ice can appear on the output valve of the tank while shooting and it can cause damage or slow the gun’s performance down, if it works its way into some control components, including the barrel of the gun. Hence, it is crucial to obtain a scientific understanding of carbon dioxide behavior and further the...

THERMO-ANEMOMETRIC DETERMINATION OF LIQUID WATER CONTENT IN WET AIRSTREAM

The paper is focused on the experimental study of possibilities of the thermoanemometric analysis for determination of the liquid water content in the stream of wet air. The developed method is based on the measurement and comparison of stream velocity of wet and dry air by the hot-wire thermal anemometric probe. Experiments were performed in the small icing wind tunnel using the standard thermal anemometer Testo 425. There was found the correlation between the liquid water content and the difference in measured velocity of the wet and dry airstreams. The conclusion of the paper pays attention for the interpretation and formulation the final analyses and recommendations.