Analysis of Options to Reduce Noise Exposure to Shooters on Sport Shooting Ranges

The intensive development of sport shooting and the significant increase in the number of people using sport and recreational shooting ranges also increases the risk of hearing damage to shooters, due to exposure to impulse noise from the shots of firearms. This article discusses the methodology for assessing shooters’ exposure to noise and identifies and extensively discusses possible ways to minimise this exposure. It then describes a research experiment carried out to measure and calculate the effectiveness of noise reduction by means of acoustic silencers when shooting with typical weapons in the most popular sporting and hunting calibres. The experiment also included firing tests with subsonic ammunition. On this basis, conclusions were drawn regarding the possibility of reducing impulse noise during shooting and the possibility of eliminating the risk of hearing damage.

Evaluation of the high-frequency oscillation parameters of a liquid-propellant rocket engine with an annular combustion chamber

The high-frequency instability (HF instability) of a liquid-propellant rocket engine (LPRE) during static firing tests is often accompanied by a significant increase in dynamic loads on the combustion chamber structure, often leading to the chamber destruction. This dynamic phenomenon can also be extremely dangerous for the dynamic strength of a liquid-propellant rocket engine with an annular combustion chamber. Computation of the parameters of acoustic combustion product oscillations is important in the design and static firing tests of such rocket engines. The main aim of this paper is to develop a numerical approach to determining the parameters of acoustic oscillations of combustion products in annular combustion chambers of liquid-propellant rocket engines taking into account the features of the configuration of the combustion space and the variability of the physical properties of the gaseous medium depending on the axial length of the chamber. A numerical approach is proposed. The approach is based on mathematical modeling of natural oscillations of a “shell structure of an annular chamber – gas” coupled dynamic system by using the finite element method. Based on the developed finite-element model of coupled spatial vibrations of the structure of the annular combustion chamber and the combustion product oscillations, the oscillation parameters of the system under consideration (frequencies, modes, and effective masses) for its dominant acoustic modes, the vibration amplitudes of the combustion chamber casing, and the amplitudes of its vibration accelerations can be determined. The operating parameters of the liquid-propellant rocket engine potentially dangerous for the development of thermoacoustic instability of the working process in the annular combustion chamber can be identified. For the numerical computation of the dynamic gains (in pressure) of the combustion chamber, a source of harmonic pressure excitation is introduced to the finite element model of the dynamic system “shell structure of an annular configuration – gas” (to the elements at the start of the chamber fire space). The developed approach testing and further analysis of the results were carried out for an engine with an annular combustion chamber (with a ratio of the outer and inner diameters of 1.5) using liquid oxygen – methane as a propellant pair. The system shapes and frequencies of longitudinal, tangential and radial modes are determined. It is shown that the frequency of the first acoustic mode in the case of a relatively low stiffness of the combustion chamber casing walls can be reduced by 40 percent in comparison with the frequency determined for a casing with rigid walls.

Determination of receiver consumption characteristics using computer simulation

The problem of implementing the detonation mode of fuel combustion in thermal propulsion systems has been widely studied last decade. There are many works on fundamental and applied research on pulsating detonation. Solid propellant detonation engines can develop significant forces for a short time at low structural masses, and therefore they are ideal for auxiliary systems for the removal of separated rocket parts. In addition, detonation processes can be used to create control forces for correcting the trajectory of aircraft. All these facts determine the relevance of the area of work. For studying detonation installations, it is necessary to create test stands, but the design of test installations is an urgent and complex optimization problem. It is advisable to solve this problem with the help of computer simulation. In the existing experimental methods, for designing, it is necessary to determine in advance the geometric parameters of receivers and pipelines that provide the necessary gas consumption for firing tests of detonation rocket engines. The work is devoted to the development of a method for determining the flow characteristics of a receiver with a pipeline of complex configuration based on the constructed model of the stand. Based on the initial data, a computer simulation of the air leakage process from the receiver was carried out, for which the Solid Works software package was used. The places of pressure drop, maximum flow rate, and air mass flow are determined. The low value of the flow rate factor is due to the complex configuration of the pipeline with numerous bends and two bellows. Comparison of calculation results with experimental data was held. The difference between the experimental and calculated values does not exceed 3.6%. The obtained information is used to select the required value of the oxidizer excess coefficient during firing tests of detonation rocket engine models. Keywords: flow rate, gas leakage, receiver, model.

Research of Fireproof Capability of Coating for Metal Constructions Using Calculation-Experimental Method

Determination of characteristic of fireproof capability of examined fire-retardant coating by experiment-calculated method solving the inverse heat conduction problems based on the firing tests data. With the aim of determining the fire-resistance time of metal sheets with fire-retardant coating there are used experimental research methods of patterns behavior during heating according to the requirements of National Standards of Ukraine B.V. 1.1.-4-98 are used; mathematical and computer modelling of processes of unsteady heat transfer in the system “metal sheet – fire-retardant coating”; determination of thermal characteristics and characteristic of coating fireproof capability. Firing tests of metal sheets covered by the flame retardant “Amotherm Steel Wb” are carried out. Based on the obtained data (temperature from the unheated sheet surface) there are determined the thermal characteristics of formed coating depending on temperature and the characteristic of fireproof capability of examined coating for 30 minutes fire-resistance time. The effectiveness of intumescent coating “Amotherm Steel Wb” is proved and the dependence between its heat conduction coefficient and temperature during heating in experimental stove of metal sheet with this coating in standard temperature conditions is specified. The co-relation between the thickness of intumescent coating “Amotherm Steel Wb” and fire-retarding quality of metal constructions is identified. Besides the necessary minimum thicknesses of such coating from the thickness of metal sheet for importance of 30 minutes fire-resistance time are calculated.

PROTECTIVE EFFECTIVENESS OF ARMOUR MADE OF NANOBAINITIC STEEL

The article presents the results of tests on resistance to perforation of nanobainitic steel plates with a thickness in the range of 6–9 mm with the use of projectiles with different perforation mechanisms. Firing tests were carried out using 7.62×39 mm BZ ammunition in accordance with the requirements of the NATO Stanag 4569A standard document (level 2) and 7.62×54R mm B32 ammunition to determine the V50 parameter for selected variants and plate thickness. The plates constituting the testing material were manufactured on an industrial scale from two heats with different chemical composition. The nanobainitic steel plates were subjected to heat treatment including austenitisation, controlled cooling and direct isothermal annealing, the parameters of which were optimised in order to achieve the highest protective capacity. Microstructure studies were carried out in places where the projectile and the plate interacted, in order to analyse the effects of firing in detail. The obtained test results indicated limit values of projectile velocities and plate thicknesses for which ballistic protection is effective. The range of mechanical properties determined in a static tensile test as well as the type of microstructure were determined, including the content and form of retained austenite, guaranteeing compliance with the required level of resistance to perforation. Based on the results of the firing tests, heat treatment variants were selected for plates of a certain thickness intended for the armour of an observation and protective container. The studies and tests were carried out as part of the POIR 04.01.04-00-0047/16 project, the main goal of which is to reduce the weight of a LOOK container armour.

Optimisation of parameters for the production of perforated armour panels made of nanobainitic steel using dynamic hardness measurement methodology

The study is a continuation of the development of material characteristics in order to expand the range of products for the production of which nanostructured bainitic steels can be used. The tests included measurement of dynamic properties important in the material qualification process for firing tests and for other applications requiring dynamic wear resistance. The novelty of the implemented development of the innovative grade of nanostructured steel and the technology of manufacturing products – including armour systems containing perforated panels made of this grade of steel, consisted in developing the basics of dynamic hardness measurement methods and dynamic indentation tests using a Gleeble simulator.

Systems for assuring safety of static firing tests of oxygen/hydrogen propulsion units

Static firing tests of oxygen-hydrogen propulsion units with propellant tank load of up to 2700 kg of hydrogen are run with special safety precautions and using emergency test protection system covering up to 60% of contingencies. Test on propulsion units with higher hydrogen propellant loads (up to 7000 kg) require additional safety measures, based on improved effectiveness of the fire and explosion prevention systems, emergency protection, and the coverage ratio for emergency (off-nominal) situations. The key factors for improving off-nominal situations coverage ratio during tests are research into systems for earlier detection of hydrogen leaks and the use of inhibitors with nitrogen as the phlegmatizing agent to prevent explosion of the hydrogen/air (oxygen) mixtures. The paper presents results of studies into systems for early detection of hydrogen leaks and design of monitoring equipment based on fiber optics and microcavity structures that have higher speed of response, selectivity, immunity to noise and reliability. Key words: propulsion system, safety, emergency protection system, off-nominal situation, hydrogen leak, fiber-optic technology.