Compact silencers with discrete baffle elements for new-generation light small arms

This paper presents the results of the development of silencers, whose design features discrete baffle elements. The advisability of silencers of this type is confirmed by their operational reliability and shot sound suppression efficiency in their actual service as part of light small arms of different types. To design advanced silencers, technical requirements for their design were developed. The paper describes the possibility of using discrete elements (cones, hemispheres, flat baffles, etc.) as the key component of a powder gas spreader. Differently shaped elements are used as additional elements that form a powder gas flow inside a silencer: for example, cylindrical elements, including perforated ones to provide a powder gas flow between the expansion chambers. One way to increase silencer efficiency is an additional expansion chamber that embraces the external part of the barrel and is gas-dynamically connected to a traditional muzzle silencer. In deciding on an optimum design for compact silencers, the following was redetermined: the number of expansion chambers and the dimensions thereof, the powder gas energy converter design, the baffle type, the presence of a gas flow between the chambers near the inner surface of the silencer body, and, if so, the gas flow rate. The silencer design was optimized based on simulating the processes inside the silencer using the authors’ efficiency calculation procedure for silencers with different internal components. Comparison tests of the silencers developed and foreign silencers confirmed a high efficiency of the former. The silencers with discrete baffles for light small arms developed at the Institute of Technical Mechanics of the National Academy of Ukraine and the State Space Agency of Ukraine compare well in performance with their best foreign counterparts. The designs of some of them are covered by Ukrainian patents.

Green Shipping—Multifunctional Marine Scrubbers for Emission Control: Silencing Effect

Scrubber systems abate the sulphur oxide emissions of engines when cheap fuel oils that are high in sulphur content are employed as combustibles. However, the ships with these voluminous devices installed on board is space demanding. This work analyses the feasibility of incorporating the acoustic abatement of the exhaust gas noise functionality into the scrubber design to provide a combined scrubber–silencer system. For this purpose, a finite element analysis is performed on a simple expansion chamber, which is assessed using both analytical and experimental data. The transmission loss is the acoustic parameter chosen in this work. The numerical model depicts a good correlation with the transmission loss measured on a model scale scrubber. Finally, scrubber geometry modifications alter the transmission loss, changing and/or enhancing its featuring. These abilities indicate the feasibility to confer to scrubber silencing effects.

Flow field of impinging sweeping jets

Sweeping jets are oscillating jets generated by fluidic oscillators, i.e., devices designed to produce an oscillation of the flow without the use of any moving parts (Raghu, 2013). A typical configuration of such devices consists of an expansion chamber connected to a high-pressure supply via a converging nozzle and provided with feedback channels. The oscillating motion in the expansion chamber is triggered by an inherent flow instability and sustained by the flow rate across the feedback channels. Recently, sweeping jets have been studied in flow control applications for noise reduction, separation and circulation control over airfoils, control of resonant cavity oscillations and deflection of jets. The advantageous features of fluidic actuators, among which are the wide range of operating frequencies (up to kHz with meso-scale) and the distributed momentum addition, have also stimulated an increasing interest in their application to electronics cooling. Several recent studies on the convective heat transfer from impinging sweeping jets (e.g., Hossain et al., 2018; Park et al., 2018) have shown that, compared to conventional round jets, they offer higher cooling rates with better uniformity at least for small jet-to-plate spacings.

Tuning acoustic performance of multi-chamber hybrid mufflers

In this paper, we investigate the functional acoustic performance of multi-chamber mufflers using a numerical approach. The wave propagation governing in expansion chamber domains is first introduced and solved by the finite element method. Our numerical results of selected muffler configurations are compared with the reference predictions model and experiments in order to validate the present procedure. Then, the influence of the geometry characteristics of typical and hybrid configurations of multi-chambered mufflers (number of sub-chambers, micro-perforated tube structure) on their sound transmission loss is studied. The obtained results indicate that the structure of the considered muffler has a strong effect on their acoustical performance, and the location and the high level of resonances of the sound transmission loss behavior are strongly related to the number of sub-chambers as well as micro-perforated tube characteristics. By tuning geometrical parameters (e.g., having a small perforation ratio), we enable to design mufflers having a higher sound transmission loss (up to 110 dB) at low frequencies (~ 195 Hz) but a constraint space (e.g., acoustic chamber length of 300 mm).

Compact silencers for new-generation light small arms

This paper presents the results of the development of silencers, whose design feature is a central perforated tube, at the institute of Technical Mechanics of the National Academy of Sciences of Ukraine and the State Space Agency of Ukraine (ITM of NASU and SSAU). The advisability of silencers of this type is confirmed by their operational reliability and shot sound suppression efficiency in their actual service as part of light small arms of different types. To design high-efficiency advanced silencers, technical requirements for their design were developed. The paper describes the possibility of using a central perforated tube as the key component of a powder gas spreader. Differently shaped elements or a combination thereof are used as additional elements that form a powder gas flow inside a silencer: conical and spherical axisymmetric baffles coaxial with the silencer body, cylindrical shells (including perforated ones) that provide a powder gas flow between the expansion chambers along the internal axis of the central channel, helicoidal elements, and peripheral labyrinth-vortex contours. One way to increase silencer efficiency is an additional expansion chamber that embraces the external part of the barrel and is gas-dynamically connected to a traditional muzzle silencer. In deciding on an advisable design for compact silencers, the following was redetermined: the number of expansion chambers, the powder gas energy converter design, the baffle type, the presence of a gas flow between the chambers along the inner surface of the silencer body, and, if so, the gas flow rate. The silencer design was optimized based on simulating the silencer gas dynamics using the authors’ efficiency calculation procedure for silencers with a central perforated tube and different internal components. The paper describes the procedure and presents the results calculated with its help. Comparison tests of the silencers developed and foreign silencers confirmed a high efficiency of the former. The silencers with a central perforated tube for light small arms developed at the ITM of NASU and SSAU compare well in performance with their best foreign counterparts. The designs of some of them are covered by Ukrainian patents.

Numerical Study of Pressure Attenuation Effect on Tunnel Structures Subjected to Blast Loads

This study used experimental and numerical simulation methods to discuss the attenuation mechanism of a blast inside a tunnel for different forms of a tunnel pressure reduction module under the condition of a tunnel near-field explosion. In terms of the experiment, a small-scale model was used for the explosion experiments of a tunnel pressure reduction module (expansion chamber, one-pressure relief orifice plate, double-pressure relief orifice plate). In the numerical simulation, the pressure transfer effect was evaluated using the ALE fluid–solid coupling and mapping technique. The findings showed that the pressure attenuation model changed the tunnel section to diffuse, reduce, or detour the pressure transfer, indicating the blast attenuation effect. In terms of the effect of blast attenuation, the double-pressure relief orifice plate was better than the one-pressure relief orifice plate, and the single-pressure relief orifice plate was better than the expansion chamber. The expansion chamber attenuated the blast by 30%, the one-pressure relief orifice plate attenuated the blast by 51%, and the double-pressure relief orifice plate attenuated the blast by 82%. The blast attenuation trend of the numerical simulation result generally matched that of the experimental result. The results of this study can provide a reference for future protective designs and reinforce the U.S. Force regulations.

The Portable Ice Nucleation Experiment (PINE): a new online instrument for laboratory studies and automated long-term field observations of ice-nucleating particles

Atmospheric ice-nucleating particles (INPs) play an important role in determining the phase of clouds, which affects their albedo and lifetime. A lack of data on the spatial and temporal variation of INPs around the globe limits our predictive capacity and understanding of clouds containing ice. Automated instrumentation that can robustly measure INP concentrations across the full range of tropospheric temperatures is needed in order to address this knowledge gap. In this study, we demonstrate the functionality and capacity of the new Portable Ice Nucleation Experiment (PINE) to study ice nucleation processes and to measure INP concentrations under conditions pertinent for mixed-phase clouds, with temperatures from about −10 to about −40 ∘C. PINE is a cloud expansion chamber which avoids frost formation on the cold walls and thereby omits frost fragmentation and related background ice signals during the operation. The development, working principle and treatment of data for the PINE instrument is discussed in detail. We present laboratory-based tests where PINE measurements were compared with those from the established AIDA (Aerosol Interaction and Dynamics in the Atmosphere) cloud chamber. Within experimental uncertainties, PINE agreed with AIDA for homogeneous freezing of pure water droplets and the immersion freezing activity of mineral aerosols. Results from a first field campaign conducted at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) observatory in Oklahoma, USA, from 1 October to 14 November 2019 with the latest PINE design (a commercially available PINE chamber) are also shown, demonstrating PINE's ability to make automated field measurements of INP concentrations at a time resolution of about 8 min with continuous temperature scans for INP measurements between −10 and −30 ∘C. During this field campaign, PINE was continuously operated for 45 d in a fully automated and semi-autonomous way, demonstrating the capability of this new instrument to also be used for longer-term field measurements and INP monitoring activities in observatories.