ARTICLE | doi:10.20944/preprints202104.0546.v1
Subject: Engineering, Mechanical Engineering Keywords: helicopter, tail rotor, aeroacoustic, finite element method, computational fluid dynamic
Online: 20 April 2021 (13:19:15 CEST)
With the increasingly stringent airworthiness standards, the noise generated during the rotorcraft flight is gradually attracting people’s attention. It widely operated helicopters at low altitudes because of their maneuverability. The way to reduce the noise caused by the complex airflow of the helicopter rotor system has progressively become a hot topic for researchers. Using a hybrid acoustic analysis method, this paper investigates the improvement of the noise and thrust of the helicopter’s tail rotor through the tail rotor structural parameters. For the basic model, the turbulence simulation is performed using an incompressible detached eddy simulation (DES) method, and the Lighthill acoustic analog equation is calculated using the finite element method (FEM). We verified the accuracy of the method through wind tunnel tests. We chose a series of structural parameters for sound simulation and fluid simulation calculations. The results indicate that the modified tail rotor noise reduced by 16.5 dBA and the total thrust increased by 19.9% from the prototype model. This work can enhance the duct tail rotor design to improve aerodynamic and aeroacoustic performance.
ARTICLE | doi:10.20944/preprints201802.0032.v1
Subject: Physical Sciences, Acoustics Keywords: inverse acoustic problem; helicopter rotor; Ffowcs Williams and Hawkings equation; aerodynamic constraint; Thikhonov method
Online: 5 February 2018 (11:34:30 CET)
An inverse aeroacoustic problem for a helicopter rotor combined with aerodynamic constraint is proposed based on Ffowcs Williams and Hawkings equation in subsonic. The rotor noise includes thickness noise and loading noise when quadrupole noise is neglected. Thickness noise is related to geometry and motion conditions. Loading noise is related to the pressure on the wall. Therefore, the equation between pressure on the wall and far-field noise can be established, thus the pressure on the wall can be obtained by solving this equation. Since this equation is an ill-posed, the singular value decomposition combined with the regulation method is applied and the aerodynamic constraint is taken into account. The direct noise prediction is verify firstly and then the inverse problem is solved. The reconstruction pressure is compared to the input data. The result is in good agreement with the input value. At the same time, the influence of interference noise is also considered. Under low signal-to-noise ratio, the reconstruction result is also reasonable.
ARTICLE | doi:10.20944/preprints202310.0668.v1
Subject: Public Health And Healthcare, Health Policy And Services Keywords: airlift; job performance; doctor; helicopter; RPISD
Online: 11 October 2023 (05:05:59 CEST)
The purpose of this study is to develop and evaluate the effectiveness of a medical helicopter air transport training program for emergency medical personnel. The program was developed according to Rapid Prototyping Instructional System Design (RPISD) and finalized after content validity and usability evaluation. The effectiveness of the program was evaluated using a single-arm pre-post design to measure the performance of 11 convenience-sampled emergency medical technicians after the program was applied. Data analysis was performed using the SPSS 26.0 Program and Wilcoxon Signed-Rank test. The results of this study are summarized as follows. First, the developed doctor helicopter air transport training program applied RPISD, and the development stage was divided into analysis, design and usability evaluation, and development stages; the final program was derived. Secondly, the developed medical helicopter air transport training program is composed of a blended learning training program that combines online theory lectures and offline simulations for a total of 8 sessions. Third, as a result of applying the developed doctor helicopter air transport training program to 11 emergency medical workers, both pre- and post-air transport subjective job performance and objective job performance were statistically significantly increased. The Dr. Helicopter air transport training program developed in this study was found to be a program that can sufficiently evaluate the job performance of emergency medical personnel in air transport. Through this study, we hope that this training program can directly contribute to improving the survival rate of critically ill patients in the actual air transport field.
ARTICLE | doi:10.20944/preprints202201.0128.v1
Subject: Engineering, Mechanical Engineering Keywords: helicopter loads; fatigue and strength tests; pullup/pushover and diving maneuvers
Online: 10 January 2022 (15:43:44 CET)
The aim of the study is to assess the loads that are transferred from the main rotor and the tail rotor to the helicopter fuselage. These loads change in the various phases of the transient flight as a result of the variable control of the maneuver and as a result of the variable flow around the blades. The knowledge of the loads allows for the proper selection of the level of excitations that should load the fuselage structure during fatigue and strength tests. The simulation model describing the helicopter flight is discussed. This model takes into account the motion of each blade relative to its hinges. Results are shown for two maneuvers - pullup/pushover and diving. The values of extreme loads transferred to the fuselage were obtained.
ARTICLE | doi:10.20944/preprints202306.1509.v1
Subject: Engineering, Aerospace Engineering Keywords: helicopter; cabin noise reduction; microperforated panel; composite acoustic structure; sound field analysis; acoustic metamaterials
Online: 21 June 2023 (08:51:08 CEST)
The high level of noise in helicopter cabins considerably compromises the comfort and safety of the pilot and passengers. To verify the feasibility and effectiveness of microperforated panel composite sound absorption structures for noise suppression in helicopter cabins, simulation and experimental studies were conducted on a model of a light helicopter cabin. First, three microperforated composite sound absorption structures for the helicopter cabin wall panel were designed. Then, a finite element model of the main gear/body acoustic vibration coupling was established to obtain the target frequencies of the microperforated composite sound absorption structures; the acoustic effect was verified by simulation. Finally, a model helicopter cabin equipped with the three microperforated composite sound absorption structures was built, and a cabin noise test was performed. The test results showed that the combined microperforated panel acoustic structure and microperforated panel–porous material composite structure realized an overall cabin sound pressure level attenuation of 8–10 dB, on average, in the wide frequency range of 500–2000 Hz, with an amplitude of more than 20 dB. The microperforated panel–acoustic supermaterial composite structure achieved low-frequency sound absorption in the frequency range of 300–450 Hz. The sound absorption effect reached 50%, and it also exhibited good noise reduction effects in the middle- and high-frequency bands.
ARTICLE | doi:10.20944/preprints202210.0295.v2
Subject: Biology And Life Sciences, Ecology, Evolution, Behavior And Systematics Keywords: Aaerial survey; animal detection; distance sampling; helicopter; monitoring; strip transect; Svalbard; total count; ungulate
Online: 2 December 2022 (03:36:25 CET)
Conservation of wildlife depends on precise and unbiased knowledge on the abundance and distribution of species. It is challenging to choose appropriate methods to obtain a sufficiently high detectability and spatial coverage matching the species characteristics and spatiotemporal use of the landscape. In remote regions, such as in the Arctic, monitoring efforts are often resource-intensive and there is a need for cheap and precise alternative methods. Here, we compare an uncrewed aerial vehicle (UAV; quadcopter) pilot-survey of the non-gregarious Svalbard reindeer to traditional population abundance surveys from ground and helicopter to investigate whether UAVs can be an efficient alternative technology. We found that the UAV survey underestimated reindeer abundance compared to the traditional abundance surveys when used at management relevant spatial scales. Observer variation in reindeer detection on UAV imagery was influenced by the RGB greenness index and mean blue channel. In future studies, we suggest to test long-range fixed-wing UAVs to increase the sample size of reindeer and area coverage and incorporate detection probability in animal density models from UAV imagery. In addition, we encourage focus on more efficient post-processing techniques, including automatic animal object identification with machine learning and analytical methods that account for uncertainties.