Research on the performance of buffer for landing gear based on the drop test

Based on the drop test of the articulated main landing gear of Seagull 300 light multifunctional amphibious airplane, a further study has been conducted to establish buffer performance under different air chamber pressures and attitude angles. Through comparative analysis of the test results, the influencing rule of air chamber pressure and attitude angle on the buffer performance parameters (system capacity, vertical load, buffer compression, system efficiency and buffer efficiency) was obtained. The results demonstrate that air chamber pressure has a significant effect on the buffer system efficiency, while the attitude angle influences the system capacity a lot. With air chamber pressure increasing system efficiency decreases first, then gradually increases after reaching its minimum at 2.15 MPa and decreases at last after reaching its maximum at 2.7 MPa. Buffer efficiency decreases first and then increases after reaching its minimum at 2.2 MPa. When the attitude angle is between 3 and 12 degrees, the smaller the attitude angle, the more energy the system absorbs and the better the buffer performance is. The rate of change of performance parameters varies linearly with attitude angle. With the increase of angle, system capacity, maximum vertical load and system efficiency increase, and the change rate of buffer compression decreases correspondingly. The rate of change of system efficiency has the fastest growth

Dynamics simulation study on civil aircraft planned pavement emergency landing

Engine pylon is one of the most important components of large civil aircraft, playing an essential role in structure connecting and load bearing. It is chosen as the research target, and a full sized engine-pylon-wing finite element model is established. By conducting the simulations of different landing and impacting conditions, dynamical responses and separation status of the pylon are obtained. Some main factors that affect the pylon’s separation are found out on the basis of preliminary analysis. The reasonable pylon separations for belly landing with small pitch angles and dead-stick landing are achieved. At last, further measures to improve the modeling method and achieve better pylon separations are discussed based on a comparative analysis of all the simulation results. The proposed dynamical modeling method along with the emergency landing parameters and simulation results can provide certain reference to similar studies, pylon structure designs and validation tests

Aeroacoustic testing of the landing gear components

The sound field generated by full scale landing gear components was studied in an acoustic wind tunnel. Noise characteristics were evaluated. The noise contribution of each part was investigated by removing the gear part individually. Three design parameters were also obtained to assess the noise reduction potential. Test results indicate that the noise spectrum of the component is essentially broadband and mainly dominated by some peaks corresponding to the constant St. Sound pressure level scales with the sixth power velocity law. Noise radiation from the components has obvious directivities. The main strut is the least contributor while the bogie is the largest contributor to the total noise. It is also found that the noise level increases with the gear installation angle from 0° to 16.5° while it decreases via changing the torque link layout from the front of the main strut to its back or modifying the bogie shape by filling its holes

Aeroacoustic noise reduction design of a landing gear structure based on wind tunnel experiment and simulation

In the process of aircraft landing, the aerodynamic noise of the landing gear constitutes an appreciable part of the airframe noise. Therefore it is important to dedicate research efforts to study of aerodynamic noise of landing gear and its structural parts. Acoustic wind tunnel test on landing gear is designed to measure aerodynamic noise of structural parts of landing gear such as pillar and torque arm. Aerodynamic noise spectrum characteristic and radiation directive characteristic of structural parts in different velocities are established. The effect of flow velocity to noise is analyzed. Two noise reduction designs are proposed in the paper. The effect of the relative position of pillar and torque arm to structural noise is considered based on simulations and testing. Simulation method to assess the noise reduction effect of torque arm shape modification is adopted. The results demonstrate that structural noise can be appreciably reduced by placing torque arm behind the pillar as well as by modifying the shape of the torque arm. In total, the study holds reference value to the ongoing research activities on aerodynamic noise of landing gear and design method for low noise operation of the gear

A method for estimation of critical stress intensity factor for welded sheet

Welded structures subjected to vibration loads in modern aerospace vehicles during practices have the hazard of undergoing fatigue. Critical stress intensity factor is the key parameter in the fatigue failure criterion. Usually fracture toughness is used as an approximation of the critical stress intensity factor in fatigue crack propagation calculation, however it can be seriously influenced by welding and thickness effects when applied to sheet metal welded joints. To solve the problem, this study analyzes these effects both experimentally and theoretically. The paper considers a method for estimation of the critical stress intensity factor based on crack size at the fatigue fracture location. Fatigue tests are conducted on welded specimens made of 2219-T87 aluminum alloy and critical stress intensity factors are calculated. The relationship for critical stress intensity factor results is determined from fracture crack sizes under different loading modes. Results reveal that the estimation method that was applied to measure the factor based on the fracture crack size excludes influences of welding and thickness effects in a convenient way of measurement and calculation. The method can be adopted for welded structures in spacecrafts subjected to vibration loads for fatigue failure analysis and reference of fracture toughness in engineering practice

Aeroacoustic noise reduction design of a landing gear structure based on wind tunnel experiment and simulation

In the process of aircraft landing, the aerodynamic noise of the landing gear constitutes an appreciable part of the airframe noise. Therefore it is important to dedicate research efforts to study of aerodynamic noise of landing gear and its structural parts. Acoustic wind tunnel test on landing gear is designed to measure aerodynamic noise of structural parts of landing gear such as pillar and torque arm. Aerodynamic noise spectrum characteristic and radiation directive characteristic of structural parts in different velocities are established. The effect of flow velocity to noise is analyzed. Two noise reduction designs are proposed in the paper. The effect of the relative position of pillar and torque arm to structural noise is considered based on simulations and testing. Simulation method to assess the noise reduction effect of torque arm shape modification is adopted. The results demonstrate that structural noise can be appreciably reduced by placing torque arm behind the pillar as well as by modifying the shape of the torque arm. In total, the study holds reference value to the ongoing research activities on aerodynamic noise of landing gear and design method for low noise operation of the gear

Recent progress in low-carbon binders

The development of low-carbon binders has been recognized as a means of reducing the carbon footprint of the Portland cement industry, in response to growing global concerns over CO2 emissions from the construction sector. This paper reviews recent progress in the three most attractive low-carbon binders: alkali-activated, carbonate, and belite-ye'elimite-based binders. Alkali-activated binders/materials were reviewed at the past two ICCC congresses, so this paper focuses on some key developments of alkali-activated binders/materials since the last keynote paper was published in 2015. Recent progress on carbonate and belite-ye'elimite-based binders are also reviewed and discussed, as they are attracting more and more attention as essential alternative low-carbon cementitious materials. These classes of binders have a clear role to play in providing a sustainable future for global construction, as part of the available toolkit of cements

Antibiotic prescribing practices in secondary and tertiary hospitals in Shaanxi province, western China, 2013-2015.

IntroductionThe irrational use of antibiotics is a major driver of antimicrobial resistance. This study aimed to explore how antibiotics were used in secondary and tertiary hospitals in Shaanxi Province, western China from 2013 to 2015.MethodA retrospective study was conducted with a sample of 16 hospitals in Shaanxi Province (2 tertiary and 14 secondary hospitals; 8 public and 8 private hospitals) using a stratified random sampling method. All of the macro data from these hospitals from 2013 to 2015 were analyzed. All collected data were double-entered and analyzed using Excel 2007.ResultsThe percentage of injectable antibiotic prescriptions was 26.6% of all of the antibiotic prescriptions in the secondary hospitals and 14.2% in the tertiary hospitals. Injectable antibiotic prescriptions in private tertiary hospitals (enter %) were more than two times that of public tertiary hospitals (enter %). In both tertiary and secondary hospitals, the percentage of antibiotic prescriptions for outpatients, emergency patients and inpatients were within the scope of the national standards, while the intensity of antibiotic use was higher than the national standard of 40 DDD/100 bed-days. The prophylactic antibiotic use rate in clean surgery was 40.4% in tertiary hospitals and 60.7% in secondary hospitals, which were both higher than the national standard of 30%. The preventive use rate of antibiotics in private tertiary hospitals (55.00%) was more than two times that of public tertiary hospitals (25.90%), and the rate was also higher in private secondary hospitals (61.50%) than in public secondary hospitals (59.70%).ConclusionsSubstantial antibiotic abuse occurred in the sample Chinese hospitals, especially in secondary hospitals. The government should continue to strengthen the administration of antimicrobial use in hospitals. At the same time, medical professional training and interventions for physicians should be conducted to fundamentally reduce the irrational use of antibiotics