Search

Objective The noise generated by air-conditioning system is a primary source of static noise in trams, with most of the interior noise originating from the air-conditioning supply fan. Aimed at reducing the noise in air-conditioning duct, research focusing on the duct structure is carried out to design a low-frequency, broadband noise elimination and reduction structure. Method Noise reduction optimization is performed on the noise transmission path of the air-conditioning return air duct in trams. Referring to the original air return structure, a composite noise reduction device is designed, which is based on a perforated plate combined with porous sound-absorbing materials, to mitigate the fan noise transmitted through the return air duct. A statistical energy model that includes the return air duct and the fan noise source is established. Combined with the theoretical calculation of sound absorption structure, the noise reduction characteristics of diversion and noise elimination air duct are calculated and analyzed. Result & Conclusion The adoption of a flow division and noise elimination duct effectively decreases the noise transmitted by the fan. By building a test platform for air-conditioning duct, the feasibility of using the noise reduction duct to eliminate tram air-conditioning system noise is validated.

Carbon fiber reinforced polymer (CFRP) and aluminum alloys (Al) are widely used in the new generation of commercial aircraft due to their excellent mechanical/physical properties. CFRP/Al countersink bolted structures are important connection forms, where the radius of the countersink fillet affects the mechanical connection performance. The countersink fillet radius is an important factor affecting the mechanical performance of bolted joints. In this paper, the countersink fillet radius is controlled by specially-designed drill-countersink tools with different countersink fillet radii. Meanwhile, the finite element model based on the progressive damage method of composite material is established and utilized to simulate the mechanical performance of different composite/metal bolted joints. The failure mechanism of CFRP/Al bolted joints is analyzed. The results show that the countersink fillet radius can be effectively controlled by specially-designed drill-counterbore tools. The ultimate strength of bolted joints with dimple in the CFRP layer is higher than that in the aluminum alloy layer. In terms of the countersink fillet radius, both CFRP and aluminum alloy materials have the maximum strength when the countersink fillet radius is 1.0 mm. That is, the countersink fillet radius should be slightly larger than the bolt fillet radius, which is conducive to a better mechanical performance.

Urbanisation significantly alters the interaction between land surface and the lower troposphere, impacting occurrences of natural hazards. The influence of urbanisation on natural hazards like heatwaves, hailstorms, and flooding remains debated. However, it is well established that impervious surfaces in urban areas can lead to flooding amplification. Singapore, amidst rapid urbanisation, experiences frequent flooding, exacerbated by its tropical-monsoon climate and climate change. Utilising high-temporal-resolution rainfall data from 2017 onwards, we examined the dynamics of urban flooding in Singapore. In total, 108 flooding events were reported for the period 2017–2023, all of a transient nature, primarily linked to cloudbursts. Based on the unique precipitation characteristics associated with urban flash flooding, the term ‘burst flooding’ is introduced to refer to urban floods caused by intense, short-duration rainfall events. A notable increase in cloudburst occurrences in November and December during La Niña years emphasises the role of global climate phenomena in local weather.

The nanoscratch test has been identified as one of the important tools for evaluating the mechanical and tribological properties of materials. This paper reviews the current researches on the nanoscratch test using to characterise the mechanical properties of three typical materials, including thin film, polymer composite and concrete, from the perspectives of the Berkovich indenter, parameter selection, mode selection, and analysis of resulting data. In addition, to provide a deep understanding on the test from different magnitude, a comparison between the microscratch test and nanoscratch test on the evaluation of tribological performance is also provided in this paper. The characterisation by nanoscratch test of two structural samples, in terms of layered film structures (thin film and coating sample) and single layer block structure (polymer composite sample and concrete samples) are also described in this paper, which aims to provides a deep understand on the evaluation the adhesion, tribological and interfacial properties of the typical materials samples by nanoscratch test. Finally, the coefficient of friction and critical load are discussed, which are two important parameters in tribological properties and adhesion properties.

Our understanding of climate dynamics during millennial-scale events is incomplete, partially due to the lack of their precise phase analyses under various boundary conditions. Here we present nine speleothem oxygen-isotope records from mid-to-low-latitude monsoon regimes with sub-centennial age precision and multi-annual resolution, spanning the Heinrich Stadial 2 (HS2) - a millennial-scale event that occurred at the Last Glacial Maximum. Our data suggests that the Greenland and Antarctic ice-core chronologies require +320- and +400-year adjustments, respectively, supported by extant volcanic evidence and radiocarbon ages. Our chronological framework shows a synchronous HS2 onset globally. Our records precisely characterize a centennial-scale abrupt "tropical atmospheric seesaw" superimposed on the conventional "bipolar seesaw" at the beginning of HS2, implying a unique response/feedback from low-latitude hydroclimate. Together with our observation of an early South American monsoon shift at the HS2 termination, we suggest a more active role of low-latitude hydroclimate dynamics underlying millennial events than previously thought.