Precast concrete segmental bridges (PCSBs) are prone to weakness at the joints. To ensure accurate positioning and effective force transmission between segments, steel shear keyed joints were designed in the present study. A comprehensive investigation was also conducted into the shear performance of such joints, drawing on existing experimental research and theoretical analysis, so as to facilitate more comprehensive understanding of the shear mechanism and calculation methods involved. The results reveal that the steel shear keyed joint effectively transmitted shear force through the contact pressure between the steel key and concrete, aided by confining pressure. The steel keyed joint was also found to possess high shear capacity and exhibit good ductility. A mechanical model of the steel shear keyed joint was constructed, and the shear mechanism and failure modes were revealed, including shear failure of the steel key, local compression failure of concrete, and tearing failure of concrete. Finally, the present authors suggest that the shear failure of the steel key should be used as the basis for the shear resistance design of steel shear keyed joints, which can be calculated according to the formula (F=tau center dot A). The strength of concrete around the steel key should also be checked.
Heavy-duty diesel engines equipped with turbochargers is an effective way to alleviate energy shortage and reduce gas emissions, but their compressor aerodynamic noise emissions have become an important issue that needs to be addressed urgently. Therefore, to study the aerodynamic noise emission characteristics of a compressor during the full operating range, experimental and numerical simulation methods were used to analyze the aerodynamic noise emissions. The results showed that aerodynamic noise's total sound pressure level (SPL) increased with increased speed under the test conditions. At low speeds, the total SPL of aerodynamic noise was affected by the mass flow of the compressor more obviously. The maximum difference of aerodynamic noise total SPL was 1.55 dB at 60,000 r/min under different mass flows. At the same speed, the compressor could achieve lower aerodynamic noise emissions by operating in the high-efficiency region (middle mass flows). In the compressor aerodynamic noises, the blade passing frequency (BPF) noise played a dominant role. The transient acoustic-vibration spectral characteristics and fluctuation pressure analysis indicated that BPF and its harmonic frequency noises were mainly caused by the unsteady fluctuation pressure. As the speed increased, the BPF noise contributed more to the total SPL of the aerodynamic noise, and its percentage was up to 75.35%. The novelty of this study was the analysis of the relationship between compressor aerodynamic noise and internal flow characteristics at full operating conditions. It provided a theoretical basis for reducing the heavy-duty diesel engine turbocharger compressor aerodynamic noise emissions.
By combining the multi-scale decomposition and sparse representation,an image fusion algorithm based on multi-morphological component analysis(MCA)is proposed in this paper.The fusion method based on joint sparse representation(JSR)is employed to fuse the redundant and complementary information in the cartoon sub-images,and the fusion method based on directional feature is used to fuse the texture sub-images with more detailed information and noise.The results show that the proposed algorithm is superior to the state-of-the-art image fusion methods in subjective visual effects and objective evaluation metrics.
为提升聚己二酸‒对苯二甲酸丁二酯(PBAT)共混物的水蒸气阻隔性和耐候性能,通过熔融共混和吹塑方法制备了不同配比的PBAT/聚碳酸亚丙酯(PPC)共混物薄膜,研究了材料组成对共混物薄膜水蒸气阻隔性、力学性能、热性能、微观形貌、透光率等影响,并对其进行了自然老化表征.结果表明,PPC的加入提高了PBAT基薄膜的水蒸气阻隔性,但力学性能和热稳定性有所下降,加入质量分数为20%的PPC可使薄膜的水蒸气透过系数下降54.5%;自然老化试验表明,PPC能够提升PBAT基薄膜的耐候性.
Due to the heterogeneous properties of constituent materials, traditional Multi-channel analysis of surface wave (MASW) method is unsuitable for evaluating ballastless track as surface waves exhibit different dispersion patterns. To overcome this limitation, firstly, the implementation process of MASW was introduced, and the phase shift method was employed to perform dispersion analysis of multi-channel surface wave signals. Secondly, a wave field solution model of ballastless track was established using the time-domain finite-difference method. Subsequently, the stiffness matrix method was improved to account for the heterogeneous properties of the constituent materials and to calculate the theoretical surface wave dispersion curve of ballastless track, followed by the analysis of surface wave dispersion characteristics in ballastless track and the proposal of an inversion method. Finally, the optimal excitation central frequency and receivers' deployment were analyzed in the MASW method, and the inversion analysis of ballastless track degradation were conducted. Results shown that the surface wave dispersion curve is more sensitive to CA mortar degradation at low frequencies and concrete slab degradation at high frequencies. Appropriate excitation central frequency and receivers' deployment are essential for accurately extracting the surface wave dispersion curve from the dispersion energy of ballastless tracks. The inversion method proposed in this study provides a more accurate evaluation of ballastless track degradation compared to assuming ballastless track as a homogeneous structure during inversion analysis.
