Many countries which seek to understand the acoustic performance of railway noise barriers have established standards for the conduct of in-situ experiments.However,there are no universally acknowledged receiver posit...Many countries which seek to understand the acoustic performance of railway noise barriers have established standards for the conduct of in-situ experiments.However,there are no universally acknowledged receiver positions for the evaluation of the barrier performance,a fact which may be leading to uncertainty over the noise reduction capabilities of available barriers.In terms of the descriptor of the barrier performance,the general recommendation is the A-weighted sound pressure level,although the latter is considered to underestimate low frequencies for railway noise barrier.Thus,in this study,the comparison of receiver positions and the descriptors among existing Chinese,ISO and European standards were investigated.Based upon a combination of diffraction theory and standards,a rearrangement of receiver positions and one-third-octave-band analysis were proposed.In addition,in line with improved methods,an in-situ measurement of insertion loss for a 1.5 mhigh railway noise barrier was designed and conducted.The results of the experiment validate as effective and applicable the new receiver positions.These results also suggest that one-third-octave-band analysis is indispensable.展开更多
Fiber Fabry-Perot (FFP) filters have been widely used in optical fiber communications, and insertion loss (IL) is one of its important characteristics. Based on theoretically analysis, factors related to IL were discu...Fiber Fabry-Perot (FFP) filters have been widely used in optical fiber communications, and insertion loss (IL) is one of its important characteristics. Based on theoretically analysis, factors related to IL were discussed. In order to investigate the IL of different structures, simulations are carried out with finite-difference time-domain (FDTD) algorithm. Comparisons are made between the optimized structure and full-size-mirror FFP filter, and fiber-inserted FFP filter as well. Simulation results demonstrated that the finite- size-mirror structure can confine the mode size of the open resonator, hence reduce the IL of FFP filter.展开更多
The speed of an Electro-Hydrostatic Actuator(EHA) pump can recently reach 20000 r/min, and its churning losses increase obviously with an increasing speed, which results in low efficiency and thus increasing heat in a...The speed of an Electro-Hydrostatic Actuator(EHA) pump can recently reach 20000 r/min, and its churning losses increase obviously with an increasing speed, which results in low efficiency and thus increasing heat in aircraft EHA systems. In order to reduce churning losses at high speeds, more attention should be given to the design of an insert. In this paper, the effect of an insert with different design parameters on churning losses is investigated through Computational Fluid Dynamics(CFD) simulation and experiments by calculating the difference between churning losses torques of the test pump with and without the insert based on a high-speed churning losses test rig.Analytical results show that the gap between the insert and the cylinder is critical for churning losses reduction. It is found that the churning losses of the test pump can be reduced with a decreasing gap between the cylinder block and the insert at high speeds. This is because the insert can decrease the turbulence occurrence at high speeds. The results can be used for flow field analysis and optimization of the high-speed EHA pump and provide a new method for improving efficiency of high-speed EHA pumps.展开更多
Insertion loss （IL） is one of the important parameters of asymmetrical digital subscriber loop （ADSL） transformers. In different frequency bands, the factors that affect insertion loss are different. Windings main...Insertion loss （IL） is one of the important parameters of asymmetrical digital subscriber loop （ADSL） transformers. In different frequency bands, the factors that affect insertion loss are different. Windings mainly affect insertion loss in mid and high frequency bands. The effects of winding ways, winding wire diameter and winding turns on insertion loss were discussed. The presented experiment shows that the insertion loss of an ADSL transformer could be under 0.4 dB in mid frequency band when the winding is 30 turns, in which the ADSL transformer satisfies the requirement of total harmonic distortion （THD）. Our experiments also show that the sandwich winding structure is better than the side by side winding structure and the twisted-pair winding structure, and the increase of winding diameter is one means to reduce insertion losses of an ADSL transformer in mid frequency band.展开更多
基金supported in part by the National Natural Science Foundations of China (Nos.51708422, 51678446,51408434)China Scholarship Council and cole Nationale des Ponts et Chaussées,for providing necessary financial assistance to LI Qiutong to pursue her Ph.D.in France
文摘Many countries which seek to understand the acoustic performance of railway noise barriers have established standards for the conduct of in-situ experiments.However,there are no universally acknowledged receiver positions for the evaluation of the barrier performance,a fact which may be leading to uncertainty over the noise reduction capabilities of available barriers.In terms of the descriptor of the barrier performance,the general recommendation is the A-weighted sound pressure level,although the latter is considered to underestimate low frequencies for railway noise barrier.Thus,in this study,the comparison of receiver positions and the descriptors among existing Chinese,ISO and European standards were investigated.Based upon a combination of diffraction theory and standards,a rearrangement of receiver positions and one-third-octave-band analysis were proposed.In addition,in line with improved methods,an in-situ measurement of insertion loss for a 1.5 mhigh railway noise barrier was designed and conducted.The results of the experiment validate as effective and applicable the new receiver positions.These results also suggest that one-third-octave-band analysis is indispensable.
文摘Fiber Fabry-Perot (FFP) filters have been widely used in optical fiber communications, and insertion loss (IL) is one of its important characteristics. Based on theoretically analysis, factors related to IL were discussed. In order to investigate the IL of different structures, simulations are carried out with finite-difference time-domain (FDTD) algorithm. Comparisons are made between the optimized structure and full-size-mirror FFP filter, and fiber-inserted FFP filter as well. Simulation results demonstrated that the finite- size-mirror structure can confine the mode size of the open resonator, hence reduce the IL of FFP filter.
基金financial supports from the National Basic Research Program of China(973 Program)(No.2014CB046403)the National Natural Science Foundation of China(No.1737110)
文摘The speed of an Electro-Hydrostatic Actuator(EHA) pump can recently reach 20000 r/min, and its churning losses increase obviously with an increasing speed, which results in low efficiency and thus increasing heat in aircraft EHA systems. In order to reduce churning losses at high speeds, more attention should be given to the design of an insert. In this paper, the effect of an insert with different design parameters on churning losses is investigated through Computational Fluid Dynamics(CFD) simulation and experiments by calculating the difference between churning losses torques of the test pump with and without the insert based on a high-speed churning losses test rig.Analytical results show that the gap between the insert and the cylinder is critical for churning losses reduction. It is found that the churning losses of the test pump can be reduced with a decreasing gap between the cylinder block and the insert at high speeds. This is because the insert can decrease the turbulence occurrence at high speeds. The results can be used for flow field analysis and optimization of the high-speed EHA pump and provide a new method for improving efficiency of high-speed EHA pumps.
文摘Insertion loss （IL） is one of the important parameters of asymmetrical digital subscriber loop （ADSL） transformers. In different frequency bands, the factors that affect insertion loss are different. Windings mainly affect insertion loss in mid and high frequency bands. The effects of winding ways, winding wire diameter and winding turns on insertion loss were discussed. The presented experiment shows that the insertion loss of an ADSL transformer could be under 0.4 dB in mid frequency band when the winding is 30 turns, in which the ADSL transformer satisfies the requirement of total harmonic distortion （THD）. Our experiments also show that the sandwich winding structure is better than the side by side winding structure and the twisted-pair winding structure, and the increase of winding diameter is one means to reduce insertion losses of an ADSL transformer in mid frequency band.
