Coupled metallic ring gap waveguide

Employing the surface plasmon polaritons (SPPs), a kind of coupled metallic squareness ring waveguide structure is presented. Its properties has been analyzed with the finite different time domain method and the coupling length has been derived from the coupled mode theory. It is demonstrated that the SPPs excited by the light with different wavelength will come out from different output port due to different coupling length. By appropriately designing the structure, it can be utilized to realize some optics devices such as multiple-wavelength sorter and beam splitter. This will break through the diffraction limit of traditional optical devices.     

Vibro-acoustic characterization of railway wheels

For many years the problem of noise generated by trains has had an increasing importance; in this paper, attention is focused on the noise generated by the train wheels due to their vibration. Today there are many kinds of railway wheels which are affected by different noise generation mechanisms. If the traditional and well known solid wheel is considered, a lot of data is already present in the literature both concerning the vibration and the noise point of view. On the other hand, the widely used resilient wheels are not so well known in their vibratory and acoustic behaviour as in the case of solid ones. The extensive experimentation presented and commented in this paper looks for a confirmation of some literature data first, and then it gives new results. Particularly the vibro-acoustic characterization of different kinds of wheels (both solid and resilient ones) has been carried out, in order to have a comparison between the behaviour of the newly built wheels and the older ones, representing the state of the art. Besides it has been shown that a detailed modal analysis of the suspended wheel coupled to sound measurements can give useful information about the wheel noise emission in its normal operating conditions.     

Self-assembly of graphene nanoribbon ring on metallic nanowires

Molecular dynamics simulations demonstrate that metallic nanowires (NWs) can activate and guide the self-assembly of graphene nanoribbon rings (GNR), allowing them to adopt a bilayered helical configuration on NWs. This unique technology attributes to the combined effects of the van der Waals force and the π–π stacking interaction. The size and chirality effects of GNR on the self-assembly of GNR–NW system are calculated. Diverse NWs, acting as an external force, can initiate the conformational change of the GNRs to form bilayered helical structures. The stability of the formed nanosystems is further analyzed for numerous possible applications.     

Influence of expanding ring roads on traffic noise in Beijing City

The road network in Beijing is expanding in the form of loop-lines. Following the 2nd and 3rd ring roads, the 4th has been completed and come into operation in 2002. Traffic noise surveying and analysis was performed along four main roads in the Beijing urban area—the 2nd, 3rd and 4th ring roads circling the central downtown area and Chang-An Avenue, a major east-west corridor through the heart of the city. Measured noise data along the 2nd, 3rd and Chang-An Avenue were compared with the data surveyed before the completion of the 4th ring road for determining influence of expanding ring roads on traffic noise pattern in Beijing City. The results indicate that these main roads remain overloaded by traffic flow during daytime, and noise levels due to road traffic along these roads exceeds relavent environmental standards by 5 dBA. Reduced traffic noise level was observed along the northern half of the 2nd and 3rd ring roads, and along the central section of Chang-An Avenue. Increased traffic noise level was observed along the southern half of the 2nd and 3rd ring roads, and along the non-central section of Chang-An Avenue. Expanding ring roads mitigate heavy traffic flow in the central part of Beijing City, but spread high traffic noise outwards at the same time.     

Investigation on the intensity noise characteristics of the semiconductor ring laser

Based on the frequency-domain multimode theoretical model, detailed investigations on the noise characteristic of the semiconductor ring laser （SRL） are first performed in this paper. The comprehensive nonlinear terms related to the third order nonlinear susceptibility Z3 are included in this model; the Langevin noise sources for electric field and carrier density fluctuations are also taken into account. As the injection current increases, the SRL may present several operation regimes. Remarkable and unusual low frequency noise enhancement in the form of a broad low frequency tail extending all the way to the relaxation oscillation peak is observed in any of the operation regimes of SRLs. The influences of the backscattering coefficient on the relative intensity noise （RIN） spectrum in typical operation regimes are investigated in detail.     

单块非平面环形腔激光器的强度噪声抑制技术研究

研究了LD泵浦1319nm单块非平面环形腔(NPRO)激光器的强度噪声特性,发现随着输出功率的增加,弛豫振荡峰频率从100kHz向280kHz移动,同时弛豫振荡峰宽度增加但幅度降低,且在弛豫振荡峰处发生π相位跃变,在600kHz以上频率区域,噪声已经接近量子噪声极限。自行设计的噪声抑制电路在实现足够大增益的同时,在500kHz附近获得了约65°的相位超前,由此获得了优于通常同类实验的噪声抑制结果:当弛豫振荡峰频率为230kHz时,弛豫振荡峰处和低频区域的强度噪声幅度分别被抑制了45dB和20dB。     

低噪声环形腔掺铒光纤激光器的研究

分析了环形腔掺铒光纤激光器的输出特性,给出了稳态下的激光器输出功率、阈值泵浦功率和斜率效率的解析表达式,为激光器结构的优化提供了依据。搭建了全保偏环形腔掺铒光纤激光器,利用未泵浦铒纤中由驻波干涉和饱和吸收诱发的自写入光纤光栅的窄带滤波特性及反射波长的自适应特性,有效地解决了激光器的跳模问题。通过测量得到激光器系统的泵浦阈值为15.3mW,斜率效率为2.8%,输出偏振度为32dB。利用非平衡光纤干涉仪系统和相位产生载波(PGC)调制解调技术测得激光器的相位噪声为3×10-5rad/Hz~1/2(1kHz)。     

The noise directivity of railbuses

In this paper the noise generated by the railbuses is analysed. To find the directivity index of the railbuses a method of its estimation was proposed. This method is based on the assumption of symmetrical changes in the sound level during the passage of a railbus. The four directivity indices were analysed: monopole, cosine, squared cosine and cubed cosine. We find that the monopole directivity is the best to describe the noise generation by the moving railbuses.     

基于电磁超声换能器的火车轮探伤研究

利用电磁超声探伤方法对检测火车轮表面及近表面缺陷进行实验探究,从而保证车轮质量,避免事故发生。文章介绍了火车车轮电磁超声探伤的原理和方法。根据电磁超声表面波辐射扩散角的分布情况,得出利用电磁超声表面波进行车轮踏面探伤的可行性。将制作的小巧换能器探头与便携式电磁超声探伤仪配合,能够实现对车轮的快速探伤检测。通过大量的车轮探伤实验,检出了典型车轮踏面缺陷。根据检测波形特点并结合生产工艺情况,分析得出产生缺陷的原因。研究表明:电磁超声无损检测方法能够快速、有效检出车轮踏面缺陷。     

浅海舰船噪声声强流的垂直方向性

浅海环境中,确定性声源的多途声信号干涉使得接收点处声强流的方向发生改变,不再与声源位置处的声强流方向一致。只测量声场的标量声强时,无法得到接收点处声强流的垂直方向性,而基于简正波矢量场建模和仿真,可获得理想条件下宽带点声源激发声场声强流的垂直方向性。本文采用单矢量水听器进行海上实验,获得了海洋环境噪声和干扰条件下舰船噪声声强流的垂直方向性。仿真和实验结果表明:远场条件下,浅海干涉现象引起接收点处声强流的方向(极角)随频率和距离变化,其时间-频率分布呈现与LOFAR谱干涉条纹相似的条纹,声强流的极角值主要分布在70?～110?范围内。     

气流管道有源降噪研究

如何消除气流的影响是管道有源降噪的难点之一，本文分析了湍流对有源降噪系统的影响，并开发了一种抗湍流传声器探管，最后在某种通风系统的进气管段进行了降噪试验，气流速度为２０ｍ／ｓ时，在６０－６３０Ｈｚ频带取得了１５ｄＢ（Ａ）的降噪效果。     

声发射技术在铁路系统检测中的研究和应用

高速铁路的快速发展,给我国经济和社会发展带来了巨大的推动作用,同时对铁路系统的安全性提出了更高的要求。针对声发射技术在铁路系统安全检测中的研究和应用,介绍了声发射技术及其在检测应用中的优点,综述了目前国内外声发射技术在铁路系统检测研究中的情况,包括钢轨伤损检测、车轮伤损检测、轮轴轴承伤损检测、铁路结构安全监测以及车体材料安全监测等,特别针对钢轨裂纹伤损引起的钢轨断裂这一铁路安全中的主要事故,着重分析了声发射技术在钢轨裂纹伤损检测研究中的情况,并介绍了在高速铁路方面的应用探索。最后在上述分析总结的基础上,指出了声发射技术在铁路系统特别是高速铁路检测研究中的前景及研究难点。     

阻抗复合消声器声学性能有限元预测方法及分析

为计算和分析具有复杂结构的阻抗复合式消声器的宽频消声性能,建立了一种高效声学有限元方法,给出了不同边界条件下的边界积分处理细节,得到有限元全局系数矩阵表达式,设计出计算程序框架以实现这些算法,其求解规模和计算速度与商业软件相比有优势。为计算阻抗复合式消声器的传递损失,通过阻抗管测量和数据拟合得到了吸声材料声学特性的经验公式。计算和测量了两通穿孔阻抗复合式消声器的传递损失,二者良好的吻合验证了声学有限元方法和计算程序的正确性。研究表明,插管长度影响消声器在中高频段的消声特性,右侧隔板上穿孔会消除共振峰,中高频消声性能随着出口管穿孔率的增加而提升。     

圆环振动拍的调整实验

根据非对称圆环点冲击下拍的理论模型分析拍的分布特性,该文提出了一种调整圆环拍周期和清晰度的方法。阐明圆环结构拍的发生原理,从而控制清晰度;在圆环上添加质量或研磨可以改变非对称性进而调整拍频。引入等效圆环的概念,通过在轴对称圆环上添加一个质量,建立与非轴对称圆环振动特性相同的等效圆环模型。利用该模型,计算要在非轴对称圆环添加质量的大小和位置,以便获得拍的最佳周期及清晰度。用实验和有限元法验证了该方法的有效性。     

Theoretical investigation of the sound attenuation of membrane-type acoustic metamaterials

Membrane-type acoustic metamaterials have been recently shown to exhibit good performance of sound attenuation in a low frequency range. An analytical approach for the fast calculation of sound transmission loss of the membrane-type acoustic metamaterials is presented here. The discussion indicate that the first transmission loss valley and the transmission loss peak depend strongly on the attaching mass, while the second transmission loss valley is mainly influenced by the membrane properties. The effects of membrane tension and mass position on the transmission loss and characteristic frequencies are also discussed in detail.     

Vibro-acoustic modelling of a railway bridge crossed by a train

This paper presents a vibro-acoustic modelling of a railway bridge excited by a moving train. The modelling of the bridge-train system is carried out by the modal superposition method taking into account the train mass, the viscoelastic suspension of the vehicles with an unlimited number of trucks and spans of the bridge. The numerical resolution of the coupled equations of motion is carried out by the Newmark’s method with an iterative process. we studied on one hand the influence of the track irregularities on the dynamic behaviour of the bridge-train system on the other hand the noise radiated by the bridge due to the passage of the train. The acoustic pressure is obtained by solving the wave equation which has as excitations source the bridge acceleration, they are considered as acoustic monopoles.     

The identification of tyre induced vehicle interior noise

Sound transmission into a vehicle is classified as either airborne or structure borne sound. From the point view of noise control, the reduction of noise transferred by different paths requires different solutions. Coherence function analysis is often used to identify transmission paths. However it can be difficult to separate the airborne from structure borne components. The principle of acoustic reciprocity offers a convenient method for overcoming this difficulty. The principal states that the transfer function between an acoustic volume velocity source and an acoustic receiver is independent of a reversal of the position of source and receiver. The work done on this study involves exciting a stationary tyre and measuring the surface velocity of the tyre at a number of discrete points. The acoustic transfer functions between each point on the tyre and a receiver point are measured reciprocally. Two sets of measurements are then combined to yield a measure of the sound pressure due to a point force on the tyre via the acoustic transmission path only. This technique also provides information on the relative contributions of various regions of the tyre wall to the resultant noise. Also the sound radiation characteristics, the horn effect, and resonance at the wheel housing are identified through the reciprocal measurement.     

Ultrasound-assisted electrodeposition and synthesis of alloys and composite materials: A review

The development of electrodeposited materials with improved technological properties has been attracting the attention of researchers and companies from different industrial sectors. Many studies have demonstrated that the electrodeposition and synthesis of alloys and composite materials assisted by ultrasound may promote the de-agglomeration of particles in the electrolytic solution due to microturbulence, microjets, shock waves, and breaking of Van der Waals forces. The sonoelectrochemical technique, in which the ultrasound probe acts as a working electrode, also has been used for the formation of nanostructures in greater quantity, in addition to accelerating the electrolysis process and eliminating the reaction products on the electrode surface. Regarding the morphological aspects, the acoustic cavitation promotes the formation of smooth and uniform surfaces with incorporated particles homogeneously distributed. These changes have a direct impact on the composition and physical properties of the material, such as corrosion resistance, magnetization, wear, and microhardness. Despite the widespread use of acoustic cavitation in the synthesis of nanostructured materials, the discussion of how process variables such as acoustic power, frequency, and type of ultrasound device, as well as their effects still are scarce. In this sense, this review discusses the influence of ultrasound technology on obtaining electrodeposited coatings. The trends and challenges in this research field were reviewed from 2014 to 2019. Moreover, the effects of process variables in electrodeposition and how these ones change the technological properties of these materials were evaluated.     

Suppression of brake squeal noise applying finite element brake and pad model enhanced by spectral-based assurance criteria

An enhanced dynamic finite element (FE) model with friction coupling is applied to analyze the design of disc brake pad structure for squeal noise reduction. The FE model is built-up from the individual brake component representations. Its interfacial structural connections and boundary conditions are determined by correlating to a set of measured frequency response functions using a spectral-based assurance criterion. The proposed friction coupling formulation produces an asymmetric system stiffness matrix that yields a set of complex conjugate eigenvalues. The analysis shows that eigenvalues possessing positive real parts tend to produce unstable modes with the propensity towards the generation of squeal noise. Using a proposed lumped parameter model and eigenvalue sensitivity study, beneficial pad design changes can be identified and implemented in the detailed FE model to determine the potential improvements in the dynamic stability of the system. Also, a selected set of parametric studies is performed to evaluate numerous design concepts using the proposed dynamic FE model. The best pad design attained, which produces the least amount of squeal response, is finally validated by comparison to a set of actual vehicle test results.     

超硬磨料砂轮激光修整技术的现状与展望

阐述脉冲激光修整技术的基本原理和特点,从超硬磨料砂轮激光修整技术的工艺参数优化、数值模拟仿真两方面对其研究进展进行综述,指出该技术目前正面临的主要问题,并对其发展方向进行预测和展望。超硬磨料砂轮激光修整技术目前已经取得了较大的进步,但基础科学理论、砂轮表面质量评价、在线精密修整技术等关键性技术仍然是该领域非常棘手的难题,有待对其进行更深层次的探索和研究。