驾驶室内部噪声分析与阻尼降噪

基于有限元和边界元方法,运用ANSYS和SYSNOISE软件建立驾驶室声—固耦合有限元模型和声学边界元模型,计算在指定工况下壁板的振动和驾驶员右耳旁的声压级。在此基础上,进行面板声学贡献度分析,确定对驾驶员右耳声压贡献突出的壁板。通过采用沥青型阻尼材料对壁板进行减振降噪处理,有效地降低驾驶员右耳旁噪声。     

客车车外噪声源识别及整车降噪研究

目前客车的车外噪声普遍偏高,成为城市中主要噪声污染源之一.以一款苏州金龙客车作为研究对象,采用选择运行法对其进行声源识别,结果显示风扇、消声器、油底壳为最主要噪声源.通过对主要噪声源采取吸声、隔声、消声等技术措施,有效地衰减了其向外辐射噪声.经权威检测部门测试,该车的整车噪声下降了4.6dB(A),达到了GB1495-2002第二阶段车外加速噪声限值要求.     

车辆驾驶室内噪声仿真及低频降噪处理

首先建立车辆驾驶室白车身有限元模型并进行自由模态分析,通过与模态试验结果的对比进行模型修正,控制前8阶固有频率偏差在3%以内;其次建立结构-声场耦合有限元模型,计算两种试验工况下结构激励引起的内声场声压,计算结果与试验测试结果有较高的一致性,验证方法和模型的准确性;最后在低频段分析驾驶室面板声压贡献量,采用添加自由阻尼层的方法对驾驶室进行降噪处理,计算表明取得了良好的降噪效果。     

Characterization of the Input Noise Sources of a dc SQUID

From the theory of the intrinsic noise in a dc SQUID by Tesche and Clarke, we derive the expressions of the current and voltage input noise spectral densities in a dc SQUID current amplifier operated in a flux locked mode. The expected current and voltage noises are compared, at audio frequencies, with the experimental results obtained with a low noise dc SQUID in which the input load (resonant and not) and the operating temperature (1–4 K) are changed. In order to evaluate the input voltage noise, which is directly related to the current noise around the SQUID loop and is usually neglected, we have used as the input circuit a LC resonator with a very high quality factor (10⁶). Both the voltage and current input noises exceed the expected values by the same factor of about 8. This means that the modulus the optimum source impedance of the SQUID amplifier is still in agreement with the value expected from the theory, which is approximately given by the product of the input coil inductance and the angular frequency. To explain the excess noise results, we propose a model in which the voltage and current input noises are due to a thermal magnetic noise source which is present near the SQUID.     

某轮胎辐射噪声的仿真

在ABAQUS中建立某型号轮胎的有限元模型,采用计算模态分析和实验模态分析对比,验证有限元模型的正确性,并仿真轮胎在某一路面上的滚动过程。基于声传递向量概念,结合有限元和边界元方法,利用MATV技术计算了随机激励下轮胎振动的辐射噪声响应,对轮胎辐射噪声进行分析研究。     

Noise intensity in the field of a subsonic turbulent jet

Results are shown of digital-computer calculations pertaining to the acoustic properties of subsonic jets, by a method proposed earlier in [1, 2]. The gasdynamic and turbulence parameters of a jet, needed for calculating the acoustic radiation, have been determined before-hand.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 24, No. 2, pp. 282–289, February, 1973.     

地铁车内噪声超标分析

针对某地铁车内噪声超标问题,从车辆、轮轨两个方面展开研究,利用BrüelKj?r测试系统分析车辆的牵引、空调系统,车辆结构,轮轨粗糙度等因素对车内噪声的影响特性。研究表明,牵引、空调系统对运行车辆车内噪声影响较小。车内噪声的显著频带为400 Hz~800 Hz、1 105 Hz,与车轮非圆没有直接关系;1 105 Hz与钢轨打磨后磨痕有关。车内噪声主要与以下两个因素有关:一是透射噪声,车辆内移门存在漏风问题,车外噪声传入车内;二是结构传声,轮轨或轨道以上频段的振动激励经过轴箱-构架-车体传递,进而激励车内内装等结构振动产生辐射噪声。此研究对地铁车辆降噪有一定的参考价值。     

Calculation of the Noise Temperature of Microwave Transistor Low-Temperature Noise Generators

A method of calculating the noise temperature of a microwave transistor low-temperature noise generator by using reference data on the noise parameters and the coefficients of the scattering matrix of the transistor is developed for the 8–40 GHz frequency band.     

小型医用制氧机振动噪声测试与降噪设计

为降低制氧机的运行噪声,在对制氧机的壳体振动和辐射噪声测试分析后,发现主要的噪声源是壳体振动和空气压缩泵工作噪声。根据制氧机结构振动的传递路径,在空气压缩泵和底板之间加装弹簧减振装置,同时在壳体内表面粘贴隔声吸声材料。试验结果表明,降噪措施能有效减小制氧机结构振动,降低工作噪声,降噪后制氧机工作状态噪声由51.9 dB(A)降低到44.3 dB(A)。     

Shot Noise in a Spin-Diode Geometry

We apply the master equation technique to calculate shot noise in a system composed of single level quantum dot attached to a normal metal lead and to a ferromagnetic lead (NM-QD-FM). It is known that this system operates as a spin-diode, giving unpolarized currents for forward bias and polarized current for reverse bias. This effect is observed when only one electron can tunnel at a time through the dot, due to the strong intradot Coulomb interaction. We find that the shot noise also presents a signature of this spin-diode effect, with a super-Poissonian shot noise for forward and a sub-Poissonian shot noise for reverse bias voltages. The shot noise thus can provide further experimental evidence of the spin-rectification in the NM-QD-FM geometry.     

Tunnel Junction as a Noise Probe

The paper investigates theoretically effects of noise on low-bias parts of IV curves of tunnel junctions. The analysis starts from the effect of shot noise from an additional (noise) junction on the Coulomb blockaded Josephson junction in high-impedance environment. Asymmetry of shot noise characterized by its odd moments results in asymmetry of the IV curve of the Josephson junction. At high currents through the noise junction the IV curve is sensitive to electron counting statistics. The theory is generalized on another type of noise (phase noise of a monochromatic AC input) and on a normal Coulomb blockaded tunnel junction. The effect of shot noise on the IV curve of a superconducting Josephson junction in low-impedance environment is also analyzed. From this effect one can obtain information on the time necessary for an electron to tunnel through the junction responsible for shot noise. In summary, the analysis demonstrates, that the low-bias part of the IV curves of tunnel junctions can be a sensitive probe of various types of noise.     

Noise in a point-contact dc SQUID

Measurements of five variations of a toroidal point-contact dc superconducting quantum interference device (SQUID) are presented. The energy resolution and other parameters of these SQUIDs are examined and compared with the predictions of the Resistively Shunted Junction model. For these SQUIDs, the measured minimum energy resolution was approximately 2×10^–30 J/Hz. Excess noise in the point contacts was found to limit the energy resolution of the SQUIDs. A comparison between the typical junction parameters and noise obtained for our niobium-niobium point contacts and those of others is given. TheI–V characteristics of the junctions showed the effects of Joule heating. The white voltage noise spectral density was found to have an approximately parabolic dependence on the average voltage for bias currents larger than the critical current. While this parabolic dependence is consistent with heating effects in the junctions, the amplitude of the noise cannot be explained in terms of a heating model. The low-frequency noise of the point contacts has also been investigated.     

抗噪声源物理噪声引起的尖峰噪声的抑制

抗噪声源时滞与实际电路器件的干扰都是影响有源降噪实际应用效果的潜在因素。针对物理实验中引起的抗噪声源尖峰噪声,分析物理实验抗噪声源中尖峰噪声的机理,并利用小波变换的门限消噪法,对由物理噪声产生的尖峰噪声进行处理。该方法中,门限阈值的选取与信号分解层数的确定是两个核心问题。利用层数自适应确定的小波阈值消噪法可以抑制有源噪声控制中产生的尖峰噪声,通过仿真验证该方法对抑制尖峰噪声有良好的效果。     

近轨低矮声屏障降噪效果影响因素分析

针对城轨交通近轨低矮声屏障,为了量化分析其降噪特性和效果,以对称点声源模拟轮轨声源,考虑车体和轨道结构的空间几何构型及声学边界特性,采用声学边界元法,建立城轨列车车外噪声预测分析模型,对有无声屏障以及不同吸声处理方式下的空间声场响应进行对比分析。研究结果表明:对标准评价点(距轨道中心线7.5 m远,距轨面1.2 m高),0.25 m高直立型无吸声声屏障的插入损失为-1.7 dB(A);若其高度每增加0.25 m,插入损失将增加0.4dB(A)~2.9 d B(A);若在1.0 m高直立型无吸声声屏障的屏体内侧以及轨道增设吸声边界条件,插入损失增加6.1 dB(A);若对1.0 m高直立型无吸声声屏障增设Y头型,插入损失将增加2.7 dB(A)。相关研究可为城轨交通减振降噪提供科学指导。     

基于噪声模型的通风机房降噪控制

通过对煤矿通风机房噪声调查监测,提出利用通风机房噪声模型采取降噪措施,并将实际测量与理论计算值进行比较证明模型是正确的,措施是可行的。     

Evaluation of a Nitrided Case Depth by the Magnetic Barkhausen Noise

Applicability of magnetic methods for non-destructive evaluation of plasma nitrided cases was investigated comprehensively. Nitrided layers of 60–800 \(~\upmu \hbox {m}\) thicknesses were produced on a 16MnCr5 steel surface varying the plasma temperature, the nitriding time and atmosphere. Low-frequency Barkhausen noise was measured by a unique laboratory system to obtain physically grounded data. The laboratory measurements were performed at the triangular waveforms of the magnetizing voltage and the surface magnetic field. A typical rms envelope with a single peak positioned near the hysteresis coercive field was obtained for the unnitrided homogeneous sample. All nitrided samples with the hardened surface layer demonstrated an additional envelope peak at higher fields. Deeper nitridation suppressed both envelope peaks equally making the classical rms parameter sensitive to variation of the nitrided case depth. An industrial method of detection of the Barkhausen noise was tested for comparison using a commercial Rollscan device. The industrial measurements gave a single-peak envelope for all studied samples and a lower depth sensitivity of the rms parameter. Bulk testing methods, the magnetic hysteresis and the magneto-acoustic emission, were not able to detect the nitrided cases.     

某电厂球磨机噪声控制

对某电厂球磨机噪声进行了现场数值测定和频谱分析,针对其宽频特性选择新型隔声罩噪声控制设计和装置结构,取得了很好的隔声效果,噪声值达到了0级标准即安全作业标准,受到企业和车间工作人员的好评。     

直冷电冰箱的降噪改进

对噪声较高的某类型直冷电冰箱进行噪声频谱分析,在此基础上对不同的降噪措施进行了分析和实验研究,最终获得了很好的降噪效果.     

A Noise Doubling Radiometer for the Absolute Calibration of High-Frequency Noise Sources

A switching type radiometer is described in which the comparison of the standard and the unknown noise sources is performed without the physical disconnection of any of the sources. This ensures that no impedance change takes place in the relatively wide frequency band of the measurement. Thus reception of the 'reverse radiation' of the receiver reflected back into the receiver remains constant during the measurement and so may be nulled initially.