失谐驻波管及其极高纯净驻波场性质的研究

由直径不同的两级直圆管连接而成的两级突变截面驻波管具有失谐性,即高阶共振频率不是一阶共振频率的整数倍. 两级突变截面驻波管的失谐性质能够很好地抑制一阶共振频率激励下的大振幅非线性驻波畸变产生的高次谐波,从而获得大振幅纯净驻波场. 通过对两级突变截面驻波管失谐性质的研究,采用大功率扬声器正接等措施,利用两级突变截面驻波管的失谐性质在一阶共振频率激励下获得了184 dB的极高纯净驻波场,并对二至五阶共振频率激励下的声场进行了相应的实验研究. 在二阶、四阶共振频率激励下分别获得了180和166 dB波形比较规整的大振幅非线性驻波,并在三阶、五阶共振频率激励下观察到了谐波饱和现象和锯齿波. 关键词： 失谐驻波管 大振幅驻波 畸变 饱和     

突变截面驻波管和极高纯净驻波场的实验研究

突变截面驻波管属于失谐驻波管,即其高阶共振频率不是一阶共振频率的整数倍。通过对STAS的优化设计,利用STAS的失谐性质在一阶和二阶共振频率下激励分别获得了180 dB和177 dB的极高纯净驻波声场。尽管声压级已经很高,但在接下来的对一阶和二阶共振频率激励下的声波波形畸变和谐波饱和情况进行的实验研究中仍然没有观察到谐波饱和现象。与此同时,对三阶共振频率激励下的声场进行了实验研究,由于三阶共振频率激励下的大振幅非线性声场的二次谐波频率接近六阶共振频率,在声压级达到170 dB时观测到了三阶共振频率激励下的声波波形畸变和谐波饱和现象。     

等截面驻波管内大振幅驻波场的实验研究

通过改进等截面驻波管实验系统,在1阶峰值共振频率激励下获得了182.1 dB大振幅驻波场,并对1~5阶峰值共振频率激励下的大振幅驻波场谐波饱和情况以及波形畸变进行了实验研究。研究发现,尽管1阶峰值共振频率激励下声压级已达到182.1 dB,但波形畸变最小,谐波并未表现出饱和现象,而3阶峰值共振频率激励下的大振幅驻波场表现出了饱和趋势。对谷值共振频率激励下获得的大振幅驻波场进行对比实验研究,发现谷值共振频率激励下,1阶谷值共振频率所获得的驻波场声压级最大,但波形畸变也最大。在相同声源驱动电压下,1阶峰值共振频率激励下获得的驻波场声压级始终大于1阶谷值共振频率激励下获得的驻波场声压级。由此可见,利用扬声器在等截面驻波管中获取大振幅驻波场,驻波管由1阶峰值共振频率激励较为合适。     

谐振管形状对热声发动机内非线性声场的影响

研究了谐振管一端受活塞声源激励,另一端刚性封闭条件下,管道形状对热声发动机谐振管内部非线性声场的影响。基于流体力学基本方程建立了渐变截面谐振管内一维非线性声场的模型,考虑了黏性耗散及非线性效应的影响。利用伽辽金法数值求解了该模型的速度势方程,分析了谐振管形状、活塞振动速度及激励频率对管内声场的影响。将双曲形、指数形、锥形、正弦形等四种变截面谐振管内的非线性声场与圆柱形直管的情况进行了比较。结果反映了谐振管内声场的压力波动受活塞振动速度及谐振管形状的影响;显示了当活塞振动幅度较大时,谐振管内出现的波形畸变、频率曲线偏移、共振频率滞后等非线性现象;揭示了变截面谐振管在抑制管内的高阶谐波及提高压比等方面的优越性。     

有限振幅驻波声场中的分岔实验研究

在一维有限振幅驻波声场中观察到了分岔现象。除了理论所预期的高次谐波存在外,次谐波、分数谐波亦存在于有限振幅驻波声场中。随基波声压级提高,最终达到混饨状态。     

昆特管实验原理分析

根据声学原理对昆特管演示实验进行分析,给出了对实验现象细节的一种物理解释,即在昆特管中除主驻波模式之外还激励起了最低一级高次驻波模式振动,昆特管内的声波场实际上是主驻波模式和最低一级高次驻波模式叠加形成的声波场.     

大振幅驻波的实验研究——Ⅰ：二次谐波的特性

本文对一维大振幅驻波场进行了较为全面的实验研究,介绍了实验研究系统,着重讨论二次谐波的特性、实验研究结果表明：二次谐波的量值在基波产压级为定值的条件下是驱动频率的函数.其变化曲线可用一简谐函数近似描述之。大振幅驻波场在频域内可划分为四个区域。在称之为\     

非线性驻波现象的数值模拟与实验结果的比较

强非线性驻波实验研究发现很多重要的物理现象,如高次谐波成倍增长、饱和、分岔和混沌等。采用Euler方程和MacCormack四阶精度差分方法,成功地数值模拟了非线性驻波高次谐波成倍增长和饱和现象,并与相应的实验结果作了详细比较,符合很好。     

大振幅驻波的实验研究Ⅱ：驻波场谐波的饱和

大振幅驻波在激波形成前的过程中,谐波声压级随基波声压级（L_p1）增长而出现饱和现象。在L_p1<153 dB时,m次谐波声压振幅p_m与基波声压幅值p₁;呈p_m~p₁^m关系。基波升高1 dB,m次谐波升高m dB。之后,各次谐波均开始趋于饱和。次数越高,饱和越快,p_m~p₁^m的关系逐渐变为p_m~p₁的趋向。在频率域内,变化过程大致可划分为三个区域：I.线性区;Ⅱ.变化区;Ⅲ.激波区。三个区域对应了时域的激波形成。L_p1>160dB后,即可认为激波已经形成。基波与电信号的关系也呈饱和现象,但与频率有关。上述结果有助于理论研究工作的进一步深入。     

基于原子-腔耦合系统下线宽压窄内腔四波混频信号的产生

本文实验研究了基于原子-腔耦合系统下的内腔四波混频效应。当一束驻波耦合场作用于该复合系统时,实验发现在原子共振频率中心,产生的反射波混频信号无法在腔内形成共振,而当耦合光频率偏离原子共振频率中心时,反射信号能在腔内共振,从而产生线宽压窄的共振输出;进一步实验研究了不同耦合光频率失谐下,腔模失谐对内腔四波混频效率的影响。理论上,基于内腔介质在驻波耦合场驱动下的吸收特性及耦合光泵浦引起的强吸收效应对实验现象进行了定性的分析。     

Experimental study on the standing-wave tube with tapered section and its extremely nonlinear standing-wave field

A standing-wave tube with tapered section(STTS) was evolved from a standing-wave tube with abrupt section(STAS) whose abrupt section was replaced with tapered section. The research was intended to compare the acoustic properties and the extremely nonlinear pure standing waves of STTS with those of STAS.The acoustic properties of the STTS were studied with transfer matrix.It was proved,like the STAS,that the STTS was dissonant standing-wave tube.With its dissonant property,the 181 dB extremely nonlinear pure standing wave was obtained in the STTS excited at its first resonance frequency.Then the comparative experimental studies on the saturation properties of the extremely nonlinear standing waves were carried out in the STTS and the STAS with the same length.It was found that the STTS could suppress the harmonics and meanwhile reduce energy loss of the standing wave more effectively.Compared with the STAS,under the same voltage of loudspeaker,the STTS obtained a higher extremely nonlinear pure standing wave.Moreover,it was found for the STTS that the third harmonic of the third resonance frequency was close to the seventh resonance frequency of sound source impedance,to which the valley value of the sound pressure level transfer function corresponded.Because of this,the third harmonic increased rapidly with the increase of fundamental wave and tended to saturate.     

Experimental investigation on standing-wave tube with abrupt section and extremely nonlinear pure standing-wave field

Standing-wave tube with abrupt section （STAS） was a dissonant standing-wave tube whose higher resonance frequencies were not integral multiplies of the first one. Making use of the dissonant property of STAS and through the optimization of the system, extremely nonlinear pure standing-wave field of 180 dB at the first resonance frequency and that of 177 dB at the second resonance frequency have been obtained. At the two resonance frequencies, distortion of waveform and saturation of harmonics were studied experimentally, but saturation did not appear even though under such high sound pressure levels. However, while nonlinear sound field was experimentally studied at the third resonance frequency, it was found that the frequency for the second harmonic of the third resonance frequency was close to the sixth resonance frequency of the STAS and the distortion of waveform and the saturation of harmonies appeared as the sound pressure level approached 170 dB.     

Experimental study of large-amplitude standing-wave field obtained in a standing-wave tube with uniform cross section

A large-amplitude standing-wave field of 182.1 dB is obtained under the excitation at the resonant frequency of the lst-order peak of the sound pressure transfer function in an improved standing-wave tube experimental system,and saturation of harmonics and waveform distortion are investigated experimentally for the large-amplitude standing-wave fields obtained under the excitations at the resonant frequencies of the 1 st-to the 5 th-order peaks.The results show that although the sound pressure level has reached 182.1 dB under the excitation at the resonant frequency of the 1 st-order peak,the waveform distortion is the minimum and the harmonic saturation is not observed.However,the large-amplitude standing-wave field excited at the resonant frequency of the 3 rd-order peak exhibits the trend of the harmonic saturation.Comparison of the large-amplitude standing-wave fields obtained under the excitations at valley resonant frequencies shows that the standing-wave field excited at the resonant frequency of the 1 st-order valley has the largest SPL,but also has the largest waveform distortion.Under the same source-driving voltage,the standing-wave field excited at the resonant frequency of the 1 st-order peak always has greater SPL than the standing-wave field excited at the resonant frequency of the 1 st-order valley.Hence,to obtain a large-amplitude standing-wave field,it's better to excite at the resonant frequency of the 1 st-order peak of the SPTF by using loudspeaker in a standing-wave tube with uniform cross section.     

Influence of resonance tube geometry shape on performance of thermoacoustic engine

Based on the linear thermoacoustics, a symmetrical standing-wave thermoacoustic engine is simulated with a cylindrical tube and a tapered one as the resonance tube, respectively. The experiments with both cylindrical and tapered tubes are carried out. The suppression of nonlinear effects due to tapered tube as the resonance tube is discussed. Both simulation and experimental results show that the performance of the tapered tube is better than cylindrical one as the resonance tube.     

弹性微管内气泡的非线性受迫振动

将弹性管壁视为膜弹性结构, 探索在外部声场作用下弹性微管内液柱-气泡-管壁构成耦合振动系统的非线性特征. 利用逐级近似法对系统非线性共振频率、基频和三倍频振动幅值响应、 分频激励共振机理等进行了理论分析. 基频和三倍频振动的幅-频响应数值结果表明: 气泡的轴向共振和管壁共振不能同时出现; 两垂直方向的振动均表现出幅值响应多值性, 进而可能引起系统的不稳定声响应; 三倍频振动在低频区的声响应强于高频区. 关键词： 弹性微管 受迫振动 非线性振动 气泡声响应     

Experimental investigation on finite-amplitude standingwaves:Ⅰ. The properties of second harmonic

I.IntroductionInrecentyears,theresearchworkonnonlinearacousticshasbeendcvelopedrapid1ybe-causethehigh-intensitysoundismoreandmoreimportantincontcmporarytechnology.Aerodynamicnoiseemittedbyrockctorjetengines,noisetestofairframcs,u1trasonicpro-cessing,andothcrs,a1linvo1vefinitc-amplitudesoundwavesand,mostlystandingwaves.Athcoryofonc-dimensiona1finitc-amp1itudestandingwavesinlosslessmediahasbeenproposedbyMAAonthebasisofthcfundamenta1principlesofhydrodynamics['l,inwhichformulasofstcadywavcformsa…     

谐振管谐振频率计算方法的研究

为了准确地计算声谐振管的谐振频率,提出了基于对管内声压分布进行理论模拟的声压模拟法,以及基于驻波最小点位置与管两端声阻抗关系的驻波最小点法。结果表明这两种方法因为考虑了声谐振管两端的声阻对谐振频率的影响,所得谐振频率更加精确、严格,所以特别适用于要求谐振管的谐振频率严格控制的声学领域。同时表明:声压模拟法与驻波最小点法虽然出发点不同,但谐振频率的计算结果完全相同。驻波最小点法计算比较方便,而声压模拟法在计算出谐振频率的同时,还可以给出管中的声压随位置的分布情况。