【作者】 朱从云；

【导师】 黄其柏；

【作者基本信息】 华中科技大学 ， 机械设计及理论， 2005， 博士

【摘要】 主动消声是利用声波之间的相消性干涉原理,使声场局部区域声能相互抵消,从而达到降低噪声的目的。由于声场的复杂性,加之实际声源场的再现具有相当的难度,致使主动消声方法实际应用并不理想。而有别于主动消声的主动吸声方法是从噪声传播途径上和受声体进行控制,它的控制目标是使入射声波的反射系数很小或接近于零,形成“黑洞”现象,使得吸声系数达到最大,从而达到吸声降噪的目的。国外从20 世纪90 年代初开始对主动吸声进行研究,但是研究成果少见报道,国内的研究目前尚是空白。本论文基于主动吸声降噪的特点,围绕其若干关键技术问题,在理论和计算等方面进行了研究与探讨。论文回顾了主动消声、吸声降噪的发展历史与现状,阐述了主动吸声降噪有待解决的关键技术问题,提出了论文的主攻目标和研究内容。研究了多层均匀吸声材料吸声系数的理论计算方法。采用声电类比与递推方法推导了由穿孔板、多孔吸声材料及空腔组成的多层吸声结构吸声系数计算的理论模型。通过数值计算,揭示了不同组合方式吸声结构与吸声系数的关系。基于空腔深度与共振频率的关系,提出了穿孔板主动吸声结构的吸声理论与方法。经过数值计算,得到了空腔深度变化与共振吸声系数的关系,在此基础上,提出了在穿孔板共振的条件下,通过一定流速的气流,可进一步提高穿孔板主动吸声结构的吸声效果。针对宽频带吸声降噪问题,提出了基于声阻抗的两种主动吸声理论与方法。第一种方法研究了移动刚性壁进行主动吸声的方法。该主动吸声方法由一层吸声材料和吸声材料背后可以移动的刚性壁组成,根据入射声波的频率,调节吸声材料背后刚性壁的位置,使吸声材料表面的声阻抗与空气的声阻抗相匹配,吸声材料的吸声系数达到最大。但是该主动吸声方法频率调节能力相对较差,对单一的低中频峰值频率较为有效。为此,提出了另外一种基于声阻抗的主动吸声方法。该吸声方法由一层吸声材料和吸声材料背后的扬声器组成,调节吸声材料背后扬声器的辐射阻抗,使得吸声材料的表面声阻抗率和空气的声阻抗率相匹配,从而使吸声系数达到最大,数值计算结果表明,该吸声系统在低频时能取得较好的吸声效果,高频声通常由吸声材料来达到吸声降噪的目的。更多还原

【Abstract】 Active noise control is achieved by introducing a canceling “anti-noise”wave of equal amplitude and opposite phase using a secondary source. It is controlled with incident sound wave, yet active sound absorption is controlled with reflected sound wave and the absorption coefficient is maximal for the reflected coefficient is reached to zero. Active sound absorption is vacant in china till now, yet it is researched in foreign country from 1990’s and the correlative achievement is seldom reported, so the main content of the dissertation is focused on the study with active sound absorption. It presents the development of modern techniques about active sound absorption and then puts emphasis on the study about theoretical calculation absorption coefficient of the multi-layer absorber, the active absorption system based on the air stream, the active absorption system based on the characteristic impedance, the active absorption system based on the piezoelectric materials and the principle of the active absorption and active isolation based on piezoelectric materials. A theoretical method to calculate the absorption coefficient of the multi-layer absorber is proposed in this dissertation. For the multi-layer absorber composed of perforated plate, composed of perforated plate and cavity, composed of perforated plate, porous absorption material and cavity, the absorption coefficient is theoretically calculated. At last, the absorption coefficient of the different assembled absorber is calculated using the method mentioned in this dissertation. The results denoted that the method to calculate the absorption coefficient mentioned in this dissertation is feasible. The theory of active absorption using perforated plate is proposed in this dissertation. The perforated plate is used as the material of active absorption. The frequency is measured in order to get the resonate frequency and the depth between the perforated plate and the rigid wall, then the rigid wall is moved in order that the depth between the perforated plate and the rigid wall is satisfied with the resonate frequency, so the absorption coefficient is maximal and the aim of active absorption is reached. Numerical calculation denoted that the absorption effect is not obvious, so, on the condition of the resonate frequency of the perforated plate, the air stream is passed through the cavity between the perforated plate and the rigid wall so that the absorption coefficient is about 1.0. The theoretical calculation results denoted that the active sound absorption method is feasible. The method of active absorption based on the characteristic impedance is proposed and two systems are designed in this dissertation. One of the systems is consisted of the absorption material and the moved rigid wall, the depth between the absorption material and the rigid wall is adjusted to make the surface characteristic impedance of the absorption material match with the air characteristic impedance so that the absorption coefficient is maximal. Yet this system is effective for the single frequency sound wave and noneffective for the wide frequency sound wave, so the second system is posed which is consisted of two microphones, the absorption material and two loudspeakers, the incident wave is measured by the two microphones, the sound impedance is controlled in order to make the surface impedance match with the air impedance to reach the aim of active absorption. Numerical calculation denoted that the second system is effective for the low frequency sound wave and noneffective for the high frequency sound wave in which the absorption material is effective. In this dissertation, the active sound absorption system is posed. The piezoelectric material is applied as the absorption material in active sound absorption system. Two PVDF (Poly Vinylidene Fluoride) films with equal distance are placed in front of the piezoelectric material in order to measure the sound pressure of the incident wave. The voltage is applied on the surface of the piezoelectric material in order to make the reflected wave zero according to the method of electro-acoustic analogy. At last, the experiment is carried out. The results denoted that the active sound absorption method is feasible. On the base of the theory of active sound absorption using one piece of piezoelectric material, the active sound absorption and the active sound isolation using two pieces of piezoelectric materials is posed in this dissertation. Two pieces of piezoelectric materials are used as the main materials of active sound absorption and active sound isolation. The voltageis applied on the surface of the two piezoelectric materials respectively in order to make the reflected wave and the transmission wave zero according to the measured sound pressure of the incidence plane wave using two pieces of PVDF (Poly Vinylidene Fluoride). The experimental results denoted that the active sound absorption and active sound isolation method is feasible.更多还原