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1.
制备了晶格常数同声波波长同数量级的二维钢/空气体系声子晶体结构模型。研究了在填充分数较小(F〈0.082)的情况下,单一方向(FX)声波在二维声子晶体的声传播特性,得出其禁带频率范围。对1400Hz-3200Hz的声波垂直通过管阵列结构模型前后的声压级(SPL)进行了实验测试,多处表现出频段声压的加强与减弱。研究了在管子直径及结构列间距不变的情况下增加排数及改变排间距两种情况下的禁带频率范围,得出了禁带宽度及最大插入损失的位置变化规律。  相似文献   

2.
空气中周期管阵列的声波禁带研究   总被引:10,自引:1,他引:10  
本文以不锈钢管正方形排列在空气中形成的二维声子晶体为对象,使用平面波展开法计算并通过实验测试的方法,分析了该二维声子晶体的声波禁带,讨论了晶格常数对声波禁带的影响.结果表明,随着晶格常数的减小,ΓX方向禁带宽度增加,禁带上下边界频率增大.  相似文献   

3.
使用平面波展开法,讨论了单元结构尺寸对正方形排列的不锈钢/空气二雏声子晶体声波禁带的影响。结果表明,当填充率(晶格常数)增大时,最低禁带宽度增大(减小);最低禁带中心频率基本不受散射体半径的影响,但随晶格常数的增大而降低。  相似文献   

4.
声子晶体能够产生完全的弹性波禁带,可以阻止声波或者振动在其内部传播。采用平面波算法研究了二维正方点阵声子晶体的禁带结构。在甲醇/水银双组分二维(2D)液相体系中发现了很大的完全禁带,到目前为止,在固相体系和其他液相体系中还没有发现相同宽度和相同数量的完全禁带。还研究了声子晶体中散射体的横截面为圆形和绕其中心轴旋转任意角度的正方形时完全禁带的产生规律,探索了第一禁带宽度与第一禁带中心频率的比值△Ω1/Ωc1和填充率F之间的关系,以及前50个频带中禁带的总宽度∑△Ωn/Ωcn和填充率F之间的关系。  相似文献   

5.
声子晶体的研究进展及应用前景   总被引:16,自引:1,他引:16  
声子晶体是近10年来提出的一类概念、声学材料,这种周期性结构所具有的声波带隙特性可以认为具有某种过滤效应,即当多种频率的振动或声波通过此类晶体时,由于布拉格散射,便会分裂为导带和禁带,处于禁带频率范围内的振动或声波将被禁止在晶体中传播,而处于导带频率范围内的振动或声波则能顺利通过声子晶体。通过求解声波在晶体中的波动方程可以设计所需要的声子禁带和导带。文中对声子晶体的概念和基本特征、研究进展、理论方法、潜在应用等方面进行了阐述,并对声子晶体的研究工作进行了展望。  相似文献   

6.
为了研究弹性波在固-液结构声子晶体中的能带特性,推导出了弹性渡斜入射固-液结构声子晶体的转移矩阵.利用它计算了固-液结构声子晶体中弹性波的透射系数.结果表明,当介质的分层厚度固定时,在透射渡中出现了多级禁带,禁带的频率中心随入射角的增加而向高频方向移动.当入射角固定时,禁带的频率宽度随介质的分层厚度近似呈反比变化,禁带的频率中心也随介质的分层厚度近似呈反比变化.  相似文献   

7.
声子晶体是一种具有声波带隙特性的新型功能材料。运用平面波展开法研究了二维声子晶体的带结构,二维声子晶体由横截面为正方形的散射体按正方形排列植入环氧树脂基体中形成。结果表明:通过改变散射体的取向可以调节系统的带隙,当填充率较低时,带隙宽度随散射体旋转角的增加先减小再增加,而填充率较高时,带隙宽度随散射体旋转角的增加而先稍有增加然后再减小。  相似文献   

8.
0引言弹性波禁带的存在是声子晶体的重要特征。过去的近二十年中,有很多关于复合材料和声子晶体中弹性波的禁带结构理论研究,以及关于存在声禁带的实验研究[1-8]。Chen[4]等严格计算了一维复合薄板中兰姆波能带结构。Hsu和Wu[5]运用平面波展开法研究了二维声子晶体板中兰姆波的声传播。  相似文献   

9.
以二维铁/水正方形排列声子晶体平板为主板模型,用时域有限差分法(FDTD)分析栅板对主板声波通透性的影响,结果发现,栅板的材料、填充率、位置、厚度、密排结构等都会影响主板的声波通透性。其中,极软材料的栅,主要阻碍低频声波的传播;大填充率栅板的影响较小填充率栅板的大;多层栅板的影响较单层栅板的大;密排结构的栅板会极大地影响主板的声通透性,甚至引入高频带隙。栅板对主板的调节作用可望在声滤波、声聚焦、超声成像等方面有重要应用。  相似文献   

10.
0引言作为一种新型功能材料,声子晶体(周期性结构材料)对在其内部传播的声波表现出良好的通带和禁带特性.由于声子晶体的这些特性在减振、降噪等领域具有极佳的潜在应用前景[1,2],近几十年来研究者对声子晶体做了相当多的理论和实验研究[2-4].随着研究的逐渐深入,研究者对声子晶体的  相似文献   

11.
In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.  相似文献   

12.
13.
A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.  相似文献   

14.
On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……  相似文献   

15.
A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.  相似文献   

16.
Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……  相似文献   

17.
In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M2(B,C), (W,Mo)2(B,C), M3(B,C), M23(B,C)6 type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm2. The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K1 mill housing of bar mill.  相似文献   

18.
We associate a variety of innovations with the term "Industry 4.0". The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...  相似文献   

19.
The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...  相似文献   

20.
Several researches have been reported about the characteristic of β-Ga2O3 nanowires which was synthesized on nickel oxide particle. But indeed, recent researches about synthesis of β-Ga2O3 nanowires on oxide-assisted transition metal are limited to nickel or cobalt oxide catalyst. In this work, Gallium oxide (β-Ga2O3 ) nanowires were synthesized by a simple thermal evaporation method from gallium powder in the range of 700 - 1000℃ using the iron, nickel, copper, cobalt and zinc oxide as a catalyst, respectively. The β-Ga2O3 nanowires with single crystalline without defects were successfully synthesized at the reaction temperature of 850, 900 and 950℃ in all the catalysts. But optimum experimental condition in synthesis of nanowires varied with the kind of catalyst. As increasing synthesis temperature,the morphology of gallium oxide nanowires changed from nanowires to nanorods, and its diameter increased. From these results, we could be proposed that the growth mechanism of β-Ga2O3 nanowires was changed with synthesis temperature of nanowires. Microstructure and morphology of Synthesized nanowire was characterized by HR-TEM, FE-SEM, EDX and XRD.  相似文献   

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