共查询到20条相似文献,搜索用时 31 毫秒
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Vibro-acoustic analysis of complex systems 总被引:13,自引:0,他引:13
P.J. Shorter 《Journal of sound and vibration》2005,288(3):669-699
A general method is presented for predicting the ensemble average steady-state response of complex vibro-acoustic systems that contain subsystems with uncertain, or random, properties. The method combines deterministic and statistical techniques to produce a non-iterative hybrid method that incorporates equations of dynamic equilibrium and power balance. The method is derived explicitly without reference to statistical energy analysis (SEA); however, it is seen that the wave approach to SEA can be viewed as a special case of the proposed method. The proposed method provides a flexible way to account for necessary deterministic details in a vibro-acoustic analysis without requiring that an entire system be modeled deterministically. The method therefore provides a potential solution to the mid-frequency problem (in which a system is neither entirely deterministic nor entirely statistical). The application of the method is illustrated with a numerical validation example. 相似文献
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利用网络分析仪,根据需要在设定的频率范围进行扫频测量,网络分析仪的端口1输出的微波信号经过微波传输转换器进入与待测非标准元件匹配连接的连接段(如波导);网络分析仪的端口2连接定向耦合器,用于监测传输段内的反射微波信号。首先,在非标准接口端面连接短路面,通过网络分析仪测量反射信号在设定频点的相对幅度值;然后去掉短路面,在非标准接口端面连接待测元件,再次测量反射信号在特定频点的相对幅度值;最后根据本文推导的公式得出驻波系数。该方法的测量误差与定向耦合器的方向性(方向性系数越大越好)和待测元件驻波系数有关。将该方法运用在非标准接口匹配负载驻波系数的测量中,定向耦合器方向性系数取为40 dB,测得其驻波系数小于1.2,误差小于20%。该方法简便可行,可以用于测量常用的非标准接口元件尤其是非标准低驻波系数元件的驻波系数。 相似文献
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焦距法测试自聚焦透镜折射率分布常数 总被引:1,自引:0,他引:1
本文介绍了一种测量自聚焦透镜折射率分布常数的方法─—焦距法,并进行了原理公式推导,和精度分析,其测量不确定度为±1×10 ̄(-3);其次,简要地介绍了实验方法。实验结果证明了焦距法是测量自聚焦透镜折射率分布常数的简单实用的方法,它具有装置简单、数据处理也不复杂的特点,是一种非破坏性的测试方法。 相似文献
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This paper presents a method of diffraction correction for the log-spectral difference method to estimate quantitatively attenuation of a solid in the immersion case. The correction method is established based on the angular spectrum approach that is used to calculate the echoes from the front and back surfaces of the immersed solid. An example is given of a copper plate submerged in water and inspected by a linear array with a cylindrically curved surface. The correction method is first applied to a theoretical estimation of attenuation which is linearly dependent on frequency. The results have shown that the evaluated attenuation coefficient is in excellent agreement with the exact value. Then the method is applied to a real situation, in which the results have shown that the method yields reasonable evaluated attenuation values. This work has demonstrated that the method is able to correct effectively the diffraction effect so as to achieve a quantitative estimation of attenuation. 相似文献
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《Journal of computational physics》2008,227(1):376-399
In this paper, we develop a finite-volume scheme for the KdV equation which conserves both the momentum and energy. The main ingredient of the method is a numerical device we developed in recent years that enables us to construct numerical method for a PDE that also simulates its related equations. In the method, numerical approximations to both the momentum and energy are conservatively computed. The operator splitting approach is adopted in constructing the method in which the conservation and dispersion parts of the equation are alternatively solved; our numerical device is applied in solving the conservation part of the equation. The feasibility and stability of the method is discussed, which involves an important property of the method, the so-called Jensen condition. The truncation error of the method is analyzed, which shows that the method is second-order accurate. Finally, several numerical examples, including the Zabusky–Kruskal’s example, are presented to show the good stability property of the method for long-time numerical integration. 相似文献
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The intensity coherence function of time for partially saturated acoustic propagation through internal waves is calculated with a method that is improved over previous treatments. Two specific improvements are introduced: the usual expansion in (1/lambdaphi2) is carried out to a higher order, and then the terms of that expansion are calculated with a new perturbative method. The method is applied to propagation without a sound channel, for both phase-screen and continuous-medium cases. The validity of the new perturbative method is estimated by calculating the next order error terms. Accuracies at the few-percent level are found. The new analytic formulas are also corroborated with numerical integration. Finally, the method is applied to a specific ocean-acoustic experiment [Azores Fixed Acoustic Range (AFAR)]. In order to achieve good agreement with experiment it will be necessary to add an accurate treatment of the sound channel to the present perturbation method. 相似文献
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The one-port source characteristics in a duct system, viz., source impedance and strength, can be determined by using the four-load method. In this paper, to avoid the instability problem of the conventional four-load method, a new formulation for the multiload method has been proposed, which employs an error function based on the linear, time-invariant source model. It is shown that the method is less sensitive to input errors compared to the previous methods. For a 10% input error, the proposed method yields a relative error in the source resistance that is about 1/100 times smaller than for the conventional method. The effectiveness of the present method is demonstrated by two test examples, a loudspeaker and a blower, each operating in a duct. It is observed that the conventional and least-squares methods result in large errors, whereas the present method yields far better agreement with the actual source parameters, as measured by the direct method. The present method is then used to obtain the source parameters on the exhaust side of an operating internal combustion engine. The radiated sound spectrum from the exhaust opening is predicted by using the measured source parameters and the calculated result agrees very well with the measured one. 相似文献
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研究了温盐双扩散系统的多组分格子Boltzmann方法.通过对二维方腔的温盐双扩散系统的数值模拟,检验了方法的可行性及有效性,所得到的结果与差分法结果符合良好,继而将此方法推广到三维,建立了三维温盐双扩散系统的格子Boltzmann方法,对三维方腔双扩散问题进行了模拟和分析,并与差分法模拟的结果进行了比较,结果令人满意.最后,分析了格子Boltzmann方法在模拟双扩散对流问题时存在的局限性.
关键词:
格子Boltzmann方法
温盐双扩散
Boussinesq近似
数值模拟 相似文献
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In the proposed method, as in the boundary element method (BEM), a field problem is solved on its boundary along which nodes are distributed. The distinct feature of the proposed method is related to the fact that no interpolation functions between the nodes are required, so that the basic collocation method is employed to satisfy a given boundary condition. This approach reduces a large amount of numerical calculation induced due to the interpolation functions. Unlike the method of auxiliary sources (MAS), in the proposed method only the regular functions that have finite functional values everywhere including the origins are employed as basis functions. As a result, the proposed method does not need the auxiliary surface, the construction of which is a troublesome work because its form, dimension, shifting, etc. strongly influence the accuracy of the MAS. The eigenvalues calculated by the proposed method rapidly converge to the exact values thanks to the simplicity of the method. Moreover, the method gives mode shapes successfully without using the interpolation functions between the nodes. The efficiency and accuracy of the method are verified through several applications. 相似文献
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能量色散X射线荧光分析中改进型基本参数法研究 总被引:2,自引:0,他引:2
能量色散X射线荧光分析方法是目前常用的一种多元素分析方法,但该方法检出限和分析精度,受到分析基体的影响。基本参数法是目前一种常用的分析方法,但在使用过程必须获取净峰面积和基体所有成分,而在实际使用时,尤其在分析低含量样品时,净峰面积计算、基体中“暗物质”影响了测量精度,制约了基本参数法的应用。针对基本参数法的不足,将谱线解析方法与基本参数法融合,将重叠峰剥离过程嵌入基本参数法迭代过程中。在含量计算过程中,采用分析样品特征X射线分支比的理论系数,对重叠峰进行剥离,解决能量色散X射线荧光测量中净峰面积计算和定量分析问题;在计算过程中,对“暗物质”进行均一化处理。通过对标准物质测量分析,结果表明对于Ni,Cu,Zn三个元素改进型基本参数法(改进型FP)测量结果准确度高于影响系数法。 相似文献
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和Hamilton-Jacobi方法类似,Vujanovi?场方法把求解常微分方程组特解的问题转化为寻找一个一阶拟线性偏微分方程(基本偏微分方程)完全解的问题,但Vujanovi?场方法依赖于求出基本偏微分方程的完全解,而这通常是困难的,这就极大地限制了场方法的应用.本文将求解常微分方程组特解的Vujanovi?场方法改进为寻找动力学系统运动方程第一积分的场方法,并将这种方法应用于一阶线性非完整约束系统Riemann-Cartan位形空间运动方程的积分问题中.改进后的场方法指出,只要找到基本偏微分方程的包含m(m≤ n,n为基本偏微分方程中自变量的数目)个任意常数的解,就可以由此找到系统m个第一积分.特殊情况下,如果能够求出基本偏微分方程的完全解(完全解是m=n时的特例),那么就可以由此找到≤系统全部第一积分,从而完全确定系统的运动.Vujanovi?场方法等价于这种特殊情况. 相似文献
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针对包含近源障碍物条件下的电波传播问题,提出了一种新颖的电波传播预测混合建模方法:矩量法(MOM)和圆柱坐标系抛物方程法(PEM)混合建模方法(MOM-PEM);MOM用于包含辐射源和近源障碍物的小圆柱区域内的电波传播建模,PEM用于MOM计算空间外的大区域范围内电波传播建模。MOM和PEM的计算过渡区域进行精细化网格剖分处理以避免场强数值传递的不兼容。仿真模拟了三类近源障碍物存在场景下的电波传播问题:有限开窗屏障碍物、立方体障碍物以及包含辐射源的半封闭空间障碍物,并将混合算法计算得到的结果和相同环境下采用全矩量法计算得到的结果进行了数值对比,结果表明混合算法和矩量法在精度上吻合较好。 相似文献
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Application of a multivariable input-output subspace identification technique in structural analysis
In this paper a multivariable subspace-based identification method is applied to experimental modal analysis. The method shows its efficiency in the identification of data which is contaminated by a great amount of external noise. Numerical simulation is used to present the main characteristics of the method and compare its performance against other techniques currently used in experimental modal analysis. The subspace identification method is also applied to data from a modal test of a practical engineering structure. 相似文献
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FAAS法对三种制备样品方法的研究 总被引:8,自引:0,他引:8
在FAAS法分析中,样品预处理始终占有极为重要的位置。本文比较了三种样品消化方式,即传统酸消化法,灰化法及微波消化法。传统的消化方式过程长、速度慢、效率低、而且被测元素易受到损失及易污染等不足,而微波是一种非常快捷、省时、省试剂和无污染的消化方式。通过对校准物质贻贝中的铜、锌、铁的测定结果证明微波消化方式比传统的消化方式优点多。 相似文献