共查询到20条相似文献,搜索用时 46 毫秒
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提出圆柱薄壳的圆截面内运动假设,从声学角度将环肋对壳体的作用等效为径向作用力,根据Hamilton原理建立了简支非均匀加筋圆柱壳的振动控制方程,利用驻波形式解对其径向模态机械阻抗进行了研究。分析表明:对于加筋圆柱壳,环肋与圆柱薄壳的径向模态机械阻抗具有串联连接方式,通过调整环肋的几何参数增大环肋自身的径向模态机械阻抗,可以达到壳体减振降噪的目的,并指出了利用环肋的反共振特性进行加筋圆柱壳结构减振的设计方向。 相似文献
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螺旋桨在艇体艉部不均匀伴流场中旋转产生的脉动推力激励起推进轴系纵向振动,振动经推力轴承基座传递至艇体,引起艇体水下低频辐射噪声。通过建立推进轴系、推力轴承基座和艇体耦合结构模型,分析推进轴系─艇体的耦合振动模态,结果显示,艇体弹性支撑边界条件对推进轴系的纵向振动特性有一定影响。采用基于模态叠加法的有限元结合边界元方法分析推进轴系纵向振动激励下的艇体水下辐射声场,分析表明,艇体第1阶纵向振动模态是参与艇体水下声辐射的主模态。进一步在推力轴承及其基座间安装动力吸振器以减小推进轴系纵向振动向艇体的传递,使艇体水下辐射噪声得到一定程度上的控制。 相似文献
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基于结构动力分析原理,以"设备-基座"振动系统为例,证明结构动力分析时力边界与运动边界的统一性;针对结构局部动力参数未知情况,通过保障结构运动边界条件一致,构造结构动力分析"虚拟力",提出结构动力分析的运动边界相似法,解决动力参数未知时给定运动边界条件的结构动力分析问题,并对其有效性进行验证;将运动边界相似法用于船舶结构水下振动声辐射研究,分析船舶水下声辐射特性。结果表明,船舶水下振动声辐射与激励作用位置、激励频率等因素密切相关。船舶结构水下辐射噪声主要集中于激励源附近的中部区域,尾部次之,船首最小;低频段船舶水下声辐射沿船长分布均匀,但随激励频率的提高,水下辐射声场不均匀性逐渐增大,指向性更明显。 相似文献
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针对水下双层圆柱壳中低频声辐射预报,分别利用基于流固耦合的FE-IBEM法和基于声固耦合的FE-IBEM法进行水下声辐射计算,比较上述两种算法在计算特性方面的差异,并通过算例对这两种算法进行分析。另外,还研究了环肋间距以及环肋厚度等对双层圆柱壳结构水下辐射噪声的影响。研究结果表明,流固耦合模式由于忽略了流体的可压缩性使得计算结果偏小,声固耦合模式充分考虑了流体对结构的耦合作用使得计算结果更合理,基于声固耦合模式的FE-IBEM法是计算结构水下辐射噪声的优选方法;合理选择环肋间距以及增加环肋厚度可以降低结构中低频水下辐射噪声。 相似文献
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《噪声与振动控制》2020,(1)
以鹅蛋为原型,通过Kitching方程描述鹅蛋的形状函数,开展多个蛋形壳交接仿生耐压壳的远场水下辐射噪声特性研究。采用有限元和无限元方法建立水下多蛋交接仿生耐压壳的流固耦合模型,分析蛋形壳个数和主要设计参数对辐射噪声的影响规律。研究结果表明,对于四个以下、长轴为2.4 m的蛋形壳交接耐压壳体,在每个蛋壳相同垂向激励位置引起的声辐射曲线特征相近。相对于单个蛋壳,交接蛋壳数量增加时声辐射曲线会出现低频弯曲峰值线谱,但不显著影响整体声学特性。蛋壳长轴越短,交接后的耐压壳辐射噪声越低,越有利于辐射噪声控制。在满足工程需求的前提下,应协调优化蛋壳长轴的长度和交接数量以保证较优的结构力学特性和辐射噪声特性。分析结果可为低噪声水下仿生耐压壳结构设计应用提供有效参考。 相似文献
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A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling. 相似文献
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Liebert A Wabnitz H Grosenick D Möller M Macdonald R Rinneberg H 《Applied optics》2003,42(28):5785-5792
A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue. 相似文献
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O'Brien RS 《Radiation protection dosimetry》2003,105(1-4):95-100
Australia has several uranium mines and a large number of mineral sand mines, with associated processing facilities. Exposures resulting from these mining and processing operations usually involve intakes of mixtures of radionuclides. This work describes the development of a suite of first order, linear compartment models, based on the ICRP Publication 66 respiratory tract model, and an analytical solution to the decay equations, for assessing the consequences of such intakes. The computer programs based on these models directly compute excretion, organ retention and organ and whole-body doses for intakes of either single radionuclides or any mixture of radionuclides belonging to the same radioactive decay chain. The intake can be via inhalation, ingestion or injection, and can be acute, chronic or of limited duration. The starting concentration and degree of secular (dis)equilibrium can be specified for each radionuclide. No assumptions need to be made about the relative magnitudes of the radioactive half-lives of the different nuclides. 相似文献
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Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995. 相似文献
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本文根据多年的实践检定经验 ,参照JJF1 0 59- 1 999《测量不确定度评定与表示》以及《测量不确定度表达 1 0讲》 ,对卧式金属罐容量的测量结果不确定度进行了评定。 相似文献
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由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。 相似文献