In this paper,a model is established with application of the spectral-wave guide method,which has higher accuracy and can serve as a rapid calculation tool for sound transmission calculations.Based on this calculation...In this paper,a model is established with application of the spectral-wave guide method,which has higher accuracy and can serve as a rapid calculation tool for sound transmission calculations.Based on this calculation model,some numerical results of circumferentially non-uniform lined annular/circular ducts are carried out,and some physical mechanisms can be discovered.The numerical results show that periodical impedance distributions along the circumferential direction will lead to discontinuous scattered modes with regular spacing;and mirror-symmetric structure liner will converge the energy of opposite modes.Relying on this mechanism,the potential of acoustic scattering can be further developed by suppressing lower or enhancing higher order modes with expressly designed segmented liner configurations.In particular,the intrinsic mechanism of mode redistribution brought about by the non-uniform liner can be subtly utilized to attenuate broadband noise.The present work indeed shows that circumferentially non-uniform liner is conducive to the reduction of the practical broadband sound source.Furthermore,the effects of nonuniform flow are considered in the model,then distinction of noise attenuation and scattered modes energy in different flows is shown.A possible mechanism is proposed that refraction effects in complex flows lead to the distinction.These works show that the current model has profound potential and availability for the research and designs of circumferentially non-uniform liner.展开更多
为了提高一维海浪谱的风涌浪成分划分精度,本文基于美国国家数据浮标中心(Na-tional Data Buoy Center,NDBC)和海浪波谱仪一维海浪谱数据,提出了一种风涌浪成分划分方法。该方法主要包括两个部分,谱模型参数优化部分和决策函数判别部分...为了提高一维海浪谱的风涌浪成分划分精度,本文基于美国国家数据浮标中心(Na-tional Data Buoy Center,NDBC)和海浪波谱仪一维海浪谱数据,提出了一种风涌浪成分划分方法。该方法主要包括两个部分,谱模型参数优化部分和决策函数判别部分,分别对应海浪谱中海浪成分的划分和风涌浪识别。首先,使用北海联合波浪项目开发的谱模型来拟合一维海浪谱进行海浪成分划分。每个谱模型代表了一个海浪成分,谱模型参数通过双重模拟退火算法进行迭代优化。其次,基于2022年12月4个浮标数据,采用支持向量机建立关于波周期与风速的决策函数来识别每个海浪成分为风浪或涌浪。最后,合并属于同种海浪成分的谱模型,得到一个风浪成分和一个涌浪成分。利用2022年6月另外2个浮标数据对方法进行了检验。结果表明:相较于目前美国国家数据浮标中心采用的修正波陡法,本文方法与二维谱风涌浪分离方法的一致性更好。此外,该方法也可用于海浪波谱仪一维海浪谱数据的风涌浪划分。展开更多
基金supported by the National Natural Science Foundation of China(No.52106038)the Science Center for Gas Turbine Project of China(No.P2022-B-Π-013-001).
文摘In this paper,a model is established with application of the spectral-wave guide method,which has higher accuracy and can serve as a rapid calculation tool for sound transmission calculations.Based on this calculation model,some numerical results of circumferentially non-uniform lined annular/circular ducts are carried out,and some physical mechanisms can be discovered.The numerical results show that periodical impedance distributions along the circumferential direction will lead to discontinuous scattered modes with regular spacing;and mirror-symmetric structure liner will converge the energy of opposite modes.Relying on this mechanism,the potential of acoustic scattering can be further developed by suppressing lower or enhancing higher order modes with expressly designed segmented liner configurations.In particular,the intrinsic mechanism of mode redistribution brought about by the non-uniform liner can be subtly utilized to attenuate broadband noise.The present work indeed shows that circumferentially non-uniform liner is conducive to the reduction of the practical broadband sound source.Furthermore,the effects of nonuniform flow are considered in the model,then distinction of noise attenuation and scattered modes energy in different flows is shown.A possible mechanism is proposed that refraction effects in complex flows lead to the distinction.These works show that the current model has profound potential and availability for the research and designs of circumferentially non-uniform liner.
文摘针对工作在毫米波频段下的去蜂窝大规模多输入多输出(cell-free massive multiple-input multipleoutput,CF-mMIMO)系统中混合预编码设计面临的链路开销大与数值不稳定等问题,提出了一种适配分布式架构的基于列正交约束的正交匹配追踪(orthogonal matching pursuit,OMP)算法。在模拟预编码阶段,采用基于旋转不变性技术的信号参数最小二乘估计(least squares estimation of signal parameters via rotational invariance technique,LS-ESPRIT)算法,基于接收信号直接估计信号到达角,并重构波束码本,有效压缩了反馈开销;在数字预编码阶段,引入列正交约束并推导了最优因子,重构了优化目标函数,规避了病态矩阵求逆问题,提升了预编码矩阵的数值稳定性与匹配精度。仿真结果表明,该算法在不同接入点分布结构与系统参数设置下均能保持稳定且明显的频谱效率性能提升,验证了其在CF-mMIMO系统中的鲁棒性与优越性。
文摘为了提高一维海浪谱的风涌浪成分划分精度,本文基于美国国家数据浮标中心(Na-tional Data Buoy Center,NDBC)和海浪波谱仪一维海浪谱数据,提出了一种风涌浪成分划分方法。该方法主要包括两个部分,谱模型参数优化部分和决策函数判别部分,分别对应海浪谱中海浪成分的划分和风涌浪识别。首先,使用北海联合波浪项目开发的谱模型来拟合一维海浪谱进行海浪成分划分。每个谱模型代表了一个海浪成分,谱模型参数通过双重模拟退火算法进行迭代优化。其次,基于2022年12月4个浮标数据,采用支持向量机建立关于波周期与风速的决策函数来识别每个海浪成分为风浪或涌浪。最后,合并属于同种海浪成分的谱模型,得到一个风浪成分和一个涌浪成分。利用2022年6月另外2个浮标数据对方法进行了检验。结果表明:相较于目前美国国家数据浮标中心采用的修正波陡法,本文方法与二维谱风涌浪分离方法的一致性更好。此外,该方法也可用于海浪波谱仪一维海浪谱数据的风涌浪划分。
