有限元法(finite element method,FEM)具有几何适应性强但随分析频率增加计算时间成本迅速增加的特性,而波函数法(wave based method,WBM)拥有收敛性好但几何适应性差的特性。为减小离散单元带来的误差和提高分析频率,采用基于声压和法...有限元法(finite element method,FEM)具有几何适应性强但随分析频率增加计算时间成本迅速增加的特性,而波函数法(wave based method,WBM)拥有收敛性好但几何适应性差的特性。为减小离散单元带来的误差和提高分析频率,采用基于声压和法向速度连续性条件实现有限元法和波函数法混合建模的混合(finite elementwave based method,FE-WBM)。以车内声腔为例,建立了车内声腔的二维FE-WBM模型,实现了车内声学响应预测。FE-WBM模型与参考有限元模型的声压云图和响应点声压频响曲线对比的结果表明,FE-WBM模型与参考有限元模型的计算结果很好吻合,验证了混合FE-WBM的有效性。分别以模型自由度和CPU运行时间为自变量,以响应点相对误差为因变量,比较两种方法的收敛特性。结果表明,在相同误差水平下,FE-WBM模型在模型自由度和CPU运行时间方面较传统有限元都有明显的优势。展开更多
In this paper,the hydrodynamically generated noise by the flow over an open cavity is studied.First,aeroacoustic theories and computational aeroacoustic(CAA) methodologies are reviewed in light of hydrodynamic acousti...In this paper,the hydrodynamically generated noise by the flow over an open cavity is studied.First,aeroacoustic theories and computational aeroacoustic(CAA) methodologies are reviewed in light of hydrodynamic acoustics,based on which,a hybrid method is presented.In the coupling procedure,the unsteady cavity flow field is computed using large-eddy simulation(LES) ,while the radiated sound is calculated by the Ffowcs Williams-Hawkings(FW-H) acoustic analogy with acoustic source terms extracted from the time-dependent solutions of the unsteady flow.The hybrid LES-FW-H acoustic analogy method is tested with an open cavity flow at Mach number of 0.006 and Reynolds number of 105 .Following the reflection theorem of Powell,the contributions from different source terms are quantified,and the terms involving wall-pressure fluctuations are found to account for most of the radiated intensity.The radiation field is investigated in the frequency domain.For the longitudinal direction,the sound propagates with a dominant radiation downstream the cavity in the near-field and a flatter directivity in the far-field,while for the spanwise direction,the acoustic waves have a similar propagation along+z and-z directions,with no visible directivity.展开更多
Pre-knowledge of machined surface roughness is the key to improve whole machining efficiency and meanwhile reduce the expenditure in machining optical glass components.In order to predict the surface roughness in ultr...Pre-knowledge of machined surface roughness is the key to improve whole machining efficiency and meanwhile reduce the expenditure in machining optical glass components.In order to predict the surface roughness in ultrasonic vibration assisted grinding of brittle materials,the surface morphologies of grinding wheel were obtained firstly in the present work,the grinding wheel model was developed and the abrasive trajectories in ultrasonic vibration assisted grinding were also investigated,the theoretical model for surface roughness was developed based on the above analysis.The prediction model was developed by using Gaussian processing regression(GPR)due to the influence of brittle fracture on machined surface roughness.In order to validate both the proposed theoretical and GPR models,32sets of experiments of ultrasonic vibration assisted grinding of BK7optical glass were carried out.Experimental results show that the average relative errors of the theoretical model and GPR prediction model are13.11%and8.12%,respectively.The GPR prediction results can match well with the experimental results.展开更多
The article presents the results of traffic noise measurement research conducted in Szczecinek Center. The measurements were supported by European initiative called CIVITAS Reanissance. The measurements results were u...The article presents the results of traffic noise measurement research conducted in Szczecinek Center. The measurements were supported by European initiative called CIVITAS Reanissance. The measurements results were used for preparation of documents related to Sustainable Urban Transport Mobility Plan and Noise Action Plan. Traffic congestion is the main source of noise emission in the center Szczecinek. So there was a need to assess the noise emission level. Noise measurements were part of the measure implemented in Szczecinek during the CIVITAS project. It was made during implementation one of the ten measures implemented in Szczecinek. The main objectives of the measure were preparation and acoustic maps of the city center and prognosis the change of traffic noise in the future.展开更多
文摘有限元法(finite element method,FEM)具有几何适应性强但随分析频率增加计算时间成本迅速增加的特性,而波函数法(wave based method,WBM)拥有收敛性好但几何适应性差的特性。为减小离散单元带来的误差和提高分析频率,采用基于声压和法向速度连续性条件实现有限元法和波函数法混合建模的混合(finite elementwave based method,FE-WBM)。以车内声腔为例,建立了车内声腔的二维FE-WBM模型,实现了车内声学响应预测。FE-WBM模型与参考有限元模型的声压云图和响应点声压频响曲线对比的结果表明,FE-WBM模型与参考有限元模型的计算结果很好吻合,验证了混合FE-WBM的有效性。分别以模型自由度和CPU运行时间为自变量,以响应点相对误差为因变量,比较两种方法的收敛特性。结果表明,在相同误差水平下,FE-WBM模型在模型自由度和CPU运行时间方面较传统有限元都有明显的优势。
基金Supported by National High Technology Research and Development Program of China("863"Program,No.2006AA09A312)National NaturalScience Foundation of China(No.50705063)
文摘In this paper,the hydrodynamically generated noise by the flow over an open cavity is studied.First,aeroacoustic theories and computational aeroacoustic(CAA) methodologies are reviewed in light of hydrodynamic acoustics,based on which,a hybrid method is presented.In the coupling procedure,the unsteady cavity flow field is computed using large-eddy simulation(LES) ,while the radiated sound is calculated by the Ffowcs Williams-Hawkings(FW-H) acoustic analogy with acoustic source terms extracted from the time-dependent solutions of the unsteady flow.The hybrid LES-FW-H acoustic analogy method is tested with an open cavity flow at Mach number of 0.006 and Reynolds number of 105 .Following the reflection theorem of Powell,the contributions from different source terms are quantified,and the terms involving wall-pressure fluctuations are found to account for most of the radiated intensity.The radiation field is investigated in the frequency domain.For the longitudinal direction,the sound propagates with a dominant radiation downstream the cavity in the near-field and a flatter directivity in the far-field,while for the spanwise direction,the acoustic waves have a similar propagation along+z and-z directions,with no visible directivity.
基金Project(51375119) supported by the National Natural Science Foundation of China
文摘Pre-knowledge of machined surface roughness is the key to improve whole machining efficiency and meanwhile reduce the expenditure in machining optical glass components.In order to predict the surface roughness in ultrasonic vibration assisted grinding of brittle materials,the surface morphologies of grinding wheel were obtained firstly in the present work,the grinding wheel model was developed and the abrasive trajectories in ultrasonic vibration assisted grinding were also investigated,the theoretical model for surface roughness was developed based on the above analysis.The prediction model was developed by using Gaussian processing regression(GPR)due to the influence of brittle fracture on machined surface roughness.In order to validate both the proposed theoretical and GPR models,32sets of experiments of ultrasonic vibration assisted grinding of BK7optical glass were carried out.Experimental results show that the average relative errors of the theoretical model and GPR prediction model are13.11%and8.12%,respectively.The GPR prediction results can match well with the experimental results.
文摘The article presents the results of traffic noise measurement research conducted in Szczecinek Center. The measurements were supported by European initiative called CIVITAS Reanissance. The measurements results were used for preparation of documents related to Sustainable Urban Transport Mobility Plan and Noise Action Plan. Traffic congestion is the main source of noise emission in the center Szczecinek. So there was a need to assess the noise emission level. Noise measurements were part of the measure implemented in Szczecinek during the CIVITAS project. It was made during implementation one of the ten measures implemented in Szczecinek. The main objectives of the measure were preparation and acoustic maps of the city center and prognosis the change of traffic noise in the future.
