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Fourier time spectral method for subsonic and transonic flows
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作者 Lei Zhan Feng Liu Dimitri Papamoschou 《Acta Mechanica Sinica》 SCIE EI CAS CSCD 2016年第3期380-396,共17页
The time accuracy of the exponentially accurate Fourier time spectral method(TSM) is examined and compared with a conventional 2nd-order backward difference formula(BDF) method for periodic unsteady flows. In part... The time accuracy of the exponentially accurate Fourier time spectral method(TSM) is examined and compared with a conventional 2nd-order backward difference formula(BDF) method for periodic unsteady flows. In particular, detailed error analysis based on numerical computations is performed on the accuracy of resolving the local pressure coefficient and global integrated force coefficients for smooth subsonic and non-smooth transonic flows with moving shock waves on a pitching airfoil. For smooth subsonic flows, the Fourier TSM method offers a significant accuracy advantage over the BDF method for the prediction of both the local pressure coefficient and integrated force coefficients. For transonic flows where the motion of the discontinuous shock wave contributes significant higherorder harmonic contents to the local pressure fluctuations,a sufficient number of modes must be included before the Fourier TSM provides an advantage over the BDF method.The Fourier TSM, however, still offers better accuracy than the BDF method for integrated force coefficients even for transonic flows. A problem of non-symmetric solutions for symmetric periodic flows due to the use of odd numbers of intervals is uncovered and analyzed. A frequency-searching method is proposed for problems where the frequency is not known a priori. The method is tested on the vortex shedding problem of the flow over a circular cylinder. 展开更多
关键词 Fourier time spectral method(TSM) Pitching airfoil Transonic flow Non-symmetric solution Computational efficiency Vortex shedding flow frequency search
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INVESTIGATION OF DOMINANT FREQUENCIES IN TRANSITION REYNOLDS NUMBER RANGE OF FLOW AROUND A CIRCULAR CYLINDER PARTⅡ: THEORETICAL DETERMINATION OF THE RELATIONSHIP BETWEEN VORTEX SHEDDING AND TRANSITION FREQUENCIES AT DIFFERENT REYNOLDS NUMBERS 被引量:1
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作者 AHMED N A 《Chinese Journal of Mechanical Engineering》 SCIE EI CAS CSCD 2006年第3期317-321,共5页
An attempt has been made to explore whether the power relation can be obtained from theoretical considerations. The classical laminar and turbulent boundary layer concepts have been employed to determine appropriate v... An attempt has been made to explore whether the power relation can be obtained from theoretical considerations. The classical laminar and turbulent boundary layer concepts have been employed to determine appropriate values of the scaling lengths associated with vortex shedding and shear layer frequencies to predict the power law relationship with Reynolds number. The predicted results are in good agreement with experimental results. The findings will provide a greater insight into the overall phenomenon involved. 展开更多
关键词 Vortex shedding Transition Separated flow Shear layer frequency Power spectral density
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Hydrological simulation approaches for BMPs and LID practices in highly urbanized area and development of hydrological performance indicator system 被引量:1
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作者 Yan-wei SUN Qing-yun LI +2 位作者 Lei LIU Cun-dong XU Zhong-pei LIU 《Water Science and Engineering》 EI CAS CSCD 2014年第2期143-154,共12页
Urbanization causes hydrological change and increases stormwater runoff volumes, leading to flooding, erosion, and the degradation of instream ecosystem health. Best management practices (BMPs), like detention ponds... Urbanization causes hydrological change and increases stormwater runoff volumes, leading to flooding, erosion, and the degradation of instream ecosystem health. Best management practices (BMPs), like detention ponds and infiltration trenches, have been widely used to control flood runoff events for the past decade. However, low impact development (LID) options have been proposed as an alternative approach to better mimic the natural flow regime by using decentralized designs to control stormwater runoff at the source, rather than at a centralized location in the watershed. For highly urbanized areas, LID stormwater management practices such as bioretention cells and porous pavements can be used to retrofit existing infrastructure and reduce runoff volumes and peak flows. This paper describes a modeling approach to incorporate these LID practices and the two BMPs of detention ponds and infiltration trenches in an existing hydrological model to estimate the impacts of BMPs and LID practices on the surface runoff. The modeling approach has been used in a parking lot located in Lenexa, Kansas, USA, to predict hydrological performance of BMPs and LID practices. A performance indicator system including the flow duration curve, peak flow frequency exceedance curve, and runoff coefficient have been developed in an attempt to represent impacts of BMPs and LID practices on the entire spectrum of the runoff regime. Results demonstrate that use of these BMPs and LID practices leads to significant stormwater control for small rainfall events and less control for flood events. 展开更多
关键词 hydrological simulation approach best management practices low impactdevelopment flow duration curve peak flow frequency exceedance curve runoff coefficient
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Vibrational frequency analysis of finite elastic tube filled with compressible viscous fluid 被引量:2
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作者 Ilyess Mnassri Adil El Baroudi 《Acta Mechanica Solida Sinica》 SCIE EI CSCD 2017年第4期435-444,共10页
The vibrational frequency analysis of finite elastic tube filled with compressible viscous fluid has received plenty of attention in recent years. To apply frequency analysis to defect detection for example, it is nec... The vibrational frequency analysis of finite elastic tube filled with compressible viscous fluid has received plenty of attention in recent years. To apply frequency analysis to defect detection for example, it is necessary to investigate the vibrational behavior under appropriate boundary conditions. In this paper, we present a detailed theoretical study of the three dimensional modal analysis of compressible fluid within an elastic cylinder. The dispersion equations of flexura], torsional and longitudinal modes are derived by elastodynamic theory and the unsteady Stokes equation. The symbolic software Mathematica is used in order to find the coupled vibration frequencies. The dispersion equation is deduced and analytically solved. The finite element results are compared with the present method for validation and an acceptable match between them are obtained. 展开更多
关键词 frequency analysis Compressible Stokes flow Coupled vibration Elastodynamic
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