An analysis was performed of the turbulent data obtained from Yucheng experimental station in the Shandong Province in 1984. [t is shown that at variant wind speed, the spectra of streamwise velocity remain similar an...An analysis was performed of the turbulent data obtained from Yucheng experimental station in the Shandong Province in 1984. [t is shown that at variant wind speed, the spectra of streamwise velocity remain similar and the intensity of wind fluctuations is proportional to wind speed in the downwind area of shelter belt. Therefore, we may decide the similarity of wind fluctuations by a speed scale and a length scale which is not correlated with stability, σu /V0 = F(X / H). The -5/3 power range of temperature spectra extends to lower frequency. The variation of ratio σ0 /T. with stability becomes σ0 / T . = C(X / H)( - Z / L)-1/3 . There is not such an extension of -5 / 3 power range in the humidity spectra.展开更多
In this paper,we investigate the stability for a finite harmonic lattice under a certain class of boundary conditions.A rigorous eigenvalue study clarifies that the invalidity of Fourier modes as the basis results in ...In this paper,we investigate the stability for a finite harmonic lattice under a certain class of boundary conditions.A rigorous eigenvalue study clarifies that the invalidity of Fourier modes as the basis results in the deficiency of standard reflection coefficient approach for stability analysis.In a certain parameter range,unstable surface modes exist in the form of exponential decay in space,and exponential growth in time.An approximate eigen-polynomial is proposed to ease the stability analysis.Moreover,the eigenvalues with small positive real part quantitatively explain the long time instability in wave propagation computations.Numerical results verify the analysis.展开更多
文摘An analysis was performed of the turbulent data obtained from Yucheng experimental station in the Shandong Province in 1984. [t is shown that at variant wind speed, the spectra of streamwise velocity remain similar and the intensity of wind fluctuations is proportional to wind speed in the downwind area of shelter belt. Therefore, we may decide the similarity of wind fluctuations by a speed scale and a length scale which is not correlated with stability, σu /V0 = F(X / H). The -5/3 power range of temperature spectra extends to lower frequency. The variation of ratio σ0 /T. with stability becomes σ0 / T . = C(X / H)( - Z / L)-1/3 . There is not such an extension of -5 / 3 power range in the humidity spectra.
基金supported in part by NSFC under contract number 10872004National Basic Research Program of China under contract number 2007CB814800the China Ministry of Education under contract numbers NCET-06-0011 and 200800010013.
文摘In this paper,we investigate the stability for a finite harmonic lattice under a certain class of boundary conditions.A rigorous eigenvalue study clarifies that the invalidity of Fourier modes as the basis results in the deficiency of standard reflection coefficient approach for stability analysis.In a certain parameter range,unstable surface modes exist in the form of exponential decay in space,and exponential growth in time.An approximate eigen-polynomial is proposed to ease the stability analysis.Moreover,the eigenvalues with small positive real part quantitatively explain the long time instability in wave propagation computations.Numerical results verify the analysis.
