Probability Density Function Of Intensity Research Articles

Urban storm water management: Distribution of flood volumes

The frequency distribution of the volume of water above a given threshold discharge is developed. This is done using basic and accessible information like the joint probability density function of rainfall intensity and duration together with expressions, to be derived, relating the volume of interest to rainfall intensity and duration. The resulting distribution function is in a closed analytical form containing only a few climatological and physical parameters of a catchment. This distribution function will be of great value in the design of storage devices, flood control systems, and storm water treatment facilities in urban areas.

Reduction of speckle by a moving aperture - first order statistics

In two previous papers the second-order statistics of time-averaged speckle were investigated for speckle patterns formed through moving apertures, in one case for speckle patterns produced in the far-field and in the other case for speckle patterns produced in an image plane. In the present paper attention is devoted to the first-order statistics, with two forms of solution being obtained for the probability density function of intensity, one an exact solution and the other an approximate solution. Both forms of solution are shown to apply equally to either the far-field scheme or the image-plane scheme. With the image-plane scheme it is found that, just as for the second-order statistics, the result is not influenced either by the aberrations of the lens or by the object having non-uniform brightness, subject to the previously obtained condition that the brightness fluctuations are slow in comparison to the size of the point spread function of the lens. As in the two previous papers, the theory only applies when there is a large number of independent scattering points contributing to any given point in the speckle pattern.

Calculations of the effect of tangential eddy diffusivity on a non-symmetric turbulent diffusion in a plain tube

The dispersion of a passive scalar downstream of a wall-mounted cube is examined using direct numerical simulations and turbulence models applied to the Reynolds equations. The scalar is released from a circular source located on top of the obstacle, which is immersed in a developing boundary-layer flow. Direct simulations are performed to give insight into the mixing process and to provide a reference database for turbulence closures. Algebraic flux models are evaluated against the standard eddy-diffusivity representation. Coherent structures periodically released from the cube top are responsible for a counter-diffusion mechanism appearing in the streamwise scalar flux. Alternating vortex pairs form from the lateral edges of the cube, but the intensity profiles and probability density functions of scalar fluctuations suggest that they do not cause a significant flapping movement of the scalar plume. The gradient-transport scheme is consistent with the vertical and spanwise scalar flux components. From the comparative study with our direct simulations, we further stress that Reynolds stress predictions must be carefully evaluated along with scalar flux closures in order to establish the reliability of Reynolds-averaged computations. However, the analysis also shows that algebraic closures provide a significant improvement which cannot be achieved with the standard eddy-diffusivity model.