Numerical modeling of flow in riverine basins using an improved dynamic roughness coefficient

Various parameters such as bed and bank materials, shape and irregularity of the section, vegetation, river meanders, plan of the river path etc. affect the flow hydraulic resistance. In open channel hydraulics the effects of all these parameters are generally considered as the roughness coefficient. The Manning’s equation is one of the most practical equations to flow resistance analysis, in which the surface roughness is defined by Manning coefficient. Since many parameters are effective on the value of this coefficient, in this research study it was tried to define the roughness coefficient somehow that it be able to dynamically change with different river and hydraulic conditions. The collected data in Karun River (Iran) for two periods were used as the case study. It is shown that the accuracy of model predictions for water surface elevations were improved more than 13% in error estimation in comparison with the corresponding results obtained for a constant roughness coefficient. The roughness coefficient (n) for Karun River was also estimated using the empirical method proposed by Cowan for two different dry and wet periods. These values were then successfully compared with the average corresponding roughness coefficients calculated by the numerical model for those periods.     

Response of a 2-story test-bed structure for the seismic evaluation of nonstructural systems

A full-scale, two-story, two-by-one bay, steel braced-frame was subjected to a number of unidirectional ground motions using three shake tables at the UNR-NEES site. The test-bed frame was designed to study the seismic performance of nonstructural systems including steel-framed gypsum partition walls, suspended ceilings and fire sprinkler systems. The frame can be configured to perform as an elastic or inelastic system to generate large floor accelerations or large inter story drift, respectively. In this study, the dynamic performance of the linear and nonlinear test-beds was comprehensively studied. The seismic performance of nonstructural systems installed in the linear and nonlinear test-beds were assessed during extreme excitations. In addition, the dynamic interactions of the test-bed and installed nonstructural systems are investigated.     

Dynamic response of an eccentrically lined circular tunnel in poroelastic soil under seismic excitation

An exact analysis for two-dimensional dynamic interaction of monochromatic progressive plane compressional and shear seismic waves with a permeable circular tunnel lining of circumferentially varying wall thickness buried in a boundless porous elastic fluid-saturated formation is presented. The novel features of Biot dynamic theory of poroelasticity in conjunction with the translational addition theorems for cylindrical wave functions, along with the appropriate wave field expansions and the pertinent boundary conditions are employed to develop a closed-form solution in form of infinite series. The analytical results are illustrated with numerical examples in which an air-filled and water-saturated permeable tunnel lining of variable wall thickness, embedded within water-saturated surrounding formations of distinct frame properties (soft, stiff, and stiff viscoelastic soil), is insonified by fast compressional or shear waves at selected angles of incidence. The effects of liner eccentricity, interface permeability, formation material type, incident wave frequency, and angle of incidence on the hoop stress amplitude are evaluated and discussed for representative values of the parameters characterizing the system. Limiting cases are considered and good agreements with the solutions available in the literature are obtained.