Ljubodrag Savić

Computation of Thermal-Stresses and Contraction Joint Distance of RCC Dams

A new approach in 3D numerical modeling for unsteady phased thermal-stress analysis of a massive concrete hydraulic structure is presented. The temperature field is computed first, providing a drive for the unsteady, nonlinear, viscoelastic, stress-strain analysis. This model is devised with actual initial and boundary conditions, appropriate material properties, and the observed concrete placement schedule. The verification is based on the field investigations of the Platanovryssi dam. The results of a long-term analysis have shown close agreement with the observed dam conditions. The proposed model presents a reliable tool for thermal-stress computation and transverse contraction joint distance evaluation.

Supercritical flow in circular conduit bends

ABSTRACT A complex flow pattern occurring in a circular conduit bend with supercritical flow has been studied. The main objective was to obtain reliable criteria for prediction of the onset of helical and choking flow, in order to facilitate the design of bottom outlets, tunnel spillways and drainage collectors with bends. A series of scale model experiments provided data for developing empirical relationships describing the effects of the bend curvature, bend deflection angle and approach flow conditions (relative flow depth and Froude number) on the inception of helical and choking flow. Expressions for the energy bend loss coefficient were also proposed. The bend curvature and approach flow conditions proved to have a major influence on the onset of helical flow, while the deflection angle becomes an important parameter for angles less than 45°. Bend curvature and deflection angle have commensurable influence on the onset of choking flow.

Converging stepped spillway flow

ABSTRACT Wall deflection in supercritical flow induces standing waves which significantly influence the flow field close to the wall. This paper analyses the flow in the converging stepped spillway, using two scale-models with different step heights and convergence angles. Results show that the height and the width of the standing wave increase with the increase of the convergence angle. Air concentration decreases while the air–water mixture velocity and residual energy head increase in the vicinity of the converging wall and gradually attain the values for the undisturbed flow outside the standing wave. Compared to the prismatic chutes of equal upstream width, converging spillways are less efficient energy dissipators. Equations for predicting the maximum flow depth and the width-averaged residual energy are proposed.

Numerical modelling of supercritical flow in circular conduit bends using SPH method

The capability of the smoothed-particle hydrodynamics (SPH) method to model supercritical flow in circular pipe bends is considered. The standard SPH method, which makes use of dynamic boundary particles (DBP), is supplemented with the original algorithm for the treatment of open boundaries. The method is assessed through a comparison with measured free-surface profiles in a pipe bend, and already proposed regression curves for estimation of the flow-type in a pipe bend. The sensitivity of the model to different parameters is also evaluated. It is shown that an adequate choice of the artificial viscosity coefficient and the initial particle spacing can lead to correct presentation of the flow-type in a bend. Due to easiness of its implementation, the SPH method can be efficiently used in the design of circular conduits with supercritical flow in a bend, such as tunnel spillways, and bottom outlets of dams, or storm sewers.

Closure to “Supercritical flow in circular conduit bends” by M. KOLAREVIC, L. SAVIC, R. KAPOR and N. MLADENOVIC, J. Hydraulic Res. 53(1), 2015, 93–100

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Wave propagation in fluids: models and numerical techniques, second edition

Prof. Vincent Guinot presents an up-to-date and comprehensive consideration of transient propagation principles and modelling in hydraulics and gas dynamics. The author is well known in the field of hydraulic transient modelling, with wide experience in theoretical and applied research. The second edition of this book is updated and enlarged with four additional chapters on finite elements, source term treatment, sensitivity analysis, and modelling in practice. The book is divided into 11 well-structured and organized chapters: Introduction, Scalar hyperbolic conservation laws in one dimension of space, Hyperbolic systems of conservation laws in one dimension of space, Weak solutions and their properties, The Riemann problem, Multidimensional hyperbolic systems, Finite difference methods for hyperbolic systems, Finite volume methods for hyperbolic systems, Finite element methods for hyperbolic systems, Treatment of source terms, Sensitivity equations for hyperbolic systems, Modeling in practice, and Appendices on Linear algebra, Numerical analysis, Approximate Riemann solvers, and Summary of the formulae. Each chapter begins with the basic assumptions and ends with the derivation of equations in conservative and non-conservative form. Carefully designed examples are given next, leading from the simplest type of equations and/or flows to more and more complex forms. At the end of each chapter is a summary, with carefully designed exercises (particularly in the first six chapters). The detailed exercise solutions, in the form of PDF and Excel files, are accessible on the author’s site. The book offers a perfect balance of physical, mathematical, and numerical materials. The book is intended for postgraduate students, who already have a good knowledge and understanding of fluid mechanics and hydraulics, as well as for model developers and users of mathematical models in the hydraulics and the fluid dynamicsfields. The author’s intention is to introduce a reader to the physics of wave propagation in fluids, the assumptions and governing equations, to explain the general behaviour of the physical systems through simple mathematical techniques, and finally to present the main families of numerical solutions most commonly found in simulation-software packages. This book considers general topics of hyperbolic PDEs in fluid mechanics, and, although it covers a vast range of subjects (contaminant transport, water hammer, river flow, aerodynamics), it cannot be a substitute for the books devoted in detail to a specific field. However, it will be a valuable supplement to such specialized books. The first chapter addresses 1D scalar hyperbolic laws. The conservative, non-conservative, and characteristics form of equations are presented. The phase-space representation, with the domain of dependence and influence, and the boundary and the initial conditions are also introduced. The linear advection equation, Burgers equation, free-surface kinematic wave equation, Buckley–Leverett equation, and advection with adsorption/desorption are all treated as separate examples. The Journal of Hydraulic Research Vol. 49, No. 3 (2011), pp. 420–421 doi:10.1080/00221686.2011.584374