António Betâmio de Almeida
To introduce the problem and the importance of pressure fluid transient regimes in hydraulic systems engineering.
To present the nature and types of potential problems (accidents and incidents) associated with these transients and the surge protection systems most used in engineering systems.
To show examples of cases (accidents) that have or may occur.
To show examples of surge protection systems in pumping and hydropower systems.
To highlight some future trends to support the systems analysis and to mitigate the risks.
It will be an introductory session based on the personal experience of the speaker and a team from the Universidade de Lisboa and the essential contribution that has been transmitted over time by many colleagues from different parts.
The detailed development of the topics will be the subject of other sessions of the course.
Mohamed S. Ghidaoui
This lecture focuses on the physics rather than the mathematics of waves. The content is built around the following questions: what is a wave and what are the necessary ingredients for a wave? How do these ingredients influence the character, speed and type of a wave? Most fluid books tells you that compressibility is negligible when Mach number is small; so why do we have compressibility (waterhammer) waves although Mach number is about 0.001!? What are the fundamental principles needed to model waves? How do numerical solutions alter the physics of waves? Why are waves time reversible even in the presence of damping and why is this of paramount importance in practice?
The friction in unsteady pipe flow is different from that in steady pipe flow. 1D mathematical model. 2D mathematical model. Numerical methods. Pipe networks. Unsteady friction and viscoelasticity. Unsteady friction and cavitation.
Jim C. P. Liou
Line packing and drafting are significant for long transmission pipelines. The former can result in pressures significantly exceeding the Joukowsky head rise. The latter can lead to column separation. These phenomena are easy to model but difficult to explain. A physical explanation and how to quantify them are given.
Arris S. Tijsseling
Water hammer is such a severe load that pipes may move and vibrate.
Stresses in pipe walls interact with pressures in the liquid.
Dynamic liquid-pipe interaction is explained, modelled and solved.
Water hammer is not only the cause of severe overpressures: much information about possible defects can be extracted from pressure waves propagating along a pipe. This is the principle on which fault detection techniques using transient tests are based. Experimental evidence of such a feature is given with regard to both laboratory and real systems.
Various methods of water hammer control are available to reduce the magnitude of water hammer pressures during valve closure or pump operations and to also prevent column separation. Some of these include air vessels, surge tanks, one-way surge tanks, additional moment of inertia (fly wheels) for pumps and pressure relief valves. Modelling of these as well as examples of usage will be described.
M. H. Chaudhry
Modeling of hydraulic transients in free-surface and pressurized flows will be discussed along with transition from free-surface to pressurized flows. Applications to a number of real-life projects will be presented for illustration purposes.
Free surface flow is frequently modelled with the help of the shallow water approximation. In realistic conditions, topography and friction are two relevant factors that participate as source terms in the hyperbolic system of equations. Finite volume methods able to deal with them enabling stable and robust numerical schemes will be explained. Examples will be presented and solved.
Sandra Soares Frazao
Classical measurement devices are often intrusive, this is a problem particularly for fast transient flows. When sediment transport is involved, this is even worse, as the measurement device can disturb the flow. Image-based techniques for water level, water velocity and sediment bed level measurements will be presented and discussed.
Rapid filling processes in nearly horizontal conduits and the need for ventilation
Transient processes associated with trapped air and modeling issues
What we have learned about geyser formation at vertical shafts in sewer systems
Water hammer itself is often problematic in pressurized flow systems, but the combined presence of water and air, or water in both liquid and vaporous states, under transient states often gives rise to particularly difficult design and analysis challenges.
Some of the key challenges of system design and representation are summarized with particular attention to line filling and draining, and to the presence of residual air pockets, as well as to system response under transient conditions. Although specialized devices and analysis tools are available, the strengths and weaknesses of such tools must be clearly understood by the system designer.
All design challenges in engineering require that the behaviour of matter and energy be taken seriously, but this behaviour is much more difficult to predict or anticipate when a system’s response is non-linear, non-monotonic or unstable. Such complications are often present case when 2-phase mixtures are encountered in pressurized water systems, a reality that requires careful design, operation, maintenance and caution.
Column separation usually occurs as a result of low pressures during water hammer events in pipelines.
The pipeline is exposed to vacuum and large over-pressures.
Discrete cavity model with consideration of unsteady skin friction is presented, verified and validated.
« Go back to the IAHR Online Short Course on Transient Flows for more details