National honour for American Hydro President19 June 2009
Selim Chacour has been elected into the US National Academy of Engineering. To celebrate this honour, IWP&DC looks back at the career of one of the US’ most successful designers of hydraulic turbines
The president and founder of the american-hydro Corporation, Selim A Chacour, has been elected to the prestigious US National Academy of Engineering (NAE). The honour recognises a lifetime of engineering achievements involving creative mechanical and hydraulic design, the development of advanced computational codes and the successful leadership of two US organisations involved in the design and manufacture of hydraulic machinery.
The National Academy of Engineering is an independent, non-profit institution. Its members consist of the US’ premier engineers who are elected by peers for seminal contributions to engineering. NAE was established in 1964 and election is considered among the highest professional distinctions accorded to an engineer. Academy membership honours those who have made outstanding contributions to:
• Engineering research, practice or education including, where appropriate, significant contributions to the engineering literature.
• Pioneering of new developing fields of technology.
• Making major advancements in traditional fields of engineering.
• Developing/implementing innovative approaches to engineering education.
Selim A Chacour was elected to the academy on 6 February 2009 for pioneering three-dimensional finite element computations in mechanical and hydraulic design, leadership in hydro turbine research and development, and business stewardship.
Chacour considers himself first and foremost a designer of hydraulic turbines. Working as a young engineer for Allis-Chalmers his natural abilities for artistic structural design and standard mechanical analysis served not only to create sound designs but also to highlight the need to accurately calculate the stresses in these massive machines. His professional life from then on was dominated by a unique ability to understand an engineering need and to develop advanced computational tools necessary to provide the engineering analysis.
In the late 1960s Chacour became aware of a new technique to predict structural behaviour. Rather than looking at an entire component, that component was subdivided and deflections were calculated for each finite element. He recognised the power of this new approach, studied it, and by 1970 had personally developed a complete three-dimensional finite element code (Danuta). This static and dynamic structural analysis was so powerful that it is not only used today in the hydro turbine industry, but was licensed by Allis-Chalmers in the 1970s to McDonnell-Douglas for aircraft analysis and to the Canadian nuclear power industry for analysis of nuclear power plant components. The cubic sub-parametric element developed by Chacour is so powerful that comparisons with commercial codes today show that his finite element grid can have fewer elements and yet provide more accurate results.
Chacour now had the tool he needed and throughout the 1970s he pioneered the use of the finite element method to design and analyse hydro turbines. His design interest centred on the sophisticated pump-turbine. One pump-turbine can provide up to 500MW of power with heads over 366m. Chacour developed numerous unique concepts to optimise the structural design of such important pump-turbines at projects including Rio Grande, Bath County, Raccoon Mountain and Bad Creek, as well as the 700MW Grand Coulee Francis turbines. His designs were not only structurally sound but also advanced the techniques the industry used to design more functional units.
The finite element code provided a means to understand deflections and how the unit would behave under load. Chacour led the industry by designing turbine components such that they would provide optimum performance in their deformed state. As an example, his design for spherical inlet valves for high head pump-turbines is based on the deformed shape of the rotor. The stationary seat ring is machined to cancel the rotor’s deflected shape thus presenting a flat surface to the mating seal ring. In older designs much of the closing energy actually went into bending the seal ring against the deformed rotor seat. The new design reduced the closing effort required to achieve complete seal contact.
With component mechanical design well in-hand, Chacour turned his attention to the turbine/generator interaction. Powerful Francis and pump-turbines sometimes had surprising instabilities in their bearing systems. These instabilities could not be predicted with the bearing analysis available at that time. To supplement linear static and dynamic analysis in his Nathalie programme, he developed a new computer code for non-linear shafting system analysis. The Anne programme utilised a unique finite difference solution to shafting system dynamics. This was used by Chacour to analyse complete shafting systems including the non-linear bearing support in the design of new installations and to solve existing vibration problems in units such as Helms and Raccoon Mountain.
Another operational challenge which accompanied ‘pushed’ pump turbine technologies involved fluid inertia in penstock systems and its effect on turbo machinery and powerhouse structures. Chacour studied state-of-the art techniques for evaluating water hammer pressure associated with time dependent flow through a network of penstock conduit. Using the powerful method of characteristics, he developed his general purpose hydraulic transient programme, CORA.
This tool accurately models the reservoir-to-reservoir flow in and out of the interconnecting water passage segments, valves, surge tanks, pumps and turbines. He further customised the analyses to predict the associated transient reservoir elevations, distributed flow, surge tank capacity, pressure and speed rise, hydraulic thrust, wicket gate and valve torques and their associated fatigue damage. The static and dynamic response of any or all of these parameters can be evaluated at any point within the modelled segments. This computer programme is used to avoid fluid resonant vibration and identify unstable operating regimes at design stage. It has also been used to diagnose cause and prove solutions for instabilities encountered at several high head generating and pumping stations.
In the late 1970s, Chacour recognised that the same solution technique he developed for mechanical design was applicable to optimise hydraulic designs especially for the critical runner blade shapes. He developed the three-dimensional finite element flow analysis code Anthony, helping to revolutionise the way runners were designed throughout the hydro turbine industry.
Chacour realised that the finite element flow analysis would only be useful as a design tool if the programme input was automatic. He accomplished this by writing the Lilly programme that is an interactive design programme to develop runner geometry. Combining the Lilly and Anthony codes, Chacour now had a system that allowed a runner designer to optimise the blade shapes with immediate feedback on how the runner performed.
Chacour has developed hundreds of runner designs using this approach. Notable examples are the Bad Creek, Yards Creek, and Taum Sauk pump-turbines and the Aswan High Dam in Egypt, Hoover Dam and Smith Mountain Francis turbines.
This computerised design and analysis not only led to much higher performance designs but Chacour directed Allis-Chalmers into a whole new concept for the hydraulic industry. Before 1980, any new runner was refined using physical model testing. This was a tedious, expensive and crude means to develop high performance runners.
In 1981 Chacour directed that each new runner would be fully optimised through computer design. The accuracy of the computer tools was such that Allis-Chalmers would guarantee performance for a fully optimised runner that had never been model tested. This concept was particularly important for the upgrade of existing hydro plants. It has resulted in much higher performance from the country’s hydro stations.
In 1986 the hydro turbine division of Allis-Chalmers was sold to the German firm, Voith. Chacour believed this would have marked the end of any significant hydro turbine design and manufacturing in the US, and, as a result he founded American Hydro Corporation.
At his new firm, Chacour developed five axis milling codes to machine blade shapes. He developed plate cutting and nesting codes to minimise plate usage and run flame and plasma cutters. He integrated manufacturing techniques with the hydraulic designs to provide optimum hydraulic performance at minimum cost.
As a result of Chacour’s leadership, business sense, and technology, American Hydro has grown to be one of the leading firms in hydro turbine upgrades throughout North America. All manufacturing of the turbine components (with some weighing well over 100 tons) is done in York, Pennsylvania. Using Chacour’s integrated design and manufacturing system, the American Hydro Runner Design System (AHRDS), it is possible to take a new order, completely design a new runner, and begin cutting the blades all in the same day. Throughout the hydroelectric industry, deliveries are months instead of years, power increases for turbine upgrades are 20-50% instead of 10%, and turbine price increases over the last 22 years have not kept pace with the cost of living. The result is significantly more energy from existing hydro facilities nationwide, with minimal ecological impact, and reduced energy costs.
Further details on American Hydro Corporation can be found at www.ahydro.com