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Current Filter: CAD>>>>>Case Study> Putting the roar of the crowd to the test Editorial Type: Case Study Date: 05-2015 Views: 3962 Key Topics: CAD Construction CFD 3D Modelling Building Performance Key Companies: ANSYS ESSS Key Products: ANSYS Multiphysics Key Industries: | |||
| Simulation specialists ESSS have used ANSYS Multiphysics to test wind and other factors on the National Stadium in Brasilia. Paulo de Mattos Pimenta, Professor at the Polytechnic School at University of São Paulo, Brazil, explains Brazilians are noted for their passion for football, so when a national stadium had to undergo a major renovation, it was not only the wind that had to be factored in to the safety analysis but the structure itself, and the activities of the ebullient, cheering crowds. Because time constraints on the project meant that a wind tunnel solution was unrealistic, ANSYS multiphysics tools were used instead, allowing CFD tools for wind testing to be used together with ANSYS Mechanical structural analysis for gravitational testing of the spectators' actions, under the umbrella of Ansys Workbench environment. Estádio Nacional Mané Garrincha, a 70,000-seat football stadium in BrasÃlia, Brazil, was rebuilt in 2013 and hosted seven games of the 2014 FIFA World Cup Brazil, including a quarter-final. Validating the design of a stadium of this size for wind loads normally requires wind tunnel testing, which is time consuming and costly, and runs the risk of scaling errors - a scale model that fits in a wind tunnel does not exhibit the same precise behaviour as an extremely large building. With assistance from the CFD simulation specialists at ESSS, the ANSYS channel partner in Latin America, the engineering consultant for the project used ANSYS multiphysics capabilities to verify the safety of the stadium. The ESSS team used CFD tools to predict airflow around the stadium and pressure on the stadium cover. Then a structural analysis was performed to study the combined effects of wind, stadium infrastructure and the cheering crowd. The study recommended several changes, such as increasing the number of cables and cable tension. This is believed to be the first time that CFD analysis has been used to replace wind tunnel testing in the design of a major stadium in Brazil. The analysis was completed in only two weeks. Simulation reduced costs by one-third and took one-tenth the time of wind tunnel testing.
MAJOR RENOVATION PROJECT The renovation cost approximately $500 million (U.S.). NOVACAP, a Brazilian state company involved in construction in BrasÃlia, contacted ESSS to validate the safety of the stadium design from a wind-loading perspective. Traditionally, this is done by building a scale model and testing it in a wind tunnel while measuring loads on the model. More recently, projects have been completed by using CFD to predict the loads on the structure, then using a wind tunnel to validate CFD simulation. However, stadium CFD simulation has progressed to the point that wind tunnel validation is no longer mandatory, saving substantial time and money. In any case, the validation had to be done in only 15 days, far less time than is required to build a scale model and perform wind tunnel testing.
CFD SIMULATION The model of the stadium used quadrilateral, tetrahedral and pyramidal elements which, together in the completed model, amounted to 20 million computational cells with 120 million degrees of freedom. The team iterated to remove details of the geometry that did not impact the flow, hence speeding up simulation without any loss in accuracy. Wind speeds were taken from the Brazilian building code, which specifies a velocity of 35 meters per second. The team applied wind from two orthogonal directions as a boundary condition at the edge of the solution domain and employed the k-epsilon turbulence model. ANSYS CFD simulation took about four hours to complete on a high performance computing cluster with 12 nodes, 24 processors and 96 gigabytes of RAM.The results of the analysis provided the pressures, both positive and negative, exerted by the wind on the structure's various elements.
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