How to leverage CFD

September 2010 » Features » MANUFACTURER'S TURN
Using visualization tools to improve the integrity and safety of structures
Mike Peery

In the post-9/11 world, safety and integrity in structural engineering and design are more paramount than ever before. The use of advanced analysis to solve the kinds of problems we now face in ensuring the safety of buildings, infrastructure, and military installations is imperative. This is especially true in light of the progressive collapse of the World Trade Center and Oklahoma City’s Alfred P. Murrah Federal Building, as well as in the construction of new buildings, bridges, and even maritime design.

To develop the detailed analyses needed to design and build safer structures, engineers at Weidlinger Associates employ an advanced numerical simulation and computational fluid dynamics (CFD) visualization tool, to create state-of-the-art visual simulations. Weidlinger Associates is a structural engineering firm that designs and rehabilitates buildings, bridges, and infrastructure as well as provides special services in applied science, forensics, and physical security. Tecplot 360 is a visual tool that enables their engineers to quickly make sense of vast amounts of complex information.

“Just think of it in terms of post-processing,” says Adam Hapij, senior associate at Weidlinger Associates. “You’ve conducted your analysis, you have a vast amount of data, and now you have to somehow harness it to understand what has actually been computed. Tecplot 360 offers many different ways to look at the data. And because you can see a lot of data at the same time, you can develop the biggest possible picture.”

Weidlinger leverages advanced analysis to solve problems that concern the safety of tall buildings, infrastructure, and military installations. Weidlinger was the chief engineering firm to analyze why the World Trade Center towers collapsed after the 9/11 attacks, and the firm received a National Grand Conceptor Award from the American Council of Engineering Companies for the investigation. The firm also designed a more robust replacement of the Oklahoma City’s Alfred P. Murrah Federal Building, and has engineered numerous other structures, including the new U.S. Embassy in Berlin to shield occupants from terrorist acts. In addition, Weidlinger has many ongoing research grants to study progressive collapse and the effects of explosives and multiple hazards on structures, including warships and submarines.

Visualizing the effects of blasts on structures
Using Tecplot 360 CFD visualization tool, Weidlinger engineers can calculate the scenarios or conditions that would cause a structural element — a column, for example — to fail and collapse. They can then determine how much of the remaining structure would also fail if the column was destroyed, and can systematically remove the key gravity load-carrying elements from the perimeter of the structure and confirm the results. They can also design the remaining structure to redistribute the loads in order to better withstand a catastrophe and help avoid a large-scale collapse.

According to Hapij, Tecplot 360 is ideal for exploring a number of “what-if” scenarios in rapid succession. In terms of underwater structures, Hapij says: “Modeling a significant amount of fluid at a high resolution and being able to see the propagation of the pressure wave in 3D is not a trivial task. Using Tecplot 360, we’ve been able to see both the structural deformations and the colored contours representing different intensities of water pressure.”

Weidlinger’s engineers have integrated Tecplot 360 with the firm’s own simulation software to easily generate detailed 2D and 3D visualizations of structural behavior. “We’ve interfaced with the Tecplot 360 software in a way that we can write out PLT files directly. This allows us to read the data promptly in whatever style we wish,” says Hapij. “We also rely on macros quite a bit to generate animations. We use the animations for a number of purposes, but first and foremost, we use them for presenting information to clients.”

For example, the firm has been able to create 3D progressive collapse visualizations that combine the effects of several types of loads, such as blast, seismic shaking, and crash impact, to determine where a structure may be vulnerable. Taking slices of the data, engineers can see where there are errors in the data, and go back and rework the analysis. Once the data is completely accurate, they can easily and quickly interpret the information to improve design.

With the ability to handle large amounts of data, Tecplot 360 lets Weidlinger’s engineers get a clear picture of how an explosion affects a structure and present this information to clients visually.

“Before, in some cases, we had to actually slice through the data outside of the software and bring it into the application in pieces,” Hapij says. “Now we can do it as a straight shot. The more you see in a single frame, the better overall picture you get.”

The ability to animate large amounts of data also makes it possible for engineers to interpret data quickly. “In days past, if you had a very large representation of a structure, just being able to refresh the data on the screen would be inconceivable,” Hapij says. “Files that couldn’t even load before because they were too big are now easy to view. That saves us a lot of time.”

Finally, Tecplot’s powerful analysis tools and sophisticated visual output make it possible for Weidlinger to obtain highly accurate pictures of its data. “When you have files that involve 100 megabytes of input and gigabytes of output, reviewing them can be a daunting task,” Hapij says. “The visual screening methods offered by Tecplot 360 give us the quality control we need.”

These benefits, in turn, make it possible for Hapij and his colleagues to offer better and faster recommendations to their clients, resulting in more secure structures at lower costs. “The sooner we can obtain some level of confidence, the sooner we can begin development,” says Hapij. “Without this confidence, decisions made in early phases of design may need to be modified later, which increases the cost.”

Designing a safer future
Employing CFD visualization tools enable structural engineers to make sense of a perilous collapse. It helps engineers to predict what may happen and why, enabling them to design more secure structures and protect the people who utilize these structures.

Mike Peery is the president and CEO of Tecplot, Inc. To learn more about Tecplot visit www.tecplot.com

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