Expert testimony involving the science of computational fluid dynamics (CFD) is admissible to prove patent infringement, the U.S. Court of Appeals for the Federal Circuit decided June 1.
The court deep-sixed the defendants' objections to the testimony, finding that its concerns went to the testimony's weight, not its admissibility.
The CFD testimony came in a case involving "slurry tanks" – tanks used to store and process chemicals and organic waste products for later reuse. A maker of one such tank, Liquid Dynamics Corp. (LDC), alleged that rival Vaughan Company Inc. infringed its patented system.
A jury found in LDC's favor and further determined that the infringement was willful. It awarded LDC damages of $1.1 million. Based on the jury's willfulness finding, the district court trebled the award. The court also awarded LDC attorneys' fees of $1.5 million.
Vaughan appealed on several grounds, including the admissibility of computer simulations and expert testimony using CFD.
The patent at issue involved a system of pumps that stir mixtures of solids and liquids in large, million-gallon tanks. Its primary use is in mixing wastewater and manure. The patent involved a storage tank equipped with submerged agitators capable of generating a flow of liquid throughout the tank.
To prove its case, LDC had to show that the flow of liquid in Vaughan's allegedly infringing tanks matched helical and rotational patterns claimed in the patent. Its expert witness, Richard M. Lueptow, a Mechanical Engineering Professor at Northwestern University, presented computer simulations showing these flows.
In its appeal to the Federal Circuit, Vaughan challenged Lueptow's testimony on two grounds, first arguing that the parameters used to run the simulations were inaccurate and then contending that the simulations did not show the required rotations.
The court characterized Vaughan's challenges as being to "the admissibility and reliability of Lueptow's expert scientific analysis and opinion." However, citing Daubert v. Merrell Dow Pharmaceuticals, 509 U.S. 579, 589 (1993), the court said that Vaughan’s argument was actually directed not to the reliability of CFD analysis in general, but to the parameters the expert applied in performing the analysis.
"Indeed," the court noted, "CFD analysis has been previously recognized in the scientific community and has been recognized as reliable by at least one circuit."
This meant, the court continued, that Vaughan’s challenge went to the weight of the evidence rather than to the admissibility of the expert's testimony and analysis under Daubert.
"Though he admitted that his models did not exactly match the various accused tanks, this fact was fully discussed on cross examination," the court said. "[H]is models were not the perfect models of each individual tank, but they were based on reliable scientific methodology and subject to cross examination and the proffering of further scientific analysis by Vaughan."
A reasonable juror could weigh this testimony in LDC's favor, the court concluded. "Therefore, we will not contravene the province of the jury by reweighing Lueptow’s testimony."
As to Vaughan's second challenge – that the simulations did not show the required rotations – the court again found in LDC's favor.
Vaughan argued that the simulations did not incorporate a sufficient number of iterations to replicate the tank's actual operation. But the court said that this argument did not discount the expert's testimony, which he based not only on his own simulations, but also on ones performed by others, including Vaughan.
"[S]ufficient evidence still existed for a reasonable juror to find infringement," the court reasoned.
In light of these determinations, the circuit court affirmed the decision of the district court.
The case is Liquid Dynamics Corp. v. Vaughan Company Inc., Case Numbers 05-1105, 05-1325, 05-1366, 05-1399 (Fed. Cir. June 1, 2006).