ON YOUR MARK…GET SET…DRAG!
An engineering consultant ensures safety
of an amusement park ride with Algor FEA.
Located in amusement parks around the United States and in
Japan, the Top Eliminator (TM) amusement ride was created by ThrillTime
Entertainment International, Inc., of Burnaby, British Columbia,
Canada, with help from engineering consultant Les Okreglak of
Pol-X West, Inc., Carson City, Nevada. Mr. Okreglak used FEA software
from Algor, Inc., Pittsburgh, Pennsylvania, to analyze the frame
of the dragster car. Photo courtesy of ThrillTime
Entertainment International, Inc.
September, 4 1998, Pittsburgh, Pennsylvania - It
has a 350 cubic-inch engine with a four-barrel carburetor and
a horsepower rating of 300 bhp @ 5000 rpm, rear disc brakes, a
tube steel space frame, drag slick rear tires and seating capacity
for one. No, it's not one of those new, compact high-performance
sports cars -- it's a dragster, which anyone over 56 inches tall
can drive at amusement parks around the United States and in Japan.
The Top Eliminator (TM) is a dragster racing simulation ride created
and produced by ThrillTime Entertainment International, Inc.,
Burnaby, British Columbia, Canada. It gives thrill-seeking drivers
of all ages a license to "floor it" and experience the adrenaline
rush of drag racing without the danger associated with actual
auto racing.
To ensure the safety of the ride, ThrillTime hired Les Okreglak,
P.E., principal engineer and president of Pol-X West, Inc., an
engineering consulting firm in Carson City, Nevada, to analyze
the dragster frame using FEA software. Mr. Okreglak chose the
linear static stress analysis capabilities of engineering software
from Pittsburgh-based Algor, Inc.
Get Your Motor Running
Up to 10 dragsters are positioned on 200-ft. long parallel tracks.
Each dragster has a 12-foot long guide blade bolted to the frame
that sets in an underground channel system to keep the dragster
from leaving its lane. As green lights indicate the start of the
race, participants step on the gas pedal and feel the power of 1.1
g's of force as they accelerate from 0 to 75 mph in a few seconds.
At the finish line, a computer-controlled braking system causes
roller coaster brakes to clamp onto the underground guide blade
and stop the car in less than 120 feet. Riders experience a decelerating
force of -2.8 g's at normal operation.
Before green lights ever flashed "Go!" at a Top Eliminator track,
Mr. Okreglak modeled and analyzed the dragster frame, which supports
a large Chevy engine, guide blade, fiberglass body and roll cage.
"The goal of the analysis was to verify that the existing frame
design would be able to withstand stresses resulting from the acceleration
and deceleration of the dragster," said Mr. Okreglak. He closely
monitored stresses at the engine mounts in the rear of the car,
as well as overall displacement.
Mr. Okreglak used AutoCAD to create a 3-D wireframe of the existing
design and transferred the data in an IGES format to Superdraw III,
Algor's precision finite element model-building tool. The model
was comprised of 340 beam elements, which represented the 1.5-in.
diameter round steel tubing used in the frame. According to Mr.
Okreglak, he increased the number of elements and nodes from the
original model to enable more detailed analysis information.
Mr. Okreglak used several different models to address the acceleration
and deceleration concerns. Using Algor's Beam Design Editor, he
applied acceleration loading to seven points in the model: at each
of the wheel connections and at engine mounts in the center of the
frame. To account for the deceleration loading, Mr. Okreglak applied
a boundary condition at the point where the roller coaster brakes
would clamp onto the guide blade during braking.
Next, a series of linear static stress analyses was performed to
determine the maximum stresses resulting from acceleration and emergency
deceleration. Based on the von Mises and displacement results, Mr.
Okreglak determined that stresses resulting at the engine mounts
exceeded the allowable limit. To correct this problem, he increased
stiffness by adding an additional support member to the frame.
Additional members were added to reinforce the tube steel
space frame (optimized design shown left) based on displacement
(shown right) and stress results. Models courtesy
of Les Okreglak, Pol-X West, Inc. Photo courtesy of ThrillTime
Entertainment International, Inc.
Further, Mr. Okreglak found displacements of the frame to be
minor. Nonetheless, he still added small members throughout the
frame to reinforce it. Once the design was optimized, a prototype
was built to test the dragster's reliability.
Taking a Test Drive
Acceleration and emergency braking tests were performed on the dragster
prototype using Keithley data acquisition software and an accelerometer.
The accelerometer was fixed to the car, which was driven by a computer.
According to Mr. Okreglak, the accelerometer tests yielded a maximum
deceleration force of 5.0 g's as compared to analysis results of
4.85 g's. The stresses calculated by the Algor software were verified
by strain gauging.
"By using Algor FEA, we optimized the design before producing prototypes
of the dragster," Mr. Okreglak said. "Ultimately, we built fewer
prototypes and needed fewer test runs to ensure the safety of the
design."
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