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."
Algor, Inc. provides finite element analysis, Mechanical Event Simulation
for Virtual Prototyping, CAD interfacing and piping analysis products to more
than 16,000 engineers located in over 60 countries. In addition, the Algor
Publishing Division offers books, videos and multimedia products which help
engineers do better design, simulation and analysis with virtually any
engineering software.
For more information, contact Virginia Goebel at Algor, Inc., +1 (412)
967-2700.