Download Acceleration Testing Handout

2/10/2015
Understanding Acceleration Testing
NAARSO ‐ NJAA OUTREACH SEMINAR February 2015
Why do we perform accelerometer testing of amusement rides?
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Why do we perform accelerometer testing of amusement rides?
• Design Verification – M
Measuring the motion of an amusement ride allows verification i th
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of the ride design, construction and installation. It allows us to answer the question: Does the ride perform and move as intended?
• Patron Safety – A properly designed, manufactured, installed and maintained ride will not expose Patrons to forces that exceed established limits. Testing allows this to be verified and documented.
• Ride Maintenance
– Regular testing of the motion dynamics produced on an amusement ride allows the changes in the ride dynamics over time to be analyzed, understood and, where necessary, corrected through ride maintenance.
What published consensus standards apply to measuring and analyzing the motion dynamics of amusement rides?
• ASTM International F24 committee manages and publishes a number of consensus standards that relate to the amusement industry. Two of these standards are particularly focused on the testing and analysis of the motion dynamics of amusement rides:
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What published consensus standards apply to measuring and analyzing the motion dynamics of amusement rides?
• ASTM F2291, Standard Practice for Design of Amusement Rides and Devices
– Section 7 of F2291 specifically addresses limits on the acceptable accelerations that a patron may experience on an amusement ride. This is a design
experience on an amusement ride. This is a design standard and applies to all amusement rides and devices that have been commissioned or subject to major modification since publication of the standard in 2003.
What published consensus standards apply to measuring and analyzing the motion dynamics of amusement rides?
• ASTM F2137, Standard practice for Measuring the Dynamic Characteristics of Amusement Rides and Devices
– This entire standard applies to the acquisition of quality, repeatable, documented test data measuring the motion dynamics of amusement rides. Of particular application to this discussion is Section 12, which specifies the Standardized Amusement Ride Characterization or SARC test. The SARC test represents the gold standard of amusement ride dynamics testing. Testing that is carried out in compliance with the specifications of a SARC test will produce high quality, repeatable and well‐documented test data. SARC test results can be reliably used to compare the ride dynamics of one ride with another, the same ride with itself or to compare against accepted limits as may be found in F2291, Section 7.
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What published consensus standards apply to measuring and analyzing the motion dynamics of amusement rides?
• The SARC test represents the gold standard of amusement ride dynamics testing. Testing that is carried out in compliance with the specifications of a SARC test will produce high quality, repeatable and well‐documented test data. SARC p
test results can be reliably used to compare the ride dynamics of one ride with another, the same ride with itself or to compare against accepted limits as may be found in F2291, Section 7.
What are the fundamental principles upon which the dynamic testing of amusement rides is based?
• In order to explore some of the basic principles related to the motion or dynamics it will be helpful to define some terms:
– Dynamics , Displacement, Velocity, Acceleration
g, g Force, Vector, Coordinate System and Accellerometer
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Dynamics
• The branch of mechanics dealing with motion of physical objects and the external forces that influence the motion.
Measurement
• The result of assigning a specific numerical value to a physical phenomenon.
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Displacement
• Length or distance; Examples: feet, miles, meters.
Velocity
• Rate of change of displacement or Displacement/Time; Examples: ft/sec, miles/hour, m/sec.
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Acceleration
• Rate of change of velocity or Velocity/Time; Examples g, ft/sec2, m/sec2.
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• The acceleration resulting from Earth’s unopposed gravitational force on an object.
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g-Force
• The force gravity imposes on any object near the earth. One g‐force equals what an object weights on Earth. If you are experiencing 1g, you are feeling your weight. We feel this downward force all the time when we are at rest on or near the surface of the earth. If you are experiencing 1.25g, you are experiencing a force equal to 1.25 times your body weight This could happen in an elevator as it accelerates
weight. This could happen in an elevator as it accelerates upward to move to a higher floor. If you are experiencing 0g, you are in free fall under the influence of gravity. Neglecting aerodynamic drag, this is what happens when your parachute fails!
Vector
• A physical quantity that possesses characteristics of magnitude and direction, Examples: Displacement, Velocity, Acceleration and Force. It may be helpful to think of a vector as an arrow: it has a head a tail and length The length
has a head, a tail and length. The length represents the magnitude of the vector and the head relative to the tail represents the direction of the vector.
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Coordinate System
• An orthogonal system of three linear axes or directions.
HOLD ON
• WHAT IN THE WORLD IS “ORTHOGONAL”?
– intersecting or lying at right angles
– Mutually prependicular
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Accelerometer
• A device that detects and measures acceleration. Neither an accelerometer nor a patron can distinguish between the acceleration produced by an external force or by gravity.
• The concept of a coordinate system needs further explanation. An orthogonal coordinate system allows space and direction to be defined and quantified. We are familiar with a 2‐ Dimension (2D) coordinate system that may be used to define a planar or X‐Y graph (Figure 1). • We exist in a 3‐Dimensional (3D) universe that can be ( )
represented by a 3D coordinate system such as Length, Width and Height or X, Y and Z (Figure 2). 10
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• As may be seen in Figure 3, any point in space can be uniquely defined as being at some distance from the coordinate system origin in the X, Y and Z directions. If you know the location of the coordinate system origin and you know the unique X, Y and Z coordinates, you absolutely know the location of the point in space. • It is useful to recognize that breaking any vector quantity in 3D space into three component vectors oriented along the coordinate system axes is simply a tool that
coordinate system axes is simply a tool that makes dynamics analysis and physical measurements easier. In the case of a force vector, physical objects in space cannot distinguish between the effects of a single composite force vector or three separate component force vectors that are oriented along the axes of a coordinate system.
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• In order to be useful a coordinate system must be attached to an object or a point in space. The Patron Coordinate System is
Coordinate System is attached to the patron as shown in Figure 3. This means that as the patron’s orientation in 3D space changes though the course of the amusement ride experience, the Patron Coordinate System also changes orientation with respect to the earth and gravity (Figure 4).
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Basic Concepts of Dynamics – Space, Time, Mass and Force
• All quantities related to dynamics can be defined in terms of these four fundaments concepts. We conceive of Space as a 3D structure within which we exist and move Think of the concept of a
within which we exist and move. Think of the concept of a coordinate system. We define and utilize Time to give a chronological order to events and to define the rate at which something occurs. Mass is a characteristic of all physical objects (with the exception of some sub‐atomic particles) and is inherent in our ability to experience gravity and inertia. Forces are what shape and change our existence. It is a force that accelerates us away from a stoplight. Rising from a chair requires force (and it seems the older we get the greater the required force!). Force is what keeps us g
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attached to the amusement ride. Other forces are those that feel like they want to detach us from the amusement ride. Gravity is a force that exists between objects that have mass. On Earth, unopposed gravity will produce a 1g acceleration (free fall).
Newton’s Laws of Motion
1. A body at rest, or moving at constant velocity, remains so unless acted on by an unbalanced external force.
2 Force = Mass * Acceleration 2.
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*THIS IS A BIG DEAL*
3. For every force acting on a body, the body exerts an equal and opposite reaction force.
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All three of Newton’s laws are essential and fundamental to the analysis of dynamic motion. However, it is the second law that underlies the entire concept of accelerometer testing of
underlies the entire concept of accelerometer testing of amusement rides. The second law defines the principle that force is proportional to acceleration and the proportionality constant is equal to mass.
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Velocity, Acceleration and Force ‐
Force is our Primary Focus.
• Velocity is the least interesting to our purposes. • Traveling to this seminar, many of you traveled by airplane. g
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Much of your trip was spent in excess of 500 mph. However, there was very little drama resulting from the high speed. • As they say when a person falls from a great height, it is not the high terminal velocity that produces the problem ‐ it is the high rate of change of velocity at the end of the fall that creates the problem! • Rate of change of velocity is the definition of acceleration. • Strictly speaking, it is not the high deceleration (or negative acceleration) that is the problem; it is the high force that is proportional to the high deceleration.
Velocity, Acceleration and Force ‐
Force is our Primary Focus.
• Force is what directly affects patrons and structures. Force has the capacity to fail a structure (bones,
Force has the capacity to fail a structure (bones, connective tissues, soft tissues, axles, beams, columns, etc.). • Unfortunately, external forces acting on a moving body or structure may be difficult to measure. But acceleration is relatively easy to measure and, again, acceleration is proportional to force.
acceleration is proportional to force. • Measuring acceleration allows the forces associated with ride motion to be quantified and analyzed.
• This is why we perform accelerometer testing.
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Velocity, Acceleration and Force ‐
Force is our Primary Focus.
• The tolerance of a patron to a force depends on the magnitude direction and duration of the
the magnitude, direction and duration of the force and the characteristics of the patron supporting structures such as the seat, headrest and restraints. • An extremely high force that has a similarly extremely short duration may be hardly felt y
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(think of fingernails tapping on a steel anvil) while a force that produces a 15g acceleration for 10 seconds could be fatal.
So how is accelerometer testing accomplished?
• Adhering to the provisions of ASTM F2137 establishes a foundation for generating reliable
establishes a foundation for generating reliable, repeatable and adequately documented test results. • It covers in detail instrumentation performance specifications, test procedures and test documentation. • It applies whenever dynamic measurements are made on an amusement ride or device, not just accelerometer testing.
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So how is accelerometer testing accomplished?
• Section 7 of ASTM F2137 describes and specifies the Standard Amusement Ride
specifies the Standard Amusement Ride Characterization (SARC) test. This test specification:
1. Is specific to characterizing the motion dynamics of a ride or device.
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2. Specifies 3 orthogonal axes of acceleration using a tri‐axial l
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accelerometer.
3. Defines instrumentation axes that conform to the ASTM Patron Coordinate System.
So how is accelerometer testing accomplished?
• Section 7 of ASTM F2137 describes and specifies the Standard Amusement Ride
specifies the Standard Amusement Ride Characterization (SARC) test. This test specification:
4. Places the origin of the Patron Coordinate System at a specified location relative to the seat pan and back.
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5. Defines and specifies many additional technical details of d
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the test procedure, measurement system and test documentation that allow data acquired by different test personnel to be directly compared and uniformly analyzed.
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So how is accelerometer testing accomplished?
• Section 7 of ASTM F2137 describes and specifies the Standard d
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Amusement Ride Characterization (SARC) test. This test specification:
• It is recommend that any person who will be yp
reviewing amusement ride accelerometer test results as part of their employment responsibilities obtain a copy of the ATSM F2291 and F2137 standards.
SARC Test Instrumentation
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What do the accelerometer test results look like and how are they interpreted?
• Traditional Wood Coaster – Out and back, Figure 5.
• Few turns. Generally the turns are low speed
• Prominent hills and valleys
• Most of the forces are in the Z‐axis
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Steel Coaster – Out and back, Figure 6.
Few turns
• Prominent hills and valleys
• Most of the forces are in the Z‐axis
•
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Twister Wood Coaster, Figure 7.
Many turns, some significantly b k d h l
banked, others less so
• Significant forces in both the Z‐axis and Y‐axis
• High and low points in the track g
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elevation rather than simple hills and valleys
•
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Multiple Inversion Steel Coaster, Figure 8.
• Low forces in the Y‐axis. Significantly banked turns
• Generally higher forces in the X‐axis than other coaster styles
• Most of the forces are in the Z‐axis
• High and low points in the track elevation rather than simple hills and
elevation rather than simple hills and valleys
• Few significant pitch‐down events. Little or no airtime
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Steel Coaster Comparison Plots Figure 9.
• Comparison Plots – Allows multiple tests of a ride to be directly compared Note the data
ride to be directly compared. Note the data are plotted versus distance along the track rather than versus time. • Steel Coaster, Figure 9.
• Fatigue cracking required installation of a new section of track tube
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• Track repair poorly executed – then corrected
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Wooden Coaster Comparison Plots Figure 10.
• Comparison Plots – Allows multiple tests of a ride to be directly compared Note the data are
to be directly compared. Note the data are plotted versus distance along the track rather than versus time. • On the wood coaster comparison plots, note the bent numbers plotted along the top of the comparison plots. p
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• Rough track documented in both the Y‐axis and Z‐axis
• Track maintenance work produced significant improvements
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Light Train E‐Stop Braking Action, Figure 11.
• Significant seatback angle effects the determination of the worst‐case deceleration in the end‐of‐ride brakes during an E‐Stop.
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In Conclusion ‐ Key Points
• The motion dynamics of an amusement ride or device are important to us. • They relate directly to external forces acting on the patrons and structures, and forces have the potential to injure patrons and to damage or degrade structures.
In Conclusion ‐ Key Points
• Forces are difficult to measure, accelerations are much easier, and force is proportional to acceleration. • Problem solved! We’ll measure acceleration.
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In Conclusion ‐ Key Points
• Regular testing, documents conformance to published standards and allows amusement rides and devices to be maintained so they function as intended by the y
designer/manufacturer.
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