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ï RACE CAR PISTONS
Everybody
in NASCAR is looking for the edge (within the rules, of course). Lightweight
yet stiff engine components are a good approach, but must operate
in very harsh environments of forces and temperatures. Convergence
helps one custom component maker by optimally designing parts using
a system approach, where interactions of piston, wrist pin, and rod
are all considered. Finite element tools are used to simulate
multiple designs via automated modeling macros, enabling quick iterations.
The piston design used a novel web stiffener approach to maximize
stiffness per unit weight.
(Graphic: Finite element model of NASCAR piston, pin, and rod end.)
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RACE CAR PISTONS ð
Optimal design requires good loads and material strength information. In the case of a piston, the greatest uncertainty
concerns thermal gradients that may overstress the part. Convergence
performed thermal analysis to estimate temperatures, and followed
up with both thermal and pressure/inertia induced stress analysis
to ensure fatigue reliability of the hot aluminum part. At the same time, the stiffness was kept high to avoid piston
flex that can degrade ring sealing and cause power loss. Early analysis
corroborated actual prototype piston cracking in tests.
(Graphic: Finite element steady state temperature of a NASCAR piston.)
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RACE CAR WRIST PINS ð
The
dimensions of the NASCAR wrist pin are especially important for
good weight efficiency. Made of steel, its weight can be substantial,
and how it bends in response to loads through the piston has a lot
to do with how the piston deflects. Convergence built automated FEA modeling
and analysis routines to provide a quick custom pin design with
piston flex effects. Optimization capabilities of ANSYS were also
used to minimize weight as a function of application.
Similar analysis was done on drag racing engine piston pins.
(Graphic: Von Mises stresses in a NASCAR piston pin
at instant of maximum piston force (just after top dead center of
combustion).)
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ï DRAG RACER FRAME
NHRA
Top Fuel dragsters are incredible power-producing machines, but
they also must get their power to the ground.
The long frame and bulbous tires serve as suspension components
for this purpose, but it has mostly been a “black art”
to determine how best to design the frame to minimize tire traction
variations. Convergence is working with the BME Top Fuel team to
engineer the frame for best designs to smooth tire hook-up and minimize
bounce as the tires grow at the green light power-on and over bumps.
(Graphic: Exaggerated flex of a Top Fuel dragster frame under maximum
rear wheel torque. Note
unusual “S” shape due to truss design of front end frame,
unlike a simple beam.)
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SEPARATOR CENTRIFUGE
ð
Large
centrifugal separators are popular in the oil refining and chemical
process industries, where heavy and light fluids and/or solids must
be separated continuously. Such
separation is a major throughput bottleneck in many cases, so separator
makers are looking for ways to increase machine sizes and speeds. Convergence helps one producer design new machines and check older
designs with consideration of complex fluid flow dynamics, rotordynamics,
critical speeds, and vibration control. Details of internal stresses
are important to check for long maintenance-free fatigue life.
(Graphic: Stresses in the shell of a spinning separator rotor under
process solids unbalance load at one end, shown as red arrows.)
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| SEPARATOR CENTRIFUGE ð
The
work by Convergence includes careful consideration of flexible housing
and unit mounting structural dynamics, including rolling element
bearing simulation. Dynamics
and critical speeds of large rotors are substantially influenced
by housing and floor mount structural design.
Often, maximum vibrations of the unit are due to mount resonances
as opposed to rotor flex or bearing deflections. In some cases,
hard or soft snubbers or stiffener links must be used to alter the
dynamic behavior.
(Graphic: Exaggerated lateral motion vibration response
of a separator rotor due to floor mount system flexibility.)
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ï EARTHQUAKE RETROFIT
Earthquake retrofit systems are being developed
to improve survivability of older construction buildings and to
enhance new ones. One particular problem is weakening of structures
by garage doors, especially in bottom floors of multi-story buildings.
Convergence provides mechanical design and analysis expertise to
a new company for design of systems to stiffen and provide energy
dissipation as part of garage door systems. Analysis includes earthquake
simulation of elastic-plastic response of hybrid steel and wood
framed systems.
(Graphic: Elastic/plastic stresses in an anchor part of a garage door
earthquake retension system.)
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EARTHQUAKE RETROFIT
ð
Improving wood framed building survivability includes
predicting its stresses and strains, with and without retrofit systems
installed. Convergence optimized the retrofit system’s elastic
vs. plastic behavior to maximize earthquake deflection reduction with
maximum design simplicity. Systems
were devised that would provide the equivalent stiffness of a full
wall, but automatically disengage and move with the garage door when
it is opened.
(Graphic: Elastic/plastic stresses in a typical wood framed 3 story
wall with a garage door opening under earthquake shear.)
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ELASTOMER TRACTION DRIVE ð
Convergence provided extensive engineering analysis,
prototype development, and testing support to a new company developing
a special purpose traction drive.
The drive used elastomer wheels in a continuously variable
transmission for a new application. Convergence performed complex
kinematic and dynamic analysis to design the system, including nonlinear
elastomer behavior. Extensive laboratory testing of elastomer
traction capacity and durability was done by CEC.
(Graphic: Nonlinear stresses in incompressible elastomer
coated wheel while rolling on a flat surface.)
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ï NETWORK BATTERY
STANDS
Earthquake survival is important for battery stands
used in World Wide Web backup power systems. Convergence performed iterative FE structural design and analysis
of these stands and their floor tiedown systems to survive major earthquakes
with large battery loads up to 3000 lb. These stands were made of
reinforced sheet molding compound (SMC), an inexpensive form of polymer
matrix and fiber composite.
(Graphic: View showing the great detail used in a battery stand FE model,
including inclined surfaces for battery acid drainage.)
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NETWORK BATTERY STANDS ð
The desire to use tall and narrow stand configurations
of battery stands made earthquake survival a big challenge. Tiedown
systems that would accommodate stand legs leaving the floor under
large overturning forces were required. The design of such systems
required complex nonlinear transient and piecewise linear modal analysis
methods. Convergence is also performing seismic qualification
testing of all required battery options.
(Graphic: Exaggerated earthquake deformation with stress contour colors,
response of a tall and narrow configuration (batteries not shown).)
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COOLING FLOW TESTER ð
Convergence is involved in numerous research projects
in liquid fuel rocket propulsion. Convergence provides steady state
and transient thermal heat transfer and structural stress analysis
of flow test channels, including electric resistance heaters. Structures must withstand simultaneous thermal
and pressure loads with low complexity designs to minimize test costs.
Heat transfer requirements are high, intended to simulate rocket chambers,
so designs involve controlled material plasticity. Instrument ports
are also a challenge.
(Graphic: Steady state temperatures in a flow test channel assembly.)
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ï ROCKET CHAMBER
Convergence also performs simulations of test chamber
firings, both steady state and transient heat transfer. In this case,
the chamber is a heat sink design, where the firing duration is determined
by transient response of throat and injector temperatures, as the
temperature continues to rise during the test. Analysis includes temperature
dependent material properties and heat transfer coefficients, and
test sequencing changes such as purges before and after firing.
(Graphic: Time histories of chamber throat and injector temperatures,
including initial drop due to manifold cold fuel purging.)
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ROCKET CHAMBER ð
The chamber model includes details of the fuel and
ox injector systems, including thermal and structural behavior. The
design was iterated by Convergence to reduce injector face temperatures,
using an insulator plate that doubles as a Helmholtz resonator cavity
sizing part. Instantaneous temperatures were observed with color animation
to understand the response behavior, where the injector face is heated
by combustion while the opposite side sees cold fuel.
(Graphic: Injector area instantaneous temperatures during firing.)
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ROCKET CHAMBER ð
Convergence also performed all necessary stress analysis
at instants in time, including unusual properties of the heat resistant
composite used for the chamber liner. The structural model included nonlinear contact interactions between
mating injector parts and flanges.
Transient temperatures and pressures were applied as quasi-steady
loads.
(Graphic: Chamber hoop stresses during firing.)
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ï AIRCRAFT RADOME
Convergence performed extensive design analysis of a new composite
radome for the carrier-based NAVY E2-C Hawkeye aircraft. Both carbon graphite and fiberglass laminates
were used in the design to provide high stiffness to weight, but allow
high radar transparency. Loading was somewhat complex, consisting
of variable surface pressures for several flight and test environmental
conditions. High stiffness
to weight was required to avoid aeroelastic problems in flight (flutter).
(Graphic: Finite element model of carbon graphite and fiberglass radome,
top removed to see internal rib structure.)
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| AIRCRAFT RADOME ðThe radome design was driven by high internal loads
generated by pressure overturning moments in extreme flight maneuver
scenarios. All load must be sustained by a relatively small central
tube interface. Also, stringent internal packaging requirements for
the high power radar system created difficult mechanical and structural
design tradeoffs.
(Graphic: Surface pressure induced deflections of carbon graphite and
fiberglass radome.)
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AIRCRAFT RADOME ð
Buckling of the complex composite structure required
careful analysis. The load carrying behavior of the structure was
highly indeterminate, i.e. there were multiple elastic load paths.
Panels were doubly curved and had transverse surface pressures as
well as variable internal edge loads , so simplified single panel
models and linear eigenvalue buckling methods were not appropriate.
Nonlinear large deflection analysis of the whole radome was
therefore used to check panels for buckling.
(Graphic: Load-deflection curves for a typical radome
panel under buckling loads.)
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ULTRA-ACCURATE REFLECTOR ð
Modern communications and remote sensing applications require extremely
tight satellite reflector surface accuracies for operation at high
GHz over wide temperature ranges in space. This 2 meter diameter reflector was especially challenging, requiring
rms surface errors within 1 micron over –120 to +140°C,
within tough weight limitations.
Zero CTE carbon graphite laminates were developed and tested,
and sophisticated 3-D solids conduction, radiation, thermal strain,
modal, and structural response analyses were required to verify the
design. Special low CTE adhesives were also required.
(Graphic: Exaggerated natural frequency mode shape deformations are
shown. Structural sizing
depended greatly on modal frequency criteria.)
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ï HARD DRIVE PACKAGING
Design
of computer hard drive shipping packages for shock protection and
low cost is no simple task, requiring substantial trial and error. Sophisticated nonlinear plastic and large deflection analyses
were used to speed up the design process for thin thermoform plastic
low cost approaches. Many
iterations were performed to optimize “crush” behavior to
meet payload acceleration allowables. The need to re-work thermoform
tools was substantially reduced.
(Graphic: Plastic stress response to lateral g loads, due to the inertial
load from the hard drive held within the thin thermoform package.
A half model is shown.)
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MILITARY SEMI- TRAILER
ð
A new 35 ft fiberglass/steel hybrid construction semitrailer was
developed for the Army (TACOM). The objective was to produce a lower
cost and lighter weight van using commercial construction that increases
transport value for the Army. Convergence performed all structural
and detailed design to meet stringent military specifications, such
as aircraft, rail, ship, off-road and on-road transport environments.
Design analysis included static g loads, dynamic road roughness inputs,
shock, vibration, lifting sling loads, tiedown loads, and snow/wind
loads.
(Graphic: Exaggerated deflection under lifting sling loads against the
roof, which was locally stiffened with extra fiberglass plies to
withstand this loading condition.)
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MSW SEMI-TRAILER ð
A
new 48 foot long fiberglass/steel hybrid construction semitrailer
was developed for municipal solid waste hauling (MSW).
The objective was to produce a lighter weight trailer that
increases payload, and therefore profit, in the competitive waste
hauling industry. Convergence performed all structural and
detailed design to meet MSW requirements, including adaptation of
a hydraulic moving floor unloading system.
Construction was similar to the military trailer with tailoring
of wall skins, elimination of the roof, and use of a low profile
suspension to maximize hauling cubage.
The result was a trailer 3,000 lb lighter (17%) and more
reliable.
(Graphic: Hydraulic moving floor actuator response
at the trailer nose, showing stress in the steel floor spine and
hydraulics adaptor plate weldment.)
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ï AEROSPACE BATTERYA
lightweight and high thermal conductivity mounting system for aerospace
batteries was designed. The
highly directional (orthotropic) structural and thermal conductivity
properties of advanced carbon graphite composites were utilized to
advantage to maximize battery cooling and performance under severe
operational conditions without compromising structural integrity.
Analysis included transient heat transfer given battery charging/discharging
sequences, modal vibration, and quasistatic g loads.
(Graphic: Battery transient thermal response at maximum battery temperature
gradient, shown on a slice of the battery with the carbon graphite
shell and base mounting structure.
High temperature in red "soaks" to the heat sink
at the base (blue) via the high conductivity path.)
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LARGE RADOME ð
A large ground-based radome was designed of E-glass composite. Loading cases investigated included severe
wind conditions. Edge joint
details were critical to the integrity of the design, involving local
bending of the shell, and interaction with flexible mounting seals
and aluminum frame.
(Graphic: Radome stress response to lateral 70 mph wind.)
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ï SPACE STATION MTAM
A
special Mass-Thermal-Acoustic Model (MTAM) was needed to simulate
a space station solar array transformer in full scale acoustic testing.
The structure is a complex honeycomb sandwich box with a myriad
of internal structures and electronic components.
It was necessary to match weight, C.G., and panel dynamic response
to acoustic loads with low cost non-electronic hardware.
Mass properties were matched within 1% and dynamic modes matched
within 5%, determined during successful acceptance vibration testing
directed by Convergence.
(Graphic: Interior portion of MTAM, detailed 3-D solid/shell element
model used for mass/C.G. matching and modal analysis)
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CRYO ROCKET ENGINE
ð
Structural dynamics and acousto-structural responses were predicted
for a new 650,000 lb thrust cryogenic rocket engine.
Variable density chamber gas, acoustic/structural coupling,
flexible ablative material, and injector mechanical vibration within
the acoustic field were simulated.
Potential dynamic instabilities were avoided by design by investigating
structural, acoustic, and fluid feed system natural frequencies and
mode shapes.
(Graphic: Cryo rocket engine model, including acoustic cavity. Variable gas density indicated by color codes)
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CRYO ROCKET ENGINE ð
Structural dynamics and acousto-structural responses were predicted
for the same rocket engine in a ground test stand firing configuration.
Vibration response levels at piping connections, response dynamics
of the fixture thrust measurement system, and fixture structural stresses
were predicted.
(Graphic: Cryo rocket engine model, including test
fixturing beam and spring model.
A typical coupled mode shape, with exit nozzle “bell”
modal behavior, is shown in exaggerated deformation form.)
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NEW ENGINE DESIGN ð
This is
a new engine design using spherical balls for pistons and an eccentric
track to stroke the balls in cylinders within a spinning rotor.
Sophisticated multi-energy domain dynamic analysis was used
to simulate the mechanical, combustion, and thermodynamic behavior
of the system. Eccentric track
design was devised to completely eliminate inertial tangential loads
that contributed to friction losses.
(Graphic: Engine cross section schematic)
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ï ENGINE SUBSCALE TESTER
Subscale
tests were performed to quantify the key physics of operation of the
new engine design above. This tester allowed measurement of the friction
coefficient at the cylinder wall/ball piston contact, and blow-by
leakage. The test apparatus
simulated actual operating loads by the use of a single cylinder arrangement
with an eccentric drive wheel. Results
for blow-by and friction were equal to or better than previous design
assumptions made by Convergence Engineering.
The subscale tester was used for iterative tests to optimize
material selection of cylinder and ball piston.
(Graphic: Subscale tester schematic)
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ï WIND TURBINE DYNAMICS
The
structural dynamic behavior of a new concept wind turbine ( of the
Darrieus type) was studied in depth, leading to a new prototype currently
in operation at Tehachapi, California. Convergence Engineering performed most design
analysis of the dynamic system and components, including new technology
pultruded fiberglass airfoil blades. Convergence also developed an automated analysis system to enable
“over-night” system design iterations, compared to several
months with previous methods.
(Graphic: A typical Campbell diagram, or “fan
plot” of the new concept machine is shown.
This is a major tool in system design, which the designer
uses to avoid matching of natural frequencies and operating excitation
frequencies.)
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WIND TURBINE NONLINEAR ANALYSIS
ð
The
system analysis of the wind turbine required highly specialized nonlinear
methods for accurate prediction of operating stresses.
Due to the “soft” nature of the rotor, large deflection
nonlinearity was considered, including bending the blade from the
straight as-manufactured shape into the “bowed” installed
shape. In fact, the actual
installation with cranes was simulated with models to ensure against
installation damage. The response
stresses were also verified with strain gage measurements.
(Graphic: Surface stresses in the fiberglass blade under gravity and
spin loads.)
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ï TITANIUM BIKE FRAME
A
new low cost Titanium mountain bike frame was designed for a southern
California manufacturer. The design was particularly geared for using
low cost off the shelf tubing, and was optimized with this constraint.
Welds were explicitly modeled in addition to the tubes with a dense
finite element mesh. The project also included completely defining
the mountain bike load spectrum for high reliability, including braking,
jump, pedaling, and maneuvering loads as well as rough terrain traverse.
(Graphic: von Mises stress for maximum load on the bottom bracket area,with
explicit welds removed for clarity.)
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AIRCRAFT RETROFIT FOR INSTRUMENTS ð
The
structural design of retrofit hardware for installation of instrumentation
in a C-130 aircraft cargo bay was performed.
Loading conditions included ultimate pressure differential
for the sealed installation, maneuvering g’s, and crash g’s.
Design of the deep-machined lightweight structure was iterated
for maximum weight savings within safety specifications. The project was performed within tight time
schedule constraints, enabling the client to deliver hardware on time.
(Graphic: Stresses under downward g loads of the main side panel of
the deep-machined frame structure.
Web thickness was iterated to give acceptable ultimate stresses.)
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BOEING 757 & 777 THRUST REVERSERS
ð
This
was one of the most difficult modeling projects ever performed by
Convergence. The thrust reversers
are "doors" that deploy and block the outer plenum air flow
during braking, and act as sound absorbers during flight when retracted,
making up part of the plenum walls. The doors are complex anisotropic structures,
consisting of multiple layers of carbon graphite cloth built up around
a honeycomb core, with metallic interface hardware bonded into the
carbon structure. One side
of the thick sandwich structure is also perforated, allowing the honeycomb
to act as a multiplicity of Helmholtz resonators. The structure was
modeled with 3-D laminate solid finite
(Graphic: External view of the composite structure model.)
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elements,
including adhesive bonds and metallic hardware. Static pressure load and random vibration responses were predicted
to evaluate stresses for ultimate and fatigue durability. In addition, Convergence performed all vibration
qualification testing of actual hardware, and directed static and
fatigue qualification tests. Accuracy
of ultimate load predictions and deflection response was within 5%,
extremely good for such a complex structure.
High accuracy is attributed to 1) initial sample analysis by
Convergence to establish a valid modeling approach, and 2) a complete
material characterization program performed with Convergence direction.
A total of 6 door designs were completed, for 757 and 777 aircraft,
and various 777 engines.
(Graphic: Back structure von Mises stress response to air blockage dynamic
pressure loading is shown.)
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MD-80 AIRCRAFT WING HEATER ð
The
subject of this project was mechanical and thermal design of a new
design wing heater for de-icing aircraft wings.
The heater consisted of a composite laminate, including an
embedded etched metallic heating element within the plies.
The structure must withstand wing deflections and dynamic pressure
loading, as well as thermal heating.
The model included edge riveting and adhesive bonds, including
nonlinear characteristics and peel potential of the adhesive used
to mount to the wing.
(Graphic: The model is shown with outer aluminum surface von Mises stress
response to a wing deflection condition. The “holes” are fuel tank access cover locations)
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AIRCRAFT INSTRUMENT FAIRINGS FOR P3 BOMB BAY ð
Composite
aluminum/fiberglass/urethane foam fairings were designed and analyzed
for a new instrument bomb bay installation for the P3 aircraft.
The design was tuned to withstand differential pressure, maneuvering
and crash g’s, for ultimate and fatigue reliability, including
estimated turbulence oscillatory loads.
Orthotropic skin and filler foam properties were accounted
for. Convergence performed the complete design effort, and delivered
drawings for immediate fabrication by the client’s model shop.
(Graphic: Fiberglass skin stresses under suction pressure loads.)
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ï P3 INSTRUMENT MOUNTING FRAME
The supporting bomb bay mounting frame for the P3 installation
was also checked for design adequacy by Convergence.
The combined beam and shell model was constructed with particular
interest in accurate prediction of interface fastener loads. Shear panel stress, beam stress, and fastener loads were all checked
for ultimate and fatigue durability.
The existing design, done by the client, was adequate with
some adjustments to fastener specifications.
(Graphic: Mounting frame shear panel stresses were investigated, as
well as beam stresses in frame members (fore-aft 10 g crash load
case shown).)
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ï NEW DESIGN REEFER THERMAL DESIGN
The thermal performance of a new fiberglass refrigerated trailer
design was investigated and compared with existing design trailers.
The 2-D and 3-D models incorporated solar insolation, nonlinear
radiation with ambient air and hot road asphalt, internal cooling
air convection cooling, and material conduction and heat capacity,
including surrounding air. Steady
state and transient non-linear analyses were performed. Results showed marked improvement in maintaining payload temperature
below freezing.
(Graphic: Payload temperature profiles are compared
after 80 hours of heat soak and non-operation of refrigeration. Note gray indicates reaching melting temperature
of frozen food.)
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REMOVABLE DISK WRITER DYNAMIC
DESIGN ð
The structural dynamic performance of a new removable computer
disk design with a plastic hub was evaluated.
In addition, the structural dynamics of the machine that pre-formats
the disks was also investigated.
Disk formatting requires very high precision servo control,
and resonances as well as vibration transmission from the environment
must be minimized. Modal analysis including rotating flexible
structure effects was used to tune the writer machine structure, and
hub instabilities were predicted for the first hub design.
(Graphic: The plot shows a natural mode of vibration at about 400 Hz
involving “drum” vibration of the subject disk coupled
with bending of the formatting machine magnetic head arm.)
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ï GRAPE SPRAYER FRAME
The
support structure for a new concept “environmentally friendly”
agricultural sprayer was designed for fatigue reliability and deflection
control. The unit is three-point
hitch mounted to a wheel tractor, and loading conditions for design
included oscillating loads due to tractor/terrain dynamics.
Plate stresses were used in fatigue analysis, including weld
stress concentration effects. Also, auxiliary hardware was designed using
model load responses. The
sprayer is now in production after successful prototype testing.
(Graphic: Sprayer support structure model, made of
shell finite elements. Exaggerated
deformed geometry under tractor fore-aft braking g load is shown.)
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ï EXPERT WITNESS - CHAIR FAILURE
One
area of work at Convergence is expert witness testimony in cases involving
mechanical hardware and failure analysis.
This particular project involved detailed finite element modeling
of a welded chair frame, and prediction of stress levels in normal
use. The results in graphical
form are excellent visual aids for arbitration or trial use.
The analysis results corroborated the hypothesized failure
mode, and supported a design defect case.
(Graphic: Close-up of welded joint model of a modern office chair.
The von Mises stresses for the maximum back pull load case
are shown.)
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