Mechanical Engineering Design and Analysis
The home page has well summarized the design/analysis capabilities of CEC. Some of the largest and most extensive projects executed by CEC have included:
Following is a summary of these and other design/analysis projects executed by CEC.
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JSF Composite Duct
CEC performed a Phase I and II SBIR for the Air Force, WPAFB. The Joint Strike Fighter engine bypass duct ( high temp Maverick MM10.8 braided carbon graphite, with VTOL side ducts) was studied. The project developed high accuracy predictive tools to design the duct for high buckling load, in the presence of side duct anomalies. Large deflection nonlinear FEA was used to predict both pre and post-buckling behavior. The project also included extensive testing of braided coupons, flange samples, and complete half scale ducts (see CEC test summaries) and test/analysis correlation. The result was an optimal very high performance design.
Boeing 757 & 777 Thrust Reversers
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 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.
MD-80 Aircraft Wing Heater
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.
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).
The 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.
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.
CEC performed design adequacy analysis of a lightweight aluminum turret for instrument mounting on the belly of aircraft. Loading conditions included static and aerodynamic loads, transient shocks, and vibrations. Studies included details of loading transmitted through complex joint/drive gimbal structures.
Aircraft Retrofit For Instruments
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.
Aircraft Instrument Fairings For P3 Bomb Bay
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.
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.
New attitude control thruster assemblies were being added to Space Station airlock structures. Extensive analysis was performed by CEC to verify the design for thermal, static, vibration, and acoustic loads. Detailed thermo-structural analysis of the thruster assemblies for numerous firing scenarios was done to verify adequate LCF life of the nozzles and associated hardware. Sine vibration analysis was performed to establish dynamic response transfer functions of acceleration and stress. Acoustic simulation of the structure within a reverberant chamber was performed to verify adequacy of the design to withstand specific max sound pressure levels.
CEC performed all design analysis of a very high accuracy very large (approx 4m) space antenna. The extremely stringent deflection limits, along with tight weight specs required designing the dish with a substantial tubular back structure and octagonal base frame with special fillers. Zero CTE laminates were necessarily used, along with minimal and strategic use of bonds to mitigate thermal influences of the higher CTE adhesives.
CEC performed extensive analytical FEA design and trade studies to optimize this small “mini-shuttle” type of air/space vehicle for Air Force missions of various kinds. Special emphasis was directed at weight-optimal design using a load-bearing integral tank structure suitable for cryogenic bi-propellants. The tank design was unique, using internal foam and liner insulation to keep exterior structural interfaces simpler and lighter, without insulation and the need for thermal dams. Aerodynamic and piggy-back launch and landing loads, and well as propellant thermal and pressure effects, were investigated.
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 +140C, 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.
Radome structure stresses for an operational condition during transient mission event.
A 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.
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.
Cryo Rocket Engine
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.
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.
Small Rocket Chambers
Convergence also performs simulations of test chamber firings, both steady state and transient heat transfer. In the particular case shown here, 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.
The chamber model includes details of the fuel and ox injector systems as well, 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.
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 for the structural stress analysis phase.
USET Rocket Engine
CEC provided major support to colleagues Sierra Engineering to develop a new upper stage cryogenic engine with Northrop Grumman. The project developed higher accuracy multi-disciplinary optimization tools for preliminary design than ever before, and the tools were exercised to arrive at an optimal design. Of great importance to optimization was to trade off design of TPAs vs. the chamber/nozzle for the greatest system benefit (weight/performance). The optimization model included substantial detail of turbomachinery design, regeneratively cooled chamber-nozzle LCF life, combustion heating, and engine flow system performance.
A major contribution by CEC was the integration of the ANSYS FEA code into the modeling tool to allow accurate LCF evaluation of combustor hot parts within the optimization. Nonlinear transient thermo-structural FEA was fully automated to analyze numerous cross section locations within the combustor. The analysis was fully coupled to the engine system thermodynamic, flow, and combustion analysis.
In follow-on SBIR work, the optimization model was enhanced to add the ability to predict hardware reliability to the optimization. CECs probabilistic experience helped greatly to develop computationally efficient algorithms to achieve this, with reasonable run times, including design and material statistical variabilities.
CEC also developed a high speed computer platform to conduct the analysis, based on multiprocessor multi-threading 64 bit PC architecture and high speed disk systems. Multitasking and parallelization of the FEA and other solutions enabled a reduction of run time of about 4 times, making serious optimization practical with a relatively inexpensive PC platform.
CEC performed detailed LCF and burst analysis with a 3-D FE model, including nonlinear thermal and structural behavior. Important features requiring special consideration were internal posts and the external wall, including their complex interaction with a hot face plate of different material.
Vacuum Rocket Engine Test Facility
Extensive design analysis was performed by CEC in support of Sierra Engineeering to design a large vacuum test facility for upper stage rocket engines. The diffuser (with hot wall from engine plume and water jacket cooling) required thermo-structural LCF analysis, as well as checking of buckling resistance under vacuum, which was an exceedingly challenging application of nonlinear large deflection thermo-structural FEA.
The vacuum in the chamber is developed by a powerful supersonic steam injection system. CEC performed all the design FEA on those components as well, designing for long cycle life and prevention of creep and burst.
Cooling Flow Testers
Steady state temperatures in a flow test channel assembly.
CEC performed detailed design and analysis of a very large (approx 8x8 ft) deployable radome for a heavy military truck vehicle. Loading included multi-directional wind loading and transport vibration and shocks. Stringent surface deflection limits required careful design of the Spectra/foam sandwich composite structure.
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. A prototype, built with direction from CEC, was subjected to severe durability testing at Aberdeen Proving Ground, and performed well.
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 than current designs.
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.
Drag Racer Chassis
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. CEC/ST worked 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 track bumps.
CEC/ST was also the major engineering force behind solving NHRA Top Fuel chassis failure problems in recent years. Serious work began after Cory MacClenathen’s car “folded in half” at a national race. CEC diagnosed problems were due to use of sub-standard hardened chrome-moly tubing in chassis building. Extensive FEA was performed, with loads measured by ST on-track competition testing, to fully understand and resolve the frame problems. CEC/ST’s work was the first to accurately quantify all operational loads and responses of these cars. As a result, rules were changed and a stringent tube properties verification testing program was implemented, quite successfully solving the problems.
Funny Car Chassis
Hardened chrome moly tubing may have also been a factor in the fatal accident of Eric Medlen and the serious injury/accident of John Force in NHRA Funny Cars in 2006-07. CEC/ST again was retained to help investigate the Funny Car chassis problems, along with other organizations such as Ford Motor Company. Again, rule changes were made and the Funny Cars were subjected to the same tube properties verification that was successful for Top Fuel. At this point in time, it appears that structural problems in the premier Nitro classes have been solved (at least for now, until engine power goes even higher).
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, BME, 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.
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 forged/machined 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 dyno tests.
NASCAR Wrist Pins
The dimensions of the NASCAR wrist pin are especially important for good weight efficiency. Made of very high strength 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.
Of great importance to optimal wrist pin design is accurate modeling of the interfaces of the pin with piston and rod/top end bushing. CEC’s model included all these effects via nonlinear contact modeling and full geometric representation. Similar analysis has also been done on drag racing engine piston pins.
NHRA Nitro Rocker Arm
Drag racers are always looking for ways to improve their hardware to avoid engine failures, like valve rocker cracking and possible catastrophic failure. CEC uses FEA to optimize even the smallest regions of engine parts, such as the exact machined contour at the end of a rocker arm.
Motocross is an extreme sport and the conditions the motorcycles are put through are harsh. CEC/SquidTech provides the analysis and lab testing tools necessary to design components that will withstand these conditions as well as being optimized for light weight and market competitiveness. A very important part of such jobs is developing good design loads, based on engineering analysis and/or field testing. CEC also provides consulting to producers on proper quality control activities with foreign hardware manufacturers.
MX Clutch Perch
The motocross industry is always looking to cut weight of parts without loss of strength, and special capabilities that set a product apart are important as well. One example is a new break-away control lever. CEC/ST skills were applied to develop this new design to provide the desirable new function without loss of reliability. Very difficult weight targets were met by unusual material choices and careful FEA and lab testing of prototypes. OF particular interest was not to introduce “mushiness”, or loss of stiffness, into the design.
An extremely lightweight and stiff graphite composite optical bench was designed and analyzed by CEC for a composite fabrication house for a Boeing application. Objectives were to have very low thermal and gravity deformations and meet stringent minimum natural frequency requirements. The structure was designed by detailed FEA of thermal and mechanical loading conditions, including vibration and shock.
One major requirement of the lightweight bench was the need to carry heavy electro-mechanical assemblies on the underside. The loading conditions were extremely challenging to design for, within weight bogies. Special highly efficient internal composite structures, interfacing with metallic mounting inserts, were designed to carry the heavy loads. CEC later also successfully performed qualification load testing of the same design in the CEC test lab.
SSL Antenna Mount
Convergence performed exploratory sizing analysis for a large positioner/mount structure for an RF antenna test facility. Stringent requirements of antenna mount point deflection limits were dealt with, looking at metals or composites and various geometries for the best low cost yet technically acceptable design.
New Engine Design
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.
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.
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.
Wind Turbine Dynamics
The structural dynamic behavior of a new concept wind turbine (with a high height/diameter ratio, of the Darrieus type) was studied in depth, leading to a new prototype operated at Tehachapi, California wind farms. 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.
Wind Turbine Nonlinear Analysis
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.
Wind Turbine Test / Analysis Correlation
Two wind turbine prototypes were successfully built, erected, and operated “on the top of the hill” in Tehachapi, CA. Extensive testing and test/analysis correlations were done, including modal characterization and operational vibration. Correlation with design analysis was excellent, and the machines were successfully operated for power generation (350 kW rating).
Elastomer Traction Drive
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 as well.
Eliptical Workout Machine
Home fitness machines have spawned a huge industry. Large deflection analysis was used by CEC to model a new adjustable elliptical machine for mechanical functionality and life estimation. Stress and deflection results from full-cycle nonlinear kinematic/kinetic mechanism analysis with flexible elements (via ANSYS FEA code) were used to design linkage parts. CEC recommended design sizing and material selection of the linkage parts to provide long life and cost effective production approaches.
CEC provided FEA support for plastic clip optimal design for functionality and life.
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.
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, speeds, and throughputs. Convergence helps one producer in Northern Nevada 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.
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.
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.
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.
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.
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 also performed seismic qualification testing of all stands for required battery options, using subcontracted shaker resources in Southern and Northern CA.
Large Building Radome
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.
Removable Disk Writer Dynamic Design
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.)
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.
Mechanical Engineering Design and Analysis
The home page has well summarized the design/analysis capabilities of CEC. Some of the largest and most extensive projects executed by CEC have included:
Following is a summary of these and other design/analysis projects executed by CEC.