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資源目錄里展示的全都有，所見即所得。下載后全都有,請(qǐng)放心下載。原稿可自行編輯修改=【QQ：401339828 或11970985 有疑問可加】 Mechanical Engineerings Role inMulti-Di-sciplinary Radar DesignWiliam c. Dawson & Alan B. RohwerRaytheon CompanyABSTRACTsolution to our design challenges from the perspective ofthe mechanical engineer.Successful execution of a program and full satisfactionof the customers requirements is a challenge for anycontractor. Raytheon Company responds to this challengeby following a proven program execution methodology.The methodology includes all program aspects fromfinancial planning to engineering to validation and test.This discusses the engineering team and the role of themechanical engineer. A radar system is ultimately anassembly of advanced electronics and software. However,the design, fabrication, assembly, integration, and test Ofthis complex system requires a coherentmulti-disciplinary approach. Raytheon, like manycontractors, chooses to assemble an integrated productteam (IPT) including all engineering disciplines.Mechanical engineering is integral to satisfyingperformance requirements, performing preliminary anddetailed design, transition of the design to manufacturing,and implementation of the hardware in the field. Duringdefinition, mechanical engineering assists fundamentalarchitecture development, conceptual design, andrequirements development which precludes issues thatare sometimes ignored to the detriment of manyprograms. These design issues include environmentalprotection, structural stiffness to meet deflectionrequirements, cooling system capacity to properly removedissipated heat, manufacturabilit3 to control cost,maintainability to enable repair in the field, andtransportability. Recognizing and trading off these issuesearly greatly increases the Probability Of satisfyingcustomer objectives. This discusses the approachRaytheon is taking to ensure an overall multi-disciplinaryAuthors C-urrent Address:W.C. Dawson and A.B. Rohwer, 528 Boston Post Road, Sudbury, MA 01776, USA.Based on a presentation at Radar 2007.0895/8985M08 $25.00 USA 0 IEEE 2008Fig. 1. Complex programs require team execution toprovide customer satisfactionINTRODUCTIONRaytheon Company and other large contractors Partnerwith our customers to produce complex new systems and toupgrade existing systems to new missions. The resourcesrequired to execute these contracts are often quite substantial.Successful reliable execution of the contract is the paramountconcern for both the contractor and the customer. Teamworkand collaborative design across multiple disciplines isrequired to produce a product that meets or exceeds allrequirements and expectations. This discusses the mechanicalengineers role in this collaborative process.Satisfaction of the customers requirements andexpectations starts with recognition of the mission andConcept of Operations. Understanding these fundamentalsprovides a foundation for the entire program. Programs thatlack this foundation will ultimately need redirection with asubstantial penalty in cost, time, and customer satisfaction.33IEEE A&E SYSTEMS MAGAZINE, NOVEMBER 2008Fig. 2. The Raytheon Integrated Product Development System enables successful program executionThe requirements that flow down from Mission and Conceptof Operations include both major system performanceparameters, such as radar probability of detection, andhardware implementation parameters, such as transportabilityrequirements or the theater of operations.Major systems, like those shown in Figure 1, feature highperformance radars required to achieve state-of-the-artsearch, track, discrimination, and illumination functionality.They must also meet these requirements before, during, andafter exposure to severe natural and induced environments.For example, the Theater High Altitude Air Defense(THAAD) system shown in the upper right panel of thefigure is a region-wide air defense radar.It is required to meet stressing radar performancerequirements, to interface with other sensors and weapons,and to operate before, during, and after exposure toenvironments such as very high ambient temperature andstrong winds laden with sand and dust. The THAAD radar isalso designed to be highly transportable, which limits theaperture size and weight.As another example, the Zumwalt Class Destroyer(DDG 1000) shown in the upper left panel of the figurefeatures a large number of high performance sensors andcommunications systems. Each of these equipment sets mustalso be designed to withstand and/or operate without repairafter exposure to the shock environments resulting fromunderwater explosion.Assuring our customers complete mission successrequires the contractor to produce a system that achieves thecombination of performance and implementation. Thisdictates that design disciplines must work together in closepartnership. Understanding of the coupling between diversePrOgramn ManagerAdmin inancFig. 3. Cross-discipline organization structureencourages interactionrequirements enables the program team to provide thecustomer a high level of satisfaction.This discusses a variety of topics starting with programprocess and organization. Several of the key areas ofmechanical involvement are also described.INTEGRATED PRODUCT DEVELOPMENT SYSTEMAll designers, design teams, and organizations need tofollow a robust design process. While design processes come34IEEE A&E SYSTEMS MAGAZINE, NOVEMBER 2008The Perfect Designctr Irar Ti.Ld XPatteornThe Spec Compliant Design0.00 -1(3 IlL)3O O0-)3C) 00-to 006000-40 (IC)-?t3 00Fig. 4. Implementation of idealized design models in hardware requires recognitionof all requirements to meet all customer Mission needsin many forms, the fundamentals are the same for everyone.Large organizations that contract for major programs anddeal with hundreds of projects simultaneously require arigorous process. Raytheon Company follows the IntegratedProduct Development System.As shown in Figure 2, the process starts with businessstrategy and planning. Corporations must establish a businessstrategy and pursue opportunities that match the strategy.Program planning, leadership, management, and controlfollow. The vast majority of program resources fall withinthe subsequent steps. Requirements and Architectureestablishes and documents the program needs and the toplevel design to meets these needs. Design and developmentdefines what the products and system will look like in detailand how the products and system will be implemented inhardware. Finally, verification and validation is the first-timebuild and test of the products. Production and deploymentfollow and transition into long-term operations and support.Detailed descriptions of each step of this process establisha path for repeatable execution. These descriptions enablerecognition of all performance and implementation demands.The process enforces the desired collaborative effort.ORGANIZATIONAn important part of the design process is the programorganization. Figure 3 shows a typical cross-disciplineprogram organization. This matrix-type structure startswith a single program manager with responsibility to thecustomer. The system is divided into integrated productteams (IPTs), each focusing on a major sub-system. Thetwo 1IPs shown, Radar and Platform, are typical of manyprograms. The engineering teams cross the IPTs, so thatdiscipline expertise is shared by the many IPTs. Thisstructure encourages communication and interactionbetween the sub-assembly teams.THE ROLE OF THE MECHANICAL ENGINEERAll disciplines that participate in the design of a complexradar system have a unique set of skills, each of which isrequired for total program success. Each discipline needs tounderstand the skills and focus of the other disciplines if acoordinated team approach is to be achieved. Among manytasks, the role of the mechanical engineers is to developimplementation solutions to optimize performance, ensurethe hardware will operate successfully in the full set ofnatural and induced environmental conditions, and transitionthe designs into manufacturable hardware.When the mission, concept of operations, and full set ofrequirements are not fully understood by the entire team,design conflicts can occur. This may also be the case if thespecific demands of each discipline are not understood. Eachdiscipline will consider that the actions of the other teammembers are sub-optimizing their work. Some of the drivingrequirements placed upon the mechanical engineers that canimpact predicted system and product performance areoutlined herein.These factors include design for the natural environments,thermal loads, temperature ranges, induced structural loadsfrom all sources, design for manufacturing, and materialsselection. Development of a design that approaches idealizedperformance, while simultaneously solving for all of thesefactors, is the ultimate goal of the cross-discipline team.The left side of Figure 4 shows an example of a theoreticalfar field pattern for an antenna system. This pattern exhibitsidealized behavior. There is a sharp, well-defined energypeak with a smooth taper away from the main beam. Theright side of the figure shows the pattern after the design isimplemented in hardware, fully compliant with non-idealizeddemands on the hardware. Note that the off-peak spikes ofenergy are safely below the customers specification limit.In this example, the product delivered to the customermeets all mission and concept of operations needs. The35IEEE A&E SYSTEMS MAGAZINE, NOVEMBER 2008Fig. 5. The demands on thermal system designare increasing rapidly 1solution is non-idealized but is successful, nonetheless. Theoff-axis behavior could result from any number of sourcessuch as dimensional tolerances, resulting from acost-effective manufacturing process, or the antennamisalignment due to deflections under wind loads. Thedesign team successfully engineered this product andachieved customer satisfaction.Thermal DesignThermal environments and thermal loads are significantfactors in any design of electronics systems. Environmentsinclude both the ambient conditions of temperature, solarradiation, and humidity at the operations location and thelocal environment to the specific articles of equipment. Forexample, a shelter system may be placed in very severeoutdoor conditions while providing a fairly benignenvironment to the enclosed electronics. Thermal loads arisefrom power dissipation of the operating electronics.The mechanical design engineer is tasked to solve for bothof these requirements. The design for the natural thermalenvironment includes selection of materials and finishescapable of withstanding the temperature extremes. Both hotand cold extreme temperatures are a design challenge. It is ofparticular interest to note that few commercially availableparts are rated for the typical cold temperatures required bymilitary hardware.In order to protect sensitive electronics and achieveimproved performance, environmental control systems andinsulation are used to provide narrower temperature rangeswithin shelters. Radomes are used to cover the radiatingsurfaces of antenna systems. Environmental control systemsrequire power to operate and must be included in systemreliability calculations. A radome provides protection but willreduce the performance of the protected antenna and alsorequire a substantial volume. Anti-icing equipment isnecessary to preclude damaging accumulation of ice for somesystems. Anti-icing requires substantial power and can limitperformance in specific cases.Thermal loads require the design of a thermal controlsystem to achieve two major goals. Thermal controlmaintains the electronics below maximum temperatures forimproved reliability. The design engineer must trade highreliability vs. cooling system cost and the cost of spares. Asshown in Figure 5, the power density and power dissipatedby processors has been increasing steadily for the last 6 yearsand is expected to increase dramatically in the future. Thecomplexity of thermal control systems has been increasingaccordingly.The thermal control system may also create temperatureconsistency across an entire system for best possibleperformance. The level of temperature consistency is afunction of packaging approach, time variation ofdissipations, and ambient temperatures.One final consideration that applies for all thermal designis thermal expansion and contraction. Nearly all materialschange dimension with changing temperature.This dimensional change can result in performnancechanges in electronics and can produce stresses in materialsleading to failures in extreme cases.Fig. 6. Natural and Induced Structural EnvironmentsInfluence all designs 2Structural DesignThe design of structures starts with an analysis of theintended use of the equipment and the environments to whichit will be exposed. This analysis starts with the customersmission and concept of operations and concludes with adetailed understanding of the set of load cases. There areoften many load cases to consider, any of which can have animpact on the performance of the system.An example of a load case based on intended use is thedesign of large radar apertures where structural deflectionunder mechanical motion and gravity must be limited. Thisdesign results in a trade of antenna performance as impactedby deflection vs. the cost of the support structure to limit the36IEEE A&E SYSTEMS MAGAZINE, NOVEMBER 2008ELAUV COS of TOLUANCESFig. 7. Manufacturing tolersat higher relatiUncorrelated Errors:ToleranceE -lt latness Jia Ter it ToleranceW Hlh ToleranceInCornmenstlon Erro- I rc eH ost tit Ton mmZ- Axis ErrorsPe-ak sma0.002 0.0010.014 0.0080.005 0.0030.010 0.0060.010 0.0060.005_ 0.0030 .010 0.0060.6,008 0.0050.014 0.0090.005 0.0030.003 0.0020.029 0.0180.040 0.030I 0.011 0.012FabricationMeasureMeasureFabricationFabriatioflcatnionFabricationFabricationIFabricationlFig. 8. Detailed error budgets are usedto calculate design margindeflection. The antenna designer must include aperturedeflection as an error term in the analysis while the structuredesigner must find ways to limit the deflection as efficientlyas possible. A very similar trade is often required for systemsexposed to wind loads.Figure 6 shows several examples of induced structuralenvironments that are common for ground tactical andshipboard systems. Shown are the tests of an equipment trucktraveling over a road course, the test of shipboard systemsexposed to underwater explosion, a road simulator test, and atest for helicopter slinging. These load cases demandsignificant structural design. The structures cannot deformexcessively or fail under load. The design team is oftenchallenged with the conflicting demands of systemperformance and structural adequacy.DIELECTRIC Yield CE DielectricMATERIALS (Ksi) (ImIC) ConstantTeflon 7 3.5 100 27.1Ultemn 2200 20 250 4.2F polycarbonate 101 68 3.1.polystyrene 8 70 2.5SPEC-ALTY Modulus CestE DilctrdcRAOEMATERIALS Moli mIC Im-C.0_sanRoAI el oa 300 5 11.8 1.13RoaISc4O/Foa 20 3 12.1 1304CUMOO/2 35 51.8 117Kovar 21 6.3 14.2Alloy42 21 4.4 11.5Fig. 9. PropertieS Of some common materaiasA typical example is the sizing of electronics cabinetsexposed to shock loads. The required size of structuralmembers and addition of shear panels may result in reducedequipment capacity and poor access.Manufacturing and ToleranceAll systems and products that have been simulated andmodeled to maximize performance must ultimately bemanufactured and delivered to the customer. Therefore,design for manufacturing is a key concern for most hardware.Design engineering must take manufacturability into accountfrom the start of design.There are a large number of potential manufacturingprocesses and the selection of the part-specific process mustbe made early. Cost, schedule, design details, structuralstrength, and, most importantly, tolerances are keyed by thisdecision. For example, castings offer a cost advantage formany parts but require lead time to prepare the tooling,require draft angles to be designed into the part, and can havereduced properties relatively to commonly used wroughtalloys.All manufacturing process is subject to tolerance, which isthe variation of the as-built dimension from the desireddimension. The level of tolerance is a function of the process,the quality of the equipment, the materials selected, and theskill of the personnel. As shown in Figure 7, the cost ofmanufacturing increases rapidly to achieve tight tolerances.The absolute tolerances vary widely with manufacturingprocess, but the concept is the same. The design team must37IEEE A&E SYSTEMS MAGAZINE, NOVEMBER 2008cqtk- NCHncscan be minimizedyecost 1RSS TcAaAllocation from budgetiDesign Margiftrade manufacturing cost vs. tolerance and relatedperformance.Errors enter into the as-built configuration throughout themanufacturing, assembly, and measurement sequence.Fabrication tolerances discussed above are only one line itemin the error budget of a carefully considered design. Figure 8shows a sample error budget for a typical assembly.Uncorrelated errors are those errors that occur independentlyof one another. The table shows some typical errors includingfabrication tolerances, alignment target tolerance, operatoraccuracy, and analytical prediction error. The design teamhas a variety of statistical analysis choices to make. In thisexample, both peak and I sigma errors are calculated.Because the errors are uncorrelated, a root sum squaredanalysis can be used, which produces a more realisticworst-case prediction.Many program teams have failed to provide a high level ofcustomer satisfaction due to problems encountered at themanufacturing phase. It is very common for the root cause ofthese problems to be traced to the teams lack ofconsideration of manufacturing issues during the outset of thedesign.Material SelectionHardware design engineers, particularly of electronic andelectromagnetic systems, have numerous physical propertiesto take into account when making material choices. Figure 9shows the varying properties which must be traded whendesigning such items as r.f. devices, radomes, and otherspecialized electronics. The best electrical material may notalways be the best overall material. For example, Teflon is aterrific dielectric material but has poor structural properties.Kevlar has very good stiffness and dielectric properties butabsorbs moisture, rendering it unusable in some applications.Various specialty materials are used in electronic packagingbecause of a combination of thermal conductivity, expansioncoefficient, and elastic modulus. In these design cases, thematerial selection itself must become a multi-disciplineeffort.SUMMARYThis describes the collaborative design effort requiredacross multiple disciplines to produce a product that meets orexceeds all requirements and expectations. Emphasis isplaced on the mechanical engineers role in this collaborativeprocess. The discussion starts with program process andorganization and extends into key areas of mechanicalengineering involvement such as thermal, structural,manufacturing variations, and material selection issues.ACKNOWLEDGEMENThe authors wish to acknowledge their systems, electrical,and software colleagues with whom they have worked overthe years, including those within Raytheon, supplier, andcustomer communities. These design collaborators haveassisted the authors in learning how to flow down systemrequirements into optimized radar hardware solutions.REFERENCESII Semiconductor Industry Association,The International Technology Roadmap for Semiconductors,2002 Update. SEMATECH:Austin, TX, 2002.Semiconductor Industry Association,The International Technology Roadrnap for Semiconductors,2003 edition. SEMATECH:Austim, TX 2003.21 US Army Aberdeen Test Center,Facilities/Capabilities Guide, links:http:/wwwaticAymil/fac guide/faci litieslmun son. html,h-ttp:/wwwatcarmyvmil/fac 2iuide/faciIi ties/undex.html,http:/wwwatcarmyvmil1/fac gtuide/facilities/tiednwn htmnlhttp:/wwwatcarinymil/fac euide/faci lities/roadwaysiin html.3 R.D. Marcus, E.H. Shef