Tutorial Exercises and Case Studies. Design Tutorials

Transcription

1 Dsign Tutorials 1

2 Introduction This modul uss a numbr of small hypothtical dsign xrciss to ncourag studnts to dvlop thir undrstanding of th principls and tchniqus involvd. Ths xrciss ar thn put into practic in a singl cas study towards th nd of th modul whr studnts ar rquird to undrtak a concpt dsign study and dmonstrat how formal dsign principls /tchniqus covrd in th labs can b applid. 2

3 Tutorial Exrcis 1 Background You hav bn askd by a high volum car manufacturr to dsign a car jack for changing car whls. This jack will b supplid by th manufacturr as a standard fit on a rang of modls. Th jack will b fittd intrnally within th car. Th scop of your dsign brif dos not covr tools for rmoving whl trim or whl nuts. You would b abl to rqust modifications to th form and gomtry of jacking points but for structural rasons it not likly that you would b abl to chang th position of jacking points. Objctiv To think about, documnt and analys customr rquirmnts. Ky qustions; Who ar th customrs? What ar thir objctivs What problms might thy fac? Ar thr any minoritis that you nd to tak into account? What ar th xtrm scnarios that you nd considr? Rmmbr: You nd to us languag and trminology that th customr groups would undrstand and rcognis Idally th rquirmnts should b un-biasd and solution-nutral. You will nd to bias and normalis th rlativ importanc of th customr rquirmnts (as discussd in th lctur). Dlivrabls Clar st of customr rquirmnts (aim for at last 12 distinct rquirmnts) Construct a binary wighting matrix to stablish rlativ importanc. Entr binary dcisions. Construct a spradsht that can invrt th lowr triangular part of th matrix and summat. Us th spradsht to gnrat a st of normalisd rlativ importanc scors. 3

4 Tutorial Exrcis 2 Objctiv To slct a dsign concpt as a candidat to valuat in furthr dtail. To practic idation and filtring. Procdur Th dtail dsign phas of a projct is xpnsiv. In ordr to nsur that you invst ffort in th right concpt you nd to gnrat a larg rang of candidat dsign concpts which adquatly covr th scop of th dsign spac documnt ach concpt as a distinct ntity Filtr out concpts that clarly do not mt any hard constraints that you hav idntifid Rank th rmaining concpts Slct th most highly rankd concpt Tchniqus An important considration is th nd to partition th concpt analysis procss: Stag 1 Th objctiv of th first stag is to gnrat idas. Th succss of this stag is masurd in trms of th rang, novlty and numbr of distinct idas and concpts gnratd. This rquirs a constructiv attitud/ mindst/ atmosphr. Stag 2 Th scond stag concrns slcting th bst ida/concpt in a structurd and logical (auditabl!) way. This nds critical appraisal and rquirs a judgmntal and discriminativ attitud/ mindst/ atmosphr. In an industrial stting it is important to nsur that ths two stags ar divorcd from ach othr as thy ar not complimntary activitis. In many companis th two functions ar undrtakn by two sparat parts of th organisation. 4

5 Tutorial Exrcis 3 Objctiv To idntify th ky dsign paramtrs and, through a mapping procss, idntify th rlativ importanc of ths paramtrs. Procdur You will start with th rankd list of customr rquirmnts and th rlativ importanc factors that you gnratd in Tutorial 2. You will nd to think about th ky dsign variabls and list thm. All of th dsign variabls nd to b masurabl and should b xprssd in trms of a spcific nginring unit such as viscosity, mass, forc tc. You nd to ntr th customr rquirmnts and dsign paramtrs into a spradsht matrix. You nd to idntify and quantify whthr thr is a rlationship btwn ach of th rquirmnt/dsign paramtr pairs. Typically this is xprssd as a variabl btwn 0 and 1. To simplify this mapping procss this is oftn quantisd basd on : strong (0.9), mdium (0.5) and wak (0.1) rlationships. Masur of dsign importanc Using this matrix of mappings you nd to us th spradsht to gnrat a normalisd st of wightings for th st of dsign paramtrs. Sanity chcks Within th mapping matrix ar thr any mpty rows? What might this suggst? Ar thy any mpty columns? What might this suggst? Rank th dsign paramtrs by wighting and try and rationalis this. Ar ths prioritis snsibl? Do thy accord with common sns and judgmnt? You cannot chat by dirctly altring ths but you can rviw th matrix ntris. 5

6 Tutorial Exrcis 4 Objctiv To undrstand th ffct of conflicts within a dsign mapping matrix. To b abl to prform a first-ordr approximation of non-linar mapping functions and to us ths to b abl to undrtak simpl automatd dsign sarch (optimisation). Scnario; A nw aircraft is bing dsignd. A part of th dsign sarch spac concrns tyr slction and a singl dsign paramtr namly th hardnss of th lastomr slctd for th tyr. Elastomr hardnss is masurd using th Shor scals A and D. ( Customr rquirmnts This matrix shows that w ar considring thr customr rquirmnts; How long tyrs last Grip Punctur rsistanc Th rlativ importanc of ach of ths is givn in th matrix shown towards th nd of this sction. 6

7 Rlationship Equations Th thr dfault charactristic mapping functions ar givn blow; Max Min opt whr pv np tol = = = = = = paramtr nutral tolranc pv np np pv 1 point pv tol np valu 2 Procdur Copy th partly filld in matrix into a spradsht. You will notic that thr ar all thr typs of rlationship in this xampl. This suggsts that; For tyr lif lastomr harnss nds to b maximisd For grip lastomr harnss nds to b minimisd For punctur rsistanc lastomr harnss nds to b optimisd around a valu of 80 with a nutral point tolranc of 10. 7

8 Us th quations to calculat th mrit against ach of th rlationships Tak a wightd man of th individual mrit scors using th rlativ importanc of th customr rquirmnts. This rprsnts th ovrall dsign mrit. Th ovrall dsign mrit should rang in valu from 0 to 1. Th highr th valu th bttr as this rprsnts th dgr to which customr rquirmnts ar satisfid. Bcaus this xampl involvs a thr-way trad-off, a compromis has to b rachd in satisfying conflicting customr rquirmnts. An ovrall dsign mrit of 1 is not possibl. Dsign Sarch Th dsign sarch involvs finding th valu of harnss (Valu (pv)) that maximiss th ovrall dsign mrit. You will notic that th matrix includs constraints (U cstrnt, L cstrnt) giving th uppr and lowr bounds for th lastomr hardnss. Your sarch spac should not go byond ths constraints as thy rprsnt, for xampl, th maximum and minimum valus that supplirs can achiv. Microsoft Excl has an add-in that includs a simpl optimisation algorithm (shown blow). This allows an objctiv function, constraints and paramtrs to b spcifid in ordr to find a maximum or minimum. Us solvr to find th optimum valu for th aircraft tyr lastomr hardnss. 8

9 Partly filld in dsign matrix Ovrall Dsign Mrit Elastomr hardnss (Shor A) 0 Valu (pv) U cstrnt L cstrnt Customr rqmt c n rta o p Im tiv R l a ip h s n tio la r f o t h ig W How long tyrs last max Grip min Punctur rsistanc opt ip h s n tio la r f o p y T t in o p t rg /ta l tra u N c n ra l o T rit M rit m d t h ig w 9

10 Tutorial Exrcis 5 Objctiv To intgrat th dsign paramtr mapping, conflict analysis and optimisation using a singl dsign as an illustration. Givn a st of customr rquirmnts and numbr of dsign variabls th objctiv is to maximis th dsign mrit ( goodnss of th dsign). Customr Rquirmnts Th customr rquirmnts you hav bn givn ar. Light wight Good impact rsistanc Good visibility Low nois Easy to put on/rmov Comfortabl 10

11 Dsign paramtrs Th dsign paramtrs and constraints ar Shll thicknss (mm) uppr constraint 8mm, lowr constraint 1mm. Linr thicknss (mm) uppr constraint 40mm, lowr constraint 5mm. Linr dnsity (Kg/m2) uppr constraint 10 Kg/m2, lowr constraint 0.2 Kg/m2. Visor ara (cm2) uppr constraint 200 cm2, lowr constraint 100 cm2. Procdur Carry out a binary wighting matrix to stablish normalisd, biasd, non-linar wightings. Dtrmin strngth of rlationships btwn customr rquirmnts and dsign paramtrs Dtrmin rlationship mapping function btwn customr rquirmnt and dsign paramtr (Max, Min, Opt) Calibrat rlationship function by idntifying nutral points and nutral band tolranc (for opt functions). Calculat th wightd, normalisd, sum of th mapping functions. This rprsnts th ovrall dsign Mrit and should rang from 0 (a dsign that fails to satisfy customr rquirmnts to any dgr) to 1 (a prfct dsign). 11

12 Tutorial Exrcis 6 Objctiv Th objctiv of this xrcis is to plot th valu vctor for a dsign showing th two orthogonal dimnsions of cost and dsign mrit. A hirarchical cost modl will b dvlopd which is abl to ract to changs in th dsign paramtrs. Softwar You will b using a tool calld DcisionPro (Vanguard). This nabls hirarchical calculations to b structurd and prsntd in a logic tr(s blow). matrial cost total matrial pr part matrial cost rat Undfind matrial prparation cost forming procss cost Undfind procss cost mtal rmoval cost hat tratmnt cost Gnric Part cost Surfac tratmnt cost assmbly costs Quality assuranc costs logistics cost transportation packing tooling dsign non_rcurring costs margin Undfind procss planning Undfind CNC programming Undfind Procdur Using th dsign paramtrs givn in tutorial 5 as variabls (assum any othr rlvant dsign variabls ar fixd) crat a cost modl for your motorcycl hlmt. You nd to: Construct a simpl BOM (Bill of Matrial or Product Data-Structur) tr Approximat (guss) th cost factors such as raw matrial, procss costs (at this stag it dos not mattr too much if you gt ths wrong. What is mor important is to gt th modl structur corrct) Crat xprssions (and simpl gomtrical calculations) that caus th cost modl to vary if any of th givn dsign paramtrs vary. 12

13 Stochastic analysis DcisionPro has a vry sophisticatd st of tools to allow snsitivity and uncrtainty analysis to b undrtakn. For uncrtain inputs you might want to put in a stochastic variabl to rprsnt th confidnc intrvals associatd with stat of knowldg of a valu in th cost modl. DcisionPro can thn b usd to undrtak snsitivity analysis and to sampl from stochastic inputs to provid a dpr undrstanding of th cost uncrtaintis for your modl. Valu Vctor If you plot cost against mrit this allows bst valu solutions (masurd by th invrs drivativ of th cost/mrit rlationship) to b idntifid. Ultimatly th combination of cost and mrit-basd dsign modls can b usd to optimis for valu. Cost C Mrit 13

14 Tutorial groups and tams In gnral studnts ar rquird to work individually on th tutorial xrciss. Howvr, is may prov usful to work in small groups to undrtak som of th xrcis. All th xrciss ar individually assssd and thrfor studnts nd to nsur that all work is proprly documntd in individual log books Each studnt must hav copis of all rlvant computr-basd work which thy will b rquird to show to tutors and for which thy nd to dmonstrat undrstanding. For th final cas study studnts will b working in small tams. 14