Pages 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 12952 result(s) returned

1.2.2 Thermoplastics and thermosets

As already stated, polymers including rigid plastics were first developed in the last century from natural precursors. The sealing wax employed by the Victorians, for example, was usually based on the natural polymer shellac, an exudate of the Indian lac insect. Shellac is an early natural thermoplastic – defined as a material which softens and hardens reversibly on heating and cooling. In theory these reversible physical changes will take place without a corresponding change in the chemica
Author(s): The Open University

License information
Related content

Except for third party materials and/or otherwise stated (see terms and conditions) the content in OpenLearn is released for use under the terms of the Creative Commons Attribution-NonCommercial-Share

1.2 Polymer types

Traditionally, the industry has produced two main types of synthetic polymer – plastics and rubbers (Figure 3). The distinction is that plastics are, by and large, rigid materials at service temperatures while rubbers are flexible, low modulus materials which exhibit long-range elasticity. Plastics are further subdivided into
Author(s): The Open University

License information
Related content

Except for third party materials and/or otherwise stated (see terms and conditions) the content in OpenLearn is released for use under the terms of the Creative Commons Attribution-NonCommercial-Share

1 1The growth of poymers

Polymers, or materials composed of long molecular chains, are now well-accepted for a wide variety of applications, both structural and non-structural, and for mass-manufactured as well as one-off speciality products. The growth in their use has continued in the last two decades or more, despite the effects of several recessions in industrial activity (Author(s): The Open University

Learning outcomes

After studying this unit you should be able to:

  • isolate the key design features of a product which relate directly to the material(s) used in its construction;

  • indicate how the properties of polymeric materials can be exploited by a product designer;

  • describe the role of rubber-toughening in improving the mechanical properties of polymers;

  • identify the repeat units of particular polymers and specify the isomeric structures which can e
    Author(s): The Open University

    License information
    Related content

    Except for third party materials and/or otherwise stated (see terms and conditions) the content in OpenLearn is released for use under the terms of the Creative Commons Attribution-NonCommercial-Share

Introduction

Polymers are materials composed of long molecular chains that are well-accepted for a wide variety of applications. This unit explores these materials in terms of their chemical composition, associated properties and processes of manufacture from petrochemicals. The unit also shows a range of products in which polymers are used and explains why they are chosen in preference to many conventional materials.

This unit is from our archive and it is an adapted extract from Design and ma
Author(s): The Open University

License information
Related content

Except for third party materials and/or otherwise stated (see terms and conditions) the content in OpenLearn is released for use under the terms of the Creative Commons Attribution-NonCommercial-Share

References

Checkland, P. (1981) Systems Thinking, Systems Practice, Chichester, Wiley.

Author(s): The Open University

License information
Related content

Except for third party materials and/or otherwise stated (see terms and conditions) the content in OpenLearn is released for use under the terms of the Creative Commons Attribution-NonCommercial-Share

3.3 Types of quantitative systems model

There is a wide range of quantitative models, of varying degrees of sophistication and complication. In this pack, we will only cover those that I think you are likely to encounter in systems studies or could use to good effect. The techniques available subdivide broadly into two major classes, static models and dynamic models. The distinction between these will become clearer as you look at some detailed examples. Essentially, dynamic models are those where the set of calculations comprising
Author(s): The Open University

License information
Related content

Except for third party materials and/or otherwise stated (see terms and conditions) the content in OpenLearn is released for use under the terms of the Creative Commons Attribution-NonCommercial-Share

3.2 Why quantitative models

The stage of choosing a model could include consideration of diagrams or conceptual models as well as quantitative models. So when should you consider a quantitative model as the appropriate next step? There are four main conditions that are necessary for a quantitative model to be an appropriate choice.

  1. At the chosen level of aggregation, all the significant features or behaviours of the system must be adequately quantified, i.e. measured. If this co
    Author(s): The Open University

    License information
    Related content

    Except for third party materials and/or otherwise stated (see terms and conditions) the content in OpenLearn is released for use under the terms of the Creative Commons Attribution-NonCommercial-Share

2.4 Models as part of systems work

Thinking systemically involves identifying systems relevant to some situation, and models are invariably used as part of this process. An example of this forms part of Checklands' Soft Systems Methodology (SSM) (Checkland, 1981). One aspect of this methodology concerns the formulation of a root definition of some system that is relevant to the situation of interest and the construction of a conceptual model of this system. The root definition is a concise, verbal description of what a
Author(s): The Open University

License information
Related content

Except for third party materials and/or otherwise stated (see terms and conditions) the content in OpenLearn is released for use under the terms of the Creative Commons Attribution-NonCommercial-Share

2.2 Mental models: implicit and explicit

We all have mental models of the world in which we live. We have mental models of ‘how X will react if I ask her to do a particular job’, of what would be ‘a nice holiday’, ‘what should happen if I turn up the thermostat on this heater’ and so on. Virtually all these models are so taken-for-granted that we do not even realise that they are models, i.e. that they are simplifications of the complexity around us. The significance of these implicit mental models is that they constrain
Author(s): The Open University

License information
Related content

Except for third party materials and/or otherwise stated (see terms and conditions) the content in OpenLearn is released for use under the terms of the Creative Commons Attribution-NonCommercial-Share

Learning outcomes

After working through these materials you should be able to:

  • describe and use a general classification of models;

  • outline and discuss the process of systems modelling, where models are used as part of a systemic approach to a range of different situations;

  • recognise that systems models may be used in different ways as part of a process for: improving understanding of a situation; identifying problems or formulating opportunities; supporting decision
    Author(s): The Open University

    License information
    Related content

    Except for third party materials and/or otherwise stated (see terms and conditions) the content in OpenLearn is released for use under the terms of the Creative Commons Attribution-NonCommercial-Share

Introduction

Maps and plans, architects‗ and engineers‗ drawings, graphs and tables: all are models we use in everyday life. This unit will introduce you to the modelling process enabling you to recognise that systems models may be used in different ways as part of a process for: improving understanding of a situation; identifying problems or formulating opportunities and supporting decision making.

This unit is from our archive and is an adapted extract from a course which is no longer taught b
Author(s): The Open University

License information
Related content

Except for third party materials and/or otherwise stated (see terms and conditions) the content in OpenLearn is released for use under the terms of the Creative Commons Attribution-NonCommercial-Share

References

Abram, J. (2001) The Contribution of the Product Definition Process to a Successful High Volume Software Application, unpublished MSc dissertation, Milton Keynes, The Open University, p. 48.
Andriole, S.J. and Freeman, P.A. (1993) ‘Software systems engineering: the case for a new discipline’, Software Engineering Journal, vol. 8, no. 3, pp. 165–79. Reprinted in Dorfman and Thayer (1997), pp. 29–
Author(s): The Open University

License information
Related content

Except for third party materials and/or otherwise stated (see terms and conditions) the content in OpenLearn is released for use under the terms of the Creative Commons Attribution-NonCommercial-Share

5.3 The systems engineering methodology used in the course

The aim of systems engineering is to achieve a solution that is effective and sustainable through its life cycle, together with the associated processes and facilities needed to realise the system and introduce it into the real world. Therefore it is important that systems engineering is itself conducted in full consideration of the following five systems:

  • the technology development system that provides new or modified technology for the other systems
    Author(s): The Open University

    License information
    Related content

    Except for third party materials and/or otherwise stated (see terms and conditions) the content in OpenLearn is released for use under the terms of the Creative Commons Attribution-NonCommercial-Share

5.1 Introduction: the general framework

The general framework of systems engineering adopted in the course consists of: a hierarchy of elements; aims associated within its outputs and process; a set of principles; a division into technical and managerial components of the process.

The lexicon of system engineering used in the course contains the hierarchy of elements:

  • strategy: meaning the accumulated decisions concerning the areas in which an organisation operates and its lon
    Author(s): The Open University

    License information
    Related content

    Except for third party materials and/or otherwise stated (see terms and conditions) the content in OpenLearn is released for use under the terms of the Creative Commons Attribution-NonCommercial-Share

4.7 Summary

This topic has examined the historical development of systems engineering and modern concepts of the subject. It has discussed:

  • the beginnings and early development of the subject as policy analysis

  • the use of systems engineering in organisations

  • the development of methodologies associated with information technology.


Author(s): The Open University

License information
Related content

Except for third party materials and/or otherwise stated (see terms and conditions) the content in OpenLearn is released for use under the terms of the Creative Commons Attribution-NonCommercial-Share

4.4 The use of systems engineering in organisations: different organisational arrangements

Hall identified three different organisational arrangements that might provide a framework within which systems engineering work could take place within the organisation. The first of these, which he termed the departmental form and regarded as the lowest level of arrangement, was essentially a temporary team of specialists brought together, under the management of a team leader, to undertake a specific project. The team consisted of members of each of the specialist development departments a
Author(s): The Open University

License information
Related content

Except for third party materials and/or otherwise stated (see terms and conditions) the content in OpenLearn is released for use under the terms of the Creative Commons Attribution-NonCommercial-Share

4.3 The use of systems engineering in organisations

The development of systems engineering was contemporaneous with that of systems analysis in public policy. Though its origins can be traced back to the 1930s and 1940s (Hall, 1962, p. 7), its more widespread application can be dated from the early 1950s. The earliest formal teaching of systems engineering was a course presented in 1950 at the Massachusetts Institute of Technology by G.W. Gilman, who was then Director of Systems Engineering at Bell Laboratories. Gilman was a strong promoter of
Author(s): The Open University

License information
Related content

Except for third party materials and/or otherwise stated (see terms and conditions) the content in OpenLearn is released for use under the terms of the Creative Commons Attribution-NonCommercial-Share

4.2 The use of systems analysis in public policy

The application of mathematical techniques to military operations was pioneered in Britain during the Second World War (see Box 7) and became known by a variety of names (Hoos, 1972, p. 42). At the end of the war, the United States Air Force sponsored the application of those techniques and methods to problems of US national security. Funds to investigate the effects of new weapons systems and for the exploration of defence policy issues were allocated to defence contractors. From one of thes
Author(s): The Open University

License information
Related content

Except for third party materials and/or otherwise stated (see terms and conditions) the content in OpenLearn is released for use under the terms of the Creative Commons Attribution-NonCommercial-Share

4.1 Beginnings

Systems engineering has its roots in three linked strands of thinking: the concepts of systems science, engineering and public policy problem resolution. The first of these can be traced back to the work of von Bertalanffy (1968, pp. 8–15, 96–98) and others during the 1920s and 1930s but received a significant impetus when, in 1954, the Society for General Systems Theory was established at the annual meeting of the American Association for the Advancement of Science. The society later cha
Author(s): The Open University

License information
Related content

Except for third party materials and/or otherwise stated (see terms and conditions) the content in OpenLearn is released for use under the terms of the Creative Commons Attribution-NonCommercial-Share

Pages 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648