در این بخش فایل DEM با دقت 30 متر بخش مرکزی شهرستان شیراز که شامل شهر شیراز نیز می گردد، برای دانلود قرار داده شده است. فایل پیشنمایش این محصول مربوط به آن است و میتواند موقعیت دقیق آن و مناطق تحت پوشش آن را نمایش بدهد.
در این بخش فایل DEM با دقت 30 متر بخش مرکزی شهرستان شیراز که شامل شهر شیراز نیز می گردد، برای دانلود قرار داده شده است. فایل پیشنمایش این محصول مربوط به آن است و میتواند موقعیت دقیق آن و مناطق تحت پوشش آن را نمایش بدهد.
List of contents
1 General introduction..............................................................................................................1
1.1 World fertilizer production and needs..............................................................................1
1.2 Centrifugal spreading in agriculture.................................................................................1
1.3 Need for spreader modelling ............................................................................................3
1.4 Existing spreader models .................................................................................................3
1.5 Introduction DEM in agriculture......................................................................................4
1.6 Objectives of the research ................................................................................................5
1.7 Outline of the research .....................................................................................................6
2 The Discrete Element Method...............................................................................................7
2.1 Introduction ......................................................................................................................7
2.2 DEM Algorithm flow .......................................................................................................8
2.3 Model parameter settings .................................................................................................9
2.4 Initializing the simulation.................................................................................................9
2.5 Contact resolution ..........................................................................................................11
2.5.1 Introduction ............................................................................................................11
2.5.2 Sphere-sphere contact ............................................................................................11
2.5.3 Sphere-rectangle contact ........................................................................................12
2.5.4 Sphere-cylinder contact..........................................................................................13
2.5.5 Sphere-disc contact ................................................................................................14
2.5.6 Contact with edges .................................................................................................16
2.6 Search algorithms...........................................................................................................18
2.7 Force calculation in DEM simulations...........................................................................19
2.7.1 Introduction ............................................................................................................19
2.8 Normal contact force models .........................................................................................22
2.8.1 Introduction ............................................................................................................22
2.8.2 The Kelvin–Voight model......................................................................................23
2.8.3 The Kono-Kuwabara model ...................................................................................23
2.8.4 Other normal contact models .................................................................................26
2.9 Tangential contact forces ...............................................................................................26
2.9.1 Introduction ............................................................................................................26
2.9.2 Linear model implementation ................................................................................27
2.10 Moments of forces..........................................................................................................29
2.11 Body Forces....................................................................................................................30
2.11.1 Aero dynamical drag force.....................................................................................30
2.11.2 Magnus effect.........................................................................................................31
2.12 Time integration algorithms ...........................................................................................31
2.12.1 Introduction ............................................................................................................31
2.12.2 Integration of Newton’s second law.......................................................................32
2.12.3 Euler method ..........................................................................................................32
2.12.4 Leapfrog method ....................................................................................................33
List of contents viii
2.12.5 Other integrators.....................................................................................................33
2.12.6 Choice of the time step...........................................................................................34
2.12.7 Integration of Euler’s law.......................................................................................35
2.12.8 Leapfrog integration...............................................................................................38
2.12.9 Integration errors ....................................................................................................38
2.13 Program overview ..........................................................................................................40
2.14 Conclusions ....................................................................................................................40
3 Particle measuring methods as input for numerical models............................................42
3.1 Introduction ....................................................................................................................42
3.2 Particle mass ( p m ) ........................................................................................................43
3.3 Particle radius ( p R ) and shape .......................................................................................43
3.3.1 Manual procedure...................................................................................................43
3.3.2 Automatic procedure ..............................................................................................44
3.3.3 Particle shape approximation .................................................................................45
3.3.4 Surface roughness ..................................................................................................50
3.4 Particle density (ρ ) p .....................................................................................................52
3.5 Particle stiffness (k ) ....................................................................................................52
3.5.1 Stiffness for sphere-sphere indenting.....................................................................53
3.5.2 Stiffness for sphere-cylinder indenting ..................................................................53
3.6 Particle damping coefficient (c) and restitution coefficient (e) ..................................54
3.6.1 Sphere-sphere damping ..........................................................................................58
3.7 Particle fracture resistance ( ) max N ................................................................................58
3.7.1 Impact with vanes and vane edges .........................................................................61
3.7.2 Static pressure in the bin ........................................................................................62
3.8 Particle friction coefficient (μ ) .....................................................................................62
3.8.1 Wall-particle friction ( wp μ ) ...................................................................................63
3.8.2 Particle-particle friction ( pp μ )................................................................................64
3.8.3 Static friction ..........................................................................................................65
3.9 Particle Aerodynamical drag coefficient ( d C ) ...............................................................65
3.10 Errors of the measurement methods...............................................................................66
3.11 Conclusions ....................................................................................................................67
4 Single particle simulations...................................................................................................68
4.1 Introduction ....................................................................................................................68
4.2 Comparison with analytical models ...............................................................................68
4.2.1 The rolling and friction force .................................................................................68
4.2.2 The centrifugal force ..............................................................................................71
4.2.3 The Coriolis force...................................................................................................73
4.3 Experimental methods....................................................................................................74
4.4 Experimental verification of single particle trajectories ................................................75
4.5 Analysis of the rotational motion in single particle trajectories.....................................79
4.6 Analysis of bouncing in single particle trajectories .......................................................83
4.7 Non - spherical particle simulations...............................................................................86
List of contents ix
4.8 Conclusions ....................................................................................................................88
5 Multi particle simulations....................................................................................................89
5.1 Introduction ....................................................................................................................89
5.2 Materials and methods ...................................................................................................90
5.2.1 Introduction ............................................................................................................90
5.2.2 Cylindrical measurements ......................................................................................90
5.2.3 Rectangular measurements (TSP) ..........................................................................91
5.2.4 Fertilizer choice and property measurements.........................................................93
5.2.5 Choice of disc type and bin ....................................................................................96
5.3 Computational setup.......................................................................................................99
5.3.1 Introduction ............................................................................................................99
5.3.2 Initial conditions in the bin...................................................................................100
5.3.3 Spinning disc simulations.....................................................................................103
5.3.4 Ballistic model......................................................................................................104
5.3.5 Model output variables.........................................................................................104
5.3.6 Characterisation time of the simulated pattern.....................................................104
5.3.7 Sensitivity to bin filling........................................................................................105
5.4 Results and discussion..................................................................................................105
5.4.1 Cylindrical spread pattern measurements ............................................................105
5.4.2 TSP measurements ...............................................................................................111
5.5 Conclusions of the experiments ...................................................................................118
6 Model parameter sensitivity..............................................................................................120
6.1 Introduction ..................................................................................................................120
6.2 Definition of sensitivity................................................................................................120
6.3 Influence of friction coefficient....................................................................................123
6.3.1 Particle-wall friction.............................................................................................123
6.3.2 Particle-particle friction........................................................................................128
6.3.3 Conclusion on friction coefficients ......................................................................129
6.4 Influence of elasticity and damping .............................................................................130
6.4.1 Influence of particle stiffness ...............................................................................130
6.5 Influence of bulk flow ..................................................................................................132
6.5.1 Flow rate...............................................................................................................133
6.5.2 Influence of orifice shape.....................................................................................134
6.6 Influence of particle diameter and segregation ............................................................136
6.6.1 Particle diameter...................................................................................................136
6.6.2 Segregation...........................................................................................................140
6.7 Influence of particle shape ...........................................................................................141
6.7.1 Introduction ..........................................................................................................141
6.7.2 Results ..................................................................................................................143
6.8 External forces..............................................................................................................146
6.9 Interaction of parameters..............................................................................................147
6.9.1 Friction - particle shape........................................................................................148
6.9.2 Friction - bulk flow rate .......................................................................................149
6.9.3 Bulk flow segregation ..........................................................................................149
6.9.4 Friction – working width......................................................................................151
6.10 Particle interception......................................................................................................151
6.11 Discussion on sensitivity...........................................................................................152
List of contents x
6.12 Conclusions ..................................................................................................................159
7 Case study: DEM simulations of a new concept for lawn spreaders.............................161
7.1 Introduction ..................................................................................................................161
7.2 Situation and current technology..................................................................................161
7.3 Design of the new concept ...........................................................................................162
7.4 Flow rate regulation of the pocket system ...................................................................163
7.5 DEM simulations..........................................................................................................166
7.5.1 Introduction ..........................................................................................................166
7.5.2 Simulation of ideal conditions, current technology .............................................167
7.5.3 Simulation of modified conditions.......................................................................168
7.6 Conclusions ..................................................................................................................170
8 General conclusions and future outline............................................................................171
8.1 General conclusions .....................................................................................................171
8.2 Suggestions for future work .........................................................................................174
9 Bibliography .......................................................................................................................177
مدل DEM نقشه رقومی ارتفاعی است که پستی و بلندی زمین را توسط یک شبکه سلولی نمایش می‌دهد. هر سلول (پیکسل) از این شبکه با یک کد رقمی که نشاندهنده ارتفاع واقعی آن نقطه میباشد مشخص می‌گردد. در این مدل هر خط یا سطح تراز زمین با یک رنگ خاص نمایش داده می‌شود. مدل DEM هم بصورت دو بعدی و هم بصورت سه بعدی قابل نمایش در محیط GIS میباشد. لازم به ذکر است که مدل DEM بعنوان مبنای کار آنالیزها در آرک ویو میباشد.
DEM چیست؟ تین ( TIN ) نوعی مدل میباشد .ساختار یک لایه تین از نود ( نقطه ) و خطوط تشکیل شده است. نود هاارزش ارتفاعی را ذخیره میکنند و توسط خطوطی ( edge) به هم متصل میشوند .
این خطوط هیچ گاه به روی همدیگر نمیافتند و نمایی مثلثی شکل به مدل میدهند.خطوط در یک نقشه تین میتواند نشان دهنده آبراهه یا ستیغ باشد .چون توزیع نود ها در سطح نامنظم است ، در نواحی که سطح بسیار متغیر است و یا مواقعی که دقت و جزییات زیادی لازم است ، تین قدرت تفکیک بالاتری نسبت به رستر دارد .در نواحی که لایه مورد نظر تغییرات کمی داشته باشد ( یکنواخت باشد . مثلا تغییراتارتفاع کم باشد ) . دقت لایه های نوع تین کمتر است .از جمله مشکلاتی که برای ایجاد این نوع مدل وجود دارد ،این است که هزینه جمع آوری داده های منبع ( اولیه ) مناسب برای ایجاد تین زیاد است .همچنین پردازش این نوع مدل ها از کارایی و کیفیت کمتری نسبت به رستر برخوردار است که به خاطر پیچیدگی ساختار داده های تین میباشد .معمولا تین ها برای مدل سازی با دقت بالا در نواحی کوچک به کار میروند. مثلادر انجام کار های مهندسی .چار که محاسبات مساحت پلانیمتری ، مساحت سطحی و حجم را می سر میسازد.