Chapter 5 Concluding Remarks
5.2 Recommendation for the future work
Based on the studies presented in this thesis, several important future works are outlined as follows:
1. To study more detailed collision dynamics of the pair droplets considering the followings, but not limited to:
i. Size effects of the two droplets;
ii. Relative sizes effects of the two droplets;
iii. Parametric effects of the inter-atomic potential between droplet and background gas;
iv. Rotational effects of the colliding droplets;
v. More realistic intermolecular potential models such as REBO [Brenner et. al., 2002] for hydrocarbon droplets;
2. To study multi-droplet collision dynamics under various kinds of test conditions, for example, three-droplet collision;
3. To study the droplet-solid collisions under various kinds of conditions;
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Tables
* System of Units Used in Soft-Sphere Molecular Dynamics Programs * Fundamental Quantities:
Mass m = mass of one atom Length σ
Energy ε Time σ m/ε
Derived Quantities:
Adiabatic compressibility ks* =ksε/σ3
Configurational internal energy Uc* =Uc/Nε = u* = u/Nε Density ρ* =Nσ3/V
Force F* =Fσ/ε Heat capacity Cv* =Cv/Nk Radial position r* =r/σ Pressure P* =Pσ3 /ε Temperature T* =kT/ε Thermal pressure coefficient γv* =γvσ3/k Total energy E* =E/Nε
Velocity υ* =υ m/ε
Table. 1 nondimensionalize
Temp.(T*) Density (ρ*) No. of Link-cells
condensed 0.7 0.7 75*75*75
vaporized 1.1 0.7 75*75*75
supercritical 0.7 0.7 39*39*39
Table. 2 Simulation conditions for three different cases via PCMD code (condensed, vaporized and supercritical states).
(a)
(b)
(c)
(d)
Figures
Fig. 1. 1 Terminology of possible droplet-droplet collision outcome, (a) bounce, (b) coalescence, (c) disruption and (d) fragmentation.
(Fig of Pan, K. L. and Law, C. K., The 42nd AIAA Aerospace Sciences Meeting & Exhibit.)
Fig. 1. 2 Schematic of different droplet collision regimes as function of Weber number (We) and impact number (b).
Fig. 2. 1 Cartesian frame
X Y
Z
O
r
iatom i
Fig. 2. 2 Lennard-Jones (LJ) pairwise intermolecular potential
Repulsive
Attractive force
O
(distance between atoms)X Y
potential u*(r)
force f*(r)
Fig. 2. 3 Water molecules i and j.
H
4H
3H
1H
2O
5O
6r
56i
j
-2q -2q
q q
q q
M
7M
8r
OH=0.09572 nm r
OM=0.024994 nm
∠HOH=104.52
Fig. 2. 4 periodic boundary conditions
(a)
(b)
(c)
Fig. 2. 5 (a.)all pair, (b)cell link, and (c)Verlet list methods
Fig. 2. 6 Verlet list
Fig. 2. 7 Verlet +Cell link
Fig. 2. 8 Surface tension concept by Tabor [1991]
Start
velocities of atoms in the neighbor list
Compute force
Send force data to other atoms in the neighbor list
Integrate to update positions & velocities of atoms
Apply boundary conditions
Fig.3. 1 Proposed flow chart for parallel molecular dynamics simulation using dynamic domain decomposition.
(a)
(b)
(c)
Fig. 3. 1 Evolution of domain decomposition for large problem size using 25 processors at start and final. (a) condensed state; (b) vaporized state; (c) supercritical state.
0 50000 100000
Atoms number per CPU. upper threshold value (+20%).
lower threshold value (-20%).
(a)
Atoms number per CPU. upper threshold value (+20%).
lower threshold value (-20%).
(b)
Atoms number per CPU. upper threshold value (+20%).
lower threshold value (-20%).
(c)
Fig.3.3 Distribution of the number of atoms in each processor as a function of simulation time steps (25 processors). (a) condensed state; (b) vaporized state; (c) supercritical state.
0 10 20 30 40 50
Number of Processors
0 10 20 30 40 50
Speedup
Ideal speedup Condensed Vaporized Supercritical
Vaporized (non-repartition **)
Sym. Data*
* 1million L-J atoms
** non-repartition after 30,000 steps
Fig.3.4 Parallel speedup as a function of the number of processors for three different test cases (condensed, vaporized and supercritical states).
0 500 1000 1500
Relative Velocity(m/sec) 0
25 50 75 100
b (A)
Droplet-Collision under V acuum:
Direct Coalescence Strecting Separation Shattering
Fig. 4. 1 Distribution map of various regimes under vacuum ambient.
0 500 1000 1500 Relative Velocity (m/sec)
0 25 50 75 100
b (A)
Droplet-Collision under 0.055atm ambient gas:
Direct Coalescence Stretching Coalescence Stretching Separation Shattering
Fig. 4. 2 Distribution map of various regimes under low pressurized ambient (~0.055 atm).
0 500 1000 1500 Relative Velocity (m/sec)
0 25 50 75 100
b (A)
Droplet-Collision under 0.55atm ambient gas:
Direct Coalescence Stretching Coalescence Stretching Separation Shattering
Fig. 4. 3 Distribution map of various regimes under high pressurized ambient (~0.55 atm).
40 80 120 160 200 Time-Step
0 0.02 0.04 0.06 0.08
Evaporation Rate (%)
Evaporation rate:
Vacuum
Low pressurized ambient (0.055 atm) High pressurized ambient (0.55 atm)
Fig. 4. 4 The evaporation rate of simulation case which b=0.25 V=250 m/s, under vacuum, low pressurized ambient and high pressurized ambient, respectively.
(a) (b)
(c) (d)
Fig. 4.5 Head-on (b= 0) droplets pair collision initial setup, (a) y-z plane without vapor ambient, (b) x-z plane without vapor ambient, (c) y-z plane under vapor ambient, (d) x-z plane under vapor ambient
(a)
(b)
Fig. 4.6 Non-head-on (ex; b= 0.5) droplets pair collision initial setup, (a) x-y plane without vapor ambient, (b) x-y plane under vapor ambient.
(a) (b)
(c) (d)
(e) (f)
Fig. 4.7 Snapshot of droplet pair collision under vacuum b=0 V=1250 m/s, at (a)10ps, (b)50ps, (c)75ps, (d)100ps, (e)125ps, (f)175ps.
(a) (b)
(c) (d)
(e) (f)
Fig. 4.8 Snapshot of droplet pair collision under vacuum, b=0, V=1375 m/s, at (a)10ps, (b)40ps, (c)75ps, (d)150ps, (e)200ps, (f)300ps.
(a) (b)
(c) (d)
(e) (f)
Fig. 4.9 Snapshot of droplet pair collision under vacuum, b=0, V=1500 m/s, at (a)10ps, (b)30ps, (c)75ps, (d)100ps, (e)175ps, (f)300ps.
(a) (b)
(c) (d)
(e) (f)
Fig. 4.10 Snapshot of droplet pair collision under low pressurized ambient (~0.055 atm), b=0, V=1250 m/s, at (a)10ps, (b)40ps, (c)75ps, (d)100ps, (e)125ps, (f)200ps.
(a) (b)
(c) (d)
(e) (f)
Fig. 4.11 Snapshot of droplet pair collision under low pressurized ambient (~0.055 atm), b=0, V=1375 m/s, at (a)10ps, (b)40ps, (c)75ps, (d)100ps, (e)150ps, (f)250ps.
(a) (b)
(c) (d)
(e) (f)
Fig. 4.12 Snapshot of droplet pair collision under low vapor ambient, b=0, V=1500 m/s, at (a)10ps, (b)40ps, (c)60ps, (d)90ps, (e)150ps, (f)250ps.
(a) (b)
(c) (d)
(e) (f)
Fig. 4.13 Snapshot of droplet pair collision under high vapor ambient, b=0, V=1250 m/s, at (a)10ps, (b)40ps, (c)75ps, (d)100ps, (e)125ps, (f)200ps.
(a) (b)
(c) (d)
(e) (f)
Fig. 4.14 Snapshot of droplet pair collision under high vapor ambient, b=0, V=1375 m/s, at (a)10ps, (b)40ps, (c)75ps, (d)100ps, (e)250ps, (f)325ps.
(a) (b)
(c) (d)
(e) (f)
Fig. 4.15 Snapshot of droplet pair collision under high vapor ambient, b=0, V=1500 m/s, at (a)10ps, (b)40ps, (c)60ps, (d)90ps, (e)150ps, (f)250ps.
(a) (b)
(c) (d)
(e) (f)
Fig. 4.2 Snapshot of droplet pair collision under vacuum, b=0.25, V=250 m/s, at (a)10ps, (b)50ps, (c)100ps, (d)200ps, (e)250ps, (f)375ps. This case is classified in Coalescence regime.
(a) (b)
(c) (d)
(e) (f)
Fig. 4.3 Snapshot of droplet pair collision under vacuum, b=0.625, V=1000 m/s, at (a)10ps, (b)40ps, (c)75ps, (d)100ps, (e)150ps, (f)250ps. This case is classified in Stretching Separation regime.
(a) (b)
(c) (d)
(e) (f)
Fig. 4.4 Snapshot of droplet pair collision under vacuum b=0.25, V=1375 m/s, at (a)10ps, (b)40ps, (c)75ps, (d)100ps, (e)150ps, (f)250ps. This case is classified in Shattering regime.
(a) (b)
(c) (d)
(e) (f)
Fig. 4.5 Snapshot of droplet pair collision under low pressurized ambient,
b=0.25, V=250 m/s, at (a)10ps, (b)50ps, (c)100ps, (d)200ps, (e)250ps, (f)375ps. This case is classified in Coalescence regime.
(a) (b)
(c) (d)
(e) (f)
Fig. 4.20 Snapshot of droplet pair collision under low pressurized ambient, b=0.25, V=750 m/s, at (a)10ps, (b)40ps, (c)75ps, (d)150ps, (e)250ps, (f)500ps. This case is classified in Stretching Coalescence regime.
(a) (b)
(c) (d)
(e) (f)
Fig. 4.21 Snapshot of droplet pair collision under low pressurized ambient, b=0.625, V=1000m/s, at (a)10ps, (b)40ps, (c)75ps, (d)100ps, (e)150ps, (f)250ps.
This case is classified in Stretching Separation regime.
(a) (b)
(c) (d)
(e) (f)
Fig. 4.22 Snapshot of droplet pair collision under low pressurized ambient, b=0.
25, V=1375m/s, at (a)10ps, (b)40ps, (c)75ps, (d)100ps, (e)150ps, (f)250ps. This case is classified in Shattering regime.
(a) (b)
(c) (d)
(e) (f)
Fig. 4.23 Snapshot of droplet pair collision under high pressurized ambient, b=0.25, V=250 m/s, at (a)10ps, (b)50ps, (c)100ps, (d)200ps, (e)250ps, (f)375ps. This case is classified in Coalescence regime.
(a) (b)
(c) (d)
(e) (f)
Fig. 4.24 Snapshot of droplet pair collision under high pressurized ambient, b=0.25, V=750 m/s, at (a)10ps, (b)40ps, (c)75ps, (d)150ps, (e)250ps, (f)500ps. This case is classified in Stretching Coalescence regime.
(a) (b)
(c) (d)
(e) (f)
Fig. 4.25 Snapshot of droplet pair collision under high pressurized ambient, b=0.625, V=1000m/s, at (a)10ps, (b)40ps, (c)75ps, (d)100ps, (e)150ps, (f)250ps.
This case is classified in Stretching Separation regime.
(a) (b)
(c) (d)
(e) (f)
Fig. 4.26 Snapshot of droplet pair collision under high pressurized ambient, b=0.25, V=1500m/s, at (a)10ps, (b)40ps, (c)75ps, (d)100ps, (e)150ps, (f)250ps. This case is classified in Shattering regime.
(a) (b)
(c) (d)
(e) (f)
Fig. 4.27 Snapshot of droplet pair collision under high pressurized ambient, b=0, V=10 m/s, at (a)25ps, (b)250ps, (c)500ps, (d)750ps, (e)1000ps, (f)1250ps. This case is classified in Bounce regime.
(a) (b)
(c) (d)
(e) (f)
Fig. 4.28 Snapshot of droplet pair collision under high pressurized ambient, b=0, V=30 m/s, at (a)25ps, (b)250ps, (c)500ps, (d)750ps, (e)1000ps, (f)1250ps. This case is classified in Bounce regime.
(a) (b)
(c) (d)
(e) (f)
Fig. 4.29 Snapshot of droplet pair collision under high pressurized ambient (0.55 atm, T=324K ), b=0, V=10 m/s, at (a)25ps, (b)250ps, (c)500ps, (d)750ps, (e)1000ps, (f)1200ps. This case is classified in Bounce regime.
(a) (b)
(c) (d)
(e) (f)
Fig. 4.30 Snapshot of droplet pair collision under high pressurized ambient (0.55 atm, T=324K ), b=0, V=30 m/s, at (a)25ps, (b)250ps, (c)500ps, (d)750ps, (e)1000ps, (f)1250ps. This case is classified in Bounce regime.
0 4000 Size of Fragments8000 12000 16000 20000
Fig. 4.31 Snapshot of density contour and clusters size distribution under vacuum, b=0, V=1250 m/s, at (a)25ps, (b)75ps, (b)150ps. This case is classified in Stretching Coalescence regime.
4000 Size of Fragment8000 12000 16000 20000
Fig. 4.32 Snapshot of density contour and clusters size distribution under low pressurized ambient, b=0, V=1250 m/s, at (a)25ps, (b)75ps, (b)150ps. This case is classified in Stretching Coalescence regime.
4000 Size of Fragment8000 12000 16000 20000
Fig. 4.33 Snapshot of density contour and clusters size distribution under high pressurized ambient, b=0, V=1250 m/s, at (a)25ps, (b)75ps, (b)150ps. This case is classified in Stretching Coalescence regime.
0 4000 Size of Fragments8000 12000 16000 20000
Fig. 4.34 Snapshot of density contour and clusters size distribution under vacuum, b=0, V=1500 m/s, at (a)25ps, (b)75ps, (b)150ps. This case is classified in Shattering regime.
4000 Size of Fragment8000 12000 16000 20000
Fig. 4.35 Snapshot of density contour and clusters size distribution under low pressurized ambient, b=0, V=1500 m/s, at (a)25ps, (b)75ps, (b)150ps. This case is classified in Shattering regime.
4000 Size of Fragment8000 12000 16000 20000
Fig. 4.36 Snapshot of density contour and clusters size distribution under high pressurized ambient, b=0, V=1500 m/s, at (a)25ps, (b)75ps, (b)150ps. This case is classified in Shattering regime.
0 100 200 300 400 500
Fig. 4.37 Measurements of largest fragment of droplet pair collision under vacuum, b=0.25, V=250 m/s, (a)Number of atoms, (b)Vibrational temperature (k), (c)Rotational energy, (d)Angular momentum, respectively. This case is classified in Coalescence regime.
0 100 200 300 400
Fig. 4.38 Measurements of largest fragment of droplet pair collision under
vacuum, b=0.625, V=1000 m/s, (a)Number of atoms, (b)Vibrational temperature (k), (c)Rotational energy, (d)Angular momentum, respectively. This case is classified in Stretching Separation regime.
0 100 200 300
Fig. 4.39 Measurements of largest fragment of droplet pair collision under
vacuum, b=0.25, V=1375 m/s, (a)Number of atoms, (b)Vibrational temperature (k), (c)Rotational energy, (d)Angular momentum, respectively. This case is classified in Shattering regime.
0 100 200 300 400 500
Fig. 4.40 Measurements of largest fragment of droplet pair collision under low pressurized ambient, b=0.25, V=250 m/s, (a)Number of atoms, (b)Vibrational temperature (k), (c)Rotational energy, (d)Angular momentum, respectively. This case is classified in Coalescence regime.
0 200 400 600
Fig. 4.41 Measurements of largest fragment of droplet pair collision under low pressurized ambient, b=0.25, V=750 m/s, (a)Number of atoms, (b)Vibrational temperature (k), (c)Rotational energy, (d)Angular momentum, respectively. This case is classified in Stretching Coalescence regime.
0 100 200 300 400
Fig. 4.42 Measurements of largest fragment of droplet pair collision under low pressurized ambient, b=0.625, V=1000m/s, (a)Number of atoms, (b)Vibrational temperature (k), (c)Rotational energy, (d)Angular momentum, respectively. This case is classified in Stretching Separation regime.
0 100 200 300
Fig. 4.43 Measurements of largest fragment of droplet pair collision under low pressurized ambient, b=0.25, V=1375m/s, (a)Number of atoms, (b)Vibrational temperature, (c)Rotational energy, (d)Angular momentum, respectively. This case is classified in Shattering regime.
0 100 200 300 400 500
Fig. 4.44 Measurements of largest fragment of droplet pair collision under high pressurized ambient, b=0.25, V=250 m/s, (a)Number of atoms, (b)Vibrational temperature (k), (c)Rotational energy, (d)Angular momentum, respectively. This case is classified in Coalescence regime.
0 200 400 600
Fig. 4.45 Measurements of largest fragment of droplet pair collision under high pressurized ambient, b=0.25, V=750 m/s, (a)Number of atoms, (b)Vibrational temperature (k), (c)Rotational energy, (d)Angular momentum, respectively. This case is classified in Stretching Coalescence regime.
0 100 200 300 400
Fig. 4.46 Measurements of largest fragment of droplet pair collision under high pressurized ambient, b=0.625, V=1000m/s, (a)Number of atoms, (b)Vibrational temperature (k), (c)Rotational energy, (d)Angular momentum, respectively. This case is classified in Stretching Separation regime.
0 50 100 150 200 250
Fig. 4.47 Measurements of largest fragment of droplet pair collision under high pressurized ambient, b=0.25, V=1500m/s, (a)Number of atoms, (b)Vibrational temperature, (c)Rotational energy, (d)Angular momentum, respectively. This case is classified in Shattering regime.
0 200 400 600
Fig. 4.48 Measurements of largest fragment of droplet pair collision under high pressurized ambient, b=0, V=30m/s, (a)Number of atoms, (b)Vibrational
temperature (k), (c)Rotational energy, (d)Angular momentum, respectively. This case is classified in Bouncing regime.
50 60 70 100
1000 10000
100 1000 10000
Atoms distributed at various time (PS):
25 250 500 750 1000 1250
Fig. 4.49 The atoms distributions in X direction of bounce case under high pressurized ambient, b=0, V=10 m/sec.
50 60 70 100
1000 10000
100 1000 10000
Atoms distributed at various time (PS):
25 250 500 750 1000 1250
Fig. 4.50 The atoms distributions in X direction of bounce case under high pressurized ambient, b=0, V=30 m/sec..
50 60 70
Position of X-Axis
100 1000 10000
Number of atoms
100 1000 10000
Atoms distributed at various time (PS):
25 250 500 750 1000 1250
Fig. 4.51 The atoms distributions in X direction of bounce case under high pressurized ambient (0.55 atm, T=324 K), b=0, V=10 m/sec.
50 60 70
Position of X-Axis
100 1000 10000
Number of atoms
Atoms distributed at various time (PS):
25 250 500 750 1000 1250
100 1000 10000
Fig. 4.52 The atoms distributions in X direction of bounce case under high pressurized ambient(0.55 atm, T=324 K), b=0, V=30 m/sec..
Fig. 4.53 The variation of surface tensions distributions of coalescence case under low pressurized ambient (0.055 atm, T=216 K), b=0.25, V=750 m/sec..
T=2.5 ps
T=5 ps
T=7.5 ps
T=10 ps
T=50 ps
T=150 ps
T=250 ps
T=500 ps
Fig. 4.54 The variation of surface tensions distributions of separation case under low pressurized ambient (0.055 atm, T=216 K), b=0.625, V=1000 m/sec..
T=10 ps T=40 ps
T=75 ps T=100 ps
T=250 ps T=150 ps
.
Fig. 4.55 The variation of surface tensions distributions of bouncing case under low pressurized ambient (0.055 atm, T=216 K), b=0, V=30 m/sec..
T=250 ps
T=750 ps
T=1000 ps
Autobiography
Yu-Lin Hsu (許 祐 霖)
Phone:+886-3-5712121-55175 E-mail:[email protected]
Education:
1999-Pressent PhD Program in Mechanical Engineering,
National Chiao-Tung University, Hsin-chu, Taiwan The research emphasized on numerical methods of the Parallel Cellular Molecular Dynamics simulation (PCMD) code and analysis the Droplet-Droplet collision dynamics by using the PCMD code.
1997-1999 M. S. in Mechanical Engineering,
Chung-Yuan Christian University, Chung-Li, Taiwan The research emphasized on numerical analysis by using the Molecular Dynamics simulation method for studying the rupture process of thin polymer solution films.
1995-1997 B. S. in Mechanical Engineering,
Yuan-Ze College of Engineering, Chung-Li, Taiwan
Language:
Mandarin Chinese, Taiwanese and English
List of Publications
Referred Papers:
1. J.-S. Wu, and Y.-L. Hsu, “Derivation of VSS model Parameters in Direct Simulation Monte Carlo Method Using Quantum Chemistry Computation,”
Japanese Journal of Applied Physics, Vol. 42, pp.7574-7575, 2003.
2. J.-S. Wu, Y.-L. Hsu and Y.-M. Lee, “Parallel Implementation of Molecular Dynamics Simulation for Short-Ranged Interaction,” Computer Physics Communications, Vol. 170, pp. 175-185, 2005.*
3. Y.-L. Hsu, C.-H. Chiang, Y.-M. Lee and J.-S. Wu, “MD Simulation of Two Colliding Nanoscale Argon Droplets Under Vacuum and Pressurized
Environments,” 2006 (Preparing).*
4. Y.-L. Hsu, C.-H. Chiang, Y.-M. Lee and J.-S. Wu, “MD Simulation of Two Bouncing Nanoscale Argon Droplets,” 2006 (Preparing).*
International Conference Papers:
1. Y.-L. Hsu, J.-S. Wu, C.-H. Chiang and Y.-M. Lee, “MD Simulation of Two Colliding Nanoscale Argon Droplets Under Vacuum and Pressurized
Environments,” 25th Internal Symposium on Rarefied Gas Dynamics, July 21- 28, 2006, Saint-Petersburg, Russia.*
National Conference Papers:
1. J.-S. Wu, Y.-L. Hsu and U.-M. Lee, “平行化分子動力學模擬方法之發展 (Parallel Cellular Molecular Dynamics Simulation for Short-Ranged
Interaction),” The 11th National Computational Fluid Dynamics Conference (0405), 2004.*
2. J.-S. Wu, J.-S. Wu, U.-M. Lee and Y.-L. Hsu, “Argon 離子轟擊引致銅濺現象 之分子動力學模擬(Molecular Dynamics Simulation of Sputtering of Copper Atoms Due to Argon Ion Bombardment),” The 11th National Computational Fluid Dynamics Conference (1504), 2004.
(* are those presented in this thesis)