Tomoya Omata
January 13, 2022
51

# Research_kosen

January 13, 2022

## Transcript

1. Advanced CC Engineering Course, National Institute of Technology, Kisarazu College
Department of Civil Engineering, National Institute of Technology, Kisarazu College
Simulation of water droplet movements on the surface
by means of MPS
TOMOYA OMATA
TATEKI ISHII
The deterioration on the structure by salt damage is being currently at issue and
therefore numerical simulation on prediction of salt adhesion on the structure
surface was performed. However, there are currently many studies that focus on
the transportation of sea-salt particles caused by the wind. Salt damage impact
that rainwater gives to the structure surface in seashore vicinity is different from
that in the upcountry rejoin, but, in both areas, the deterioration degree of the
structure tends to depend on the raindrop movements. In addition, its
movements vary depending on droplet size, the adhesion behavior simulation
that assumed every raindrop size is needed.
INTRODUCTION
SUMMARY
DEFORMATION BEHAVIOR SIMULATION
The main influence of raindrop adhesion
Seashore vicinity
Upcountry region
The sea
Rainwater : Purifying action
Structure
Sea salt particles By wind
Rainwater : Salt damage
By rain
Young’s formula
MPS METHOD
MPS Method : The calculation method to be able to reproduce a fluid interface clearly
▼ Governing equation
p This method calculate by considering a distance between
particles (𝑟) in effective radius (𝑟!
) as heaviness.
𝛾! : Interfacial energy of solid
1
𝜌
𝐷𝒖
𝐷𝑡
= −𝛻𝑃 + 𝜇𝛻!𝒖 + 𝒇
implicit explicit
▼ Surface tension model
𝑟#\$%: Initial distance between
particles
▼ Particle interaction model
p The surface tension of the droplet on the surface is
reproduced by using the potential between particles.
▼ Wettability model of the solid wall
𝑷 𝒓 : Potential between the liquid particles
𝑃 𝑟
𝑃 𝑟
𝑃 𝑟 : Attractive force
𝑟 > 𝑟#\$%
𝑃 𝑟 : Repulsive force
𝑟 ≤ 𝑟#\$%
p Wettability of the solid wall depicts in contact angle
defined in Young’s formula.
p The potential of wettability acts to form the contact
angle inputted.
𝛾"
− 𝛾#"
− 𝛾#
𝑐𝑜𝑠𝜃 = 0
Solid wall
𝑟 : Distance between particles
𝛾&! : Interfacial energy between fluid and solid
𝛾& : Interfacial energy of fluid
▼ Consideration
0.1s later…
Droplet size 𝐦𝐦𝟑 2-5
Number of particles 125
Mass density of the fresh water kg/m# 1000
Mass density of the salt water kg/m# 1030
Kinematic viscosity of fluid P + s
1.36
×10\$#
Gravity acceleration m%/s 9.8
Effective radius of surface tension model 2.1×𝑟&'(
Time step s 1.0×10\$)
Surface tension coefficient N/m 0.0728
Contact angle ° 90
Table.1 Calculation condition
Fig.1. Measurement result of the droplet thickness for the droplet size
▼ Measurement result of droplet thickness
(a) 𝑉 = 2mm3 (b) 𝑉 = 3mm3
(c) 𝑉 = 4mm3 (d) 𝑉 = 5mm3
(a) 𝑉 = 2mm3 (b) 𝑉 = 3mm3
(c) 𝑉 = 4mm3 (d) 𝑉 = 5mm3
▼ Visualization of the adhesion behavior
▼ Condition
Fig.2. Comparison of the fresh water droplet behavior by the droplet size
Fig.3. Comparison of the salt water droplet behavior by the droplet size
This research simulated the adhesion behavior of the droplet in different size by using means of MPS.
And, I examined them as follows from the results (fig.1) (fig.2) (fig.3).
- The attaching droplet become easily to spread and be crushed with increase of droplet volume.
- The attaching droplet thickness is inversely proportional to the liquid density when the droplet size is more than capillary length.
𝜅&' =
𝛾(
𝜌𝑔
capillary length : The droplet length that gravity
becomes more dominant than surface tension
𝜿&𝟏 (𝐓𝐡𝐞 𝐟𝐫𝐞𝐬𝐡 𝐰𝐚𝐭𝐞𝐫 ) : 2.726mm
Given to capillary length, because the range of droplet size that the fresh water
droplet cannot keep thickness is 2mm³－3mm³, gravity becomes more dominant than
surface tension, and the droplet became easily to be crushed from this range. In
addition, it was revealed that the droplet thickness is smaller than assumed when the
fluid density went up because the droplet thickness of the salt water is smaller than
that of the fresh water.
!
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!"\$
!"%
#&''() *&''() \$&''() +&''()
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!"#\$%'"\$()*#&
!"#\$')+*\$()*#&
𝜃 = 90°