Research_kosen

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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
   𝑟" : Effective radius
   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 2.1×𝑟&'(
   Effective radius of surface tension model 2.1×𝑟&'(
   Time step s 1.0×10$)
   Surface tension coefficient N/m 0.0728
   Contact angle ° 90
   Table.1 Calculation condition
   Fig.1. Measurement result of the droplet thickness for the droplet size
   ▼ Measurement result of droplet thickness
   (a) 𝑉 = 2mm3 (b) 𝑉 = 3mm3
   (c) 𝑉 = 4mm3 (d) 𝑉 = 5mm3
   (a) 𝑉 = 2mm3 (b) 𝑉 = 3mm3
   (c) 𝑉 = 4mm3 (d) 𝑉 = 5mm3
   ▼ Visualization of the adhesion behavior
   ▼ Condition
   Fig.2. Comparison of the fresh water droplet behavior by the droplet size
   Fig.3. Comparison of the salt water droplet behavior by the droplet size
   This research simulated the adhesion behavior of the droplet in different size by using means of MPS.
   And, I examined them as follows from the results (fig.1) (fig.2) (fig.3).
   - The attaching droplet become easily to spread and be crushed with increase of droplet volume.
   - The attaching droplet thickness is inversely proportional to the liquid density when the droplet size is more than capillary length.
   𝜅&' =
   𝛾(
   𝜌𝑔
   capillary length : The droplet length that gravity
   becomes more dominant than surface tension
   𝜿&𝟏 (𝐓𝐡𝐞 𝐟𝐫𝐞𝐬𝐡 𝐰𝐚𝐭𝐞𝐫 ) : 2.726mm
   Given to capillary length, because the range of droplet size that the fresh water
   droplet cannot keep thickness is 2mm³－3mm³, gravity becomes more dominant than
   surface tension, and the droplet became easily to be crushed from this range. In
   addition, it was revealed that the droplet thickness is smaller than assumed when the
   fluid density went up because the droplet thickness of the salt water is smaller than
   that of the fresh water.
   !
   !"#
   !"$
   !"%
   #&''() *&''() $&''() +&''()
   ,-.
   /01234567138'4
   !"#$%'"$()*#&
   !"#$')+*$()*#&
   𝜃 = 90°
   

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