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Tomoya Omata

January 13, 2022


  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°