Effects of density on flow in a nano channel using a molecular-continuum hybrid method

Kim, Youngjin,Jeong, Myunggeun,Zhou, Wenjing,Tao, Wen Quan,Ambrosia, Matthew Stanley,Ha, Man Yeong Elsevier 2017 Computers & fluids Vol.156 No.-

<P><B>Abstract</B></P> <P>A molecular-continuum hybrid method was developed to simulate micro- and nano-scale fluid flows that cannot be predicted using continuum fluidics. Molecular dynamics simulation was used near stationary solid surfaces, and Navier-Stokes equations were used in other regions. We carried out Couette flow simulation using this hybrid method and validated the results by comparing them with the analytical solution. We also studied the dependence of the velocity slip and slip length on the surface energy, liquid density, and roughness for a liquid channel flow with and without nano-structures on the solid surface. The behavior of the liquid near the solid wall changed with the surface energy as well as the liquid density. The variation of the velocity slip and slip length according to the surface energy also depended on the liquid density as well as the surface roughness. We compared the required computational time obtained from the molecular-continuum hybrid method with that obtained from full molecular dynamics simulation under the same computational condition, giving much shorter computational time for the case using the molecular-continuum hybrid method than that for full molecular dynamics simulation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The velocity slip and slip length decrease with increasing the surface energy. </LI> <LI> The locking boundary condition is enhanced with the structure. </LI> <LI> The trends of <I>u<SUB>s</SUB> </I> and <I>L<SUB>s</SUB> </I> at each liquid density are changed on the smooth surface. </LI> <LI> The trends at each liquid density differ between the rough and smooth surface. </LI> </UL> </P>

A comprehensive molecular dynamics study of a single polystyrene chain in a good solvent

Sajad Rasouli,Mohammad Reza Moghbeli,Sousa Javan Nikkhah 한국물리학회 2018 Current Applied Physics Vol.18 No.1

In this study, molecular characteristics of polystyrene (PS) was calculated measuring its dilute-solution properties in toluene at 288.15 K via molecular dynamics (MD) simulations. The solution models consisted of PS chains with different number of repeating units all of which were in a dilute regime. In order to investigate the compatibility between the polymer and the solvent molecules, interaction energy and Flory-Huggins (FH) interaction parameter were estimated. The simulation results indicate that increasing the chain repeating units enhanced the interaction between the solute and the solvent. Additionally, the chain dimensions were evaluated calculating the radius of gyration (Rg) and end-to-end distance, r0. To determine the dynamic behavior of the chains in the solutions, mean square displacement (MSD) and diffusivity coefficient were calculated. The simulation results indicated that the chain rigidity at low molecular weight and chain flexibility with increasing the molecular weight influenced chains dynamic behavior and diffusivity. Moreover, radial distribution function (RDF) illustrated the effect of steric hindrance of the chains in dilute solution on capturing the solvent molecules. In addition, solution viscosity was calculated by performing non-equilibrium molecular dynamics simulation (NEMD). The obtained results of chain characteristics and viscosity showed a good agreement with experimental results published previously. This agreement confirms the accuracy of the applied simulation method to characterize the dilute solutions and the chains characteristics.

MD 시뮬레이션을 이용한 실린더 형태 나노와이어의 접촉면적에 관한 연구

김현준(Hyun-Joon Kim) 한국트라이볼로지학회 2016 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.32 No.1

Contact between solid surfaces is one of the most important factors that influence dynamic behavior in micro/nanoscale. Although numerous theories and experimental results on contact behavior have been proposed, a thorough investigation for nanomaterials is still not available owing to technical difficulties. Therefore, molecular dynamics simulation was performed to investigate the contact behavior of nanomaterials, and the application of conventional contact theories to nanoscale was assessed in this work. Particularly, the contact characteristics of cylindrical nanowires were examined via simulation and contact theories. For theoretical analysis, various contact models were utilized and work of adhesion, Hamaker constant and elastic modulus those are required for calculation of the models were obtained from both indentation simulation and tensile simulation. The contact area of the cylindrical nanowire was assessed directly through molecular dynamics simulation and compared with the results obtained from the theories. Determination of the contact area of the nanowires was carried out via simulation by counting each atom, which is within the equilibrium length. The results of the simulation and theoretical calculations were compared, and it was estimated that the discrepancy in the results calculated between the simulation and the theories was less than 10 except in the case of the smallest nanowires. As the result, it was revealed that contact models can be effectively utilized to assess the contact area of nanomaterials.

Accelerating Molecular Dynamics Simulation Using Graphics Processing Unit

Hun Joo Myung,Sik Lee,오광진,Ryuji Sakamaki,Tetsu Narumi,Kenji Yasuoka 대한화학회 2010 Bulletin of the Korean Chemical Society Vol.31 No.12

We have developed CUDA-enabled version of a general purpose molecular dynamics simulation code for GPU. Implementation details including parallelization scheme and performance optimization are described. Here we have focuse on the non-bonded force calculation because it is most time consuming part in molecular dynamics simulation. Timing results using CUDA-enabled and CPU versions were obtained and compared for a biomolecular system containing 23558 atoms. CUDA-enabled versions were found to be faster than CPU version. This suggests that GPU could be a useful hardware for molecular dynamics simulation.

Atomistic molecular dynamics simulation study on thermomechanical properties of poly(1,3,5-trimethyl-1,3,5-trivinyl cyclotrisiloxane) dielectric insulator for soft electronics

양승화,윤수진,권선영 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.5

While poly(1,3,5-trimethyl-1,3,5-trivinyl cyclotrisiloxane, pV3D3) is a promising dielectric material, synthesized from an iCVD process, the physical properties of pV3D3 film have yet to be studied in detail. In this study, the thermoelastic properties of pV3D3 are investigated by molecular dynamics simulations. An amorphous molecular unit cell of pV3D3 is modeled with periodic boundary conditions. The PCFF force field is applied to describe all the inter- and intramolecular interactions. Through classical ensemble simulations, the mechanical properties including the stress-strain curves in tension and compression are determined. The glass transition temperature and the coefficient of thermal expansion are determined from the simulation of cooling-down from an elevated temperature. The simulation results show that the pV3D3 is in an almost rubbery state near room temperature. Moreover, a clear hydrostatic pressure effect is observed in the compressive loading condition of pV3D3 and its elastic modulus is within the range of typical thermoplastic.

Accelerating Molecular Dynamics Simulation Using Graphics Processing Unit

Myung, Hun-Joo,Sakamaki, Ryuji,Oh, Kwang-Jin,Narumi, Tetsu,Yasuoka, Kenji,Lee, Sik Korean Chemical Society 2010 Bulletin of the Korean Chemical Society Vol.31 No.12

We have developed CUDA-enabled version of a general purpose molecular dynamics simulation code for GPU. Implementation details including parallelization scheme and performance optimization are described. Here we have focused on the non-bonded force calculation because it is most time consuming part in molecular dynamics simulation. Timing results using CUDA-enabled and CPU versions were obtained and compared for a biomolecular system containing 23558 atoms. CUDA-enabled versions were found to be faster than CPU version. This suggests that GPU could be a useful hardware for molecular dynamics simulation.

분자-연속체 하이브리드 기법을 이용한 나노 채널에서의 Couette 유동에 대한 수치적 연구

김영진(Youngjin Kim),정명근,김효정,하만영,장준경 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11

Molecular-continuum hybrid method is developed for simulating micro- and nano-scale fluid where continuum fluidics cannot predict. Molecular dynamics simulation is used near the solid surface which cannot be predicted by continuum fluidics and Navier-Stokes equation is used in other regions. We carried out Couette flow simulation using the hybrid method and full MD simulation and compared the results with analytic solution for validation of the hybrid method. Also, we conducted study of the roughness effect in liquid channel flow with nano structures on the solid surface. Molecular-continuum hybrid method can predict flow field near the nano structure which continuum fluidics cannot and is able to simulate large domain size which MD cannot calculate due to finite computer memory capacity, while saving computational time.

Molecular dynamics simulation of carbon molecular sieve preparation for air separation

Elham Yaghoobpour,ALI AHMADPOUR,Nafiseh Farhadian,Mojtaba Shariaty-Niassar 한국화학공학회 2015 Korean Journal of Chemical Engineering Vol.32 No.3

Carbon deposition process on activated carbon (AC) in order to produce carbon molecular sieve (CMS)was simulated using molecular dynamics simulation. The proposed activated carbon for simulation includes microporeswith different characteristic diameters and lengths. Three different temperatures of 773 K, 973 K, and 1,273 K wereselected to investigate the optimum deposition temperature. Simulation results show that the carbon deposition processat 973 K creates the best adsorbent structure. While at lower temperature some micropore openings are blockedwith carbon atoms, at higher temperature the number of deposited carbons on the micropores does not change significantly. Also, carbon deposition process confirms the pseudo-second-order kinetic model with an endothermic behavior. To evaluate the sieving property of adsorbent products, nitrogen and oxygen adsorption on the initial and finaladsorbent products are examined. Results show that there is not any considerable difference between the equilibriumadsorption amounts of nitrogen and oxygen on the initial and final adsorbents especially at low pressure (P<10 atm). Although, adsorption kinetics curves of these gases change significantly after the carbon deposition process in comparisonwith the initial sample. These observations indicate that the final adsorbent has high selectivity towards oxygencompared with the nitrogen, so it can be called a carbon molecular sieve. All simulated results are in good agreementwith experiments.

Molecular-dynamic simulation on the equilibrium and dynamical properties of fluids in a nano-channel

H. Hoang,S. Kang,Y. K. Suh 한국전산유체공학회 2008 한국전산유체공학회 학술대회논문집 Vol.2008 No.-

The equilibrium molecular-dynamic simulations have been performed to estimate the properties of the three kinds of fluids (the Lennard-Jones fluid, water and aqueous sodium-chloride solution) confined between two plates that are separated by 1.086 nm; included in the equilibrium properties are the density distribution and the static structure, and the diffusivity in the dynamic property. Three kinds of fluids considered in this study are. The water molecules are modeled by using the SPC/E model and the ions by the charged Lennard-Jones particle model. To treat the water molecules, we combined the quaternion coordinates with Euler angles. We also proposed a plausible algorithm to assign the initial position and direction of molecules. The influence of polarization of water molecules as well as the presence of ions in the solution on the properties will be addressed in this study. In addition, we performed the non-equilibrium molecular-dynamic simulation to compute the flow velocity for the case with the gravitational force acting on molecules.

Analysis of phase transition, structural and dynamical properties of R290 using molecular dynamics simulation

Md. Sarwar Alam,Ji Hwan Jeong 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.10

Propane (R290), a hydrocarbon refrigerant, is an excellent choice of cooling fluids for use in refrigeration and air conditioning systems considering the environmental point of view and system performance. The phase transition phenomenon and structural and dynamic properties of R290 were analyzed through a molecular dynamics (MD) simulation. The densities, isobaric heat capacities and viscosities were computed and the variations of density, volume, potential energy and the nucleation process were examined to investigate the effects of condensation temperature on the phase transition rate. The mean square displacement and velocity autocorrelation function for different temperatures were simulated for dynamical analysis. Radial distribution functions were investigated to get insight into the structural analysis at the atomic level. Shear viscosity and isobaric heat capacity obtained by the present simulation showed a good agreement with the REFPROP data. The structural analysis revealed that the phase transition of R290 did not affect its intramolecular structure.