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Molecular Dynamics Study of Thermodynamic Properties of Nanoclusters for Additive Manufacturing
Truong Quoc Vo,김보흥 한국정밀공학회 2017 International Journal of Precision Engineering and Vol.4 No.3
4D printing is a new process that involves the use of 3D-printed objects and materials able to change shape over time. Therefore, a comprehensive understanding of 3D-printed objects is needed prior to developing 4D-printed ones. Selective laser melting (SLM) is a very promising 3D printing technique; however, because of the intense heat input, problems such as balling phenomena, deteriorated surface finish, tensile residual stress, and part distortion are still frequently observed in the SLM process. For such cases, micro-/nano-scale heat management becomes a key problem. Indeed, heat conduction during the SLM process is significantly affected by powder diameter and compactness. The thermodynamic behaviors of powder due to laser heating are considerably different from that of a solid bulk body. In this paper, molecular dynamics (MD) and empirical embedded atom computational methods are applied to study the thermodynamic properties of Ag nanoclusters, which are 2.1-6.9 nm in diameter during the heating and cooling process. We find that the melting point, heat of fusion, entropy of fusion, and surface energy are highly dependent on nanocluster size. Remarkably, we define the mesoscale regime where the properties of nanoclusters can be described in terms of macroscopic concepts with well-defined bulk and surface thermodynamic properties.
Truong Quoc Vo,박부성,박초희,김보흥 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.4
In this paper, we use molecular dynamics (MD) simulations to investigate changes in fluid flow at a solid/liquid interface. The flow isdriven by shearing FCC structured solid molecular walls under isothermal conditions using previously developed interactive thermal wallmodels. For the nano-scale thin liquid film flows, a fluid molecular layer attached to the wall molecules behaves as an extended walllayer, which induces increased shearing in the middle of the fluid by reducing the width of the flow region. Small variations in moleculardiameter length at the interface significantly affect flow characteristics. Shear locking on strong wetting surfaces caused by the dynamicstructuring of fluid molecules (i.e., the fluid molecules layering on the solid surface due to the wall force field) increases the density andviscosity and decreases the shear rate and the heat dissipation ratio on the interface, which are important in nano-scale fluid flow analysis.
Interface Thermal Resistance between Liquid Water and Various Metallic Surfaces
Truong Quoc Vo,김보흥 한국정밀공학회 2015 International Journal of Precision Engineering and Vol. No.
Enhancing thermal transport mechanisms in nanostructures and nanomaterials are important factors for their use in green renewable energy applications. The behaviors and reliability of nanoscale devices strongly depend on the way the systems dissipate heat. Therefore, using non-equilibrium molecular dynamics (MD) simulations, we investigated the interface thermal resistance between liquid water and various metallic surfaces in nanochannels. Solid-liquid interface thermal resistance is well known as the Kapitza length. In this study, we model heat transfer through two parallel solid walls separated by liquid water, holding each solid wall at a different temperature to impose a temperature gradient. Silicon with a diamond crystal lattice structure and copper, silver, gold, and platinum with face-centered cubic (FCC) crystal lattice structure were chosen as the solid materials due to their extensive applications in nanotechnology. Temperature jumps at such solid-liquid interfaces are due to thermal transport between the dissimilar materials, resulting in an interface thermal resistance. We observed the behaviors of liquid water molecules in the vicinity of the metallic surfaces, revealing that the Kapitza length varies as a function of solid-liquid interaction strength, and confirming the effect of Lennard-Jones (LJ) interaction added to long-range Coulombic interaction in the liquid model, and using liquid water instead of simple LJ liquid.
Implementation of Rehabilitation Platform based on Augmented Reality Technology
Nguyen Truong Thinh,Nguyen Anh Quoc,Nguyen Vo Tam Toan,Tran The Luc 제어로봇시스템학회 2021 제어로봇시스템학회 국제학술대회 논문집 Vol.2021 No.10
Stroke is now one of the leading causes of death and disability in both motor and cognitive functions. In addition, rehabilitation for stroke survivors also faces many physical and human difficulties. To address this issue, we studied the use of Augmented Reality (AR) in rehabilitation using a system called RARS. This system creates limbs rehabilitation exercises in the form of games using an AR interface. The goal of the RARS is to increase patient’s positive emotions, which motivates them to enjoy rehabilitation exercises. As a result, recovery efficiency will be improved, and the burden on physiotherapists will be reduced. The RARS is evaluated through a research about the effectiveness of this system on rehabilitation for patients after stroke (n=10). Reported results showed that the RARS produced significant improvement in the patient’s indicators of functional status. From that, this system shows that it not only creates great benefits for personnel and economic but also bring about huge potential for future growth.
Viscous heating and temperature profiles of liquid water flows in copper nanochannel
Quyen Van Dinh,Truong Quoc Vo,김보흥 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.7
Understanding nanoscale fluidic transport becomes increasingly important due to the rapid development of nanotechnology and nanofabrication. By using molecular dynamics (MD) simulations, we investigated the viscous heating of water flows in copper nanochannels. The two scenarios that were studied are Couette flows and Poiseuille flows. We observed the scale effects on the distribution of fluid density, streaming velocity, fluid viscosity, and temperature across the channel. The results revealed the significant effects of surface forces on causing a large deviation between simulation results and classical hypothesis. We found that the energy equation coupled with the thermal-slip boundary conditions still fails to predict the temperature distributions. Hereby, further scale effects are taken into account, which leads to better predictions. The model that we developed in this study shows the relative deviation to the simulation data within 5 %, which is small compared to the conventional continuum approach (i.e., up to 51 %).