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Lee, Jeongmin,Lee, Hyung Ju,Ryu, Jaiyoung,Lee, Seong Hyuk Elsevier 2018 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.117 No.-
<P><B>Abstract</B></P> <P>The present study numerically investigated the three-dimensional turbulent flow and heat transfer characteristics of longitudinal vortices embedded in a turbulent boundary layer in a bent channel and examined the effects of a spanwise pressure gradient on the distortion of the turbulent boundary layer. The commercial code (ANSYS Fluent v17.0) was used for the simulation with the Reynolds stress model (RSM) to consider anisotropic effects. The simulation results showed that an asymmetric distortion of the turbulent boundary layers and a substantial change in the vortex shape were caused by the presence of an additional mean shear rate, originated from the spanwise pressure gradient. It was also found that an increase in the spanwise pressure gradient contributed to an enhancement of production of turbulent kinetic energy, resulting in stronger mixing flows. In particular, the Stanton number had an asymmetric distribution mainly in the bent region where the spanwise pressure gradient was dominant.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The effect of spanwise pressure gradient on flow and heat transfer characteristics is examined. </LI> <LI> The simulation shows an asymmetric distortion of the turbulent boundary layers. </LI> <LI> The Stanton number increases because of the spanwise pressure gradient. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Stackable Disk-Shaped Triboelectric Nanogenerator to Generate Energy from Omnidirectional Wind
Joon-seok Lee,Hyungseok Yong,Yeong In Choi,Jaiyoung Ryu,Sangmin Lee 한국정밀공학회 2022 International Journal of Precision Engineering and Vol.9 No.2
Wind energy is a highly effective renewable energy source that can be used to alleviate environmental problems worldwide. However, the variability of wind inhibited the development of wind power generators such as limited directional conditions, restrictions pertaining to the installation sites, occurrence of mechanical failures, and limited wind speed ranges. In here, to overcome these limitation, we developed a stackable disk-shaped wind-rolling triboelectric nanogenerator (DWR-TENG) to generate energy from omnidirectional wind. Its disk-shaped design ensures that the device does not involve any restrictions related to the wind direction or installation. Furthermore, lightweight charged spheres in the device can reduce the occurrence of mechanical failures and expand the wind speed range (operating in 6.5–17.5 m/s) for the generator operation. The performance of the DWR-TENG was evaluated considering various design parameters by conducting experiments and an FEM simulation. Specifically, the DWR-TENG can be easily stacked in several layers, thereby exhibiting an enhanced charging efficiency.
Doughnut Effect removing Scheme in sensor networks
Inbo Sim,Jaiyoung Lee 대한전자공학회 2007 ITC-CSCC :International Technical Conference on Ci Vol.2007 No.7
In sensor networks, nodes neighboring the sink node consume power very fast and then fail, compared with other nodes. Because of this, the network cannot transmit data any more. To solve this problem called “Doughnut Effect” in, this paper proposes a scheme that, after dividing the network and allocating the optimal buffer threshold in each divided network, stores data in a buffer and transmits the data when the buffer size exceeds the optimal buffer threshold so that packet overhead is reduced and Doughnut Effect can be removed. Also, we evaluate the performance of this scheme in terms of various parameters by using simulation, and show that this proposed scheme considerably improves the power efficiency in sensor networks.
A design of mobility metric using 3-waypoint in mobile ad hoc networks
Hyunchang Kim,Jaiyoung Lee 대한전자공학회 2007 ITC-CSCC :International Technical Conference on Ci Vol.2007 No.7
The mobility metric is intended to capture and quantify the motion of mobile nodes. It is an important value to be considered in order to select a proper clusterhead for clustering. In this paper, we propose a mobility metric that is based on an area value which is evaluated by 3-waypoint for MANET. The waypoint is a collection of places where mobile nodes change in a course while they are on a long journey. In order to know the mobility metric, we calculate an area of a triangle with the sequenced waypoint of three and can estimate how far mobility of the mobile nodes is. This mobility metric is a combination of the velocity, direction and distance component of mobile nodes. Therefore, we believe in using the mobility metric results in a more stable configuration.