Study on Trend of Formation of Taylor-Couette Flow

Jo Apr 19, 2024

Taylor-Couette flow, the flow in the gap between two independently rotating coaxial cylinders, is one of the most discussed problems in fluid mechanics, due to its conception simplicity and applications in processing technology.

In the case of a circular Couette flow with superimposed axial throughput, the flow patterns are expected to be more complicated due to strong interactions between axial and rotating flows.

Recently, there have been some reports that Taylor-Couette flow could be used for production of nano materials. Due to the very strong shear rate of particles in the Taylor-Couette flow, the shaking particles in the fluid tend to split with time and so this is one of the main reasons that Taylor-Couette systems are used to produce nano materials.

Ju Jong Min, a section head at the Faculty of Materials Science and Technology, has developed a machine for producing nano materials by deciding the geometrical dimension of a system and the rotating speed of inner cylinder to form TC flow in Taylor-Couette system without axial flow.

Observing Taylor-Couette vortex at Reynolds number of 500~2 000, he chose rotating speed, viscosity of fluid and geometrical structure of system like the radii of inner and outer cylinders and its ratio and the aspect ratio of system suitable for obtaining steady Taylor-Couette flow. He concluded from the experiment that the rotating speed of 800r/min, the viscosity of fluid of 0.1Pa•s and the radius ratio of 0.88 are appropriate for steady Taylor-Couette flow.

Digital Adaptive Filtering for Reduction of Effect ...

Jo Apr 16, 2024

Specific algorithms for elaboration and digital filtering of pulse signals generated in X-ray detectors have been studied and optimized. A signal pulse at the output of a proper analog conditioning circuit is digitized and then the samples undergo a digital filtering procedure.

Jong Kyong Su, a researcher at the General Assay Office, has developed an algorithm for reliable detection of “X-ray informative” pulses partially buried in noise on digital boards which use programmable devices such as DSP or FPGA.

He focused on the application of least mean square (LMS) adaptive filter, which plays an important role in modern digital signal processing (DSP) such as telephone echo cancellation, noise cancellation, equalization of communications channels, biomedical signal enhancement, adaptive control systems, etc. The adaptive filter is a digital filter that can adjust its filter coefficients automatically to adapt input signals via an adaptive algorithm.

He compared two digital processing methods by traditional filters with fixed filter coefficients and a least-mean-squares (LMS) adaptive filter for applications in high resolution X-ray spectroscopy.

The requirements on peak reproducibility and SNR are better met by the LMS filter, thanks to the capability to adapt the parameters to the non-stationary environment of the detectors. The simulation showed that fast settlement of coefficients can be achieved with an algorithm of medium-level complexity, with elaboration time scaling linearly with the filter order.

Phase Synchronization for Distributed Solar Power S...

Jo Apr 15, 2024

Energy and environmental problems are two challenges today and production and use of recycled energy is the focus of world attention. More and more attention is being drawn to more reliable solar power generating systems, and more than 50GW solar power generating capacity is being constructed in the world every year.

At present, there are two widely-used types of solar power systems—central or distributed. The main problems in the construction of distributed solar power systems are to guarantee flexibility of distributed power sources, stability of voltage and frequency of the weak grids, optimized management and distribution of electric systems and improvement of electric power quality.

O Yong Nam, a section head at the Faculty of Physical Engineering, has designed a novel phase synchronization method for distributed power systems by combining good harmonic and DC offset cancellation characteristics of the discrete Fourier transform (DFT) and frequency adaptation characteristics of phase locked loop (PLL). The validation of the suggested method has been simulated with Microsoft Excel and MATLAB Simulink software.

The proposed method has shown to be effective for grid voltage signal synchronization in non-ideal grid conditions with frequency variation and harmonic distortion and for reference signal synchronization in multi-inverter standalone systems. Also, it is not sensitive to the DC offset in the measurement process.