Composite shell structures with varying thickness are often used in different industrial fields because it could exhibit structural advantages at minimum material cost.

Recently, many works have been reported for static and dynamic analyses of different structures with variable thickness. Various methods such as Haar wavelet method, Jacobi-Ritz method spectral-Tchebychev method, dynamic stiffness method, finite element method and meshfree method have been employed for numerical analysis of composite structures. In recent years, the meshfree method has attracted significant attention of many scholars.

Jo Ju Chol, a researcher at the Faculty of Mechanical Science and Technology, developed a meshfree Jacobi-radial point interpolation (Jacobi-RPI) method for free vibration and stochastic response analyses of laminated composite sectorial and annular plates with straight fibers and variable thickness.

First, he adopted the Hamilton’s principle to establish the equations of motion of the laminated composite sectorial plate with straight fiber and variable thickness in the framework of first-order shear deformation theory (FSDT). Then, he approximated the displacement components of the plate by using the meshfree Jacobi-RPI shape function. As the laminated annular plate with straight fiber is not symmetrical, he obtained its motion equations by combining the equations of several sectorial plates.

He validated the accuracy and reliability of the proposed method through a sufficient number of numerical studies.

For more details, you can refer to his paper “A meshfree formulation for free vibration and stationary stochastic response analyses of laminated composite annular plate with straight fibers and variable thickness” in “Acta Mech” (SCI).

As is known, in a ball screw–driven servomechanism, the servo motor and the ball screw can be connected directly or via a tooth belt drive, a gear pair or a commercial reducer. However, more complex systems cause more kinematic errors in the machines, so in precision machine tools, the former is more common, but in conventional machine tools it is more economical to use the latter. This is because the latter can improve the resolution in an open system, replace the output of a high-speed low-torque servo motor with the output of a low-speed high-torque unit, significantly reduce the load inertia torque in terms of the motor shaft to favor inertial matching and has the potential to significantly reduce electric consumption by reducing the size of the motor. Especially, tooth belt drives are commercially available and inexpensive but have a relatively small backlash compared to other speed reducers, which makes them a large part of industrial applications. On the other hand, since the former is a special case of the latter, the results of the latter study can also be applied to the former. Certainly, the study on optimal selection of the key components of ball screw–driven servomechanisms with tooth belt drives is a subject of great socio-economic significance.

Jang Rim Chol, a researcher at the Faculty of Mechanical Science and Technology, proposed a method for determining the optimal combination of the key components (servo motor, ball screw, and tooth pulley pair) of a ball screw–driven servomechanism with a tooth belt drive transmission. The proposed method deals with a more generalized optimization problem because it focuses on the optimization of a ball screw–driven servomechanism with a reducer (tooth belt drive transmission) unlike previous works that focused only on the optimization of a system where the servo motor and the ball screw are directly connected.

The proposed method enables optimal selection of the key components of a ball screw–driven servomechanism for different purposes including machine tools, without subjective selection or prediction of some components or some parameters for different objective functions.

You can find the details in his paper “Selection of key components in ball screw–driven servomechanisms with toothed belt drive transmission for machine tools through combinational optimization” in “The International Journal of Advanced Manufacturing Technology” (SCI).

Hydrogen, the cleanest future fuel, can replace fossil fuel based on carbon. During the past decades, many methods for hydrogen production and storage have been studied for practical use. In particular, storage and transport of hydrogen has recently become a focus of intensive research for large-scale application of hydrogen energy systems.

One of the major challenges in the quest for feasible hydrogen-fueled vehicles is to develop lightweight materials with high hydrogen densities (>5wt %) which can absorb and release hydrogen in the range of 1-10 bar and 298-473 K.

Recently, perovskite materials have emerged as a multifunctional material for photovoltaics, luminescence, photocatalytics and hydrogen storage applications.

Ri Sol Hyang, a lecturer at the Faculty of Online Education, theoretically investigated the materials properties such as structural, electronic and lattice dynamics properties and mechanical and dynamical stabilities of the hydride perovskites ACaH₃ (A = Li, Na) in cubic phase for its application as a hydrogen storage material by using the first-principles calculations.

The results show that cubic LiCaH₃ is regarded as a potential H₂ storage material due to its high H₂ storage capacity, stability and suitable dehydrogenation temperature.

For more information, please refer to her paper “Perovskite-type hydrides ACaH₃ (A = Li, Na): computational investigation on materials properties for hydrogen storage applications” in “RSC Advances” (SCOPUS).