Beom-Soo Kang

Bio: Beom-Soo Kang is an academic researcher from Pusan National University. The author has contributed to research in topics: Finite element method & Hydroforming. The author has an hindex of 27, co-authored 264 publications receiving 3049 citations.

Finite element analysis and modeling of structure with bolted joints

Abstract: In this work, in order to investigate a modeling technique of the structure with bolted joints, four kinds of finite element models are introduced; a solid bolt model, a coupled bolt model, a spider bolt model, and a no-bolt model. All the proposed models take into account pretension effect and contact behavior between flanges to be joined. Among these models, the solid bolt model, which is modeled by using 3D solid elements and surface-to-surface contact elements between head/ nut and the flange interfaces, provides the best accurate responses compared with the experimental results. In addition, the coupled bolt model, which couples degree of freedom between the head/nut and the flange, shows the best effectiveness and usefulness in view of computational time and memory usage. Finally, the bolt model proposed in this study is adopted for a structural analysis of a large marine diesel engine consisting of several parts which are connected by long stay bolts.

Various design techniques to reduce cogging torque by controlling energy variation in permanent magnet motors

Abstract: Using energy method, this paper analytically reveals that the cogging torque can be reduced by controlling N/sub L/th harmonic components of the square of airgap permeance function and flux density function, where N/sub L/ denotes the least common multiple of number of poles and number of slots. As for design tools, it introduces various design techniques to reduce cogging torque with analytical formulation and FEM examples.

Constitutive modeling for the dynamic recrystallization evolution of AZ80 magnesium alloy based on stress–strain data

Abstract: In order to improve the understanding of the dynamic recrystallization (DRX) behaviors of as-cast AZ80 magnesium alloy, a series of isothermal upsetting experiments with height reduction 60% were performed at the temperatures of 523 K, 573 K, 623 K and 673 K, and the strain rates of 001 s−1, 01 s−1, 1 s−1 and 10 s−1 on a Gleeble 1500 thermo-mechanical simulator Dependence of the flow stress on temperature and strain rate is described by means of the conventional hyperbolic sine equation By regression analysis, the activation energy of DRX in the whole range of deformation temperature was determined to be Q = 21582 kJ mol−1 Based on dσ/dɛ versus σ curves and their processing results, the flow stress curves for AZ80 magnesium alloy were evaluated that they have some characteristic points including the critical strain for DRX initiation (ɛc), the strain for peak stress (ɛp), and the strain for maximum softening rate (ɛ*), which means that the evolution of DRX can be expressed by the process variables In order to characterize the evolution of DRX volume fraction, the modified Avrami type equation including ɛc and ɛ* as a function of the dimensionless parameter controlling the stored energy, Z/A, was evaluated and the effect of deformation conditions was described in detail Finally, the theoretical prediction on the relationships between the DRX volume fractions and the deformation conditions were validated by the microstructure graphs

Design and manufacturing of fiber reinforced elastomeric isolator for seismic isolation

Abstract: In this paper an experimental analysis is presented for the mechanical characteristics of multi-layer elastomeric isolation bearings where the reinforcing element—normally steel plates—are replaced by a fiber reinforcement. The fiber reinforced elastomeric isolator (FREI), in contrast to the steel reinforced elastomeric isolator (SREI) which is assumed to be rigid both in extension and flexure, is assumed to be flexible in extension, but completely lacking flexural rigidity. The FREI is designed and fabricated for evaluation of the performance on seismic isolation. Experiments are carried out to evaluate and compare the performances of fiber reinforcement with performance of steel reinforcement, and the differences in performance among different kinds of fiber reinforcements. From the experiments, the performance of the FREI is shown to be superior to that of the SREI in view of horizontal stiffness and vertical stiffness of the isolator. Therefore, it is possible to produce an FREI that matches the behavior of an SREI. Consequently, the FREI could replace the conventional SREI for seismic isolation with low-cost manufacturing and lightweight installation.

Stochastic approach to kinematic reliability of open-loop mechanism with dimensional tolerance

Abstract: Open-loop mechanisms are usually employed in industrial applications to position or orient an object, where high accuracy, repeatability and stability of operations are required. Deviations in link dimensions and joint clearances in manufacturing and assembling operations decrease the degree of accuracy and repeatability of the systems. Due to the random nature of dimensional tolerance and clearance, a stochastic approach to figure out reliability of the open-loop mechanism should be required. In this work, firstly, with the assumption that all kinematical parameters are normally distributed random variables, stochastic model of links with dimensional tolerances and of revolute joints with clearances are presented. The kinematical reliability for the positioning and orientation repeatability is then calculated analytically based on an advanced first-order second moment (AFOSM) method and verified with a Monte Carlo simulation method. Finally, the proposed methods are numerically illustrated with an RRR spatial manipulator.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

An Accurate Subdomain Model for Magnetic Field Computation in Slotted Surface-Mounted Permanent-Magnet Machines

Abstract: The paper presents an accurate analytical subdomain model for computation of the open-circuit magnetic field in surface-mounted permanent-magnet machines with any pole and slot combinations, including fractional slot machines, accounting for stator slotting effect. It is derived by solving the field governing equations in each simple and regular subdomain, i.e., magnet, air-gap and stator slots, and applying the boundary conditions to the interfaces between these subdomains. The model accurately accounts for the influence of interaction between slots, radial/parallel magnetization, internal/external rotor topologies, relative recoil permeability of magnets, and odd/even periodic boundary conditions. The back-electromotive force, electromagnetic torque, cogging torque, and unbalanced magnetic force are obtained based on the field model. The relationship between this accurate subdomain model and the conventional subdomain model, which is based on the simplified one slot per pole machine model, is also discussed. The investigation shows that the proposed accurate subdomain model has better accuracy than the subdomain model based on one slot/pole machine model. The finite element and experimental results validate the analytical prediction.

Permanent Magnet Synchronous Motor Magnet Designs with Skewing for Torque Ripple and Cogging Torque Reduction

Abstract: This paper examines the torque ripple and cogging torque variation in surface mounted permanent magnet synchronous motors with skewed rotor. The effect of slot/pole combinations and magnet shapes on the magnitude and harmonic content of torque waveforms in a PMSM drive has been studied. Finite element analysis (FEA) and experimental results show that for certain magnet designs and configurations the skewing with steps does not necessarily reduce the ripple in the electromagnetic torque, but may cause it to increase. The electromagnetic torque waveforms including cogging torque have been analyzed for four different PMSM configurations having the same envelop dimensions and output characteristics.

Systems and methods for uav battery exchange

Abstract: Systems and methods are provided for swapping the battery on an unmanned aerial vehicle (UAV). The UAV may be able to identify and land on an energy provision station autonomously. The UAV may take off and/or land on the energy provision station. The UAV may communicate with the energy provision station. The energy provision station may store and charge batteries for use on a UAV.

Analytical Methods for Minimizing Cogging Torque in Permanent-Magnet Machines

Abstract: Cogging torque in permanent-magnet machines causes torque and speed ripples, as well as acoustic noise and vibration, especially in low speed and direct drive applications. In this paper, a general analytical expression for cogging torque is derived by the energy method and the Fourier series analysis, based on the air gap permeance and the flux density distribution in an equivalent slotless machine. The optimal design parameters, such as slot number and pole number combination, skewing, pole-arc to pole-pitch ratio, and slot opening, are derived analytically to minimize the cogging torque. Finally, the finite-element analysis is adopted to verify the correctness of analytical methods.