Changwan Han

Design and Performance Evaluation of a Rotary Magnetorheological Damper for Unmanned Vehicle Suspension Systems

We designed and validated a rotary magnetorheological (MR) damper with a specified damping torque capacity, an unsaturated magnetic flux density (MFD), and a high magnetic field intensity (MFI) for unmanned vehicle suspension systems. In this study, for the rotary type MR damper to have these satisfactory performances, the roles of the sealing location and the cover case curvature of the MR damper were investigated by using the detailed 3D finite element model to reflect asymmetrical shapes and sealing components. The current study also optimized the damper cover case curvature based on the MFD, the MFI, and the weight of the MR damper components. The damping torques, which were computed using the characteristic equation of the MR fluid and the MFI of the MR damper, were 239.2, 436.95, and 576.78 N·m at currents of 0.5, 1, and 1.5 A, respectively, at a disk rotating speed of 10 RPM. These predicted damping torques satisfied the specified damping torque of 475 N·m at 1.5 A and showed errors of less than 5% when compared to experimental measurements from the MR damper manufactured by the proposed design. The current study could play an important role in improving the performance of rotary type MR dampers.

A new methodology for detecting adhesion location in aluminum tube expansion

During the expansion forming of aluminum tube, the efficiency of heat exchanger diminishes due to the adhesion of groove and expansion ball inside the tube. Despite its importance, a limited number of researches on the adhesion problems in aluminum tube expansion have been published. This study aims to analyze the adhesion occurring during the expansion forming of aluminum tube for heat exchanger and to identify its location. For this, the method of using the statistical analysis of geometry by image processing and the slope of force measured from expansion forming was suggested. The new method discovers the adhesion location from the standard deviation of groove height measured before and after expansion of tube and the differentiation of force measured from expansion forming. To prove this method, the area with deviation of groove height above average was discovered, and it was confirmed that from the actual expansion of tube cross-sectional images, the height of some grooves was abnormally shorter due to adhesion. Also, from this method, it was confirmed that the changes in differentiation of force occurring from the expansion of the tube also include the information on adhesion location.

A parametric study of spar-type floating offshore wind turbines (FOWTs) by numerical and experimental investigations

The use of spar platforms as a substructure for floating offshore wind turbines (FOWTs) is a new concept that is developing quickly in the offshore wind industry owning to the excellent stability and adaptability to different water depths. However, the lack of studies about the dynamic response and design guidelines of spar-type FOWTs is a barrier to further development of the offshore wind industry. Therefore, the goal of this study is to carry out dynamic response analysis and to develop design guidelines for spar-type FOWTs. To achieve this goal, the dynamic responses of full-scale spar-type FOWT models with different values of three design variables (spar diameter, depth, and concrete ratio) were first numerically obtained in the time domain and experimentally validated by considering all environmental conditions such as wind, regular wave, and constant current loads, as well as the mooring line loads. Then, regression and perturbation analyses, which were also validated by the analysis of variance method, were performed to analyse the effects of the design variables and to propose design guidelines of spar-type FOWTs.

Role of Post Weld Treatment Methods in the Improvement of Fatigue Life for T-type Welded Structures Made by SM 50A Steel

This study aims to investigate the effect of the post weld treatments on the fatigue life of T-type welded structure made by a SM50A steel material, generally used for excavators, because changes in the geometry, material and surface properties of welded regions affect the fatigue life of welded structures. T-type test specimens were prepared by the CO2 welding of rolled steel plates (SM50A steel) with a thickness of 10 mm at a welding speed of 30 cm/min and these Ttype welded specimens were further treated by UIT (Ultrasonic Impact Treatment) and/or toegrinding post welding treatment methods. In order to investigate improvements on the fatigue life of the samples. 3-point bending fatigue tests were conducted with a stress ratio of R

Dynamic Response of Polyvinyl Alcohol(PVA)-Hydrogel With Different PVA Concentrations

Polyvinyl Alcohol-Hydrogel (PVA-H) is a biomaterial used for manufacturing contact lenses as well as for the medium of drug delivery. Previous studies have also showed that PVA-H exhibits superior biocompatibility with hydrophilic elastic nature. The aim of this study is to examine the possible usage of the PVA-H as cartilage replacement material by determining the static and dynamic mechanical properties of PVA-H with different ratios of polyvinyl alcohol (PVA) and phosphate buffered saline (PBS) compositions.Three different types of PVA-H specimens were made by changing the ratio of PVA (Sigma-Aldrich) and PBS (Sigma-Aldrich) compositions (PVA-H1: 10 wt% PVA and 90 wt% PBS; PVA-H2: 20 wt% PVA and 80 wt% PBS; PVA-H3: 25 wt% PVA, 45 wt% PBS and DMSO 30 wt%). Static and dynamic tensile tests under the loading frequencies of 0.001, 0.01, 0.1, and 1 Hz were carried out to measure the biomechanical properties of PVA-H1, -H2 within PBS solution and -H3 within PBS/ DMSO solution.The equilibrium Young’s moduli (EY) of PVA-H1, -H2 and -H3 evaluated from the static displacement control were 84.2±35.1 kPa (n=10), 254±32.2 kPa (n=10) and 588±38.9 kPa (n=5), respectively. The amplitudes of dynamic tensile moduli were varied from 86.3±33.4 kPa (n=10) at 0.001 Hz to 96.9±42.0 kPa (n=10) at 1 Hz for PVA-H1, from 282.7±26.4 kPa (n=10) at 0.001 Hz to 309.1±32.2 kPa (n=10) at 1 Hz for PVA-H2 and from 643.8±49.8 kPa (n=10) at 0.001 Hz to 747.7±67.7 kPa (n=5) at 1 Hz for PVA-H3. According to the current results, the frequency dependence of the magnitude of the dynamic modulus confirms the viscoelastic nature of PVA-H material. However, it can be noted that the dynamic modulus increases by up to a factor of 1.15 for PVA-H1, 1.22 for PVA-H2 and 1.27 for PVA-H3, showing insignificant viscoelasticity compared with that for cartilage. The result that static and dynamic moduli of PVA-H3 are larger than those of PVA-H1 and PVA-H2 also suggests that the amount of PVA composition in PVA-H plays an important role in improving both static and dynamic mechanical strengths of PVA-H material. The phase angle decreased from 5.2±2.1 ° at 0.001 Hz to −0.3±1.7 ° at 1 Hz for PVA-H1, from 5.6±0.6 ° at 0.001 Hz to −0.3±0.7 ° at 1 Hz for PVA-H2 and from 8.2±1.1 ° at 0.001 Hz to 0.7±0.7 ° at 1 Hz for PVA-H3.Copyright

Biomechanical Effects of Kaempferol Treatments on the Bone Healing Process of Murine Tibia

Kaempferol is a typical flavonol-type flavonoid and has a protective effect on postmenopausal bone loss, and previous studies have reported that kaempferol treated groups show an increase in the callus size and bone mineral density as well as improvement in biomechanical behaviors in comparison with untreated control groups in the bone healing process. The present study aims at investigating the effect of kaempferol treatments on fractured murine tibia, by measuring kaempferol dose-dependent mechanical properties in the bone healing process of murine tibia fracture models.A stabilized fracture was generated at tibia by minor modification of the Hiltunen method for 8 weeks old ICR mice weighting 29.0 ∼ 30.5 g. Experimental mice were divided into 4 groups. Kaempferol of 0.2, 1.0, 5.0 mg/kg (body weight) with 20 % ethanol was administered to 3 groups and the remaining one group was only treated with 20 % ethanol as a control group. Three-point bending fracture tests were conducted to measure the mechanical properties (fracture load, fracture energy, stiffness) of murine tibiae at non-fractured regions near fracture sites 21 days after kaempferol treatments, via a custom-made biomechanical testing system (BTS, KST Co., Korea).The 5.0 mg/kg kaempferol treated group shows higher fracture load (20.54 ±5.04 N) than the control group (17.82 ±5.94 N). Fracture energy, total energy applied to tibia up to bone fracture, exhibited no significant differences between the control group and any of the kampferol treated groups, although both the 1.0 mg/kg kaempferol treated and control groups showed a little higher fracture energy than the 0.2 and 5.0 mg/kg kaempferol treated groups. Bone stiffness also did not show statistically significant differences between the control group and any of the kaempferol treated groups, with the highest stiffness value observed in the 1.0 mg/kg kaempferol treated group.Copyright