Journal of Mechanical Science and Technology最新文献

The probe chuck is an inspection device assessing the thermal durability of semiconductor wafers in various temperature environments before shipping. It is most important to ensure that the temperature of the chuck upper surface, on which the wafers are placed, is uniform. This study presents an axisymmetric chuck model to improve surface temperature uniformity in both radial and circumferential directions. The local distribution of the flow path height in the axisymmetric chuck was adjusted to make the chuck upper surface with a constant wall heat flux to simultaneously become as uniform temperature as possible. Three optimization algorithms, namely the genetic algorithm (GA), deep q-network (DQN), and actor-critic (AC) were applied. The optimized shape of the flow pathway, improved temperature uniformity, pressure drop, and local heat transfer coefficient profile by three different optimization algorithms are presented in detail. As a result, the surface temperature difference was significantly reduced from 7.137 K in the existing spiral model to 0.682 K. The optimal axisymmetric chuck could reduce surface temperature differences up to 90 % compared with the conventional spiral chuck.

In this study, the heat transfer performance of a two-phase closed thermosyphon with super-hydrophobic (SH-phobic) condenser and super-hydrophilic (SH-philic) evaporator is investigated, and the results are compared with those of a bare condenser. At 100–200 W, the total thermal resistance on the SH-phobic surface decreases by up to 10.40 %, 0.41 % and 27.44 % compared with the bare condenser surface at filling ratios of 0.25, 0.5, and 0.75, respectively. However, the total thermal resistance increases by 55.06 %, 411.35 % and 128.33 % from 300 to 400 W, respectively. The critical heat flux for the SH-phobic surface is lower than for the bare surface. The SH-phobic surface performs better than bare surface in the low-power region (100–200 W), but not in the high-power region above 300 W. Therefore, the input power should be considered when applying the SH-phobic surface to the condensing section.

Conceptual design plays an important role in determining the basic characteristics and final product performances. However, there are many uncertainties in the conceptual design, such as the vagueness of customer requirements, uncertainty of design parameters, and diversity of the decision-making, which will lead to fluctuations in the performance or even failure of the scheme in many cases. To solve this problem, a conceptual design model was constructed by considering multi-uncertainties. First, taking satisfaction, performance, and production cost as design objectives, a conceptual design optimization model was established. Secondly, an improved non-dominated sorting genetic algorithm-II (NSGA-II) based on the expectation-possibility-probability hybrid model was proposed to search the Pareto solutions of conceptual design. Finally, the optimal conceptual design scheme was selected from the Pareto set by using the intuitionistic fuzzy λ-Shapely Choquet integral method. The effectiveness and efficiency of the proposed method were validated by the polishing machine conceptual design.

The paper provides a detailed overview of the development of a containment pressure and temperature (P/T) analysis methodology for advanced power reactor 1400 (APR1400) nuclear power plants (NPPs). The study addresses the restrictions on exporting independent nuclear power plants by utilizing the containment analysis package (CAP) computer code developed in Korea. One of the key aspects highlighted in the paper is the comparison of results obtained from the CAP code with those from the CONTEMPT-LT/028 code which is used P/T analysis. The analysis focuses on two types of accidents: loss of coolant accidents (LOCA) and main steam line break (MSLB) accidents, which are considered as design basis accidents. By comparing the outcomes of both codes, the paper evaluates the performance and effectiveness of the CAP code in predicting the P/T behavior within the containment during these accidents. The paper also discusses the criteria and technical standards for the containment P/T analysis. It emphasizes the importance of ensuring that the peak P/T remain within the safety related systems, equipment, and structures of NPP. The design pressure is identified as a critical factor in achieving these objectives. In conclusion, the study presents the successful development of a containment P/T analysis methodology using the CAP computer code for APR1400. The methodology considers the specific characteristics of Korean NPPs and new code, CAP. The paper emphasizes the applicability and effectiveness of the CAP code in this context. However, further research and validation efforts are recommended to enhance the accuracy and reliability of the methodology for various design basis accidents. The developed methodology is expected to contribute to the safe and efficient operation of APR1400 NPPs and support Korea’s ambitions in exporting NPPs’ technology to other countries.

The elastic surface algorithm (ESA) is an iterative inverse design method for airfoils, considering the airfoil wall as an elastic curved beam pinned at its beginning and ending points. This structure deforms in response to the disparity between existing and target pressure distributions. This paper introduces an improvement to the ESA, allowing controlled movement of the airfoil’s leading edge within a vertical groove. This advancement enables the adjustment of the angle of attack during the inverse design process, enhancing the airfoil’s robustness and flexibility. In contrast to a fixed angle of attack approach, the proposed method prevents unrealistic geometric features, such as airfoil fishtailing, improving convergence potential. The developed method was validated through the inverse design of NACA0012 and FX63-137 airfoils in a viscous subsonic flow regime. The flow solver was validated using existing experimental results, showing good agreement. Finally, the pressure distribution of the FX63-137 airfoil was modified to increase lift or decrease drag. The corresponding geometries were obtained via the advanced ESA method, resulting in an almost 4 % increase in the lift-to-drag ratio.

The effect of longitudinal groove cavities on drag and flow behavior was investigated for the axisymmetric model acquired by different conical boattail models. The angle of the boattail was changed from 0 to 22° to understand the influence of cavities on the aerodynamic drag and flow behaviors. The Reynolds averaged Navier-Stokes (RANS) equation with turbulent model k-ω SST was used for the investigation. The simulation was conducted at a velocity of 22 m/s by Ansys Fluent software. Numerical results of the boundary layer, velocity fields, pressure, and drag were first validated by experiments at the same flow conditions. Our results indicate that the grooved cavity allows a reduction of aerodynamic drag up to 24 % for the boattail model of 22°. Additionally, a 6 % drag reduction was also observed for the boattail model of around 14°, where the drag is minimal. The decreasing drag is connected to an increasing base pressure, which is from shortening wake structure and increasing boattail pressure around the shoulder. The longitudinal grooves are found an effective passive control device for narrowing flow separation on the boattail. The details of pressure distributions, flow structure at the surface, and near-wake structure were investigated.

X-ray diffraction (XRD) and the finite element technique (FET) to measure the residual stresses (RS) inside Al1060 rods produced by forming operation at three different half extrusion angles (HEA = 20°, 40°, and 60°) were applied. The results of the experimental work and FET illustrate a good convergence in terms of the relationship between extrusion force and displacement with an error ratio reaching 15 %. The effect of HEA = 20° on extrusion force is the lowest compared to others. Moreover, the behavior of the obtained residual stresses from XRD and FET is in good agreement with the existence of some variation in their values. The profile of these stresses is in a tensile state near the rod surface and a compressive state near the axis at HEA = 20° and 40°. In contrast, compressive residual stresses are obtained close to the surface and center of the extruded rod at HEA = 60°.

In order to improve the problem of poor sedimentation and easy leakage when applied to MR devices of magnetorheological (MR) fluid, this work made a magnetorheological grease (MRG) material with 70 % carbonyl iron powder and used Anton Paar rheometer to test its flow curve under different currents. The Bingham model is selected and the Origin software is used for fitting calculation. In addition, due to the advantages of rheological properties of MRG, the double rod MRG damper applied to the vibration reduction system was designed. The calculation of the main component parameters and the dimensions of the magnetic field Road size were conducted during the design process. After the physical completion of the MRG damper, its mechanical performance was tested, and the results showed that the maximum damping force reached 1.1 kN when the current was 1.8 A. Subsequently, the Bouc Wen model and Dahl model were introduced to describe the nonlinear behavior of the magnetorheological grease damper. The prediction accuracy of the two models was compared using a coefficient of determination, and it was found that the Bouc Wen model can more accurately and efficiently simulate the dynamic characteristics of the magnetorheological grease damper, with a coefficient of determination value above 0.99. Finally, the relationship between model parameters and current was established through least squares fitting, and most of the parameters were fitted with a cubic polynomial relationship with current.

γ-TiAlNb intermetallic compound is a highly promising material for aircraft structural components. A 46Ti-46Al-8Nb intermetallic compound was prepared and subjected to three different heat treatments. The changes in phase composition, microstructure, and hardness of the as-cast samples and heat-treated samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and Rockwell hardness. Subsequently, the material was designed for milling of thin-wall structures, with a focus on side milling. The milling process was investigated under different axial and radial cutting depths, and the variations in multi-directional cutting forces were analyzed, taking into consideration the surface quality of the machined parts. The results indicate that the γ-TiAlNb intermetallic compound possesses high hardness and brittleness. With increasing heat treatment temperature, the content of TiAl phase significantly decreases, while the content of AlTi₃ phase increases notably. The β-Ti phase containing Nb remains nearly unchanged and is mainly located at grain boundaries. Heat treatment can enhance the machinability of the TiAlNb intermetallic compound. A heat treatment process involving a 1-hour hold at 1200 °C followed by furnace cooling results in reduced Rockwell hardness, lower milling forces in three directions and improved surface quality.

Generated rotor (gerotor) pumps have commercial applications in oil supply pumps and compressors. Unfortunately, they produce an excessive amount of noise while in operation. The present study focuses on reducing the noise, which is caused due to pressure oscillations in the fluid, and vibration levels when a gerotor pump is in operation. Three-dimensional numerical simulations were performed on the gerotor pump using the dynamic mesh method. The flow field was simulated using the commercial software Ansys Fluent. The mesh motion was provided in the form of a user-defined function. Computational fluid dynamics analysis was performed for different combinations of delivery pipe length and diameter, and their effects on delivery pressure were analyzed. It is observed from numerical results that the pressure oscillations are reduced around 20 % by increasing volume of port or pipe region, which in turn reduces the noise levels. It is concluded that the pressure oscillations during the fluid flow are highly dependent on the volume of the delivery pipe.