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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Transactions of the Korean Society of Mechanical Engineers A
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Journal DOI :
The Korean Society of Mechanical Engineers
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Volume & Issues
Volume 40, Issue 9 - Sep 2016
Volume 40, Issue 8 - Aug 2016
Volume 40, Issue 7 - Jul 2016
Volume 40, Issue 6 - Jun 2016
Volume 40, Issue 5 - May 2016
Volume 40, Issue 4 - Apr 2016
Volume 40, Issue 3 - Mar 2016
Volume 40, Issue 2 - Feb 2016
Volume 40, Issue 1 - Jan 2016
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Shape Optimization of a Hole for Water Jetting in a Spudcan for a Jack-up Rig
Seong, Jeong Hyeon ; Han, Dong Seop ; Park, Young Chul ;
Transactions of the Korean Society of Mechanical Engineers A, volume 40, issue 4, 2016, Pages 337~342
DOI : 10.3795/KSME-A.2016.40.4.337
A spudcan is mounted on the lower leg of the jack-up rig, a device for preventing a rollover of a structure and to support the structure in a stable sea floor. At the time of inserting the surface of the spud can to penetrate when the sand layer is stable and smoothly pulled to the clay layer, and at that time of recovery when uploading the spud can is equipped with a water injection device. In this study, it is significant to optimize the shape of pipelines holes for water injection device and it was set in two kinds of shape, the oval and round. Interpretation of the subject into the site of Gulf of Mexico offshore Wind Turbine Installation Vessels (WTIV) was chosen as a target platform. Using the ANSYS Workbench commercial programs, optimal design was conducted. The results of this study can be applied to the hole-shaped design of various marine structures.
Real-Time Flight Testing for Developing an Autonomous Indoor Navigation System for a Multi-Rotor Flying Vehicle
Kim, Hyeon ; Lee, Deok Jin ;
Transactions of the Korean Society of Mechanical Engineers A, volume 40, issue 4, 2016, Pages 343~352
DOI : 10.3795/KSME-A.2016.40.4.343
A multi-rotor vehicle is an unmanned vehicle consisting of multiple rotors. A multi-rotor vehicle can be categorized as tri-, quad-, hexa-, and octo-rotor depending on the number of the rotors. Multi-rotor vehicles have many advantages due to their agile flight capabilities such as the ability for vertical take-off, landing and hovering. Thus, they can be widely used for various applications including surveillance and monitoring in urban areas. Since multi-rotors are subject to uncertain environments and disturbances, it is required to implement robust attitude stabilization and flight control techniques to compensate for this uncertainty. In this research, an advanced nonlinear control algorithm, i.e. sliding mode control, was implemented. Flight experiments were carried out using an onboard flight control computer and various real-time autonomous attitude adjustments. The feasibility and robustness for flying in uncertain environments were also verified through real-time tests based on disturbances to the multi-rotor vehicle.
Non Linear Viscoelastic Constitutive Relation of Elastomers for Hysteresis Behavior
Yoo, Sairom ; Ju, Jaehyung ; Choi, Seok-Ju ; Kim, Dooman ;
Transactions of the Korean Society of Mechanical Engineers A, volume 40, issue 4, 2016, Pages 353~362
DOI : 10.3795/KSME-A.2016.40.4.353
An accurate hysteresis model of an elastomer is important for quantifying viscoelastic energy loss. We suggest a highly nonlinear hyper-viscoelastic constitutive model of elastomers. The model captures a nonlinear viscoelastic characteristic by combining Yeoh's hyperelastic model and Hoofatt's hysteresis model used Neo-Hookean hyperelastic model. Analytical and numerical models were generated from uniaxial cyclic tests of an elastomer under a sinusoidal load with a mean strain of 150%, amplitudes of 20~80%, and frequencies of 0.02~0.2Hz. The viscoelastic model can highly capture the viscoelastic energy loss up to a strain of 230%.
Topology Optimization of a Vibrating System of Rigid and Flexible Bodies for Maximizing Repeated Eigenfrequencies
Ahn, Byungseong ; Kim, Suh In ; Kim, Yoon Young ;
Transactions of the Korean Society of Mechanical Engineers A, volume 40, issue 4, 2016, Pages 363~372
DOI : 10.3795/KSME-A.2016.40.4.363
When a system consisting of rigid and flexible bodies is optimized to improve its dynamic characteristics, its eigenfrequencies are typically maximized. While topology optimization formulations dealing with simultaneous design of a system of rigid and flexible bodies are available, studies on eigenvalue maximization of the system are rare. In particular, no work has solved for the case when the target frequency becomes one of the repeated eigenfrequencies. The problem involving repeated eigenfrequencies is solved in this study, and a topology optimization formulation and sensitivity analysis are presented. Further, several numerical case studies are considered to demonstrate the validity of the proposed formulation.
Method of Fast Interpolation of B-Spline Volumes for Reconstructing the Heterogeneous Model of Bones from CT Images
Park, Jun Hong ; Kim, Byung Chul ;
Transactions of the Korean Society of Mechanical Engineers A, volume 40, issue 4, 2016, Pages 373~379
DOI : 10.3795/KSME-A.2016.40.4.373
It is known that it is expedient to represent the distribution of the properties of a bone with complex heterogeneity as B-spline volume functions. For B-spline-based representation, the pixel values of CT images are interpolated by B-spline volume functions. However, the CT images of a bone are three-dimensional and very large, and hence a large amount of memory and long computation time for the interpolation are required. In this study, a method for resolving these problems is proposed. In the proposed method, the B-spline volume interpolation problem is simplified by using the uniformity of pixel spacing of the image and the properties of B-spline basis functions. This results in a reduction in computation time and the amount of memory used. The proposed method was implemented and it was verified that the computation time and the amount of memory used were reduced.
Improvement of Euler-Bernoulli Beam Theory for Free Vibration and Buckling Analyses via Saint-Venant's Principle
Jeong, Yong-Min ; Kim, Jun-Sik ;
Transactions of the Korean Society of Mechanical Engineers A, volume 40, issue 4, 2016, Pages 381~387
DOI : 10.3795/KSME-A.2016.40.4.381
In this paper, the methodology applied to the improvement of stress analyses is extended to free vibration and buckling analyses. The essence of the methodology is the Saint-Venant's principle that is applicable to beam and plate models. The principle allows one to dimensionally reduce three-dimensional elasticity problems. Thus the methodology can be employed to vibration and buckling as well as stress analysis. First, the principle is briefly revisited, and then the formations of classical beam theories are presented. To improve the predictions, the perturbed terms (unknowns) are introduced together with the warping functions that are calculated by stress equilibrium equations. The unknowns are then calculated by applying the equivalence of stress resultants (i.e., Saint-Venant's principle). As numerical examples, cantilever and simply supported beams are analytically solved. The results obtained are compared with those of the classical beam theories. It is shown that the methodology can be used to improve the predictions without introducing shear correction factors.
Optimization of Parallel Lift of a Wheel Loader Through Analysis of Working Characteristics of Links
Park, Hyun Gyu ; Jang, Jin Seok ; Yoo, Wan Suk ; Kim, Min Seok ; Lee, Hee Jong ;
Transactions of the Korean Society of Mechanical Engineers A, volume 40, issue 4, 2016, Pages 389~395
DOI : 10.3795/KSME-A.2016.40.4.389
Wheel loaders are utilized not only on construction sites, but also for general purposes, such as manufacturing and transportation. Therefore, during the basic design stage of this type of working device equipment, the designer should consider specifications as well as working performance. In this research, a characteristic analysis program was developed for use in the basic design stage of construction equipment using multibody dynamics analysis. In addition, through the optimization of its links, improvements to the lifting capability of a Z-bar-linkage-type wheel loader were suggested. Using the developed program and process, it is possible to reduce the time required for the basic design of the working device.
Development of a Similarity Evaluation System for Offshore Plants' 3D Piping CAD Models Created Using Aveva Marine and SmartMarine 3D
Lee, Jaesun ; Kim, Byung Chul ; Kim, Hyungki ; Cheon, Sanguk ; Cho, Mincheol ; Lee, Gwang ; Kim, Jin-Hyun ; Mun, Duhwan ; Han, Soonhung ;
Transactions of the Korean Society of Mechanical Engineers A, volume 40, issue 4, 2016, Pages 397~406
DOI : 10.3795/KSME-A.2016.40.4.397
Diverse stakeholders engaged in design, construction, and operation and maintenance of offshore plants typically operate heterogeneous plant 3D CAD systems. Engineering, procurement, and construction (EPC) companies are required to submit plant design result to the owner in the form of a plant 3D CAD model, as specified in the contract. However, because of the limitations of data interface of plant 3D CAD systems, EPC companies frequently perform manual remodeling to fulfill the terms and conditions of the contract. Therefore, comparison should be performed between the source plant 3D CAD model and the remodeled plant 3D CAD model to prove the validity of the remodeled plant 3D CAD model. To automate the comparison process, we have developed a system for quantitatively assessing the similarity of the plant 3D CAD models. This paper presents the architecture and detailed functions of the system. In addition, experimental results using this system are explained.
Evaluation of Dynamic Thrust Under Wind Shear in Wind Turbine Below Rated Wind Speed
Lim, Chae-Wook ;
Transactions of the Korean Society of Mechanical Engineers A, volume 40, issue 4, 2016, Pages 407~414
DOI : 10.3795/KSME-A.2016.40.4.407
As wind turbines are getting larger in size with multi-MW capacity, the blades are getting longer, over 40 m, and hence the asymmetric loads produced during the rotation of the rotor blades are increasing. Some factors such as wind shear, tower shadow, and turbulence have an effect on the asymmetric loads on the blades. This paper focuses on a method of modeling the dynamic load acting on a blade because of thrust variation under wind shear. A method that uses thrust coefficient is presented. For this purpose, "wind shear coefficient of thrust variation" is defined and introduced. Further, we calculate the values of the "wind shear coefficient of thrust variation" for a 2 MW on-shore wind turbine, and analyze them for speeds below the rated wind speed. Then, we implement a dynamic model that represents the thrust variation under wind shear on a blade, using MATLAB/Simulink. It is shown that it is possible to express thrust variations on three blades under wind shear by using both thrust coefficient and "wind shear coefficient of thrust variation."
Dynamic Analysis of Gimbal Structure System Including Nonlinear Elastic Rubber Vibration Isolator with Shock Acceleration
Lee, Sang Eun ; Lee, Tae Won ;
Transactions of the Korean Society of Mechanical Engineers A, volume 40, issue 4, 2016, Pages 415~422
DOI : 10.3795/KSME-A.2016.40.4.415
When shock acceleration is applied to a mechanical system, it may cause malfunctioning and damage to the system. Hence, to prevent these problems when developing a gimbal structure system for observation reconnaissance, the MIL-STD-810G shock standard must be satisfied as a design specification. Rubber vibration isolators are generally assembled on the base of the system in order to reduce the shock transferred from the aircraft. It is difficult to analyze the transient behavior of the system accurately, because rubber has a nonlinear load-deformation curve. To treat the nonlinear characteristic of the rubber, bilinear approximation was introduced. Using this assumption, transient responses of the system under base shock acceleration were calculated by the finite element method. In addition, experiments with a true prototype were performed using the same conditions as the analytical model. Compared with experimental data, the proposed numerical method is useful for the transient analysis of gimbal structure systems, including rubber vibration isolators with nonlinear stiffness and damping.
Study for Fracture in the Last Stage Blade of a Low Pressure Turbine
Lee, Gil Jae ; Kim, Jae Hoon ;
Transactions of the Korean Society of Mechanical Engineers A, volume 40, issue 4, 2016, Pages 423~428
DOI : 10.3795/KSME-A.2016.40.4.423
The last stage blades of a low pressure (LP) turbine get frequently fractured because of stress corrosion cracking. This is because they operate in a severe corrosive environment that is caused by the impurities dissolved in condensed steam and high stress due to high speed rotation. To improve the reliability of the blades under severe conditions, 12% Cr martensitic stainless steel, having excellent corrosion resistance and higher strength, is widely used as the blade material. This paper shows the result of root cause analysis on a blade which got fractured suddenly during normal operation. Testing of mechanical properties and microstructure examination were performed on the fractured blade and on a blade in sound condition. The results of testing of mechanical properties of the fractured blade showed that the hardness were higher but impact energy were lower, and were not meeting the criteria as per the material certificate specification. This result showed that the fractured blade became embrittled. The branch-type crack was found to have propagated through the grain boundary and components of chloride and sulfur were detected on the fractured surface. Based on these results, the root cause of fracture was confirmed to be stress corrosion cracking.