• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.26 no.4
• /
• pp.247-254
• /
• 2013

In this paper, dynamic response analysis of a heave compensation system is performed for offshore drilling operations based on multibody dynamics. With this simulation, the efficiency of the heave compensation system can be virtually confirmed before it is applied to drilling operations. The heave compensation system installed on a semi-submersible platform consists of a passive and an active heave compensator. The passive and active heave compensator are composed of several bodies that are connected to each other with various types of joints. Therefore, to carry out the dynamic response analysis, the dynamics kernel was developed based on mutibody dynamics. To construct the equations of motion of the multibody system and to determine the unknown accelerations and constraint forces, the recursive Newton-Euler formulation was adapted. Functions of the developed dynamics kernel were verified by comparing them with other commercial dynamics kernels. The hydrostatic force with nonlinear effects, the linearized hydrodynamic force, and the pneumatic and hydraulic control forces were considered as the external forces that act on the platform of the semi-submersible rig and the heave compensation system. The dynamic simulation of the heave compensation system of the semi-submersible rig, which is available for drilling operations with a 3,600m water depth, was carried out. From the results of the simulation, the efficiency of the heave compensation system were evaluated before they were applied to the offshore drilling operations. Moreover, the calculated constraint forces could serve as reference data for the design of the mechanical system.

• The Korean Journal of Nuclear Medicine Technology
• /
• v.23 no.1
• /
• pp.75-79
• /
• 2019

Purpose Cadmium-zinc-telluride (CZT) camera with semiconductor detector is capable of dynamic myocardial perfusion SPECT for coronary flow reserve (CFR). Image acquisition with the heart positioned within 2 cm in the center of the quality field of view (QFOV) is recommended because the CZT detector based on focused multi-pinhole collimators and is stationary gantry without rotation. The aim of this study was to investigate the optimal method for measuring position of the heart within the center of the QFOV when performing dynamic myocardial perfusion SPECT with the Discovery NM 530c camera. Materials and Methods From June to September 2018, 45 patients were subject to dynamic myocardial perfusion SPECT with D530c. For accurate heart positioning, the patient's heart was scanned with a mobile ultrasound and marked at the top of the probe where the mitral valve (MV) was visible in the parasternal long-axis view (PLAX). And, the marked point on the patient's body matched with the reference point indicated CZT detector in dynamic stress. The heart was positioned to be in the center of the QFOV in rest. The coordinates of dynamic stress and rest were compared statistically. Results The coordinates of the dynamic stress using mobile ultrasound and those taken of the rest were recorded for comparative analysis with regard to the position of the couch and analyzed. There were no statistically significant differences in the coordinates of Table in & out, Table up & down, and Detector in & out (P > 0.05). The difference in distance between the 2 groups was measured at $0.25{\pm}1.00$, $0.24{\pm}0.96$ and $0.25{\pm}0.82cm$ respectively, with no difference greater than 2 cm in all categories. Conclusion The position of the heart taken using mobile ultrasound did not differ significantly from that of the center of the QFOV. Therefore, The use of mobile ultrasound in dynamic stress will help to select the correct position of the heart, which will be effective in clinical diagnosis by minimizing the image quality improvement and the patient's exposure to radiation.

• Journal of the Korean Solar Energy Society
• /
• v.36 no.6
• /
• pp.1-12
• /
• 2016

A control algorithm for a 100 kW wind turbine is designed in this study. The wind turbine is operating as a variable speed variable pitch (VSVP) status. Also, this wind turbine is a permanent magnet synchronous generator (PMSG) Type. For the medium capacity wind turbine considered in this study, it was found that the optimum tip speed ratios to achieve the maximum power coefficients varied with wind speeds. Therefore a commercial blade element momentum theory and multi-body dynamics based program was implemented to consider the variation of aerodynamic coefficients with respect to Reynolds numbers and to find out the power and thrust coefficients with respect tip speed ratio and blade pitch angles. In the end a basic power controller was designed for below rated, transition and above rated regions, and a load reduction algorithm was designed to reduce tower vibration by the nacelle motion. As a result, damage equivalent Load (DEL) of tower fore-aft has been reduced by 32%. From dynamic simulations in the commercial program, the controller was found to work properly as designed. Experimental validation of the control algorithm will be done in the future.

• Journal of Biomedical Engineering Research
• /
• v.28 no.2
• /
• pp.218-228
• /
• 2007

Modem concepts of gait rehabilitation after stroke favor a task-specific repetitive approach. In practice, the required physical effort of the therapists limits the realization of this approach. Therefore, a mechanized gait trainer enabling nonambulatory patients to have the repetitive practice of a gait-like movement without overstraining therapists was constructed. In this study, we developed an active gait training system for patients with gait disorder. This system provides joint movements to patients who cannot carry out an independent gait. It provides a normal stance-swing ratio of 60:40 using an eccentric configuration of two gears. Joint motions of the knee and the ankle were evaluated with using the 3D motion analysis system and compared with the results from the multi-body dynamics simulation. In addition, clinical investigations were also performed for low stroke patients during the 6-week gait training. Results from the dynamics simulation showed that joint movements of the knee and the ankle were affected by the gear size, the step length and the length of the foot plate, except the radius of curvature of the foot guide plate. Also, the 6-week gait training revealed relevant improvements of the gait ability in all low subjects. Functional ambulation category levels of subjects after training were 2 in three patients and 1 in a patient. The developed active gait trainer seems feasible as an adjunctive tool in gait rehabilitation after stroke.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.14 no.6
• /
• pp.49-56
• /
• 2015

For designing working devices of construction equipment, it is necessary to consider not only sufficient working ability but also available working range. Therefore, it is important to select the appropriate pivot positions of links. This paper presents a study on selection of pivot points of links used in construction equipment. To analyze the effect of each pivot point, a design program for pivot selection is developed. A conventional pivot design method requires a complicated process because it needs to create a certain working position manually to evaluate its performance. However, the developed program includes an automatic link assembly algorithm; thus, the working device can easily be analyzed by using pivot information of links. The developed program also included a kinematic/static analysis module and characteristic analysis algorithms. Therefore, it is possible to easily analyze a working device model created through the automatic assembly algorithm, whereby users can easily analyze the effect of each link pivot point for the actual product design.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.22 no.5
• /
• pp.50-58
• /
• 2014

The PRT(Personal Rapid Transit) system is highly interested to meet a need for demand-responsive transport service and increasing demands of traffic in Korea recently. And it is being spotlighted as an eco-friendly transportation system. For these reasons, researches on the PRT system are actively undergoing in Korea. In this study, we evaluated the static structural and fatigue strengths based on ASCE-APM standards and ERRI B 12/RP 17 by means of FE simulation. We also evaluate the running stability by multi-body dynamic analyses and the rollover safety by a theoretical static stability factor according to the road modeling scenarios for the PRT system. From the results of this study, we confirmed the durability and running stability of the Korean PRT under development.

• Journal of the Korean Academy of Clinical Electrophysiology
• /
• v.5 no.2
• /
• pp.35-45
• /
• 2007

The purpose of this study was to examine spiral way movement of a trunk exerts on the movement ability. The details established to achieve for this article. This examination confirmed the weight, weight/height2 index, ratio of lumbar to pelvic, musculoskeletal quantity, push up for 2 minute, pitch a ball and voluntary isometric contraction with flexion and extension of knee joint of the subjects with spiral direct movement. Healthy eighteen subjects who understand fully the significance of procedure, consented to a plan, without neuromuscular disease were participated in two groups of experiment. The group were a spiral movement(9), rectilinear movement(9). Trunk movement tested 2 sessions of a spiral movement and rectilinear movement with a push up for 2 minute, 5days per a week, for the 4 weeks. This experiment tested 3 times with a sufficient rest for fatigue limitation. An analysis of the results used a paired samples t-test for difference from before and after experiment. The following results were obtained; At an internal change of the body, the musculoskeletal quantity was increased significantly to spiral movement group, but the weight was increased significantly, the musculoskeletal quantity was not significant to rectilinear movement. The movement ability evaluation for a external change was increased significantly in a push up for 2 minute, pitch a ball, isometric contraction with extension of knee joint of a spiral movement group, but a push up for 2 minute was increased significantly in a push up for 2 minute on the abdominal muscle training of a rectilinear movement group. As compared with a rectilinear movement, a spiral movement was more effect by cooperation with nerve and musculoskeletal system and an increase in movement ability was caused by learning acknowledgment, muscular reeducation. These results lead us to the conclusion that a spiral movement of trunk was more effect than a rectilinear movement, the coordination of nerve and musculoskeletal system was of importance of Multi-direction movement. Therefore, A further studies concerning the therapeutic exercise intervention and active-dynamic analysis could enhance the development of the most effect on the trunk.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.45 no.11
• /
• pp.951-966
• /
• 2017

In this work, numerical analyses are carried out and the behaviors are investigated for three types of double-acting oleo-pneumatic shock absorbers along with the mathematical models proposed in the part I of this work. After presenting each numerical algorithm corresponding to each model, the numerical algorithms are implemented as user-subroutines in MSC/ADAMS commercial multi-body dynamic software. By using the developed user-subroutines, numerical studies are carried out for compression/stretch test as well as drop test. From the comparative studies, we investigated the salient feature of each double-acting oleo-pneumatic shock absorber. Results identifies that it is possible to increase the absorbing efficiency in accordance with the requirements for aircraft landing conditions.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.39 no.6
• /
• pp.561-566
• /
• 2015

In this paper, the operating stiffness of a parallel robot used to handle heavy packages is optimized. Because the studied model, called a "pick and place robot," is applied for packaging logistics, it is important for the robot to be lightweight so that it may respond rapidly and have high stiffness to allow sufficient operating precision. However, these two requirements of low weight and high stiffness are mutually exclusive. Thus, the dynamic characteristics of the robot are analyzed through multibody dynamics analysis, and topology optimization is conducted to achieve this exclusive performance. Lastly, the reliability of the topology optimization is verified by applying the optimized design to the parallel robot.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.9
• /
• pp.84-90
• /
• 2018

In constructing the multi-body dynamics model to analyze the behavior of the railway vehicle, it is very important to understand the properties of the suspension elements that constitute the suspension system. Among them, coil springs, which are mainly used in primary and secondary suspension systems, clearly show the axial stiffness in the drawings, but the lateral properties of the coil springs are not specified clearly, making it difficult to construct a dynamic analysis model. Therefore, in this paper, the model for analyzing the lateral stiffness of the coil spring is examined. A finite element method was applied to analyze the lateral stiffness of the coil spring and numerical analysis was performed by applying the coil spring lateral stiffness analysis model proposed by Krettek and Sobczak. And the test to analyze the lateral stiffness of coil spring was conducted. As a result of comparing with the test results, it was found that the results obtained by applying the lateral stiffness analysis model of Krettek and Sobczak and correcting the correction coefficient are similar to those of the test results.