• Journal of Sensor Science and Technology
• /
• v.31 no.3
• /
• pp.156-162
• /
• 2022

This study estimates the relative position between body segments using segment orientation and segment-to-joint center (S2J) vectors. In many wearable motion tracking technologies, the S2J vector is treated as a constant based on the assumption that rigid body segments are connected by a mechanical ball joint. However, human body segments are deformable non-rigid bodies, and they are connected via ligaments and tendons; therefore, the S2J vector should be determined as a time-varying vector, instead of a constant. In this regard, our previous study (2021) proposed a method for determining the time-varying S2J vector from the learning dataset using a regression method. Because that method uses a deformation-related variable to consider the deformation of S2J vectors, the optimal variable must be determined in terms of estimation accuracy by motion and segment. In this study, we investigated the effects of deformation-related variables on the estimation accuracy of the relative position. The experimental results showed that the estimation accuracy was the highest when the flexion and adduction angles of the shoulder and the flexion angles of the shoulder and elbow were selected as deformation-related variables for the sternum-to-upper arm and upper arm-to-forearm, respectively. Furthermore, the case with multiple deformation-related variables was superior by an average of 2.19 mm compared to the case with a single variable.

• Ocean and Polar Research
• /
• v.36 no.4
• /
• pp.495-503
• /
• 2014

This paper focuses on the dynamic responses of a tracked vehicle crawling on extremely cohesive soft soil, each side of which is composed of two parallel tracks. The tracked vehicle consisted of 2 bodies. One body is the tracked vehicle body, which is assumed to be a rigid body with 6 DOFs. The other body is the buoy body. The two bodies are connected by a revolute joint. In order to evaluate the travelling performance of a 7 DOFs vehicle, a dynamic analysis program for the tracked vehicle was developed using Newmark's method and the incremental-iterative method. The effects of road wheels on the track and soil are not taken into account. A terra-mechanics model of extremely cohesive soft soil is implemented in form of relationships: normal pressure to sinkage, shear resistance to shear displacement, and dynamic sinkage to shear displacement. Pressure-sinkage relationship and shear displacement-stress relationship should represent the non-linear characteristics of extremely soft soil. Especially, since the shear resistance of soft soil is very sensitive to shear displacement, spatial distribution of shear displacement occurring at the contact area of the tracks should be calculated precisely. The proposed program is developed in FORTRAN.

• Journal of Ocean Engineering and Technology
• /
• v.20 no.6 s.73
• /
• pp.101-107
• /
• 2006

Recently, with the increase in requirements for marine development, a marine urbanism is being visualized, with more and more huge-scale structures at the scope of the ocean space utilization. In particular, a pontoon-type structure has attracted attention, since The Floating Structures Association of Japan proposed a new concept as the most suitable one of floating airports. The Very Lage Floating Structure (VLFS) is considered a flexible structure, for a quite large length-to-breadth ratio and its geometrical flexibility. The main objective of this study is to makean exact and convenient prediction about the hydro-elastic response on very large offshore structures in waves. The numerical approach for the hydro-elastic responses is based on the combination of the three dimensional source distribution method and the dynamic response analysis method, which assumed a dividing pontoon type structure, as many rigid bodies connected elastic beam elements. The established hydo-elastic theory was applied to the radiation forces caused by motions of a whole structure, formulated using the global coordinate system, which has the origin at the center of the structure. However, in this paper, we took radiation forces, occurred by individual motions of floating bodies, into consideration. The calculated results show good agreement with the experimental and calculated results by Yago.

• Journal of the Korea Society of Computer and Information
• /
• v.27 no.3
• /
• pp.63-69
• /
• 2022

In this paper, we propose a new GPU-based framework for quickly calculating adaptive and continuous SDF(Signed distance fields), and examine cases related to rendering/collision processing using them. The quadtree constructed from the triangle mesh is transferred to the GPU memory, and the Euclidean distance to the triangle is processed in parallel for each thread by using it to find the shortest continuous distance without discontinuity in the adaptive grid space. In this process, it is shown through experiments that the cut-off view of the adaptive distance field, the distance value inquiry at a specific location, real-time raytracing, and collision handling can be performed quickly and efficiently. Using the proposed method, the adaptive sign distance field can be calculated quickly in about 1 second even on a high polygon mesh, so it is a method that can be fully utilized not only for rigid bodies but also for deformable bodies. It shows the stability of the algorithm through various experimental results whether it can accurately sample and represent distance values in various models.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.29 no.2 s.233
• /
• pp.270-276
• /
• 2005

This paper develops the flexible computational model of a heavy truck by interfacing the frame modeled as a flexible body to the heavy truck's computational model composed of rigid bodies. The frame is modeled by the finite element method. Three torsional modes and three bending modes of the frame are considered for the interface of the heavy truck's computational model. The actual vehicle test is conducted off road with a velocity of 20km/h. The vertical accelerations at the cab and front axle are measured in the test. For the verification of the developed computational model, the measured vertical acceleration profiles are compared with the simulation results of the heavy truck's flexible computational model. E grade irregular road profile of ISO is used as an excitation input in the simulation. The verified flexible computational model is used to compare the vibration characteristics of a front suspension system having a multi-leaf spring and that having a tapered leaf spring. The comparison results show that the front suspension having a tapered leaf spring has a higher vertical acceleration at the front axle but a lower vertical acceleration at the cab than the suspension system having a multi-leaf spring.

• Journal of Energy Engineering
• /
• v.23 no.3
• /
• pp.163-173
• /
• 2014

In this study, a modeling method is based on representing a road generation system with several rigid bodies, i.e, pad, shaft, torsional damper, oneway-clutch, gear system, and electricity generator. The simulation software is developed to evaluate the performance of a road generation system. It is used to determine parametric dimension for optimal design with the theoretically calculated results from the simulation software. The parametric dimensions are included as capacity, length, and angle of equipment. The transient responses at the conditions of low and high vehicle speed are compared with the calculated results as torque, power, out energy etc. Consequently, before manufacturing system, the analysis of simulation results shows that the proposed concept and system has efficiency and confidence.

• Journal of Korean Society of Transportation
• /
• v.20 no.2
• /
• pp.81-92
• /
• 2002

An automobile crash with a pedestrian generates a trajectory which is crucial to identify the cause of the crash. Previous researches have been carried out for pedestrian movement using simple explicit formulae. The formulae are derived from elementary physics. Therefore, they could not sufficiently include variables of a vehicle and a pedestrian. To overcome such a limitation, a simulation is utilized for the pedestrian behavior in crash environment. A dynamic software called MADYMO is utilized for the simulation. A simulation model is established. The automobile body and a dummy are modeled with rigid bodies, joints and springs. The simulation results are compared with those from explicit formulae. It is found that the explicit formulae did not fit to pedestrian conditions. Simulations are performed for various velocities of automobiles. Results are discussed for the usage of the simulation.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2010.09a
• /
• pp.598-604
• /
• 2010

The drilled pier foundation is widely used to support transmission line structures due to its simplicity of construction. When this foundation type is used in conjunction with a single shaft or H-frame structure, it is subjected to a high overturning moment, combined with modest vertical and shear loads. Since the length and diameter of drilled piers are often governed by a maximum permissible deflection, many drilled piers being installed today are very conservatively designed. In this study, Nine prototype field-tests (1/8 scale) have been conducted in order to determine the vertical and lateral resistance of drilled pier foundation for single pole structures. These test results reveal the test piers behaved essentially as rigid bodies in soil (6D) and the center of rotation of the pier were typically 0.6~0.4 of the pier depth below ground surface. Test results also show the relationship between the applied load and the deflection at the top of the pier is highly nonlinear.

• Journal of the Korean Society for Precision Engineering
• /
• v.17 no.2
• /
• pp.80-88
• /
• 2000

This paper presents a method to optimize the bump steer characteristics (the change of toe angle with vertical wheel travel) with respect to hard points in the double wishbone front suspension of the four-wheel-drive vehicle using the design of experiment, multibody dynamics simulation, and optimum design program. Front and rear suspensions are modeled as the interconnection of rigid bodies by kinematic joints and force elements using DADS. The design variables with respect to the kinematic characteristics are obtained through the experimental design sensitivity analysis. An object function is defined as the area of absolute differences between the desired and experimental toe angle. By the design of experiment and regression analysis, the regression model function of bump steer characteristics is extracted. The design variables that make the toe angle optimized are selected using the optimum design program DOT. The lane change simulations and tests of the full vehicle models are implemented to evaluate the improvement of vehicle handling performances by the optimization of front bump steer characteristics. The results of the lane change simulations show that the vehicle with optimized bump steer has the weaker understeer tendency than the vehicle with initial bump steer.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2004.10a
• /
• pp.681-685
• /
• 2004

A media-feeding (or media-transport) system is a key component in daily consumer systems such as printers, copiers and ATM's. The role of the media-transport system is to feed a medium, which is usually in the form of a thin film, to the main process in a uniform and repeatable manner. Even small slippage between the media and the feeding rollers could significantly degrade the performance of the entire system. The slippage between the medium and the feeding rollers is determined by many parameters which include the friction coefficient between the feeding rollers and the medium material, the angular velocity of the feeding rollers, and the normal force applied by feeding rollers on the medium. This paper investigates the effect of the normal force and the angular velocity of feeding rollers on the slippage of the medium. Authors have constructed a test bed for experiments, which consists of a feeding module and various measuring devices. Using regular paper as media being fed, the authors experimentally measured the slippage of the medium under various normal forces and angular velocities of driving feeding roller. Also the authors developed a novel two-dimensional simulation model for the media-transport system. The paper medium is modeled as a set of multiple rigid bodies interconnected by revolute joints and rotational springs and dampers. Simulations were executed using a multi-body dynamic analysis tool called RecurDy $n^{ⓡ}$. The slippage obtained by the simulation is compared to experimental results.ults.