• Journal of Computational Design and Engineering
• /
• v.2 no.4
• /
• pp.206-217
• /
• 2015

This paper presents a complete S-shape feed rate scheduling approach (CSFA) with confined jerk, acceleration and command feed rate for parametric tool path. For a Non-Uniform Rational B-Spline (NURBS) tool path, the critical points of the tool path where the radius of curvature reaches extreme values are found firstly. Then, the NURBS curve is split into several NURBS sub-curves or blocks by the critical points. A bidirectional scanning strategy with the limitations of chord error, normal/tangential acceleration/jerk and command feed rate is employed to make the feed rate at the junctions between different NURBS blocks continuous. To improve the efficiency of the feed rate scheduling, the NURBS block is classified into three types: short block, medium block and long block. The feed rate profile corresponding to each NURBS block is generated according to the start/end feed rates and the arc length of the block and the limitations of tangential acceleration/jerk. In addition, two compensation strategies are proposed to make the feed rate more continuous and the arc increment more precise. Once the feed rate profile is determined, a second-order Taylor's expansion interpolation method is applied to generate the position commands. Finally, experiments with two free-form NURBS curves are conducted to verify the applicability and accuracy of the proposed method.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
• /
• v.19 no.1
• /
• pp.51-56
• /
• 2013

From the time the product is manufactured until it is carried and ultimately used, the product is subjected to some form of handling and transportations. During this process, the product can be subjected to many potential hazards. One of them is the damage caused by shocks. In order to design a product-package system to protect the product, the peak acceleration or G force to the product that causes damage needs to be determined. When a corrugated fiberboard box loaded with products is dropped onto the ground, part of the energy acquired due to the action of the gravitational acceleration during the free fall is dissipated in the product and the package in various ways. The shock absorbing characteristics of the packaging cushion materials are presented as a family of cushion curves in which curves showing peak accelerations during impacts for a range of static loads are shown for several drop heights. The new method for determining the shock absorbing characteristics of cushioning materials for protective packaging has been described and demonstrated. It has been shown that cushion curves can be produced by combining the static compression and impact characteristics of the material. The dynamic factor was determined by the iterative least mean squares (ILMS) optimization technique in which the discrepancies between peak acceleration data predicted from the theoretical model and obtained from the impact tests are minimized. The approach enabled an efficient determination of cushion curves from a small number of experimental impact data.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.17 no.1
• /
• pp.78-89
• /
• 1993

A new theory based on the modified momentum and energy conservation has been proposed in order to overcome the drawbacks included in previous theories which are used for the determination of dynamic yield stresses and the investigation of dynamic behavior of metals. Then the improvements suggested by the new theory have been manifested through the analysis of the error included in the measurement of deformed length and through the comparison between the new theory, existing theories, and experimental results performed by previous workers. Meanwhile rod impact test has been performed which uses a compressed- air system for the acceleration of flat-ended cylindrical free-cutting brass rods. From the geomtrical measurements of deformed length, the dynamic yield stress of free-cutting brass has determined.

• Bulletin of the Society of Naval Architects of Korea
• /
• v.23 no.2
• /
• pp.1-13
• /
• 1986

The nonlinear hydrodynamic forces acting on a two-dimensional circular cylinder, oscillating with large amplitude in the free surface, are calculated by using the Semi-Lagrangian Time-Step-ping Method used by O.M. Faltinsen. In present calculation the position and the potential value of free surface are calculated using the exact kinematic and dynamic free surface boundary condition. At each time step an integral equation is solved to obtain the value of potential and normal velocity along the boundaries, consisting of both the body surface and the free surface. Some effort was devoted to the elimination of instability arising in the range of high frequency. Numerical simulations were performed up to the 3rd or 4th period which seems to be enough for the transient effect to die out. Each harmonic component and time-mean force are obtained by the Fourier transform of forces in time domain. The results are compared with others' experimental and theoretical results. Particularly, the calculation shows the tendency that the acceleration-phase 1st-harmonic component(added mass) increases as the motion amplitude increases and a reverse tendency in the velocity-phase 1st-harmonic component(damping coefficient). The Yamashita's experimental result also shows the same tendency. In general, the present result show relatively good agreement with the Yamashita's experimental result except for the time-mean force.

• Transactions of the Korean hydrogen and new energy society
• /
• v.23 no.4
• /
• pp.404-411
• /
• 2012

This research numerically analyses the effects of the damping device on the operation characteristics of a free piston linear engine. In this paper, the free piston linear engine uses spring as a damping device. The investigated parameter is spring hardness which is varied at 0.5, 1, 2.9, and 14.7 N/mm. The effects of spring hardness on the dynamic characteristic, thermodynamic characteristic and electric power of the engine are investigated. Beside, the equivalent ratio is also changed to provide more information for this study. The simulation results show that, by increasing spring hardness from 0.5 to 14.7 N/mm, all of parameters related to dynamic characteristic such as piston velocity, acceleration, displacement, and frequency increase accordingly. Beside, the peak pressure in the cylinder and electric power are also increased when increasing spring hardness. The tendency is also observed at varied equivalent ratios.

• Journal of Positioning, Navigation, and Timing
• /
• v.7 no.2
• /
• pp.91-103
• /
• 2018

Conventional inertial measurement units cannot be used in the spinning vehicle with high rotation rate due to gyro's narrow operation range. By the way, angular acceleration can be measured using the accelerometer array distributed in the vehicle. This paper derives a mechanization for the gyro-free INS in the navigation frame, and proposes a gyro-free INS algorithm based on the derived mechanization. In addition, the proposed algorithm is used to estimate angular velocity, attitude, velocity, and position of a spinning vehicle with high rotation rate. A MATLAB-based software platform is configured in order to show validation of the proposed algorithm. The reference trajectory of a spinning vehicle at 3 round per second, 30 round per second are set up, and the outputs of accelerometer are generated when triads of accelerometer are located at the origin and all the axes. Navigation results of the proposed algorithm for the generated output are presented. The results show that the proposed navigation algorithm can be applied to the spinning vehicle with high rotation rate.

• Journal of the Society of Naval Architects of Korea
• /
• v.34 no.1
• /
• pp.41-49
• /
• 1997

Computational results from Navier-Stokes equations are presented for the Stokes-wave/flat-plate boundary-layer and wake for small wave steepness(Ak=0.01), including exact and approximate treatments of the viscous free-surface boundary conditions. The macro-scale flow indicate that the variations of the external-flow pressure gradients cause acceleration or deceleration of the streamwise velocity component and alternating direction of the cross flow. Remarkably, the wake displays a greater response, i.e., a bias with regard to favorable as compared to adverse pressure gradients. The micro-scale flow indicates that the free-surface boundary conditions have a profound influence over the boundary layer and near/intermediate wake. Order-of-magnitude estimates are conformed to the computational results. And appreciable errors are introduced through approximations to the free-surface boundary conditions.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 1996.10a
• /
• pp.131-137
• /
• 1996

To perform condition monitoring of P.C. Box girder bridge under ambient traffic, dynamic characteristics were identified using the results of load test an analysis. It was found that natural frequencies obtained from the measured acceleration data for the forced vibration part and free vibration part were nearly identical. Thus it can be concluded that dynamic parameters are properly determined under ambient traffic condition. Finite element model for analysis was calibrated using measured frequencies. Change of dynamic characteristics were predicted through analysis of the established finite element model with anticipated change.

• Journal of the Korean Chemical Society
• /
• v.15 no.6
• /
• pp.359-366
• /
• 1971

The extended Huckel calculations on five organic accelerators of vulcanization have been carried out. Various MO quantities e.g., electron populations and AO coefficients, are used to explain accelerator reactivity of the compounds. Results of these analyses lead us to support free radical mechanism of acceleration in vulcanization.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 1998.10a
• /
• pp.314-321
• /
• 1998

This paper presents motion based design methodology for structures. Current design methodologies are primarily strength-based. Such methods are adequate when strength is expected to govern the design. But as the slenderness of structures increases, motion such as displacement and acceleration becomes the dominant criterion. In this paper, a preliminary design approach for beam-type buildings, where motion dominates the design, is discussed by effectively distributing the magnitude of structural stiffness to control the distribution of displacement under service load. This analytic development is illustrated using a cantilever beam as the structure under static loads, free vibration, and forced vibration.