• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.8 s.179
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• pp.1949-1957
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• 2000

All the loads in the real world act dynamically on structures. Since dynamic loads are extremely difficult to handle in analysis and design, static loads are utilized with dynamic factors. The dyna mic factors are generally determined based on experiences. Therefore, the static loads can cause problems in precise analysis and design. An analytical method based on modal analysis has been proposed for the transformation of dynamic loads into equivalent static load sets. Equivalent static load sets are calculated to generate an identical displacement field in a structure with that from dynamic loads at a certain time. The process is derived and evaluated mathematically. The method is verified through numerical tests. Various characteristics are identified to match the dynamic and the static behaviors. For example, the opposite direction of a dynamic load should be considered due to the vibration response. A dynamic bad is transformed to multiple equivalent static loads according to the number of the critical times. The places of the equivalent static load can be different from those of the dynamic load. An optimization method is defined to use the equivalent static loads. The developed optimization process has the same effect as the dynamic optimization which uses the dynamic loads directly. Standard examples are solved and the results are discussed

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.1
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• pp.106-113
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• 2004

Most of mechanical structures are composed of many substructures connected to one another by various types of mechanical joints. In automotive engineering, it is important to study these connected structures under various dynamic forces for the evaluations of fatigue life and stress concentration exactly. In this study, the dynamic response of vehicle structure to external forces is classified an inverse problem involving strains from the experiment and the analysis. The practical dynamic forces are determined by the combination of the analytical and experimental method with analyzed strain by quasi-static finite element analysis under unit force and with measured strain by a strain gage under driving load, respectively. In a stressed body, inter-molecular chemical bonds are failed beyond the certain magnitude. The failure of molecular structure in material is considered as a time process of which rate is determined by mechanical stress. That is, the failure of inter-molecular chemical bonds is the fatigue lift of material. This kinetic concept is expressed as lethargy coefficient. And S-N curve is obtained with the lethargy coefficient from quasi-static tensile test. Equivalent practical dynamic force is obtained from the identification of practical dynamic force for one loading point. Using the practical dynamic force and S-N curve, fatigue life of a window pillar is analyzed with FEM under the identified force by the procedure of above mentioned.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.8
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• pp.617-622
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• 2016

The article describes the determination of the dynamic stability for an observation antenna, considering the rotational speed by the payload driving motor. A finite element model of the observation antenna was made using the solid and beam elements. The connecting parts between the solid and the beam was adequately coupled. The boundary conditions were made by restriction of the degree of freedoms in the supporting points. With the comparison between the modal analysis results and the rotating speed of the payload driving motor, no resonance for the structure of antenna was identified and first natural frequency was determined under 33 Hz (Seismic Cut-Off Frequency). Therefore, the dynamic stability of the antenna was confirmed by the comparism between the seismic safety criterion and the stress results of the dynamic analysis applied the loading conditions and required response spectrum (RRS).

• Journal of Mechanical Science and Technology
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• v.16 no.11
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• pp.1412-1419
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• 2002

Dynamic shear tests for the tough-pitch copper at high strain and high strain rate was performed. The Split Hopkinson Pressure Bar (SHPB) compression test system was modified to yield a shear deformation in the specimen. Hat-shaped specimens for the tough-pitch copper were adopted to generate high strain of γ=3～4 and high strain-rate of γ= 10$^4$/s. The dynamic analysis by ABAQUS 5.5/EXPLICIT code verified that shear zone can be localized in hat-shaped specimens. A proper impact velocity and the axial length of the shear localization region wert determined through the elastic wave analysis. The displacement in a hat-shaped specimen is limited by a spacer ring which was installed between the specimen and the incident bar. The shear bands were obtained by measuring the direction of shear deformation and the width of deformed grain in the shear zone. The decrease of specimen length has been measured on the optical displacement transducer. Dynamic shear stress-strain relations in the tough-pitch copper were obtained at two strain-rates.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.2 s.95
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• pp.218-224
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• 1999

In the feed drive systems of machine tools that consist of many mechanical components such as motor, coupling, ballscrew, nut or table, a torsional vibration is often generated because of its elastic elements in torque transmission. Generally, the accuracy of motion control system is strongly influenced by the dynamic behavior of coupled transmission components. Especially, a torsional vibration caused by the elasticity of mechanical elements might deteriorate the quick movement of system and lead to shorten the life time of the mechanical transmission elements. So, it is necessary to analyze the electromechanical system mathematically to optimize the dynamic characteristics of the feed system. In this paper, the mathematical model of a feed drive system was developed and its mechanical characteristics were analyzed on the basis of the proposed model. The design concepts of speed control loop to stabilize a feed drive system were also proposed.

• Journal of Mechanical Science and Technology
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• v.19 no.spc1
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• pp.444-451
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• 2005

The analysis of human arm motion during steering maneuver is carried out for investigation of man-machine interface of driver and steering system Each arm is modeled as interconnection of upper arm, lower arm, and hand by rotational joints that can properly represents permissible joint motion, and both arms are connected to a steering wheel through spring and damper at the contact points. The joint motion law during steering motion is determined through the measurement of each arm movement, and subsequent inverse kinematic analysis. Combining the joint motion law and inverse dynamic analysis, joint stiffness of arm is estimated. Arm dynamic analysis model for steering maneuver is setup, and is validated through the comparison with experimentally measured data, which shows relatively good agreement. To demonstrate the usefulness of the arm model, it is applied to study the effect of steering column angle on the steering motion.

• Journal of Mechanical Science and Technology
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• v.16 no.4
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• pp.448-453
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• 2002

This paper presents a modeling method for the vibration analysis of translationally accelerated cantilever plates. An accurate dynamic modeling method, which was introduced in the previous study, is employed to obtain the equations of motion for the vibration analysis. Dimensionless parameters are identified to generalize the conclusions from numerical results. The effects of the dimensionless parameters on the natural frequencies and mode shapes are investigated. Particularly, the magnitude of critical acceleration which causes the dynamic buckling of the structure is calculated. Incidentally, the natural frequency loci veering phenomena are observed and discussed.

• Structural Engineering and Mechanics
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• v.55 no.2
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• pp.263-280
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• 2015

This paper describes a study of the collision of hard steel spheres against aluminium thin circular plates at speeds up to 140 m/s. The tests were monitored by a high speed camera and a chronoscope, which allowed the determination of the ballistic limit and the plate deformation pattern. Quasi-static material parameters were obtained from tests on a universal testing machine and dynamic mechanical characterization of two aluminium alloys were conducted in a split Hopkinson pressure bar. Using a damage model, the perforation of the plates was simulated by finite element analysis. Axisymmetric, shell and solid elements were employed with various parameters of the numerical analysis being thoroughly discussed, in special, the dynamic model parameters. A good agreement between experiments and the numerical analysis was obtained.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.2
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• pp.467-478
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• 1994

This paper deals with dynamic behaviors of a free-piston Vuilleumier heat pump system, which are characterized by stroke of each diplacer/stroke ratio, operating frequency and phase angle. Based on the Isothermal Model, basic equations of motion are derived and linearized. In particular, dependence of damping coefficients of the dynamic parameters are taken into account in the formulation, which does not bring additional difficulties in the analysis. In order to investigate effects of design conditions on the dynamic parameters are taken into account in the formulation, which does not bring additional difficulties in the analysis. In order to investigate effects of design conditions on the dynamic characteristics, calculations are performed for the prototype made by Schulz and Thomas and results are qualitatively compared with their data obtained from the analysis as well as the experiment. It appears that they made a mistake in evaluating the hysteresis loss of the gas spring in their analysis. And, the present results show a better agreement with their experimental data than those by their own analysis. Although there are some unresolved aspects such as frequency variations with respect to the mean pressure and the hot space temperature, it is expected that the present analysis may be an effective tool for prediction of dynamics of a free- pistion VM machine at the preliminary design stage.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.8 s.239
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• pp.1085-1092
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• 2005

The OHT(Over Head Transportation) Vehicle transports heavy products quickly and repeatedly at the industrial workplace. The belt in the OHT vehicle is used to support the weight of the OHT Cage. The fatigue of the belt is caused by the dynamic load during the operation time. Since the fatigue fracture of the belt affects the safety at the workplace, the correct prediction of the dynamic load is necessary to calculate the fatigue life of the belt on the design step. In this paper a computer aided analysis method is proposed for the belt in the early design stage using dynamic analysis, stress analysis, belt tensile test, belt fatigue test and fatigue lift prediction method. From the dynamic load time histories and the stress of the belt FE model, a dynamic stress time history is produced. Using linear damage law and cycle counting method, fatigue life cycle is calculated. The method developed in this paper is used to reduce the time and cost for designing the OHT belt in different environment and condition.