• Journal of KSNVE
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• v.9 no.1
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• pp.163-173
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• 1999

Precise and reasonable modelling is necessary and indispensable to the analysis of dynamic characteristics of mechanical structures. Also. the effective prediction of the change of modal properties due to the variation of design parameters is required especially for the application of finite element method to the structural dynamics problems. To meet those necessity and requirement, three model updating algorithms are proposed for finite element methods. Those algorithms are based on sensitivity analysis of the modal data obtained from experimental modal analysis(EMA) and analytical modal analysis(AMA). The adapted sensitivity analysis methods of the algorithms are 1)eigensensitivity(EGNS) method. 2)frequency response function sensitivity(FRFS) method. 3)sensitivity based element-by-element method (SBEEM), Singular value decomposition(SVD) is used for performing eigenanalysis and parameter estimation in the updating process. Those algorithms are applied to finite element of a plate and the updating capability of each algorithm is compared in terms of accuracy. reliability and stability of the updating process. It is shown that the model updating method using frequency response function is superior to the other methods in view of various updating capabilities.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.1
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• pp.110-116
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• 2013

Curvic coupling of mill turret should maintain disk weight and the cutting resistance which occurs the machining operation and must also have power transmission function. In order to improve machining operation range, the ejecting distance from curvic coupling to the disk must increase as much as possible. But moment is increased by the lack of capacity of the curvic coupling. Increase of moment is the cause of vibration/noise and degradation of machining performance not only stability problem. The manufacturer of mill turret has no the design information between the ejecting distance and the cutting resistance with safety of curvic coupling. Therefore this study describes a finite element analysis model of mill turret using ANSYS workbench. The structural analyses and modal analyses with varying of the ejecting distances and cutting resistances are performed. Finally the equation for relationship between the critical ejecting distance and the cutting resistance is defined under 5 of the safety factor for the maximum von-Mises stress at the curvic coupling.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.6
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• pp.447-456
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• 2014

In this paper, a new damage-detection method based on structural vibration is proposed. The essence of the proposed method is the detection of abrupt changes in rotation. Damage-induced rotation (DIR), which is determined from the modal flexibility of the structure, initially occurs only at a specific damaged location. Therefore, damage can be localized by evaluating abrupt changes in rotation. We conducted numerical simulations of two damage scenarios using a 10-story cantilever-type building model. Measurement noise was also considered in the simulation. We compared the sensitivity of the proposed method to localize damage to that of two conventional modal-flexibility-based damage-detection methods, i.e., uniform load surface (ULS) and ULS curvature. The proposed method was able to localize damage in both damage scenarios for cantilever structures, but the conventional methods could not.

• Journal of Biosystems Engineering
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• v.28 no.1
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• pp.27-34
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• 2003

Present combustion engines have reached almost at the limit of development due to the fundamental structural problems. This study was carried out to propose a new concept internal combustion engine which has great potential advantages to the conventional engines. Proposed new concept engine is a kind of rotary engine. A rotor is rotating concentrically in a cylinder which is divided into two partitioning valves. and it makes four compartments in the cylinder. The volumes of each of four compartments are changing continuously with the rotor movement, and performs the functions of intake, compression. expansion and exhaust simultaneously. The results of this study can be summarized as follows. 1. Expected theoretical thermal efficiency is 44.9 percent at the condition of 1000rpm and compression ratio of 8.0. which is almost the same as that of the conventional engines. i.e., piston and Wankel rotary engine. 2. The new concept engine has 2. working strokes in every revolution. Therefore. the new concept engine can reduce the specific weight and volume than four-stroke piston engine. 3. The torque variation is very small. therefore minimal noise and vibration are expectable. 4. The new concept engine can reduce mechanical energy loss than piston engine because neither crank mechanism nor eccentrical motion exists.

• Computers and Concrete
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• v.27 no.1
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• pp.29-39
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• 2021

This study aimed to develop a method for the determination of the damaged story in reinforced concrete (RC) structure with ambient vibrations, based on modified jerk energy methodology. The damage was taken as a localized reduction in the stiffness of the structural member. For loading, random white noise excitation was used, and dynamic responses from the finite element model (FEM) of 4 story RC shear frame were extracted at nodal points. The data thus obtained from the structure was used in the damage detection and localization algorithm. In the structure, two damage configurations have been introduced. In the first configuration, damage to the structure was artificially caused by a local reduction in the modulus of elasticity. In the second configuration, the damage was caused, using the Elcentro1940 and Kashmir2005 earthquakes in real-time history. The damage was successfully detected if the frequency drop was greater than 5% and the mode shape correlation remained less than 0.8. The results of the damage were also compared to the performance criteria developed in the Seismostruct software. It is demonstrated that the proposed algorithm has effectively detected the existence of the damage and can locate the damaged story for multiple damage scenarios in the RC structure.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.12
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• pp.3109-3117
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• 1994

To operate a flexible mechanism in high speed its weight must be reduced as far as the structural strength does not decrease too much, but a light-weighted mechanism causes undesirable elastodynamic responses deteriorating the system performance. Besides, clearance within the connections of mechanisms causes rapid wear, increased noise and vibration. Even if the problems described above must be considered in the initial design stage, there has been no effective design process which takes account of the correlation between dynamic characteristics of flexible mechanism and the clearance effect at the joint. In this study, the generalized elastodynamic governing equations which include dynamic characteristics and boundary conditions of flexible mechanism are derived by variational calculus and solved by using FFM theory. To take the clearance effect at joint into account a new dynamic model is presented and also the method of modified stiffness/damping matrix is proposed to activate the dynamic clearance model, which cooperates with the developed governing equation very easily. As the results of this study, the proposed method(modified stiffness/damping matrix) to calculate clearance effect was proved to be superior to the existing one(force reaction method) in solution convergency and calculation performance. Besides this method can be easily adopted to the complex shape joint without calculation of reaction force direction.

• Journal of KSNVE
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• v.2 no.1
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• pp.21-31
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• 1992

In the previous paper, we report a practical floor impact sound level prediction method for a heavyweight impact source(Tire), soft impact source such as children jumping and running. According to these results, the calculated value and the measured value correspond comparatively well, regardless of differences in the floor structures. And the floor impact sound for a heavyweight impact source, soft source was strongly influenced by structural factors such as floor slab stiffness and peripheral support conditions. But the floor impact sound for a light impact source (Tapping machine), hard impact source was influenced by resilient layers, composed of multi-layer in floor structures. Thus, In this paper, 4 actual floor structures, all with differing resilient layers, were calculated using impedance method. When these calculation values were compared with the measured values, approximately all the values fell with one rank of the sound insulation grade, reference curve(L curve) by the JIS standard. So, a sample of measured values and calculated values from floor structures is presented to show the accuracy and appropriateness of the impedance method in domestic.

• Steel and Composite Structures
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• v.22 no.1
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• pp.63-77
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• 2016

Top-down construction is a construction technique in which pit excavation and structure construction are conducted simultaneously. Reducing construction time and minimizing noise and vibration which affect neighboring structures, the technique is widely employed in constructing downtown structures. While H-steel columns have been commonly used as core columns, concrete filled steel tube (CFT) columns are at the center of attention because the latter have less axial directionality and greater cross-sectional efficiency than the former. When compared with circular CFT columns, square CFT columns are more easily connected to the floor structure and the area of percussion rotary drilling (PRD) is smaller. For this reason, square CFT columns are used as core columns of concrete encased and filled square (CET) columns in underground floors. However, studies on the structural behavior and concrete stress transfer of CET columns have not been conducted. Since concrete is cast according to construction sequence, checking the stress of concrete inside the core columns and the stress of covering concrete is essential. This paper presents the results of structural tests and analyses conducted to evaluate the usability and safety of CET columns in top-down construction where CFT columns are used as core columns. Parameters in the tests are loading condition, concrete strength and covering depth. The compressive load capacity and failure behavior of specimens are evaluated. In addition, 2 cases of field application of CET columns in underground floors are analyzed.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.2
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• pp.145-151
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• 2017

As an alternative to conventional explosive methods for demolition of concrete structures and rocks, the use of non-explosive demolition agents can be considered to reduce noise, vibration, and dust emissions during the demolition process. In this study, we conduct finite element analysis for crack initiation and propagation caused by the expansion of non-explosive demolition agents in square concrete structures. The predicted crack patterns are compared with the experimental results in the literature. The minimum values of the required expansion pressure of non-explosive demolition agents are also estimated, which depend upon the arrangement of non-explosive demolition agents and empty holes. Furthermore, we investigate the effect of empty holes on the fragmentation of concrete structures, and discuss the effective arrangement of non-explosive demolition agents and empty holes for fragmentation improvement.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.6
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• pp.1-8
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• 2012

Multidisciplinary design optimization (MDO) for a suspension component of the vehicle front suspension was performed in this research. Shapes and thicknesses of the subframe were optimized to satisfy multi-disciplinary design requirements; weight, fatigue, crash, noise, vibration, and harshness (NVH), and kinematic and compliance (K&C). Analyses procedures of the performance disciplines were integrated and automated by using the process integration and design optimization (PIDO) technique, and the integrated and automated analyses environments enabled various types of analytic design methodologies for solving the MDO problem. We applied an approximate optimization technique which involves sequential sampling and metamodeling. Since the design variables for thicknesses should be dealt as discrete variables. the evolutionary algorithm is selected as optimization technique. The MDO problem was formulated three types of problems according to the order of priorities among the performance disciplines, and the results of MDO provided design alternatives for various design situations.