• Journal of Mechanical Science and Technology
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• 제19권6호
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• pp.1304-1312
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• 2005

The ride and noise characteristics of a vehicle are significantly affected by the vibration transferred to the body through the chassis mounting points in the engine and suspension. It is known that body attachment stiffness is an important factor of idle noise and road noise for NVH performance improvement. The body attachment stiffness serves as a route design aimed at isolating the vibration generated inside the car due to the exciting force of the engine or road. The test result of the body attachment stiffness is shown in the FRF curve data; the stiffness level and sensitive frequency band are recorded by the data distribution. The stiffness data is used for analyzing the parts that fail to meet the target stiffness at a pertinent frequency band. The analysis shows that the target frequency band is between 200 and 500 Hz. As a result of the comparison in a mounted suspension, the analysis data is comparable to the test data. From these results, there is a general agreement between the predicted and measured responses. This procedure makes it possible to find the weak points before a proto car is produced, and to suggest proper design guidelines in order to improve the stiffness of the body structure.

• Steel and Composite Structures
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• 제42권2호
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• pp.221-241
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• 2022

Perfobond rib connectors are widely used in composite structures to achieve the composite action between the steel and the concrete, and empirical expressions for their strength and secant stiffness have been obtained by numerical simulations or push-out tests. Since perfobond connections are generally in an elastic state in the service process and the structural analysis are always based on the elastic properties of the members, the secant stiffness is not applicable for the normal structural analysis. However, the tangent stiffness of perfobond connections has not been introduced in previous studies. Moreover, the perfobond connections are bearing tension and shear force simultaneously when the composite beams subjected to torque or local loads, but the current studies fail to arrive at the elastic stiffness considering the combined effects. To resolve these discrepancies, this paper investigates the initial elastic stiffness of perfobond connections under combined forces. The calculation method for the elastic stiffness of perfobond connections is analyzed, and the contributions of the perfobond rib, the perforating rebar and the concrete dowel are investigated. A finite element method was verified with a high value of correlation for the test results. Afterwards, parametric studies are carried out using the reliable finite element analysis to explore the trends of several factors. Empirical equations for predicting the initial elastic stiffness of perfobond connections are proposed by the numerical regression of the data extracted by parametric studies. The equations agree well with finite element analysis and test results, which indicates that the proposed empirical equations reflect a high accuracy for predicting the initial elastic stiffness of perfobond connections.

• Composites Research
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• 제30권6호
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• pp.331-337
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• 2017

복합재 격자 구조물은 무게가 가볍고 비강성, 비강도가 높다는 장점이 있으며 주로 압축 하중이 작용하는 발사체구조에 적용된다. 그러나 필라멘트 와인딩 기법으로 제작되므로 섬유가 겹쳐지는 부분에서 기공과 결함이 발생하게 된다. 설계 하중 도출을 위한 해석 모델 검증을 위해 구조물의 강성, 강도 확인이 필요하지만 Full scale 시험의 경우 시간, 공간상의 제약이 따르며 구조물의 형상이 복잡하므로 시험에 어려움이 많다. 따라서 강성 확인을 위한 Subelement 단위의 시험법이 필요하다. 본 논문에서는 복합재 격자 구조물을 단위격자구조로 가공하였으며 각각 압축, 굽힘 시험을 수행하여 나선 리브, 원주 리브의 강성을 확인하였다. 휘임, 비틀림 형상을 가진 원통형 복합재 격자 구조물의 강성 평가를 위한 압축, 굽힘 시험법을 제안하였으며 유한요소해석을 수행하여 시험결과와 비교하였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.102-106
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• 2003

An experimental modal analysis and dynamic stiffness evaluation of a moving body structure of a high speed machining center are presented in this paper. The natural frequencies and corresponding modes, and dynamic compliance of a moving body structure of high speed machining center are investigated by using F.E.M., hydraulic exciter test, and impulse hammer test. The lowest three natural frequencies were found to be 56.6 Hz, 112.7 Hz, and 142.7 Hz by FEA respectively, while those were 55 Hz, 112 Hz, 131 Hz by experimental analysis. Furthermore, both computed and measured absolute dynamic compliances of the moving body structure in iso-direction showed good agreement especially at the first two mode frequencies. With our experimental data, the dynamic characteristics of the machining center can be exploited to get a new development of structural dynamic design and modification.

• 한국산학기술학회논문지
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• 제19권9호
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• pp.84-90
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• 2018

철도차량의 거동을 해석하기 위하여 다물체 동역학 모델을 구성함에 있어 현가시스템을 구성하는 스프링, 댐퍼와 같은 현가요소에 대한 스프링강성이나 감쇠계수와 같은 물성치 파악은 매우 중요하다. 그 중 1차, 2차 현가시스템에 주로 활용되고 있는 코일스프링에 대한 동역학 모델을 구성함에 있어 축방향 강성은 도면이나 설계자료에 명확하게 명시되어 있지만 횡방향에 대한 물성은 명시되어 있지 않아 동역학 해석 모델 구성에 어려움을 안고 있다. 따라서 본 논문에서는 철도차량의 현가시스템에 폭 넓게 적용되고 있는 코일스프링에 대한 횡강성을 해석하기 위한 모델에 대하여 검토하고자 한다. 코일스프링 시료에 대한 횡강성을 해석하고자 유한요소해석 방법을 수행하였고 Krettek와 Sobczak의 코일스프링 횡강성 해석모델을 적용하여 수치해석을 수행하였다. 그리고 코일스프링 시료를 대상으로 횡강성 특성시험을 수행하여 해석모델과의 적합성을 검토하였다. 시험결과와 비교한 결과, Krettek와 Sobczak의 코일스프링 횡강성 해석모델을 적용하고 보정계수를 수정한 결과가 시험결과에 근사한 결과를 얻을 수 있었다.

• Tribology and Lubricants
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• 제31권6호
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• pp.294-301
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• 2015

In this paper, we predict the rotordynamic force coefficients of tilting pad journal bearings (TPJBs) with rocker-back pivots, and we compare the predictions to recently published predictions and test data. The present TPJB model considers the rocker-back pivot stiffness calculated based on the Hertzian contact-stress theory, which is nonlinear with the application of a force . For the five-pad TPJB in load-between-pad and load-on-pad configurations, the predictions show the pressure- and film-thickness distributions, the deflection and stiffness of the individual pivots, and bearing stiffness and damping coefficients. The minimum film thickness and peak pressure occur at the bottom pad on which the applied load is directed. Because of the preload, the pres- sure is positive even at the upper pad in the opposite direction to the applied load. The pivot deflection and stiff- ness are maximum at the bottom pad that receives the heaviest pressure load. The predicted stiffness coefficients increase as the static load and rotor speed increase, while the damping coefficients decrease as the rotor speed increases, but increase as the static load increases. In general, the predicted stiffness coefficients agree well with the test data. The predicted damping coefficients overestimate the test data, particularly for large static loads. In general, the current predictive model considering the pivot stiffness improves the accuracy of the rotordynamic performance compared to previously reported models.

• Structural Engineering and Mechanics
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• 제65권5호
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• pp.547-556
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• 2018

Based on the shaking table tests of a 1:3.52 scale one-bay and one-story ancient wooden structure, a simplified structural mechanics model was established, and the structural state equation and observation equation were deduced. Under the action of seismic waves, the damage rule of initial stiffness and yield stiffness of the joint was obtained. The force hammer percussion test and finite element calculations were carried out, and the structural response was obtained. Considering the 5% noise disturbance in the laboratory environment, the stiffness parameters of the mortise-tenon joint were identified by the partial least squares of singular value decomposition (PLS-SVD) and the Extended Kalman filter (EKF) method. The results show that dynamic and static cohesion method, PLS-SVD, and EKF method can be used to identify the damage degree of structures, and the stiffness of the mortise-tenon joints under strong earthquakes is reduced step by step. Using the proposed model, the identified error of the initial stiffness is about 0.58%-1.28%, and the error of the yield stiffness is about 0.44%-1.21%. This method has high accuracy and good applicability for identifying the initial stiffness and yield stiffness of the joints. The identification method and research results can provide a reference for monitoring and evaluating actual engineering structures.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.921-924
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• 2005

Diesel generator sets with resilient mounts often experience resonances by major excitations which come from diesel engine and their foundation with rigid body modes. Because their natural frequency is determined by moment of inertia and stiffness of resilient mount vibration problems are resolved by changing location and stiffness of resilient mounts. But the calculated natural frequencies are inaccurate due to uncertainty of the inertia and mount stiffness. So this result can be useless on the design stage. In this paper, the stiffness of mount is evaluated on result from mount stiffness test in laboratory and generator set vibration test and a simple calculation method for moment of inertia is proposed. Based on these data, the procedure to select optimized mount stiffness and location on the design stage is set up.

• 한국정밀공학회지
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• 제13권5호
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• pp.30-37
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• 1996

The objective of this research is to explore the analysis and test method for the reliable design and fabrication of a high precision dynamically tuned gyroscope. The tuning frequency is decided by the calculation of mass moment of inertia of rotor and gimbal and the stiffness of flexures. Due to the complex geometry of the flexure, calculation of the stiffness of the suspension flexure is difficult. In this paper, three analytical methods for obtaining the stiffness of the flexure are porposed and a special testing method is used for checking the accuracy of the computed results.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2001년도 춘계학술대회 논문집
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• pp.281-288
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• 2001

In order to evaluate the effect of impact load at support stiffness transition area, the field estimations are performed at the transition zone between earthwork and bridge on test operation of KTX. Due to differential settlement caused by the variations of track support stiffness, large impact forces are investigated. However, the measured values such as wheel load, rail stress, displacement and acceleration in the transition area shows that the stiffness changes in the transition area are not abrupt, and the stiffness in the infra track structure varies continuously. In this experimental study, the parameters influencing safety of transition area are not governed by partial or local stiffness because cumulative passing loads are not sufficient on test operation of KTX.