• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2012.04a
• /
• pp.632-637
• /
• 2012

Antenna equipment is transported being assembled to moving equipment and often subjected to vibration and shock excitation during transportation. In these circumstances, structural safety of antenna equipment must be secured. Wire rope isolators are assembled between moving equipment and antenna equipment to reduce the level of vibration and shock. In this paper, a isolator that are suitable to the system is selected and dynamic characteristics analysis of driving on antenna equipment is conducted using real system and the result is compared with response analysis. Also modal test of array-antenna pack-assembly is conducted and structural safety of that is secured by reinforcing its structure.

• Structural Engineering and Mechanics
• /
• v.39 no.5
• /
• pp.669-682
• /
• 2011

A Chebyshev spectral method (CSM) for the dynamic analysis of non-uniform Timoshenko beams under various boundary conditions and concentrated masses at their ends is proposed. The matrix-based Chebyshev spectral approach was used to construct the spectral differentiation matrix of the governing differential operator and its boundary conditions. A matrix condensation approach is crucially presented to impose boundary conditions involving the homogeneous Cauchy conditions and boundary conditions containing eigenvalues. By taking advantage of the standard powerful algorithms for solving matrix eigenvalue and generalized eigenvalue problems that are embodied in the MATLAB commands, chebfun and eigs, the modal parameters of non-uniform Timoshenko beams under various boundary conditions can be obtained from the eigensolutions of the corresponding linear differential operators. Some numerical examples are presented to compare the results herein with those obtained elsewhere, and to illustrate the accuracy and effectiveness of this method.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.7 no.2
• /
• pp.107-112
• /
• 2006

In this paper, described is a research on the modal analysis of small DC motor by finite element method fer the vibration reduction. An impact test is performed to obtain the natural frequencies and modal shapes of DC motor, which valuate the usefulness of the finite element analysis model. From the study, we show that this finite element analysis model can be applicable for designing a new motor with improvement in vibration characteristics. As an example, a shape modification of DC motor is performed and its vibration characteristics is discussed in comparison with those of original shape.

• Structural Engineering and Mechanics
• /
• v.25 no.1
• /
• pp.53-73
• /
• 2007

In this study, an effective load increment method for multi modal adaptive non-linear static (pushover) analysis (NSA) for building type structures is presented. In the method, lumped plastisicity approach is adopted and geometrical non-linearties (second-order effects) are included. Non-linear yield conditions of column elements and geometrical non-linearity effects between successive plastic sections are linearized. Thus, load increment needed for formation of plastic sections can be determined directly (without applying iteration or step-by-step techniques) by using linearized yield conditions. After formation of each plastic section, the higher mode effects are considered by utilizing the essentials of traditional response spectrum analysis at linearized regions between plastic sections. Changing dynamic properties due to plastification in the system are used on the calculation of modal lateral loads. Thus, the effects of stiffness changes and local mechanism at the system on lateral load distribution are included. By using the proposed method, solution can be obtained effectively for multi-mode whereby the properties change due to plastifications in the system. In the study, a new procedure for determination of modal lateral loads is also proposed. In order to evaluate the proposed method, a 20 story RC frame building is analyzed and compared with Non-linear Dynamic Analysis (NDA) results and FEMA 356 Non-linear Static Analysis (NSA) procedures using fixed loads distributions (first mode, SRSS and uniform distribution) in terms of different parameters. Second-order effects on response quantities and periods are also investigated. When the NDA results are taken as reference, it is seen that proposed method yield generally better results than all FEMA 356 procedures for all investigated response quantities.

• 제어로봇시스템학회:학술대회논문집
• /
• 2000.10a
• /
• pp.150-150
• /
• 2000

We as modal parameter estimation technique by developing a residual based system reconstruction and using the system matrix coordinate transformation. The modal parameters can be estimated from and residues of the system transfer functions expressed in modal coordinate basis, derived from the state space system matrices. However, for modal parameter estimation of multivariable and order structural systems over broad frequency bands, this non-iterative algorithm gives high accuracy in the natural fre- and damping ratios. From vibration tests on cross-ply and angle-ply composite laminates, the natural frequencies and damping ratios on be estimated using tile coordinates of the structural system reconstructed fro the experimental frequency response. These results are compared with those of finite element analysis and single-degree-of-freedom curve-fitting.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.21 no.1
• /
• pp.83-90
• /
• 2015

The car ferry operating between the mainland and the island plays an important role on transportation of goods and passengers. Therefore, the improvement of efficiency and safety as well as economic factor are importantly considered in the development process of car ferry. Double-ended car ferry is already popularized because of its economic feasibility and convenience for passenger in Europe and developed countries, and the demand is booming in domestic. In this paper, dynamic characteristics of propeller shaft and strength in double-ended car ferry are analyzed using campbell diagram and modal analysis. Based on the analysis of dynamic characteristics, resonant phenomenon and critical speed are stable when occurring the propeller shaft vibration due to forward and reverse propeller shaft working.

• International Journal of Precision Engineering and Manufacturing
• /
• v.2 no.4
• /
• pp.30-39
• /
• 2001

This paper investigates vibrational motion of a flexible beam fixed on a moving cart and carrying a moving mass. The equations of motion of the beam-mass-cart system are analysed through the unconstrained modal analysis. The exact normal mode solution used in modal analysis correspond to the eigenfrequencies for each position of the moving mass and to the ratios of the weight of the beam-mass-car system. Time solutions of normal modes are also transformed properly according to the position of the moving mass. Numerical simulations are carried out to obtain open-loop responses of the system in tracking pre-designed paths of the moving mass. The simulation results show that the model predicts the dynamic behavior of the beam-mass-cart system well. Experiments are carried out to show the validity of the proposed analytical method.

• Nuclear Engineering and Technology
• /
• v.30 no.5
• /
• pp.416-423
• /
• 1998

Many studies for the perforated plates have been done, especially on the subject of static behavior and stress distribution in the plate. Equivalent elastic properties are one of the successive concepts for this problem. However little effort was taken to get their dynamic characteristics. In this paper finite element modal analysis was performed for the perforated plates having square and triangular hole patterns. An attempt to use existing equivalent elastic properties into the modal analysis of the plate was carried out. To verify feasibility of the finite element models, modal test was also performed on one typical perforated plate. System parameters such as natural frequencies and mode shapes were extracted and compared with the analysis results.

• Journal of the Korean Society for Precision Engineering
• /
• v.16 no.11
• /
• pp.204-212
• /
• 1999

In this paper, the vibrational motion of a flexible beam clamped on a translating base and carrying a moving mass is investigated. The equations of motion which describe the total dynamics of the beam-mass-cart system are derived and the coupled dynamic equations are solved by unconstrained modal analysis. In modal analysis, the exact normal mode solutions corresponding to the eigenfrequencies for the position of the moving mass and the ratios of the mass of the flexible beam, the moving mass and the base cart are used. Proper transformations of the time solutions between the normal modes for a position and those for the next position of the moving mass are also adopted. Numerical simulations are carried out to obtain the open-loop responses of the system in tracking the pre-designed path of the moving mass.

• Computers and Concrete
• /
• v.10 no.3
• /
• pp.277-294
• /
• 2012

The aim of the study is to determine the modal parameters of a prototype damaged arch dam by operational modal analysis (OMA) method for some damage scenarios. For this purpose, a prototype arch dam-reservoir-foundation model is constructed under laboratory conditions. Ambient vibration tests on the arch dam model are performed to identify the modal parameters such as natural frequency, mode shape and damping ratio. The tests are conducted for four test-case scenarios: an undamaged dam with empty reservoir, two different damaged dams with empty reservoirs, and a damaged dam with full reservoir. Loading simulating random impact effects is applied on the dam to crack. Cracks and fractures occurred at the middle of the upper part of the dams and distributed through the abutments. Sensitivity accelerometers are placed on the dams' crests to collect signals for measurements. Operational modal analysis software processes the signals collected from the ambient vibration tests, and enhanced frequency domain decomposition and stochastic subspace identification techniques are used to estimate modal parameters of the dams. The modal parameters are obtained to establish a basis for comparison of the results of two techniques for each damage case. Results show that approximately 35-40% difference exists between the natural frequencies obtained from Case 1 and Case 4. The natural frequencies of the dam considerably decrease with increasing cracks. However, observation shows that the filled reservoir slightly affected modal parameters of the dam after severe cracking. The mode shapes obtained are symmetrical and anti-symmetrical. Apparently, mode shapes in Case 1 represent the probable responses of arch dams more accurately. Also, damping ratio show an increase when cracking increases.