• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.3
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• pp.423-429
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• 1997

A simplified method for determining the mode components of the strain energy release rate of free-edge delaminations in laminated composite is proposed. The interlaminar stresses are evaluated as an interface moment and interface shear forces that are obtained from the equilibrium equations at the interface between the adjacent layers. Deformation of an edge-delaminated laminate is calculated by using a generalized quasi-three dimensional classical laminated plate theory developed by the authors. The analysis provides closed-form expression for the three components of the strain energy release rate. Comparison of results with a finite element solution using the virtual crack closure technique shows good agreement. In the present study, laminated composite with stacking sequences of [30/-30/90]$_{s}$ were examined. The simple nature of the method makes it suitable for primary design analysis for the delaminations of laminated composite.e.

• Smart Structures and Systems
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• v.12 no.3_4
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• pp.427-440
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• 2013

A growing need has developed in the United States to obtain more specific knowledge on the structural integrity of infrastructure due to aging service lives, heavier and more frequent loading conditions, and durability issues. This need has spurred extensive research in the area of structural health monitoring over the past few decades. Several structural health monitoring techniques have been developed that are capable of locating damage in structures using modal strain energy of mode shapes. Typically in the past, bending strain energy has been used in these methods since it is a dominant vibrational mode in many structures and is easily measured. Additionally, there may be cases, such as pipes, shafts, or certain bridges, where structures exhibit significant torsional behavior as well. In this research, torsional strain energy is used to locate damage. The damage index method is used on two numerical models; a cantilevered steel pipe and a simply-supported steel plate girder bridge. Torsion damage indices are compared to bending damage indices to assess their effectiveness at locating damage. The torsion strain energy method is capable of accurately locating damage and providing additional valuable information to both of the structures' behaviors.

• Journal of the Korea institute for structural maintenance and inspection
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• v.7 no.3
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• pp.147-156
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• 2003

In this paper, a damage detection method using mode shapes of truss structures is presented. The theory is formulated based on the changes in the modal strain energy in a truss type structures due to damage. To examine the feasibility, the theory is applied to an experimental data of a 1:6 scale model of a typical hexagonal truss structure. The experiment consists of 17 damage scenarios subjected to three different types of damage. The damage evaluation results show that the proposed method detects successfully damage in truss elements and also show that the performance of proposed method can be significantly impacted by the noise in the measurement data for small damage.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.834-837
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• 2005

Structural Dynamics Modification (SDM) is a very effective technique to improve structure's dynamic characteristics by adding or removing auxiliary structures, changing material properties and shape of structure. Among those of SDM technique, the method to change shape of structure has been mostly relied on engineer's experience and trial-and-error process which are very time consuming. In order to develop a systematic method to change structure shape, surface grooving technique is studied and successfully applied to HDD cover model. At first, to check the effect of mesh size, surface grooving technique was tested to the fine HDD cover FEmodel. And fur the more efficient method, the algorithm is modified. Removing the low-valued modal strain energy element among the target domain, computational effort can be greatly reduced and the result of simulation is similar with the other simulation result.

• Smart Structures and Systems
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• v.12 no.3_4
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• pp.441-463
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• 2013

In this paper, a simplified planar model is developed for damage estimation of interlocked caisson systems. Firstly, a conceptual dynamic model of the interlocked caisson system is designed on the basis of the characteristics of existing harbor caisson structures. A mass-spring-dashpot model allowing only the sway motion is formulated. To represent the condition of interlocking mechanisms, each caisson unit is connected to adjacent ones via springs and dashpots. Secondly, the accuracy of the planar model's vibration analysis is numerically evaluated on a 3-D FE model of the interlocked caisson system. Finally, the simplified planar model is employed for damage estimation in the interlocked caisson system. For localizing damaged caissons, a damage detection method based on modal strain energy is formulated for the caisson system.

• Structural Engineering and Mechanics
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• v.20 no.2
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• pp.143-160
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• 2005

Modal analysis of cracked cantilever composite beams, made of graphite-fibre reinforced polyamide, is studied. By using the finite element and component mode synthesis methods, a numeric model applicable to investigate the vibration of cracked composite beams is developed. In this new approach, from the crack section, the composite beam separated into two parts coupled by a flexibility matrix taking into account the interaction forces. These forces are derived from the fracture mechanics theory as the inverse of the compliance matrix calculated with the proper stress intensity factors and strain energy release rate expressions. Numerical results are obtained for modal analysis of composite beams with a transverse non-propagating open crack, addressing the effects of the location and depth of the crack, and the volume fraction and orientation of the fibre on the natural frequencies and mode shapes. By means of modal data, the position and dimension of the defect can be found. The results of the study confirmed that presented method is suitable for the vibration analysis of cracked cantilever composite beams. Present technique can be easily extended to composite plates and shells.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.656-661
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• 2005

An optimization formulation of unconstrained damping treatment on beams is proposed to minimize vibration responses using a numerical search method. The fractional derivative model is combined with RUK's equivalent stiffness approach in order to represent nonlinearity of complex modulus of damping materials with frequency and temperature. The loss factors of partially covered unconstrained beam are calculated by the modal strain energy method. Vibration responses are calculated by using the modal superposition method, and of which design sensitivity formula with respect to damping layout is derived analytically. Plugging the sensitivity formula into optimization software, we can determine optimally damping treatment region that gives minimum forced response under a given boundary condition. A numerical example shows that the proposed method is very effective in minimizing vibration responses with unconstrained damping layer treatment.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11b
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• pp.77-80
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• 2005

This paper presents a theoretical and experimental study on the damage identification of structures. In civil and aerospace, significant work has been done in the area of detecting damage in structures by using changes in the dynamic response of the structure. In this paper a method based on the changes in the strain energy of the structure will be discussed. To evaluate the effectiveness of the method it will be applied to both beam and LNG(liquefied natural gas) carrier.

• Journal of KSNVE
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• v.2 no.4
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• pp.305-315
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• 1992

In order to investigate the effects of layer-wise in-plane displacements on vibration and damping characteristics of composite laminated plates, the finite element method based on the generalized laminated plate theory(GLPT) has been formulated. Specific damping capacity of each mode was obtained by modal strain energy method. To see the effect of transverse shear on deformation, the strain energy of stress components was computed. The accuracy of this study was examined for the cylindrical bending vibration of cross-ply plate strip. The results were very accurate compared with 3-D solutions. The numerical results show that through-thickness variation of in-plane displacements has not so much influence on the natural frequency, but has a great influence on the damping of composite plates, especially on the damping of thick composite plates since the damping is affected by local behavior while the natural frequency is affected by global behavior.

• Journal of Navigation and Port Research
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• v.36 no.3
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• pp.163-168
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• 2012

Recently, people's desire for the waterfront space has been increasing, and more people want to spend their leisure time close to the water. This paper proposes a damage detection technique using the static strain for the floating structure. An existing damage index, in which the modal strain energy was utilized to identify possible location of damage, is expanded to apply the static strain. The new damage index is expressed in terms of the static strains of undamaged and damaged structures. After calculating damage index, the possible damage locations in the structure are determined by the pattern recognition technique. The accuracy and feasibility of the proposed method is demonstrated by using experimental strain data from a scale model of floating structure.