• Proceedings of the Computational Structural Engineering Institute Conference
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• 2007.04a
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• pp.99-104
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• 2007

In this paper a dynamic behavior(natural frequency) of a cracked cantilever beam with tip mass and follower force is presented. In addition. an analysis of the flutter and buckling instability of a cracked cantilever beam subjected to a follower compressive load is presented. Based on the Euler-Bernouli beam theory, the equation of motion can be constructed by using the Lagrange's equation. The vibration analysis on such cracked beam is conducted to identify the critical follower force for flutter ins stability based on the variation of the first two resonant frequencies of the beam. Besides. the effect of the crack's intensity and location on the flutter follower force is studied. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments. The crack is assumed to be in the first mode of fracture and to be always opened during the vibrations.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.7 s.124
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• pp.605-610
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• 2007

In this paper a dynamic behavior(natural frequency) of a cracked cantilever beam subjected to follower force is presented. In addition, an analysis of the flutter and buckling instability of a cracked cantilever beam subjected to a follower compressive load is presented. Based on the Euler-Bernoulli beam theory, the equation of motion can be constructed by using the Lagrange's equation. The vibration analysis on such cracked beam is conducted to identify the critical follower force for flutter instability based on the variation of the first two resonant frequencies of the beam. Besides, the effect of the crack's intensity and location on the flutter follower force is studied. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments. The crack is assumed to be in the first mode of fracture and to be always opened during the vibrations.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2006.04a
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• pp.703-708
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• 2006

In this paper a dynamic behavior(natural frequency) of a cracked simply supported pipe conveying fluid is presented. In addition, an analysis of the buckling instability of a cracked pipe conveying fluid subjected to a follower compressive load is presented. Based on the Euler-Bernouli beam theory, the equation of motion can be constructed by using the Lagrange's equation. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments. TI1e crack is assumed to be in the first mode of fracture and to be always opened during the vibrations.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.10
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• pp.1002-1009
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• 2007

In this paper, the dynamic stability of a cracked simply supported pipe conveying fluid with an attached mass is investigated. Also, the effect of attached mass on the dynamic stability of a simply supported pipe conveying fluid is presented for the different positions and depth of the crack. Based on the Euler-Bernouli beam theory, the equation of motion can be constructed by the energy expressions using extended Hamilton's principle. The crack section is represented by a local flexibility matrix connecting two undamaged pipe segments. The crack is assumed to be in the first mode of a fracture and to be always opened during the vibrations. Finally, the critical flow velocities and stability maps of the pipe conveying fluid are obtained by changing the attached mass and crack severity.

• Transactions of Materials Processing
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• v.21 no.7
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• pp.412-419
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• 2012

The ingot-breakdown scheme of a tower flange material (low-alloy steel) for offshore wind turbine was investigated using finite element (FE) simulations and experimental analyses. Based on compression test results of the low-alloy steel, a deformation processing map was generated using the superposition approach between the dynamic materials model (DMM) and Ziegler's instability criterion. The deformation processing map allowed determination of the optimum process conditions for the tower flange material. Within the FE simulations of the ingot breakdown process, the Cockcroft-Latham criterion, which considers ductile fracture, was used to predict the possibility of forming defects during the hot working process. In general, the critical value for the ductile fracture of steel is 0.74. During the ingot-breakdown under optimum process conditions, the actual tower flange forgings exhibited a relatively uniform shape without any forming defects.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.12
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• pp.1161-1169
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• 2007

In this paper, the dynamic stability of a rotating cantilever pipe conveying fluid with a crack is investigated by the numerical method. That is, the influence of the rotating angular velocity, mass ratio and crack severity on the critical flow velocity for flutter instability of system are studied. The equations of motion of rotating cantilever pipe are derived by using extended Hamilton's principle. The crack section of pipe is represented by a local flexibility matrix connecting two undamaged pipe segments. The crack is assumed to be in the first mode of fracture and always opened during the vibrations. Generally, the critical flow velocity for flutter is proportional to the rotating angular velocity of a pipe. Also, the critical flow velocity and stability maps of the rotating pipe system for the variation each parameter are obtained.

• Journal of Korean Neurosurgical Society
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• v.45 no.4
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• pp.209-212
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• 2009

Objective : Avascular necrosis (AVN) of the vertebral body is known as a relatively uncommon phenomenon in a vertebral compression fracture (VCF). The outstanding radiologic findings of AVN are intravertebral vacuum phenomenon with or without fluid collection. Several reports revealed that PVP or balloon kyphoplasty might be the effective treatment modalities for AVN. We also experienced excellent results when using PVP for the treatment of AVN of the vertebral body, and intend to describe the treatment's efficacy in this report. Methods : Thirty-two patients diagnosed with AVN of the vertebral body were treated with PVP. We measured the pre- and post-operative anterior body height and kyphotic angulation. The visual analogue scale (VAS) was used to determine the relief of back pain. Results : The anterior body height (pre-operative : 1.49 cm, post-operative : 2.22 cm) and kyphotic angulation (pre-operative : 14.47 degrees, post-operative : 6.57 degrees) were significantly restored (p<0.001). VAS was improved from 8.9 to 3.7. Pseudoarthrosis was corrected in all cases, which was confirmed by dynamic radiographs. Fluid collection was found in sixteen cases and was aspirated with serous nature. No organism and tumor cell were noted. Conclusion : PVP proved to be an effective procedure for the treatment of AVN of the vertebral body, which corrected dynamic instability and significantly restored the anterior body height and kyphotic angulation.

• Structural Engineering and Mechanics
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• v.81 no.6
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• pp.715-728
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• 2022

A new type of buckling-restrained braces (BRBs) with a longitudinally profiled steel plate working as the core (LPBRB) is proposed and experimentally investigated. Different from conventional BRBs with a constant thickness core, both stiffness and strength of the longitudinally profiled steel core along its longitudinal direction can change through itself variable thickness, thus the construction of LPBRB saves material and reduces the processing cost. Four full-scale component tests were conducted under quasi-static cyclic loading to evaluate the seismic performance of LPBRB. Three stiffening methods were used to improve the fatigue performance of LPBRBs, which were bolt-assembled T-shaped stiffening ribs, partly-welded stiffening ribs and stiffening segment without rib. The experimental results showed LPBRB specimens displayed stable hysteretic behavior and satisfactory seismic property. There was no instability or rupture until the axial ductility ratio achieved 11.0. Failure modes included the out-of-plane buckling of the stiffening part outside the restraining member and core plate fatigue fracture around the longitudinally profiled segment. The effect of the stiffening methods on the fatigue performance is discussed. The critical buckling load of longitudinally profiled segment is derived using Euler theory. The local bulging behavior of the outer steel tube is analyzed with an equivalent beam model. The design recommendations for LPBRB are presented finally.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.1
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• pp.101-109
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• 2008

The stability of a rotating cantilever pipe conveying fluid with a crack and tip mass is investigated by the numerical method. That is, the effects of the rotating angular velocity, mass ratio, crack severity and tip mass on the critical flow velocity for flutter instability of system are studied. The equations of motion of rotating pipe are derived by using the Euler-Bernoulli beam theory and the extended Hamilton's principle. The crack section of pipe is represented by a local flexibility matrix connecting two undamaged pipe segments. Also, the crack is assumed to be in the first mode of fracture and always opened during the vibrations. When the tip mass and crack are constant, the critical flow velocity for flutter is proportional to the rotating angular velocity of pipe. In addition, the stability maps of the rotating pipe system as a rotating angular velocity and mass ratio ${\beta}$ are presented.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.5A
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• pp.861-872
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• 2006

The element free Galerkin method is extended by the local partition of unity method to model the cohesive cracks in two dimensional continuum. The shape function of a particle whose domain of influence is completely cut by a crack is enriched by the step enrichment function. If the domain of influence contains a crack tip inside, it is enriched by a branch enrichment function which does not have the LEFM stress singularity. The discrete equations are obtained directly from the standard Galerkin method since the enrichment is only for the displacement field, which satisfies the local partition of unity. Because only particles whose domains of influence are influenced by a crack are enriched, the system matrix is still sparse so that the increase of the computational cost is minimized. The condition for crack growth in dynamic problems is obtained from the material instability; when the acoustic tensor loses the positive definiteness, a cohesive crack is inserted to the point so as to change the continuum to a discontiuum. The crack speed is naturally obtained from the criterion. It is found that this method is more accurate and converges faster than the classical meshless methods which are based on the visibility concept. In this paper, several well-known static and dynamic problems were solved to verify the method.