• Title/Summary/Keyword: theoretical mode

Search Result 935, Processing Time 0.025 seconds

Fatigue Crack Growth Rates and Directions in STS304 under Mode I and Mixed Mode (단일 및 혼합모드하에서 304스테인리스강의 피로균열 진전속도와 방향특성)

  • 권종완;양현태
    • Transactions of the Korean Society of Machine Tool Engineers
    • /
    • v.11 no.3
    • /
    • pp.102-109
    • /
    • 2002
  • The fatigue crack growth under mixed mode condition has been discussed within the scope of linear fracture mechanics such as maximum tangential stress, maximum tangential principal stress and minimum strain energy density. The purpose of this study is to investigate the characteristics of fatigue test crack growth in 304 stainless steel under mixed node. The fatigue test results carried out by using inclined pre-crack specimens was compared to both of the theoretical predictions of the criteria, maximum tangential stress and stain energy density. As difference from theoretical analysis, the transition region from mixed mode to mode I appeared in the fatigue test. There is deep relationship between the angle of slanted pre-crack and transition. Therefore, as applying the different stress intensity factor to each node I+II and mode I, the directions and rates of fatigue crack growth are evaluated more accurately under mixed mode.

Analysis and simulation of multi-mode piezoelectric energy harvesters

  • Zhang, Ying;Zhu, Binghu
    • Smart Structures and Systems
    • /
    • v.9 no.6
    • /
    • pp.549-563
    • /
    • 2012
  • Theoretical analysis is performed on a multi-mode energy harvester design with focus on the first two vibration modes. Based on the analysis, a modification is proposed for designing a novel adaptive multi-mode energy harvester. The device comprises a simply supported beam with distributed mass and piezoelectric elements, and an adaptive damper that provides a 180 degree phase shift for the motions of two supports only at the second vibration mode. Theoretical analysis and numerical simulations show that the new design can efficiently scavenge energy at the first two vibration modes. The energy harvesting capability of the multi-mode energy harvester is also compared with that of a cantilever-based energy harvester for single-mode vibration. The results show that the energy harvesting capacity is affected by the damping ratios of different designs. For fixed damping ratio and design dimensions, the multi-mode design has higher energy harvesting capacity than the cantilever-based design.

Analytical study of the failure mode and pullout capacity of suction anchors in sand

  • Liu, Haixiao;Peng, Jinsong;Zhao, Yanbing
    • Ocean Systems Engineering
    • /
    • v.5 no.4
    • /
    • pp.279-299
    • /
    • 2015
  • Suction anchors are widely adopted and play an important role in mooring systems. However, how to reliably predict the failure mode and ultimate pullout capacity of the anchor in sand, especially by an easy-to-use theoretical method, is still a great challenge. Existing methods for predicting the inclined pullout capacity of suction anchors in sand are mainly based on experiments or finite element analysis. In the present work, based on a rational mechanical model for suction anchors and the failure mechanism of the anchor in the seabed, an analytical model is developed which can predict the failure mode and ultimate pullout capacity of suction anchors in sand under inclined loading. Detailed parametric analysis is performed to explore the effects of different parameters on the failure mode and ultimate pullout capacity of the anchor. To examine the present model, the results from experiments and finite element analysis are employed to compare with the theoretical predictions, and a general agreement is obtained. An analytical method that can evaluate the optimal position of the attachment point is also proposed in the present study. The present work demonstrates that the failure mode and pullout capacity of suction anchors in sand can be easily and reasonably predicted by the theoretical model, which might be a useful supplement to the experimental and numerical methods in analyzing the behavior of suction anchors.

A Theoretical Analysis of Thermic Endfire Interstitial Applicator

  • Park, Jong-Kweon;Eom, Hyo-Joon
    • Journal of electromagnetic engineering and science
    • /
    • v.1 no.1
    • /
    • pp.60-62
    • /
    • 2001
  • A novel approach for modeling the thermic endfire interstitial applicator is presented. A hypothetical semi-infinite circular cylinder is added in the endfire direction in order to facilitate the theoretical modeling approach. The Fourier transform and mode-matching technique is utilized to obtain a solution in fast-convergent series Numerical computations for the input impedance are performed to check the Validity of the theoretical model.

  • PDF

Estimation of bridge displacement responses using FBG sensors and theoretical mode shapes

  • Shin, Soobong;Lee, Sun-Ung;Kim, Yuhee;Kim, Nam-Sik
    • Structural Engineering and Mechanics
    • /
    • v.42 no.2
    • /
    • pp.229-245
    • /
    • 2012
  • Bridge vibration displacements have been directly measured by LVDTs (Linear Variable Differential Transformers) or laser equipment and have also been indirectly estimated by an algorithm of integrating measured acceleration. However, LVDT measurement cannot be applied for a bridge crossing over a river or channel and the laser technique cannot be applied when the weather condition is poor. Also, double integration of accelerations may cause serious numerical deviation if the initial condition or a regression process is not carefully controlled. This paper presents an algorithm of estimating bridge vibration displacements using vibration strains measured by FBG (Fiber Bragg Grating) sensors and theoretical mode shapes of a simply supported beam. Since theoretically defined mode shapes are applied, even high modes can be used regardless of the quality of the measured data. In the proposed algorithm, the number of theoretical modes is limited by the number of sensors used for a field test to prevent a mathematical rank deficiency from occurring in computing vibration displacements.89The proposed algorithm has been applied to various types of bridges and its efficacy has been verified. The closeness of the estimated vibration displacements to measured ones has been evaluated by computing the correlation coefficient and by comparing FRFs (Frequency Response Functions) and the maximum displacements.

Hybrid Rocket Instability I (하이브리드 로켓 불안정성 I)

  • Rhee, Sun-Jae;Lee, Jung-Pyo;Moon, Hee-Jang;Sung, Hong-Gye;Kim, Jin-Gon
    • Proceedings of the Korean Society of Propulsion Engineers Conference
    • /
    • 2012.05a
    • /
    • pp.81-85
    • /
    • 2012
  • In this paper, the typical combustion instabilities in hybrid rocket were studied. To induce combustion instabilities in the combustor with the diaphragms were mounted, on front and rear of the fuel, and combustion experiments were performed. The calculated theoretical frequencies using Longitudinal Acoustic Mode and Helmholtz Mode are compared with experimental frequencies using FFT analysis. The theoretical calculated results showed good agreements with experimental results are compared.

  • PDF

Study on Moonpool Resonance Effect on Motion of Modern Compact Drillship

  • Yang, Seung Ho;Yang, Young Jun;Lee, Sang Beom;Do, Jitae;Kwon, Sun Hong
    • Journal of Ocean Engineering and Technology
    • /
    • v.27 no.3
    • /
    • pp.53-60
    • /
    • 2013
  • A drillship is a representative floating offshore installation. The boom in oil and gas field development has dramatically increased the demands for drillships. Drillships have a moonpool in the center area of the ship for the purpose of drilling. This moonpool has an effect on the seakeeping performance of a drillship in the vicinity of the resonance frequency. Because of the moonpool, drillships act in different resonance modes, called the sloshing mode and piston mode. The objective of this study was to find the moonpool effect on the motion of a drillship through the motion analysis of a currently operating modern compact drillship. The predicted resonance frequencies based on Molin's theoretical formula, Fukuda's empirical formula, and BEM-based numerical analysis are compared. The accuracy of the predictions using the theoretical and empirical formulas is compared with the numerical analysis and evaluated. In the case of the piston mode, the difference between the resonance frequency from theoretical formula and the resonance frequency from the numerical analysis is analyzed. The resonance frequency formula for more a complex moonpool geometry such as a moonpool with a cofferdam is necessarily emphasized.

Identification of Guided-wave Modes for on-line monitering in the pipe weldment (배관 용접부의 상시감시를 위한 유도초음파 모드 규명)

  • Park Ik-Geun;Kim Tae-Hyeong;Lee Cheol-Gu;Kim Yong-Gwon;Park Tae-Seong;Lee Jin-Hyeok
    • Proceedings of the KWS Conference
    • /
    • 2006.05a
    • /
    • pp.307-309
    • /
    • 2006
  • For efficient NDE of pipes, essential components of power plant facilities, ultrasonic guided waves were generated and received applying an air-coupled transducer and comb one as non-contact technology, Mode generation and selection were predicted based on theoretical dispersive curve and the element spaceof a comb transducer. In addition, a receiving angle of the air-coupled transducer was determined to acquire the predicted modes by theoretical phase velocity of each mode. Theoretical dispersive curve was compared with the results of the time-frequency spectroscopes based on the wavelet transform and 2D-FFT to identify the characteristics of the received mode. The received modes show a good agreement with the predicted ones.

  • PDF

Analysis of Free Vibration of a Cylindrical Shell with a Circular Plate Under Various Kinds of Boundary Conditions (다양한 경계조건에서 원판이 결합된 원통 셸의 고유진동 해석)

  • 임정식;손동성
    • Journal of KSNVE
    • /
    • v.8 no.5
    • /
    • pp.936-948
    • /
    • 1998
  • A theoretical formulation for the analysis of free vibration of a cylindrical shell with a circular plate attached at an arbitrary axial position of the shell under various kinds of boundary conditions was derived and programed to get the numerical results for natural frequencies and mode shapes of the combined system. The boundary conditions of the shell to be considered here are clamped-free, clamped-simply supported, both ends clamped and both ends simply supported. The frequencies and mode shapes from theoretical calculation were compared with those of commercial finite element code, ANSYS. The results showed good agreement with those of ANSYS in frequencies and mode shapes. The program will contribute to the design optimization of a shell/plate combined system through the analysis of natural frequencies and mode shapes for the system.

  • PDF

Constructing the mode shapes of a bridge from a passing vehicle: a theoretical study

  • Yang, Y.B.;Li, Y.C.;Chang, K.C.
    • Smart Structures and Systems
    • /
    • v.13 no.5
    • /
    • pp.797-819
    • /
    • 2014
  • This paper presents a theoretical algorithm for constructing the mode shapes of a bridge from the dynamic responses of a test vehicle moving over the bridge. In comparison with those approaches that utilize a limited number of sensors deployed on the bridge, the present approach can offer much more spatial information, as well as higher resolution in mode shapes, since the test vehicle can receive the vibration characteristics of each point during its passage on the bridge. Basically only one or few sensors are required to be installed on the test vehicle. Factors that affect the accuracy of the present approach for constructing the bridge mode shapes are studied, including the vehicle speed, random traffic, and road surface roughness. Through numerical simulations, the present approach is verified to be feasible under the condition of constant and low vehicle speeds.