• Title/Summary/Keyword: Strip Theory

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Buckling of FGM elliptical cylindrical shell under follower lateral pressure

  • Moradi, Alireza;Poorveis, Davood;Khajehdezfuly, Amin
    • Steel and Composite Structures
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    • v.45 no.2
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    • pp.175-191
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    • 2022
  • A review of previous studies shows that although there is a considerable difference between buckling loads of structures under follower and non-follower lateral loads, only the buckling load of FGM elliptical cylindrical shell under non-follower lateral load was investigated in the literature. This study is the first to obtain the buckling load of elliptical FGM cylindrical shells under follower lateral load and also make a comparison between buckling loads of elliptical FGM cylindrical shells under follower and non-follower lateral loads. Moreover, this research is the first one to derive the load potential function of elliptical cylindrical shell. In this regard, the FGM cylindrical elliptical shell was modeled using the semi-analytical finite strip method and based on the First Shear Deformation Theory (FSDT). The shell is discretized by strip elements aligned in the longitudinal direction. The Lagrangian and harmonic shape functions were considered in the circumference and longitudinal directions, respectively. The buckling pressure of the shell under follower and non-follower lateral loads was obtained from eigenvalue problem. The results obtained from the model were compared with those presented in the literature to evaluate the validity of the model. A comparison index was defined to compare the buckling loads of the shell under follower and non-follower lateral load. A parametric study was carried out to investigate the effects of material properties and shell geometry characteristics on the comparison index. For the elliptical cylindrical shells with length-to-radius ratio greater than 16 and major-to-minor axis ratio greater than 0.6, the comparison index reaches to more than 20 percent which is significant. Moreover, the maximum difference is about 30 percent in some cases. The results obtained from the parametric study indicate that the buckling load of long elliptical cylindrical shell under non-follower load is not reliable.

Free Vibrations of Circular Uniform Strips Resting on Two Parameter Elastic Foundation (두 변수 탄성지반으로 지지된 원호형 등단면 띠기초의 자유진동)

  • Lee, Jong-Cheon
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.13 no.1 s.53
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    • pp.125-134
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    • 2009
  • This paper deals with the free vibrations of circular strip foundations which have uniform solid rectangular cross-section. The ground which supports circular strips was modeled as the two parameter elastic foundation. Differential equations governing the flexural-torsional free vibrations of circular strips supported by such foundation were derived, and solved numerically for obtaining the natural frequencies and mode shapes. Boundary condition of free-free ends was considered for numerical examples. Four lowest natural frequencies according to the variations of five system parameters i.e. subtended angle, depth ratio, contact ratio, elasticity ratio and soil parameter are reported in the non-dimensional forms. Also, typical mode shapes of both deformations and stress resultants are presented in the figures. Experiment was conducted for validating the theory developed in this study.

Flight Dynamics Analyses of a Propeller-Driven Airplane (I): Aerodynamic and Inertial Modeling of the Propeller

  • Kim, Chang-Joo;Kim, Sang Ho;Park, TaeSan;Park, Soo Hyung;Lee, Jae Woo;Ko, Joon Soo
    • International Journal of Aeronautical and Space Sciences
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    • v.15 no.4
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    • pp.345-355
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    • 2014
  • This paper focuses on aerodynamic and inertial modeling of the propeller for its applications in flight dynamics analyses of a propeller-driven airplane. Unsteady aerodynamic and inertial loads generated by the propeller are formulated using the blade element method, where the local velocity and acceleration vectors for each blade element are obtained from exact kinematic relations for general maneuvering conditions. Vortex theory is applied to obtain the flow velocities induced by the propeller wake, which are used in the computation of the aerodynamic forces and moments generated by the propeller and other aerodynamic surfaces. The vortex lattice method is adopted to obtain the induced velocity over the wing and empennage components and the related influence coefficients are computed, taking into account the propeller induced velocities by tracing the wake trajectory trailing from each of the propeller blades. Aerodynamic forces and moments of the fuselage and other aerodynamic surfaces are computed by using the wind tunnel database and applying strip theory to incorporate viscous flow effects. The propeller models proposed in this paper are applied to predict isolated propeller performances under steady flight conditions. Trimmed level forward and turn flights are analyzed to investigate the effects of the propeller on the flight characteristics of a propeller-driven light-sports airplane. Flight test results for a series of maneuvering flights using a scaled model are employed to run the flight dynamic analysis program for the proposed propeller models. The simulations are compared with the flight test results to validate the usefulness of the approach. The resultant good correlations between the two data sets shows the propeller models proposed in this paper can predict flight characteristics with good accuracy.

Static Aeroelastic Analysis of Hingeless Rotor System in Hover Using Free-Wake Method (자유후류기법을 이용한 무힌지 로터 시스템의 정지비행시 정적 공탄성 해석)

  • Yoo, Seung-Jae;Lim, In-Gyu;Lee, In;Kim, Do-Hyung;Kim, Doeg-Kwan
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.36 no.2
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    • pp.156-162
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    • 2008
  • The static aeroelastic analysis of composite hingeless rotor blades in hover was performed using free-wake method. Large deflection beam theory was applied to analyze blade motions as a one-dimension beam. Anisotropic beam theory was applied to perform a cross-sectional analysis for composite rotor blades. Aerodynamic loads were calculated through a three-dimensional aerodynamic model which is based on the unsteady vortex lattice method. The wake geometry in hover was described using a time-marching free-wake method. Numerical results of the steady-state deflections for the composite hingeless rotor blades were presented and compared with those results based on two-dimensional quasi-steady strip theory and prescribed wake method. It was shown that wakes affect the steady-state deflections.

Study on Behavior of Failure of Footing through Numerical Analysis (수치해석을 통한 기초지반의 파괴거동 고찰)

  • Lee, Seung-Hyun;Jang, In-Sung
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.16 no.3
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    • pp.2212-2218
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    • 2015
  • In order to find out the load bearing behavior of sand and clay which sustain three types of shallow footing, finite element analyses were performed. Failure zone of sand which sustain strip footing was affected by relative density of sand whereas, failure zone of clay was not affected by soil strength and it was similar to the failure zone which is considered in theory. Considering the shape of load-settlement curves obtained by numerical analyses, punching shear failure can be seen in loose sand and ultimate bearing load can not be seen in dense sand whereas, yielding point can be seen in clay. Ultimate bearing loads for sand predicted by theory were greater than those obtained by numerical analyses and ultimate bearing loads for clay predicted by theory were similar to those of numerical analyses. Ultimate bearing loads determined by 1 inch settlement criteria were slightly less than those of numerical analyses.

An Experimental Investigation of Boussinesq's Theoretical Value of Vertical Stress Increment in Sandy Soil Mass Caused by Surface Strip Loading (지표면 띠하중 재하에 따른 사질토지반 지중연직응력 증가량의 Boussinesq 이론값에 대한 실험적 고찰)

  • Lim Jong-Seok
    • Journal of the Korean Geotechnical Society
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    • v.20 no.9
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    • pp.5-15
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    • 2004
  • It is worthwhile to verify the vertical stress distribution in soil mass for rigorous design of foundation. A series of laboratory model tests were performed to investigate the Boussinesq's theory on vertical stress increment in sandy soil mass caused by surface loading. The test results were also compared with Boussinesq's theoretical values. The Boussinesq's theoretical values were always smaller than test results under the footing regardless of depth. Outside of the footing the values were larger than the measured stress at the depth of just footing width. The theory and the test showed similar results when the depth reached two and three times the footing width. The vertical stress decreased as the applied load increased. These trends were confirmed to be valid for the considered range of the relative density of sand and/or the width of footing. More accurate values can be acquired by correcting the theoretical values using these results when Boussinesq's theory is used.

Strut-and-Tie Model for Shear Strength of Reinforced Concrete Squat Shear Walls (저층형 철근콘크리트 전단벽의 전단강도 평가를 위한 스트럿-타이 모델)

  • Mun, Ju-Hyun;Yang, Keun-Hyeok
    • Journal of the Korea Concrete Institute
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    • v.27 no.6
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    • pp.615-623
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    • 2015
  • The previous strut-and-tie models (STMs) to evaluate the shear strength of squat shear walls with aspect ratio less than 2.0 do not consider the axial load transfer of concrete strut and individual shear transfer contribution of horizontal and vertical shear reinforcing bars in the web. To overcome the limitation of the existing models, a simple STM was established based on the crack band theory of concrete fracture mechanics. The equivalent effective width of concrete strut having a stress relief strip was determined from the neutral axis depth and effective factor of concrete strength. The shear transfer mechanism of shear reinforcement at the extended crack band zone was calculated from an internally statically indeterminate truss system. The shear transfer capacity of concrete strut and shear reinforcement was then driven using the energy equilibrium in the stress relief strip and crack band zone. The shear strength predictions of squat shear walls evaluated from the current models are in better agreement with 150 test results than those determined from STMs proposed by Siao and Hwang et al. Furthermore, the proposed STM gives consistent agreement with the observed trend of the shear strength of shear walls against different parameters.

Study on the Sheet Rolling by a Rigid-Plastic Finite Element Method Considering Large Deformation Formulation (강소성 대변형 유한요소법을 이용한 판재 압연연구)

  • 김동원;홍성인
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.1
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    • pp.145-153
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    • 1991
  • A numerical simulation of the nonsteady state rolling process in the plane strain condition is presented in the basis of the rigid-plastic finite element method by considering large deformation. In order to apply the large deformation theory to the numerical method for sheet rolling problems, constitutive equation relating 2nd-Piola Kirchhoff stress and Lagrangian strain which reflect geometrical nonlinearity is used. To confirm the validity of the developed algorithm, the analysis of the neutral flow region, roll separating force, torque, pressure and stress/strain distributions on the workpiece is conducted from the bite of the material until the steady state is reached. The computed results of the roll force and torque in the present finite element analysis are lower than those corresponding to small strain theory. The pressure distribution at the work piece-roll interface is found to show the typical 'friction hill' type only. The peak value in near the neutral region, however, is good agrements with the existing results. the neutral region, however, is good agrements with the existing results. The frictional force at the roll interface provide detailed information about the neutral point where the shear forces change direction. In addition, the analysis also includes the effect and influence of material condition, strip thickness, work roll diameter, as well as roll speed and lubricant on each deformation process.

Propeller racing of ocean-going ships with multiple screw propellers (다축선의 프로펠러 레이싱 추정에 관한 연구)

  • Park, Jong-Heon
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.43 no.3
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    • pp.222-231
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    • 2007
  • This paper represents a basic statistical examination on the navigability of ocean-going ship from the point of estimating the time lasting period when propeller racing occurred by using the basic probability theory and the statistics. The propeller racing is one of the most important seakeeping qualities in relation to the safety of the main engine and shafting system. The trend of the racing has been mainly investigated in order to estimate allowable maximum propeller diameter, operation of ocean-going ships, etc.. In those studies, the propeller racing generally and mainly means the situation (propeller exposed) in which the relative motion amplitude between ship hull and wave surface would exceed a depth of point in rotary disk propeller. Therefore, it seems that the magnitude of the amplitude and its exceeding frequency of propeller racing have been examined as a principal subject of study as usual. However, the time during which the amplitude exceeds the depth of point, that is, the propeller exposes in the air, must be also one of most important factor affecting the trend of propeller racing. Then, this paper proposes a new practical method for estimating the time lasting of exposed propeller related to propeller racing in rough-confused seas on the basis of the linear strip theory and the statistics. And, numerical examples of estimating the propeller racing probability are given for four wide ship forms. Finally the usefulness of the proposed method for predicting propeller racing based on the time lasting period is discussed.

Aeroelastic Stability Analysis of Bearingless Rotors with Composite Flexbeam in Hover (복합재 유연보를 갖는 무베어링 로우터 시스템의 정지 비행시 공탄성 안정성 해석)

  • Lim, In-Gyu;Choi, Ji-Hoon;Lee, In;Han, Jae-Hung
    • Composites Research
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    • v.17 no.3
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    • pp.29-37
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    • 2004
  • The aeroelastic stability analysis of composite bearingless rotors is investigated using a large deflection beam theory in hover. The bearingless rotor configuration consists of a single flexbeam with a wrap-around type torque tube and the pitch links located at the leading edge and trailing edge of the torque tube. The outboard main blade, flexbeam and torque tube are all assumed to be an elastic beam undergoing flap bending, lead-lag bending, elastic twist and axial deflections, which are discretized into beam finite elements. For the analysis of composite bearingless rotors, flexbeam is assumed to be a rectangular section made of laminate. Two-dimensional quasi-steady strip theory is used for aerodynamic computation. The finite element equations of motion for beams are obtained from Hamilton's principle. The p-k method is used to determine aeroelastic stability boundary. Numerical results are presented for selected bearingless rotor configurations based on the lay-up of laminae in the flexbeam and pitch links location. A systematic study is made to identify the importance of the stiffness coupling terms on aeroelastic stability for various fiber orientation and for different configuration.