Pretwist Angle Research Articles

Effect of crack on drilling vibration

Effect of drill parameters and the local crack on the dynamic characteristics of a drill during the drilling through process is investigated in this study. A pre-twisted beam with a local crack is used to simulate the cracked drill. The release energy model is employed to characterize the stiffness variation around the crack. A moving Winkler-type elastic foundation assumption is used to approximate the time dependent work piece stiffness distribution on rotating drill during the drilling process. In this article, a drill vibration model with time varied boundary condition is presented. The effects of cracks, rotational speed, pre-twisted angle and thrust force on the vibration of drill are considered. A serious vibration is observed at the moment as the drill touch the work piece in a drilling process. The simulated results also indicate that the local crack may aggravate the vibration.

Theory of Thin-Walled, Pretwisted Composite Beams with Elastic Couplings

In this work, the structural response of thin-walled composite beams with pretwist angle is investigated by using a mixed beam approach that combines the stiffness and flexibility methods in a unified manner. The Reissner's semi-complimentary energy functional is used to derive the stiffness matrix that approximates the beam in an Euler–Bernoulli level for extension and bending and Vlasov level for torsion. The bending and torsion-related warpings induced by the pretwist effects are derived in a closed form. The developed theory is validated with available literature and detailed finite element structural analysis results using the MSC/NASTRAN. Pretwisted composite beams with rectangular solid and thin-walled box sections are illustrated to validate the current approach. Acceptable correlation has been achieved for cases considered in this study. The effects of pretwist and fiber orientation angles on the static behavior of pretwisted composite beams are also studied.

Dynamic stability analysis of pretwisted aerofoil cross-section blade packets under rotating conditions

This paper presents a finite element model for the static and dynamic stability of a rotating pretwisted aerofoil cross-section two-bladed packet subjected to uniform radial periodic force. The effects of various parameters such as shroud dimensions, pretwist angle, stagger angle, rotational speed and distance of shear center from the centroid on the stability of the blade packets are presented. The numerical results show that pretwist angle and the coupling effect are important in high-frequency modes depending on shear center distance from the centroid on dynamic stability regions. The increase in stagger angle makes the pretwisted two-bladed packet less stable. However, the increase in rotational speed makes the pretwisted two-bladed packet more stable.

Formulation for flutter and vibration analysis of a hingeless helicopter blade in hover: part II. Results of flutter stability and vibration analysis of a hingeless helicopter blade in hover

PurposeThis study aims to carry out flutter stability and vibration analysis of a uniform hingeless rotor blade in hovering flight conditions.Design/methodology/approachThe perturbation equations are obtained using the governing differential equations of motion derived in Part I (Aircraft Engineering and Aerospace Technology, Vol. 79 No. 2, 2007). The differential transform method (DTM) is applied to the perturbation equations of motion and the transformed equations are coded in the computer package Mathematica.FindingsThe effects of the built‐in pretwist angle and the rotational speed ratio on the natural frequencies are investigated and the results are compared with the results in literature.Originality/valueThis study, in carrying out an analysis of flutter stability and vibration of a uniform hingless rotor blade, is in good agreement with previous studies in the literature.

Vibration control of pre-twisted rotating composite thin-walled beams with piezoelectric fiber composites

Rotating composite beam structures like blades are applied in many fields of aerospace and mechanical engineering. In this research, bending vibration control of the pre-twisted rotating composite thin-walled beam is studied. The formulation is based on single cell composite beam including a warping function, centrifugal force, Coriolis acceleration, pre-twist angle and piezoelectric effect. A negative velocity feedback control algorithm is applied to realize the adaptive capability of the beam. Using a finite-element method, numerical simulations show that macro-fiber composite (MFC) actuators which are piezoelectric fiber composites and PVDF sensors can generate active vibration control effect. Relations between active vibration control effect and design parameters of beams such as rotating speeds, pre-twist angles and fiber orientations in a host structure are investigated in detail. Besides, a case study conformed that the effective damping performance can be obtained by suitable arrangement and distribution of the sensor and actuator pairs.

The dynamic stability of a rotating pre-twisted asymmetric cross-section blade subjected to lateral parametric excitation

The dynamic stability of a pre-twisted rotating blade having asymmetric aerofoil cross-section subjected to lateral parametric excitation is studied by using the finite element method. The Bernoulli–Euler theory is employed in the analysis. Solutions referred to as combination resonance are investigated. The effects of coupling due to centre of flexure distance from the centroid, rotation and the stagger angle on the stability are considered. The change in these effects due to pretwist angle is investigated. It is concluded from the results that the pretwist angle has an influence on the effects of coupling and rotation.

The dynamic stability of a rotating pre-twisted asymmetric cross-section Timoshenko beam subjected to lateral parametric excitation

A finite element model is presented to study the dynamic stability of a pre-twisted Timoshenko beam having asymmetric aerofoil cross-section subjected to lateral parametric excitation. Solutions referred to as combination resonance are investigated. The effects of shear deformation and rotary inertia are included in the analysis. The effects of coupling due to centre of flexure distance from the centroid and the shear coefficient on the stability are considered. The change in these effects due to pre-twist angle is investigated. It is concluded from the results that the pre-twist angle has an influence on the effects of coupling and the shear coefficient.

Dynamic stability of a rotating pre-twisted asymmetric cross-section Timoshenko beam subjected to an axial periodic force

A finite element model is presented to study the static and dynamic stability of a pre-twisted Timoshenko beam having asymmetric aerofoil cross-section subjected to an axial periodic force. The change in the effects of coupling due to centre of flexure distance from the centroid and the shear coefficient on the stability due to the pre-twist angle is considered. It is concluded from the results that the pre-twist angle has an influence on the effects of coupling and the shear coefficient.

Three-dimensional finite element analysis of critical pre-twist strain angle for torsional axis

A three-dimensional clasto-plastic finite element analysis of pre-twist process for a torsional axis made of 45GrNiMoVA steel, was carried out using a commercial finite element analysis code, MSC MARC 2001. The results show that the critical pre-twist strain angle is 0.027 rad and the maximum elastic shear stress after pre-twist is 1 694 MPa for the torsional axis.

Vibration Analysis of a Drill in the Drilling Process

The dynamic characteristics of the drilling process are investigated in this study. A pre-twisted Bernoulli-Euler beam is used to simulate the drill. The eigenvalue problem of a rotating pre-twisted beam under axial loading on an elastic foundation is numerically formulated using the differential quadrature method (DQM). Effects of the number of sampling points, rotation speed, pre-twist angle, axial loading, and elastic foundation stiffness on the calculated natural frequencies are also studied. Numerical results demonstrate the validity and the efficiency of the DQM in treating this type of problem. The computation times using DQM are smaller than the computation times using FEM. A varying-length elastic foundation is used to approximate the drilling process. The numerical results indicate that the natural frequency of the drill is increased as the drill moves into the work piece.

Stability of Laminated Composite Pretwisted Cantilever Panels

This article deals with the stability analysis of angle-ply laminated composite twisted panels using the finite element method. Here, a eight-noded isoparametric quadratic shell element is used to develop the finite element procedure. To investigate the vibration and stability behavior of twisted panels, the effect of various geometrical parameters like angle of twist, aspect ratio, lamination parameters, shallowness ratio, etc. are studied. The influence of various parameters on the vibration and stability characteristics of twisted panels have been examined. Numerical results are presented to show the effects of pretwist angles, geometry, and lamination details on the stability characteristics of twisted plates.

고온에서 외부 가진력을 받는 회전하는 경사기능 박간 블레이드의 동적응답 해석

This paper is dedicated to the thermoelastic modeling and dynamic response of the rotating blades made of functionally graded ceramic-metal based materials. The blades are modeled as non-uniform thin walled beams fixed at the hub with various selected values of setting angles and pre-twisted angles. In this study, the blade is rotating with a constant angular velocity and exposed to a steady temperature field as wen as external excitation. Moreover, the effect of the temperature gradient through the blade thickness is considered. Material properties are graded in the thickness direction of the blade according to the volume fraction power law distribution. The numerical results highlight the effects of the volume fraction, temperature gradient, taper ratio, setting angle and pre-twisted angle on the dynamic response of bending-bending coupled beam characteristics and pertinent conclusions are outlined.

Twist of Anti-symmetric Laminate Blades due to Pre-twist Angle under Centrifugal Force

In order to establish some basic concepts on the development and design of smart blades of FRP, the influence of the pre-twist angle and the stacking sequence on the twist of anti-symmetric laminate blades under centrifugal force was analyzed by FEM (Finite Element Method).It was found that the twist direction of a blade depends only on the anti-symmetric stacking sequence and that the twist angle depends on the pre-twist.Two stacking sequences were investigated.It was shown that, for different sequences, to twist-backward is easy however to forward-twist is hard as the pre-twist angle increases.Furthermore, it was demonstrated that the twist angle of blade depends more on the coupling of the stacking sequence than it does on the pre-twist.

Natural vibration of arbitrary spatially curved rectangular rods with pre-twisted angles

For the natural vibration of rods of pre-twisted rectangular cross-sections with its centerline spatially curved and twisted arbitrarily, a system of non-dimensional ordinary differential equations is obtained in three translation displacements and three rotational angles of the rod. The eigenvalue problem is solved for the natural frequencies of various pre-twisted angles of the rectangular cross-section area, aspect ratios, slenderness ratio, end conditions and functions of varying cross-section area along the rods by using a numerical method of Runge–Kutta integration. The eigenvalues are determined by the vanishing of a rank-six determinant whose column vectors are obtained at the end of six independent numerical integrations. The differential equations of the adjoint operator system for the eigenvalue problem with its associated boundary conditions are also derived and solved for the eigenvalues to check with that of the vibration system. It is found that the effect of increasing pre-twisted angle of the rod is that the lowest natural frequency of an arbitrary curved rod will asymptotically tend to be a constant, in spite of slenderness ratio, aspect ratio of the rectangular cross-section, E / G ratio, types of end conditions, or the functions of the cross-section area along the rod.

Dynamic stability of spinning pre-twisted sandwich beams with a constrained damping layer subjected to periodic axial loads

The dynamic stability problems of spinning pre-twisted sandwich beams with a constrained damping layer subjected to periodic axial loads are studied by using the finite element method. The complex modulus representation is used for the viscoelastic material. The gyroscopic effects for small perturbations are linearized as a skew symmetric damping matrix. The effects of pre-twisted angles and spinning speeds on unstable regions are studied. The influences of the core thickness, shear parameter, core loss factor and stiffness of constraining layer on the unstable regions are also discussed.

Nonlinear Dynamic Analysis of an Orthotropic Composite Rotor Blade

This work presents the nonlinear dynamic analysis of orthotropic composite rotor blade using differential quadrature method (DQM). It can be found that the same efficient and procedure of DQM for both uniform composite beam and pre-twisted non-uniform composite beam. In this approach, only nine sample points are needed to achieve convergence. Dynamic responses of orthotropic composite rotor blade with various rotor rotation speeds are determined. Both linear and nonlinear dynamic responses have been obtained in order to study the significance of the nonlinear effect. The transient responses of the derived systems are calculated by using Newmark method. The bending-torsion coupled beam model is used to characterize the composite rotor blade. Kelvin-Voigt internal and linear external damping coefficients are employed and determined for the orthotropic composite rotor blade. The DQM is used to transform the partial differential equations of a composite rotor blade into a discrete eigenvalue problem. In this study, the effects of the fiber orientation, internal damping, external damping, pre-twisted angle and the rotation speed on the dynamic behavior for an orthotropic composite beam are investigated. The effect of the number of sample points on the accuracy of the calculated natural frequencies is also discussed. The integrity and computational efficiency of the DQM in this problem will be derived in this paper.

Buckling and dynamic stability of a rotating pretwisted asymmetric cross-section blade subjected to an axial periodic force

This paper presents a finite element model for the static and dynamic stability study of a pretwisted aerofoil cross-section rotating blade subjected to an axial periodic force. The blade is modeled as an Euler–Bernoulli beam and Bolotin's method is used to show the effects of coupling due to the shear center distance from the centroid, pretwist angles, rotational speeds and stagger angles on the stability. The results show that pretwist angle and coupling are very important on static buckling loads and dynamic stability regions.

Buckling and dynamic stability of a rotating pretwisted asymmetric cross-section blade subjected to an axial periodic force

This paper presents a finite element model for the static and dynamic stability study of a pretwisted aerofoil cross-section rotating blade subjected to an axial periodic force. The blade is modeled as an Euler–Bernoulli beam and Bolotin's method is used to show the effects of coupling due to the shear center distance from the centroid, pretwist angles, rotational speeds and stagger angles on the stability. The results show that pretwist angle and coupling are very important on static buckling loads and dynamic stability regions.

Vibration of turbomachinery rotating blades made-up of functionally graded materials and operating in a high temperature field

The vibration of turbomachinery rotating blades made-up of functionally graded materials and operating in a temperature field is considered. In this context, the blade is modeled as a thin-walled beam mounted on a rigid hub at a presetting angle, rotating with a constant angular velocity, and exposed to a steady temperature field of a prescribed gradient through the blade wall thickness. The effect of the initial twist of the blade is also taken into consideration. Results are presented for two constituents, metal-ceramic based materials that are assumed to be temperature-dependent and graded in the thickness direction according to a simple power law distribution. Numerical results highlighting the effects of the volume fraction in conjunction with those of the presetting and pretwist angles, temperature gradient, rotating speed and hub radius are presented, and pertinent conclusions are outlined.

Dynamic stability of rotating pre-twisted blades with a constrained damping layer

The stability problems of a rotating pre-twisted blade with a viscoelastic core constrained by a laminated face layer subjected to a periodic axial load are studied by using the finite element method. The complex modulus representation is used for the viscoelastic material. A set of equations of motion governing the bending and extensional displacements are derived by Hamilton’s principle. The regions of instability are determined by using Bolotin’s procedure that modified for the complex case. The effects of rotating speed, pre-twisted angle, setting angle and static axial load on the first static buckling load under different shear parameter and core loss factor are presented. The influences of core loss factor, core thickness ratio and stiffness parameter on the unstable regions are also studied. The shear parameter exists an optimal range in which the width of unstable region is narrowest.