Vibration Analysis of a Composite Helicopter Rotor Blade at Hovering Condition

2016 ◽  
Author(s):  
Pratik Sarker ◽  
Colin R. Theodore ◽  
Uttam K. Chakravarty
Keyword(s):  
Mathematical Model ◽  
Rotor Blade ◽  
Structural Integrity ◽  
Initial Conditions ◽  
Helicopter Rotor ◽  
Mode Shapes ◽  
Vibration Level ◽  
Cross Sectional ◽  
Helicopter Rotor Blade ◽  
The Mathematical Model

The helicopter is an essential and unique means of transport nowadays and needs to hover in space for considerable amount of time. During hovering flight, the rotor blades continuously bend and twist causing an increased vibration level that affects the structural integrity of the rotor blade leading to ultimate blade failure. In order to predict the safe allowable vibration level of the helicopter rotor blade, it is important to properly estimate and monitor the vibration frequencies. Therefore, the mathematical model of a realistic helicopter rotor blade composed of composite material, is developed to estimate the characteristics of free and forced bending-torsion coupled vibration. The cross-sectional properties of the blade are calculated at first and are then included in the governing equations to solve the mathematical model. The natural frequencies and mode shapes of the composite helicopter rotor blade are evaluated for both the nonrotating and rotating cases. The time-varying bending and torsional deflections at the helicopter rotor blade tip are estimated with suitable initial conditions. The validation of the model is carried out by comparing the analytical frequencies with those obtained by the finite element model.

A Case Study of the Unsteady Response of a Hingeless Helicopter Rotor Blade

2019 ◽  
Author(s):  
Pratik Sarker ◽  
Uttam K. Chakravarty
Keyword(s):  
Mathematical Model ◽  
Steady State ◽  
Rotor Blade ◽  
Degrees Of Freedom ◽  
Forced Response ◽  
Helicopter Rotor ◽  
Mode Shapes ◽  
Response Analysis ◽  
Steady State Condition ◽  
Helicopter Rotor Blade

Abstract The helicopter is an essential means of transport for numerous tasks including carrying passengers and equipment, providing air medical services, firefighting, and other military and civil tasks. While in operation, the nature of the unsteady aerodynamic environment surrounding the rotor blades gives rise to a significant amount of vibration to the helicopter. In this study, the unsteady forced response of the Bo 105 hingeless helicopter rotor blade is investigated at the forward flight in terms of the coupled flapping, lead-lag, and torsional deformations. The mathematical model for the steady-state response of the rotor blade is modified to include the unsteady airfoil behavior by using the Theodorsen’s lift deficiency function for three degrees of freedom of motion. The nonlinear mathematical model is solved by the generalized method of lines in terms of the time-varying deflections of the rotor blade. The unsteady airloads are found to create larger deformations compared to that of the steady-state condition for a given advance ratio. The azimuth locations of the peak loadings also vary with different degrees of freedom. The first three natural frequencies and mode shapes of the rotor blade are presented. The model for the forced response analysis is validated by finite element results.

Design optimization of helicopter rotor using kriging

2018 ◽  
Vol 90 (6) ◽  
pp. 937-945 ◽  
Author(s):  
Saijal Kizhakke Kodakkattu ◽  
Prabhakaran Nair ◽  
Joy M.L.
Keyword(s):  
Rotor Blade ◽  
Optimization Problem ◽  
Torsional Stiffness ◽  
Helicopter Rotor ◽  
Vibration Level ◽  
Content Type ◽  
Aeroelastic Analysis ◽  
Kriging Metamodel ◽  
Helicopter Rotor Blade ◽  
Trailing Edge Flaps

Purpose The purpose of this study is to obtain optimum locations, peak deflection and chord of the twin trailing-edge flaps and optimum torsional stiffness of the helicopter rotor blade to minimize the vibration in the rotor hub with minimum requirement of flap control power. Design/methodology/approach Kriging metamodel with three-level five variable orthogonal array-based data points is used to decouple the optimization problem and actual aeroelastic analysis. Findings Some very good design solutions are obtained using this model. The best design point in minimizing vibration gives about 81 per cent reduction in the hub vibration with a penalization of increased flap power requirement, at normal cruise speed of rotor-craft flight. Practical implications One of the major challenges in the helicopters is the high vibration level in comparison with fixed wing aircraft. The reduction in vibration level in the helicopter improves passenger and crew comfort and reduces maintenance cost. Originality/value This paper presents design optimization of the helicopter rotor blade combining five design variables, such as the locations of twin trailing-edge flaps, peak deflection and flap chord and torsional stiffness of the rotor. Also, this study uses kriging metamodel to decouple the complex aeroelastic analysis and optimization problem.

A Study of the Aerodynamics of a Helicopter Rotor Blade

2019 ◽  
Author(s):  
Mohammad Khairul Habib Pulok ◽  
Uttam K. Chakravarty
Keyword(s):  
Rotor Blade ◽  
Angle Of Attack ◽  
Helicopter Rotor ◽  
Mode Shapes ◽  
Scaled Model ◽  
Rapid Variation ◽  
Tip Vortices ◽  
Aerodynamic Loading ◽  
Resonance Frequencies ◽  
Helicopter Rotor Blade

Abstract In any congested area, where a fixed-wing aircraft cannot perform, rotary-wing counterparts are the best-suited option for its vertical take-off and landing capacity. The vibration induced by the rotor blade is a significant problem in helicopter performances. Rotor aerodynamic loading, rotor dynamics, and fuselage dynamics are the elements that contribute to the vibration of a helicopter. Among these elements, the key reason for the helicopter vibration is the aerodynamic loading. Determining aerodynamic loading is one of the most important criteria to design a rotor blade and to minimize vibration. Rotor harmonic airloads are generated from the rapid variation of flow around the rotor blade due to the vortex wake. A rapid drop in the circulation near the blade tip causes tip vortices which are the reason for the maximum lift at the tip of the blade. Consequently, tip vortices become the primary source of harmonic airloads. In this study, a specimen of Bo 105 helicopter rotor blade is considered to observe the aerodynamic characteristics under the external flow of air. The coefficients of lift and drag of the specimen for different angles of attack and azimuth angles are estimated. The resonance frequencies and the mode shapes are obtained. Computational results are validated by the experimental analyses of a small-scaled model of the rotor blade. From the study, the coefficient of lift is found to increase with the angle of attack up to a critical value. Similarly, the coefficient of drag increases with the angle of attack. The resonance frequencies significantly change with scaling the rotor blade.

scholarly journals On the Dragging Trajectory of Anchors in Clay for Merchant Ships

2021 ◽  
Vol 9 (2) ◽  
pp. 118
Author(s):  
Xinqing Zhuang ◽  
Keliang Yan ◽  
Pan Gao ◽  
Yihua Liu
Keyword(s):  
Mathematical Model ◽  
Structural Integrity ◽  
Indirect Measurement ◽  
Test System ◽  
Flow Rule ◽  
Burial Depth ◽  
Proposed Model ◽  
Depth Increase ◽  
Two Parameters ◽  
The Mathematical Model

Anchor dragging is a major threat to the structural integrity of submarine pipelines. A mathematical model in which the mechanical model of chain and the bearing model of anchor were coupled together. Based on the associated flow rule, an incremental procedure was proposed to solve the spatial state of anchor until it reaches the ultimate embedding depth. With an indirect measurement method for the anchor trajectory, a model test system was established. The mathematical model was validated against some model tests, and the effects of two parameters were studied. It was found that both the ultimate embedding depth of a dragging anchor and the distance it takes to reach the ultimate depth increase with the shank-fluke pivot angle, but decrease as the undrained shear strength of clay increases. The proposed model is supposed to be useful for the embedding depth calculation and guiding the design of the pipeline burial depth.

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