Numerical and experimental analysis on the helicopter rotor dynamic load controlled by the actively trailing edge flap

Reducing the rotor dynamic load is an important issue to improve the performance and reliability of a helicopter. The control mechanism of the actively controlled flap on the rotor dynamic load is numerically and experimentally investigated by a 3-blade helicopter rotor in this paper. In the aero-elastic numerical approach, the complex motion of the rotor such as the stretching, bending, torsion and pitching of the blade including the deflection of the actively controlled flap (ACF) are all taken into consideration in the structural formulation. The aerodynamic solution adopted the vortex lattice method combining with the free wake model, in which the influence of ACF on the free wake and the aerodynamic load on the blade is taken into account as well. While the experimental method of measuring hub loads and acoustic was accomplished by a rotor rig in a wind tunnel. The result shows that the 3/rev ACF actuation can reduce the $3\omega$ hub load by more than 50\% at maximum, which is significantly better than the 4/rev control. While 4/rev has greater potential to reduce BVI loads than 3/rev with $\mu=0.15$. Further mechanistic analysis shows that by changing the phase difference between the dynamic load on the flap and the rest of the blade, the peak load on the whole blade can be improved, thus achieving effective control of the hub dynamic load, the flap reaches the minimum angle of attack at 90°-100° azimuth under best control condition; when the BVI load is perfectly controlled, the flap reaches the minimum angle of attack at 140° azimuth, and by changing the circulation of the wake, the intensity of blade vortex interaction in the advancing side is improved. Moreover, an interesting finding in the optimal control of noise and vibration is that an overlap point exist on the motion patterns of the flap with different frequencies.

The Development of a Flight Test Platform to Study the Body Freedom Flutter of BWB Flying Wings

A flight test platform is designed to conduct an experimental study on the body freedom flutter of a BWB flying wing, and a flight test is performed by using the proposed platform. A finite element model of structural dynamics is built, and unsteady aerodynamics and aeroelastic characteristics of the flying wing are analyzed by the doublet lattice method and g-method, respectively. Based on the foregoing analyses, a low-cost and low-risk flying-wing test platform is designed and manufactured. Then, the ground vibration test is implemented, and according to its results, the structural dynamics model is updated. The flight test campaign shows that the body freedom flutter occurs at low flight speed, which is consistent with the updated analytical result. Finally, an active flutter suppression controller is designed using a genetic algorithm for the developed flying wing for future tests, considering the gains and sensor location as design parameters. The open- and closed-loop analyses in time- and frequency-domain analyses demonstrate that the designed controller can improve the instability boundary of the closed-loop system effectively.

Effect of Stress Shadow Caused by Multistage Fracturing from Multiple Well Pads on Fracture Initiation and Near-Wellbore Propagation from Infill Wells

Summary Multistage fracturing with multiwell pads (MSFMP) is an essential technology for the efficient development of unconventional oil and gas reservoirs, but the reservoir area between two well pads is often not stimulated. Fracture initiation and near-wellbore propagation from infill horizontal wells drilled with different azimuth from the optimal azimuth in the unstimulated area is poorly understood, largely because of the stress shadow (or induced stress) caused by MSFMP. In this study, we propose an integrated method for calculating the stress shadow caused by MSFMP and then determine optimal completion parameters for infill horizontal wells in the unstimulated connecting area between two well pads. First, we develop a theoretical stress shadow model caused by MSFMP on the basis of the dislocation theory. Considering two extreme cases, fully open and completely closed propped fractures, the range of stress shadow in the unstimulated area after MSFMP of 20 horizontal wells in Platform H of tight reservoirs in the Changqing Oilfield, China, is considered as an example. Second, we import the calculated stress shadow into a 3D perforated fracturing model that is built based on the discrete lattice method. Then, we investigate the influence of perforation technology, horizontal wellbore azimuth, phase angle, and injection rate on fracture initiation and near-wellbore propagation. Our results show that this model is capable of calculating stress shadow at any position and then can be used to optimize the fracturing interval for the middle unstimulated area. We find that appropriate perforation and fracturing parameters significantly decrease the complexity of near-wellbore fractures. The models and results presented in this paper provide a new method and new insight for quantifying and optimizing fracture initiation and propagation for infill horizontal wells to maximize reservoir stimulation efficiency.

The influence of Human Hair on Kenaf and Grewia Fibers based Hybrid Natural Composite Material: An Experimental Study

The demand for natural composite products is continuously increasing to make various industrial and commercial products to protect the environment. In this paper, the Hybrid Plant Fiber composite (HPFC) is produced using 64 wt.% of the resin matrix and 36 wt.% of natural fibers (Kenaf, Grewia, and Human hair) by hand layup moulding method. The influences of natural fiber’s weight on tensile, flexural, and impact strengths were investigated by the simplex lattice method. It was revealed that the percentage of contribution of Kenaf and Human hair fibers is higher on Tensile strength, Flexural, and Impact strengths than Grewia fiber. The optimum weight percentage of fibers: 13.5 wt.% of Kenaf, 15.3 wt. % of Human hair and 7.2 wt.% of Grewia of fibers weights have been used to produce desirable mechanical strengths of HPFC. The mechanical properties of HPFC have been compared to HPFC without Human hair. Tensile, flexural, and impact strength of HPFC is 17.95%, 11.1%, and 19.79% higher than the HPFC without Human hair. The predicted optimum HPFC is recommended to make commercial products for fulfilling consumer demand.

The Dynamic Lattice Method - Vibrations and Wave Propagation in Discontinuous and Heterogeneous Media

The development of a new dynamic lattice element method (dynamicLEM) as well as its application in the simulation of wave propagation in discontinuous and heterogeneous media is the focus of this research paper. The conventional static lattice models are efficient numerical methods to simulate crack initiation and propagation in cemented geomaterials. The advantage of the LEM and the developed dynamic solution, such as simulation of arbitrary crack initiation and propagation, illustration and simulation of existing inherent material heterogeneity as well as stress redistribution upon crack opening, opens a new engineering field and tool for material analysis. To realize the time dependency of the dynamic LEM, the governing Newton's second law is solved while using the Newmark-β method and implementing the non-linear Newton-Raphson Jacobian. The method validation is done according to the results of a boundary element method (BEM) in the plane P-SV-wave propagation within a plane strain domain. Further validation tests comparing the generated wave types, simulation and study of crack discontinuities as well as inherent heterogeneities in the geomaterials are conducted to illustrate the accurate applicability of the new dynamic lattice method. The results indicate that with increasing heterogeneity within the material, the wave field becomes significantly scattered and further analysis of wave fields according to the wavelength/heterogeneity ratio become indispensable. Therefore, in a heterogeneous medium, the application of continuum methods in relation to structural health monitoring should be precisely investigated and improved. The developed dynamic lattice element method is an ideal simulation tool to consider particle scale irregularities, crack distributions and inherent material heterogeneities and can be easily implemented in various engineering applications.

Comprehensive Design Method for Open or Ducted Propellers for Underwater Vehicles

A comprehensive method which determines the most efficient propeller blade shapes for a given axisymmetric hull to travel at a desired speed, is presented. A nonlinear optimization method is used to design the blade, the shape of which is defined by a 3-D B-spline polygon, with the coordinates of the B-spline control points being the parameters to be optimized for maximum propeller efficiency, for given effective wake and propeller thrust. The performance of the propeller within the optimization scheme is assessed by a vortex-lattice method (VLM). To account fully for the hull/propeller interaction, the effective wake to the propeller and the hull resistance are determined by analyzing the designed propeller geometry by the VLM, coupled with a Reynolds-Averaged Navier-Stokes (RANS) solver. The optimization method re-designs the optimum blade with the updated effective wake and propeller thrust (taken to be equal to the updated hull resistance), and the procedure continues until convergence of the propeller performance. The current approach does not require knowledge of the wake fraction or the thrust deduction factor, both of which must be estimated a priori in traditional propeller design. The method is applied for a given hull to travel at a desired speed, and the optimum blades are designed for various combinations of propeller diameter and RPM, in the case of open and ducted propellers with provided duct shapes. The effects of the propeller diameter and RPM on the designed propeller thrust, torque, propeller efficiency, and required power are presented and compared with each other in the case of open and ducted propellers. The present approach is shown to provide guidance on the design of propulsors for underwater vehicles, and is applicable to the design of propulsors for surface ships.