Flexible Blades Research Articles

Geometrically exact physics-based modeling and computer animation of highly flexible 1D mechanical systems

This paper presents a geometrically exact beam theory and a corresponding displacement-based finite-element model for modeling, analysis and natural-looking animation of highly flexible beam components of multibody systems undergoing huge static/dynamic rigid-elastic deformations. The beam theory fully accounts for geometric nonlinearities and initial curvatures by using Jaumann strains, concepts of local displacements and orthogonal virtual rotations, and three Euler angles to exactly describe the coordinate transformation between the undeformed and deformed configurations. To demonstrate the accuracy and capability of this nonlinear beam element, nonlinear static and dynamic analysis of two highly flexible beams are performed, including the twisting a circular ring into three small rings and the spinup of a flexible helicopter rotor blade (Graphical abstract). These numerical results reveal that the proposed nonlinear beam element is accurate and versatile for modeling, analysis and 3D rendering and animation of multibody systems with highly flexible beam components.

Flexible blade for in-line measurement of low-range viscosity

A new type of viscometer is proposed for measuring viscosity in low viscosity fluids. Viscosity is determined by rotating a flexible blade at a constant angular velocity within a cylindrical vessel. As the blade rotates a torque transducer measures changes in strain or deflection of the flexible blade. We show that the deflection during rotation is directly proportional to the sample viscosity. We provide measurements in standard materials and show that blade strain monotonically increases with rotational rate. The rate of increase of the blade strain with rotation rate provides the viscosity through a calibration curve. The measurements performed here are inherently fast, averaging about 3min per sample. The instrument presented here can be used for simple, fast, and inexpensive in-line viscosity measurements.

Use of B-spline surface to model large-deformation continuum plates: procedure and applications

The absolute nodal coordinate formulation (ANCF) has been used in the analysis of large deformation of flexible multibody systems that encompass belt drive, rotor blade, and cable applications. As demonstrated in the literature, the ANCF finite elements are ideal for isogeometric analysis. The purpose of this investigation is to establish a relationship between the B-splines, which are widely used in the geometric modeling, and the ANCF finite elements in order to construct continuum models of large-deformation geometries. This paper proposes a simplified approach to map the B-spline surfaces into ANCF thin plate elements. Matrix representation of the mapping process is established and examined through numerical examples successfully. The matrix representation of the mapping process is used because of its suitability of computer coding and to minimize the calculation time. The error estimation is carried out by analyzing the gap between the points of each ANCF element and the corresponding points of the portion of the B-spline surface. The Hausdorff distance is used to study the effect of the number of control points, the degree of interpolation, and the knot multiplicity on the mapped geometry. It is found that cubic interpolation is recommended for optimizing the accuracy of mapping the B-spline surface to ANCF thin plate elements. It is found that thin plate element in ANCF missing a number of basis functions which considered a source of error between the two surfaces, as well as it does not allow to converting the ANCF thin plate elements model to B-spline surface. In this investigation, an application example of modeling large-size wind turbine blade with uniform structure is illustrated. The use of the continuum plate elements in modeling flexible blades is more efficient because of the relative scale between the plate thickness and its length and width and the high flexibility of its structure. The numerical results are compared with the results of ANSYS code with a good agreement. The dynamic simulation for mapped surface model shows a numerical convergence, which ensures the ability of using the proposed approach for applications of dynamics for design and computer-aided design.

2A2-Q01 板バネ脚機構を有するバルーン歩行ロボットの開発(ホーム&オフィスロボット)

In this paper we described the balloon walking robot of soft legs mechanism in consideration of familiarity with human relations. The robot has the flexible blade spring mechanism which imitated the sport artificial leg in addition to heart-shaped appearance. This robot was designed for human support robot which is used in care worker, in order to use for prosthesis. This robot consists of three unit, interconnected by the soft joints of leaf spring legs mechanism and balloon. The three units are driven by on-off control using SMA. We propose the robot which controls buoyancy and explain walk operation of the soft lightweight robot.

Experimental investigation on the effect of channel width on flexible rubber blade water wheel performance

A laboratory scale flexible rubber blade water wheel has been investigated at the hydraulic laboratory of University of Southampton. The effect of channel width on water wheel performance has been studied. Different upstream and downstream channel widths are set for the tests. In this paper, the experimental set up, tested water wheel and the measurement procedure are described and the experimental results are shown. Results show significant improvement in power output and efficiency in reduced channel width.

Variance-constrained control of maneuvering helicopters with sensor failure

This article presents the novel results obtained using variance-constrained controllers and maneuvering helicopters also when some helicopter sensors fail. For this purpose, complex, control oriented, and physics-based helicopter models are used. A nonlinear model of the helicopter, which includes blade flexibility, is first linearized around specific maneuvering flight conditions (i.e. level banked turn and helical turn). The resulting linearized models are used for the design of variance-constrained controllers (i.e. output and input variance-constrained controllers). Then, the robustness of the closed-loop systems with respect to modeling uncertainties (i.e. flight conditions and helicopter inertial parameters variations) is studied. Next, variance-constrained controllers are designed for these maneuvering helicopter models when some helicopter sensors fail. Several sensor failure cases are examined and robustness properties of the closed-loop systems with respect to modeling uncertainties are also examined. Limitations of the control design process due to the number and type of failed sensors are investigated as well. Finally, the possibility to adaptively switch between controllers in order to mitigate sensor failure is studied.

Analysis of Structural Parameters of Flexible Spiral Conveyor Blades and Study of its Transmission Power

A way of using flexible spiral blade as the executive part for spiral transportion was proposed, the mathematical model of its transportation resistance torque was set up, and the impact of structure parameter of flexible spiral blades on transportation power was analyzed. A experiment set-up was rigged, and tests were made to verify the theoretical model. The results of the experiment are in good agreement with the theoretical analysis. The research has enlightened the the parameter design of flexible spiral blades

Experimental Study of an Extremely Flexible Rotor for Microhelicopters

This paper describes the development and testing of a rotor with extremely flexible blades, focusing on application to a microhelicopter. The goal is to develop rotor blades that are so flexible that they can be rolled into a compact volume and stowed inside the rotor hub. The design of an 18-in-diameter two-bladed rotor with flexible blades is presented. Stiffening and stabilization of the rotor blades are enabled by centrifugal forces acting on a tip mass. The relationship between blade-design parameters, aeroelastic stability boundaries, and hover performance is explored by a systematic set of experiments. It is observed that rotational speed and collective pitch angles have a significant effect on rotor stability. In addition, a large negative spanwise twist is induced in the flexible blades during stable operation, resulting in a decreased efficiency compared with rigid rotor blades having an identical planform and airfoil section. Different approaches to passively tailor the induced twist distribution are investigated. The highest efficiency was measured on a configuration making use of the propeller moment acting on a tip mass located at an index angle to the blade chord. A maximum figure of merit of 0.51 was measured at a blade loading of 0.14, which is comparable to the efficiency of rigid rotor blades.

Fluid–structure interaction modeling of wind turbines: simulating the full machine

In this paper we present our aerodynamics and fluid---structure interaction (FSI) computational techniques that enable dynamic, fully coupled, 3D FSI simulation of wind turbines at full scale, and in the presence of the nacelle and tower (i.e., simulation of the "full machine"). For the interaction of wind and flexible blades we employ a nonmatching interface discretization approach, where the aerodynamics is computed using a low-order finite-element-based ALE-VMS technique, while the rotor blades are modeled as thin composite shells discretized using NURBS-based isogeometric analysis (IGA). We find that coupling FEM and IGA in this manner gives a good combination of efficiency, accuracy, and flexibility of the computational procedures for wind turbine FSI. The interaction between the rotor and tower is handled using a non-overlapping sliding-interface approach, where both moving- and stationary-domain formulations of aerodynamics are employed. At the fluid---structure and sliding interfaces, the kinematic and traction continuity is enforced weakly, which is a key ingredient of the proposed numerical methodology. We present several simulations of a three-blade 5~MW wind turbine, with and without the tower. We find that, in the case of no tower, the presence of the sliding interface has no effect on the prediction of aerodynamic loads on the rotor. From this we conclude that weak enforcement of the kinematics gives just as accurate results as the strong enforcement, and thus enables the simulation of rotor---tower interaction (as well as other applications involving mechanical components in relative motion). We also find that the blade passing the tower produces a 10---12 % drop (per blade) in the aerodynamic torque. We feel this finding may be important when it comes to the fatigue-life analysis and prediction for wind turbine blades.

타워와 블레이드의 탄성효과를 고려한 부유식 해상풍력발전기의 동적거동해석

부유식 해상풍력발전기의 시뮬레이션을 위해서 본 연구에서는 2㎿ 육상 풍력발전기에 부유구조물인 Tension Leg Platform(TLP) 구조를 추가하였다. 기상청 관측데이터와 해수면으로부터의 높이에 대해 풍속을 정의하는 지수법칙을 이용하여 풍하중을 산출하고 블레이드와 타워에 일정한 높이간격으로 적용하였다. 상대모리슨 방정식을 이용하여 파랑하중을 모델링하였다. 블레이드의 회전속도를 정격속도인 18rpm 으로 고려하고, 풍하중과 파랑하중 작용 시 2㎿ 의 부유식 해상풍력기의 동적거동 해석을 수행하였다. 파랑하중에 대한 해상풍력기의 공진특성을 조사하기 위해 타워와 블레이드의 탄성체 모델을 구성하여 해상풍력기의 고유진동수를 계산하였다. 타워와 블레이드의 탄성효과가 해상풍력기의 거동에 미치는 영향을 분석하기 위해 타워만 탄성체로 구성된 탄성타워모델과 타워와 블레이드가 탄성체로 고려된 탄성타워 블레이드모델을 각각 강체 모델과 비교하였다.

Heat transfer enhancement analysis of a cylindrical surface by a piezoelectric fan

Piezoelectric fans consist of a thin flexible blade attached to a vibrating piezoelectric patch, and provide an effective means of enhancing the heat transfer in low convective regions. In this study, the characteristics of the three-dimensional heat and fluid flow fields generated by the vibrating fan are examined by performing numerical simulations and experimental measurements. In performing the simulations, the fluid domain is discretized using a dynamic meshing scheme to take account of the time-varying shape and position of the vibrating blade. The results show that two counter-rotating screw-type flow structures on either side of the blade appeared on either edge of the blade, and a pair of asymmetric vortex is formed around the fan tip. The experiment is conducted with a total of eighteen T-type thermocouples attaching to the cylindrical surface to measure the variation of temperature. The experimental and numerical results indicate that the piezoelectric fan improves the heat transfer coefficient by 1.2–2.4 times. Moreover, the augmentation of local heat transfer coefficient can be achieved by 2.85 times.

초기 비틀림각이 고려된 블레이드-축 통합 시스템의 동적 특성

A nonlinear dynamic model for the shaft-disk-blade unit is developed in this study. In this regard, the rotating flexible blade, with a pre-twist angle, attached to a rigid disk driven by a shaft which is flexible in torsion is developed. The rotor-blade coupled model is derived using Lagrange equation in conjunction with the assumed mode method to discretize the blade deformation. The equations of motion are analyzed based on the small deformation theory for the blade and shaft torsional deformation to obtain the system natural frequencies for various system parameters.

Hydrodynamics of vegetated channels

This paper highlights some recent trends in vegetation hydrodynamics, focusing on conditions within channels and spanning spatial scales from individual blades, to canopies or vegetation patches, to the channel reach. At the blade scale, the boundary layer formed on the plant surface plays a role in controlling nutrient uptake. Flow resistance and light availability are also influenced by the reconfiguration of flexible blades. At the canopy scale, there are two flow regimes. For sparse canopies, the flow resembles a rough boundary layer. For dense canopies, the flow resembles a mixing layer. At the reach scale, flow resistance is more closely connected to the patch-scale vegetation distribution, described by the blockage factor, than to the geometry of individual plants. The impact of vegetation distribution on sediment movement is discussed, with attention being paid to methods for estimating bed stress within regions of vegetation. The key research challenges of the hydrodynamics of vegetated channels are highlighted.

Effect of viscoelasticity on liquid transfer during gravure printing

Roll-to-roll patterning of small-scale features on a rapidly moving web is an industrially important process with a wide array of commercial applications both old and new. Examples include magazine printing and more recently the pattering of flexible electronics. Among the many existing web coating techniques for large-scale fabrication, slit die and gravure coating are the most commonly used. In gravure coating, an engraved roller with a regular array of shallow cavities/cells is used to pick up fluid from a bath. It is then passed through a flexible doctoring blade in order to meter off excess fluid before printing the fluid onto a flexible substrate. Here we present an experimental investigation into the effect that viscoelasticity has on the dynamics of liquid transfer from an idealized gravure cell to a flat rigid substrate. Although the dynamics of the actual gravure coating process is quite complex, we chose to study a simplified process by imposing an extensional flow using a modified filament stretching rheometer in which one of the endplates is replaced by a cell containing a single truncated conical gravure cell. The deformation and stretching of the resulting liquid bridges, the motion of the contact line within the gravure cell and the total amount of fluid removed from the gravure cell are studied as a function of the imposed stretch rate, the fluid rheology, and the geometry of the gravure cell. Two different viscoelastic solutions of high molecular weight polyethylene oxide in water were studied and compared to a series of Newtonian fluids. The results show that the primary impact of viscoelasticity is the addition of an elastic stress which increases the tension along the liquid bridge and significantly increases the bridge lifetime. For stretches where the gravure cell was placed on the bottom and the top plate moved vertically, viscoelasticity was found to significantly reduce the amount of fluid transferred to the top plate. However, by placing the gravure cell on top and reversing the relative direction of the inertial and gravitational stresses, viscoelasticity was found to significantly increase the amount of fluid transferred. Increasing the stretch rate was found to amplify these observations. Finally, increasing the contact angle between the fluid and the gravure cell and decreasing the aspect ratio of the gravure cell were both found to increase the amount of fluid transferred.

Modal Analysis of Three Rotating Blades of Large Wind Turbine

Abstract: Based on the Multi-body dynamics, the dynamics equation of the flexible blade in wind turbine is established by discretizing the rotating blade using finite element method. The simulation analysis of the single blade and the vibration modes of a 5MW wind turbine rotor are carried out by MATLAB. The first six natural frequencies and modes of the single blade and the rotor are figured out, and whose results are analyzed. The simulation results indicates that the coupling effect of the rotor can lead to dynamic stiffening. In comparison to the results in FAST, these simulation results show an outstanding agreement with the results calculated by FAST and hence approve the simulation method is valid and meanwhile give reference for large wind turbine design and running.

Lost treasures: Miraculous Damascus steel

European Crusaders told of Islamic warriors wielding super-sharp, implausibly flexible blades. Were the swordsmiths unwittingly using nanotechnology?

Flow and Transport in Regions with Aquatic Vegetation

This review describes mean and turbulent flow and mass transport in the presence of aquatic vegetation. Within emergent canopies, the turbulent length scales are set by the stem diameter and spacing, and the mean flow is determined by the distribution of the canopy frontal area. Near sparse submerged canopies, the bed roughness and near-bed turbulence are enhanced, but the velocity profile remains logarithmic. For dense submerged canopies, the drag discontinuity at the top of the canopy generates a shear layer, which contains canopy-scale vortices that control the exchange of mass and momentum between the canopy and the overflow. The canopy-scale vortices penetrate a finite distance into the canopy, δe, set by the canopy drag. This length scale segregates the canopy into two regions: The upper canopy experiences energetic turbulent transport, controlled by canopy-scale vortices, whereas the lower canopy experiences diminished transport, associated with the smaller stem-scale turbulence. The canopy-scale vortices induce a waving motion in flexible blades, called a monami.

Review of aeroelasticity for wind turbine: Current status, research focus and future perspectives

Aeroelasticity has become a critical issue for Multi-Megawatt wind turbine due to the longer and more flexible blade. In this paper, the development of aeroelasticity and aeroelastic codes for wind turbine is reviewed and the aeroelastic models for wind turbine blade are described, based on which, the current research focuses for large scale wind turbine are discussed, including instability problems for onshore and offshore wind turbines, effects of complex inflow, nonlinear effects of large blade deflection, smart structure technologies, and aerohydroelasticity. Finally, the future development of aeroelastic code for large scale wind turbine: aeroservoelasticity and smart rotor control; nonlinear aeroelasticity due to large blade deflection; full-scale 3D computational fluid dynamics (CFD) solution for dynamics; and aerohydroelasticity are presented.

An alternative approach for Mohs surgery using a combination of a flexible blade and the traditional scalpel

Mohs surgery is a specialized surgical and pathological technique used for the removal of high-risk neoplasms. Previous reports show the ability of using a flexible blade for Mohs surgery. We utilized a technique combining the traditional #15 blade and scalpel with a flexible blade to perform excisions for Mohs surgery. The use of the flexible blade alone in Mohs may yield jagged tissue peripheral edges after cutting on the cryostat. The classic technique with a scalpel excision often results in a deeper cut than desired, resulting in a larger defect. We modified both the traditional Mohs technique and the flexible blade by combining both. We have performed this method in approximately over 100 cases on the scalp, face and ears, preserving tissue, minimizing bleeding and avoiding alopecia.

Aeroelastic Analysis of a Micro-Air-Vehicle-Scale Cycloidal Rotor in Hover

This paper describes the aeroelastic model to predict the blade loads and the average thrust of amicro-air-vehiclescale cycloidal rotor. The analysis was performed using two approaches: one using a second-order nonlinear beam finite element method analysis for moderately flexible blades and a second using a multibody-based largedeformation analysis (especially applicable for extremely flexible blades) incorporating a geometrically exact beam model. An unsteady aerodynamic model is included in the analysis with two different inflow models: single streamtube and double-multiple streamtube inflowmodels. For the cycloidal rotors usingmoderately flexible blades, the aeroelastic analysis was able to predict the average thrust with sufficient accuracy over awide range of rotational speeds, pitching amplitudes, and number of blades. However, for the extremely flexible blades, the thrust was underpredicted at higher rotational speeds, and thismaybebecause of the overprediction of blade deformations. The analysis clearly showed that the reason for the reduction in the thrust-producing capability of the cycloidal rotorwith blade flexibility may be attributed to the large nosedown elastic twisting of the blades in the upper half cylindrical section, which is not compensated by a noseup pitching in the lower half-section. The inclusion of the actual blade pitch kinematics, unsteady aerodynamics, and flow curvature effects was found crucial in the accurate lateral force prediction.