Biometrics can be classified into two types Behavioral (signature verification, keystroke dynamics, etc.) and Physiological (iris characteristics, fingerprint, etc.). Handwritten signature is one of the first few biometrics used even before computers. Signature verification is widely studied and discussed using two approaches. On-line approach and offline approach. Offline systems are more applicable and easy to use in comparison with on-line systems in many parts of the world however it is considered more difficult than on-line verification due to the lack of dynamic information. This paper presents the State-of-the-Art about offline signature verification system; this biometric identification method that had more attraction in recent years because of its necessity for use in daily life routines and when the signature needs to be immediately verified like bank checks. In this paper, we present signature forgery types, features types and recent methods used for features extraction in signature verification systems and approaches used for verification in signature systems. Then we discuss these approaches and for which type of forgeries its suitable. Finally, we suggest new interesting ideas to be incorporated in the future.

State-of-the-art in offline signature verification system

In this work, the aerodynamic performance of beetle wing in free-forward flight was explored by a three-dimensional computational fluid dynamics (CFDs) simulation with measured wing kinematics. It is shown from the CFD results that twist and camber variation, which represent the wing flexibility, are most important when determining the aerodynamic performance. Twisting wing significantly increased the mean lift and camber variation enhanced the mean thrust while the required power was lower than the case when neither was considered. Thus, in a comparison of the power economy among rigid, twisting and flexible models, the flexible model showed the best performance. When the positive effect of wing interaction was added to that of wing flexibility, we found that the elytron created enough lift to support its weight, and the total lift (48.4 mN) generated from the simulation exceeded the gravity force of the beetle (47.5 mN) during forward flight.

https://royalsocietypublishing.org/doi/pdf/10.1098/rsif.2013.0312

Improvement of the aerodynamic performance by wing flexibility and elytra--hind wing interaction of a beetle during forward flight.

Significant advancements in computational fluid dynamics (CFD) and their coupling with computational structural dynamics (CSD, or comprehensive codes) for rotorcraft applications have been achieved recently. Despite this, CSD codes with their engineering level of modeling the rotor blade dynamics, the unsteady sectional aerodynamics and the vortical wake are still the workhorse for the majority of applications. This is especially true when a large number of parameter variations is to be performed and their impact on performance, structural loads, vibration and noise is to be judged in an approximate yet reliable and as accurate as possible manner. In this article, the capabilities of such codes are evaluated using the HART II International Workshop database, focusing on a typical descent operating condition which includes strong blade–vortex interactions. A companion article addresses the CFD/CSD coupled approach. Three cases are of interest: the baseline case and two cases with 3/rev higher harmonic blade root pitch control (HHC) with different control phases employed. One setting is for minimum blade–vortex interaction noise radiation and the other one for minimum vibration generation. The challenge is to correctly predict the wake physics—especially for the cases with HHC—and all the dynamics, aerodynamics, modifications of the wake structure and the aero-acoustics coming with it. It is observed that the comprehensive codes used today have a surprisingly good predictive capability when they appropriately account for all of the physics involved. The minimum requirements to obtain these results are outlined.

The HART II international workshop: an assessment of the state-of-the-art in comprehensive code prediction

How Could Beetle’s Elytra Support Their Own Weight during Forward Flight?

Over the past decade, there have been significant advancements in the accuracy of rotor aeroelastic simulations with the application of computational fluid dynamics methods coupled with computational structural dynamics codes (CFD/CSD). The HART II international workshop database, which includes descent operating conditions with strong blade–vortex interactions (BVI), provides a unique opportunity to assess the ability of CFD/CSD to capture these physics. In addition to a baseline case with BVI, two additional cases with 3/rev higher harmonic blade root pitch control are available for comparison. The collaboration during the workshop permits assessment of structured, unstructured, and hybrid overset CFD/CSD methods from across the globe on the dynamics, aerodynamics, and wake structure. Evaluation of the plethora of CFD/CSD methods indicates that the most important numerical variables associated with most accurately capturing BVI include the use of either a two-equation RANS model or detached eddy simulation-based turbulence model and a sufficiently small time step. An appropriate trade-off between grid fidelity and spatial accuracy schemes also appears to be important for capturing BVI on the advancing side of the rotor disk. Overall, the CFD/CSD methods generally fall within the same accuracy; cost-effective hybrid Navier-Stokes/Lagrangian wake methods tend to correlate less accurately with experiment and have larger data scatter than the full CFD/CSD methods for most parameters evaluated. The importance of modeling the fuselage is observed, and other requirements are discussed.

The HART II international workshop: an assessment of the state of the art in CFD/CSD prediction

Three-dimensional Euler and Navier-Stokes equations are solved using an overlapped grid system to compute the unsteady flow field around helicopter rotor blade in forward flight. To verify the automated overlapped grid solver, the unsteady flow field and airloads on Caradonna-Tung NACA0012 and AH-1G rotor blade models in forward flight were computed. Two equation turbulence model k-ω Wilcox Durbin(WD+) is used. For spatial discretization Roe FDS(Flux Difference Splitting) scheme and Weighted ENO(Essentially Non-Oscillatory) scheme are applied. Good agreement between computed and measured surface pressure distributions was seen for the Caradonna and Tung rotor’s forward flight simulation. The effects of background wake grid spacing, spatial accuracy and viscosity were examined in the AH-1G rotor simulation. Surface pressure distributions, sectional thrust and oscillatory pitching moment coefficients were compared with flight test data. A better variation for sectional thrust and oscillatory pitching moment were found by using the Navier-Stokes analysis.

Euler and Navier-Stokes Simulations of Helicopter Rotor Blade in Forward Flight Using an Overlapped Grid Solver

A three-dimensional compressible Navier-Stokes solver, KFLOW, using overlapped grids has recently been developed to simulate unsteady flow phenomena over helicopter rotor blades The blade-vortex interaction is predicted for a descending flight using measured blade deformation data The effects of computational grid resolution and azimuth angle increments on airloads were examined, and computed airloads and vortex trajectories were compared with HART-II wind tunnel data The current method predicts the BVI phenomena of blade airloads reasonably well It is found from the present study that a peculiar distribution of vorticity of tip vortices in an approximate azimuth angle range of 90 to 180 degrees can be explained by physics of the shear-layer interaction as well as the dissipation of numerical schemes

/pdf/kflow-results-of-airloads-on-hart-ii-rotor-blades-with-2l2gvq3llu.pdf

KFLOW Results of Airloads on HART-II Rotor Blades with Prescribed Blade Deformation

In this work, the Blade Vortex Interaction (BVI) airloads characteristic for a rotor in descending flight condition is investigated using a nonlinear flexible multibody dynamics analysis code DYMORE. A free vortex wake model is incorporated into the comprehensive analysis system and improvement of airloads prediction as well as collective and cyclic pitch control settings is obtained over the finite-state dynamic inflow model that is adopted in the conventional DYMORE analysis. The three test conditions in the HART (Higher harmonic control Aeroacoustic Rotor Test) II are considered to illustrate the present investigation. It is found that the BVI airloads characteristic is significantly influenced by the higher harmonic pitch control inputs. The influence of BVI oscillatory peaks along with the miss-distance between the blade and the vortices is studied in detail to identify the mechanism of reducing noise and vibration in the HART II experiment.

/pdf/correlation-study-of-a-rotor-in-descending-flight-using-4cojo65z5j.pdf

Correlation study of a rotor in descending flight using DYMORE with a freewake model

A rotor blade for a rotary wing aircraft, which rotates about and is combined with a rotation shaft of the rotary wing aircraft. The rotor blade includes a body combined with the rotation shaft and including a leading edge that is a front edge in a direction of rotation; and a plurality of deformable protrusions formed on the leading edge of the body in a radial direction of rotation, and deformable between a first shape protruding forward in the direction of rotation and a second shape not protruding forward in the direction of rotation such that BVI noise generated when a vortex formed near a blade tip collides with the rotor blade is selectively reduced whenever necessary. The deformable protrusions are formed in a region from a point spaced apart from the rotation shaft by 75% of a radius of rotation to a point spaced apart from the rotation shaft by 90% of the radius of rotation.

Rotor blade for rotary wing aircraft having deformable protrusions to reduce blade vortex interaction noise

A technique for the generation of overlapped grid using a simple shooting method, that is a cut-paste algorithm, is presented. It makes possible to generate overlapping grids with moderate mesh interface region. To generate overlapped grids with minimal amount of user inputs, the advancing-front technique using the fringe points as facets is used. To remove hole points initially, fronts using solid bodies and the zones of interference algorithm are used. The overlapped grids are generated for several cases using present algorithms and Euler equations are solved for two/three-dimensional steady state flow fields. To demonstrate the capability of present method, the two dimensional store separation with trajectory mode of three-DOF is computed in an unsteady flow field.

Yung Hoon Yu

Papers

Euler and Navier-Stokes Simulations of Helicopter Rotor Blade in Forward Flight Using an Overlapped Grid Solver

KFLOW Results of Airloads on HART-II Rotor Blades with Prescribed Blade Deformation

Correlation study of a rotor in descending flight using DYMORE with a freewake model

Rotor blade for rotary wing aircraft having deformable protrusions to reduce blade vortex interaction noise

An Efficient Multigrid Method for Overlapped Grid System to Integrated System Analysis