Theoretical analysis of perching and hovering maneuvers

Unsteady aerodynamic phenomena are encountered in a large number of modern aerospace and non-aerospace applications. Leading edge vortices (LEVs) are of particular interest because of their large impact on the forces and performance. In rotorcraft applications, they cause large vibrations and torsional loads (dynamic stall), affecting the performance adversely. In insect flight however, they contribute positively by enabling high-lift flight. Identifying the conditions that result in LEV formation and modeling their effects on the flow is an important ongoing challenge. Perching (airfoil decelerates to rest) and hovering (zero freestream velocity) maneuvers are of special interest. In earlier work by the authors, a Leading Edge Suction Parameter (LESP) was developed to predict LEV formation for airfoils undergoing arbitrary variation in pitch and plunge at a constant freestream velocity. In this research, the LESP criterion is extended to situations where the freestream velocity is varying or zero. A point-vortex model based on this criterion is developed and results from the model are compared against those from a computational fluid dynamics (CFD) method. Abstractions of perching and hovering maneuvers are used to validate the low-order model's performance in highly unsteady vortex-dominated flows, where the time-varying freestream/translational velocity is small in magnitude compared to the other contributions to the velocity experienced by the leading edge region of the airfoil. Time instants of LEV formation, flow topologies and force coefficient histories for the various motion kinematics from the low-order model and CFD are obtained and compared. The LESP criterion is seen to be successful in predicting the start of LEV formation and the point-vortex method is effective in modeling the flow development and forces on the airfoil. Typical run-times for the low-order method are between 30-40 seconds, making it a potentially convenient tool for control/design applications

Circuit Theory

Contains research objectives and reports on four research projects

Nonlinear Diffusion on the 2D Euclidean Motion Group

Linear and nonlinear diffusion equations are usually considered on an image, which is in fact a function on the translation group. In this paper we study diffusion on orientation scores, i.e. on functions on the Euclidean motion group SE(2). An orientation score is obtained from an image by a linear invertible transformation. The goal is to enhance elongated structures by applying nonlinear left-invariant diffusion on the orientation score of the image. For this purpose we describe how we can use Gaussian derivatives to obtain regularized left-invariant derivatives that obey the non-commutative structure of the Lie algebra of SE(2). The Hessian constructed with these derivatives is used to estimate local curvature and orientation strength and the diffusion is made nonlinearly dependent on these measures. We propose an explicit finite difference scheme to apply the nonlinear diffusion on orientation scores. The experiments show that preservation of crossing structures is the main advantage compared to approaches such as coherence enhancing diffusion

A modelling framework for the assessment of the impacts of alternative policy and management options on the sustainability of Finnish agrifood systems

Recently, a new project focussing on integrated assessment modelling of agrifood systems (IAM-Tools) has been launched at MTT Agrifood Research Finland to gather, evaluate, refine and develop these component models and to link tem in an IAM framework for Finnish conditions

Management Accountant's Role and Functions in the Enterprise Resource Planning Environment - Author's Own Research into Enterprises in Poland

This article seeks to answer whether the implementation of an ERP system has an effect on the management accountant's tasks and functions, especially in the field of performance measurement and internal reporting. The ERP impacts on the controller's role in the organization will be evaluated using field studies on six enterprises owned by multinational corporations. The question that should be asked here is whether controller's functions and tasks will also be unaffected.Celem badania jest próba odpowiedzi na pytanie czy zastosowanie zintegrowanego systemu informatycznego w przedsiębiorstwie zmienia zadania i funkcje specjalisty do spraw rachunkowości zarządczej. Na podstawie studium przypadku sześciu przedsiębiorstw będących częścią koncernów międzynarodowych zostaje dokonana ocena wpływu zastosowania ERP na rolę kontrolera w organizacji. Autor odpowiada również na pytanie czy w funkcjach i zadaniach kontrolera nie zaobserwowane zostaną zmiany w związku z implementacją ERP

Controls on inorganic nitrogen leaching from Finnish catchments assessed using a sensitivity and uncertainty analysis of the INCA -N model

The semi-distributed, dynamic INCA-N model was used to simulate the behaviour of dissolved inorganic nitrogen (DIN) in two Finnish research catchments. Parameter sensitivity and model structural uncertainty were analysed using generalized sensitivity analysis. The Mustajoki catchment is a forested upstream catchment, while the Savijoki catchment represents intensively cultivated lowlands. In general, there were more influential parameters in Savijoki than Mustajoki. Model results were sensitive to N-transformation rates, vegetation dynamics, and soil and river hydrology. Values of the sensitive parameters were based on long-term measurements covering both warm and cold years. The highest measured DIN concentrations fell between minimum and maximum values estimated during the uncertainty analysis. The lowest measured concentrations fell outside these bounds, suggesting that some retention processes may be missing from the current model structure. The lowest concentrations occurred mainly during low flow periods; so effects on total loads were small

Circuit Theory

Contains research objectives and reports on one research project.Lincoln Laboratory, Purchase Order DDL-B222Department of the ArmyDepartment of the NavyDepartment of the Air Force under Contract AF19(122)-45

Aerodynamics of Pitching Wings: Theory and Experiments

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140444/1/6.2014-2881.pd

Model Reduction in Discrete Vortex Methods for 2D Unsteady Aerodynamic Flows

In this paper, we propose a method for model reduction in discrete-vortex methods. Discrete vortex methods have been successfully employed to model separated and unsteady airfoil flows. Earlier research revealed that a parameter called the Leading Edge Suction Parameter (LESP) can be used to model leading-edge vortex (LEV) shedding in unsteady flows. The LESP is a measure of suction developed at the leading edge, and whenever the LESP exceeds a critical value, a discrete vortex is released from the leading edge so as to keep the LESP at the critical value. Though the method was successful in predicting the forces on and the flow field around an airfoil in unsteady vortex-dominated flows,it was necessary to track a large number of discrete vortices in order to obtain the solution. The current study focuses on obtaining a model with a reduced number of leading-edge vortices, thus improving the computation time. Vortex shedding from the leading edge is modelled by a shear layer that comprises of a few discrete vortices, and a single concentrated vortex whose strength varies with time. The single vortex at the end of the shear layer accounts for the concentrated vortical structure that comprises several discrete vortex elements in conventional vortex methods. A merging algorithm is initiated when the edge of the shear layer starts rolling up. Suitable discrete vortices are identified using a kinematic criterion, and are merged to the growing vortex at every time step. The reduced order method is seen to bring down the number of discrete vortices shed from the leading edge significantly