Analytical modeling of helicopter static and dynamic induced velocity in GRASP

The methodology used by the General Rotorcraft Aeromechanical Stability Program (GRASP) to model the characteristics of the flow through a helicopter rotor in hovering or axial flight is described. Since the induced flow plays a significant role in determining the aeroelastic properties of rotorcraft, the computation of the induced flow is an important aspect of the program. Because of the combined finite-element/multibody methodology used as the basis for GRASP, the implementation of induced velocity calculations presented an unusual challenge to the developers. To preserve the modelling flexibility and generality of the code, it was necessary to depart from the traditional methods of computing the induced velocity. This is accomplished by calculating the actuator disc contributions to the rotor loads in a separate element called the air mass element, and then performing the calculations of the aerodynamic forces on individual blade elements within the aeroelastic beam element

Vloga ekonomije v gozdnem načrtovanju in ocena gozdne politike v Sloveniji

This paper explores the current status of the forest sectors in Slovenia, identifies potential issues in the management and use of the forests, and discusses a means by which policy makers can identify opportunities to enhance the role played by forests and their related goods and services in Slovenia. Specifically, a framework is proposed to assess the relationships between the economic, social, and ecological aspects of Slovenia%s forestseffects of changes in economic conditions on forest demands and useseconomic impacts of ecological, social, and business conditionseffects of current or proposed policiesand opportunities for the sustainable economic development of wood-based and forest-dependent enterprises. Such a framework is critical for managing Slovenia\u27s forests and forestry sector in such a manner to optimize the ecological and economic potential.Prispevek prikazuje raziskavo stanja gozdarskega sektorja v Sloveniji, pokaže na potencialne težave v upravljanju in rabi gozdov ter odpira razpravo o orodjih, s katerimi bi lahko pripravljavci politik opredelili priložnosti za krepitev vloge gozdov v Sloveniji in z njimi povezanih dobrin in storitev. Podan je predlog okvira za analizo: povezav med ekonomskimi, socialnimi in ekološkimi vidiki gozdov v Slovenijivplivov spremenjenih ekonomskih razmer na povpraševanje in rabo gozdnih virovekonomskih vplivov ekoloških in socialnih razmer ter poslovnega okoljaučinkov veljavnih in predlaganih politikin priložnosti za trajnostni ekonomski razvoj podjetništva v lesno-predelovalni panogi in gozdarskem podjetništvu. Tovrstni okvir je ključen za gospodarjenje z gozdovi Slovenije z vidika optimiziranja ekološkega in ekonomskega potenciala gozdarskega sektorja

Forest Certification and Nonindustrial Private Forest Landowners: Who Will Consider Certifying and Why?

Nonindustrial private forest owners in western Tennessee who own 40 or more acres of forestland were sent a mail survey to assess their awareness, acceptance, and perception of forest certification. More than eight in 10 participants indicated a willingness to consider certification. Landowners who would most likely consider certifying their forest were typically well-educated new forest owners, and had received advice or information about their forestland. They would certify for both utilitarian and environmental reasons, and they most trust the State Division of Forestry and consulting foresters as potential third-party certifiers

Costing the Forest Operations and the Supply of Hardwood in Tennessee

The purpose of this paper is to assess the delivered cost of pulpwood from natural hardwood stands in the State of Tennessee using forest operations supply chain analysis. The study is based on primary production and equipment data collected from logging firms using a statewide in-depth harvesting and transportation survey. Survey results were used to develop estimates for the delivery cost of hardwood pulpwood removed per green tonne unit hour. Findings revealed not only the variability of inputs attached to costing harvesting operations, but also the difficulty in identifying one typical harvest system for the state. This may be explained by the very diverse operating conditions and systems, as well as the low stumpage prices and high cost of harvesting and delivery that are predominantly managed by small scale operations. Results have shown that the cost of harvesting a tonne of wood for a distance of up to 50 km ranges from an average minimum of $43 per tonne to an average maximum of$51 per tonne. After this distance, the cost increases exponentially. The fact that this study is the first for the state that looks at the operations logistics indicates the lack of available knowledge of the true cost incurred by operators that may have a lasting impact not only on the continuity of logging operations but also the sustainability and availability of forest products and workforce

Costing the Forest Operations and the Supply of Hardwood in Tennessee

The purpose of this paper is to assess the delivered cost of pulpwood from natural hardwood stands in the State of Tennessee using forest operations supply chain analysis. The study is based on primary production and equipment data collected from logging firms using a statewide in-depth harvesting and transportation survey. Survey results were used to develop estimates for the delivery cost of hardwood pulpwood removed per green tonne unit hour. Findings revealed not only the variability of inputs attached to costing harvesting operations, but also the difficulty in identifying one typical harvest system for the state. This may be explained by the very diverse operating conditions and systems, as well as the low stumpage prices and high cost of harvesting and delivery that are predominantly managed by small scale operations. Results have shown that the cost of harvesting a tonne of wood for a distance of up to 50 km ranges from an average minimum of $43 per tonne to an average maximum of$51 per tonne. After this distance, the cost increases exponentially. The fact that this study is the first for the state that looks at the operations logistics indicates the lack of available knowledge of the true cost incurred by operators that may have a lasting impact not only on the continuity of logging operations but also the sustainability and availability of forest products and workforce

General Rotorcraft Aeromechanical Stability Program (GRASP): Theory manual

The general rotorcraft aeromechanical stability program (GRASP) was developed to calculate aeroelastic stability for rotorcraft in hovering flight, vertical flight, and ground contact conditions. GRASP is described in terms of its capabilities and its philosophy of modeling. The equations of motion that govern the physical system are described, as well as the analytical approximations used to derive them. The equations include the kinematical equation, the element equations, and the constraint equations. In addition, the solution procedures used by GRASP are described. GRASP is capable of treating the nonlinear static and linearized dynamic behavior of structures represented by arbitrary collections of rigid-body and beam elements. These elements may be connected in an arbitrary fashion, and are permitted to have large relative motions. The main limitation of this analysis is that periodic coefficient effects are not treated, restricting rotorcraft flight conditions to hover, axial flight, and ground contact. Instead of following the methods employed in other rotorcraft programs. GRASP is designed to be a hybrid of the finite-element method and the multibody methods used in spacecraft analysis. GRASP differs from traditional finite-element programs by allowing multiple levels of substructure in which the substructures can move and/or rotate relative to others with no small-angle approximations. This capability facilitates the modeling of rotorcraft structures, including the rotating/nonrotating interface and the details of the blade/root kinematics for various types. GRASP differs from traditional multibody programs by considering aeroelastic effects, including inflow dynamics (simple unsteady aerodynamics) and nonlinear aerodynamic coefficients

Need-Based Aid, Participation in Education Abroad, and Program Type Choice

Although education abroad in the US offers participants demonstrable benefits, direct and opportunity costs are cited as primary barriers to broader participation. Yet the degree to which low-income status deters studying abroad and whether additional need-based aid beyond Pell Grants encourages participation remain uncertain. Moreover, not all education abroad programs are equivalent in terms of costs. This study is the first to examine whether need-based aid recipients differentially choose programs of varying duration or programs offered by various provider types. The sample consisted of 221,981 students from 36 institutions of the Consortium for Analysis of Student Success through International Education (CASSIE). Within that sample, 60,477 received Pell grants. Of those recipients, 39% received additional need-based aid. Regression models controlling for student background and context indicated that Pell grant recipients were 3% less likely to study abroad than peers receiving no such aid, and receipt of additional aid increased likelihood by 1% relative to Pell-only recipients. While aid was unrelated to study abroad duration, low-income students were less likely to study with third-party providers. The findings invite financial aid officers to determine thresholds of additional aid necessary to increase participation and to collaborate more systematically with counterparts in international education