Shorter Oars Are More Effective

2009 ◽  
Vol 25 (1) ◽  
pp. 1-8 ◽  
Author(s):  
Volker Nolte
Keyword(s):  
Significant Role ◽  
Equations Of Motion ◽  
Point Of View ◽  
Blade Design ◽  
Record Times ◽  
Factorial Anova ◽  
Performance Improvements ◽  
Biomechanical Models ◽  
Mechanical Connection ◽  
Rowing Performance

The purpose of this investigation was to clarify the effects of blade design and oar length on performance in rowing. Biomechanical models and equations of motion were developed to identify the main forces that affect rowing performance. In addition, the mechanical connection between the propelling blade force and the force that the rower applies on the handle was established. On this basis it was found that the blade design and oar dimensions play a significant role on the rowing performance. While rowers have found empirically that larger and/or hydrodynamically more efficient blade shapes need to be rowed with shorter oars, this article explains this tendency from a biomechanical point of view. Based on the presented evidence, it can be concluded that shorter oars will allow rowers to improve the propelling forces without increasing the handle forces. These findings explain tendencies that started with the introduction of new blade shapes in 1991. A 2 × 2 factorial ANOVA was used to test the significance of the oar shortenings that occurred with the introduction of larger blade surfaces while international record times improved during all those years. Consequently, the findings of this investigation encourage coaches to further experiment with shorter oars and oar manufacturers to continue their blade development that would lead to even shorter oars, with the goal of continuous rowing performance improvements.

A Highly Accurate Beam Finite Element for Curved and Twisted Helicopter Blades

2011 ◽  
Author(s):  
Yan Skladanek ◽  
Paul Cranga ◽  
Guy Ferraris ◽  
Georges Jacquet ◽  
Re´gis Dufour
Keyword(s):  
Finite Element ◽  
Twist Angle ◽  
Experimental Investigations ◽  
Rotating Frame ◽  
Blade Design ◽  
Helicopter Blades ◽  
Performance Improvements ◽  
Blade Optimization ◽  
Model Reliability ◽  
Numerical Tools

Blade optimization is more than ever a crucial activity for helicopter manufacturers, always looking for performance improvements, noise reduction and vibratory comfort increase. Latest studies have led to design new blade concepts including a double swept plan shape, an evolutionary and increased twist angle at the tip and a new layout for internal components like roving spars. Such blades exhibit a highly coupled behavior between torsion, longitudinal and bending motions that should be accurately modeled for predictive numerical tools. In this research a highly accurate beam finite element is formulated in the rotating frame to improve the static deformation calculation under aerodynamic and centrifugal loads and thus enhance dynamic and stability analysis usually performed for a helicopter development. Numerical and experimental investigations are performed to demonstrate the model reliability both for academic beams with extreme shape and for actual blade design.

UNUSUAL HYDRODYNAMICS

1987 ◽  
Vol 02 (05) ◽  
pp. 1591-1615 ◽  
Author(s):  
V.A. BEREZIN
Keyword(s):  
Black Hole ◽  
Cosmological Model ◽  
Production Process ◽  
Particle Production ◽  
Energy Momentum Tensor ◽  
Equations Of Motion ◽  
Momentum Tensor ◽  
Point Of View ◽  
Modified Equations ◽  
Nonsingular Cosmological Model

A method for the phenomenological description of particle production is proposed. Correspondingly modified equations of motion and energy-momentum tensor are obtained. In order to illustrate this method we reconsider from the new point of view of (i) the C-field Hoyle-Narlikar cosmology, (ii) the influence of the particle production process on metric inside the event horizon of a charged black hole and (iii) a nonsingular cosmological model.

El papel de los medios electrónicos en la lucha contra la corrupción

2016 ◽  
pp. 199-235
Author(s):  
Agustí CERRILLO I MARTÍNEZ
Keyword(s):  
Significant Role ◽  
Legal Order ◽  
Point Of View

LABURPENA: Bitarteko elektronikoek berebiziko garrantzia dute ustelkeriaren kontrako borrokan. Indarreko legeriak tresna batzuk ditu eta beste batzuk esperientzia pilotuak dira zenbait herrialdetan, baina Espainian aplikatu nahi bada, arau batzuk egin edo aldatu beharko dira. Artikuluan bitarteko elektronikoei ematen ari zaizkien erabilerak —ustelkeria prebenitzeko eta eta haren kontra borrokatzeko— aztertzen dira eta euren bideragarritasuna aztertzen da Espainiako antolamendu juridikoaren ikuskeratik. RESUMEN: Los medios electrónicos tienen un papel significativo en la lucha contra la corrupción. La legislación vigente ya recoge algunos instrumentos mientras que otros son aún experiencias piloto en diversos países cuya aplicación en España puede llegar a exigir la adopción o la reforma de algunas normas. En el artículo se exploran los diferentes usos que se están dando a los medios electrónicos en la prevención y la lucha contra la corrupción y se analiza su viabilidad desde la perspectiva del ordenamiento jurídico español. ABSTRACT: Electronic means have a significant role in the fight against corruption. The current legislation does already mention some tools while others are so far pilot experiences in several countries whose application in Spain might require the adoption or amendment of some provisions. In this article we explore the different usages given to electronic means in the prevention and fight against corruption and we analyze their viability from the point of view of the Spanish legal order.

scholarly journals COMPARATIVE STUDY OF VARIATIONAL CHAOS INDICATORS AND ODEs' NUMERICAL INTEGRATORS

2012 ◽  
Vol 22 (10) ◽  
pp. 1230033 ◽  
Author(s):  
L. A. DARRIBA ◽  
N. P. MAFFIONE ◽  
P. M. CINCOTTA ◽  
C. M. GIORDANO
Keyword(s):  
Numerical Technique ◽  
Equations Of Motion ◽  
General System ◽  
Detailed Comparison ◽  
Dynamical Problem ◽  
Point Of View ◽  
The Other ◽  
Numerical Integrators ◽  
Fast Lyapunov Indicator ◽  
The Times

The reader can find in the literature a lot of different techniques to study the dynamics of a given system and also, many suitable numerical integrators to compute them. Notwithstanding the recent work of [Maffione et al., 2011b] for mappings, a detailed comparison among the widespread indicators of chaos in a general system is still lacking. Such a comparison could lead to select the most efficient algorithms given a certain dynamical problem. Furthermore, in order to choose the appropriate numerical integrators to compute them, more comparative studies among numerical integrators are also needed. This work deals with both problems. We first extend the work of [Maffione et al., 2011b] for mappings to the 2D [Hénon & Heiles, 1964] potential, and compare several variational indicators of chaos: the Lyapunov Indicator (LI); the Mean Exponential Growth Factor of Nearby Orbits (MEGNO); the Smaller Alignment Index (SALI) and its generalized version, the Generalized Alignment Index (GALI); the Fast Lyapunov Indicator (FLI) and its variant, the Orthogonal Fast Lyapunov Indicator (OFLI); the Spectral Distance (D) and the Dynamical Spectra of Stretching Numbers (SSNs). We also include in the record the Relative Lyapunov Indicator (RLI), which is not a variational indicator as the others. Then, we test a numerical technique to integrate Ordinary Differential Equations (ODEs) based on the Taylor method implemented by [Jorba & Zou, 2005] (called taylor), and we compare its performance with other two well-known efficient integrators: the [Prince & Dormand, 1981] implementation of a Runge–Kutta of order 7–8 (DOPRI8) and a Bulirsch–Stöer implementation. These tests are run under two very different systems from the complexity of their equations point of view: a triaxial galactic potential model and a perturbed 3D quartic oscillator. We first show that a combination of the FLI/OFLI, the MEGNO and the GALI 2N succeeds in describing in detail most of the dynamical characteristics of a general Hamiltonian system. In the second part, we show that the precision of taylor is better than that of the other integrators tested, but it is not well suited to integrate systems of equations which include the variational ones, like in the computing of almost all the preceeding indicators of chaos. The result which induces us to draw this conclusion is that the computing times spent by taylor are far greater than the times consumed by the DOPRI8 and the Bulirsch–Stöer integrators in such cases. On the other hand, the package is very efficient when we only need to integrate the equations of motion (both in precision and speed), for instance to study the chaotic diffusion. We also notice that taylor attains a greater precision on the coordinates than either the DOPRI8 or the Bulirsch–Stöer.

Applying New and Improved Technology to an Existing Generator-Drive Steam Turbine

2002 ◽  
Author(s):  
Mike Mindock ◽  
Jerry DiOrio ◽  
Sam Golinkin
Keyword(s):  
Modern Technology ◽  
Design Analysis ◽  
Capital Expenditures ◽  
Blade Design ◽  
Performance Improvements ◽  
Path Design ◽  
Analysis Methods ◽  
Power Generation Equipment ◽  
Significant Performance ◽  
Improved Technology

There is growing pressure to reduce the pay back period of major capital expenditures, and in most cases, revamping existing turbomachinery provides more attractive economics than new equipment. Moreover, revamping existing power generation equipment with modern technology mitigates the expenses associated with obtaining new environmental licensing. Today, innovative application of technological advancements in mechanical and aero-thermodynamic design/analysis methods combined with new manufacturing methods is yielding significant performance improvements. This paper details the revamping of a 36 MW generator-drive turbine that resulted in an eleven point improvement in steam rate. Details of the steampath thermodynamic design/ analysis methods, sealing, diaphragm construction, blade design and low-pressure steam path design, etc. are presented.

scholarly journals Unified formalism for higher-order variational problems and its applications in optimal control

2014 ◽  
Vol 11 (04) ◽  
pp. 1450034 ◽  
Author(s):  
Leonardo Colombo ◽  
Pedro Daniel Prieto-Martínez
Keyword(s):  
Optimal Control ◽  
Equations Of Motion ◽  
Variational Problems ◽  
Higher Order ◽  
Point Of View ◽  
Regular Case ◽  
Underactuated Mechanical Systems ◽  
Interesting Application ◽  
Principal Bundles ◽  
Order Constraints

In this paper, we consider an intrinsic point of view to describe the equations of motion for higher-order variational problems with constraints on higher-order trivial principal bundles. Our techniques are an adaptation of the classical Skinner–Rusk approach for the case of Lagrangian dynamics with higher-order constraints. We study a regular case where it is possible to establish a symplectic framework and, as a consequence, to obtain a unique vector field determining the dynamics. As an interesting application we deduce the equations of motion for optimal control of underactuated mechanical systems defined on principal bundles.

Periodic Motions of a Two-Body System Subjected to Repetitive Impact

1969 ◽  
Vol 91 (4) ◽  
pp. 931-938 ◽  
Author(s):  
David L. Sikarskie ◽  
Burton Paul
Keyword(s):  
Steady State ◽  
High Speed ◽  
Equations Of Motion ◽  
Point Of View ◽  
State Behavior ◽  
State Response ◽  
Stability Of Solution ◽  
Straightforward Method ◽  
Parametric Studies ◽  
Repetitive Impact

The dynamics of a widely used class of hammer impact machines are investigated on the basis of a two-degree-of-freedom idealization. The difficulty in the problem is due to the repetitive impact which introduces a nonlinearity in the system. It is the purpose of the analysis to develop a solution for the steady-state behavior of the system. There are several ways this can be done. One of the most efficient ways, from the point of view of ease of parametric studies of the system, is to convert the problem to a “boundary” value problem. With this technique, the system is governed by the equations of motion between impacts, and further satisfies additional conditions at the beginning and end of each impact cycle. Since the solution is obtained in only one cycle, it thus represents a straightforward method of studying the effect of various system parameters. A fundamental assumption in the analysis is that the steady-state response of the system has a period equal to the forcing period. This is verified for one set of parameters through the use of high-speed movies of an actual machine. There are several other interesting features in the analysis, including multivaluedness of the solution, allowable solution domain, and stability of solution, which have not been completely resolved to date.

scholarly journals Sociological Studies Of International Academic Mobility

2019 ◽  
Vol 1 (2) ◽  
pp. 103-117 ◽  
Author(s):  
Maksim A. Yurevich ◽  
Vadim A. Malahov
Keyword(s):  
Significant Role ◽  
Research Funding ◽  
Point Of View ◽  
Significant Part ◽  
Social Benefits ◽  
Academic Mobility ◽  
Russian Scientific ◽  
Technological Complex ◽  
Material Goods ◽  
Sociological Studies

Academic mobility is a significant part of a scientist’s career both in the world’s leading scientific countries and in peripheral ones. The data of sociological surveys show that the main incentive to change the country of scientific employment in most cases is the desire to gain experience in international teams, to get under the care of eminent scientists, to expand scientific ties. Material incentives such as wages, social benefits or access to research funding tools usually rank middle in the hierarchy of motives to move in countries with a developed scientific and technological complex. In countries that can be considered lagging behind from this point of view, the picture is somewhat different-material goods play a more significant role. Regarding the representatives of the Russian scientific Diaspora, there are also mainly purely economic prerequisites for leaving abroad, and a fairly low proportion of the scientists who left Russia declared their desire to return. At the same time, remote cooperation with Russian researchers for scientists-compatriots is quite an attractive form of interaction.

scholarly journals Kinematic support modeling in Sage

2020 ◽  
Vol 28 (2) ◽  
pp. 141-153
Author(s):  
Oleg K. Kroytor ◽  
Mikhail D. Malykh ◽  
Sergei P. Karnilovich
Keyword(s):  
Rigid Body ◽  
Computer Algebra ◽  
Computer Algebra System ◽  
Seismic Isolation ◽  
Equations Of Motion ◽  
Classical Mechanics ◽  
Vertical Plane ◽  
Base Plate ◽  
Euler Method ◽  
Point Of View

The article discusses the kinematic support, which allows reducing the horizontal dynamic effects on the building during earthquakes. The model of a seismic isolation support is considered from the point of view of classical mechanics, that is, we assume that the support is absolutely solid, oscillating in a vertical plane above a fixed horizontal solid plate. This approach allows a more adequate description of the interaction of the support with the soil and the base plate of the building. The paper describes the procedure for reducing the complete system of equations of motion of a massive rigid body on a fixed horizontal perfectly smooth plane to a form suitable for applying the finite difference method and its implementation in the Sage computer algebra system. The numerical calculations by the Euler method for grids with different number of elements are carried out and a mathematical model of the support as a perfectly rigid body in the Sage computer algebra system is implemented. The article presents the intermediate results of numerical experiments performed in Sage and gives a brief analysis (description) of the results.

scholarly journals Microcosm of evolution: One current philosophical discussion

2018 ◽  
Vol 61 (4) ◽  
pp. 105-122
Author(s):  
Eva Kamerer
Keyword(s):  
Natural Selection ◽  
Significant Role ◽  
Point Of View ◽  
Evolution Of Cooperation ◽  
Cell Populations ◽  
Philosophical Discussion ◽  
Cancerous Cell ◽  
Multi Level

In recent years a discussion is ongoing about whether the idea of Darwinian populations and the principle of natural selection related to this idea can play a significant role in the explanation of neoplastic formation. According to one view, cancerous cell populations are only minimal Darwinian populations whose characteristics are not complex adaptations, while the advocates of the second point of view insist that carcinogenesis corresponds to a large extent to the evolution of the paradigmatic Darwinian populations in which selection acts at more than one level. The aim of this article is to show why the concept of multi-level selection and the evolution of cooperation represent a valuable approach in explaining the carcinogenesis.

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