scholarly journals Оscillations of closed conical shells with complex rotation

2020 ◽  
pp. 127-132
Author(s):  
Petro Lizunov ◽  
Eduard Kriksunov ◽  
Oleksandr Fesan
Keyword(s):  
Angular Velocity ◽  
Center Of Mass ◽  
Shell Element ◽  
Inertial Forces ◽  
Centrifugal Forces ◽  
Construction Engineering ◽  
Conical Shells ◽  
Gyroscopic Moment ◽  
Axis Of Symmetry ◽  
The Right

The paper consider a system of two closed conical shells connected by a central rigid insert rotating in opposite directions in a central force field with a constant angular velocity around the axis of symmetry of the system. The shell element is subjected to a load consisting of gravitational and inertial forces, but at large values of the angular velocity of the system, the gravitational loads can be neglected. The gyroscopic interaction between the rotational portable motion of the system and the relative elastic oscillations of the elements is a source of excitation of precession oscillations, which may be resonant or unstable. Occurring when changing the axis of orientation of the system gyroscopic moment causes the appearance of alternating stresses, which significantly affect the strength and reliability of the shells. Such problems arise in construction engineering, mechanical engineering, aircraft construction, space engineering and other sectors of the economy. The main load acting on the elements of such systems are significant centrifugal forces of inertia, which significantly affect the strength characteristics of structures. Taking into account the periodicity of the right-hand side and the coefficients of the system of resolving equations, with the help of the projection method it is possible to reduce the resolving equations to the system of ordinary differential equations, which approximately replaces the original one. The solution of the obtained system of equations makes it possible to determine the forms of oscillations and forces in a composite conical shell at various parameters of the shell and the ratios of the velocities of the shell's own rotation and the rotation of its center of mass.

Cylindrical tank of fluid oscillating about a state of steady rotation

1970 ◽  
Vol 41 (3) ◽  
pp. 581-592 ◽  
Author(s):  
Chang-Yi Wang
Keyword(s):  
Boundary Layer ◽  
Angular Velocity ◽  
Flow Field ◽  
Boundary Layers ◽  
Experimental Measurements ◽  
Centrifugal Forces ◽  
Cylindrical Tank ◽  
Side Walls ◽  
Steady Rotation ◽  
Axis Of Symmetry

A cylindrical tank, full of fluid, is oscillating with frequency ω and rotating with angular velocity Ω about its axis of symmetry. It is assumed that the amplitude of oscillation, δ, is small and the viscosity is low such that boundary layers exist. Analysis shows that the unsteady boundary layer is of thickness [ε/(1 − 2Ω/ω)]½ on the top and bottom plates and of thickness ε½ on the side walls, where ε = ν/2ω. The interior unsteady flow shows source-like behaviour at the corners. The steady flow field is caused by the steady component of the non-linear centrifugal forces coupled with an induced steady rotation of the interior. This rotation, of order δ2ω, is prograde when Ω/ω < 0·118 and retrograde otherwise. Maximum retrograde rotation occurs at Ω/ω = 0·5. A steady boundary layer of thickness [ε/(1 − 2Ω/ω)]½ exists on the top and bottom plates, and of thicknesses \[ \epsilon^{\frac{1}{2}},\quad (\nu/L^2\Omega)^{\frac{1}{3}},\quad (\nu/L^2\Omega)^{\frac{1}{4}} \] on the side walls. Experimental measurements of the interior induced steady rotation compare well with theory.

The Relationship between Consistency of Propulsive Cycles and Maximum Angular Velocity during Wheelchair Racing

2008 ◽  
Vol 24 (3) ◽  
pp. 280-287 ◽  
Author(s):  
Yong “Tai” Wang ◽  
Konstantinos Dino Vrongistinos ◽  
Dali Xu
Keyword(s):  
Angular Velocity ◽  
Upper Limb ◽  
Wheelchair Propulsion ◽  
Upper Arm ◽  
Wheelchair Athletes ◽  
Angular Velocities ◽  
Limb Kinematics ◽  
Analysis System ◽  
The Right ◽  
The Relationship

The purposes of this study were to examine the consistency of wheelchair athletes’ upper-limb kinematics in consecutive propulsive cycles and to investigate the relationship between the maximum angular velocities of the upper arm and forearm and the consistency of the upper-limb kinematical pattern. Eleven elite international wheelchair racers propelled their own chairs on a roller while performing maximum speeds during wheelchair propulsion. A Qualisys motion analysis system was used to film the wheelchair propulsive cycles. Six reflective markers placed on the right shoulder, elbow, wrist joints, metacarpal, wheel axis, and wheel were automatically digitized. The deviations in cycle time, upper-arm and forearm angles, and angular velocities among these propulsive cycles were analyzed. The results demonstrated that in the consecutive cycles of wheelchair propulsion the increased maximum angular velocity may lead to increased variability in the upper-limb angular kinematics. It is speculated that this increased variability may be important for the distribution of load on different upper-extremity muscles to avoid the fatigue during wheelchair racing.

Successful project delivery in complex brownfield environments

2011 ◽  
Vol 51 (2) ◽  
pp. 694
Author(s):  
J Sofra ◽  
Andrew Stewart
Keyword(s):  
Cost Effective ◽  
Project Delivery ◽  
Special Focus ◽  
Construction Engineering ◽  
Simultaneous Operations ◽  
Operations And Maintenance ◽  
Management Project ◽  
Engineering Effort ◽  
The Right ◽  
The Impact

Delivering services and projects in a brownfield environment has unique challenges. Brownfield, by its very nature, involves highly constrained and dynamic environments. This requires stakeholders to work collaboratively and be creative and nimble. Effective communication between client and service provider is essential. This is because the decision-making horizons are significantly shorter and consequences are more immediate. Brownfield projects are typically organised to minimise inter-discipline interfaces, with seamless delivery from engineering through to construction. Engineering effort needs to be the right sized based on the level of complexity and risk involved to ensure the effort and cost expended is appropriate for the modification or upgrade. When planning and executing brownfield projects, the following areas require special focus: health, safety and the environment—to cope with the inherently higher risks due to live inventory, lack of space, simultaneous operations and increased personnel; interface with operations—to plan, manage and minimise disruption to production; live systems—to assess the impact/disruption to energised systems and coordinate tie-ins; production—to minimise disruption and ensure that the project is executed safely while production continues; hot work—to a minimum and where necessary contain naked flame and spark activity on site; integrity—to ensure the condition of the asset is well understood and any sub-system upgrades to accommodate the modification are identified; limited space—to accommodate temporary project facilities, minimising the impact on operations and maintenance activities; and, access—to ensure that the project is planned to lessen disruption, maximise off-site preparation and to minimise on-site construction. Systematic program management, project engineering, and a tiered engineering approach are essential to cost effective and timely delivery. For each of the eight key areas we detail some of the subtle and enabling strategies/tools that distinguish brownfield project delivery from greenfield.

Slow steady rotation of axially symmetric bodies in a viscous fluid

1961 ◽  
Vol 10 (1) ◽  
pp. 17-24 ◽  
Author(s):  
R. P. Kanwal
Keyword(s):  
Angular Velocity ◽  
Flow Field ◽  
Viscous Fluid ◽  
Stokes Flow ◽  
Flow Problem ◽  
Analytic Solutions ◽  
The Body ◽  
Axially Symmetric ◽  
Steady Rotation ◽  
Axis Of Symmetry

The Stokes flow problem is considered here for the case in which an axially symmetric body is uniformly rotating about its axis of symmetry. Analytic solutions are presented for the heretofore unsolved cases of a spindle, a torus, a lens, and various special configurations of a lens. Formulas are derived for the angular velocity of the flow field and for the couple experienced by the body in each case.

scholarly journals INERTIAL FORCES AS VIEWED FROM THE ADM SLICING AND THEIR BEHAVIOUR FOR PARTICLES IN NON-CIRCULAR GEODESICS

2002 ◽  
Vol 17 (28) ◽  
pp. 1835-1845 ◽  
Author(s):  
A. R. PRASANNA
Keyword(s):  
Black Holes ◽  
Angular Velocity ◽  
Radial Velocity ◽  
Centrifugal Force ◽  
Test Particle ◽  
Physical Parameters ◽  
Inertial Forces ◽  
Shift Vector ◽  
Definition Of ◽  
Lapse Function

Considering the definition of inertial forces acting on a test particle, following non-circular geodesics, in static and stationary space–times, we show that the centrifugal force reversal occurs only in the case of particles following prograde orbits around black holes. We first rewrite the covariant expressions for the acceleration components in terms of the lapse function, shift vector and the three-metric γij, using the ADM 3 + 1 splitting and use these, for different cases as given by pure radial motion, pure azimuthal motion and the general non-circular motion. It is found that the reversal occurs between 2m and 3m, only when the azimuthal angular velocity of the particle supersedes the radial velocity, which indeed depends upon the physical parameters E, ℓ and the Kerr parameter a.

Body Segment Contributions to Javelin Throwing during Final Thrust Phases

1994 ◽  
Vol 10 (2) ◽  
pp. 166-177 ◽  
Author(s):  
Mero Antti ◽  
Paavo V. Komi ◽  
Tapio Korjus ◽  
Enrique Navarro ◽  
Robert J. Gregor
Keyword(s):  
High Speed ◽  
Olympic Games ◽  
Center Of Mass ◽  
The Body ◽  
Body Segment ◽  
Male And Female ◽  
Body Center ◽  
Joint Center ◽  
The Right ◽  
Release Speed

This study investigated body segment contributions to javelin throwing during the last thrust phases. A 3-D analysis was performed on male and female javelin throwers during the finals of the 1992 Olympic Games in Barcelona. The subjects were videotaped from the right sight of the throwing area by two NAC high-speed cameras operating at 100 frames per second. Both men’s and women’s grip of javelin and body center of mass displayed a curved pathway to the right from the left (bracing) foot during the final foot contact. The position of the body center of mass decreased at the beginning of the final foot contact, but after the decrease period it began to increase. Simultaneously with the increase, the peak joint center speeds occurred in a proper sequence from proximal to distal segments and finally to the javelin at release. Release speed correlated significantly with throwing distance in both male and females.

scholarly journals Stride-to-Stride Variability of the Center of Mass in Male Trained Runners After an Exhaustive Run: A Three Dimensional Movement Variability Analysis With a Subject-Specific Anthropometric Model

2021 ◽  
Vol 3 ◽  
Author(s):  
Felix Möhler ◽  
Bernd Stetter ◽  
Hermann Müller ◽  
Thorsten Stein
Keyword(s):  
Center Of Mass ◽  
Three Dimensional ◽  
Vertical Direction ◽  
Uncontrolled Manifold ◽  
Position Vector ◽  
Movement Variability ◽  
Lateral Direction ◽  
Relevant Variable ◽  
The Right ◽  
Trained Runners

The motion of the human body can be described by the motion of its center of mass (CoM). Since the trajectory of the CoM is a crucial variable during running, one can assume that trained runners would try to keep their CoM trajectory constant from stride to stride. However, when exposed to fatigue, runners might have to adapt certain biomechanical parameters. The Uncontrolled Manifold approach (UCM) and the Tolerance, Noise, and Covariation (TNC) approach are used to analyze changes in movement variability while considering the overall task of keeping a certain task relevant variable constant. The purpose of this study was to investigate if and how runners adjust their CoM trajectory during a run to fatigue at a constant speed on a treadmill and how fatigue affects the variability of the CoM trajectory. Additionally, the results obtained with the TNC approach were compared to the results obtained with the UCM analysis in an earlier study on the same dataset. Therefore, two TNC analyses were conducted to assess effects of fatigue on the CoM trajectory from two viewpoints: one analyzing the CoM with respect to a lab coordinate system (PVlab) and another one analyzing the CoM with respect to the right foot (PVfoot). Full body kinematics of 13 healthy young athletes were captured in a rested and in a fatigued state and an anthropometric model was used to calculate the CoM based on the joint angles. Variability was quantified by the coefficient of variation of the length of the position vector of the CoM and by the components Tolerance, Noise, and Covariation which were analyzed both in 3D and the projections in the vertical, anterior-posterior and medio-lateral coordinate axes. Concerning PVlab we found that runners increased their stride-to-stride variability in medio-lateral direction (1%). Concerning PVfoot we found that runners lowered their CoM (4 mm) and increased their stride-to-stride variability in the absorption phase in both 3D and in the vertical direction. Although we identified statistically relevant differences between the two running states, we have to point out that the effects were small (CV ≤ 1%) and must be interpreted cautiously.

scholarly journals ON STABILIZATION OF UNSTABLE ROTATION IN THE RESISTING MEDIUM OF THE LAGRANGE GYROSCOPE USING THE SECOND GYROSCOPE AND ELASTIC HINGES

2021 ◽  
Vol 3 (2) ◽  
pp. 103-116
Author(s):  
Ya. Sviatenko ◽  
Keyword(s):  
Fixed Point ◽  
Angular Momentum ◽  
Angular Velocity ◽  
Elastic Recovery ◽  
Center Of Mass ◽  
Uniform Rotation ◽  
Resisting Medium ◽  
The Common ◽  
Elastic Coefficients ◽  
Kinetic Moment

The possibility of stabilizing an unstable uniform rotation in a resisting medium of a "sleeping" Lagrange gyroscope using a rotating second gyroscope and elastic spherical hinges is considered. The "sleeping" gyroscope rotates around a fixed point with an elastic recovery spherical hinge, and the second gyroscope is located above it. The gyroscopes are also connected by an elastic spherical restorative hinge and their rotation is supported by constant moments directed along their axes of rotation. It is shown that stabilization will be impossible in the absence of elasticity in the common joint and the coincidence of the center of mass of the second gyroscope with its center. With the help of the kinetic moment of the second gyroscope and the elasticity coefficients of the hinges, on the basis of an alternative approach, the stabilization conditions obtained in the form of a system of three inequalities and the conditions found on the elasticity coefficients at which the leading coefficients of these inequalities are positive. It is shown that stabilization will always be possible at a sufficiently large angular velocity of rotation of the second gyroscope under the assumption that the center of mass of the second gyroscope and the mechanical system are below the fixed point. The possibility of stabilizing the unstable uniform rotation of the "sleeping" Lagrange gyroscope using the second gyroscope and elastic spherical joints in the absence of dissipation is also considered. The "sleeping" gyroscope rotates at an angular velocity that does not meet the Mayevsky criterion. It is shown that stabilization will be impossible in the absence of elasticity in the common joint and the coincidence of the center of mass of the second gyroscope with its center. On the basis of the innovation approach, stabilization conditions were obtained in the form of a system of three irregularities using the kinetic moment of the second gyroscope and the elastic coefficients of the hinges. The condition for the angular momentum of the first gyroscope and the elastic coefficients at which the leading coefficients of these inequalities are positive are found. It is shown that if the condition for the angular momentum of the first gyroscope is fulfilled, stabilization will always be possible at a sufficiently large angular velocity of rotation of the second gyroscope, and in this case the center of mass of the second gyroscope can be located above the fixed point.

scholarly journals An analysis of the barbell motion depending on its weight in disabled powerlifting

2014 ◽  
Vol 6 (3) ◽  
Author(s):  
Wojciech Seidel ◽  
Anna Zurowska
Keyword(s):  
Angular Velocity ◽  
Upper Limb ◽  
Bench Press ◽  
Upper Limbs ◽  
Movement Onset ◽  
The Right ◽  
Flexion And Extension

AbstractThe aim of the study was to assess the symmetry of flexion and extension movements in upper limbs in disabled powerlifters during bench press with different barbell loads.29 disabled athletes from the National Powerlifting Team were examined. Mean age was between 23.9 ± 6.1. Mean sport experience was 5.4 ± 3.6 years.Both flexion and extension movement were performed symmetrically, which was indicated by an insignificant (p < 0.05) difference in the movement onset in the left and the right upper limb.Time differences in the movement onset and the achievement of maximal angular velocity were statistically insignificant in all trials (loads from 40% to 95% 1RM). During extension with loads over 60% 1RM differences in time of achieving maximal angular velocity were statistically significant or close.

scholarly journals Combination machine for soil preparation and sowing of gourds

2021 ◽  
Vol 264 ◽  
pp. 04035
Author(s):  
Dustmurod Chuyanov ◽  
Golib Shodmonov ◽  
Gayrat Ergashov ◽  
Islom Choriyev
Keyword(s):  
Classical Mechanics ◽  
The Body ◽  
Basic Principles ◽  
Simultaneous Formation ◽  
Soil Preparation ◽  
Left And Right ◽  
Axis Of Symmetry ◽  
Minimum Expenditure ◽  
The Right ◽  
Longitudinal Distance

The purpose of the study is to substantiate the method and design scheme of a combined machine for preparing the soil and sowing melons. The authors propose a new method of soil preparation and sowing, as well as a machine for its implementation. The basic principles and methods of classical mechanics, mathematical analysis, and statistics were used in this study. The method of preparing the soil and planting gourds provides a combination of the following technological processes: the turnover of the layers of the upper layer of soil, the sowing area to the left and to the right, shallow tilling the soil of the field with the left and right sides of the sowing area, deep tillage seeding areas with simultaneous formation of irrigation furrows and the local application of fertilizers, soil preparation for sowing in line sowing and sowing seeds of melons. The machine consists of lister housings installed along the axis of symmetry of the unit, flat cutters, parallel-type deep-diggers, furrowers, coulters for fertilizing, and a sowing device. It was found that preparation of soil for sowing and planting of melons with a minimum expenditure of energy is provided by the width of Lusternik buildings 86 cm, the width of tillers and cultivators, respectively, 45 and 33 cm, the longitudinal distance between the body and the plane of 35 cm between the cultivators of 42.3 cm, and longitudinal spacing of the chisel cultivator and sowing device 110 cm.

Sign in / Sign up

Export Citation Format

Share Document