Humans Jumping on Flexible Structures: Effect of Structural Properties

Volume 2 ◽  
2004 ◽  
Author(s):  
ShiPing Yao ◽  
Robert E. Harrison ◽  
Jan R. Wright ◽  
Aleksandar Pavic ◽  
Paul Reynolds
Keyword(s):  
Structural Integrity ◽  
Damping Ratio ◽  
Flexible Structures ◽  
Vertical Motion ◽  
Drop Out ◽  
Mass Ratio ◽  
Test Rig ◽  
Near Resonance ◽  
The Subject ◽  
Force Drop

The behaviour of humans jumping on flexible structures has become a matter of some importance for both structural integrity and also human tolerance. The issue is of great interest for stadia, footbridge and floor structures. A test rig has been developed for exploring the forces, accelerations and displacements that occur when a human subject jumps on a flexible structure where motion can be perceived. In tests reported earlier, it was found that the human is able to generate near resonant response of the structure but it was extremely difficult, if not impossible, to jump at or very near to the natural frequency of the structure when the structural vertical motion is significant. Also, the force developed by the subject was found to drop significantly near resonance. In this paper, the effect of the subject-to-structure mass ratio and the damping ratio of the structure on the ability of the subject to jump near resonance, and on the force drop out, is presented. It is shown that as the structure becomes more massive and more highly damped it moves less for nominally the same jumping excitation. In this situation, it becomes easier to jump near resonance and the degree of force drop out reduces, though it is still significant.

The Heave Response of a Central Spar Fish Cage

2002 ◽  
Author(s):  
David W. Fredriksson ◽  
M. Robinson Swift ◽  
James D. Irish ◽  
Barbaros Celikkol
Keyword(s):  
Structural Integrity ◽  
Damping Ratio ◽  
Vertical Direction ◽  
Field Tests ◽  
Vertical Motion ◽  
Nonlinear Damping ◽  
Test Results ◽  
Natural Period ◽  
Reynolds Number Effects ◽  
Motion Characteristics

As the aquaculture industry considers moving into the open ocean, understanding the dynamic response of fish containment structures becomes critical. Identification of possible resonant conditions and motion characteristics is necessary for system structural integrity and maximizing fish survivability. In this study, heave (vertical motion) free release tests of a central spar fish cage were conducted using a combination of physical and finite element models and field observations. These tests were performed to investigate the added mass, damping ratio and natural period of the system in the vertical direction. The test results were analyzed considering both linear and nonlinear damping. The comparison of these tests show that (1) the damped natural period of this fish cage is longer than 20 seconds, (2) the numerical model underestimates the damping and the cage oscillates longer and at a higher frequency than observed with the field tests and (3) the physical model is nearly critically damped near equilibrium due to Reynolds number effects at the model scale.

Proposed evaluation methods for vibration serviceability of long span cable bridges

2021 ◽  
Author(s):  
E.-S. Hwang ◽  
M. T. Hwang ◽  
D. Y. Kim ◽  
K. J. Park
Keyword(s):  
Heavy Traffic ◽  
Damping Ratio ◽  
Flexible Structures ◽  
Evaluation Methods ◽  
Monitoring Data ◽  
Long Span ◽  
Vibration Serviceability ◽  
Long Term Monitoring ◽  
Term Monitoring

<p>Vibration serviceability becomes more important considerations in design and maintenance, especially for slender and flexible structures such as long span cable bridges. In this study, various evaluation methods for vibration serviceability for long span cable bridges are proposed. These methods are based on short and long-term monitoring data such as accelerations and displacements of bridges. Proposed methods include (1) method of evaluating vibration amplitude based on Reiher-Meister curves, (2) method of evaluating variations in natural frequencies and damping ratio,</p><p>(3) method of weighted rms(root-mean-square) acceleration based on ISO 2631-1, and (4) probabilistic analysis using long-term monitoring data. These methods are applied to example cable bridge and cases of normal traffic, heavy traffic, windy condition and sudden abnormal vibration are considered. The results of this study are expected to be implemented to real bridge monitoring system for real-time and periodic evaluation of vibration serviceability.</p>

Nonlinear Adaptive Vibration Absorber for the Control of Plate Vibrations

2001 ◽  
Author(s):  
Osama N. Ashour ◽  
Ali H. Nayfeh
Keyword(s):  
Control Strategy ◽  
Flexible Structures ◽  
Digital Signal ◽  
Nonlinear Effects ◽  
Frequency Measurement ◽  
Control Technique ◽  
Vibration Absorber ◽  
Plate Vibrations ◽  
Near Resonance ◽  
Modeling Software

Abstract A nonlinear adaptive vibration absorber to control the vibrations of flexible structures is investigated. The absorber is based on the saturation phenomenon associated with dynamical systems possessing quadratic nonlinearities and a two-to-one internal resonance. The technique is implemented by coupling a second-order controller with the structure’s response through a sensor and an actuator. Energy is exchanged between the structure and the controller and, near resonance, the structure’s response saturates to a small value. Experimental results are presented for the control of a rectangular plate and a cantilever beam using piezoelectric ceramics and magnetostrictive alloys as actuators. The control technique is implemented using a digital signal processing board and a modeling software. The control strategy is made adaptive by incorporating an efficient frequency-measurement technique. This is validated by successfully testing the control strategy for a non-conventional problem, where nonlinear effects hinder the application of the nonadaptive controller.

Design and Test of an Autonomous Reconfigurable Dynamic Investigation Test-Rig on Haptics (ARDITA) for Pre-Screening of the Peripheral Neuropathy Diseases

2018 ◽  
Author(s):  
Maria Laura D’Angelo ◽  
Darwin Caldwell ◽  
Ferdinando Cannella ◽  
Paolo Liberini ◽  
Alessandro Padovani ◽  
...  
Keyword(s):  
Healthy People ◽  
Tactile Sensitivity ◽  
Peripheral Neuropathies ◽  
Test Rig ◽  
New Device ◽  
Tunnel Syndrome ◽  
The Subject ◽  
The Relationship ◽  
Dynamic Investigation ◽  
Little Finger

This work presents a new device ARDITA (Autonomous Reconfigurable Dynamic Investigation Test-rig on hAptics) that is able to indent the fingertip with sinusoidal waves. Its reconfigurability permits to change these waves in amplitude, spatial and timing frequencies. The device is designed in order to be autonomous and reconfigurable, but also the portability and the size were taken into account, because the clinicians had to move it from an hospital to the other one and because each patient arms has a different size. In this work, the authors applied this feature to investigate the relationship between the tactile sensitivity of index and little finger both in healthy people and people who suffer peripheral neuropathies as the Carpal Tunnel Syndrome (CTS). The last ones were examined also with the Electromyography (EMG). 40 healthy people and 17 ill patients were tested. The results showed that ARDITA determined not only the index and little finger performance were inverted in patients respect to the subject, but also the increment of incorrect responses were perfected correlated with the increment of the degree of the illness.

Boundaries Effects on the Movements of a Sphere Immersed in a Free Surface Flow

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
D. Mirauda ◽  
A. Volpe Plantamura ◽  
S. Malavasi
Keyword(s):  
Experimental Data ◽  
Image Analysis ◽  
Free Surface ◽  
Damping Ratio ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Mass Ratio ◽  
Amplitude Response ◽  
Charge Coupled Device ◽  
A Charge

This work analyzes the influence of boundary conditions on the movements of a sphere immersed in a steady free surface flow. The sphere is free to move both in the transverse and streamwise directions and it is characterized by the values of the mass ratio m∗ equal to 1.34 and of the damping ratio ζ equal to 0.004. In all the experiments the blockage coefficient is kept constant, while the sphere is located at different distances from the free surface and from the bottom wall of the channel. The movements of the sphere have been measured by means of the image analysis of a charge coupled device camera which provides the 2D (streamwise and transverse) displacements of the sphere with a temporal resolution of 0.02 s. The experimental data show a significant influence of the boundaries on the sphere movement and highlight a different behavior of the amplitude response between the three different experimental setups considered.

Analysis on the Influence Factors of Multi-Functional Vibration-Absorption Enclosure Wall Structures

2011 ◽  
Vol 50-51 ◽  
pp. 319-322
Author(s):  
Ming Sheng He ◽  
Jun Wei Zheng ◽  
Gui Ju Shi
Keyword(s):  
Damping Ratio ◽  
Influence Factors ◽  
Control Mode ◽  
Mass Ratio ◽  
Vibration Absorption ◽  
Wall Structures ◽  
Optimal Value ◽  
Enclosure Wall ◽  
And Control ◽  
Main Influence

Enclosure wall multi-functional vibration-absorption structures (MVEW) is a new style of damping structure, it integrates the merits of infilled frame, tuned mass control (MTMD) and the energy dissipation structures. The main influence factors of MVEW is analyzed in the paper, The results indicate that there are optimal value of the mass ratio, the stiffness ratio and the damping ratio of substructure in MVEW, and the damping effect become obvious as the increase of the number of substructure, it also shows that the best location ought to synthetically consider the number of substructure, the tuned frequency ratio and control mode instead of being fixed. In the end, the paper proposed the determine principle of the damping device’s performance parameters as well as necessary optimization of MTMD parameters according to the specific case of actual structure1.

scholarly journals Optimal Design of a Damped Single Degree of Freedom Platform for Vibration Suppression in Harmonically Forced Undamped Systems

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Jimmy S. Issa
Keyword(s):  
Objective Function ◽  
Frequency Response Function ◽  
Damping Ratio ◽  
Optimal Solution ◽  
Vibration Absorber ◽  
Primary System ◽  
Mass Ratio ◽  
Optimal Damping ◽  
Mass Ratios ◽  
Invariant Points

Vibration reduction in harmonically forced undamped systems is considered using a new vibration absorber setup. The vibration absorber is a platform that is connected to the ground by a spring and damper. The primary system is attached to the platform, and the optimal parameters of the latter are obtained with the aim of minimizing the peaks of the primary system frequency response function. The minimax problem is solved using a method based on invariant points of the objective function. For a given mass ratio of the system, the optimal tuning and damping ratios are determined separately. First, it is shown that the objective function passes through three invariant points, which are independent of the damping ratio. Two optimal tuning ratios are determined analytically such that two of the three invariant points are equally leveled. Then, the optimal damping ratio is obtained such that the peaks of the frequency response function are equally leveled. The optimal damping ratio is determined in a closed form, except for a small range of the mass ratio, where it is calculated numerically from two nonlinear equations. For a range of mass ratios, the optimal solution obtained is exact, because the two peaks coincide with the two equally leveled invariant points. For the remaining range, the optimal solution is semiexact. Unlike the case of the classical absorber setup, where the absorber performance increases with increasing mass ratios, it is shown that an optimal mass ratio exists for this setup, for which the absorber reaches its utmost performance. The objective function is shown in its optimal shape for a range of mass ratios, including its utmost shape associated with the optimal mass ratio of the setup.

CFD Investigation of Temperature Rise in a Combustor Test Rig Exhaust System

2009 ◽  
Author(s):  
Joan Boulanger ◽  
Yinghua Han ◽  
Leiyong Jiang ◽  
Shaji Manipurath
Keyword(s):  
Water Vapour ◽  
Temperature Rise ◽  
Structural Integrity ◽  
Complex Mixture ◽  
National Research Council ◽  
Exhaust System ◽  
Temperature Fields ◽  
Exhaust Pipe ◽  
Test Rig ◽  
Two Phase

This paper presents a study of temperature rise in the exhaust system of a combustor test rig, Test Cell #1, at the Gas Turbine Laboratory, Institute for Aerospace Research, the National Research Council of Canada. As the flow regime is supersonic with a mixture of hot air & water vapour, condensation of water vapour in the system is suggested to explain the temperature rise observed along the exhaust pipe. The method of Computational Flow Dynamics is used to carry out the first investigation on this hypothesis. The exhaust system is reproduced by CAD, meshed and modelled by the ANSYS-FLUENT CFD package. Simulations of a two-phase complex mixture are performed. The numerical results indicate that the pressure control devices in the exhaust flow towards the stack create phenomena similar to nozzles and yield condensed water into the system. The simulations of liquid phase content and temperature fields are qualitatively consistent with experimental observations and support the hypothesis that condensation is occurring and may therefore threaten the structural integrity of the system through thermal effects.

Paper 24: A Study of Column Separation following Valve Closure in a Pipeline Carrying Aviation Kerosine

1969 ◽  
Vol 184 (7) ◽  
pp. 57-64 ◽  
Author(s):  
J. A. Swaffield
Keyword(s):  
Computer Program ◽  
Method Of Characteristics ◽  
Hyperbolic Partial Differential Equations ◽  
Valve Closure ◽  
Test Rig ◽  
Cavity Collapse ◽  
Upstream Side ◽  
Column Separation ◽  
Series Of Experiments ◽  
The Subject

The occurrence of column separation on the upstream side of a valve following valve closure has been the subject of a series of experiments on a test rig utilizing Concorde L56 alloy fuel piping and Esso Aviation Kerosine Specification 2494. A Fortran IV computer program based on the method of characteristics has been employed to solve the quasi-linear hyperbolic partial differential equations governing the propagation of transient pressures and to predict the duration of vapour cavities formed either at the valve or at any point in the pipeline. Comparison of computer and observed results indicates an accuracy within 3 per cent for the first peak following valve closure and for the duration of the vapour cavities, and within 10 per cent for the later pressure peaks following vapour cavity collapse.

Wind Blade Material Optimization

2011 ◽  
Vol 66-68 ◽  
pp. 1199-1206
Author(s):  
Samir Ahmad ◽  
Izhar-ul-Haq
Keyword(s):  
Wind Turbine ◽  
Structural Integrity ◽  
Rotor Blades ◽  
Dust Particles ◽  
Element Analysis ◽  
Composite Blade ◽  
Material Optimization ◽  
Finite Element Analysis Simulation ◽  
The Subject ◽  
Future Direction

In recent years the wind turbine blade has been the subject of comprehensive study and research amongst all other components of the wind turbine. As our appetite for renewable energy from the wind turbine continues to increase, companies now focus on rotor blades which can go up to 80m in length. The blade material not only have to face large aerodynamic, inertial and fatigue loads but are now being designed to endure environmental effects such as Ultraviolet degradation of surface, accumulation of dust particles at sandy locations, ice accretion on blades in cold countries, insect collision on blades and moisture ingress. All this is considered to ensure that the blades complete its designated life span. Furthermore exponential increase in composite blade manufacturing is causing a substantial amount of unrecyclable material. All these issues raise challenges for wind blade material use, its capacity to solve above mentioned problems and also maintain its structural integrity. This paper takes on this challenge by optimizing from the properties, merits, demerits and cost of different possible competing materials. Then the material is checked for its structural integrity through Finite Element Analysis simulation using standards like IEC-61400-1.This paper also shows the future direction of research by elaborating the influence nanotechnology can have in the improvement of the wind blade.

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