Stability Analysis Hinged Vertical Flat Plate Rotation in a Uniform Flow

2012 ◽  
Author(s):  
Sina Mirzaei Sefat ◽  
Antonio Carlos Fernandes
Keyword(s):  
Stability Analysis ◽  
Dynamic Models ◽  
Fundamental Problem ◽  
Chaotic Oscillation ◽  
Free Fall ◽  
Vertical Axis ◽  
Sea Bed ◽  
Uniform Current ◽  
Free Falling ◽  
Insight Into

The free falling of objects is a phenomenon that has been observed in the nature. The Pendulous Installation Method (PIM) of heavy devices is an example of free falling which occurs in the installation of heavy offshore devices on sea bed. Hence, the motivation of the present research is to study the fluttering and tumbling (autorotation) motions that may occur during the free fall of object. The fluttering is a periodic or chaotic oscillation of body about a vertical axis. On the other hand, the tumbling is end-over-end rotation of body. In order to access the main physical aspects, the present work decided to attack a more fundamental problem and describes the investigations on fluttering and autorotation motions of the interaction of uniform current and freely rotating plate about a fixed vertical axis. A quasi-steady model is suggested to model the trajectories of flow induced rotation phenomenon and a stability analysis performed to gain insight into the nature of the bifurcation from fluttering to autorotation. At first, the fixed points for different models of motion is obtained and each point analyzed by using the linearized equation. Secondly, the phase diagrams as a function of angular velocity and angle of rotation have been presented for different dynamic models.

Hydrodynamic and Safety Aspects of Mooring Line Anchors in Accidental Free Fall

2009 ◽  
Author(s):  
Halvor Lie ◽  
Ivar Fylling ◽  
Erik Lehn
Keyword(s):  
Statistical Approach ◽  
Free Fall ◽  
Initial Study ◽  
Study Data ◽  
Mooring Line ◽  
Test Results ◽  
Field Development ◽  
Sea Bed ◽  
Free Falling ◽  
Water Depths

The paper presents an initial study on anchor behavior in accidental free fall. The work is related to a deepwater field development located at around 1000 m depth offshore Norway, where one wants to be able to anchor floating units for drilling vessels. As input to the present study data from model tests performed more than a decade ago were used. Here two anchor models were tested in free fall at a moderate water depth of 300 m. Results from the test are presented and discussed. Statistical distributions of the horizontal excursion for two anchor types are established. Because of limited instrumentation only some initial estimates of the free falling speed could be established. In order to determine how the results can be used for deeper water, a statistical approach for estimation of the hit position at sea bed for various water depths is outlined. Some examples on how the excursion develops for various water depths are given, based on the model test results and the statistical approach. Also a statistical model of damage risk to seabed structures by falling anchors is discussed.

Galileo Unbound

2018 ◽  
Author(s):  
David D. Nolte
Keyword(s):  
Free Fall ◽  
The Sun ◽  
Quantum Field ◽  
Many Worlds ◽  
Quantum Particles ◽  
Light Rays ◽  
History Of ◽  
And Control ◽  
The Universe ◽  
Insight Into

Galileo Unbound: A Path Across Life, The Universe and Everything traces the journey that brought us from Galileo’s law of free fall to today’s geneticists measuring evolutionary drift, entangled quantum particles moving among many worlds, and our lives as trajectories traversing a health space with thousands of dimensions. Remarkably, common themes persist that predict the evolution of species as readily as the orbits of planets or the collapse of stars into black holes. This book tells the history of spaces of expanding dimension and increasing abstraction and how they continue today to give new insight into the physics of complex systems. Galileo published the first modern law of motion, the Law of Fall, that was ideal and simple, laying the foundation upon which Newton built the first theory of dynamics. Early in the twentieth century, geometry became the cause of motion rather than the result when Einstein envisioned the fabric of space-time warped by mass and energy, forcing light rays to bend past the Sun. Possibly more radical was Feynman’s dilemma of quantum particles taking all paths at once—setting the stage for the modern fields of quantum field theory and quantum computing. Yet as concepts of motion have evolved, one thing has remained constant, the need to track ever more complex changes and to capture their essence, to find patterns in the chaos as we try to predict and control our world.

scholarly journals Multi-Camera Based Setup for Geometrical Measurement of Free-Falling Molten Glass Gob

Sensors ◽  
2021 ◽  
Vol 21 (4) ◽  
pp. 1041
Author(s):  
Mazhar Hussain ◽  
Mattias O’Nils ◽  
Jan Lundgren
Keyword(s):  
Free Fall ◽  
Frame Rate ◽  
Geometrical Parameters ◽  
Contactless Method ◽  
Molten Material ◽  
Dynamic Changes ◽  
Direct Measurements ◽  
Molten Materials ◽  
Free Falling

High temperatures complicate the direct measurements needed for continuous characterization of the properties of molten materials such as glass. However, the assumption that geometrical changes when the molten material is in free-fall can be correlated with material characteristics such as viscosity opens the door to a highly accurate contactless method characterizing small dynamic changes. This paper proposes multi-camera setup to achieve accuracy close to the segmentation error associated with the resolution of the images. The experimental setup presented shows that the geometrical parameters can be characterized dynamically through the whole free-fall process at a frame rate of 600 frames per second. The results achieved show the proposed multi-camera setup is suitable for estimating the length of free-falling molten objects.

scholarly journals Structure Formation in Anisotropic Disks

2006 ◽  
Vol 2 (S235) ◽  
pp. 143-143
Author(s):  
Eduard Vorobyov ◽  
Christian Theis
Keyword(s):  
Stability Analysis ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Disk Galaxies ◽  
Structural Elements ◽  
Small Perturbations ◽  
Gravitational Instabilities ◽  
Hydrodynamical Simulations ◽  
Axisymmetric Structures ◽  
Insight Into

The majority of normal disk galaxies are characterized by non-axisymmetric structures like spirals or bars. These structural elements have been widely discussed in the literature as a result of gravitational instabilities which are connected to growing density waves or global instabilities of disks. A first insight into the properties of galactic discs was provided by linear stability analysis. However, a disadvantage of linear stability analysis remained its restriction to small perturbations, both in amplitude and wavelength. Thus, numerical simulations, especially hydrodynamical and stellar-hydrodynamical simulations became a primary tool for the analysis of galactic evolution.

scholarly journals Converter-driven Stability Analysis of Power Systems Integrated with Hybrid Renewable Energy Sources

2021 ◽  
Author(s):  
Jianqiang Luo ◽  
Yiqing Zou ◽  
Siqi Bu
Keyword(s):  
Renewable Energy ◽  
Stability Analysis ◽  
Power Systems ◽  
Power System ◽  
Dynamic Models ◽  
Renewable Energy Sources ◽  
Energy Sources ◽  
Power Electronic ◽  
Modal Interaction ◽  
Hybrid Renewable Energy

Various renewable energy sources such as wind power and photovoltaic (PV) have been increasingly integrated into the power system through power electronic converters in recent years. However, power electronic converter-driven stability issues under specific circumstances, for instance, modal resonances might deteriorate the dynamic performance of the power systems or even threaten the overall stability. In this paper, the integration impact of a hybrid renewable energy source (HRES) system on modal interaction and converter-driven stability is investigated in an IEEE 16-machine 68-bus power system. Firstly, an HRES system is introduced, which consists of full converter-based wind power generation (FCWG) and full converter-based photovoltaic generation (FCPV). The equivalent dynamic models of FCWG and FCPV are then established, followed by the linearized state-space modeling. On this basis, converter-driven stability analyses are performed to reveal the modal resonance mechanisms of the interconnected power systems and the modal interaction phenomenon. Additionally, time-domain simulations are conducted to verify effectiveness of dynamic models and support the converter-driven stability analysis results. To avoid detrimental modal resonances, an optimization strategy is further proposed by retuning the controller parameters of the HRES system. The overall results demonstrate the modal interaction effect between external AC power system and the HRES system and its various impacts on converter-driven stability.

Light Inextensible Strings (Thread) Under Tension in the Schwarzschild Geometry

2021 ◽  
Vol 03 (02) ◽  
pp. 2150005
Author(s):  
Robin K. S. Hankin
Keyword(s):  
Free Fall ◽  
Computer Algebra Systems ◽  
Lagrange Equations ◽  
Schwarzschild Metric ◽  
Schwarzschild Geometry ◽  
Homework Problem ◽  
Straight Line ◽  
Taut Strings ◽  
Proper Length ◽  
Insight Into

Light inextensible string under tension is a stalwart feature of elementary physics. Here I show how considering such a string in the vicinity of a black hole, with the help of computer algebra systems, can generate insight into the Schwarzschild geometry in the context of an undergraduate homework problem. Light taut strings minimize their proper length, given by integrating the spatial component of the Schwarzschild metric along the string. The path itself is given by straightforward numerical solution to the Euler–Lagrange equations. If the string is entirely outside the event horizon, its closest approach to the singularity is tangential. At this point the string is visibly curved, surely a memorable and informative insight. The geometry of the Schwarzschild metric induces some interesting nonlocal phenomena: if the distance of closest approach is less than about [Formula: see text], the string self-intersects, even though it is everywhere under tension. Light taut strings furnish a third interpretation of the concept “straight line”, the other two being null geodesics and free-fall world lines. All the software used is available under the GPL.1

Plate Shape Effect on the Performance of the Vertical Axis Auto Rotation Current Turbine (VAACT)

2014 ◽  
Author(s):  
Ali Bakhshandeh Rostami ◽  
Antonio Carlos Fernandes
Keyword(s):  
Flat Plate ◽  
High Efficiency ◽  
Vertical Axis ◽  
Speed Ratio ◽  
Shape Effect ◽  
Tip Speed Ratio ◽  
Upper Limit ◽  
Plate Shape ◽  
Uniform Current ◽  
Current Turbine

The present paper explores experimentally the performance of two types of hinged plates which rotate about vertical axis when submitted to uniform current. A flat plate configuration and also a flapped plate (say, S shape) configuration have been investigated. The Vertical axis Auto rotation Current Turbine (VAACT) is one degree of freedom system (free to rotate in yaw direction). It is shown that a high efficiency for S shape type can be obtained of the order of 30 percent while flat blade type reaches approximately to 7 percent. Upper limit of tip speed ratio for flat blade type has been expanded approximately 0.9 whereas S shape approaches 1.3.

scholarly journals On-Sun Performance Evaluation of Alternative High-Temperature Falling Particle Receiver Designs

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Clifford K. Ho ◽  
Joshua M. Christian ◽  
Julius E. Yellowhair ◽  
Kenneth Armijo ◽  
William J. Kolb ◽  
...  
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Thermal Efficiency ◽  
Particle Temperature ◽  
Free Fall ◽  
Mass Flow Rates ◽  
Mesh Structures ◽  
Free Falling ◽  
The Impact

This paper evaluates the on-sun performance of a 1 MW falling particle receiver. Two particle receiver designs were investigated: obstructed flow particle receiver versus free-falling particle receiver. The intent of the tests was to investigate the impact of particle mass flow rate, irradiance, and particle temperature on the particle temperature rise and thermal efficiency of the receiver for each design. Results indicate that the obstructed flow design increased the residence time of the particles in the concentrated flux, thereby increasing the particle temperature and thermal efficiency for a given mass flow rate. The obstructions, a staggered array of chevron-shaped mesh structures, also provided more stability to the falling particles, which were prone to instabilities caused by convective currents in the free-fall design. Challenges encountered during the tests included nonuniform mass flow rates, wind impacts, and oxidation/deterioration of the mesh structures. Alternative materials, designs, and methods are presented to overcome these challenges.

Flow Induced Fluttering and Autorotation of a Hinged Vertical Flat Plate

2012 ◽  
Author(s):  
Antonio Carlos Fernandes ◽  
Sina Mirzaei Sefat
Keyword(s):  
Reynolds Number ◽  
Initial Conditions ◽  
Vertical Axis ◽  
Moment Of Inertia ◽  
Chaotic Oscillations ◽  
Uniform Current ◽  
The Stability ◽  
Rotation Motion ◽  
Rotating Plate ◽  
Vertical Flat Plate

This paper addresses the investigations on fluttering and autorotation motions which may occur in the interaction of uniform current and freely rotating plate about a fixed vertical axis. The autorotation is a name given to the case that the plate turns continuously about the vertical axis and the fluttering motion is the periodic or chaotic oscillations of the plate around the vertical axis. According to the dimensional analysis the motion in flow induced rotation motion is governed essentially by dimensionless moment of inertia, Reynolds number and initial conditions. Certain combinations define the stability boundaries between fluttering and autorotation. Hence, a bifurcation diagram was prepared by the experiments to classify different states observed the small fluttering, fluttering and autorotation based on different Reynolds number and dimensionless moment of inertia.

Validation of a Software Tool (DROPSIM) to Predict the ‘Drop and Getaway’ Behaviour of a Lifeboat

2015 ◽  
Author(s):  
Elia Palermo ◽  
Roberto Tonelli ◽  
Frans Quadvlieg ◽  
Jule Scharnke ◽  
Ingo Drummen ◽  
...  
Keyword(s):  
Software Tool ◽  
Free Fall ◽  
Model Tests ◽  
Simulation Tools ◽  
Normal Means ◽  
Strip Theory ◽  
Calm Water ◽  
Validation Procedure ◽  
Prototype Software ◽  
Free Falling

The purpose of a free fall lifeboat is to evacuate people from platforms in case of emergency, and when other, normal means of evacuation, are not possible. For instance, when the weather is too rough, and evacuation cannot be performed by helicopters, the lifeboats are the last way of escape. It is thus essential to be able to properly assess the operability of a lifeboat and the safety of its occupants upon evacuation. Over the past four years, methods to quantify the operability limits of a lifeboat were analysed in a research project carried out for Statoil. As part of this project, a prototype software (denominated DROPSIM) was developed to predict the ‘drop and sailaway behaviour’ of a lifeboat. DROPSIM is a simplified method based on strip theory, with the objective to obtain predictions that are consistent with the relevant statistical behaviour of the lifeboat, and for the same target level of probability. Particularly because DROPSIM is a simplified tool, it is vital to verify that the software is adequate for simulating thousands of random lifeboat drops, yielding robust statistical predictions with sufficient accuracy. In order to show the performance of the simulation tool, an extensive validation procedure was established, based on a large amount of model test and data from other simulation tools. The following topics were considered in the validation: A. Verification: basic checks, e.g. related to buoyancy without comparison to model tests B. Consistency of simulated and measured response for basic test cases, including free-falling wedge tests and a variety of impact tests with a bullet shaped model C. Prediction of the sailaway behaviour of a lifeboat in comparison to model tests D. Comparison with integrated drop and sailaway model tests in normal and off-design (extreme) conditions in calm water and in waves. In this paper the results of the validation of DROPSIM are presented and discussed. Another dedicated paper gives insight into the mathematical model of DROPSIM ([1]).

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