The Rion-Antirion bridge in Greece experienced vibrations in its lightning protection cables after their installation. Wind tunnel testing revealed that the vibrations were due to galloping caused by the compact arrangement of the three stainless steel ropes. Reconfiguring the ropes with spacers to separate them was found to suppress the galloping without additional damping. Alternative solutions like adding viscous dampers would only work if a high level of damping could be achieved. It was decided to change the rope arrangement with spacers to provide both separation and additional damping to resolve the vibration issues.
lightning stroke. Substation equipment and auxiliaries also can be get damaged by the lightning
strokes. This paper shows some methods to reduce the effect of lightning stroke on the substation. There
are conventional and non-conventional methods for this. This paper describes some of that methods
briefly.
lightning stroke. Substation equipment and auxiliaries also can be get damaged by the lightning
strokes. This paper shows some methods to reduce the effect of lightning stroke on the substation. There
are conventional and non-conventional methods for this. This paper describes some of that methods
briefly.
The term high voltage characterizes electrical circuits in which the voltage used is the cause of particular safety concerns & insulation requirements. High voltage is used in electrical power distribution, in cathode ray tubes, to generate x-rays & particle beams, to demonstrate arcing, for ignition, in photomultiplier tubes & high power amplifier vacuum tubes & other industrial & scientific applications .
study of lightning arrester ' working principal and working of lighning and construction of lightning arrester. and at the end what are the types of lightning arrester how these types are different from each other and what is their working principal and which is used mostly on 500kva substation.
PROTECTION AGAINST OVER VOLTAGE AND GROUNDING Part 1Dr. Rohit Babu
Generation of overvoltages in power systems
Protection against lightning overvoltages
Valve type and zinc oxide lightning arresters
Insulation coordination
BIL
Impulse ratio
Standard impulse test wave
Volt-time characteristics
Grounded and ungrounded neutral systems
Effects of ungrounded neutral on system performance
Methods of neutral grounding
Solid
Resistance
Reactance
Arcing grounds and grounding Practices
Social Media can be a very useful and affordable tool to market your company. It gives you the ability to reach many people across the globe for a pretty low cost. Putting together an effective strategy takes time. Get tips to build your business using Social Media
Workshop Arrival Reflection--Thought Provoking Quotes About Strong Sustainabi...Antony Upward
Posters placed in the hallway leading to the room in which the Workshop to design the business model for the strongly sustainable business model toolkit
The term high voltage characterizes electrical circuits in which the voltage used is the cause of particular safety concerns & insulation requirements. High voltage is used in electrical power distribution, in cathode ray tubes, to generate x-rays & particle beams, to demonstrate arcing, for ignition, in photomultiplier tubes & high power amplifier vacuum tubes & other industrial & scientific applications .
study of lightning arrester ' working principal and working of lighning and construction of lightning arrester. and at the end what are the types of lightning arrester how these types are different from each other and what is their working principal and which is used mostly on 500kva substation.
PROTECTION AGAINST OVER VOLTAGE AND GROUNDING Part 1Dr. Rohit Babu
Generation of overvoltages in power systems
Protection against lightning overvoltages
Valve type and zinc oxide lightning arresters
Insulation coordination
BIL
Impulse ratio
Standard impulse test wave
Volt-time characteristics
Grounded and ungrounded neutral systems
Effects of ungrounded neutral on system performance
Methods of neutral grounding
Solid
Resistance
Reactance
Arcing grounds and grounding Practices
Social Media can be a very useful and affordable tool to market your company. It gives you the ability to reach many people across the globe for a pretty low cost. Putting together an effective strategy takes time. Get tips to build your business using Social Media
Workshop Arrival Reflection--Thought Provoking Quotes About Strong Sustainabi...Antony Upward
Posters placed in the hallway leading to the room in which the Workshop to design the business model for the strongly sustainable business model toolkit
Load centers get generated electricity from power
stations that are usually far; uninterrupted consumption or usage
of power has increased in last few years. Transmission system is
the system by means of which electricity is transferred from place
of generation to the consumers. Overhead wires or conductors
are the medium used for transmission of power. These wires are
visible to wind, heat and ice. The efficiency of the power system
increases if the losses of these overhead wires are minimal. These
losses are based on the resistive, magnetic and capacitive nature
of the conductor. It is necessary to create or make proper design
of these conductors accompanied by proper installation. To
balance the working and strength of overhead transmission line
and to minimize its capacitive effect the conductors must be
installed in catenary shape. The sag is required in transmission
line for conductor suspension. The conductors are appended
between two overhead towers with ideal estimation of sag. It is
because of keeping conductor safety from inordinate tension. To
permit safe tension in the conductor, conductors are not
completely extended; rather they are allowed to have sag. For
same level supports this paper provides sag and tension
estimation with different wind speeds under low operating
temperature 2 °C. To calculate sag-tension estimation of ACSR
(Aluminum Conductor Steel Reinforced) overhead lines three
different cases are provided with normal and high wind speed
effects. Four different span lengths are taken for equal level
supports. ETAP (Electrical Transient and Analysis Program) is
used for simulation setup. The results shows that wind speed has
great impact upon line tension and with addition of wind speed
the sag of line remains unaltered while tension changes.
Moreover tension gets increase while increase in wind speed.
UNIT - 06 TRANSMISSION LINES AND SUBSTATIONSPremanandDesai
Code of practice for Transmission lines and substations, transmission line materials and their specifications, types of Towers, ACSR conductors and Number of Disc insulators in suspension string, strain string, span and height of towers for 66 KV, 110 KV, 220 KV transmission lines, concept of single circuit and double circuit transmission lines, method of calculating the Quantity of transmission line materials, Prepare the schedule of materials
(only) for 66 KV,110 KV and 220 KV single circuit transmission lines. 66KV/11KV, 5 MVA Substations- Single Line diagram, list of Electrical equipment's/ materials (only) and their
specifications.
Experimental stress analysis BE notes by mohammed imranMohammed Imran
7th semester, Experimental stress analysis notes as per VTU syllabus by Mohammed Imran, Asst. Prof., Department of Mechanical Engineering, Ghousia College of Engineering-Ramanagaram-562159
Behaviour Analysis of Corroded Wires Based on Statistical ModelsIJERDJOURNAL
ABSTRACT: Steel wires are the primary components of a lifting wire rope. The behaviour of a wire governs the behaviour of the whole of the cable. The physico-chemical processes like rates of degradation due to the environment (corrosion, etc.) are different for each layer, external layers being more exposed. The analysis of steel wires behaviour is traditionally based on statistical models describing the variability of its properties. For this purpose a statistical study was carried out on two populations of healthy and corroded wires by applying the Student distribution to select the most reliable results and the Weibull distribution to define the survival probability and the failure probability.
IRJET-Sensitivity Analysis of Maximum Overvoltage on Cables with Considering ...IRJET Journal
Hamed Touhidi ,Mehdi Shafiee, Behrooz Vahidi,Seyed Hossein Hosseinian, "Sensitivity Analysis of Maximum Overvoltage on Cables with Considering Forward and Backward Waves ", International Research Journal of Engineering and Technology (IRJET), Vol2,issue-01 April 2015. e-ISSN:2395-0056, p-ISSN:2395-0072. www.irjet.net
Abstract
lightning is known to be one of the primary sources of most surges in high keraunic areas. It is well-known fact that surge overvoltage is a significant contribution in cable failures. The other source of surge voltage is due to switching and it is pronounce on extra high voltage power transmission systems. The effect of both lightning and switching surges is weakening the cable insulation. The progressive weakening of such insulation will lead to cable deterioration and eventually its failure. Each surge impulse on the cable will contribute with other factors towards cable insulation strength deterioration and ultimately cable can fail by an overvoltage level below the cable basic impulse level (BIL). The maximum lightning overvoltage for a given cable depends on a large number of parameters. This paper presents the effect of model parameters (e.g., rise time and amplitude of surge, length of cable, resistivity of the core and sheath, tower footing resistance, number of sub conductors in the phase conductor (bundle), effect of surge arrester, length of lead, relative permittivity of the insulator material outside the core, power frequency voltage, stroke location, cable joints, shunt reactors, sheath thickness) on maximum cable voltage. The simulations show that the maximum overvoltage.
Electrical Design of Overhead Lines.pptAkdDeshmukh
An a.c. transmission line has resistance, inductance and capacitance uniformly distributed along its length.
These are known as constants or parameters of the line.
The performance of a transmission line depends to a considerable extent upon these constants.
These constants determine whether the efficiency and voltage regulation of the line will be good or poor.
. R = ρl/a
ii. In a single phase or 2-wire d.c line, the total resistance (known asloop resistance) is equal to double the resistance of either conductor.
iii. In case of a 3-phase transmission line, resistance per phase is the resistance of one conductor.
IDENTIFICATION OF TOWER AND BOOM-WAKES USING COLLOCATED ANEMOMETERS AND LIDAR...IAEME Publication
In this study the extent of tower and boom wake distortions were evaluated using collocated anemometers and Lidar measurement based on wind data from Amperbo, Namibia, where an existing latticed equilateral triangular communication tower was instrumented according to IEC specifications. Wind data analysed was 10-minute averaged, captured over a period of nine months (May to Sept. 2014). To enable further and independent investigation of flow modification within the vicinity of the tower, ZephIR 300 wind Lidar was installed at about 5.4 m from the foot of the tower. Wind data from pairs of collocated cup anemometers located at 16.88 m and 64.97 m above ground level (AGL) were analysed and compared to identify the range of directions that were affected by the waking of the entire tower physical structure. Mean speed and turbulence intensity (TI) were used in quantify the wake impact on the wind data observed using cup anemometers, showing a speed deficit of up to 49 % and order of magnitude increase in the TI for all the regions within the wake of the tower. Comparison with ZephIR 300 observed mean speed resulted in a speed deficit of up to 50 % which further confirmed the extent of tower distortion and wake boundaries. The Lidar also confirmed the speed-up effects and the asymmetric nature of the wake boundaries associated with the mounting booms. The results show that TI analysis has the potential to more accurately define the wake boundaries and wake distortion than traditional speed ratios analysis. The study shows that the severity of tower wake effects varies seasonally with winter months (June and July) recording the highest speed deficit when compared to December, a summer month. Root Mean Square Errors (RMSE) were further computed to ascertain the similarity degree of resource parameters from the two measurement techniques, resulting in peak values of RMSE in the wake affected regions. The TI approach consistently predicted larger wake boundaries than speed ratio analysis. Wind direction analysis clearly showed the 180° ambiguity of ZephIR 300 and the extent of deflection of the winds around the tower structure. Preliminary evaluation of wake impact on the resource parameter shows that removing the sectors affected by tower wakes leads to an increase in mean wind speed and a decrease in TI values.
Energy’s Method for Experimental Life Prediction of a 1 + 6 Strandtheijes
A method to calculate damage evolution during the life of a strand was developed in this paper. Based on simple tensile tests, it has the advantage of being time and money saving. The residual energy damage calculation was compared to the unified theory for different loading levels. The correlation between the two methods was found for a loading level of 1.49. The energy calculation method is verified comparing with another paper where the correlation was found for a loading level of 1.68 and the damage stages were the same.
Smart TV Buyer Insights Survey 2024 by 91mobiles.pdf91mobiles
91mobiles recently conducted a Smart TV Buyer Insights Survey in which we asked over 3,000 respondents about the TV they own, aspects they look at on a new TV, and their TV buying preferences.
Kubernetes & AI - Beauty and the Beast !?! @KCD Istanbul 2024Tobias Schneck
As AI technology is pushing into IT I was wondering myself, as an “infrastructure container kubernetes guy”, how get this fancy AI technology get managed from an infrastructure operational view? Is it possible to apply our lovely cloud native principals as well? What benefit’s both technologies could bring to each other?
Let me take this questions and provide you a short journey through existing deployment models and use cases for AI software. On practical examples, we discuss what cloud/on-premise strategy we may need for applying it to our own infrastructure to get it to work from an enterprise perspective. I want to give an overview about infrastructure requirements and technologies, what could be beneficial or limiting your AI use cases in an enterprise environment. An interactive Demo will give you some insides, what approaches I got already working for real.
PHP Frameworks: I want to break free (IPC Berlin 2024)Ralf Eggert
In this presentation, we examine the challenges and limitations of relying too heavily on PHP frameworks in web development. We discuss the history of PHP and its frameworks to understand how this dependence has evolved. The focus will be on providing concrete tips and strategies to reduce reliance on these frameworks, based on real-world examples and practical considerations. The goal is to equip developers with the skills and knowledge to create more flexible and future-proof web applications. We'll explore the importance of maintaining autonomy in a rapidly changing tech landscape and how to make informed decisions in PHP development.
This talk is aimed at encouraging a more independent approach to using PHP frameworks, moving towards a more flexible and future-proof approach to PHP development.
JMeter webinar - integration with InfluxDB and GrafanaRTTS
Watch this recorded webinar about real-time monitoring of application performance. See how to integrate Apache JMeter, the open-source leader in performance testing, with InfluxDB, the open-source time-series database, and Grafana, the open-source analytics and visualization application.
In this webinar, we will review the benefits of leveraging InfluxDB and Grafana when executing load tests and demonstrate how these tools are used to visualize performance metrics.
Length: 30 minutes
Session Overview
-------------------------------------------
During this webinar, we will cover the following topics while demonstrating the integrations of JMeter, InfluxDB and Grafana:
- What out-of-the-box solutions are available for real-time monitoring JMeter tests?
- What are the benefits of integrating InfluxDB and Grafana into the load testing stack?
- Which features are provided by Grafana?
- Demonstration of InfluxDB and Grafana using a practice web application
To view the webinar recording, go to:
https://www.rttsweb.com/jmeter-integration-webinar
UiPath Test Automation using UiPath Test Suite series, part 3DianaGray10
Welcome to UiPath Test Automation using UiPath Test Suite series part 3. In this session, we will cover desktop automation along with UI automation.
Topics covered:
UI automation Introduction,
UI automation Sample
Desktop automation flow
Pradeep Chinnala, Senior Consultant Automation Developer @WonderBotz and UiPath MVP
Deepak Rai, Automation Practice Lead, Boundaryless Group and UiPath MVP
Builder.ai Founder Sachin Dev Duggal's Strategic Approach to Create an Innova...Ramesh Iyer
In today's fast-changing business world, Companies that adapt and embrace new ideas often need help to keep up with the competition. However, fostering a culture of innovation takes much work. It takes vision, leadership and willingness to take risks in the right proportion. Sachin Dev Duggal, co-founder of Builder.ai, has perfected the art of this balance, creating a company culture where creativity and growth are nurtured at each stage.
Let's dive deeper into the world of ODC! Ricardo Alves (OutSystems) will join us to tell all about the new Data Fabric. After that, Sezen de Bruijn (OutSystems) will get into the details on how to best design a sturdy architecture within ODC.
Essentials of Automations: Optimizing FME Workflows with ParametersSafe Software
Are you looking to streamline your workflows and boost your projects’ efficiency? Do you find yourself searching for ways to add flexibility and control over your FME workflows? If so, you’re in the right place.
Join us for an insightful dive into the world of FME parameters, a critical element in optimizing workflow efficiency. This webinar marks the beginning of our three-part “Essentials of Automation” series. This first webinar is designed to equip you with the knowledge and skills to utilize parameters effectively: enhancing the flexibility, maintainability, and user control of your FME projects.
Here’s what you’ll gain:
- Essentials of FME Parameters: Understand the pivotal role of parameters, including Reader/Writer, Transformer, User, and FME Flow categories. Discover how they are the key to unlocking automation and optimization within your workflows.
- Practical Applications in FME Form: Delve into key user parameter types including choice, connections, and file URLs. Allow users to control how a workflow runs, making your workflows more reusable. Learn to import values and deliver the best user experience for your workflows while enhancing accuracy.
- Optimization Strategies in FME Flow: Explore the creation and strategic deployment of parameters in FME Flow, including the use of deployment and geometry parameters, to maximize workflow efficiency.
- Pro Tips for Success: Gain insights on parameterizing connections and leveraging new features like Conditional Visibility for clarity and simplicity.
We’ll wrap up with a glimpse into future webinars, followed by a Q&A session to address your specific questions surrounding this topic.
Don’t miss this opportunity to elevate your FME expertise and drive your projects to new heights of efficiency.
Transcript: Selling digital books in 2024: Insights from industry leaders - T...BookNet Canada
The publishing industry has been selling digital audiobooks and ebooks for over a decade and has found its groove. What’s changed? What has stayed the same? Where do we go from here? Join a group of leading sales peers from across the industry for a conversation about the lessons learned since the popularization of digital books, best practices, digital book supply chain management, and more.
Link to video recording: https://bnctechforum.ca/sessions/selling-digital-books-in-2024-insights-from-industry-leaders/
Presented by BookNet Canada on May 28, 2024, with support from the Department of Canadian Heritage.
Search and Society: Reimagining Information Access for Radical FuturesBhaskar Mitra
The field of Information retrieval (IR) is currently undergoing a transformative shift, at least partly due to the emerging applications of generative AI to information access. In this talk, we will deliberate on the sociotechnical implications of generative AI for information access. We will argue that there is both a critical necessity and an exciting opportunity for the IR community to re-center our research agendas on societal needs while dismantling the artificial separation between the work on fairness, accountability, transparency, and ethics in IR and the rest of IR research. Instead of adopting a reactionary strategy of trying to mitigate potential social harms from emerging technologies, the community should aim to proactively set the research agenda for the kinds of systems we should build inspired by diverse explicitly stated sociotechnical imaginaries. The sociotechnical imaginaries that underpin the design and development of information access technologies needs to be explicitly articulated, and we need to develop theories of change in context of these diverse perspectives. Our guiding future imaginaries must be informed by other academic fields, such as democratic theory and critical theory, and should be co-developed with social science scholars, legal scholars, civil rights and social justice activists, and artists, among others.
Software Delivery At the Speed of AI: Inflectra Invests In AI-Powered QualityInflectra
In this insightful webinar, Inflectra explores how artificial intelligence (AI) is transforming software development and testing. Discover how AI-powered tools are revolutionizing every stage of the software development lifecycle (SDLC), from design and prototyping to testing, deployment, and monitoring.
Learn about:
• The Future of Testing: How AI is shifting testing towards verification, analysis, and higher-level skills, while reducing repetitive tasks.
• Test Automation: How AI-powered test case generation, optimization, and self-healing tests are making testing more efficient and effective.
• Visual Testing: Explore the emerging capabilities of AI in visual testing and how it's set to revolutionize UI verification.
• Inflectra's AI Solutions: See demonstrations of Inflectra's cutting-edge AI tools like the ChatGPT plugin and Azure Open AI platform, designed to streamline your testing process.
Whether you're a developer, tester, or QA professional, this webinar will give you valuable insights into how AI is shaping the future of software delivery.
Epistemic Interaction - tuning interfaces to provide information for AI supportAlan Dix
Paper presented at SYNERGY workshop at AVI 2024, Genoa, Italy. 3rd June 2024
https://alandix.com/academic/papers/synergy2024-epistemic/
As machine learning integrates deeper into human-computer interactions, the concept of epistemic interaction emerges, aiming to refine these interactions to enhance system adaptability. This approach encourages minor, intentional adjustments in user behaviour to enrich the data available for system learning. This paper introduces epistemic interaction within the context of human-system communication, illustrating how deliberate interaction design can improve system understanding and adaptation. Through concrete examples, we demonstrate the potential of epistemic interaction to significantly advance human-computer interaction by leveraging intuitive human communication strategies to inform system design and functionality, offering a novel pathway for enriching user-system engagements.
Leading Change strategies and insights for effective change management pdf 1.pdf
Iscd2009 flamand ppa_final
1. VIBRATION OF LIGHTNING PROTECTION CABLES ON RION-ANTIRION BRIDGE
Dr. Panayoti PAPANIKOLAS
Vice-Chairman & Managing Director
GEFYRA S.A.- 2 Rizariou Str., 152 33 Halandri, Greece
Olivier FLAMAND
CSTB – 11 rue H. Picherit, 44300 Nantes – France
Olivier.flamand@cstb.fr
Introduction
The Rion-Antirion bridge is a major cable stayed structure upon the golf of Corinth in Greece. On the
27th
of January 2005, the bridge has been struck by lightning, leading to the failure of one stay cable.
The improvements of the lightning protection system consisted, among other provisions, on the
installation of stretch stainless steel ropes above the stay cables. These cables were not initially
designed to avoid wind excitation and were prone to severe vibrations under usual weather
conditions.
PRESENTATION
Lightning is a very common weather phenomenon and probability that a standing structure will be hit
by a thunderbolt is not negligible. Large vertical cable structures are particularly prone to lightning
impact because of their size, their height and metallic cables conductivity. On the 27th
of January
2005, the Rion-Antirion Bridge, one of the longest multi-span cable stay bridges, has been impacted
by a lightning strike which created a fire on one of the upper stay cables, leading finally to the
collapse of this stay cable.
The best protection of large structures against lightning consists in conductive cable net surrounding
the protected area, the aim of which is to offer a preferential way for electrostatic charges to translate
from earth to clouds. This kind of Faraday cage is commonly used in rockets launch pad.
After a series of laboratory tests at full scale that clarified the reasons of the fire one of the strategies
used for the enhancement of the lightning protection system for the Rion-Antirion Bridge consisted in
installing stretch wires above the stay cables in order to intercept most of the lightning flashes [1].
Figure 1 : principle of the stretch cables protecting Rion-Antirion bridge stays from lightning
2. Several reasons existed to justify separation of the lightning protection cables from the suspension
stays, among which the will to keep the upper stay shape unchanged for aerodynamic purpose.
The choice of stainless steel ropes for the protection cable lead to an assembly of three ropes of
common diameter in order to achieve the required conductivity and to create a redundancy in case of
lightning damage of one of them. The three ropes were bound together with intermediate collars at
specific interval locations..
After these three ropes cables were installed vibrations occurred, as reported by eye witnesses. A rapid
analysis concluded at this time it might be vortex shedding excitation and the cable provider installed
Stockbridge dampers in May 2006 and air flow spoilers, consisting in an helical strake of limited
length running around the three ropes, in august 2006.
After 9 month observation by frequent close visual inspections it was concluded that:
- Stockbridge dampers were efficient in mitigating cables vibrations but they suffered fatigue
and were removed in October 2007 before parts fall down on the road.
- Air flow spoilers didn’t avoid cables vibrations and were accused to generate new torsion
excitation.
- The lightning protection cables themselves were suffering fatigue and some broken wires were
reported, where stress concentration occurred at some deviation collars.
At this stage a deeper investigation was decided before choosing another mitigation technique. Twelve
channels of the bridge monitoring system, out of 372, were used to monitor three lightning protection
cables with six 2D accelerometers in December 2007. Four months records of vibrations, wind speed
and wind direction at a rate of 100 Hz were transmitted to CSTB for analysis.
FULL SCALE DATA ANALYSIS
Rion Antirion bridge in orientated 20° from a north-south line. The wind direction influences both the
aerodynamics of the cables and the turbulence level of oncoming wind. Wind from north-east is less
turbulent than from east direction for instance, due to steep hills surrounding.
Figure 2 : bridge orientation compared to compass and hills surrounding
As usually observed in full scale measurement there are possibly many sources of cable vibration:
vortex shedding, galloping, parametric excitation may be responsible for vibrations of the same cable
Rion-Antirion Bridge
3. at different times or locations. The first concern here was to look for a correlation between wind
events and recorded large amplitudes of cables.
Looking at wind speed history compared to RMS value of accelerations it was obvious that wind
speed modulus was not the only parameter governing cable excitation because many strong wind
events did not correspond to large vibration amplitude and contrarily many large amplitude movement
occurred with moderate wind speed.
A first ranking of data was realized as strong, moderate, light vibration or no vibration that was
plotted against wind speed and direction. This showed a difference in the wind speed required to
produce moderate or strong vibration with wind direction, especially for easterly wind. For westerly
winds, coming from the open sea, there was no difference in amplitude whatever the wind direction.
This first analysis confirmed that vibration was linked to oncoming wind turbulence intensity.
The wind speed threshold above which moderate or strong vibrations occurred was close to 6 m/s for
westerly winds and wind directions surrounding 65°, but it was higher than 15 m/s for winds coming
from directions close to 95°, after passing upon a mountainous area. This threshold was minimum for
wind direction normal to bridge axis.
Comparison of vibration occurrences on the three monitored cables showed they didn’t happen at the
same time. Eye witnesses confirmed cables of the same length on the same pylon did not usually
vibrate together.
The dynamic analysis of recorded data showed that large amplitude vibrations occurred mainly for
1.1Hz frequency and its harmonics for the 299m long cable referenced M4NE.
Cable ropes are made of austenitic stain less steel grade ASTM AISI 316, open spiral strands with 19
wires 3.18mm organized as 1+6+12. The whole rope diameter is 16mm, it weights1.24 kg/m with a
nominal tension of 180 kN. The cable, composed of three ropes, 299m long, should have a first mode
frequency of 0.37Hz. The third mode of the cable was this way mainly excited in this example. At the
same time frequencies measured on the deck in the vertical direction were 0.255Hz and 0.412Hz,
corresponding to the two first vertical modes of it and on the pylon 1.58 Hz.
Figure 3 : PSD of cable M4NE (left) and bridge deck (right) vertical acceleration during a large amplitude event.
From these observations it was deduced the large amplitude vibration was not a parametric excitation
kind, but its dependency to wind proved it could be a purely aerodynamic phenomenon. Therefore
wind tunnel experiments were undertaken in order to verify these assessments and look for efficient
countermeasures.
WIND TUNNEL STATIC TESTS
A piece of rope was provided in order to build a wind tunnel sectional model. Three ropes were first
joined together in the shape of the actual cable referred as the “compact arrangement” (figure 4), this
way the wind tunnel model was representing the whole shape and the strands. Sectional model was
1.5m long.
4. Figure 4 : shape of the actual cable referred as “compact arrangement”
Figure 5 : model on supporting frame in wind tunnel
Model was build with high concern for its shape on a flat reference surface. The three ropes were
glued together in order to provide stiffness and avoid twisting or bending deformation. Both ends
were bound to two supporting three components balances hidden in a rigid frame situated in the
middle of a 6m wide x 5m high wind tunnel. The rigid frame maintained 2 dimensional wind
conditions without development of a boundary layer on edge panels.
The model was set horizontal. The force coordinates was chosen in order to exhibit symmetry, actual
wind normal to bridge axis corresponding to -60° or +90° incidence. Drag and lift coefficients in the
wind coordinates Cdrag and Clift were measured for wind speed 5, 10 and 15 m/s and incidence
ranging from -90° to +90°. As shown Figure 7 they were not symmetrical on both sides of 0°
incidence, what may be explained by stranding of wires.
Figure 6 : force coefficients coordinates for compacted arrangement study
Wind incidence
i>0
Forces on
the model
Fx
Fy
Fdrag
Flift
5. compacted arrangement, Cdrag coefficient
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
-100 -80 -60 -40 -20 0 20 40 60 80 100
incidence (°)
Cd
u=5m/s
u=10m/s
u=15m/s
compacted arrangement, Clift coefficient
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
-100 -80 -60 -40 -20 0 20 40 60 80 100
incidence (°)
Cl
u=5m/s
u=10m/s
u=15m/s
Figure 7 : Compacted arrangement, Cdrag coefficient (left) and Clift coefficient (right) for wind incidence varying from -
90° to +90°
The slope of the lift coefficient in cable coordinates Cy (figure 8) reached twice a negative value of -1
in the wind incidence range, close to -60° and +90° that broadly corresponds on the actual bridge to
wind perpendicular to bridge axis.
The Scruton number for this cable , 2
2
D
dm
Sc
×
××
=
ρ
, calculated from damping decrement
d=0.001measured on site, cable mass m=1.24x3 kg/m, air density ρ=1.2 kg/m3 and cable apparent
diameter D=0.016x2 m, reached the value of 6, indicating a real capability of galloping for this ropes
arrangement.
Compacted arrangement, slope of the lift coefficient, dCy/di
-1
0
1
2
3
4
5
6
7
8
9
-100 -50 0 50 100
incidence (°)
u=5m/s
u=10m/s
u=15m/s
Figure 8 :Compacted arrangement, Cy coefficient slope variation with wind incidence
Another rope arrangement was suggested and its stability measured in wind tunnel.
Figure 9 : force coordinates for spaced out arrangement of ropes proposed
Wind incidence
i>0
225mm
6. This arrangement was called “spaced out” because the three ropes were maintained separated by
225mm by a thin metal spacer.
The same measurements as for the compact arrangement were realized in wind tunnel showing (figure
10 ) that force coefficients Cdrag and Clift were very uniform regarding wind incidence. With this
arrangement Cy slope never became negative as shown figure 11. As a first conclusion, changing the
arrangement of ropes could be an elegant solution avoiding lightning protection upper cable galloping.
At the same time, cable supplier’s preferred solution was to install viscous dampers at the lower end
of LPUC, what means no major work on the bridge, but aesthetically not the preferred solution by the
owner. Dynamic modeling in wind tunnel was achieved in order to evaluate this dissipative solution.
spaced out arrangement, Cdrag coefficient
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
-100 -80 -60 -40 -20 0 20 40 60 80 100
incidence (°)
Cd
u=5m/s
u=10m/s
u=15m/s
spaced out arrangement, Clift coefficient
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
-100 -80 -60 -40 -20 0 20 40 60 80 100
incidence (°)
Cl
u=5m/s
u=10m/s
u=15m/s
Figure 10 : Spaced out arrangement, Cdrag coefficient (left) and Clift coefficient (right) for wind incidence varying from -
90° to +90°
spaced out arrangement, slope of the lift coefficient, dCy/di
-1
0
1
2
3
4
5
6
7
8
9
-100 -50 0 50 100
incidence (°)
u=5m/s
u=10m/s
u=15m/s
Figure 11 :Spaced out arrangement, Cy coefficient slope variation with wind incidence
WIND TUNNEL DYNAMIC TESTING
Both sectional models designed for force measurement were used for dynamic testing. Because
models had been realized with actual pieces of ropes and included end plates and supporting devices,
final model mass was 50% higher than actual cable.
It was suspended horizontally to springs arranged in a way vertical oscillation only can occurred at
frequency 1.1Hz with a damping decrement d=0.004. Model and supporting rig were installed inside
the 4m x 2m section of a low turbulence wind tunnel.
This time models were oriented in a way 0° wind incidence in wind tunnel corresponds to wind
normal to bridge axis on site.
For the compact arrangement cable strong vibrations were observed at incidence 0° and 1° and at 54°
to 56° for wind speed as low as 4m/s.
8. For the incidence considered worse, 54°, mechanical damping was increased step by step in order to
look for the minimum damping able to mitigate galloping. Fig15 shows galloping was not suppressed
with damping level less than 1.3% of critical, that is decrement d=0.08.
Same kinds of tests were conducted for the spaced out arrangement cable without any vibration
observed, whatever the wind speed and incidence. This gave another argument to guarantee this rope
arrangement will suppress galloping excitation.
Various models of spacers had been suggested, some of them including a damping effect. For one
model, consisting in a short PU cylinder, wind tunnel tests were realized in order to check the stability
of the spaced out arrangement modified by this damper. No instability was observed in a wide range
of wind speed up to 26m/s, for wind perpendicular to cable axis.
Figure 16 : Wind tunnel test of spaced out cable stability when equipped with a PU ring acting as a damping spacer.
CONCLUSION
Vibration phenomenon of Lightning Protection Upper Cables on the Rion-Antirion bridge was
identified as galloping, due to the arrangement of the three constitutive ropes.
Another arrangement of ropes was proposed and wind tunnel studies showed its efficiency in
suppressing the galloping phenomenon..
An alternative mitigation solution was damping increase by mean of viscous dampers. Wind tunnel
tests showed this solution would be efficient only if a high level of damping could be provided.
Finally it was decided to change ropes arrangement with spacers providing additional damping.
REFERENCE
[1] A. Rousseau, L. Boutillon, A. Huynh, 2006, “Lightning protection of a cable-stayed bridge”, 28th
International Conference on Lightning Protection, Kanazawa, Japan, 18-22 september 2006.