The most common application of helical strakes is to decrease the vortex shedding that causes unacceptable vibration in towers. The strakes "confuse" the wind and reduce the movement to acceptable levels of oscillation. Tall structures for various purposes can use helical strakes.
What is a helical strake?
Helical strakes are aerodynamic stabilizers that reduce forces and deflections experienced on the stack due to vortex shedding. Strakes consist of 3 vanes which can be wrapped in a helical pattern on the upper one-third part of the stack.
Why helical strakes with your chimney?
Helical Strakes with your Chimney? Helical strakes are often used on chimneys to reduce vortex induced vibration (VIV). However, these strakes also have a significant drawback - they induce massive increases in drag and side forces that have significant structural implications for the chimney.
Why Chicago metal rolled helical strakes?
Chicago Metal Rolled can also provide clips to attach the strakes to the stacks. The most common application of helical strakes is to decrease the vortex shedding that causes unacceptable vibration in towers. The strakes "confuse" the wind and reduce the movement to acceptable levels of oscillation.
Why choose Viv solutions for your helical strake?
At VIV Solutions, we design and build each helical strake for maximum performance in the field. Our engineers will work with you to determine the best geometric profile, manufacturing materials, and fastening mechanisms required for your application.
What is helical strakes?
Helical Strakes are aerodynamic stabilizers which are sometimes used to reduce the forces and deflections of the stack experienced due to vortex shedding. Strakes consist of three (3) vanes which can be wrapped in a helical pattern on the upper 1/3 of the stack.
How do you reduce vortex induced vibration?
To prevent substantial fatigue damage, it is often prudent to install VIV suppression devices over at least part of the tubular span (to reduce the vibration amplitude and/or frequency). VIV can usually be minimized with the careful selection and design of VIV suppression devices such as helical strakes and fairings.
What are strakes on a chimney?
Helical strakes are often used on chimneys to reduce vortex induced vibration (VIV). However, these strakes also have a significant drawback - they induce massive increases in drag and side forces that have significant structural implications for the chimney.
What is VIV suppression?
Riser joint Vortex-Induced-Vibration (VIV) occurs while drilling in areas with strong ocean currents. This happens when a strong flow of water past a pipe creates vortices (turbulence) behind the pipe.
How do I stop my vortex from shedding?
0:281:10How To Reduce Vortex Shedding - YouTubeYouTubeStart of suggested clipEnd of suggested clipThere are a couple methods to overcome vortex shedding one of them may be helical strikes. They'reMoreThere are a couple methods to overcome vortex shedding one of them may be helical strikes. They're easy to design they are most common as well another method is liquid tuned dampers.
What is the frequency of vortex shedding?
Frequency of vortex shedding f = ω/2π is given by a non-dimensional number. where f is the Strouhal frequency, D is the body diameter and S is the Strouhal number.
What causes vortex induced vibration?
A cylindrical structure exposed to fluid flow periodically sheds vortices in the wake. The fluctuating lift and drag forces may cause structural vibrations, which give rise to a complex fluid structure interaction referred to as Vortex Induced Vibrations (VIV).
How does vortex shedding happen?
Vortex shedding is a phenomenon, when the wind blows across a structural member, vortices are shed alternately from one side to the other, and where alternating low-pressure zones are generated on the downwind side of the structure giving rise to a fluctuating force acting at right angles to the wind direction (Fig.
What causes Von Karman?
These so-called “von Kármán vortices” arise when winds are diverted around a blunt, high-profile area, often an island rising from the ocean. The alternating direction of rotation in the air forms swirls in the clouds. Satellites regularly spot these wind and cloud patterns around the world.
What is reduced velocity in Viv?
The reduced velocity is defined as Vr ¼ U=f nD; where f n is the natural frequency of the structure. Due to discrepancies in the VIV literature as to how the natural frequency is defined, it will be defined on a case-by-case basis.
What are the disadvantages of helical strakes?
Another disadvantage is that helical strakes can be difficult to fabricate. The tricks in fabricating strakes are not widely known, and so unless you are a company that fabricates strakes regularly, it can be challenging.
How to add a helical strake to MecaStack?
Helical strakes can be added in MecaStack. Go to the “Design”, “Damping” menu, and there is a helical strake option. The button at the right, “Damping Device Menu”, lets you enter the parameters. Although MecaStack does let you simulate helical strakes, their use still requires some engineering judgment.
How tall can a strake stack be?
A general rule of thumb that Meca uses is that helical strakes are often an economic alternative for stacks up to about 100 ft [30 m] tall, and over that it is often more economical to look to a damping solution. Another disadvantage is that helical strakes can be difficult to fabricate. The tricks in fabricating strakes are not widely known, ...
Why are segmented strakes so popular?
Segmented strakes are popular because they are much easier to fabricate. Rather than having a continuous helical strake, short segments are placed in a random or helical pattern. These strakes are not recognized by the major stack design standards.
What happens when you add strakes to a cylinder?
When strakes are added, the drag coefficient of the stack is increased greatly. A smooth cylinder will have a shape factor of 0.7, while the same stack with strakes will increase its shape factor to 1.4. Consequently the load on the top 1/3 of the stack is doubled. Since a stack is like a large cantilever beam, ...
Is vortex shedding a conical transition?
Vortex shedding is usually limited to one diameter, since the critical wind speed is based upon the diameter. It would seem that it might not be important to strake the conical transition. Our practice is that we try to avoid this situation of having a cone in the upper 1/3 of the stack whenever possible.
Can a strake be continuous?
Don’t want strakes on a flare tip. There are stiffening rings and so the strake can’t be continuous. There is a conical transition in the upper 1/3 of stack. Strakes interfere with ladders and platforms.
What is the purpose of helical strakes?
The most common application of helical strakes is to decrease the vortex shedding that causes unacceptable vibration in towers. The strakes "confuse" the wind and reduce the movement to acceptable levels of oscillation. Tall structures for various purposes can use helical strakes.
What are helical strakes made of?
Helical strakes can be made from steel bars of various sizes. The ideal size to use depends on the engineering of the stack itself. Best practice for the design of strakes or spoilers on stacks can be found at ASME STS1-2011. General guidelines include:
How wide should a helix be?
Common thicknesses can range from 10 gauge to 3/8", and widths from 2" to 12". Strakes outside of these dimensions are also able to be produced.
Can Chicago Metal cut helical strakes?
Chicago Metal can shear, saw, or torch cut the ends of helical strakes. It can provide unique markings for ease of installation in the field. And it can kit various sizes of strakes to match the requirements of each varying tower. Shipments can be staggered for a timely delivery at the customer's plant or job site.
Capacity to Produce Helical Strakes
Helical Strakes: Value-Added Services
- Chicago Metal can shear, saw, or torch cut the ends of helical strakes. It can provide unique markings for ease of installation in the field. And it can kit various sizes of strakes to match the requirements of each varying tower. Shipments can be staggered for a timely delivery at the customer's plant or job site. Chicago Metal Rolled can also provide clips to attach the strakes to …
Helical Strakes Applications
- The most common application of helical strakes is to decrease the vortex shedding that causes unacceptable vibration in towers. The strakes "confuse" the wind and reduce the movement to acceptable levels of oscillation. Tall structures for various purposes can use helical strakes. Power lines, power plants, exhaust stacks (alternately called "smoke...