Questions from Oral Presentations (9.30)

Questions from Oral Presentations (9.30)

TEAM ARES

Electromechanical Questions

• What is the effect of relocating the position of the magnet/inductor? – Changing the location of the magnet effects the distance the magnet

oscillates. In order to capture the most flux as possible one must keep the distance between the magnet and coils to a minimum, in order to operate in the high density flux lines. This means locating the magnet on the ends where belt displacement is low. If it were put further away from the ends it would generate less current as the fewer flux lines would pass through our coils and it would cause greater disturbance in flow over the belt.


• If the magnets are taking out energy, won’t they be dampening the vibrations thus changing the natural frequency calculated?– The magnets will take energy out of the system due to the effects of

Lorenz forces induced by the current flow in the stationary coils. This will affect the dynamics of belt operation but does not affect its natural frequency which are governed by the mass, stiffness and length of the belt.


• Where/what are these electrodynamic equations? You keep talking about them but you don’t show or actually explain them.– When the presentation was made the specific equations for magnetic

flux where not know by the ARES team. Shortly after the presentation the equations which are used to determine the flux of a magnet (of specified shape) with respect to distance have been found. Currently the electrodynamic equations used by the ARES team include Faraday’s Law, Coulomb’s Law, and the magnet flux equations for a permanent magnet. These equations will be in much greater detail in the next ARES presentation.


• Are these models time realistic? It seems that electromechanics are a large (missing) part of this project so without this area of knowledge … one expect to prod… reasonable amount of…

– The equation referred to in this question is Faraday’s law, in which the induced voltage in a coil of wires is governed directly by the derivative of the flux density experienced by the coils with respect to time. Our magnet will be oscillating and will then generate a varying flux density experienced by the coils thus inducing a voltage that is time based.

– In terms of if we’re going to complete these models in the allotted time for Senior Design, it is the intention of our project. We have some time considering the difficulties presented by this project and feel confident that we will successfully complete this project on time through the careful planning and hard work of the team as a whole. Gantt charts and timelines are available, but as always, are susceptible to the learning curve that is presented by this project.

Belt Materials and Manufacturing Questions

• How is belt length determined?– This variable will primarily be determined by the dimensional limits of the

wind tunnel test section, if we choose to take a path where we test everything in the wind tunnel. Otherwise, the length will probably just be "picked" as one close to the Humdinger's belt length. A seemingly "arbitrary" selection will help lower the number of parameters that we will have to optimize.


• What is the material of the belt going to be?– Several differnet types are being explored including the Mylar coated

taffeta that Humdinger used.

– Composite belts, similar to Humdinger's taffeta belt, are a big possibility. Using stiff fabrics laminated by thin flexible films will allow us to stiffen the belt in twisting directions, which may be beneficial to power generation.

– Elastomers would also make good belt materials as they typically have an exceptional resistance to cyclic fatigue.


• What is the final deliverable?– Our final deliverable will be an optimized prototype AED that can

operate under the conditions specified by our objectives. Our main goal is to make this AED as efficient as possible.


• How will fatigue of the belt affect performance?– We will be choosing materials that under our operating conditions will

not plastically deform because having the belt under a specific tension is important for efficient operation. Materials will also have enough strength to not fail due to the intense forces caused by resonance in the belt. Our main concern will be cyclic fatigue, which would result in a failure in the belt. Cyclic fatigue is being considered in the design and one design criteria is the ease of belt change.


• If constant changing of the belt is required, how will it be cost effective?– We are going to design the device so that the belt does not require

constant changing and instead only requires periodic changing. The belt is actually one of the cheapest parts of the entire device and so replacing belts is not unfeasable.


• How do you intend to manufacture a composite belt with multiple layers of the size described? (ie, very small)– We will use thin fabrics laminated with flexible films (like Mylar) with the

use of flexible ahesives. Secondly there are manufacturing techniques such as vacuum bagging that greatly reduce the thickness of the composite.

Aerodynamics Questions

• How will you compare plate vibration to a cylinder?– We intend to model a cylinder first because it is the simplest case for

analysis. By using a cylinder as a starting point for our calculations, we can assume various parameters that will allow us to output useful data that we can compare to our experimental data. Once we have completed the model for a cylinder, then the model for a flat plate can be completed. The same basic principles still apply to both cases, but more studies have been done on cylinders and hence there is more data to which we can compare our models.


• Unclear as to what Slide 20 equations are for physically… as in the amplitude– Slide 20 from our presentation discussed the minimum velocity required

to induce vortex shedding along the membrane, and thus the equation was a displacement function of the belt in the y-direction


• Are your calculations going to be determined by analytical or experimental results?– Our calculations are going to be determined using both analytical and

experimental data; first we will analytically determine how our belt will perform, and then experimentally discover how our belt actually performed to validate our mathematical calculations


• Are there any equations out there that relate wind velocity to belt vibration already? Non-dimensional?– There are equations that already exist. However, they are systems of

equations with unknown variables at this time, and that is currently what our team is working on to develop and understand through research and mathematical manipulation. Once we can find a way to calculate the unknown variables (analytical or experimental) we can then solve the system of equations giving a solution for our aeroelastic model. Non-dimensional analysis is currently underway and will be complete very shortly, as a main goal of this is to produce some non-dimensional specifications to which the wind belt should be manufactured.


• Complex Vibrations? OK

• What if you put something in front of it to induce vortex shedding before the flow gets to the belt?– As we explained in class, if we make the flow turbulent prior to reaching

the belt, we would be taking energy out of the flow in order to generate the wake an vortices. This creates a problem because the mechanical concept of the AED is that it draws energy from the viscous wake it creates- not a wake that it sits in. Therefore, placing an object in front of the windbelt to expose it to a vortex street would not produce as much power as if it were placed in the freestream.


• Nozzle?

• Converging Nozzle?– This is a valid point and suggestion. It is entirely possible that a

converging duct could be used to decrease required wind speed, and thus be beneficial to the AED. However, the AED already operates at such low wind speeds that it may not be needed.


• Any losses from torsion?– There will be some losses due to torsion, but the torsion is also key for

vortex shedding, which causes the belt to oscillate. Without it, there would not be a large amplitude displacement of the belt. It is possible the torsional forces will allow the belt to deform too much in a rotational sense, causing over-rotation which would then create an inefficient mode of vibration. Thus, a balance of torsional forces on the belt with its vibration must be balanced and will be accounted for by determining the belt’s elasticity and ensuring that it can endue the torsional forces.


• Is it only vortex shedding which causes the vibration? Can the string/beam be designed to give more vibration more energy?– Vortex shedding is required to start the vibration. It is the vortex

shedding that starts the oscillating until the belt becomes self-excited. That is, when the aerodynamic loading due to torsional displacement becomes 90 degrees out of phase with the belt displacement, this creates a self-exciting behavior. This is the way to generate the most energy from the device. With careful consideration of belt material, it can be manufactured (such as a composite that allows for equal twisting in each direction) so as to maximize the vibration


• What vibrational frequencies can you expect?– Variables that determine the frequency of vibration include belt length,

cross section, moment of inertia, mass/length of the belt, tension, and wind velocities (for torsional vibration). That being said, for the scale of our project, we can expect vibrational frequencies in the range of 20-70 Hz (estimated).


• Tunable? What does this mean?– By tunable, we mean that we want to be able to adjust parameters of

the AED such as belt length, tension and direction that it approaches the wind in order to maximize the energy we can extract the wind. The main method for “tuning” the windbelt after the belt has been manufactured is to change the tension. By doing this, the natural frequency can be changed. It can be important to change the natural frequency of vibration to tune it to the local wind speed. For example, higher wind velocities can permit a belt with a higher natural frequency, hence the tension in the belt can be increased. This will lead to a higher frequency of power generation, and more power. On the other hand, lower wind velocities require a natural frequency to be lower, so tension must decrease in order for belt resonance to occur.


• What have you actually done (no plots, charts, products)?– Our current work is mostly mathematical analysis of equations to

determine the correct mathematical interpretation of the behavior of our belt. Non-dimensional analysis is also underway to develop non-dimensional specifications for the windbelt. Since this involves a lot of time spent deciphering the equations, our progress is not easily identifiable except for in our ability to continuously better explain the vibration of the belt. The non-dimensional analysis is near completion and the mathematical model is well underway. Our goal is to have a mathematical model complete and validated (by experimental results) at the end of this semester


• Where did you get your numbers for the “Alpha model”?– By watching video of the Humdinger windbelt and estimating

dimensions. We were not trying to match any dimensions exactly, only prove the concept and take a hands-on approach to experimenting with different tension setups.


• What exactly are they doing with Windbelts? Are they re-producing Humdinger’s design? Trying to improve it? This is something the company can’t do?– When Humdinger designed this device, they were focusing on cost-

effectiveness rather than aerodynamics/electromechanical effectiveness. We’re seeking to improve upon the capabilities of this device by researching its characteristics and identifying the areas where we can optimize the design to improve efficiency of the belt. We are creating mathematical models for predicting the power generation and aeroelastic behavior of this device. Once that has been completed, it will be possible to optimize the device for maximum power generation.


• Where is vibrational fatigue analysis?– That will be completed after the mathematical model. Once we have

determined frequency and displacement data for the AED, it will be much easier to use a life-cycle analysis to predict the belt’s life


• Watch calling it “string theory” as that is a physics field: doubt you are getting into… or maybe it is and I misunderstood– We’ll be sure to make a clear distinction for our next presentations and

in our final report that by “string theory” we mean that we are modeling the membrane as a string, rather then as the quantum physics topic of string theory.

Comments

• How can a model be built with so little information and such large uncertainties?– The model we have constructed is simply a proof of concept

demonstrating the idea that wind flowing over a tensioned belt will create flutter/vibration. We have a lot of information from the Humdinger Design to give us an idea of suitable specification ranges for our future models. We also have gathered a lot of research supporting the concept. Our uncertainties lie in specific materials and dimensions of the model that should be used, which is where our equations will be applied. The equations being derived make up a large part of this project that will parallel the physical models and explain the behavior of the models tested.

• Speak Up• Good Organization• Good Explanations

Comments

• Great Update. I like the numerous calculations applied with an actual built beta model

• Current/future work slide would have been beneficial

• Should probably be more general in terms of wind speed and direction– The specifications given for wind speed are based on Melbourne

weather conditions. It is important to stay within this range so the final design could be utilized in Melbourne. A range of 4ft/s to 16ft/s is broad enough to allow for design variations. It is also important to design in consideration of wind gusts so that the model does not break.

Comments

• I liked the presentation but it was really thick with equations and calculations. I realize you had to include them though.

• Too much detail

• Pic/movies, how its gonna look visually– We provided an image of the Humdinger Design, our current CAD

model, and a video of our proof of concept. These images are appropriate for our project at this time. Since our project is also largely based on formulating equations, pictures do not apply here. The graphs presented are the appropriate type of image to use for our equations and are given and explained in the presentation.

Comments

• Label Equations where do they come from?– The equations used in our presentation were described based on what

they applied to (string theory, beam theory, strouhal equations, etc.). Many are equations we have learned in our classes, while others are derivations presented by different authors.

– For our next presentation, we will be more specific in labeling each equation so that someone viewing the PowerPoint can read what each equation is rather then having to be present for the presentation to understand what each equation means.

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Questions from Oral Presentations (9.30)