Mechanism Design for Avoiding Ice Deformation in Fixed Docks
WPI Major Qualifying Project (MQP), Jan 2023 - July 2023
Me (left) and one of my teammates Cole (right) on project presentation day. The other member, Tim, left early before this pic was taken but shoutout to him!
Abstract
This project aimed to design and create an add-on mechanism that would be retrofitted onto fixed docks to avoid deformation and possibly failure in freezing temperatures. The mechanism allows a fixed dock to (1) have room to adapt to ice freeze by horizontal and lateral movement, and (2) serve as a truly fixed dock during the warmer months, with enough strength to dock a small boat. The project spanned C, D, and E terms in the 2022-2023 school year, with research completed in C, and prototyping and analysis in D term and E1 term. A final prototype has been developed using theoretical analysis and numerical simulations. The results confirm the design is significantly more tolerant to bending and deformation than conventional fixed docks. The provisional patent 63/460,831 - Water Dock Ice Tolerance for the mechanism has been submitted as the result of this project.
The following is a brief overview of our 6 month MQP but can be further explored in our
extensive report published here on the WPI digital library . Sections 2.2, 4.3, and 6.4 are some good reads!
Background & Research
There are many types of docks, with the two main categories for consumer docks being floating or fixed. Floating docks float on top of the water, moving with the pond or lake. A fixed dock, also referred to as a stationary dock, is built above the waterline and has a permanent foundation. Each dock has positive and negative aspects, and the decision to install each type of dock varies depending on the location and personal preference.
A major negative of having a floating and some fixed docks is that it must be taken out of the water before the water freezes during colder seasons; then reinstalled after the ice melts in warmer seasons. This can be a strenuous and expensive task. Fixed docks are not suitable for deep water locations, as it is difficult and costly to construct a solid foundation in deep water. They also suffer deformation due to ice freeze as there is little to no movement in the joints; which causes binding or breaking in the pilings of the dock. These binding/braking points occur at the screw connection between the piling and the dock. Our mechanism will allow for the piling to have lateral movement so it does not have constrained screws that can shear under deformation.
Fixed dock piling suffering permanent deformation due to ice freeze
Prototype
This design involves four springs, one on each side of the piling, which accounts for movement in the North, South, East, and West directions, securing the piling in all four directions. Each spring attaches the piling and the frame of the dock. The springs essentially take the place of screws that would typically be used to attach the piling to the dock. The four springs chosen were short enough to not make the final mechanism too large while having a spring factor of 41.63 lbs./in., which based on initial calculations is an ideal spring factor for the forces the piling will be subjected to.
The final design was created in a way that would allow it to be retrofitted to existing docks or added to new docks as opposed to constructing a new dock that is compatible with the mechanism. As a result, the design was created as a 1-ft. by 1-ft. square with a pressure treaded 4x4x36inch piling, allowing it to be affixed to the corners or walls of existing fixed docks with screws or bolts.
The design also creates a simple product that consumers may buy, or buy the OTS parts, to easily equipt. The current designs on the market do not solve the issue of a fixed dock suffering deformation as the current large-scale consumer options are strictly floating docks. Our mechanism combines the advantages of a fixed dock with the solution to deformation due to ice freeze.
Prototype Upright
Prototype CAD upside down showing spring connections
Findings
Analytical Calculations and Simulations
In the real world, numerous factors cause bending forces and moments onto a dock piling. Some of the most important factors can be the strength of the current, collisions from a boat, and the main one that this project aimed to tackle ice deformation.
The implementation of the springs lessens the moment at the attachment of the piling to the dock as it lowers the distance from where the actual force from the moment occurs. For example, on a 36 in long piling, the moment on a traditional fixed dock will be from the location of the screws to the end of the piling. Contrast this to a piling of the same length but with our mechanism, the moment would be the distance between the top of the exterior box and the location of the screws, lowering the height where the force is felt to 4 in.
A simliar relationship can be seen for torsional forces.
FBD of Traditional Fixed Piling
FBD of Our Modified Spring Piling
Experimental Testing Results
We found natural frequency for a system can define its structural integrity. In the case of dock pilings, the goal of measuring natural frequency was to determine if the pilings could withstand certain external forces and vibrations without failure or permanent deformation. This was done by applying dynamic loads onto a piezoelectric force gauge and analyzing its oscillations. We found that our modified spring piling resonates at a higher nf than a traditional fixed one, meaning it can withstand higher impacts.
We also looking into static and dynamic strain testing. This was done by applying force on a strain gauge hooked up to a Wheatstone bridge and an amplifing system. For the fixed piling we analized the location where the dock screws make the piling connection and sawits corresponding strain. For the spring piling, the piling itself will theoretically not experience strain; it is infact the eye-bolts that attach the piling to the spring and then the spring to the dock that experience shearing forces from the moments produced upon impact. This in itself will ensure the connecting eyebolts will experience fewer forces than the traditional screws and will show more tolerance to shearing, and therefore, deformation
Experimental testing frame that allows us to emulate dock conditions in a lab
Practical Results
The following image was taken two weeks after the initial prototype was retrofitted to the dock, within those two weeks, the temperature went below freezing many times and reached sub-zero temperature as well. The initial prototype is highlighted by the red arrow, in the image it is evident that it is standing up vertically. On the other hand, highlighted by the blue arrow is a traditional fixed piling simply attached with screws, it is evident that the normal piling is significantly slanted. This shows that our design suffered less deformation visually when compared to the existing piling.
While analysing the spring piling, it is evident that the ice freeze caused movement of the springs in the mechanism. This is what the mechanism is designed to do, the springs lessen the force on the screws used to attach the mechanism to the dock. The spring moved to the side and was stretched, demonstrating that a torque load was applied to the piling.
Dock after 2 weeks of freezing temperatures. Spring piling (red); Fixed piling (blue)
Evidence of appliad loads on spring piling
Provisional Patent
The testing and preliminary implementation of this mechanism was noticed by Worcester Polytechnic Institute as a potential solution towards ice deformation in structures and recognized the potential for patenting this mechanism. WPI has helped our team in the process of acquiring a provisional patent, 63/460,831 - Water Dock Ice Tolerance, for which they will also help find a market our work can be applied to. The cost-effective nature of our mechanism makes it an attractive proposition to many different markets, including the consumers that own fixed docks and are unable to remove them each year. Through our diligent utilization of the resources provided by WPI, as well as our comprehensive understanding of the engineering design process, we have developed a solution that performs well against the current market. Our mechanism has the potential to be developed further and could see a utility patent in the near future.
Presentation Poster
