Group Members

Student ID	Name
0957942	N.S.A. Messaoudi
0958470	J.J.J.B. Verstappen
0955491	C. van Otterlo
0939540	M.J.M. Smits
0956810	W.J.P. Goudriaan
0953119	J.I.A. Spapen

Introduction

Since 1945 plastic is inseparable from our society, where it brought us great fortune and great use. It is used to carry drinks, package foods, toys, etc. Whereas it has a good side that helps humanity, it also has its downsides. A lot of people throw their garbage, of which most is plastic, very easily on the ground and in rivers. This means the mainland and the oceans get polluted, instead of the plastic being recycled, when it is thrown away. On the mainland there are a lot of organizations, which focus on preserving the mainland’s environment. For example by sending people to collect waste next to roads and beaches. The amount of organizations in the seas and oceans are however, greatly outnumbered. While the organizations on the mainland can hardly keep the pollution at a steady level, the pollution in the seas and oceans has risen exponentially for several years already. The plastic in the ocean decomposes gradually which results in a highly soiled sea which is more difficult to clean up. Even when the plastic decomposes into small parts, it affects and influences the marine ecosystem as a whole. A fish cannot tell food and plastic apart and slowly gets poisoned and killed by the toxic plastic in its stomach. The same happens to many birds that get their food out of the water.

The amount of organizations in the seas and oceans are however, greatly outnumbered. While the organizations on the mainland can hardly keep the pollution at a steady level, the pollution in the seas and oceans has risen exponentially for several years already. The plastics in the ocean decompose gradually which results in a highly soiled sea which is more difficult to clean up. The small parts of plastics influence the marine ecosystem as a whole. Fish cannot tell food and plastic apart and slowly gets poisoned and killed by the toxic plastic in its stomach. The same happens to many birds that gets their food out of the water and even humans can be affected by this. If a fish gets poisoned and a human will eats that fish, then the human will also be affected by the effects.

The plastic that gets in the sea, gathers in so called ‘gyres’. These are huge area’s to which the plastic floats because of the current. It slowly floats in circles in the same area. There are 5 huge gyres around the world. See Figure 1 below.

          Figure 1, the 5 gyres in the world

Currently there is a project that is cleaning up these gyres. They put down a giant net in the gyres and let the current of the gyres, pour the plastic in the gyres. This way all the plastic gets pushed into the net and collected in one place. However cleaning up the gyres alone is not enough. The plastic that is in the gyres came from somewhere and the gyres are still growing every day. That’s why it is also important to prevent the gyres from getting bigger, by cleaning up the plastic closer to its source.

The thing that we want to accomplish is preventing the gyre from becoming bigger. We start with that by looking at the coast of The Netherlands. The goal that we’ve set for ourselves is to try to let no plastic/garbage pass through the coast of The Netherlands. The current of the North Sea along The Netherlands is from the bottom to the top or the other way around, which depends on the tides. This is very convenient for setting up places for robots. When a plastic/garbage unit is not cleaned on the beginning of the flow, then it will be cleaned up later by another robot that is on another place at the coast. Also a lot of plastic comes from the beaches and the harbours. It is therefore important to stop the flow of plastic/garbage as close as possible to the source. This is the reason why the agents are placed along the coast of The Netherlands. This will mean that the plastic/garbage will be cleaned up before it comes in the gyres.

Current situation

In order to tackle the problem we set for ourselves we need a good overview of the situation. We did this by writing down all the questions we had about the garbage problem in the North sea and then we started searching for answers. Our strategy was as following; first search for the answer on internet to get a basic intuition and then contact several organizations asking them all the same questions and combine all this information into one final answer.

The main sources we used are either reports or the organizations we contacted. This are the reports we used:

Wat spoelt er aan op het strand – Stichting De Noordzee
Mariene Strategie voor het Nederlandse deel van de Noordzee 2012-2020 – Rijksoverheid
Jaarverslag 2015 – Stichting De Noordzee
Guideline for Monitoring Marine Litter on the Beaches in the OSPAR Martime Area – OSPAR commission
The vertical distribution of buoyant plastics at sea: an observational study in the North Atlantic Gyre – J. Reisser, B. Slat, K. Noble, K. du Plessis, M. Epp, M. Proietti, J. de Sonneville, T. Becker and C. Pattiaratchi

The following organizations were contacted:

CBS
Rijkswaterstaat
Kustwacht
Clean up
Greenpeace
Stichting de Noordzee

Of course not all organizations were as helpful as we would have like, but we got enough response to get a complete answer to all our questions. Here are the questions we came up with followed by the answer in italic.

Is the problem significant enough for organizations like the government to invest money in?

There are several organizations searching for solutions for this problem, which it is significant enough to be solved. Not just the pollution issue in itself is a problem for these organizations, but also the health issues when the garbage breaks down and ends up in the food chain. The government is the biggest investor since it is a societal matter and it is hard for a profit seeking company to make money off. So if we can show the government that our project is the solution for this problem, our project could be worth investing in.

Which kinds of garbage-objects are most common in the North sea?

There are multiple organizations (Rijkswaterstaat, Stichting Noordzee en NIOZ) that monitor the garbage on the beaches and in the Nortsea. With this data a list was composed, summing up the top 10 most found garbage-objects in and around the sea.

- Ropes and nets
- Plastic pieces
- Plastic bags
- lids
- Candy wrappers
- Balloons
- Plastic bottles
- Wood
- Plastic food packaging
- Industrial plastic contents

Who are responsible for the garbage in the North sea and where are they located at the coastline?

More than half of the waste comes from the maritime sector. So logically the major port cities are geographical hotspots with regard to the dumping of plastic waste in the North sea. Other pollution comes mainly from the people visiting the beaches, so crowded beaches are also potential hotspots. Also the rivers are highly polluted which makes the places were the rivers goes into the ocean as a dumping hotspot

Are there hotspots were the garbage gathers (under influence of the current), are these hotspots on the coastline and/or in sea? If they exists, were can they be found?

Generally speaking the plastic gets smaller in terms of size the further one distances itself from the coast. Our focus is mainly on the larger pieces of plastic, so in combination with the previous question, the hotspots can be recorded around the mouths of rivers and harbors and along the coastline crowded beaches.

What is the order of magnitude of the garbage that is in the North sea, do you have exact numbers?

Regarding soil pollution of the North Sea, we are talking about 110 pieces of plastic per square kilometer in the North sea. Pollution along the coastline is 380 pieces per debris 100 meters beach.

At what depth is can the garbage be found?

The greatest concentration of debris is around or on the surface. There has been measured up to a depth of 5 meters, and from this it was found that 80% of the waste was in the first 2-3 meters. Which will be further explained in the chapter garbage distribution in the Appendix.

Are you familiar with comparable project like ours, if so could u give us some information about the projects?

A similar project is the ocean clean up. The idea is to be achieved on a large scale waste in the North Pacific gyre using two long arms. However, this project is on a much larger scale with higher concentration of waste per km ^ 2 so not really applicable to our problem.

Another project undertaken by water network. It has created an autonomous agent, named Nautonomous, which navigates through the water and gathers waste on a treadmill, this agent can be seen in Figure 2.^[1]

     Figure 2, Nautonomous

Another similar project was set up by the recycled Island Foundation. they make a sort of trial and place it on the coast of Rotterdam in strategic places and capture that way plastic.

Solution

Different concepts

During the project a few different designs and possible solutions were created. These vary on a wide spectrum. Following are some of the concepts created.

The retrieval arm

The first design was to construct a boat with a number of arms on it to pick up each piece of garbage separately. While this would be a good option, since it could grab pieces that are two to three meters deep. The programming of an arm is a whole project in and of itself. also this design would make the boat too unstable when picking the garbage out of the water due to the large amount of mass moved. Nets on either side The second design was to make a boat with nets on either side that would rotate whenever a piece of garbage is caught. However this could also catch fish which is unwanted. Also the design is not energy efficient because of the fact that it needs to move the nets in a rotational way which would consume a lot of energy.

Conveyor belts

The third design was to make a boat with conveyor belts to guide the garbage to a center flow area where they would be scooped up by another conveyor into a compartment. This design also was not very energy efficient. A lot of energy would be lost in moving the conveyors and the non-hydrodynamic design. It also could only pick up garbage that floats on the surface of the water.

Ramp to catch garbage

The final design was to make a boat with a ramp in the water. This way the garbage drifting two to three meters deep in the water can be pulled to the surface where they will be transported via conveyor belts on either side of the boat into a compartment for storage. This design will generate a lot of downwards force due to the giant ramp in the water, this can however be prevented by putting a floater or engine in the front to compensate for the downwards force.

Requirements, preferences and constraints

To make sure a good design is made there is a large list of RPCs constructed. These are split up in the following categories to make it easy to read:

Dimensions:

The boat needs to be two by three by three meters. This is so that the boat can still hold a lot of garbage. It also makes sure the boat is stable and it provides a large frontal area to pick up garbage.
The compartment needs to be 1.5 by two by two meters, this way it can carry a lot of garbage without having to be emptied.
The compartment needs to be separable in order to decrease downtime when emptying.
The clips holding the compartment in place need to be easily removable for easy separation when emptying.
The vehicle needs to have two floaters on each side (0.25 by 2 by 2.5 meters) in order to keep the boat floating in the water. Via Archimedes’ law this means that the floaters will stay in the water for 80 percent with a full compartment.
The boat needs one ball-shaped floater (radius 0.6 meters) to compensate for downwards drag when moving through the water.
Space needs to be available for the conveyor belts on either side of the boat. These are needed to pull up the garbage once it is out of the water and transfer them to the compartment. This space would equate to 0.25 by 1 by 0.5 meters.
There must be a guiding slide to transfer the garbage pulled up by the conveyors. The space would equate to 0.25 by 1 by 0.2 meters.

Material:

The boat and the compartment are both made of polyester. This material is used in the construction of sailboats and is both strong and light.
The floaters need to be made of polyether since it is the most used material for floaters in general.
The whole vehicle and all of its parts need to be waterproof to prevent it from sinking.

Transferring:

The vehicle needs to have a motor to move forward.
It needs to have a fin located in the water to steer.
It needs to have a large enough battery in order to fill its compartment and return to a charging station.

Sensors:

The vehicle needs to have a laser sensor in order to check if its compartment is full and needs to emptied.
It needs a GPS system to locate its position and to make it back to the nearest pickup point when a storm is inbound.
The agent needs an internal measurement unit in order to make sure it is still on the right path when picking up garbage.
It needs to have an internet connection to check the weather for conditions in which the agent should not be on the water and to communicate with the control station if there is a part that has broken down or the agent needs to be called back to a pickup point in event of an emergency situation.

Life-cycle:

The agent needs to keep working for 25 years, to minimize costs and to make sure it can keep cleaning the ocean, which unfortunately is never done.

strategy

For the robots, to gather plastics, as efficiently as possible a gathering strategy has to be made. To overstretch the whole area, a strategy in which the robots move vertically would be a logical approach. In that way it seems that almost all of the plastic on top of the surface of the water will be gathered. However, due to the fact that most of the plastics in the North sea are found at a depth of 1-3 meters, this strategy will not be sufficient enough. Therefore a new strategy has to be considered.

To gather the plastic that are 1-3 meters deep in the water, 2 slides are designed in front of the robot. These slides are 1-3 meters deep and pushes the plastics to the surface of the water. To stimulate this upwards thrust, the strategy will be adapted to the figure below:

     Figure 3, Strategy

In this strategy the robot will navigate in the opposite direction of the current of the water. In this way the plastics will collide to the slides and will be pushed due to the cooperation of the current and the speed of the robot. The best way to stimulate the thrust is to navigate the robots horizontally, parallel to the coast. However when the total area has to be covered there will be a lot of robots needed to gather all the plastics, therefore the strategy in the figure is the final strategy. In this strategy the following are presumed. The area which the robots will clean has a width of Y meters and a height of X meter. When tides shift, the current reverse direction. The tides shift every six hours ^[2]. Furthermore the average speed of the current is equal to 1.15 meters per second. According to the RPC’s the robots need to navigate with a speed of at least 3 meters per seconds, this means that in 6 hours a robot can travel a total amount of 64800 meters. To estimate the size of the area it will be presumed that the robot finishes n spikes at the total width of Y meters. De X and Y can be calculated by the following formula

64800=2n*√(x^2+(y/2n)^2 )

When the Y varies between 100 and 300 meters we can calculate the height X with the following formula:

x= √((64800/2n)^2-(y/2n)^2 )

In the table below the different Y and X are shown, together with an approximation of the total amount of robots.

     table 1, size of the area.

We wanted the X to be around 50 meters and therefore the size of the last row is chosen, with an approximate value of n.

Furthermore, we assume that at least 10 robots should be behind each other to gather plastics when the robots in front of them miss them. Furthermore these extra robots are necessary to cover the area when the other robot is emptying its container.

In the model part, the optimal amount of robots and the optimal angle in which the robots gather the plastic in the area is chosen by simulating different robot numbers and different angles.

The question remaining now is where the robots have to be placed to clean up the North sea, while not being disturbed by boats, birds, sailors and so on. It is very difficult to take the birds that rest on the robots into account, therefore the focus lies on human disturb factors. According to the information provided in the environment chapter, the following locations are proposed:

     Figure 3, Locations

These locations are based on tourist locations, harbors and places where rivers go into the sea. These locations are according to state of the art research the hotspots where plastics goes into the North sea. As can be seen in the figure above, the direction shift of the currents are also taken into account by placing robots on both sides of the river.

Appendix

Garbage distribution

Before we can start with designing our robot we need to have an impression of where our target, the garbage, is located. After contacting several organizations we were able to make a proper estimation of how the garbage is disturbed in the North sea.

Starting off with the depth of the garbage, research has shown that in a water column of 5 meter, starting at the surface, 80% of the it can be found in the top 2 to 3 meters ^[3] . However, these numbers follow from measurements done in the North Atlantic Gyre, so do they also hold for the situation in the North sea? Without going to much in physical detail, we will try to explain if the North Atlantic ocean is comparable with the North sea. A object floats if it has a smaller density then the liquid. Density is a ratio of mass and volume and since these quantities are the same in both situations we can assume the results of the study are also applicable for the North sea.

The second variable is the distance of the plastic to the coast. Since we couldn’t find any reports with the necessary data we contacted Rijkswaterstaat. It turned out there isn’t any specific data, but the rule-of-thumb is; the further away from the coast, the smaller and less dense the garbage gets. Combining this information with location of the hotspots (outlet of rivers, harbors and beaches), only a few potential locations remain.

References

↑ https://www.youtube.com/watch?v=BYXlv8fgj80&feature=youtu.be
↑ http://www.ebvloedgetijde.nl/
↑ The vertical distribution of buoyant plastics at sea: an observational study in the North Atlantic Gyre – J. Reisser, B. Slat, K. Noble, K. du Plessis, M. Epp, M. Proietti, J. de Sonneville, T. Becker and C. Pattiaratchi