Blog 4 – Tara: Een boot op vleugels

Het spectaculairste aspect van de Solar Boat is dat deze vliegt over het water. Maar hoe zorg je ervoor dat een boot vliegt? En hoe houd je de boot stabiel? Ik zal beginnen met de eerste vraag te beantwoorden. De boot kan vliegen dankzij de draagvleugels. Als de boot vaart zorgen de draagvleugels ervoor dat de waterdruk boven de vleugels lager is dan eronder, waardoor een opwaartse kracht ontstaat en de boot dus uit het water wordt getild. Dit principe is vergelijkbaar met hoe een vliegtuig vliegt.

Mijn tweede vraag is een stuk lastiger om te beantwoorden. Wanneer een boot vaart met draagvleugels is het lastig om stabiel te blijven. Dit komt onder andere door de golven en de wind. Als oplossing hiervoor hebben we dit jaar gekozen om de boot drie vleugels te geven. Dit zorgt voor een hogere dwarsstabiliteit, maar dit is nog niet genoeg. Om de gehele boot stabiel te houden is er ook een controlesysteem nodig. Zoals je dus ziet is een boot op vleugels best ingewikkeld.

Maar nu hoor ik je denken, waarom zou een boot moeten vliegen? De meeste mensen zullen denken dat er voornamelijk maritieme techniek studenten in dit team zitten, maar dit is niet het geval. De Lucht en Ruimtevaart studenten nemen dit team over waardoor vleugels populair zijn geworden. (Maar eigenlijk moet de boot kunnen vliegen omdat er dan veel minder weerstand is van het water. 🙂 )

De grootste uitdaging van het maken van een Solar Boat die zal winnen is dat de boot zowel hydrodynamisch, stabiel én manoeuvreerbaar moet zijn. Dit alles heeft te maken met de grootte, de plaatsing en het profiel van de vleugels. Je kunt je wel voorstellen dat als je alle aspecten van de boot probeert te optimaliseren je niet tot een oplossing komt. Je moet compromissen sluiten. Dit is in mijn departement heel belangrijk, om keuzes te maken met het oog op de dynamics en stability. Het is mijn taak als chief om ervoor te zorgen dat iedereen in mijn departement dezelfde focus heeft. Dit is niet altijd even makkelijk omdat iedereen graag zijn eigen deel wilt optimaliseren. Het is daarom erg belangrijk dat iedereen goed met elkaar communiceert om zo goede keuzes te maken.

Op dit moment zijn we bezig met het gedetailleerde ontwerp en de keuzes die nu gemaakt worden hebben ook invloed op andere departementen. Wij wilden bijvoorbeeld de positie van de vleugels veranderen, maar dit was niet mogelijk met het huidige design van de romp. Hierdoor moeten er dus compromissen gesloten worden om alsnog tot een goede oplossing te komen en zo een winnende boot maken, wat het doel is!

Bedankt voor het lezen,

Tara Bolton

Blog 3 – Cas: Chief Hull and Body

Hi,
Mijn naam is Cas Rosier en ik ben Chief Hull and Body. In dit blog zal ik jullie meer vertellen over dit departement en over mijn taken.
Het doel van dit departement is het ontwerpen van een boot die in staat is alle soorten golven en weeromstandigheden aan te kunnen. Dit is belangrijk voor het winnen van de Monaco Solar Challenge en om het Kanaal over te steken. Terugkijkend op onze geschiedenis, zijn wij het eerste team dat een boot ontwerpt voor deze omstandigheden!
Dit betekent dus dat er een compleet nieuw ontwerp van de boot moet komen. Dit zal natuurlijk obstakels met zich meebrengen die we met hard werken en motivatie moeten overwinnen.
Mijn verantwoordelijkheid als Chief is om een goed overzicht te bewaren over het werk en de voortgang van het Hull en Body departement. Deze taak loopt uiteen van besprekingen met het team tot een gedetailleerde planning maken en natuurlijk veel “engineering”. Deze diversiteit van taken is de reden dat ik dit zo leuk vind om te doen!
Om de perfecte romp te maken die in staat is onze doelen te halen hebben we studenten nodig van allemaal verschillende studies. De vorm van de romp zal ontworpen worden door een Maritieme techniek student en een lucht en ruimtevaart student zal werken aan het materiaal en de opbouw van lagen die hiervoor nodig is. Ik, als werktuigbouw student, zal werken aan de bouw van de binnenkant van de boot, waarbij een uitgebreide FEM-analyse uitgevoerd zal moeten worden. Deze analyse is nodig om te zien of de boot alle externe krachten aan kan die worden uitgeoefend op de romp.
Dit zijn een paar voorbeelden van de dingen waar dit departement rekening mee moet houden. Vorige week bijvoorbeeld was ik samen met een engineer van dit departement bezig met het bekijken van verschillende load cases. Dit betekent het nadenken over alle verschillende staten waarin de boot zich kan verkeren en welke krachten hierbij komen kijken. Hierdoor krijgen wij een beter inzicht in wat de boot aan met kunnen.
Volgende week zal Tara jullie meer vertellen over Dynamics and Stability! Tot dan!

Blog 2 – Casper: Van concept tot gedetailleerd ontwerp

Alle aspecten die nodig zijn om een volledig product te ontwikkelen, worden beoefend in ons team. Van idee tot product, theorie tot praktijk en verwachting tot werkelijkheid zijn transities waar wij ook dit jaar mee te maken zullen hebben.

Naast het hebben van een concreet omschreven doel of richting, is het van belang in opeenvolgende fases te werken om kwaliteit te garanderen. In het begin van het jaar wordt bepaald wat het grove concept zal worden – Top Level Concept. Deze wordt opgevolgd door het Sub Level Concept waarin beslissingen worden genomen en een begin wordt gemaakt aan het uitwerken hiervan. De volgende fase wordt gekarakteriseerd door het gedetailleerd uitwerken van alle onderdelen van de boot – Detail Design. Aansluitend zal een productieplan gemaakt worden. Productie is de logische volgende stap. Uiteindelijk zal ons product getest worden in de test periode en zal er uiteindelijk deel worden genomen aan races.

Op het moment is het Sub-Level concept net afgerond en wordt er hard gewerkt aan het gedetailleerd uitwerken van de genomen beslissingen. Het lastige aan deze fase zijn de integratie tussen onderdelen, subtiliteit van ontwerpen en haalbaarheid/produceerbaarheid van een design. Hiernaast is het van groots belang door de bomen het bos toch nog te kunnen zien. Het moet uiteindelijk allemaal bijdragen aan een kwalitatief uitzonderlijke boot. Dat is mijn job. Mijn taak is om ervoor te zorgen dat het concept op zo’n danige manier uit gewerkt wordt dat aan alles gedacht is, integratie tussen verschillende departementen volledig is en pijnpunten van voorgaande jaren beholpen worden. Het begeleiden van de zoektocht naar de mogelijkheden om de concurrentie en begrijpen van het totaal plaatje staan bij mij hoog in het vaandel.

Het uitwerken van concept tot gedetailleerd ontwerp met een groot team op zo’n grote schaal is moeilijk op elk denkbaar vlak maar is daarnaast ontzettend leuk en natuurlijk heel leerzaam. Iets wat je, als student van de TU Delft zijnde, stiekem alleen maar vindt bij Dreamteams.

Joe,

Casper van Engelenburg

Blog 1 – Bob: Team manager 2017

Daar is ie dan, de eerste blogpost van het TU Delft Solar Boat Team 2017!

We zijn al enkele maanden druk bezig met onze nieuwe doelen van dit jaar. Onze visie is echter hetzelfde gebleven: wij geloven dat zonne-energie de toekomst heeft, ook in de maritieme sector.

Na voorgaande jaren vooral gefocust te hebben op de binnenlandse wateren, gaan we dit jaar een stapje verder. Wij zullen meer aandacht besteden aan zeewaardigheid, stabiliteit en manoeuvreerbaarheid.

Concreet hebben wij dit jaar twee doelen:
Ten eerste het winnen van de Monaco Solar Boat Challenge. Dit is een driedaagse zonnebootrace die bij de Haven van Monaco wordt gehouden.
Ook gaan wij het kanaal oversteken, van Calais naar Dover! Zo kunnen we samen met de TU Delft en onze partners laten zien dat we echt achter deze duurzame ontwikkelingen staan.

Dit jaar bestaat het team uit 28 studenten van de meest uiteenlopende faculteiten. Van Industrieel Ontwerpen tot Electrotechniek en Luchtvaart- en Ruimtevaarttechniek tot Technische Informatica. Hierdoor kunnen we de boot vanuit verschillende aspecten bekijken en hebben we wel voor elk onderdeel minimaal een student die het fijne ervan af weet. Om dit in goede banen te lopen hebben we het Team opgedeeld in vier verschillende departments.

Allereerst hebben we het Dynamics & Stability team dat dit zich dit jaar vooral bezighoudt met de nieuwe uitdagingen. Hierbij gaat het om stabiliteit bij de golven die we tegen zullen komen in zowel Monaco als in de Noordzee. Tegelijkertijd moet de boot manoeuvreerbaar genoeg zijn om te winnen in Monaco.

Daarnaast hebben we ook het Hull & Body department. Zij gaan ervoor zorgen dat onze boot de golfslag kan weerstaan maar toch licht genoeg is om genoeg snelheid te hebben.

Het Electronics Department zorgt er dan voor dat onze uit zon verkregen energie goed en efficiënt benut gaat worden.

Ten slotte hebben we het Drivetrain department. Dankzij hen komt de boot vooruit met behulp van een efficiënte motor en aandrijving.

Elke week publiceren wij weer nieuwe blog berichten waarin leden van het team wat meer vertellen over de voortgang. Hierin zullen zij wat dieper ingaan op de werking van de boot. Volgende week laten wij jullie kennis maken met de Chief Engineer!

We kijken met veel enthousiasme naar de toekomst en hopen de interesse een beetje te hebben gewekt.

 

Tot volgende week!

Blog 19 – Sarkout: The Data Acquisition System

A solar powered flying boat has a lot of sensors. All these sensors measure a lot of data. All this data has to be stored somewhere and somehow it has to be analysed and displayed. Fortunately you learn a lot as a computer science student. First of all you have to know what you have to make, a field called requirements engineering. This is the most important thing because making something no one will use is not a very good investment of the limited time available. This year I have learned for example it is not fun to make certain features no one will use. After knowing what to make you have to design the overall layout of the system. In our case we iterated the previous layout of the design and improved some parts of it.

For my fellow nerds: We used an embedded module with 4g to transfer the data from the boat to a powerful server provided by our dear friends at Hewlett Packard Enterprise. On our powerful server we parsed the data and stored it in a database. At the same time it was send to a Play framework application which sends the data to the end client by using Websockets. This means that we don’t need to query databases which can be time consuming. At the same time the data is stored for later analyzation. A meteor application on the user-side receives the data and visualizes it.

Naturally there is still a lot to do , for example determining the optimal speed for the boat depending on the weather and battery conditions is still mainly a manual task. This could be an optimized algorithm which takes all these factors in account and determines the most efficient speed for the boat. Also analysing the data could be a huge factor in determining if the strategies used in the past were indeed as effective as we thought they were. These kind of analysations need a lot power and a team who knows how to handle these amounts of data. Luckily there are new courses at the Delft University of Technology focused on Big Data and cloud powered applications. This means that we will be able automate the previous mentioned tasks as soon as possible. Which in turn could give us the final push for victory.

Blog 18 – Luc: Energy Box Mini Series Part V

In the previous part of this blog mini-series I have discussed on the fuel gauging system used in the energy box. In this part the cooling system will be the main topic.

Before I spent all of my time building solar powered hydrofoil boats, I’d like to use my free time for gaming. I even built my own ‘gaming rig’ so I could play all of my games in 1080p at 60fps. At some point in time I even decided to compete in a casemodding competition, surprisingly I actually managed to make in into the finals of the contest. One might wonder why I am telling you this in a blog about the solar boat. Well, as you may have noticed in my previous blogs, I get my inspiration for designs from seemingly unrelated topics, and with casemodding this is also the case (pun intended).

The energy box is designed to be extremely efficient in terms of power loss and weight. However, at maximum power we can discharge the battery at about 200 amperes of current. An important thing to note is that power loss due to resistance is actually the current squared times the resistance. This means that at a discharge of 200A, 1mohm of resistance dissipates 40W of power. Even though it is designed for high currents, our energy box would dissipate around 500W of power, equal to a powerful desktop computer. A desktop computer uses fans to blow away the hot air and pull cold air in. However, regulations for the Dutch Solar Challenge state that the battery may not come into contact with water, even while the boat has practically sunk. This is where it gets fun.

Using fans is of course a no-go since it requires us to make huge cut-outs through which air can flow (or water for that matter). Other possibilities include the use of heat sinks, but dissipating 500W passively through conduction would require very heavy heatsinks. Now to come back to my story of casemodding. In casemodding there is actually only one real way to go and that is water cooling. Usually water is pumped through heatsinks and led through radiators which are cooled by fans and cold air. In our case, it is pretty much the other way around. We heat up cold water in a radiator by blowing hot air in the box through the radiator. The water is then pumped through the rear strut which acts as a heatsink and is cooled by the flow  of the water we fly over. Based on my knowledge of casemodding I knew what components to find. We contacted Aquatuning, a supplier and manufacturer of casemodding components and luckily our plans were received with great enthusiasm. Before too long we got our hands on three Alphacool 360mm radiators and a large supply of liquid coolant, including red UV ink which is convenient for discovering leaks and spills (and it looks really cool under a blacklight). We also partnered up with EBM Papst for the fans that we use since we are big fans of their fans. We even selected the fans on their noise production, nobody wants a loud boat.

The nice thing about the custom watercooling loop is that we can incorporate all other hot components as well. These are the motor and the motor controller. Luckily, these components were already made to be water cooled so we did not have to make any custom parts. A practical problem is that connecting the energy box to the motor, and inside of the energy box the radiator to the motor controller would mean loss of modularity, one of our main design focuses. If we had to sever and refill the cooling loop every time we took out only one of the components, many valuable hours would be lost and the chance for errors is much greater. After scouring the casemodders fora we found yet another solution in the form of quick-release water couplings built by EPC. Normally these are used in medical centers and clean rooms, but we saw a chance for us to keep our modularity. By using the couplings we can just pop the energy box in and out of the boat without having to vent the cooling loop every time.

This is the end of part five of our mini-series on the energy box.

Blog 17 – Luc: Energy Box Mini Series Part IV

In the previous part of this blog mini-series I have discussed on the safety issues tackled by the energy box. In this part fuel gauging will be the main topic.

One key part that is needed for our strategy is something that might seem obvious, but in practice is quite difficult to determine: how full is the battery? Batteries are often said to be full at a specific voltage and empty at another voltage, e.g. a rechargeable NiMH battery is full at 1.25V and empty at 1.0V. However, a battery’s voltage drops as a current is drawn from it and so it might seem that a loaded battery is empty while in fact it still has some juice left. The way we determine how “charged” the battery is, is by actually measuring the charge stored in the battery (charge is a physical quantity with coulomb as its unit). Since current equals coulomb per second, we can determine how much charge is stored in the battery by integrating the current over time.

A major problem with this method is that even a small offset in the current measurement leads to large errors over time. If this were the case, then after a while the calculated charge will be either much lower or higher than it actually is. To tackle this problem, we have partnered with Isabellenhütte to use their IVT-MOD line of high precision current and voltage sense systems. Using this system we can very accurately tell how much charge is stored in the battery.

The charge stored in the battery gives us a fairly good indication of how much energy is stored in the battery (but not perfectly due to losses in the cell chemistry). However as I said before, the voltage of a battery cell drops with increasing current drawn from it. I have also said in a previous part of this series that we limit the cell voltage of the battery to a certain safe bottom limit. Now picture this: The boat has almost finished a stage with the finish line in sight. Of course the battery will be nearly empty at this point, but we are only a few seconds in the lead of our competitors. If they didn’t now any better, the strategy team will now tell the pilot to give all the throttle he can to make a final sprint. If this were the case, the battery might be stressed so far that the EMS triggers a shut-down of the boat to keep the minimum cell voltage above the set limit and we would lose the stage. This shows that it is very important how the voltage drop corresponds to the current.

This sounds much easier than it actually is, in reality the relationship between voltage drop and current depends on a huge number of parameters especially temperature and state-of-charge. We have given our best shot at determining the relationship anyhow using a test set-up using some very nice instruments from Keysight. The results are shown below. The characteristic shows that the voltage drop per amp (internal resistance) actually increases when the battery is near-empty. Using this graph, the strategy team can give a reasonable estimate of how much throttle the pilot can give resulting in a somewhat slower sprint but in this case we will cross the finish line.

This is the end of part four of our mini-series on the energy box. In the next episode we will talk about one of the coolest things of the energy box: the cooling system (get it?).

Blog 16 – Luc: Energy Box Mini Series Part III

In the previous part of this blog mini-series I have discussed the battery pack housed in the energy box. In this part safety will be the main topic.

Lithium-based batteries are quite nice. They can contain (fairly) large amounts of energy at a low weight will also being able to deliver lots of power. They do have their downsides however, for example they can’t be turned off. This is true for all chemical batteries but since they are so energetic it is a larger problem. Below you can see the energy that is delivered by one of our battery modules as a function of its voltage. Normally we would say that it is ’empty’ at 3.0 volts. However, this is not entirely true or rather it is entirely not true. As can be seen, the battery can be discharged even further (down at 0V when it is truly electrically empty). However, once a Lithium-ion battery is discharged below 2.4 volts it is irreversibly damaged and going down to 0 volts it is deemed dead. In most cases this very unwanted, but not very dangerous. However, if someone were to try and recharge the battery it could potentially catch fire or explode due to the chemical processes in the battery cell.

So there are two problems here. The first is that we can’t power off the battery and so the boat will continue to consume energy slowly discharging the battery. The second problem is that we need to shut down the battery in case of an emergency or when the voltage drops too low. We evade these problems by not actually shutting down the battery, but disconnecting it from the rest of the systems by means of two relays. One big Gigavac relay which can handle hundreds of currents for discharging and one smaller relay for charging. The relays are controlled by our energy management system and are wired through the emergency stop and deadman switches, interrupting the current whenever the pilot or the system detects possible danger.

Even though the relays can handle hundreds of amps and can interrupt even more, they are not meant for emergency in-operation switching. In the case something does awfully go wrong we also employ a Carling Technologies circuit breaker. This specific circuit breaker is designed to interrupt over a thousand amps. A circuit breaker acts like a fuse in the sense that it will stop the current flow when it senses the current is too high, but it has the nice ability that it is resettable and therefore does not need replacement.  Unfortunately, if the pilot is too enthusiastic the circuit breaker might trip, setting the boat to a standstill. Normally it would be necessary for the pilot to open the hatch to the energy box and manually reset the breaker. This would cost precious racing minutes, so we fitted the circuit breaker with a remotely operated motor so it can be reset with just a simple press of a button.

So now we have a system that can interrupt the current flow out of the battery in any given situation, sounds safe right? Well technically yes, but very rarely there may still be a problem. Battery technology has rapidly advanced since the development of the first lithium based battery back in the 90s allowing us to build the energy box in a very compact manner. However there is still a very slim chance that a battery cell might be faulty coming fresh out of the factory, think of the recent problems with “hoverboards”. If this is the case, our relays and circuit breakers are useless because a battery cell might catch fire just out of nothing. It would be a waste of the energy box not to speak of the danger it might be to the boat and the pilot.

A battery based fire is not easy to control. Some people may remember the “triangle of fire”, the three necessities for a fire to break out. These are heat, fuel and oxygen. Unfortunately, all of these three factors are fed to the fire by the battery cell itself and therefore a fire cannot be controlled in the traditional manner. Fortunately, the “triangle of fire” is actually the “tetrahedron of fire”, which sounds way cooler but also shows us another factor which must be present for a fire to exist: A chain reaction. A fire is nothing more than the combining of oxygen to other molecules in a chemical reaction. If you could in some way block the reaction from happening, the fire will die out. This is exactly what our firepro fire extinguisher does. It uses an aerosol mixture that interrupts the chemical reaction and thus it is able to stop a battery fire. It even leaves all of the electronics intact, unlike powder extinguishers.

This is the end of part three of our mini-series on the energy box. Want to read more about our energy box and his friends energy box 2 and energy box 3? continue reading part four which is on the topic of fuel gauging.

Blog 15 – Luc: Energy Box Mini Series Part II

In the previous part of this blog mini-series I have discussed the general layout of the energy box. In this part the battery will be the main topic.

Ten months ago, I wrote a blog about the design of the battery. At the moment of writing, I had only just selected the battery cells we would be using but I had spent almost no time in the actual design of the battery itself. I thought that choosing the right cell for the job would be the hardest part in building the battery pack. I was right but nevertheless it would take another three months and about four iterations before the first battery pack was finally finished.

As depicted in the photo, the battery pack consists of twelve battery modules placed in series to form a ‘U’ shape, having the positive and negative poles of the battery at the same end. In this way, every cell is exposed to free airflow for cooling and the pack would be just a bit smaller than a solar panel meaning we would only have to manufacture a single hatch for the electronics.

Each battery module in its place consists of fourteen cells placed in parallel. The battery tabs (plus and minus terminals) of the batteries are soldered to a copper busbar, which is very uncommon in the world of batteries. Normally, batteries are spot-welded to nickel. The drawback of nickel is that it has a higher resistivity than copper and thus it incurs more losses at high currents. Spot welding copper to the batteries to a copper strip is unfortunately impossible however. Why? You might wonder, well it is because the welder itself is also made of copper and if you were to try and weld the battery you would only end up in welding your welding equipment to the battery.
Being the naive designer I am, I said: ‘I am going to weld it anyway!’. I knew spot welding would be difficult so I had replaced spot welding with /laser/-welding, how cool is that!? Even better, the pulsed laser-welder we were using is located in the Reactor Institute Delft, an actual nuclear. The early test samples we made of busbars laser-welded to batteries came out fine and so we decided to stick with the plan I had. Then Murphy struck and we found out that one in about every hundred laser pulses was far more intense than the other pulses and could potentially penetrate the battery cell housing and damage the cell.

At this point I did not know how to solve the problem. In my desperation I turned to the previous chief electronics Gijs Bruining for advice. He had the very simple, but in my head preposterous idea of directly soldering the battery tabs to the copper. In every single paper I read on connecting batteries it was always stated that soldering batteries was a no-go since the heat of the soldering iron would damage the cell and send it to battery hell. Since I had nothing to lose I tested this method and to my astonishment, the battery was still fine and the contact resistance between the busbar and the battery was even lower than when welded. After some more samples I reluctantly thanked Gijs and mass production of battery modules started. This went slowly at first, but after some practice we got the hang of it. Fun fact, our two racing packs were built in halve a day.

After testing the battery pack thoroughly I was pleased to find it had a capacity of 1508Wh, within a percent error of the maximum and thus it would not result in a penalty.

And thus I conclude the this part on the energy box. Tune in next time for a story about safety.