VOLUME 2, JUNE 2009

by Khairul Izman Abdul Rahim

Application of pressure vessel appears in various engineering fields cover up to space exploration and down to underwater application. In ocean engineering, pressure vessel is known as pressure hull or canister which withstands external hydrostatic pressure.

Pressure hull is one of the main aspects to be considered in designing an underwater vehicle. Designer have continually strive to increase the achievable range/speed/payload of underwater vehicle while reducing the weight of structure, in the same time aiming to make the vehicle dive deeper into the sea.

There are vast scope of research that can be covered when design a pressure hull. This list can start from the design of the optimum shape to make pressure hull which can be sphere, circular cylinder, conical or composite of these. Material selection is also one of the main focuses in design processes; there is several combinations characteristic so that the pressure hull can work effectively. Some of the requirements are good corrosion resistance, high strength-to-weight ratio, able to withstand high pressure and long operating life spans of the material. As well as choosing the right material, using the right mathematical modeling and simulation to predict the behavior of pressure hull in real condition will also give great advantage in reducing the design cost and time.

There is various wall architecture uses for cylindrical pressure hulls. This article will focus on several types of the wall; thin-walled circular cylinder/ pure-monoque construction, ring-stiffened construction, tube-stiffened construction, corrugated construction, multi segment construction, sandwich structure and filament-winding mosaic pattern.

Thin-wall circular cylinder construction

Thin walled construction may be good for deep-diving craft, which are yield- dominated, but are extremely inefficient at shallow depth.

When a thin-wall circular cylinder is subjected to external hydrostatic pressure, it can fail at a fraction of pressure to cause axisymmetric yield or through non-symmetric bifurcation buckling. This node is called shell instability.

Ring-stiffened construction

One way in which the structure efficiency can be improved is by ring-stiffened the pressure wall. Ring-stiffened on the structure can be very efficient in resisting buckling.

However, if the ring-stiffened are not strong enough, the entire ring-shell combination could buckle bodily. This mean the entire ring-shell combination can fail through general instability.

Another point that need to be include, it also introducing some difficulty in full-scale manufacturing.

Tube-stiffened construction

The introduction of tube-stiffened was made by Harris in 1977. He suggested that the strength-to-weight ratio of the pressure hull

could be dramatically improved if tubes were placed in a longitudinal direction to replace the stiffening ring.

Later, Ross suggested that the placement of such tube would be better in a circumferential configuration serve pressure hull as such pressure hull generally fail due to the stresses they experience in the circumference.

Although a circumferentially tube-stiffened is another alternative to traditional ring-stiffened construction, this construction often exhibits circumferential shell buckling.

Corrugated construction

Another alternative design to the traditional ring-stiffened cylindrical pressure hull had been presented by Ross in 1987, in the form of a corrugated hull wall construction.

Corrugated into the outer cylinder can increase the shell and general instability resistance of cylindrical pressure vessel.

Ross showed that the corrugated pressure hull is structurally more efficient than the traditional ring-stiffened equivalent of same volume and weight.

However, such construction architecture did not improve the structure’s bending stiffness.

Later in 1991, Yuan showed that the corrugated cylinder could be made more structurally efficient by increasing the cone angles to certain optimum values. However, it should be noted that if the cone angle were too large the vessel would fail axisymmetrically.

Multi segment construction

Traditionally, submersibles had been associated with the concept of ‘single piece’ of a pressure hull. After the arrival of unmanned submersible, the changed of operational envelopes and the need of modular pressure hull has been established.

J. Blackut et al. studied about multi-segment underwater pressure hull. Instead of a one-piece hull, several segments of similar or the same shape are established to form modular submersible pressure hull.

Several benefits can be gain from this approach. Different material can be used to manufacture such module in order to house special equipment. Furthermore, segment with built-in batteries can be quickly swapped during resurfacing hence shortening idle time.

Damaged modules can be easily replaced and the manufacturing process can be easier for smaller modules compared to full scale size.

The research also implements the concept of bowed. The use of bowed out cylindrical shell for multi-segment pressure hull offers several benefit. Other than increasing the buoyancy, increasing collapse strength due to external hydrostatic pressure can also be achieved. This increase is also possible even for structurally non-optimized shape (for nine or more barreled segment in the vessel).

Filament-winding mosaic patterns

After the introduction of composite into engineering field, the implementation of composite had also been applied on pressure hull. The common fabrication technique of pressure hull using

composite material is by using filament winding technique. This concept is known as filament-wound composite shells of revolution and widely used in various applications, such as pipelines, pressure vessel, tanks for gases and liquids.

Structural analyses of composite shell are usually based on the implementation of mechanics of composite laminated.

Stress analysis is usually performed using the information about the number of layers, their stacking sequence and orientation, geometric and mechanical characteristic. This is because fiber orientations the decision factor in the strength of fiber-reinforced structure.

However, there are some manufacturing effects that can also affect the stress and strain fields in the thin-walled composite shells for filament-winding process. One of the effects is related to the filament-winding mosaic pattern of the composite layer.

E.V.Morozov found that the mechanical behavior of thin-walled filament-wound composite shell is sensitive to the filament-winding patterns and the stress and strain distributions are affected by the size of the triangular mosaic unit and their numbers per unit of length in both longitudinal and circumferential (hoop) directions.

Sandwich hull construction

One of the innovative design alternatives for submersible pressure hull is sandwich structure.

Sandwich structure construction consisting of a pair of high–strength, relatively thinner, stiff layers (facings), bonded to one low density, flexible layer (core), light weight, high stiffness, high structural efficiency and high durability.

In ship hull construction, commonly sandwich structure been construct by facing made of steel and cores made of a corrugated metal sheet. Due to the advantage of composite, such as, reduced weight, superior corrosion resistance, and improved hydrostatic strength etc have made the construction of pressure hull using composite provide more advantage over the use of steel.

Structure efficiency of this construction depends strongly of its core configuration and fibrous composite as face sheets. Different core configurations generate different sandwich mechanic behavior and the core configuration can be solid, cellular, honeycombed and corrugated.

Conclusion

Various types of wall architecture for pressure hull had been discuss and each of them have some advantage and disadvantage compare to the other and process of improving the concepts is still happen. As new material and engineering concept been discover, this process of design a new shape of the wall can be happen

Even thought there are multi types of wall, the objective is still the same. To make a better pressure hull so that the submersible can be more effective, dive deeper, low weight and cost efficiency.

References

[1] Liang, C.C.; Optimum Design of Filament-wound Multilayer-sandwich Submersible Pressure Hulls; Pergamon Ocean Engineering;, 30 (2003) 1941-1967.

[2] Ross, C.T.F.; A Conceptual Design of an Underwater Vehicle; Elsevier Ocean Engineering; 33 (2006) 2087-2104.

[3] Ross, C.T.F.; A Conceptual Design of an Underwater Missile Launcher; Elsevier Ocean Engineering; 32 (2005) 85-99.

[4] Ross, C.T.F. and Etheridge, J.; The Buckling and Vibration of Tube-stiffened Axisymmetric Shells under External Hydrostatic Pressure; Pergamon Ocean Engineering; 27 (2000) 1373-1390.

[5] Ross, C.T.F., Little, A.P.F., and Adeniyi, K.A.; Plastic Buckling of Ring-stiffened Conical Shell under External Hydrostatic Pressure; Elsevier Ocean Engineering; 32 (2003) 21-36.

[6] Ross, C.T.F., Little, A.P.F., Leonidas Chasapides, Jeff banks, and Daniele Attanasio; Buckling of Ring Stiffened Domes under External Hydrostatic Pressure: Science Direct Ocean Engineering; 31 (2002) 239-252.

[7] Ross, C.T.F. and Little, A.P.F.; The Buckling of a Corrugated Carbon Fiber Cylinder under External Hydrostatic Pressure; Elsevier Ocean Engineering; 28 (2001) 1247-1264.

[8] Blachut, J. and Smith, P.; Buckling of multi-segment underwater pressure hull; Elsevier Ocean Engineering; 35 (2007) 247-260.

[9] Ross, C.T.F, Terry, A., Little, A.P.F; A design chart for the plastic collapse of corrugated cylinders under external pressure; Pergamon Ocean Engineering; 28 (2001) 263-277.

[10] Morozov, E.V.; The effect of filament-winding mosaic patterns on the strength of thin-walled composite shells; Elsevier Composite Structure; 76 (2006) 123-129.

[11] Hernandez-Moreno H., Douchin, B., Collombet F., Choqueuse, D., Davies, P.; Influence of winding pattern on the mechanical behavior of filament wound composite cylinder under external pressure, Elsevier Composite Science and technology; 68 (2008) 1015-1024.

[12] Moss, D.R.; Pressure Vessel Design Manual; (Gulf Professional Publishing) 2004.

[13] Davis, M.E.; Design of a Lightweight, Multipurpose Underwater Vehicle; M.Sc. Thesis, Ocean Engineering, MIT; 1993.

[14] Yousefpour, A.; Design, Analysis, Manufacture, and Test of Composite Pressure Vessels and Finite Element Analysis of Metallic Frame for Deep Ocean Underwater Vehicle Applications; PhD Thesis; Mechanical Engineering, Univ. of Hawai’I; 2000.

[15] Murray, G.T.; Handbook of Material Selection for Engineering Application; (Marcel Dekker, Inc) 1997.

 

 

 

 

• Name: ENGR. ZULKIFLI ZAINAL ABIDIN Grad. IEM

• Joining date with URRG: 19 November 2008

• Field of Study: PhD in Robotic: Animal-inspired Swarm Intelligence and Autonomous Surface Vehicles

• Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

• Family: Wife; Hasnida Hassan (INTEL Penang), Daughters; Hana Alisha & Ariana Hani.

• Home address: Casa Perdana, Taman Pauh Jaya, Prai.

• D.O.B: 14 June 1979

• Hobby: Gadget Collector

• Sport: Badminton

• Favorite food & drink in Penang: Garlic Cheese Nan, KAPITAN & Pandan Coconut, Lorong Abu Siti, Georgetown.

Education

• B.Eng Computer & Information Engineering, IIUM, 2003
• M.Sc Electrical & Electronics Engineering, USM, 2007 (By Research). Thesis: Development of a Vision System for Ship Hull Inspection.

Professional Membership

• Board of Engineer Malaysia (BEM), Registration date: 27 Jun 2007, (52026A)

• Institute of Electrical and Electronics Engineers (IEEE), Registration date: 4 Sept 2007, (90250137). Robotics and Automation Society & Systems, Man, and Cybernetics Society. (IEEE-RAS Malaysia Exco Member)

• The Institution of Engineers Malaysia (IEM),Registration date: 21 Jan 2008 (29631), Field: Electronic.

Area of Interest

• Vision based Multi-agent System.
• Entertainment and edutainment robotics.
• Avionics.
• Underwater Robotics Technology.
• Multimedia integrated system

BIOLOGICAL BACKGROUND

In this section, we will see how the animals interact with nature in the act of searching for food, mate, provisions and their pattern in moving as a group or as an individual.

Ants

Ants are social insect. They live together in organized colonies with at least one ‘Queen’ in their nest.

In the Holy Scriptures, some verses pertaining to them are mentioned. For example, in the Holy Quran,

“At length, when they came to a (lowly) valley of ants, one of the ants said: "O ye ants get into your habitations, lest Solomon and his hosts crush you (under foot) without knowing it." (Quran 27:18.)

When foraging, a swarm of ants interact with their environment locally. Although, there is no leader nor is there a centralize command, the ants still can communicate with each other via pheromones in finding their source of foods and paths. Foraging ants travel for distances of up to 200 meters from their nest [2] and usually find their way back using pheromone trails. With an average speed of 0.5 cm per second (this varies with the species of ant); a moving ant lays some pheromones (in varying quantities) on the ground, thus marking the path by a trail of this substance. While an isolated ant moves essentially at random, an ant encountering a previously laid trail can detect it and decide with high probability to follow it, thus reinforcing the trail with its own pheromone. According to Dorigo et al. [3], the collective behaviour that emerges is a form of autocatalytic behavior where the more the number of ants following a trail, the more attractive that particular trail becomes to be followed.

a) Ants follow a path between points A and E.
b) An obstacle is interposed; ants can choose to go around it following one of the two different paths with equal probability.
c) On the shorter path more pheromone is laid down.

Bees

Bees, like ants, are specialized species of the wasp. A honey bee queen may lay 2000 eggs per day during spring buildup, but she also must lay 1000 to 1500 eggs per day during the foraging season, mostly to replace the daily casualties, most of which are workers dying of old age

It has been stated in the Holy Quran,

Your Lord revealed to the bees: "Build dwellings in the mountains and the trees, and also in the structures which men erect. Then eat from every kind of fruit and travel the paths of your Lord, which have been made easy for you to follow." From inside them comes a drink of varying colors, containing healing for mankind. There is certainly a sign in that for people who reflect. (Quran, 16:68-69) Sura 16, The Bee (Al-Nahl)

Fig. 3 Bees

A well known scientist has made the following observation,

"If the bee disappears from the surface of the earth, man would have no more than four years to live?" Albert Einstein

The foraging process begins in a colony by scout bees being sent to search for promising flower patches. Scout bees move randomly from one patch to another. Having found the patches which are rated above a certain quality threshold, these scout bees would then deposit their nectar or pollen and eventually perform a “waggle dance” when they return to the hive [4]. This dance is essential for colony communication. It is about: the direction to the source, the distance from the hive, and the quality rating [4, 5]. This information helps the colony to send its bees to the flower patches precisely, without using guides or maps. While harvesting from a patch, the bees monitor its food level. This is necessary to decide upon the next waggle dance when they return to the hive [5]. If the patch is still good enough as a food source, then it will be advertised in the waggle dance and more bees will be recruited to the particular source [6].

Approximately 75% of the bees from a colony forage within one kilometer while the young field bees only fly within the first few hundred meters. The longer foraging time is, the greater would be the nectar availability.

 

Figure 4: Distance and direction by waggling dance. Waggling straight up on the vertical comb indicates food source which is located at an azimuthal angle of 00 while waggling straight down indicates food source, located at an azimuthal angle of 1800. Figure is taken from [7].

Monkey

Primates have a highly developed brain, usually living in groups with their own complex social systems. Their high intelligence allows them to adapt their behavior successfully to different environments. Included in this group are monkeys, apes and humans.

According to A. Mucherino and O. Seref [8], when the monkey climbs up a tree for the first time, it they can only choose the branches of the tree in a random way, because it they do not have any previous experience climbing on that tree. However, when the monkey climbs up the tree again, it they would try to follow the paths that would lead them to good food, allowing the monkeys to discover a set of connected branches of the tree in which there are good food resources. When the monkey discovers a better solution, they remember it. Later, on their way down, the monkeys mark the corresponding branches, and then use these marks for deciding which branches to climb up again. This marking strategy reflects the monkey’s intentions to focus on a part of a tree where it has already found some good solutions. When the monkey decides to restart climbing up, it encounters some previously visited branches on its way up. It then climbs these branches again. The monkey chooses between one of the two tree branches based on the marks it left before. Naturally, the monkey has greater probability of choosing a branch leading to better solutions, and this probability increases with the quality of the solution the branch leads to.

Firefly

Fireflies (lightning bugs) use their bioluminescence to attract mates or prey. They live in moist places under debris on the ground, others beneath bark and decaying vegetation.

Firefly Algorithm (FA) was developed by Xin-She Yang [9] at Cambridge University in 2007. It uses the following three idealized rules: 1) all fireflies are unisex so that a firefly will be attracted to other fireflies regardless of their sex; 2) Attractiveness is proportional to their brightness; thus for any two flashing fireflies, the less brighter will move towards the brighter one. The attractiveness is proportional to the brightness and they both decrease as their distance increases. If there is no brighter firefly than a particular one, it will move randomly; 3) the brightness of a firefly is affected or determined by the landscape of the objective function. For maximization problem, the brightness can simply be proportional to the value of the objective function.

Flies

In the Holy Quran, 22, verse 73, it was stated:

Mankind! An example has been made, so listen to it carefully. Those whom you call upon besides God are not even able to create a single fly, even if they were to join together to do it. And if a fly steals something from them, they cannot get it back. How feeble are both the seeker and the sought!

The main idea behind this algorithm is based upon Drosophila’s biological behavior; 1) The fly hunts for food and a mate within a one to two month lifespan [10], 2) The fly flies with Lévy flight motion [11, 12, 13, 14]. 3) It smells the potential location (attractiveness), 4) Then tastes, if not good (fitness / profitability), rejects and goes to another location. To the fly, attractiveness is not necessarily profitable [21, 22, 10, 15]. 5) While foraging or mating, the fly also sends and receives a message with its friends about it foods and mates [16, 17, 18, 19, and 20].

The main steps of the algorithm are given in flowchart Fig. 8. When a fly decides to go for hunting, It will fly randomly (with Lévy flight motion) to find the location guided by a particular odor. While searching, the fly also sends and receives information from its neighbors and makes comparison about the best current location and fitness. If a fly has found its spot, it will then identify the fitness by taste. If the location no longer exists or the taste is ‘bitter’, the fly will go off searching again. The fly will stay around at the most profitable area, sending, receiving and comparing information at the same time. The total number of flies depends upon the number of sources. However, since most of the flies are near to the food source location, then the next generation of flies is considered to be already closeby to the potential food location.

DISCUSSION

In order to develop a completely new animal inspired algorithm, we have to observe study and learn from the creature’s nature behavior. Each being has its own unique behavior and each provide almost unlimited ways for problem solving. If we can study carefully, we are surely inspired to develop more powerful and efficient new algorithms.

As we can see, all the algorithms are based on the behavior of the animals with slight and small modifications to suit the needs of the algorithm itself. Due to the active nature of research on the particular animals which are still currently being done in laboratories, each significant behavior should be added into the algorithms instead of focusing on the process of hybridization. Although hybrid method is very popular among the researchers, we also rely upon the actual biological criteria of the animal itself. Take for example, the case of hybridization of BA with PSO; BA as we know can only send information about the nectar location on the dance floor. By adding PSO, the message will be sent out of the hive. To us, this is not consistent with the natural behavior of the bee.

Naturally, ants and bees hunt for their colony and serve the queen. Monkeys, fireflies and flies look for food and a mate for themselves. The communication medium for the ant colony is via the pheromone (which is passed from ant to ant while foraging). Bees exercise the ‘waggle dance’ in hives after foraging. There is no group searching for monkeys while climbing for food. A firefly does not share its information while at the same is engaged in finding the best mate. A fly makes contact with its neighbors via neuronal signaling (while searching) and pheromone (while mating). We can observe clearly, one of the main advantages of the fly is that, information sharing

among the group is faster than any of the other animals. Thus, the searching period for optimization for the fly will be shorter.

Theoretically, the whole ant colony loses its direction and energy when being attacked while foraging or when the food is suddenly removed. For bees, only the particular bee concerned will be affected. However if the attacker is close to the hive or swarm of bees, the whole bee colony may ‘fight brutally’. Meanwhile, a fly on the other hand, will still be flying around the potential area hunting for food. It may well be observed too that getting rid of flies while on a picnic or having a barbecue, is not actually an easy task!

Various applications have been carried out recently in the last five years. These include the combinatorial optimization, job scheduling, web-hosting allocation, engineering design optimization, function optimization, reservoir modeling and the TSP, training neural networks, forming manufacturing cells, scheduling jobs for a production machine, finding multiple feasible solutions to a preliminary design problems, data clustering, optimizing the design of mechanical components, multi-objective optimization., tuning a fuzzy logic controller and many others. It would be futile to mention all of them.

CONCLUSION

The extraordinary thing about the entire animal inspired metaheuristic algorithms is that, they all share one thing in common; in a short period of time, animals try to optimize their searching space while hunting for food and mates. As humans, we are no different i.e. we also deal with optimization our daily life, such as budgeting our expenditure, traveling from one place to another, or even looking for the perfect ‘soulmate’. However, the only difference is the way in which we carry out our deals, as compared to the creatures. The existence of too ‘many neurons’ or disturbances make our decision become more complex, even though the solution might just be right in front of our eyes! Man always indulge in the quest for perfection, which may be prove to be quite a problem, as our lifespan is not very long, some might say. However, each animal algorithm has its own list of strengths and weaknesses due to its own ‘natural’ ability.

REFERENCES

[1] Fred GLover (1986), “Future Paths for Integer Programming and Links to Artificial Intelligence,” Computer. & Ops. Res. Vol. 13, No.5, pp. 533-549.

[2] Carrol CR, Janzen DH (1973), “Ecology of foraging by ants,” Annual Review of Ecology and Systematics 4: 231–257. doi:10.1146/annurev.es.04.110173.001311.

[3] M. Dorigo, V. Maniezzo & A. Colorni (1996), “Ant System: Optimization by a Colony of Cooperating Agents,” IEEE Transactions on Systems, Man, and Cybernetics–Part B, 26 (1): 29–41.

[4] J. Deneubourg, S. Aron, S. Goss, and J. Pasteels (1990), “The self-organizing exploratory pattern of the argentine ant,” Journal of Insect Behaviour, 3:159–168.

[5] G. Iba (1989), “A heuristic approach to the discovery of macro-operators,” Machine Learning, 3:285–317.

[6] Nyree Lemmens, Steven de Jong, Karl Tuyls, and Ann Nowe (2007), “A Bee Algorithm for Multi-Agent Systems: Recruitment and Navigation Combined,” In Proceedings of ALAG, an AAMAS workshop.

[7] F. Barth. Insects and flowers (1982), “The biology of a partnership,” Princeton University Press, Princeton, New Jersey.

[8] A. Mucherino and O. Seref, (2007), “Monkey Search: A Novel Meta-Heuristic Search for Global Optimization,” AIP Conference Proceedings 953, Data Mining, System Analysis and Optimization in Biomedicine, 162–173.

[9] Yang X. S. (2008), “Nature-inspired Metaheuristic Algorithms,” Luniver Press.

[10] http://en.wikipedia.org/wiki/Drosophila_melanogaster

[11] Andy M. Reynolds, Mark A. Frye (2007), “Free-Flight Odor Tracking in Drosophila Is Consistent with an Optimal Intermittent Scale-Free Search,” Evolutionary Biology, PlusONE

[12] Bartumeus, F., M. G. E. da Luz, G. M. Viswanathan, and J.Catalan. (2005), “Animal search strategies: a quantitative. random-walk analysis,” Ecology 86:3078–3087.

[13] Viswanathan, G. M., S. V. Buldyrev, S. Havlin, M. G. E. da Luz, E. P. Raposo, and H. E. Stanley (1999), “Optimizing the success of random searches,” Nature 401:911–914.

[14] Maye, A.; Hsieh, C.; Sugihara, G. and Brembs, B. (2007), “Order in spontaneous behavior,” PLoS One, May 16.DOI number: 10.1371/journal.pone.0000443

[15] University of California - Los Angeles (2008, February 19), “Fruit Flies Show Surprising Sophistication In Locating Food,” Source.,ScienceDaily. Retrieved December 22, 2008,

[16] Ilya Nemenman, Geoffrey D. Lewen, William Bialek, Rob R. de Ruyter van Steveninck, (2008), “Neural Coding of Natural Stimuli: Information at Sub-Millisecond Resolution,” PLoS Comput Biol 4(3): e1000025. doi:10.1371/journal.pcbi.1000025.PLoS Comput Biol. 2008 March; 4(3): e1000025.

[17] Tinette S, Zhang L, Robichon A.(2004), “Cooperation between Drosophila flies in searching behavior,” Genes Brain Behav. 2004 Feb;3(1):39-50.

[18] Joshua J. Krupp, Clement Kent, Jean-Christophe Billeter, Reza Azanchi, Anthony K.-C. So, Julia A. Schonfeld, Benjamin P. Smith, Christophe Lucas, and Joel D. Levine. (2008), “Social Experience Modifies Pheromone Expression and Mating Behavior in Male Drosophila melanogaster,” Current Biology, 2008; DOI: 10.1016/j.cub.2008.07.089

[19] Clement Kent, Reza Azanchi, Ben Smith, Amanda Formosa, and Joel D. Levine. (2008), “Social Context Influences Chemical Communication in D. melanogaster Males,” Current Biology, 2008; DOI: 10.1016/j.cub.2008.07.088

[20] Cell Press (2008, September 12), “Flies, Too, Feel The Influence Of Their Peers, Studies Find,” ScienceDaily. Retrieved December 13, 2008, from http://www.sciencedaily.com¬ /releases/2008/09/080911122527.htm

[21] Gerard Manning (2008), “The WWW Virtual Library: Drosophila,”http://ceolas.org/VL/fly/index.html

[22] Frye, M.A., M. Tarsitano, and M.H. Dickinson (2003), “Odor localization requires visual feedback during free-flight in Drosophila melanogaster,” Journal of Experimental Biology (featured in Inside JEB by science journalist G.T. Huang) 206: 843-855

VOLUME 2, APRIL 2009

[by Alireza Nazem]

It is important to note that the use of the carbon-based negative electrode in the lithium ion systems does not completely prevent safety problems in these cells. Very reliable circuitry is required to ensure that defined voltage limits are never exceeded during charging. Lithium ion cells contain a number of internal safety features that are designed to prevent hazardous reactions in case of excessive internal pressure or temperature. In spite of these safety features, lithium ion cells have recently been involved in fires in laptop computers and cellular telephones.4 Although the number of incidents has been small relative to the number of cells that are in use worldwide, it is nevertheless clear that very high energy rechargeable cells even from the most reliable manufacturers can still be very dangerous. Cell packs that use lithium ion cells must be designed with scrupulous attention to safety.

 

Battery packs

Any battery power source for use in an autonomous underwater vehicle will contain multiple cells connected in series and/or parallel arrangements to provide the required voltage and current. The complications involved in connecting cells together in a pack must be considered when the cost, performance and reliability of the power source are being evaluated.

Each of the points at which cells are connected together is a potential source of impedance in the power source. The number of such interconnections should thus be minimized where possible. Failure of an individual cell can lead to over discharge of that cell within a series string, or to accidental charging in arrangements with parallel strings. Appropriate arrangements of series or parallel diodes should be provided to prevent these hazards. Fuses should also be used to prevent the risk of excessive current being drawn from a string of cells. In light of all of these considerations it is clearly desirable to minimize the number of cells in a pack where possible. Higher voltage cells are highly advantageous that can allow fewer cells to be used, with fewer interconnections and simpler arrangements of safety devices. The use of secondary cells adds additional complications to the pack design. Lithium ion cells in particular require voltage control at the individual cell level. The lithium ion cells that will be used in a pack must be carefully selected because small variations in cell impedance or capacity can lead to a situation where an individual cell is subject to overcharge, with potentially hazardous results.

Information that needs to be defined as the basis of a battery pack design includes the following:
• Physical dimensions
• Upper and lower voltage limits
• Peak current loads and durations
• Service life (capacity)
• Service and storage temperatures
• Other physical requirements (e.g., shock and vibration, external pressure)
• Regulatory compliance (e.g., ROHS)
• Connector configuration(s)

Environmental issues

All batteries will eventually be disposed of, and the ultimate fate of the battery materials should be taken into account when considering the true cost and the environmental impact of the various battery technologies. Rechargeable batteries can clearly be advantageous that they can be reused. However, because the capacity of secondary cells is lower than similar primaries, the secondary may need to be used several times to deliver the same energy as the primary. The harmful effects of the toxic heavy metals in lead acid and nickel cadmium batteries are well known. Recycling programs for both of these technologies are well established, however, the potential hazards are well controlled. Nickel metal hydride cells do not contain acutely toxic metals, but nickel is also considered a contaminant at high concentrations, so these cells must also be recycled. The various lithium ion systems are generally considered more benign. The organic carbonate electrolytes are typically biodegradable. The metal oxide cathode materials are not acutely toxic, though both nickel and cobalt can be harmful at high enough levels. Recycling of lithium ion cells is likely to become mandatory throughout the industrialized world in the future. The mercury that was formerly added to the anode in alkaline cells was eliminated throughout the industry in the early 1990’s. The components of contemporary alkaline cells are quite benign, and these cells are typically disposed of in conventional landfills. The disposal of lithium primary cells, particularly larger sizes, is best handled by hazardous waste specialists to minimize dangers that might arise from unused lithium remaining in the cell. In the lithium oxyhalide batteries, all of the active materials in an un-discharged cell are acutely hazardous. Proper neutralization of the active materials in these cells, however, results only in simple inorganic ions (e.g., sulfate and chloride); in this regard the lithium oxyhalide chemistries are unusually friendly to the environment.

Conclusions

Different types of AUV’s can have very different requirements that should be taken into account when a battery power source is chosen. Primary batteries are best for missions that require maximum service life, while secondary batteries can be attractive in cases where the batteries can be recharged between missions. Pack designs that use as few cells as possible are generally desirable. Finally, the costs of disposal and the long-term environmental effects of different battery technologies should be considered when calculating the true cost of the power source.

References

1. D. Linden, T. B. Reddy, Handbook of Batteries, 3rd Ed., McGraw-Hill, New York, 2002, pp. 7.10-11. See also tables elsewhere in this volume.

2. M. Williams, IDG News Service, “Sony details battery problems,” InfoWorld, Oct. 24, 2006: http://www.infoworld.com/article/06/10/24/HNsonydetailsproblem_1.html

3. Information about the hazardous effects of potential contaminants can be found in the US EPA Integrated Risk Information System (IRIS) database: http://www.epa.gov/iris/index.html

 

 

Point to Point Communication using Digi RF Module

By: Mad Helmi Bin Ab. Majid (PhD Student)

 

In this article, we are going to discuss about the point-to-point communication between two RF Modules (In this case Digi Xtend). The setup for testing is shown in Figure 1 for both receiver module and transmitter module. Here we use Arduino Mega 2560 as the host to the modules.

Figure 1 Transmitter and Receiver pin configuration

 

Note for point-to-point communication, default configurations can be used unless we would like to specified receiving and transmitting address which usually set for security purpose and avoiding signal interference. This change can be performed using XCTU software as shown in Figure 2. In this case only module with address of FFF could communicate with module with address of FF and vice versa.

 

Figure 2 XCTU configurations for point to point communication

 

After connection, we program the Arduino board as follow:

 

 

To ensure success of the testing connects the Receiver Arduino to a computer, open Arduino IDE serial monitor and select the corresponding port. If the connection is correct and no error occurs, the following result should be observed in the serial monitor:

123412341234123412341234….

 

In the next article, we will discuss point-to-multipoint communication and followed by peer-to-peer communication.