Browsing by Author "Ruponen, Pekka"
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- Accident susceptibility index for a passenger ship – A framework and case study
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-02-01) Montewka, Jakub; Manderbacka, Teemu; Ruponen, Pekka; Tompuri, Markus; Gil, Mateusz; Hirdaris, SpyrosThe continuous monitoring and assessment of operational vulnerability and accident susceptibility of passenger ships is crucial from the perspective of ship and passenger safety. Despite the existing solutions for vulnerability monitoring, stemming mainly from watertight door operations, a comprehensive framework for accident susceptibility assessment and monitoring is missing in the literature. Therefore, this paper offers a straightforward approach, utilizing heuristics rooted in the solid foundations of the first principles related to human performance. The proposed approach allows the evaluation of accident susceptibility of a ship in operation involved in open-sea and coastal navigation. The framework presented is based on observable and relevant factors, known to affect the navigator’s performance, and as a consequence accident probability. The layout of the framework as well as the parameters of the developed model are based on literature survey in maritime and aviation domains, knowledge elicited from maritime experts and extensive simulations with the use of an in-house developed ship-ship encounter simulator. Subsequently, the model is applied to selected case studies, involving two distinctive ship types, namely a large cruise ship and a RoPax vessel. The results obtained for the case study presented in this paper reveal that most of their time the analyzed ships operate with negligible accident susceptibility (87%), while 1% of the cases are labelled as very high accident susceptibility. The remaining share of 12% is distributed among low, moderate and high values of accident susceptibility. The results are in line with earlier studies conducted in the same area but adopting different methods. The proposed solution can be applied as an onboard decision support tool, evaluating the operational accident susceptibility and vulnerability, thus increasing the crew’s situational awareness. Additionally, it can be applied to historical data, allowing ship navigational safety diagnosis and implementation of appropriate countermeasures. - Advanced Damage Stability Analyses for Design of Cargo Ships
A4 Artikkeli konferenssijulkaisussa(2021-01-01) Lindroth, Daniel; Tompuri, Markus; Ruponen, Pekka; Haruyama, Makoto; Alway, AqmilWhile the development of stability regulations mainly has been driven by the needs for passenger ships, cargo ships are also getting an update in the newly adopted amendments to the Safety of Life at Sea (SOLAS) convention. The stability at intermediate flooding stages have previously been ignored for cargo ships, but if the ship is equipped with cross-flooding devices, intermediate filling phases will now be evaluated. In this study, the relevancy of these intermediate stages for cargo ships is investigated. The focus is on a case study of a short sea ro-ro cargo ship with cross-flooding ducts in the double bottom. In addition to the conventional regulatory calculation methods, also time-domain flooding simulation is used for realistic assessment of intermediate stages and the actual time-to-flood. Such tools have previously been used for damage stability analyses of passenger ships. The different calculation methods are compared against each other through the attained subdivision index. The results indicate that cross-flooding improves damage stability also for cargo ships, and that simulation is an applicable tool also for design and analysis of safer ships. - Aktiiviset toimenpiteet vuotavan laivan vakavuuden parantamiseksi
Insinööritieteiden korkeakoulu | Bachelor's thesis(2021-04-30) Julin, Emilia - Laskentamenetelmä ruoripotkurilaitteen ohjailuvoimille hybridipropulsiossa
Helsinki University of Technology | Master's thesis(2003) Ruponen, PekkaHybridipropulsiolla tarkoitetaan tässä työssä akselilinjan päässä olevan työntävän potkurin ja sen taakse sijoitetun vetävän ruoripotkurilaiteen muodostamaa järjestelmää, jossa potkurit pyörivät vastakkaisiin suuntiin. Työssä on kehitetty yksinkertainen, kirjallisuudessa esitettyihin teorioihin pohjautuva laskentamenetelmä ruoripotkurilaitteeseen kohdistuvien voimien arvioimiseksi. Laskennassa ruoripotkurilaite jaetaan neljään osaan: pyörivään potkuriin, varteen, moottoripesään ja alaevään. Osien väliset vuorovaikutukset on otettu huomioon yksinkertaistettuina. Menetelmän lähtökohtina ovat ruoripotkurilaitteen potkurin avovesikäyrät ensimmäisessä kvadrantissa sekä laitteen rungon yksinkertaistettu geometria. Varsi ja alaevä ovat tyypillisiä kantopintoja, joten niistä aiheutuvien voimien laskentaan sovelletaan lineaarista kantoviivateoriaa pyörrehilamenetelmällä. Moottoripesän voimien laskennassa sovelletaan pyörähdyssymmetrisille kappaleille kehitettyä ns. Allenin menetelmää. Viskoosivastuksen laskentaan käytetään ns. ITTC-57 -menetelmää, ja osien välistä interferenssivastusta approksimoidaan Hoernerin esittämällä lausekkeella. Potkurivoimat lasketaan Navier-Stokes -yhtälöihin perustuvalla menetelmällä ja ns. Gutschen menetelmällä. Siten myös näiden menetelmien soveltuvuutta on voitu vertailla. Menetelmän validointiin käytetään laajan mallikoeohjelman tuloksia. Poikittais- ja pitkittäisvoimat saadaan laskettua suhteellisen tarkasti, kun potkurivoimien laskentaan käytetään Navier-Stokes -yhtälöihin perustuvaa menetelmää. Kuitenkin kääntömomentti ja potkurimomentti saadaan laskettua tarkemmin Gutschen menetelmää käyttäen. Laskentamenetelmän tarkkuus paranee merkittävästi potkurin kuormituksen kasvaessa. Menetelmä soveltuu paremmin pelkälle vetävälle ruoripotkurilaitteelle. Tulokset ovat kuitenkin lähes yhtä hyviä hybridipropulsiossa. - Computational analysis of brash ice and flow field around simplified body
Insinööritieteiden korkeakoulu | Master's thesis(2023-05-15) Voutilainen, JuhanSea ice on the arctic waters has been decreasing in the past years, opening up possibilities for more economically feasible shipping in the area. In these waters, commercial ships are commonly navigating through icebreaker made brash ice channels. The growing interest in this area increases the need for efficient methods for predicting the interaction between ship and ice. In present days, this interaction is primarily studied with the model scale tests, which perform well for level ice, but have limitations related to the brash ice. This thesis studies the feasibility of applying coupled computational fluid dynamics and discrete element method approach for modelling the ship-ice interaction. Simulations are conducted with commercial software StarCCM+. To keep focus on the ship-ice interaction, and to make the comparison with conducted model tests simple, simulations are conducted with simplified ship-like geometry. The primary goal is to achieve good qualitative results for the trajectories of the ice particles. The secondary goal is achieving realistic resistance values. Even though some issues at lower velocities are still present, the studied CFD-DEM method is proving itself as a potential tool for modelling a ship in a brash ice channel. Especially for simple cases, with Froude number exceeding the value of 0.13, the potential is obvious, and the method could be used alongside traditional model tests. With some additional work, the method could be expanded to lower velocities as well. - Damage Stability of Ships
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2023-06) Ruponen, Pekka; Papanikolaou, Apostolos - Decision support system for countermeasures in cruise ship flooding case
Insinööritieteiden korkeakoulu | Master's thesis(2018-08-20) Peltola, HenriSeveral decision support systems have been developed during the last about ten years to assists crews of both naval and passenger ships in the decision making process during a flooding incident. NAPA Emergency Computer is a decision support system developed by Napa Ltd. for passenger ships to monitor the vulnerability of the ship and conduct a flooding prediction and a survivability assessment if ingress water is detected by the ship’s flooding sensors, and to which this thesis focuses on. There is not yet a system which would reliably combine risk assessment and flooding prediction features to a countermeasure advice to improve the situation on board. Thus, the objective of this thesis is to identify the most feasible counteractions on a cruise ship to combat a flooding situation enhancing the survivability of the ship and to be able to present these in a prototype graphical user interface of NAPA Emergency Computer. Feasible counteractions are identified from the reviewed accidents and the scientific literature. The most promising countermeasure to prevent progressive flooding and especially up-flooding after closing of watertight doors is closing of certain fire doors. The effect of that on the development of a flooding case is studied with simulations in NAPA ship design software through four probable extensive damage cases a cruise ship can encounter and with different fire door statuses. The simulations showed that closing of fire doors on the bulkhead deck above the damaged compartments between staircases and the service corridor has a very significant effect on increasing the time-to-capsize, in the best case with several hours by closing only one fire door in the SHOULDER 1 case. A logic for suggesting the right fire doors to be closed is formed in the end of the thesis and the countermeasure advice is sketched to a prototype graphical user interface of NAPA Emergency Computer. - Determination of propeller cavitation inception diagram by numerical methods
Insinööritieteiden korkeakoulu | Master's thesis(2022-03-21) Tran, VanThe thesis looks into different cavitation types on marine propellers and prepare to numerically simulate the cavitation inception diagrams which are conventionally available by conducting cavitation tests. Sheet and bubble cavitations are the main focus in this thesis. Panel method was employed and embedded in the numerical tool named ProCal. The simulation conditions and result post-processes are defined by meaning of Matlab scripting. The produced diagrams are later verified using a viscous flow solver (StarCCM+) and validated with model test results. The overall result indicates that the scripts meet the defined expectations and exceed its scope when attempting to show vortex cavitations. As the scripts were written in backward order to meet the validation stage first, the verification stage brings out different perspectives that aid in understanding the produced diagram comprehensively. Disparities between numerical methods (ProCal and StarCCM+) versus model tests are addressed and analysed. - Effect of flooding sensor arrangement on automatic breach assessment for damaged passenger ship
Insinööritieteiden korkeakoulu | Master's thesis(2016-08-22) Takkinen, EsaDecision support systems can help ship’s crew to do right decisions in an emergency situation. There are many decision support systems being developed and some are already in use both in passenger ships and in navy ships. Most of the systems are developed for navy vessels. NAPA Emergency Computer is a decision support system that monitors ships vulnerability in normal situations and ships survivability in emergency situations. IMO rule requires modern passenger ships, constructed after July 2010, to have a flooding detection system. NAPA Emergency Computer uses this system to automatically detect breaches and do progressive flooding calculation. For the system to work as well as possible the location and number of the sensors is very important. This master thesis studies three different sensor arrangements in six different damage situations and studies how well NAPA EC will perform with each sensor arrangement. Damage situations were selected to represent likely accidents which a cruise ship can suffer, such as collisions with other ships and groundings. The studied sensor arrangements were one minimal sensor amount, which covers the IMO regulation in its minimum, NAPA’s recommendation, where each water tight compartment has at least two sensors each deck and one where all the large compartments below the bulkhead deck had a flooding sensor, this version also had sensors on bulkhead deck. Reference simulations were made with NAPA software and from the reference simulations artificial sensor data was produced for all the sensor arrangements. This data was inserted to NAPA Emergency Computer server and the calculation results were compared. Minimal sensor arrangement had a lot of problems on placing the breached in right places and locations. This made the prediction wrong for long time. When the flooding progressed and the compartments started to fully flood the predictions started to be more accurate. The NAPA’s sensor arrangement performed well in all the situations and additional sensors below the bulkhead did not affect the prediction as much. In the situations when flooding progressed on to the bulkhead deck the additional sensors provided additional information to prediction. However this is already very critical situation and in many situations the capsizing of the ship happens soon after this. For this reason sensors above the bulkhead deck don’t provide much information. - Ehjän laivan vakavuusvaatimusten kehitys
Insinööritieteiden korkeakoulu | Bachelor's thesis(2023-11-29) Haapanen, Aleksanteri - Evaluation of commercial computational fluid dynamics codes in aerodynamic analysis of transonic flows over wings and airfoils
Insinööritieteiden korkeakoulu | Master's thesis(2020-12-14) Laitinen, MarkusComputational Fluid Dynamics (CFD) is an ever-growing field of study as computational resources become higher and ever so accessible for average users. Due to the increasing costs in energy consumption, traditional methods, such as wind tunnel testing, become less attractive in aerodynamic analysis. Over the past few decades, many commercially available CFD codes have been evolved. The two most commonly utilized commercial software, providing such codes, are Simcenter STAR-CCM+ by Siemens Industry Software Inc. and Ansys Fluent by Ansys Inc. This thesis evaluates the applicability of STAR-CCM+ and Ansys Fluent in transonic aerodynamic analysis based on two different criteria: accuracy and efficiency. The accuracy is measured using four different aerodynamic coefficients: lift, drag, pressure and skin friction coefficients. The results are compared to those obtained by wind tunnel testing and previously verified and alidated CFD code FINFLO. The efficiency is evaluated measuring CPU time and the amount of memory in use both in single- and multi-core calculations. The results indicate that both STAR-CCM+ and Ansys Fluent are capable of producing accurate results with decent efficiency. In addition, the possibility to run overset mesh simulations was examined. The solvers were concluded to perform well also in this aspect, which indicates that the solvers are capable of calculating more complex geometries in further studies and testing. - Evaluation of flooding simulation as a ship design tool
Helsinki University of Technology | Master's thesis(2006) Vartiainen, MikkoTämän diplomityön tavoitteena on tutkia aikatason vuotosimuloinnin käyttöä laivansuunnittelussa. Työssä keskitytään Pekka Ruposen simulointi menetelmään, joka on osa NAPA:n laivansuunnittelu ohjelmistoa. Laivan vauriovakavuutta tutkitaan eri näkökulmista. Tämä tehdään tutustumalla alan aikaisempaan tutkimukseen, onnettomuusraportteihin ja vauriovakavuuden sääntöihin. Laivansuunnittelijoita haastattelemalla selvitetään heidän tarpeensa koskien vuodon simulointia. Ruposen menetelmän perusteet, reunaehdot, tarvittavat muuttujat ja rajoitukset käsitellään. Eri muuttujien vaikutus selvitetään tekemällä esimerkkisimulointeja isolla matkustajalaivalla. Ohjeita laivan yksityiskohtien mallintamiseksi esitellään, Lisäksi selvitetään, miten simuloinnit voidaan tehdä mahdollisimman tarkasti ja tehokkaasti. Laivateollisuus on kiinnostunut vuotosimuloinnista. Vuotosimulointia tarvitaan tuvallisuustarkasteluihin ja vauriovakavuuden erikoistapausten tutkimiseen. Lisäksi laivan asuttavuudelle vaurion jälkeen on esitetty kolmen tunnin aikarajaa ja vuotosimulointi on ainoa numeerinen menetelmä, jolla vuotoaikoja voidaan laskea. Vuotosimuloinnilla on useita hyviä puolia verrattuna muihin vauriovakavuutta arvioiviin laskentamenetelmiin. Esimerkiksi vuotosimulointi lisää laskentatarkkuutta vuodon välivaiheita laskettaessa tai tapauksessa, jossa ilma puristuu vuotavassa osastossa. Vuotosimuloinnin todettiin soveltuvan laivansuunnittelun apuvälineeksi, kunhan sen rajoitukset laskennassa otetaan huomioon. Jatkotutkimukset tarkkojen simulointiparametrien määrittämiseksi ovat kuitenkin tarpeen. - Evaluation of simplified methods for judging intact stability of ships in waves
School of Engineering | Master's thesis(2013) Tompuri, MarkusIn this thesis vulnerability to intact stability failures of ships in waves was studied with simplified calculation methods. Three modes of stability failure were investigated; parametric roll, pure loss of stability and surf-riding/broaching to. This study was done following the guidelines of IMO Second Generation Stability Criteria, as it was presented in SLF55. Physics behind the each abovementioned stability failure modes were explained along with derivation and reasoning of the simplified calculation methods. Evaluation of stability with these methods was done with using one degree of freedom calculation methods. Sample calculations were carried out with 9 sample ships to evaluate the methods. Ships represented multiple different ship types. Method presented in this thesis was proven to produce a lot of valuable data about ships performance in rough conditions with relatively simple calculations. Largest conceptual inconsistency from the methods was found from vulnerability check for parametric roll, where vulnerability was addressed only in predetermined speeds and critical speeds might not be discovered. An alternative approach was suggested, where the focus would be on discovering the critical speeds for different parametric roll regions. - An evaluation of the probabilistic damage stability of a ship by time domain flooding simulation
School of Engineering | Master's thesis(2013) Simojoki, LassiThe objective of this thesis was to compare the results of calculating the probabilistic damage stability of a large passenger ship purely according to the SOLAS 2009 rules, to the results where the progression of floodwater is evaluated using time domain flooding simulation. The main focus of the study was to investigate what effect the more realistic progression of floodwater through cross-flooding devices and A-class fire rated and cold room structures have on the results. The study was carried out using the naval architecture software NAPA with a model of a 125 000 GT large passenger ship. The aim was to find which kinds of situations flooding simulations can be used and in which situations the rules correspond sufficiently to the realistic progression of the flooding. In addition the results were used to consider the suitability of using a time domain flooding simulation tool to carry out rule calculations. The A-class and cold room doors below the waterline tended to collapse immediately due to a high pressure head, whereas those closer to and above the waterline did not collapse, but seriously restricted the flow of water. In damage cases where there were A-class structures and cross-flooding devices involved, flooding through these occurred simultaneously, but at least in the case study ship this did not seem to have a significant effect on the results. However, the results indicate that at least for the case study ship, the attained subdivision index, which represents the damage stability of a ship, would be higher when calculated using time domain flooding simulation. The flooding simulation tool used in this thesis was found to be suitable for use in probabilistic damage stability calculations. Flooding simulation can especially be used to predict the actual order of flooding and therefore cut down the number of intermediate flooding stages generated due to A-class structures. On the other hand flooding simulation does not bring added value to simple damage cases, where there are no A-class structures or cross-flooding devices. - Flooding of a naval vessel
School of Engineering | Master's thesis(2010) Kurvinen, PerttuIn this thesis, the phenomena affecting the flooding of a naval vessel was studied utilizing the results given by full-scale experiments and calculations. The flooding calculation for a vessel includes parameters, such as room permeability and discharge coefficient of an opening, that vary for each case. In the reference literature some recommendation to estimate these parameters can be found but the exact values are often not known. The experiments consisted of three different flooding cases. The largest case included two watertight compartments. The heel and the trim angle of the vessel, water levels, and flow speeds inside the vessel were measured constantly. In addition, in one case the air overpressure was measured. The results obtained from experiments were compared with the results given by some basic calculations and with the results given by a simulation tool, NAPA flooding simulation. In the simulations, two different sets of values were used for permeability and discharge coefficients. The first values were those initial ones presented in literature and the second values were manually selected, "optimized" values, according to simulation results. The basic calculations gave good correspondence to the measured final heel angle of the vessel when the added weight method was used. With the lost-buoyancy method the difference was somewhat bigger, probably due to some inaccuracies in the calculation parameters and simplifications of the method. The NAPA flooding simulation gave similar results compared to the measurements with both initial and optimized parameters. With the optimized parameters the results were in most cases very close to the measured results. The effect of air compression was clearly demonstrated in the experiments. Thus, it is advised to take the air compression into consideration when flooding includes rooms where noticeable air compression can take place. According to the calculations, the initial flooding calculation parameters can be used to achieve at least rough estimates of the flooding process. The more reliable parameters should be used to confirm the accuracy of the results. The IMO Resolution MSC.245 (83) was confirmed to be a good approach to calculate discharge coefficients for air pipes. - A framework for onboard assessment and monitoring of flooding risk due to open watertight doors for passenger ships
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-10) Ruponen, Pekka; Montewka, Jakub; Tompuri, Markus; Manderbacka, Teemu; Hirdaris, SpyrosPost-accident safety of ships is governed by damage stability, affected by watertight subdivisions which limit accidental flooding. This is important for passenger ships with watertight doors (WTDs) often fitted in the bulkheads. Awareness of the ship flooding risk due to open WTDs and the conditions under which the associated risk level changes are prerequisites for proactive risk mitigation. Accident risk is often expressed as a combination of accident likelihood and its consequences. Current solutions for flooding risk mitigation often treat these elements separately, or the adopted metrics are based on quantities not allowing proper active control of risk. In this paper an attempt is made to fill this gap by introducing a novel concept for rapidly assessing the flooding risk onboard passenger ships, accounting for the two dimensions of flooding accidents. The likelihood part is based on the complexity of surrounding traffic, operational conditions, and human reliability assessment. The consequences are based on precalculated probabilistic damage stability results of ship survivability. The presented case studies indicate that active monitoring of flooding risk can increase the crew's situational awareness of the effect of open WTDs on the flooding risk, thus positively influencing the safety culture onboard the ship. - International benchmark study on numerical simulation of flooding and motions of a damaged cruise ship
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-12) Ruponen, Pekka; van Basten Batenburg, Rinnert; van't Veer, Riaan; Braidotti, Luca; Bu, Shuxia; Dankowski, Hendrik; Lee, Gyeong Joong; Mauro, Francesco; Ruth, Eivind; Tompuri, MarkusLarge cruise ships can carry 10 000 persons onboard, and consequently, survivability of the ship in the event of a flooding accident is essential. Many designers are already conducting advanced damage stability analyses beyond the regulatory requirements. With increased computing capacity, survivability analyses, by using time-domain simulation tools, are already commonly applied in the design of new cruise ships. Consequently, it is essential that such tools are properly validated, in terms of ship response and detailed flooding behavior, to assess the capability and applicability of the tools. For this purpose, an international benchmark study on simulation of flooding and motions of damaged cruise ships was conducted within the EU Horizon 2020 project FLARE, using experimental data from new dedicated model tests as a reference. The test cases include transient and progressive flooding, both in calm water and in irregular beam seas. The results indicate that capsize is properly captured by simulation codes, but there are notable differences in the flooding progression and capsize mechanisms, especially when flooding takes place in high waves. - Kalastusalusten vakavuus aallokossa
Insinööritieteiden korkeakoulu | Bachelor's thesis(2021-12-05) Metsola, Janika - Kelluvien offshore-rakenteiden vakavuuslaskenta
Insinööritieteiden korkeakoulu | Bachelor's thesis(2020-11-11) Lokka, Eelis - A literature review on model tests for flooding and motions of damaged ships
A2 Katsausartikkeli tieteellisessä aikakauslehdessä(2025-02-03) Ruponen, PekkaDuring the past decades, experiments with scale models have been widely conducted to study the flooding process and motions of damaged ships, both in calm water and in waves. Survivability tests in irregular beam seas have been well-established and widely used, also commercially, to verify the compliance with the so-called Stockholm Agreement regulatory requirements. However, model tests for both transient and progressive flooding modes have mainly targeted at obtaining experimental data for validation of numerical simulation methods. This is becoming more important as increased computing capacity has enabled practical use of first principle tools for assessing damages stability. In this review, the different model test types and typical experimental setups are analyzed. In addition, the applied scales factors are studied and some research gaps are pointed out. Despite notable achievements in the past, further model tests are still considered essential for obtaining reliable experimental data on certain flooding mechanisms. Consequently, some recommendations for future experiments are also given.
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