Browsing by Author "Naar, Hendrik"

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The Application of the Redistribution Node Method to Plastic Analysis of Ship Structures
(2000) Naar, Hendrik
Helsinki University of Technology | Licentiate thesis
Buckling analysis of stiffened plate structures in ships using screening approach
(2009) Töns, Tönis
Helsinki University of Technology | Master's thesis
Tukivoimien mallinnus offshore-rakenteen merikuljetuksessa raskaslastialuksella
(2004) Taponen, Tomi
Helsinki University of Technology | Master's thesis
Diplomityön tavoitteena oli määrittää tukivoimien jakautuminen offshore-rakenteen merikuljetuksessa raskaslastialuksella. Tukirakenteiden välittämät tukivoimat laivan ja lastin välillä ovat lähtökohta rakenteiden äärilujuustarkasteluille. Tuenta ottaa todellisuudessa vastaan vain puristuskuormia ja kuljetettava offshore-rakenne saattaa osittain irrota aluksen kannelta. Työssä perehdyttiin yksityiskohtaisemmin epälineaarisen tuennan mallintamiseen kontaktielementeillä. Mallinnuksella pyrittiin selvittämään tukivoimien jakautuminen ja niiden suuruus tyynenveden kuormilla ja suunnitteluaallonkorkeudella eri aallon taajuuksilla. Työssä rajoituttiin tarkastelemaan ainoastaan aluksen pitkittäissuuntaista tukivoimajakaumaa. Lisäksi työssä selvitettiin, mitä vaikutusta tukien sijainnilla ja tukien lukumäärällä oli tukivoimien jakautumiseen. Jotta tukivoimien jakautuminen voitiin määrittää, tuli rakenteiden globaalit ja lokaalit jäykkyydet tuntea. Globaaleilla jäykkyyksillä tarkoitetaan laivan ja spar-rakenteen taivutusjäykkyyksiä. Lokaaleilla jäykkyyksillä tarkoitetaan rakenteiden paikallisia muodonmuutoksia tukirakenteiden kohdalla. Rakenteiden jäykkyydet laskettiin I-DEAS -elementtimenetelmäohjelmistolla. Lopullinen laskenta-analyysi tukivoimien määrittämiseksi tehtiin Ansys-elementtimenetelmäohjelmistolla, jossa laiva ja spar-rakenne mallinnettiin palkkielementeillä ja niiden välinen tuenta kahden solmun välisillä kontaktielementeillä. Rakenteisiin kohdistuvat harmoniset aaltokuormat ja kiihtyvyydet muodostavat kuormitussyklin, joka jaettiin useaan kuorma-askeleeseen, joille kullekin laskettiin staattisella analyysillä tuki voimat. Tulosten mukaan voidaan helposti ja nopeasti sanoa, miten tämän tutkimuksen päämittojen spar-rakenne kannattaa tukea laivan kannelle. Tuloksista voidaan päätellä, ettei spar-rakenteen sylinteriosaa kannata tukea koko pituudeltaan. Lisäksi ristikkorakenteen tukeminen kannattaa tehdä ainoastaan yhden kohoilunvaimennustuen avulla. Tulosten suuruusluokka täsmäsi aikaisemmin tehtyjen tutkimustulosten kanssa. Epälineaaristen kontaktielementtien käyttö osoittautui hyödylliseksi ja laskenta-ajat pysyivät iteroinnista huolimatta hyvin pieninä.
Design procedure for corrugated structures in cargo ships
(2012) Lodi, Marit
School of Engineering | Master's thesis
Corrugated bulkheads are commonly utilized structures in cargo ships. They can contribute up to 30% of the total steel weight of the cargo area constructions. Therefore, the design of the bulkheads is a vital issue in the concept design process. However, currently no efficient tool exists to guide this process. The classification society rule calculations for corrugated bulkheads have limited accuracy due to the varying rigidity offered by the surrounding structures. FEA is in general not used in the concept phase due to the large amount of work required for preparing an FE model. Thus, the designs are typically accomplished by referring to previously built vessels. In this thesis a method for designing and optimizing corrugated structures in pursuit of lower weight is derived. The optimization procedure is founded on direct strength analysis and constrained by CSR rules, defining initial scantlings limitations and FEA requirements. The optimization procedure development includes a study of the possibilities for conducting FEA on local structures in the concept design phase by utilizing an initial 3D product model. In addition, the feasibility of optimizing corrugated structures with algorithms available in the applied product model environment, i.e. optimizing with a deterministic algorithm (conjugate gradient algorithm) in relation to a probabilistic one (simulated annealing algorithm) is investigated.
Dynamic FE simulations of ship collisions
(2008) Pill, Ingmar
Helsinki University of Technology | Master's thesis
The goal of this thesis was to study the possibilities of modelling external dynamics of a ship collision using explicit finite element code LS-DYNA. LS-DYNA is widely used for studying inner mechanics of ship collisions, but has not been used for simulating external dynamics. Inner mechanics deals with the behaviour of structures in a collision, external dynamics concentrates on the motions of the colliding vessels. The proposed model enables to calculate external dynamics and inner mechanics in the same simulation run. The motions of the ships are constrained to the horizontal plane. Gravity, buoyancy and restoring forces were excluded from the model as was hydrodynamic damping. Emphasis was on modelling masses and inertia of the colliding ships in order to achieve accurate results for contact force. The striking ship was modelled as a rigid bulb with attached mass points. Structure of the struck ship in the collision area was modelled in detail, the other regions of the vessel were also modelled using properly placed mass points. Hydrodynamic added masses were modelled in a way that they are activated only in certain directions. The results of the LS-DYNA model were validated with data from model-scale collision experiments. Three collision cases were investigated. First, a symmetric collision at right angle, second an eccentric collision at right angle and finally an eccentric collision at inclined angle. Results of all three simulation cases showed good agreement with model test data, which implies that the model is valid.
Equivalent shell element for ship structural design
(2012) Avi, Eero
School of Engineering | Master's thesis
This thesis presents an equivalent shell element for assessing the ship global and local static and vibration response in early design phases. The stiffened plate is considered as a three layer laminate element, where the first layer represents the plate, the second layer the stiffener web and the third the stiffener flange. The layers are described as 2D iso- and orthotropic materials, where the elasticity matrices are found by applying the Rule of Mixtures. The element includes the extension, membrane-bending coupling, bending and additionally also shear stiffness, which follows the Reissner-Mindlin plate theory for anisotropic homogenous shells. The developed shell formulation has been implemented in commercial FE software FEMAP with NX Nastran and demonstrated in three study cases: stiffened plate, passenger ship cabin area and boxlike ship. The results were validated by comparison with those obtained from 3D fine mesh analysis. All studies show that with reasonable mesh density the laminate element can be used to obtain the static and vibration response of global and local ship structure. Four 4-noded elements per vibration shape have been found to be an optimal size to evaluate eigenvalues with less than 10 % error, which fulfils the industry requirements. Compared to other available equivalent elements, the present laminate element can also predict the normal and shear stresses in stiffener web and flange.
Fatigue assessment of ship structures in early design stage
(2008) Liigsoo, Margus
Helsinki University of Technology | Master's thesis
Generally ships fatigue assessment is done in detailed design phase with the help of FE analysis. This means that the modeling and calculations are time consuming processes. To improve this process a simplified fatigue assessment approach is generated. This means that the FE analyses are neglected and therefore it could be possible to use this method in earlier design stage. Instead of FE method the beam theory or CB method is used. In this work beam theory is applied. At first the fatigue critical connections are studied together with damage statistics of tankers. This data describes the most fatigue critical connections, their locations and the type of fatigue loading. This significantly constrains the data amount for fatigue assessment. Important part of fatigue assessment is to define local stresses in fatigue critical connections. For that the stress concentration factors are defined based on literature review. This allows transforming nominal stresses into local notch stresses at fatigue critical spots. From notch stresses the fatigue parameter damage ratio is obtained and finally the fatigue life is calculated for the fatigue critical connection. The method is evaluated in case study with FE analysis. The results showed good precision of simplified method and the uncertainties were on the safe side of the deviation. The method weak point is the lack to take into account shear loading as suitable stress concentration factors are complicated to predict.
Fatigue design of the connection between ship hull and modular staircase made of steel sandwich
(2008) Viljakainen, Siim
Helsinki University of Technology | Master's thesis
The purpose of the study is to understand the behaviour and calculate the fatigue lifetime of the connection between the staircase module made of steel sandwich and conventional steel structure. Furthermore the fatigue lifetime is calculated for the connection. The analysis is made for two different connection designs. To get a comparative result the fatigue lifetime is calculated according to the geometrical and effective notch stress approaches. The analysis procedure consists of different stages. First the data from existing global FE analysis ship model is obtained. The data is used in the next stage, where the staircase model made of steel sandwich is modelled for FE analysis with the surrounding bulkheads. From the critical area obtained in the second stage two local FE models with different designs are made. According to local model's results fatigue analysis is carried trough. The comparison of the results obtained with different methods support the need for precise methods when fatigue analysis is under consideration. The difference was several times, though the result received with less precise method was feasible, because the fatigue lifetime received with this was smaller than the result received with the other method. The reason for it is the approximation and linearization of stresses in less precise method. Suggestions for further investigations are also given to understand the behaviour of the whole module if fatigue lifetime is under consideration.
Fatigue load assessment procedure for floating production storage and offloading unit
(2009) Lillemäe, Ingrit
Helsinki University of Technology | Master's thesis
A spectral fatigue load assessment procedure has been developed and implemented for fatigue analysis of FPSO (Floating Production Storage and Offloading unit) hull structures. The advantages/ influences that this time consuming approach may bring to an everyday design practice in comparison with traditional rule based method have been investigated. The procedure is based on linear theory, which means that the response is changing linearly with respect to the excitation (wave height). Wave loads have been calculated with linear 3D panel diffraction/ radiation frequency domain program, which uses source distribution (boundary integration) method. Only hull girder vertical wave bending moment is taken into account. Long-term prediction of vertical wave bending moment has been obtained by weighing several short-term predictions with their occurrence probabilities. Different operational and environmental conditions have been taken into account. Each short-term process has been assumed to be narrow banded stationary Gaussian random process, which follows Rayleigh distribution. Real fatigue damages/ lives are not calculated, the comparison has been made on fatigue load level and also on relative fatigue damage level. Relative fatigue damage is calculated assuming that fatigue loads and fatigue stresses are linearly related. Different effects on the long term load predictions were investigated and main findings are:. Spectral method predicts similar results with the rule based method, when the North Atlantic wave scatter data is used and all wave headings are equally probable. This is expected, since DNV rules also assume uniformly distributed wave headings and the worst possible environment - the North Atlantic. This shows that the procedure can reliably he applied for other conditions as well. Using North Atlantic wave scatter data gives expectedly higher fatigue loads compared with the milder FPSO environment. This results in average 16 times longer fatigue life at the used milder FPSO environment. The highest VWBM comes from the head and following seas and the lowest from the beam seas. FPSOs usually head to the waves, since motions are then smallest, which is very important from the normal operation viewpoint. Using short crested sea model gives more favourable design loads for FPSOs, since it spreads the wave energy more realistically around the main wave direction. Equally distributed wave directions predict lower fatigue loads compared with the case where 95 % of the time waves are coming from the bow. The number of wave headings considered does not influence the results significantly. In addition, the necessary steps towards full stochastic fatigue analysis were taken. Wave loads (pressures and 6 d.o.f. accelerations in COG) were transferred directly from hydrodynamic analysis to structural model including automatically all the local and global load effects and phase information. The accuracy of the transfer process was studied. Stress level full spectral fatigue analysis is, however, out of the thesis scope.
Higher-order coupled beam theory
(2020-10-19) Imala, Mikk-Markus
Insinööritieteiden korkeakoulu | Master's thesis
Today, more and more cruise ships are built every year. As the market expands, so change the requirements from new-build vessels. Typically, this means the increase in ships gross tonnage, which requires an increase in dimensions, or more complex structures due to the desired design. Despite the requirements set by the industry, the ship's internal and external structures must provide a safe voyage for passenger and the crew. In standard ship design practice, initial strength evaluation is performed with a small amount of structural detail, for which there are numerous different methods. This thesis introduces a new shear deformation theory designed for accurate assessment of global displacements and stresses. The theory utilises a beam element with 6 variables defined in each beam element node. Deflection and rotation of cross-section is defined at reference line, where as displacement due to shear and axial forces and shear deformation is defined in beam element bottom surface and top surface separately. Approximations are presented so that variables could be described over the length and width of the beam elements. Coupling of beam elements in the global matrix has been presented for the holistic behaviour of the beam theory. The thesis provides a comparative analysis between higher-order shear deformation theory calculations and FEM results performed with NX Nastran on two structures, first of which is a simple box structure and second is a nonuniform beam model, where three layers of beams are of different length. The analysis shows a very good coincidence between analytically calculated displacements and stresses and FEM results for the box struct and between displacements for the nonhomogeneous structure and FEM results. In nonhomogeneous beam element configuration, the theory proved to lack the capability of assessing peak stress values and showed deficiencies in describing vertical stress distribution. Based on the results, the theory needs additional research to be done in terms of defining boundary conditions and element coupling to provide better results in the case of more complex structures.
Mechanics of the passenger ship structure with non-longitudinal-load-carrying accomodation decks
(2012) Parmasto, Oliver
School of Engineering | Master's thesis
The current thesis investigates a cruise ship structural concept which enables to use large interchangeable modules for interior outfitting. The structure has non-longitudinal-load carrying accommodation decks and a narrow deckhouse. The hull-deckhouse interaction and performance of the proposed structure under vertical bending is determined and compared to a conventional cruise ship structure which has internal longitudinal bulkheads for carrying the shear forces in the superstructure. The investigation is conducted by implementing Finite Element Method. The results indicate that the removal of the decks from the conventional cruise ship structure does not change the nature of the hull-deckhouse interaction. The responses of the compared structures were strongly affected by shear lag hull-deckhouse interaction induced secondary effects. It is also shown that the proposed structure can achieve the same stiffness under vertical bending as the conventional cruise ship structure while achieving smaller weight and the height of the vertical centre of gravity of the steel structure. The investigation assures that even at the early design phase, the Finite Element Method is the only reliable way to evaluate the response of the modern cruise ship structures.
Model tests of springing-type wave loads on cruise vessel in regular head seas
(2008) Linnas, Ragnar
Helsinki University of Technology | Master's thesis
Open water tests of twin-propeller podded propulsion system
(2010) Leppik, Kristjan
School of Engineering | Master's thesis
The purpose of this work is to study the influence of propeller characteristics with twin-propeller propulsion system to increase the propulsive efficiency. The propulsive efficiency can be presented as the product of three efficiencies: propeller efficiency, hull efficiency and relative rotative efficiency. The propeller characteristics are expressed by the propeller efficiency, therefore one solution to increase propulsive efficiency is to increase the propeller efficiency. The idea of this thesis is to test the propeller-to-propeller interaction in open water condition with different setup cases characterized by different distances between the propellers. Open water tests are conducted with 4 different setup plates and distances between the propellers, the rotational direction of propellers for each setup plate were inward and outward respectively, thus the total amount of test cases were 8. The shortest distance between the tips of propeller blades was 4.5mm and largest 40rnm. Two setup plates were arranged with straight positioned pods while the propellers were positioned side by side in the same plane and two setup plates were with 3° toe angle while the pods were turned inward. An overlapping arrangement is not considered in this thesis. The upstream flow is assumed to be ideal and equal with advance velocity. The thrust deduction of the pods is assumed to be constant and it is not considered either. Propellers are assumed to rotate in homogeneous flow and the wake generated by the pods is not considered. The test results indicate that there was only a minor difference of propeller characteristic values while changing the distances between the propellers.
A procedure to assess the crashworthiness of a LNG tanker side structure
(2010) Körgesaar, Mihkel
School of Engineering | Master's thesis
Ship collisions and groundings are one of the greatest operational risks in maritime transportation. Yet, accidental loading due to the collision and grounding is still superficially treated by the classification societies as they have enforced little generally accepted collision and grounding design standards. These standards are currently based on design objectives, for example, oil outflow standards or survivability standards and none of them are universally accepted. However, approval procedure presented by Germanischer Lloyd (GL) aims to improve ship side structures through novel crashworthy structural arrangements. Therefore, this thesis outlines a procedure to obtain an optimized crashworthy conceptual side structure and as a case study this procedure is applied to a liquefied natural gas (LNG) tanker. Furthermore, the widely unknown crashworthiness of the LNG tanker is assessed considering the deformation restrictions of the containment system. A particle swarm optimization algorithm is utilized for the optimization of LNG tanker side structure. The classification society compliance of the conceptual design is checked through one characteristic service loading condition that is applied to the ship's hull girder. The collision simulations to assess the crashworthiness are carried out with the non-linear finite element solver LS-DYNA. An element length-dependent constant strain failure criterion is chosen to simulate possible rupture. As a result, one optimized conceptual side structure is compared with the initial rule-based concept and with the minimum weight concept. Thereby the influence of the structural concepts and the containment system restrictions on the crashworthiness is assessed and presented. It is shown that mass of the structure can be decreased while increasing the E/M ratio. Furthermore, modest increase in mass will result in considerable increase in collision energy. Therefore, this procedure considers accidental loading in the conceptual design stage and results with novel lighter structure absorbing more collision energy.
Shear-induced secondary bending response at balcony opening of passenger ship
(2011) Melk, Kaarel
School of Engineering | Master's thesis
Passenger ships with large balcony openings have complicated structural behaviour which does not follow the basic beam theory. Moreover, plates around the balcony opening can locally bend and therefore, experience large shear-induced secondary normal stresses whose values are much higher and more complicate to evaluate compared purely on the normal stress distribution over the cross-section of the hull girder. Currently, hull girder strength assessment is based on FE-analyses. Such kind of approach is time-consuming and therefore, does not fit with the structural optimization procedures. Thus, for concept design stage, simplified method should be developed for rapid response evaluation around the balcony openings. The aim of the thesis is to develop a simplified approach to estimate secondary response around balcony openings. It is assumed that this simplified calculation model with the global response analysis can considerably reduce the time spent on the nominal stress evaluation. The purpose of the simplified approach is to estimate the nominal stresses which can be later used with proper stress concentration factor in fatigue strength analyses at the ship concept design stage. Simplified approach is based on Timoshenko beam elements and calculations are conducted with FE-method. Deformation shape and boundary conditions for simplified beam model are studied and applied from global 3D FE-analyses of the hull girder. Simplified beam model is validated with corresponding plate model as this is relevant for ship side structure. Finally, response around balcony openings from different ship regions is estimated with simplified approach and results are compared with the global 3D FE-analyses. As a result, it is revealed that normal stresses are induced by shear and thus, considered as a secondary bending response. In conclusion, comparisons of normal stresses prove that simplified approach is valid for response evaluation in certain locations around ship balcony openings.
The stability of tankers at the intermediate stages of flooding
(2008) Saaliste, Artur
Helsinki University of Technology | Master's thesis
Tässä työssä on selvitetty vuodon välivaiheiden merkitystä säiliöalusten vakavuuteen vauriotilanteissa. Työn tärkein tavoite oli selvittää onko tarvetta laskea välivaiheita vakavuustarkastelussa vai riittääkö tasapainotilanteen tarkastelu. Työn toinen tavoite oli vertailla NAPAn tuloksia kirjallisuudesta saatavien approksimaatiokaavojen tuloksiin. Mahdollisimman kattavien tulosten saamiseksi käytettiin tarkastelussa neljää eri tankkerityyppiä, jotka olivat VLCC (Very Large Crude Carrier), Aframax, kemikaali- ja tuotetankkeri. Kaikilla tyypeillä laskettiin tulokset neljälle tai viidelle lastitilanteelle. Tutkimus tehtiin siten, että ensin tutkittiin vauriovakavuuteen liittyvät säännöt. Tämän jälkeen valittiin tankkerityypit ja tehtiin laskelmat NAPA ohjelmistolla. Lopuksi verrattiin NAPAn tuloksia professori Matusiakin oppikirjasta saatujen approksimaatiokaavojen pohjalta tehdyn laskentaohjelman tuloksiin. Tutkimus osoittaa että välivaiheilla ei ole merkitystä säiliöalusten vakavuustarkastelussa. Tulokset näyttävät että tasapainotila on lähes kaikissa vaurioissa pahin tilanne ja vain harvoissa vauriossa ovat välivaiheet hieman vakavampia kuin tasapainotila. Näissäkin tapauksissa erot ovat hyvin pieniä verrattuna tasapainotilanteeseen ja marginaali sääntöjen vaatimiin arvoihin suuri. Verrattaessa manuaalisesti laskettuja tuloksia NAPAsta saatuihin tuloksiin voitiin todeta, että arvot ovat lähellä toisiaan, myös välivaiheissa. Kun tarkasteltiin vain veden sisään vuotoa, tulokset olivat lähellä toisiaan, mutta kun tarkasteluun otettiin samanaikaisesti veden sisään vuoto ja lastin vuotaminen mereen tulokset NAPAn ja laskentaohjelman välillä erosivat toisistaan.
Sternship structure analysis for podded RoPax vessel
(2007) Varushkin, Sven
Helsinki University of Technology | Master's thesis
The purpose of the study is to develop a structural arrangement for the sternship region of a single-podded RoPax ship and additionally the feasibility to use twin-podded and CRP propulsion as an alternative solution in the same construction is studied. In the study a typical RoPax vessel is used. The most efficient way to fit Azipod propulsion into a RoPax vessel is above the maindeck. As twin-podded propulsion is too space-consuming and many lane meters will be lost, it is not used in calculations. As only Azipod region is studied, 18 m of sternship is considered in the analysis. FE-models of sternship are created and the missing structural areas are compensated by boundary conditions. Four different Azipod mounting block stiffening systems and three loading conditions depending on Azipod turning angle are applied to the model. This gives all together 36 different cases, which are studied. Values of equivalent stresses and deflections are calculated by FE-code FINNSAP. The biggest deflection value is obtained in case of CRP propulsion, when 8/45° frames stiffening system was used. It occurs at the mounting block, bottom shell and floors near to the mounting block. Also maximum Von Mises stresses exist in the mounting block region. In single-podded propulsion system with lower strut height (Hs.) all four stiffening systems are fulfilling the requirements for stresses according to class rules. Comparing with single-podded with higher strut height and CRP propulsion, this number is respectively three out of four and two out of four. To find the best stiffening system for CRP and single-podded propulsion system, the weight of mounting block polar arrayed structural elements is calculated and compared with maximum stresses. The bigger the speed is the more polar arrayed structural elements supporting the mounting block are needed. After 12 polar arrayed supports, the most efficient way to reinforce is increasing the bottom and maindeck plating thickness.
Toward the application of the layer-wise displacement theory in passenger ships—a quasi-static response
(2023) Imala, Mikk-Markus; Naar, Hendrik; Tabri, Kristjan; Romanoff, Jani
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
This paper introduces an application of the layer-wise displacement theory for response analysis of multilayer ship girders. Quadrilateral, 6-node finite membrane elements are used for which 8 displacement degrees of freedom at corners, and 4 shear strain degrees of freedom at mid-side nodes, are defined. This approach enables accurate estimates of the shear strain between adjacent layers with different stiffness. A simple cantilever beam, non-uniform stepped girder with constant layer stiffness, and uniform girder with varying stiffness is used in the validation analysis. An excellent agreement between the fine mesh finite element model and the proposed model is observed.
Ultimate strength of hull girder for passenger ships
(2006-03-10) Naar, Hendrik
Doctoral dissertation (monograph)
The ultimate strength of the hull girder for large passenger ships with numerous decks and openings was investigated. The collapse of the hull girder, composed of the hull itself and the superstructure, as compared to a single deck ship with a continuous structure, involves several important structural phenomena that complicate understanding of this process. In this study, a theory of a non-linear coupled beam method was created. This method enables one to estimate the non-linear response of a passenger ship with a large multi-deck superstructure subjected to longitudinal bending. The method is based on the assumption that the ship structure can be modelled as a set of coupled beams. Each deck in the superstructure and also in the main hull can be considered as a thin-walled beam with non-linear structural behaviour. These beams are coupled to adjacent beams with non-linear springs called vertical and shear members, modelling the stiffness properties of the longitudinal bulkheads, side shells and pillars. Special emphasis was placed on the modelling of the shear members. A semi-analytic formula of the load-displacement curve was developed by help of the non-linear finite element analysis. Also, the load-end shortening curves under axial load taken from the literature were validated with the finite element method. The reverse loading options are included into the behaviour of the structural members. The created approach allows the calculation of the normal stresses and vertical deflections in the arbitrary location of the whole hull girder. Average longitudinal displacements and deflections of deck structures and shear stresses in the side structures can be estimated as well. The method is a further development of the linear coupled beam method. The ultimate strength of the hull girder was studied also with the non-linear finite element method. This required an investigation of the element mesh configuration in order to find an optimum mesh type and size. The prismatic hull girder of a post-Panamax passenger ship was chosen as a case study. The ultimate strength was estimated both in hogging and sagging loading with the coupled beam method and with the finite element method. The results of these two different methods, presented in the form of the bending moment versus the deflection of the hull girder, show good correlation up to the area where the moment starts to decrease. In both loading cases, the failure starts by the shear collapse in the longitudinal bulkhead. The ultimate stage of the strength was reached in the sagging loading when the failure progressed to the lower decks and correspondingly, in the hogging loading when the bottom structures failed in compression. The results on the structural failure modes show clearly that the shear strength of the longitudinal bulkheads and side structures is a very important issue on the ultimate strength problem of a passenger ship.
Wax actuator’s empirical model development and application to underfloor heating control with varying complexity of controller modelling detail
(2023) Parts, Tuule Mall; Ferrantelli, Andrea; Naar, Hendrik; Thalfeldt, Martin; Kurnitski, Jarek
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
This paper investigates how a simulated room’s energy and temperature performance are affected if its underfloor heating control is modelled with increasing detail. Experiments were performed to develop and calibrate an empirical model of wax motor and to calibrate the valve curve. These models were used to implement and test the On/Off and proportional-integral (PI) control processes at various levels of modelling detail. Controllers were implemented by gradually adding optimized control parameters, signal delay, calibrated valve curve, signal modulation, and actuator modelling. The On/Off control dead band and PI parameters exhibited the largest impact, reducing energy use (1%–5%) and temperature fluctuations (ca 1 K). Modulating the PI output signal increased temperature fluctuations to the same amplitude as On/Off with 0.5 K dead band, increasing space heating demand by 1.3%. The wax actuator counted for less than 1%; however, it increased time delays to maximally 7 min and remarkably changed the mass flows.