| 1. |
- Cheemakurthy, Harsha, et al.
(författare)
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A lightweight ice going hull concept for freshwater ice operations
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A fundamental challenge in ice-prone waterborne public transportation systems is the need for ice-strengthening while being fuel efficient during ice-free periods. To achieve this, the use of lightweight hull structures is explored in the current study by starting with introducing a tri-layer structural concept for an ice going hull. The three layers correspond to abrasion loads, impact loads and pressure loads experienced during a typical ice-hull interaction. Several structural concepts suited towards these respective loading mechanisms are considered. Most favorable parametric variants are identified and assembled as contenders in the tri-layer concept. The assembly is tested against experimentally validated ice impact models in FEA as well as a realistic quasi-static pressure representation. Three different lightweight structural concepts including aluminum grillage, stiffened sandwich structure and metal-FRP stiffened sandwich structure are compared and discussed. It is found that the latter of the three concepts is suited best towards both quasi-static and impact loading. Ice going ferries built with ice strengthened lightweight hulls can reduce emissions, fuel consumption as well as increase the payload capacity. Such a ferry would be competitive with non-ice going ferries during ice free periods.
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| 2. |
- Cheemakurthy, Harsha, et al.
(författare)
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A modularly tailored commuter ferry platform
- 2022
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Ingår i: International Shipbuilding Progress. - Amsterdam : IOS Press. - 0020-868X .- 1566-2829. ; 69, s. 1-35
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Tidskriftsartikel (refereegranskat)abstract
- Among the challenges for implementation of Waterborne public transportation (WPT) are the difficulties in procuring efficient ferries tailored towards local requirements. Fundamental questions on the ferry’s environmental impact, speed and procurement costs linger in the public transport (PTP) mind. In this paper, a methodology for adopting a platform architecture for ferries is illustrated by a modular design approach. For this, WPT operational profiles are categorized by three route types in a structure for operational requirements including sustainability performance. Generic parameters for size and speed of WPT ferries are defined. Using these parameters as a skeletal structure, a modular commuter ferry concept is proposed as a set of basic modules. As a combination of these functionally independent modules, a ferry can be tailored to fit the operational requirements. The paper proposes standard sizes for waterborne commuter craft and shows that ferries are compatible with land-based public transport in terms of energy efficiency and speed. Suitable speed ranges for mono hulls and catamarans are investigated and the idea of modular design for rational procurement is explored and illustrated for the three type routes. The proposed concepts can make WPT more attractive for PTPs as a sustainable option to complement the existing network.
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| 3. |
- Cheemakurthy, Harsha, et al.
(författare)
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Comparison of Lightweight Structures in Bearing Impact Loads during Ice–Hull Interaction
- 2022
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Ingår i: Journal of Marine Science and Engineering. - Basel, Switzerland : MDPI AG. - 2077-1312. ; 10:6, s. 794-
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Tidskriftsartikel (refereegranskat)abstract
- The current study focuses on the impact loading phase characteristic of thin first year ice in inland waterways. We investigate metal grillages, fibre reinforced plastic (FRP) composites and nature-inspired composites using LS Dyna. The impact mode is modelled as (a) simplified impact model with a rigid-body impactor and (b) an experimentally validated ice model represented by cohesive zone elements. The structural concepts are investigated parametrically for strength and stiffness using the simplified model, and an aluminium alloy grillage is analysed with the ice model. The metal–FRP composite was found to be the most favourable concept that offered impact protection as well as being light weight. By weight, FRP composites with a Bouligand ply arrangement were the most favourable but prone to impact damage. Further, aluminium grillage was found to be a significant contender for a range of ice impact velocities. While the ice model is experimentally validated, a drawback of the simplified model is the lack of experimental data. We overcame this by limiting the scope to low velocity impact and investigating only relative structural performance. By doing so, the study identifies significant parameters and parametric trends along with material differences for all structural concepts. The outcomes result in the creation of a viable pool of lightweight variants that fulfil the impact loading phase. Together with outcomes from quasi-static loading phase, it is possible to develop a lightweight ice-going hull concept.
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| 4. |
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| 5. |
- Cheemakurthy, Harsha
(författare)
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Efficient commuter craft for urban waterborne public transportation
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There has been a recent surge in interest in waterborne public transportation (WPT). Publictransport providers (PTP) are seeing its potential in complementing the existing transportnetwork and alleviating urban traffic congestion and pollution. But the adoption of WPTtoday is challenging due to a series of technical and implementation challenges. Thesechallenges include ferry procurement practices, local legislation and policies andenvironmental factors like winter ice. Several of these challenges can be alleviated if efficientferries can be made accessible off-the-shelf with a low manufacturing time and cost. Thethesis focuses on developing such a ferry concept based on modular design whose overalldimensions are standardized and internal arrangement is customizable towards operationalrequirements, with a focus towards sustainable and safe operations in ice.Starting with the characterization of WPT, ferry routes are broadly classified into three types.These routes are described with an operational requirements framework considering allrelevant stakeholder expectations. Then, overall dimensions of vessels representative ofWPT are deduced. Using these dimensions to standardize the overall dimensions, a modularferry concept is developed as an assembly of modules and submodules. The modules arepresented as standardized units having fixed dimensions and interfaces whose internalarrangements can be tailored to meet operational requirements. Design standardizationlowers costs and manufacturing time while internal customization favours tailoring the ferryconcept. One challenge associated with this for the PTP is the difficulty in choosingappropriate modules among multiple alternatives. This is overcome through thedevelopment of a ranking and selection method which benchmarks competing designs andhelps in decision making.In terms of technical challenges for the developed ferry concept, cities like Stockholmexperience freezing of water bodies during winter months. For reliable year-roundoperations that are safe and sustainable in terms of economy and environment, there is aneed for the development of lightweight and robust ice going hulls. This thesis lays thefoundation for the development of such hulls by studying the prevalent ice data and proposesa probabilistic method for estimating the design ice pressures.One must rely on probabilistic methods since most experimental studies are based on seaice whose mechanical properties are different from freshwater ice, which is typical for WPT.Traditionally, classification society rules like the Finnish Swedish Ice Class Rules are usedfor first year light ice conditions which were developed for the Baltic Sea consideringicebreaker vessels. They work well in ensuring a safe design, but their performance forfreshwater ice, applied to commuter ferries have not been tested. Therefore, a probabilisticapproach is adopted where the unknown parameters are incorporated as random variables.The probabilistic method reduces the hull-ice interaction to a pressure and contact-arearelationship. With arctic datasets that closely match WPT conditions as the parent dataset,the probabilistic method is calibrated with exposure conditions for WPT to give the designpressure-area curve. The different uncertainties arising from operations in ice are studied using a statistical tool and the leading source of uncertainty is attributed to ice-loadprediction methods. This establishes the need for more robust methods for prediction of iceloads so that a lightweight, yet robust hull may be designed which is efficient in terms of fueleconomy and emissions.WPT presents a tremendous opportunity in complementing the existing transport network.With careful design and development of the modular ferry concept and its technicalchallenges, it would be easier for PTPs to adopt WPT globally.
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| 6. |
- Cheemakurthy, Harsha
(författare)
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Framework for holistic design of ferries focusing on lightweight ice going hulls.
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Waterborne public transportation (WPT) is slowly increasing in importance as an active component of public transportation networks in cities. City planners are looking at WPT to overcome urban congestion and pollution. However, prevalent challenges like ferry procurement, poor state of existing ferry fleets and technical challenges like the presence of ice, have created reluctance in the minds of public transport providers (PTPs). While contemporary research shows ferries can be economical and environmentally friendly, there are some fundamental challenges that need to be addressed before PTPs can feel confident.In this regard, deterrents from PTP’s perspective are identified and solutions are investigated, starting with a systematic characterization of WPT. A definite structure for operational requirements is proposed in an objective manner. Using these as basis, two standard ferry sizes that could fulfil multiple WPT roles in majority of cities are introduced. For establishing city-wise tailoring, platform-architecture based modularization of ferries is proposed. The ferry modules are tailored with respect to operational requirements in a clear and objective manner through the introduction of an evaluation methodology. The method incorporates economic, social, environmental, and regulatory stakeholders. These proposed solutions are aimed at improving PTP’s confidence in WPT and provides solutions for the marine industry to produce quick, cost efficient and tailored ferries. Next, the scope is focused towards investigating sustainable operations in freshwater ice conditions, typically found in the Stockholm region in Sweden. The ice going ferries today operate with ice strengthened heavy hulls. While they work well in ice, they perform poorly in comparison with non-ice going ferries during ice free months. Correspondingly, solutions towards lightweight ice going hulls are investigated. This investigation starts with understanding ice-hull interaction mechanisms. Then, techniques to estimate the ice loads are investigated. We adopt a probabilistic approach to tackle the limitations due to the stochastic nature of ice and a lack of experimental data. The resulting load cases are used for evaluating lightweight structural concepts. The investigation is approached by dividing ice-hull interaction into quasi-static, dynamic and abrasive loading phases. Several candidates corresponding to the first two loading phases are investigated parametrically. The range of structural concepts include metal grillages, bio-inspired composites, and sandwich structures. Realistic loading models for quasi-static and impact mechanisms are developed and validated with experiments. The winning candidates for each loading phase are combined to propose a tri-layer lightweight structural concept. Three candidates for the concept are evaluated and compared.The thesis answers several questions that riddle WPT today. But at the same time, it raises new questions. Several directions for future work are identified. With continued development, it would be possible to see modularly tailored ferries operating with lightweight hulls in WPT systems around the world.
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| 7. |
- Cheemakurthy, Harsha, et al.
(författare)
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Fuzzy AHP-Based Design Performance Index for Evaluation of Ferries
- 2022
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Ingår i: Sustainability. - : MDPI AG. - 2071-1050. ; 14:6, s. 3680-3680
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Tidskriftsartikel (refereegranskat)abstract
- Within waterborne public transportation (WPT), one often observes a mismatch between the operational requirements and ferry characteristics. A method to holistically evaluate ferries with respect to local requirements could lead to tailored procurement and targeted refurbishment of existing fleet. In this study, we develop a structure for operational requirements and use it as a basis for a ferry evaluation methodology. The requirements’ structure follows a three-level hierarchy starting from broad vessel design to mandatory requirements to performance requirements. The performance requirements are based on the three pillars of sustainability, aided by commuter surveys carried out in Stockholm ferries, interviews with public transport providers (PTP) and previous literature. The evaluation of the ferry is performed using analytic hierarchic process (AHP) to convert the PTP’s subjective preferences and ferry performance into a single dimensionless index. Rules for quantification of performance metrics including social performance are proposed. The uncertainties associated with AHP are addressed by employing fuzzy AHP based on extent analysis and fuzzy AHP in combination with particle swarm optimization. Two applications including performance assessment of existing ferries and assembly of a modular ferry are discussed. The method can lead to objective decision making in ferry evaluation, potentially leading to a more efficient WPT.
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| 8. |
- Cheemakurthy, Harsha, et al.
(författare)
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Lightweight Structural Concepts in Bearing Quasi-Static Ice Hull Interaction Loads
- 2022
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Ingår i: Journal of Marine Science and Engineering. - : MDPI AG. - 2077-1312. ; 10:3, s. 416-416
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Tidskriftsartikel (refereegranskat)abstract
- Lightweight ice-class vessels offer the possibility of increasing the payload capacity while making them comparable in energy consumption with non-ice-class vessels during ice-free periods. We approach the development of a lightweight hull by dividing ice–hull interactions into quasi-static loading and impact loading phases. Then, investigative outcomes of lightweight concepts for each loading phase may be combined to develop a lightweight ice-going hull. In this study, we focus on the quasi-static loading phase characteristic of thin first-year ice in inland waterways. We investigate metal grillages, sandwich structures and stiffened sandwich structures parametrically using the finite element method. The model is validated using previous experimental studies. In total over 2000 cases are investigated for strength and stiffness with respect to mass. The stiffened sandwich was found to be the most favorable concept that offered both a light weight as well as high gross tonnage. Further, significant parameters and their interactions and material differences for the three structural concepts were investigated and their trends discussed. The outcomes result in the creation of a viable pool of lightweight variants that fulfill the quasi-static loading phase. Together with outcomes from the impact loading phase, a lightweight ice-going hull may be developed.
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| 9. |
- Cheemakurthy, Harsha, et al.
(författare)
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Nonlinear Finite Element Analysis of Inland-Waterway Barge in Fresh Water Ice Conditions
- 2019
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Ingår i: <em>Proceedings of the Annual International Offshore and Polar Engineering Conference</em>. - Honolulu, Hawaii. - 9781880653852 ; , s. 799-806
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Konferensbidrag (refereegranskat)abstract
- There has been an increased awareness of the benefits of utilizing inland waterways (IWW) from a transport efficiency and an emission control point of view. However, due to presence of ice in water bodies, vessels designed for non-ice river operations cannot operate during the winter months. This paper analyses a grillage representative of barge’s bow region using non-linear finite element analysis (NL FEA) and assesses survivability in comparison with load limits prescribed by latest Finnish Swedish Ice Class Rules (FSICR) 2017 rules, International Association of Classification Societies (IACS) Polar Cass 6 (PC6) rules and simplified plastic collapse limit states calculated by Daley (2002). The NLFEA study included strength contributions from strain hardening and membrane stress and it was found that the limit state described by rupture stress was significantly larger. It was found that allowance for plasticity can reduce structural scantling requirements for fresh water ice operating vessels. The study also validated latest FSIRCR 2017 requirements.
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| 10. |
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