Time-domain simulation of seakeeping and manoeuvring of ships in deep and shallow water waves

The present thesis deals with the topic of ship manoeuvring in waves and the effects imposed by the shallow water. In this aspect, ship's manoeuvrability is investigated using a numerical method, which was developed according to a hybrid approach where seakeeping and manoeuvring contributions are blended. In order to ensure that the aforementioned model incorporates correctly seakeeping and calm water manoeuvring approaches, separate validation processes are followed beforehand. In case of nonlinear seakeeping analysis, parametric roll investigation is undertaken as well, as a mean to verify that the developed methodology evaluates properly the fundamental external forces, especially roll damping. In this way, a framework is established which offers the ability to perform holistic hydrodynamic assessment of marine vessels as well.;Validation of the developed computational code is conducted using experimental turning circle trajectories, which refer to deep water conditions. The case studies concern the horizontal motions of the S-175 container ship at long waves and four values of under keel clearance corresponding to medium-deep (UKC=3.0, 2.5, 2.0) and shallow waters (UKC=1.5). In this aspect, the wave forces as well as the manoeuvring-related ones are corrected using relevant methodologies. In particular, a 3D potential flow method is adopted for the evaluation of the former, whilst corrections are applied on the various manoeuvring-related force components defined by the Manoeuvring Modelling Group (Ogawa et al., 1977). Especially in case of the added resistance, near and far-field methods are implemented based on the size of the wavelength with respect to the ship's length.;The empirical corrections which refer to the manoeuvring-related forces and are used in order to incorporate the shallow water effect, concern the hydrodynamic hull forces, the calm water resistance and various hull-rudder-propeller interaction coefficients and are based on regression formulae which are functions of the under keel clearance ratio.The present thesis deals with the topic of ship manoeuvring in waves and the effects imposed by the shallow water. In this aspect, ship's manoeuvrability is investigated using a numerical method, which was developed according to a hybrid approach where seakeeping and manoeuvring contributions are blended. In order to ensure that the aforementioned model incorporates correctly seakeeping and calm water manoeuvring approaches, separate validation processes are followed beforehand. In case of nonlinear seakeeping analysis, parametric roll investigation is undertaken as well, as a mean to verify that the developed methodology evaluates properly the fundamental external forces, especially roll damping. In this way, a framework is established which offers the ability to perform holistic hydrodynamic assessment of marine vessels as well.;Validation of the developed computational code is conducted using experimental turning circle trajectories, which refer to deep water conditions. The case studies concern the horizontal motions of the S-175 container ship at long waves and four values of under keel clearance corresponding to medium-deep (UKC=3.0, 2.5, 2.0) and shallow waters (UKC=1.5). In this aspect, the wave forces as well as the manoeuvring-related ones are corrected using relevant methodologies. In particular, a 3D potential flow method is adopted for the evaluation of the former, whilst corrections are applied on the various manoeuvring-related force components defined by the Manoeuvring Modelling Group (Ogawa et al., 1977). Especially in case of the added resistance, near and far-field methods are implemented based on the size of the wavelength with respect to the ship's length.;The empirical corrections which refer to the manoeuvring-related forces and are used in order to incorporate the shallow water effect, concern the hydrodynamic hull forces, the calm water resistance and various hull-rudder-propeller interaction coefficients and are based on regression formulae which are functions of the under keel clearance ratio

Drift Capacity of Structural Walls with Lap Splices

Twelve large-scale reinforced concrete specimens with lap splices in the longitudinal reinforcement were tested at Purdue University’s Bowen Laboratory to produce data to evaluate the deformability of structural walls with lap splices at their base. Previous work on lap splices has focused mainly on splice strength. But in consideration of demands requiring structural toughness (e.g. blast, earthquake, differential settlement), deformability is arguably more important than strength.To obtain data on splice deformability and to study the response of lap splices in conditions more representative of those occurring in structural walls, eight specimens were tested under four-point bending and four additional specimens were tested as cantilevers under constant axial force and cyclic reversals of lateral displacement. All specimens failed abruptly by disintegration of the lap splice regardless of how the loading was controlled or what detailing was used. Large numbers of loading cycles in the linear range of response did not seem to have an appreciable effect on splice deformability. For structural walls with lap splices comparable to those tested, the observations collected suggest that drift capacity can be as low as 0.5% for splices with minimum cover, minimum transverse reinforcement terminating in hooks, and lap splice lengths selected to reach yielding in the spliced bars. That is, splice failure can occur as yield is reached or soon after. For lap splices 1.3 times longer, drift ratio at splice failure is projected to increase to approximately 0.75% or more. For cover twice as large and transverse reinforcement that is continuous around the lap splice, drift capacity is projected to increase to nearly 1% for splices designed to yield and 1.5% or more for lap splices 1.3 times longer.The evidence gathered suggests that lap splices with minimum cover and confined only by minimum transverse reinforcement terminating in hooks should not be used in applications requiring toughness in structural walls

Ship's hull response under extreme bending loading

Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Υπολογιστική Μηχανική

Sustainable Green Infrastructure Planning in Greece: Proposal for an Urban Greenway Network in the Greater Athens Metropolitan Area

Athens, the capital of Greece, epitomizes the opportunities and constraints of modern urbanization, sustainable mobility, green infrastructure, greenway planning, and the associated quality of contemporary Greek civic life. Though the country’s economy has been suffering tremendously for the past consecutive eight years with harsh austerity measures holding back any developmental commotion, signs of recovery and appropriate funding are lately emerging. Physically, Athens has overcome its natural containing barriers, the Pikilo and Hemmitos Mountains on east and west borders, the southern waterfront expanding over to the Thriasio and Mesogeia Fields and the island of Aegina respectively. Culturally, contemporary Athens is thriving, living up to her own historical heritage and legacy. Socially, the latest abrupt surge of immigrant and refugees influx has altered both demographical ratios and civic life in the congested downtown and CBD of the city as well as the dispersed residential neighborhoods within a chaotic urban fabric. Economically, foreign and local investors have shown a keen interest in large scale projects (e.g. the former Hellinikon International Airport) but national debts to both the International Monetary Fund (IMF) and the European Central Bank (ECB) have led to governmental hesitation and procrastination of any developmental plans, halting in turn the investors’ much anticipated and crucial momentum. Lastly, clashing stakeholders’ interests within the broader green infrastructure and targeted greenway planning process, provide the fertile basis for a wide spectrum of alternative development scenarios. One of the most discussed and highest-profile projects in Greece today is Hellinikon, an ambitious plan for converting the former Athens airport into an enormous park. The site of Hellinikon lies 8 km southwest of the center of Athens being approximately 1,500 acres and boasting a 3.5 km waterfront, including a marina. Exploiting the Hellinikon site as the main organizing impetus, this paper presents a proposal for an Urban Greenway Network in the Greater Athens Metropolitan Area (GAMA) as a response to prudent city planning, attempting to address the vision, the strategic issues, the governmental and private synergies, the planning criteria, the physical design and standards of greenway planning required for its implementation at the city scale and beyond. At the background, ecological, social, and economic issues weave the sustainability concerns and processes of green infrastructure planning

Straining Definitions

The concept of strain is ubiquitous in engineering textbooks. It is defined early in engineering education as change in length divided by initial length, and is used to quantify deformations due to things like stresses and temperature changes. The concept itself is quite straightforward and represents homogenous materials well, but homogenous materials are rarely present in engineering design. Composite materials such reinforced concrete cannot be simply defined, as their properties are heavily influenced by their non-uniformity. For example, there are large deformations around tensile cracks in reinforced concrete, where the reinforcement withstands all the tensile stress, and little deformation in uncracked regions. How should tensile strain in reinforced concrete be measured? Industry mandates that steel reinforcement samples be tested using a gage length of 8 inches on a region that includes fracture, but do these measurements portray the in situ tensile behavior of reinforced concrete? This project addresses the deceivingly simple question of what gage length to use with reinforced concrete to reconcile results from testing samples of the individual elements of reinforced concrete. The project subjects rebars encased in rectangular concrete prisms to uniaxial tension, and then uses 3d optical point tracking (e.g. Optotrak) and Digital Image Correlation (DIC) to monitor deformations. The deformations at failure are then analyzed using different gage lengths to calculate the strain occurring between two points. It was found that gage lengths greater than 6 times the average crack spacing showed converging tensile strains

ELIGMOS: time domain simulation of the maneuvering of ships in deep and shallow waters

Calm water manoeuvring simulations are commonly used at the initial design stage as they provide useful an practical insight concerning ship's manoeuvrability and compliance with the relevant IMO criteria. In this paper the authors present ELIGMOS; a time-domain numerical code utilizing a 3-DOF manoeuvring model based on the MMG method. For the validation of the code's predictions, a comparison with the experimental results on the turning ability of S-175 has been conducted. The paper presents also the investigation performed regarding the accuracy of certain empirical formulas for the derivation of the manoeuvring derivatives is also investigated, especially for the case of shallow water where experimental data and results remain scarce. The code is written in C++ programming language, adopting a modular approach for the calculation of external forces and moment (i.e. hydrodynamic hull, rudder and propeller) which allows future enhancements with the introduction of additional terms

Edessa Greenways: A Land Use Planning Tool Promoting Sustainable Development in Northern Greece

Known historically as the “City of Water”, Edessa is one of many ancient small hill towns situated in a forested river valley found at the northwest part of Greece\u27s Macedonia region. Bordering with FYROM, Albania and Bulgaria, it sits at the edge of a plateau overlooking the historically rich Plains of Hellas; atop a vast agricultural plain that extends east to Thessalonica, some 120 kilometers. Small rivers run through Edessa boasting an intricate system of waterwayscanals, rivulets, and waterfalls-intertwined with small streets, walking paths and scenic overlooks. The rivers fall spectacularly 70m down from the ledge to the plain below. These waterfalls are a well-known and celebrated natural feature. The new extended municipality includes both towns of Edessa and neighboring town Anissa encompassing a rural “green corridor” agricultural area between them. It comprises the study area which extends in the valley of the River Edesseos, rising in the Agras Nissi Vritta wetlands and Lake Vegoritida. North of Edessa recreational itineraries include abundant ski resorts, ornithological reserves, lakes and archeological sites. Unless the municipality of Edessa generates new economic growth, it will continue to lose a valuable human resource, its youth. The mayor wishes to create new hope and energy for the new municipality through economic investment and physical restructuring. Improvements here could reverberate throughout the region and potentially motivate further investment. Renovated small hotels and lodgings have emerged as outsiders begin to see the potential value of Edessa\u27s future. Egnatia Motorway, the region’s greatest infrastructural project, has already transformed travel times and accessibilities across northern Greece bringing closer the emerging economies of Western and Eastern Europe. Environmental considerations for the region are underway as two transnational agreements, the EU\u27s NATURA Network 2000 and the RAMSAR Convention of 1971, continue to ensure the preservation and protection of sensitive ecosystems and wetlands for the foreseeable future. But this green corridor, however scenic, suffers from inattention and minimal investment. As many regions of great natural beauty dotted with small agricultural towns across Europe continue their dependence upon cultural and ecological tourism, questions that define and frame broader issues of design, sustainability and growth in northern Greece, were considered throughout the planning process: a) How sustainable development and design issues of a region can be sensitively addressed, while developing a strategy that provides socio-cultural, economic and environmental sustainability? b) How can landscape and infrastructure design work synergistically to address the demands of connectivity and increased capacity while also promoting a sense of identity and placeness for a rural region? c) How can issues of sustainability and environmental stewardship be calibrated to the specifics of local culture and geography? d) How can recent shifts in the regional geopolitical sphere be actuated to bolster tourism and economic development? e) How can strategic investments in landscape and infrastructure be leveraged to provide development opportunity for the larger region? f) Can a pronounced shift toward high-end tourism reposition the developmental future of the region? g) Can a new strategy of catalytic rural landscape and infrastructure investments improve the internal structure of the landscape and enhance its connection to the larger region? Like many hill towns across continental Europe impacted by the shift away from small scale agricultural operations and the forces of an increasingly globalized economy, the structural relationship between town and country (in this case, the agrarian hinterlands) has profoundly changed. In the more targeted scope and scale of a municipality, fundamental questions remain: a) What uniquely defining characteristics does Edessa possess? b) What additional attributes does Edessa require? c) What actions can be taken to improve sustainable development and economic growth, while preserving natural resources, promoting cultural resources, and upgrading physical planning integration of Edessa’s urban and rural Mediterranean landscape