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Mooring Impacts on <i>Zostera marina</i> Meadows and Associated Epifauna in Nantucket Harbor, Massachusetts, USAMcCandless, Andrew Wright 05 July 2018 (has links)
Seagrass ecosystems are some of the most productive in the world and provide a variety of ecosystem services but are facing global decline chiefly due to anthropogenic disturbance. Mechanical disturbances to seagrass meadows from anchoring, propeller scars, and mooring scars result in losses or damage to both shoots and the underlying rhizome. I conducted a literature synthesis on the extent of, recovery from, and ecological impacts of these mechanical disturbances to seagrass meadows. The literature suggests that anchoring damage tends to be worst in deeper water where larger vessels anchor and can cause large (>100m2) loss per anchoring and recovery may take decades to over a century. Propeller damage is of largest concern in shallow (<2m) areas experiencing heavy boat traffic because propeller damage can only occur where the propeller can come close to the seagrass. Mooring damage is highly variable depending on the type of mooring used (>10m2 to >1000m2 scoured per mooring). Seagrass patches experiencing these mechanical disturbances have, in some studies, been found to have lower seagrass percent cover and shoot density than reference areas. This indicates scars can have "halos" of impacted seagrass meadow. Some seagrass systems cannot recover within a century (e.g. Posidonia oceanica meadows at the extent of their depth tolerance) while others recover annually from some disturbances (e.g., anchor scars <1m2). Systems face altered species composition when scars are preferentially recolonized by certain species and patterns of recovery are affected by altered biogeochemical conditions following disturbances. Additionally, mooring, anchoring, and propeller scarring frequently alter meadow density, cover, patch size, patch shape, patch isolation, edge area, and ratios of edge to interior meadow leading to changes in faunal community structure. Correlations between these disturbances and faunal abundances, densities, and richness in seagrass ecosystems are complex, vary temporally (sometimes on the scale of days), and may result in species showing positive, negative, or no responses to a wide range of disturbance regimes.
To explore the connections between mooring scarring, the surrounding seagrass meadow condition and epifaunal community, in the second part of this thesis I measured 30 mooring scars to determine average scar size. To explore any potential "halo" effect around mooring scars for seagrass or epifauna and to seek any difference in epifaunal community between mooring and reference sites I also sampled paired sites at eight locations in Nantucket Harbor, Massachusetts three times each in the summer of 2015. Each location consisted of a meadow site actively experiencing mooring scarring and a reference site without moorings. My conservative sampling methods of the 30 sampled mooring scars found scars to average 21.1m2. Across my paired sites, seagrass was found to have lower cover and lower canopy height in mooring versus reference sites. Seagrass cover and canopy height were lower in the first few meters (typically 2-3m) surrounding each scar in comparison to paired reference quadrats indicating a "halo" effect of each scar. I did not detect a difference in epifaunal community composition or density per blade between mooring and reference sites; however, the relatively constant per blade concentration of epifauna combined with the differences in seagrass biomass between the mooring versus reference sites indicate an overall increase in the total amount of epifauna in areas with less disturbance. Epifaunal community composition was different and between locations and sampling dates indicating these factors are more important than proximity to mooring scarring in determining epifaunal abundance and richness. When considering scar area and the "halo" of each scar I estimate that at least 32ha (2%) of Nantucket Harbor was impacted by mooring scarring. Given that the estimates of seagrass do not include areas previously denuded of this plant and that my measurements were conservative, likely a larger portion of this harbor's potential seagrass habitat is impacted. Combined with the findings of loss due to these direct boat-related physical disturbances of seagrass meadows worldwide across regions, this halo effect is likely to also be found for moorings globally. I encourage management of the issue by employing and fine-tuning mooring methods (such as deploying moorings with anchor connections that do not drag on the sea floor) to minimize these unintentional but strong effects of mooring on the recipient habitat.
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[en] FATIGUE LIFE IMPROVEMENT OF THE R4 STUCTURAL STEEL / [pt] OTIMIZAÇÃO DA VIDA-FADIGA DO AÇO ESTRUTURAL R4LUIZ DINIZ CORREA 26 April 2006 (has links)
[pt] Esta pesquisa teve como objetivo avaliar o efeito do
jateamento de partículas
(shot-peening) sobre a vida-fadiga do aço estrutural R4,
largamente adotado na
fabricação de componentes estruturais para sistemas de
ancoragem de unidades
flutuantes. Inicialmente, amostras cilíndricas do material
foram retiradas das seções
retas de elos tipo Kenter. Em seqüência, algumas amostras
foram temperadas e
revenidas em diferentes tempos de tratamento, com o
objetivo de se promover uma
homogeneidade microestrutural, bem como propriedades
mecânicas similares àquelas
dos elos tratados industrialmente. As amostras foram
submetidas a ensaios de dureza e
tração e, com base nos resultados, providenciou-se o
tratamento térmico de todas as
amostras. Dando continuidade a etapa experimental, corpos
de prova para ensaios de
fadiga foram usinados das amostras tratadas e submetidos a
jateamento com
microesferas de aço temperado sob pressões de 20 psi, 30
psi e 40 psi. Finalmente,
corpos de prova nas condições sem jateamento e após
jateamento foram submetidos a
ensaios de fadiga por flexão rotativa, com o objetivo de
se levantar a curva tensão
versus número de ciclos para a falha (curva S-N) do aço
estrutural R4 nas diferentes
condições de superfície. A extensão da vida em fadiga do
aço estrutural R4 foi
relacionada com o jateamento de microesferas. De acordo
com os resultados, houve
uma influência benéfica do tratamento de superfície sobre
a vida-fadiga do material.
Tal influência foi caracterizada por um maior número de
ciclos para a falha e aumento
do limite de resistência à fadiga. Os resultados mostraram
que a extensão da vida útil
esteve diretamente relacionada com a intensidade do
jateamento, significando que uma
maior intensidade de jateamento provocou uma maior
extensão da vida-fadiga do
material. / [en] The objective of the present work was to evaluate the
effect of shot
peening on the fatigue life of a grade R4 structural
steel, largely adopted for
fabricating offshore mooring chains. Initially,
cylindrical samples of the material
were cut of from the straight sections of Kenter links. In
the sequence, a number
of specimens were austenitized ed and tempered making use
of different treatment
times, in order to promote a microstructural homogeneity
as well as mechanical
properties similar to those associated with industrial
heat treatments. The
specimens were subjected to hardness and tensile tests and
on the basis of the
results, all samples were heat treated. After that,
fatigue specimens were machined
from the treated samples and shot peened with quenched
steel shots under
pressures of 20 psi, 30 psi and 40 psi. Finally, rotating
bend fatigue tests were
performed with unpeened and shot peened specimens aiming
to establish the
stress-life curves of the grade R4 structural steel. The
fatigue life extension of the
grade R4 structural steel was related to the shot peening.
Regarding the results, the
surface treatments affected the fatigue life of the
material beneficially. This
influence was characterized by a longer fatigue cycles and
a fatigue life
improvement. The results showed that the fatigue life
extension was directly
related to the shot peening intensity, i.e., the fatigue
life extension has increased
when increasing the shot peening intensity.
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[en] FRACTURE RESISTENCE OF THE GRADE R4 STRUCTURAL STEEL AND ITS DEPENDENCE WITH THE QUENCHING TEMPERATURE / [pt] RESISTÊNCIA À FRATURA DO AÇO ESTRUTURAL R4 E SUA DEPENDÊNCIA COM A TEMPERATURA DE TÊMPERAROBERTO ANTONIO ROCO ANTUNEZ 03 April 2006 (has links)
[pt] O presente trabalho apresenta um estudo da influência dos
tratamentos
térmicos de têmpera e revenido sôbre a resistência à
fratura do aço estrutural R4,
adotado na fabricação de elos para sistemas de ancoragem
de unidade offshore e
soldados pelo processo de centelhamento. Corpos de prova
do tipo CT foram
retirados da região da solda dos elos, usinados com
orientação L-R e submetidos a
diferentes tratamentos térmicos de têmpera (temperaturas
de austenitização de 810,
840, 870 e 900ºC) e revenido (640 e 680ºC), num total de
quatro condições
microestruturais. Após pré-trincamento em fadiga, os
corpos de prova foram
submetidos a carregamento monotônico em tração, com o
objetivo de se determinar
a resistência à fratura do material com base no parâmetro
CTOD (Crack Tip
Opening Displacement).
Os resultados do ensaio de CTOD demonstraram que houve uma
redução da
resistência à fratura do aço estrutural R4 com o aumento
da temperatura de
austenitização (810, 840 e 870°C) e temperatura de
revenido de 640°C. Entretanto,
para maiores temperaturas de austenitização (900°C) e
revenido (680°C), houve
um aumento do parâmetro CTOD. Modificações
microestruturais no material
causadas pelos tratamentos térmicos foram associadas com
as variações da
tenacidade. / [en] This study has been made concerning the influence of
quenching and
tempering heat treatments on the fracture resistance of a
grade R4 structural steel,
largely used for fabricating offshore mooring chains by
flash welding. CT
specimens were taken from the welded joints region in L-R
and machined
following orientation and subjected to different quenching
(austenizing
temperatures of 810, 840, 870 and 900ºC) and tempering
(640 ºC and 680ºC)
treatments, in a total of four microstructural conditions.
After fatigue precracking,
the specimens were monotonically loaded in tension in
order to determine the
fracture resistance of the material on the basis of the
CTOD (Crack Tip Opening
Displacement) parameter.
The results of the CTOD tests showed that the fracture
resistance of the
grade R4 structural steel has decreased when increasing
the austenitizing
temperature (810, 840 and 870°C) and tempering at 640ºC.
However, when
adopting higher austenitizing (900°C) and tempering (680°
C) temperatures, the
parameter CTOD has increased. The microstructural
modifications caused by the
heat treatments were associated with the toughness
modifications.
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Loads on Tie-Down Systems for Floating Drilling Rigs during Hurricane ConditionsBae, Yoon Hyeok 16 January 2010 (has links)
Tie-down systems are used to fasten drilling rigs to the deck of offshore
structures during harsh environmental conditions such as hurricanes. During Hurricane
Ivan (2004) and Katrina (2005), a number of offshore structures were moved and several
tie-down systems were damaged. In the present study, the reaction force and connection
capacity of tie-down systems for a TLP and SPAR are investigated. The environmental
conditions are taken from the API Bulletin 2INT-MET which has been updated after
several major storms during 2004-2005. The hydrodynamic coefficients of the TLP and
SPAR are obtained using a 3D diffraction/radiation panel method. The motions of the
TLP and SPAR are then simulated in the time domain by using the hull-mooring-riser
coupled dynamic analysis tool CHARM3D. Based on the simulated motion and
acceleration time series, the inertial and gravity loads on derrick and skid base footing
are calculated. In addition to the inertial-gravity loads, wind forces exerted on the derrick
are also calculated. All the external forces and resultant hull motions are simulated for
100-year, 200-year and 1000-year storms to observe the derrick structural integrity with
increasing environmental intensity. Various environmental headings are also considered to find the maximum reaction forces. In the present method, the phase differences
between gravity-inertia forces and wind forces are taken into consideration to obtain
more realistic loads on derrick and skid base footings. This research shows that the
maximum and minimum load values are appreciably higher for the SPAR. In addition,
the direction of external forces is also important to determine maximum reaction forces
on footings. The capacities of the clamps in slip, bolt tension, and bolt shear can be also
analyzed using the resultant data to provide guidance on appropriate design values.
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Experimental Study of a new sloshing liquid U-column wave power converter in water-tankWu, Tzu-Ching 10 September 2009 (has links)
For an offshore platform structure applied to wave-energy conversion system, in order to catch the maximum waves to generate more powers, similar to wind-energy power generators, a range of angles for the devices normal to the propagating direction of incident waves is required, particularly when the power converting system has directional preference. That is one essential reason why a single mooring offshore platform system is so important in the development of an offshore wave-energy conversion system. The single mooring-system would allow the offshore wave-energy conversion system to turn freely in accordance to the action of strong directions of propagating waves and in this way, most energy induced from the incident waves can be caught and converted into reusable powers. The aims of this study are firstly, based on previous studies to further modify a single moored offshore platform system that may subject to less wave forces in the sea and, secondly, to verify the efficiency of single-moored system by carrying out an experimental testing on a simple single-moored floating platform system in the water tank.
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Experimental response and analysis of the Evergreen Point Floating BridgePeterson, Scott Thomas, January 2002 (has links) (PDF)
Thesis (Ph. D.)--Washington State University, 2002. / Title from PDF title page (viewed on May 26, 2005). Includes bibliographical references (p. 275-279).
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Reliability-based Design of Offshore Mooring SystemsMousavi, Mir Emad 02 October 2013 (has links)
This study proposes new methods for the reliability-based design of structural systems, with emphasis on offshore mooring systems. After a brief introduction to the mooring systems, two main objectives are discussed in this dissertation.
The first objective is the calculation of the probability of failure of a structural system, which is an important input for a reliability-based design or any quantitative risk assessment. Two different methods are proposed for calculation of the probability of failure: a method based on the Monte Carlo simulations and a method based on the basic rules of probability, which is called the Progressive Reliability Method (PRM). Both methods are flexible to the definition of system failure. For example, the probability of a serviceability or ultimate-strength failure can be assessed using any of the two methods. It is shown that the two methods produce similar results, but PRM is preferred because it is exact and usually faster to implement.
The second main objective in this dissertation is to develop a method for the optimization of the design of a structural system, given a target probability of failure. In this method, using the structural analysis of a preliminary design, the ratio of the optimal to the preliminary mean capacity of each component, which is called the Optimality Factor, is determined. Two design strategies are considered. First, an optimal design is intended to achieve the maximum system integrity. System integrity is defined as the balanced contribution of system components to its reliability. To quantify the system integrity, the Integrity Index is defined, and its calculation for various systems is discussed. Second, a designated failure scenario is considered, where some components serve as a fuse to protect some other components. This design strategy is especially applicable to mooring systems with drag anchor foundations because normally, if a drag anchor is pulled out from the seabed, it can cause significant damages to nearby subsea facilities. Using the rules of probability, a method is then developed to calculate the optimality factor of each component.
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The discrete and continuous berth allocation problem models and algorithms.Gkolias, Michail D. January 2007 (has links)
Thesis (Ph. D.)--Rutgers University, 2007. / "Graduate Program in Civil and Environmental Engineering." Includes bibliographical references (p. 194-200).
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Global Talent Flow as 'Musical Chairs' : Driving Forces of Young Talents:An Examination of Italy and LithuaniaHoerstel, Jonas, Jaeger, Patrick January 2018 (has links)
This Master thesis examines the impact of the individual driving forces of young highly educated talents from Italy and Lithuania to apply for a job abroad after the graduation. By investigating the motivations and influences during this decision-making process, we clarify the role of different impulses on the individual’s decision to become part of the phenomenon known as the global talent flow. Within this study, we obtain the actor’s view, while we use an inductive approach to put the construction of meaning of the participants in the center of our study. This aim of our qualitative study is further strengthened by the use of semi-structured interviews and the usage of the phenomenology approach. The data is analyzed and interpreted according to the emerged themes and linked back to the existing theory on‘migration’, the ‘Push-Pull-Mooring’ paradigm, the ‘gravity’ model, and the knowledge flow according to ‘brain gain’, 'brain drain’, and ‘brain circulation’. This study highlights the variety of facets which are of importance to the individuals within the decision-making process of the non-rational phenomenon of the global talent flow. Although the main motivation - the opportunity to grow - is shared among all participants, a clear distinction can be made between the ‘professional’ and the ‘personal’ growth. Furthermore, our study reveals the direct influence of initiatives taken by the European Union (EU), such as the ERASMUS+ Programme on the mobility of young talents and the impact of possible unforeseen side effects such as the ‘brain drain’ in some of the member countries of the EU. Our findings contribute another layer to the understanding of the driving forces of tomorrow’s mobile workforce to apply for a job abroad. This comprehension is fundamental to policymakers, companies, the society at larger, and the young talents themselves, as it becomes crucial to attract this ‘brain’ to secure long-term development of all stakeholders of the global talent flow within the EU.
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[en] MOORING PATTERN OPTIMIZATION USING GENETIC ALGORITHMS / [pt] OTIMIZAÇÃO DA DISPOSIÇÃO DE LINHAS DE ANCORAGEM UTILIZANDO ALGORITMOS GENÉTICOSALONSO JOAQUIN JUVINAO CARBONO 03 May 2006 (has links)
[pt] Com o crescimento da demanda de óleo, as empresas de
petróleo têm
sido forçadas a explorar novas reservas em águas cada vez
mais profundas. Em
função do alto custo das operações de exploração de
petróleo, torna-se
necessário o desenvolvimento de tecnologias capazes de
aumentar a eficiência
e reduzir os custos envolvidos. Neste contexto, a
utilização de unidades
flutuantes torna-se cada vez mais freqüente em águas
profundas. O
posicionamento das unidades flutuantes durante as
operações de exploração de
óleo é garantido pelas linhas de ancoragem, que são
estruturas flexíveis
compostas, geralmente, por trechos de aço, amarras e/ou
cabos sintéticos. O
presente trabalho apresenta o desenvolvimento de um
Algoritmo Genético (AG)
para solucionar o problema da disposição das linhas de
ancoragem de unidades
flutuantes utilizadas nas operações de exploração de
petróleo. A distribuição das
linhas de ancoragem é um dos fatores que influencia
diretamente nos
deslocamentos (offsets) sofridos pelas unidades flutuantes
quando submetidas
às ações ambientais, como ventos, ondas e correntes. Desta
forma, o AG busca
uma disposição ótima das linhas de ancoragem cujo objetivo
final é a
minimização dos deslocamentos da unidade flutuante. Os
operadores básicos
utilizados por este algoritmo são mutação, crossover e
seleção. Neste trabalho,
foi adotada a técnica steady-state, que só efetua a
substituição de um ou dois
indivíduos por geração. O cálculo da posição de equilíbrio
estático da unidade
flutuante é feito aplicando-se a equação da catenária para
cada linha de
ancoragem com o objetivo de se obterem as forças de
restauração na unidade, e
empregando-se um processo iterativo para calcular a sua
posição final de
equilíbrio. / [en] With the increasing demand for oil, oil companies have
been forced to
exploit new fields in deep waters. Due to the high cost of
oil exploitation
operations, the development of technologies capable of
increasing efficiency and
reducing costs is crucial. In this context, the use of
floating units in deep waters
has become more frequent. The positioning of the floating
units during oil
exploitation operations is done using mooring lines, which
are flexible structures
usually made of steel wire, steel chain and/or synthetic
cables. This work
presents the development of a Genetic Algorithm (GA)
procedure to solve the
problem of the mooring pattern of floating units used in
oil exploitation operations.
The distribution of mooring lines is one of the factors
that directly influence the
displacements (offsets) suffered by floating units when
subjected to
environmental conditions such as winds, waves and
currents. Thus, the GA
seeks an optimum distribution of the mooring lines whose
final goal is to minimize
the units´ displacements. The basic operators used in this
algorithm are mutation,
crossover and selection. In the present work, the steady-
state GA has been
implemented, which performs the substitution of only one
or two individuals per
generation. The computation of the floating unit´s static
equilibrium position is
accomplished by applying the catenary equilibrium equation
to each mooring line
in order to obtain the out-of-balance forces on the unit,
and by using an iterative
process to compute the final unit equilibrium position.
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