Search Results (10)

This study aims at enhancing platform design and passive control technology, reducing maintenance costs, and increasing stability and efficiency. The selected site for this study is offshore water in Hsinchu, Taiwan. Owing to shallow water conditions at the selected site, an octagonal barge-type platform was chosen for investigation of its suitability in this study. A counterweight suspension system was used to improve stability and avoid pitch resonance. Meanwhile, an octagonal barge platform carrying the NREL-5MW offshore wind turbine was designed. It uses SolidWorks for modeling, Ansys AQWA for hydrodynamic calculations, and Orcina OrcaFlex for wind/wave/current coupling dynamic analysis. Key research results include optimizing the counterweight suspension system and ensuring compliance with Det Norske Veritas (DNV) regulations, covering Ultimate Limit States (ULSs), Accidental Limit States (ALS)s, Serviceability Limit States (SLSs), and Fatigue Limit States (FLSs). Thus, the major inspections include platform motions, mooring line tension, and suspension system tension during turbine operation and parking. Comparisons are made with and without the counterweight suspension system. Full article

Jehovah’s Witnesses (JWs) are known as a religious group compliant with the national laws in the case of smoking, but not-compliant when it comes to blood treatment. Their beliefs prevent them from taking part in a blood transfusion, which is widely included in standard methods of a life-saving treatment. The aim of this study was to compare the behavior of JWs regarding their approach to blood treatment and to smoking in relation to legal regulations in the field of health. We measured JWs’ compliance with health laws regarding blood treatment and smoking (the Framework Convention on Tobacco Control—FCTC). We used the concept of a semi-autonomous social field by Moore and the theory of planned behavior developed by Ajzen. Our findings show that in the case of JWs, the group rules often prevail over state rules contained in generally-binding legislation. In the case of smoking, this means that they seem compliant to the FCTC and to their group rules. In the case of blood treatment, it seems that they are breaking the national rules, because of their group rules. Breaking the latter can result in exclusion from the JWs community. JWs are compliant with national laws as long as these are congruent with their own group rules. If this is not the case, the group influence is very strong and the fear of exclusion from the JW group is often greater than the potential negative health consequences in real life. Full article

This paper evaluates the effect of a large-capacity electrical energy storage, e.g., Li-ion battery, on optimal sailing routes, speeds, fuel choice, and emission abatement technology selection. Despite rapid cost reduction and performance improvement, current Li-ion chemistries are infeasible for providing the total energy demand for ocean-crossing ships because the energy density is up to two orders of magnitude less than in liquid hydrocarbon fuels. However, limited distance zero-emission port arrival, mooring, and port departure are attainable. In this context, we formulate two groups of numerical problems. First, the well-known Emission Control Area (ECA) routing problem is extended with battery-powered zero-emission legs. ECAs have incentivized ship operators to choose longer distance routes to avoid using expensive low sulfur fuel required for compliance, resulting in increased greenhouse gas (GHG) emissions. The second problem evaluates the trade-off between battery capacity and speed on battery-powered zero-emission port arrival and departure legs. We develop a mixed-integer quadratically constrained program to investigate the least cost system configuration and operation. We find that the optimal speed is up to 50% slower on battery-powered legs compared to the baseline without zero-emission constraint. The slower speed on the zero-emission legs is compensated by higher speed throughout the rest of the voyage, which may increase the total amount of GHG emissions. Full article

This paper presents the design and analysis of a mooring buoy and its mooring systems to moor a floating platform mounting an arrayed Wave Energy Converters (WECs). The mooring buoy allows the WEC platform to weathervane around the mooring buoy freely by the prevailing environment directions, which enables consistent power generation. The WEC platform is connected to the buoy with synthetic hawsers, while station-keeping of the buoy is maintained with catenary mooring lines of chains tied to the buoy keel. The buoy also accommodates a power cable to transfer the electricity from the WEC platform to the shore. The WEC platform is designed to produce a total of 1.0 MW with multiple WECs installed in an array. Fully coupled time-domain analyses are conducted under the site sea states, including extreme 50 y and survival 100 y conditions. The buoy motions, mooring tensions and other design parameters are evaluated. Strength and fatigue designs of the mooring systems are validated with requirements according to industry standards. Global and local structural designs of the mooring buoy are carried out and confirm the design compliances. Full article

Boating and shipping operations, their associated activities and supporting infrastructure present a potential for environmental impacts. Such impacts include physical changes to bottom substrate and habitats from sources such as anchoring and mooring and vessel groundings, alterations to the physico-chemical properties of the water column and aquatic biota through the application of antifouling paints, operational and accidental discharges (ballast and bilge water, hydrocarbons, garbage and sewage), fauna collisions, and various other disturbances. Various measures exist to sustainably manage these impacts. In addition to a review of associated boating- and shipping-related environmental impacts, this paper provides an outline of the government- and industry-related measures relevant to achieving positive outcomes in an Australian context. Historically, direct regulations have been used to cover various environmental impacts associated with commercial, industrial, and recreational boating and shipping operations (e.g., MARPOL). The effectiveness of this approach is the degree to which compliance can be effectively monitored and enforced. To be effective, environmental managers require a comprehensive understanding of the full range of instruments available, and the respective roles they play in helping achieve positive environmental outcomes, including the pros and cons of the various regulatory alternatives. Full article

According to the general public in Slovakia, compliance with the law is problematic when it comes to Roma and health. Roma compliance with laws has not yet been studied. The aim of this is study was to explore the determinants of Roma behavior in the field of health laws. We used the concept of a semi-autonomous field proposed by Moore (1973) and the theory of planned behavior by Ajzen (1985). We found that Roma (non-)compliance with health laws was influenced by many different factors, such as beliefs, traditions, living conditions and culture. Group beliefs overrule national laws and also individual preferences, which tend to be subordinate to the group view. The less contact Roma from settlements have with non-Roma, the stronger their own rules are in the field of health. Roma health status is influenced by many factors: group beliefs and community traditions are stronger and overrule individual and state behavioral influence. A community-based participatory approach together with improvement of living conditions in cooperation with Roma is desirable. Full article

The paper aims at investigating the interactions between a floating wave energy device (WEC) and its mooring system under a variety of wave conditions (regular and irregular, perpendicular and oblique, ordinary and extreme). The analyzed WEC is the DEXA, a wave activated body point absorber, of the type that performs better when aligned to the incident wave direction. Two typologies of mooring systems were studied: for limited depths, the spread system, with a disposition of the lines that do not constrain the yaw movements; for large depths, the catenary anchor leg mooring (CALM) system. The spread system was experimentally investigated, including a realistic power take-off system, to capture non-linear behaviors and assess device motions, power production, and forces on mooring lines. The CALM system was numerically simulated, as mooring modelling is more reliable in deep waters and allows testing of a number of different configurations, by changing the number of the mooring lines and the mooring layout. The experiments showed that a reduction of the mooring compliancy increases the power production. The numerical simulations showed that a redundancy on the number of chains allows a better distribution of the loads, with advantages on reliability and costs. Full article

Highly-dynamic floating bodies such as wave energy convertors require mooring lines with particular mechanical properties; the mooring system must achieve adequate station keeping whilst controlling mooring tensions within acceptable limits. Optimised compliant mooring systems can meet these requirements but where compliance is achieved through system architecture, the complexity of the system increases together with the mooring footprint. This work introduces the “Exeter Tether”, a novel fibre rope mooring tether providing advantages over conventional fibre ropes. The tether concept aims to provide a significantly lower axial stiffness by de-coupling this attribute from the minimum breaking load of the line. A benefit of reduced axial stiffness is the reduction of mooring system stiffness providing a reduction of peak and fatigue loads, without increasing mooring system complexity. Reducing these loads improves system reliability and allows a reduction in mass of both the mooring system and the floating body, thus reducing costs. The principles behind the novel tether design are presented here, along with an outline of eight prototype tether variants. Results from the proof of concept study are given together with preliminary findings from sea trials conducted in Falmouth Bay. Results demonstrate that the Exeter Tether can be configured to achieve a significantly lower axial stiffness than conventional fibre rope and that the stiffness is selectable within limits for a given breaking strength. Strain values greater than 0.35 are achieved at 30% of line breaking strength; this represents more than a threefold increase of the strain achievable with a conventional rope of the same material. The tether was subjected to six months of sea trials to establish any threats to its own reliability and to inform future design enhancements in this respect. Full article

A quasi-static analysis and sensitivity investigation of two different mooring configurations—a single anchor leg mooring (SALM) and a three-legged catenary anchor leg system (CALM)—is presented. The analysis aims to indicate what can be expected in terms of requirements for the mooring system size and stiffness. The two mooring systems were designed for the same reference load case, corresponding to a horizontal design load at the wave energy converter (WEC) of 2000 kN and a water depth of 30 m. This reference scenario seems to be representative for large WECs operating in intermediate water depths, such as Weptos, Wave Dragon and many others, including reasonable design safety factors. Around this reference scenario, the main influential parameters were modified in order to investigate their impact on the specifications of the mooring system, e.g. the water depth, the horizontal design load, and a mooring design parameter. Full article

The paper presents the results of an experimental study identifying the response of a 1.5 MW Wave Dragon to extreme conditions typical of the DanWEC test center. The best strategies allowing for a reduction in the extreme mooring tension have also been investigated, showing that this is possible by increasing the surge natural period of the system. The most efficient strategy in doing this is to provide the mooring system with a large horizontal compliance (typically in the order of 100 s), which shall be therefore assumed as design configuration. If this is not possible, it can also be partly achieved by lowering the floating level to a minimum (survivability mode) and by adopting a negative trim position. The adoption of the design configuration would determine in a 100-year storm extreme mooring tensions in the order of 0.9 MN, 65% lower than the worst case experienced in the worst case configuration. At the same time it would lead to a reduction in the extreme motion response, resulting in heave and pitch oscillation heights of 7 m and 19° and surge excursion of 12 m. Future work will numerically identify mooring configurations that could provide the desired compliance. Full article