• Energy Research
• civil engineering close
• 14. Life underwater close

For both the expansion of important islands/reefs and the development of marine resources in South China Sea, a modular integrated floating structure (MIFS) system with tidal self-adaptation dolphin-fender mooring (DFM) has been proposed. The DFM, coupled with wave energy converters (WEC), can serve as an anti-motion system. Considering both the modules’ hydrodynamic interaction effect and the connectors’ mechanical coupling effect, both dynamic responses of the MIFS system and the WEC’s output power characteristics were investigated under typical sea conditions. Based on the comprehensive consideration of key factors (safety, economy, and comfort), the effects of both the DFM and module connectors were systematically studied for the MIFS system. Preliminarily optimal design parameters of corresponding connectors and WECs were suggested. The security of the MIFS system under extreme sea conditions was checked, and a promising survival strategy has been proposed. In addition, the modular expansion scheme of the MIFS system was further discussed, and the results indicated that the proposed MIFS system shows good expansibility. The WEC can not only improve both dynamic responses and the comfort of inner modules, but also make considerable wave energy contributions.

El objetivo de desarrollo sostenible (ODS) 14 de la Agenda 2030 para el Desarrollo Sostenible tiene como objetivo proteger, conservar y gestionar los ecosistemas y recursos costeros, incluso fortaleciendo su resiliencia, para evitar impactos adversos significativos. Las estructuras costeras/marinas están expuestas a condiciones ambientales agresivas, como un entorno cargado de cloruro. El deterioro de las estructuras de hormigón armado ubicadas en un entorno costero/marino puede influir en los aspectos de seguridad, económicos y de sostenibilidad de la sociedad. Por lo tanto, existe una mayor necesidad de materiales sostenibles con la capacidad de reducir los efectos del ataque de cloruro en el concreto. Este estudio experimental tiene como objetivo investigar las propiedades de ingeniería del concreto a base de metacaolín (MK) expuesto al ataque de cloruro. La investigación se realizó para diferentes relaciones w/b de 0.54–0.61. El MK, utilizado como material cementoso, se varió de 0 a 20% con un incremento de 5% y se consideraron edades de concreto de 7 a 56 días. Se investigaron los efectos de los parámetros mencionados anteriormente sobre las diversas propiedades del hormigón, como la trabajabilidad, la resistencia a la compresión y a la flexión, la durabilidad, la resistencia al ataque de cloruro y las propiedades de la microestructura de las muestras de hormigón. A partir de los resultados favorables de resistencia y durabilidad que se observaron durante el estudio experimental (resistencia a la compresión óptima de 49.8 MPa para 10% de MK y resistencia a la flexión óptima de 8.35 MPa para 5% de MK), se puede concluir que MK es un material cementoso suplementario factible para combatir el ataque de cloruro en estructuras de concreto costero/marino. Los resultados obtenidos, en combinación con la falta de dióxido de carbono CO2 liberado durante el proceso de fabricación de MK, resaltan aún más la influencia positiva de MK en la mejora de los estados de servicio y sostenibilidad de las estructuras costeras/marinas. L'objectif de développement durable (ODD) 14 du Programme de développement durable à l'horizon 2030 vise la protection, la conservation et la gestion des écosystèmes et des ressources côtières, notamment en renforçant leur résilience, afin d'éviter des impacts négatifs importants. Les structures côtières/marines sont exposées à des conditions environnementales agressives, telles qu'un environnement chargé de chlorure. La détérioration des structures en béton armé situées dans un cadre côtier/marin peut influencer les aspects de la sécurité, de l'économie et de la durabilité de la société. Par conséquent, il existe un besoin accru de matériaux durables capables de réduire les effets de l'attaque au chlorure dans le béton. Cette étude expérimentale vise à étudier les propriétés techniques du béton à base de métakaolin (MK) exposé à une attaque au chlorure. L'enquête a été menée pour différents rapports w/b de 0,54-0,61. Le MK, utilisé comme matériau cimentaire, a varié de 0 à 20% avec un incrément de 5% et des âges de béton de 7 à 56 jours ont été considérés. Les effets des paramètres susmentionnés sur les différentes propriétés du béton telles que la maniabilité, la résistance à la compression et à la flexion, la durabilité, la résistance à l'attaque au chlorure et les propriétés de microstructure des échantillons de béton ont été étudiés. D'après les résultats favorables de résistance et de durabilité observés au cours de l'étude expérimentale (résistance optimale à la compression de 49,8 MPa pour 10% de MK et résistance optimale à la flexion de 8,35 MPa pour 5% de MK), on peut conclure que MK est un matériau cimentaire supplémentaire réalisable pour lutter contre l'attaque au chlorure dans les structures en béton côtières/marines. Les résultats obtenus, en combinaison avec le manque de dioxyde de carbone CO2 libéré au cours du processus de fabrication de MK, soulignent davantage l'influence positive de MK sur l'amélioration de l'état de fonctionnement et de la durabilité des structures côtières/marines. The sustainable development goal (SDG) 14 of the 2030 Agenda for Sustainable Development aims at protection, conservation, and management of coastal ecosystems and resources, including by strengthening their resilience, to avoid significant adverse impacts. Coastal/marine structures are exposed to aggressive environmental conditions, such as chloride laden environment. Deterioration of reinforced concrete structures located in a coastal/marine setting can influence the safety, economic and sustainability aspects of the society. Hence, there is an increased need for sustainable materials with the ability to reduce the effects of chloride attack in concrete. This experimental study aims to investigate the engineering properties of metakaolin (MK) based concrete exposed to chloride attack. The investigation was conducted for different w/b ratios of 0.54–0.61. The MK, utilised as cementitious material, was varied from 0 to 20% with an increment of 5% and ages of concrete from 7 to 56 days were considered. The effects of the above-mentioned parameters on the various properties of concrete such as workability, compressive and flexural strength, durability, resistance to chloride attack and microstructure properties of the concrete samples were investigated. From the favourable strength and durability results that were observed during the experimental study (optimum compressive strength of 49.8 MPa for 10% MK and optimum flexural strength of 8.35 MPa for 5% MK), it can be concluded that MK is a feasible supplementary cementitious material for combatting chloride attack in coastal/marine concrete structures. The obtained results, in combination with the lack of carbon dioxide CO2 released during the MK manufacturing process, further highlights the positive influence of MK on improving the serviceability and sustainability states of coastal/marine structures. يهدف هدف التنمية المستدامة 14 من خطة التنمية المستدامة لعام 2030 إلى حماية النظم الإيكولوجية والموارد الساحلية وحفظها وإدارتها، بما في ذلك من خلال تعزيز قدرتها على الصمود، لتجنب الآثار السلبية الكبيرة. تتعرض الهياكل الساحلية/البحرية لظروف بيئية قاسية، مثل البيئة المحملة بالكلوريد. يمكن أن يؤثر تدهور الهياكل الخرسانية المسلحة الموجودة في بيئة ساحلية/بحرية على جوانب السلامة والاقتصاد والاستدامة في المجتمع. وبالتالي، هناك حاجة متزايدة للمواد المستدامة مع القدرة على الحد من آثار هجوم الكلوريد في الخرسانة. تهدف هذه الدراسة التجريبية إلى التحقيق في الخصائص الهندسية للخرسانة القائمة على الميتاكاولين المعرضة لهجوم الكلوريد. تم إجراء التحقيق لنسب وزن/وزن مختلفة من 0.54–0.61. تم تغيير MK، المستخدم كمواد أسمنتية، من 0 إلى 20 ٪ بزيادة قدرها 5 ٪ وتم النظر في أعمار الخرسانة من 7 إلى 56 يومًا. تم التحقيق في تأثيرات المعلمات المذكورة أعلاه على الخصائص المختلفة للخرسانة مثل قابلية التشغيل وقوة الانضغاط والانثناء والمتانة ومقاومة هجوم الكلوريد وخصائص البنية المجهرية لعينات الخرسانة. من نتائج القوة والمتانة المواتية التي لوحظت أثناء الدراسة التجريبية (مقاومة الانضغاط المثلى البالغة 49.8 ميجا باسكال لـ 10 ٪ MK وقوة الانثناء المثلى البالغة 8.35 ميجا باسكال لـ 5 ٪ MK)، يمكن استنتاج أن MK هي مادة أسمنتية تكميلية مجدية لمكافحة هجوم الكلوريد في الهياكل الخرسانية الساحلية/البحرية. تسلط النتائج التي تم الحصول عليها، جنبًا إلى جنب مع نقص ثاني أكسيد الكربون CO2 المنبعث أثناء عملية تصنيع MK، الضوء على التأثير الإيجابي لـ MK على تحسين قابلية الخدمة وحالات الاستدامة للهياكل الساحلية/البحرية.

[EN] The recently established Sustainable Development Goals recognize the importance of infrastructures for achieving a sustainable future. Along their long-lasting life cycle, infrastructures generate a series of impacts, the reduction of which has been one of the main focus of researchers¿ attention in the past years. The optimization of maintenance intervals of structures, such as bridges, has aroused the attention of the civil engineering sector, since most of the impacts of infrastructures occur during the operational phase. Thus, bridges are currently designed to attend the economic and environmental impacts derived from maintenance activities. However, the social pillar of sustainability is usually neglected in those analyses. Since no universally accepted methodology does yet exist for its consistent evaluation, the social dimension is not effectively included in the life cycle assessments of infrastructures. This communication evaluates the life cycle impacts of alternative concrete bridge deck designs in a maintenance-demanding environment near shore. Reliability-derived maintenance intervals are first optimized by minimizing the economic and environmental impacts. In a second stage of the analysis, the social dimension is included in the optimization process and results are compared. Optimization results from these combined assessments are obtained applying the Multi-Criteria Decision-Making technique AHP-TOPSIS. The present paper demonstrates how the inclusion of the social dimension may lead to different, more sustainability-oriented optimal maintenance strategies. The three-dimensional approach applied here has resulted in other alternatives to be preferred against those derived from the conventional assessment that considers the economic and environmental perspectives. Such finding supports the idea that holistic life cycle assessments are required for sustainable designs of infrastructures and that more efforts are urgently needed to integrate the social dimension in sustainability assessments of structures. The authors acknowledge the financial support of the Spanish Ministry of Economy and Competitiveness, along with FEDER funding (Project: BIA2017-85098-R).

Standard environmental condition is one of the main inputs in designing a vessel especially in assessment of stability condition. The performance based minimum stability requirements are determined by assessing vessels' dynamic failure modes. Winds as well as wind generated waves are the main factors that affect a specific vessel’s dynamics. Wind generated waves in rivers though are usually small in comparison with ocean waves may play a crucial role behind inland vessels accidents. The river condition of a crucial location in Bangladesh inland river routes is assessed where wind velocities have been taken for a specific duration from a reliable secondary source. A narrow fetch model that considers the wave generation in off-wind direction for estimating wind wave parameters has been used to consider the spiral shape of Bangladesh inland routes. The Bretschneider energy spectrum model for short term wave state is compared with the fetch limited model JONSWAP for the estimated wave condition. This study indicates the rationality of conforming the safety level of Bangladesh inland vessels equivalent to river-sea vessels as defined by other nationals and the classification societies. The wave parameters that are estimated in this study can be used to form a limited wave scatter table for predicting short term environmental conditions to assess the dynamic stability failure modes of the vessels.

In recent years, many oil and gas fields have been discovered in ultra-deep sea (UDS). Some of these fields are evaluated to have no commercial value if existing oil field development approaches are used, especially while the oil prices remain low. A new alternative field development solution, termed as Subsurface Well Completion (SWC) system, is proposed with the aim to produce oil and gas in a cost-effective manner in UDS. This system primarily consists of four parts: a tethered subsurface platform, the rigid riser, SWC equipment and flexible jumper. Obviously, central to the evaluation and application of the new SWC technology is the inherent risk relative to acceptance level. In particular, an uncontrolled release of hydrocarbons to sea, which may lead to catastrophical consequences involving personnel risk, environmental damage and economic losses, is a main contributor to the total risk and of great concern to the offshore petroleum industry. As for the new SWC system, any failure will not be a direct source of risk for the personnel on the surface installation due to its offset feature. In this context, this paper proposes a quantitative risk assessment (QRA) framework to assess such uncontrolled releases to sea with regard to the SWC system for an oil field in the production phase based on the new Subsurface Tension Leg Production (STLP) facility. According to the QRA results presented in this paper, the identified scenarios representing uncontrolled releases to sea are subsea wellhead leaks, rigid riser leaks, subsurface wellhead leaks, releases from X-mas tree and flexible jumper leaks. Among these scenarios, subsea wellhead is found to be the high-risk area. Compared with the established risk acceptance criteria (RAC), the environmental risk levels for the subsea wellhead’s leak lie within the As Low As Reasonably Practicable (ALARP) region while other risks are all below ALARP limits, which means that there is a need for improved consideration of the existing design with regard to the subsea wellhead area, and the corresponding risk reduction measures are proposed. Furthermore, the sources and effects of uncertainties are reviewed and sensitivity studies are carried out to illustrate the effect of some of the important assumptions in the risk model. It can be found that some assumptions made are conservative or optimistic while others are unknown. However, the final QRA results can be regarded as somewhat conservative. This paper concludes that the new SWC technology has a distinct advantage with respect to the leakage duration time in UDS, and thus mitigates the environmental and commercial impacts to a large extent. Besides, relaxed design requirements for the X-mas tree and flexible jumper can be accepted. It is also concluded that there are no serious and major commercial losses for all the identified accidental release scenarios, which is of great importance and attractiveness to oil producers.