National Maritime Research Institute

本研究は地熱資源の有効利用促進のために地熱発電生産井の設置に適した場所を蒸気スポットと称し，地表浅部の情報から蒸気スポットの場所を数理地質学，リモートセンシング，地球化学での手法の組合せで特定できる手法の開発とその有効性の検証を目的とした．その対象として明瞭な地表地熱兆候を確認できるインドネシア・バンドン盆地南部のWayang Windu地熱フィールド(WWGF)を選んだ．DEMの多方位陰影画像から抽出したリニアメントの卓越方位はボアホール亀裂データの最卓越走向に概ね対応し，GEOFRACで作成した3次元亀裂分布モデルは断層付近で断層の方向と平行する亀裂が多く分布したので，リニアメントの卓越方位は実際の亀裂系の卓越走向に対応する可能性が高い．熱水流体の上昇域の特定にはハイパースペクトル衛星画像解析からの熱水変質鉱物の抽出と地中ガス222Rn濃度の時間的変化パターンが有効であり，カオリナイト分布の卓越部，および高222Rn濃度で測定時間が経過しても濃度がほぼ一定のパターンを示す場所で地下深部からの流体の供給が推定された．また，このような場所直下の貯留層に分布する水は蒸気や蒸気凝縮水であると解釈できたとともに，熱水の化学組成・同位体組成から地熱流体の起源や循環状態を明らかにできた．さらに，リニアメント密度，222Rn濃度，地化学データを組合せ，蒸気スポット存在評価マップを作成したところ，生産井先端の多くが高評価部に位置することがわかった．AMT比抵抗分布より，高評価部には貯留層に繋がる連続的な亀裂が発達し，高温の地熱流体の上昇が顕著である可能性が高いと解釈できたので，蒸気スポット検出法の有効性を実証できた．

The West African coast faces intensifying vulnerabilities due to climate change, rapid urbanization, and anthropogenic pressures that threaten ecosystems, livelihoods, and infrastructure. To understand these vulnerabilities and be able to decipher solutions in West Africa, a comprehensive strategy is required. Using biannual WACA-VAR workshops between 2018 and 2024, and SCOPUS analysis over the 1998–2024 period, the VOSviewer tool was used to visualize coastal vulnerability to coastal erosion, flooding, pollution, and mangrove degradation across 14 coastal nations. The paper highlights hotspots like Senegal’s Saint-Louis, Ghana’s Volta Delta, and Nigeria’s Niger Delta. These hotspots regulate the evolution of key huge ecosystems within the subregion. The study revealed a comprehensive framework categorizing the factors, expertise, tools, and challenges associated with coastal development and management in West Africa as well as data limitations, and progress made towards addressing these vulnerabilities. The study shows remote sensing tools could be prioritized to investigate nature-based solutions. Nigeria, Ghana, Ivory Coast, Senegal, and Mauritania experience the largest vulnerability based on combined mangrove cover, water quality, and coastal hazards indices. Senegal records the highest average erosion per year, while Nigeria records the fastest decline in mangrove cover. The emergence and development of new research dynamics over the last decade within the region show some progress made to address these endeavours, yet the challenges outperform this progress. A comprehensive data management strategy focused on emerging thematic areas of research has been proposed to address large-scale and small-scale hotspots of erosion and flooding identified within this subregion. The study proposes a framework where academic, industrial, and governmental projects must be harmonized. The implementation of common standardized tools and methodologies will enhance data collection and management. It is imperative that teams, individuals, organisations, and their efforts deployed in terms of hotspot management focus on bridging existing knowledge gaps. Thematic expert teams should be provided with actionable guidelines and methodologies for the implementation of strategies at these identified hotspots.

Abstract An installation time estimation model for floating offshore wind farms (FOWFs) has been studied and validated based on the cost breakdown structure, and the unit-installation time has been estimated using data from FOWF projects. However, since the unit-installation time includes weather downtime, applying it to other areas with different weather conditions is challenging. In this paper, we propose an installation time estimation model for FOWFs that incorporates weather characteristics specific to the project site, extending upon our previous model. Using installation data from the Fukushima floating offshore wind farm demonstration project in Japan, we estimated actual unit-installation time excluding weather downtime and compared it with that of Hywind Scotland. The results showed that for the pre-anchoring process, the total of the pre-installation time per mooring line and the tensile testing time per anchor in Japan is about 4.1 times longer than those in Europe. As for submarine cables, the time for connecting one side of a riser cable to a floater is 9.3 times longer and the velocity of the trenching cables is 7.5 times slower. Assuming a theoretical FOWF, the total installation time in Japan, Korea, and Taiwan varies from 899 days to 1,214 days. After performing a sensitivity analysis, we found that the total installation time can be reduced by 61% if we adjust the actual unit-installation time and the weather restrictions from the present conditions in Japan to those in Europe. These findings indicate that our model can provide a more general framework for estimating the installation time of FOWF.

Abstract Subsea minerals have been found in the deep water within Japan’s exclusive economic zone. However, the development of subsea minerals has not reached the commercialization stage because many technical issues still need to be addressed. One of the promising lifting methods is a gas lift pumping system. For the gas lift pumping system, the internal flow in pipes is a gas–liquid–solid three-phase flow. Estimating the velocity of each phase is an essential technique for designing and operating the system. However, studies focusing on the velocity of each phase for three-phase flows are few and it is not clear that the effect of internal diameter of pipes on the correlation for the gas and solid velocities in three-phase flows. We have experimented with three-phase flows for the pipes of 26, 41, and 52 mm in internal diameter, and obtained data on the volume fractions of each phase. To investigate the effect of internal diameter on the correlation for gas and solid velocities, we experiment with three-phase flows using the pipe of 79 mm in internal diameter and obtain a new dataset for large diameter. Then, we analyze the data obtained from the present and previous experiments. When the ratio of particle diameter to pipe diameter is more than about 0.15, the distribution parameter in drift flux model is affected by the existence of solid particles. The solid velocity increases linearly with increasing liquid velocity in three-phase flows. The effect of internal diameter on the distributions of liquid velocity or solid volume fraction is small.

Abstract For the design and operation of a subsea mining system, it is important to predict pressure loss due to the hydraulic transport of solid particles in the flexible jumper, which connects a seafloor mining tool to a vertical lifting pipe via the subsea slurry pump. The jumper should have steep wave configurations so the mining tool can move freely on the seafloor. In the present paper, we propose a mathematical model to predict the pressure losses of slurry flow in curved pipes. we first calculate the pressure loss in curved pipes with steep wave configuration using the model for inclined straight pipes that we developed in the previous work. Then, we carried out the slurry transport experiment and compared the calculated results with the experimental ones. The results show that the model for straight pipes is able to predict the pressure loss in curved pipes with a high accuracy of more than 92 % for the coefficient of determination. Then we have newly considered the centrifugal forces acting on solid particles in our mathematical model. We compared the calculated results using the new model with the experimental ones. These are in further good agreement, which indicates the new model is more applicable for predicting pressure loss in a flexible jumper with steep wave configuration.

Background: The occurrence of natural disaster in Southeast Asia due to its location along the Asia Pacific Ring of Fire is high. The consequences of the natural disasters on various aspects, like that social, financial, and food security can be large. This initiative promotes the development of emergency food products to address the daily nutritional requirements of natural disaster victims, ensuring their survival. The specified standard is 2,100 kcal/day, emphasizing a balanced distribution of macronutrients (40-50% carbohydrates, 35-45% fat, and 10-15% protein). Objectives: This literature review explored the potential raw materials for emergency food products in the Southeast Asia. Methods: This review utilized databases from Google Scholar and PubMed websites, employing specific keywords for each identified category to gather the latest literature. The literature obtained was 10 article. Discussions: This review explores solutions to the challenges posed by natural disasters in Southeast Asia, focusing on the potential use of locally available resources as raw materials for emergency food products. Raw materials, including Fish Hydrolyzate Protein (FPH), offer numerous benefits due to their bioactive contents, such as antioxidant, antihyperglycemic, antimicrobial, antitumor, ACE inhibitor activity, calcium binding, and anticoagulant properties, particularly beneficial for vulnerable groups. The review also delves into the elimination of raw materials, the nutritional content of various types of emergency food products, and innovative solutions for emergency food products in Southeast Asia. Conclusions: The potential raw materials identified have the capability to yield innovative emergency food products with both excellent physicochemical quality and health potential.

Autonomous Underwater Vehicles (AUVs) playa vital role in underwater operations, such as environmental monitoring and exploration. Designing effective control systems for AUVs requires an accurate understanding of their dynamic characteristics. This study proposes a novel methodology for deriving the dynamic model of an AUV, combining simplified model-based Computational Fluid Dynamics (CFD) analyses with lift-coefficient-based hydrodynamic force estimation. Our approach is particularly advantageous in the early stages of AUV design, as it significantly reduces the time and effort needed to derive the dynamic model.

Compared to inland ship transportation, navigating through icy regions presents several challenges, such as dense sea ice and navigating in high latitude environments. Because Arctic Sea ice continues to diminish annually, the Arctic waterways may become increasingly navigable in the future. Therefore, it is crucial to assess the safety risks associated with shipping in icy areas. To identify and quantify these risks, this study introduces a novel risk assessment method. Initially, this study surveys current research trends in icy regions through the literature review and identifies risk factors based on marine casualties and accident data. Subsequently, a comprehensive risk matrix evaluation model is proposed, integrating aspects such as fault frequency, severity of worst-case outcomes, and effectiveness of mitigation measures. The Delphi method is employed to enhance scientific evaluation and establish a structured hierarchy for risk assessment. Additionally, the grey relational analysis method is introduced to verify the model’s rationality by calculating correlations between factors. Using Northwest Arctic shipping as a case study, the calculated correlation coefficients of risk factors exceed 0.8, indicating the efficacy of the established evaluation model in scientifically assessing ship navigation risks in icy areas. Furthermore, this paper recommends targeted preventive measures, offering a foundation for developing risk management strategies tailored to Arctic Northwest shipping, thereby ensuring the safety of operations in this challenging maritime environment.