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Kim, Yonghwan (Seoul National University) | Park, Dong-Min (Seoul National University) | Lee, Jae-Hoon (Seoul National University) | Lee, Jaehoon (Seoul National University) | Kim, Byung-Soo (Seoul National University) | Yang, Kyung-Kyu (Seoul National University) | Oh, Semyun (Samsung Heavy Industries) | Lee, Dong-Yeon (Samsung Heavy Industries)
In this study, the added resistance of a liquefied natural gas carrier (LNGC) in the presence of waves is studied experimentally and numerically. The ship model is an LNGC designed by Samsung Heavy Industries (SHI). Experiments on ship motion responses and added resistance under head sea conditions were conducted at the Seoul National University and SHI. The influences of the experimental methods (captive and self-propulsion methods), incident wave amplitude, and regular and irregular wave conditions on the added resistance are evaluated using the same model ship set at different scales. In the numerical studies, the motion responses and added resistance are obtained using three methods—the strip method by adopting momentum conservation; Rankine panel method using pressure integration; and computational fluid dynamics method, using the difference in the resistances in waves and calm water. The experimental and numerical results under various conditions are compared, and the characteristics of the experimental and numerical results are discussed.
Unlike the resistance in calm water, additional resistance occurs because of winds, waves, current, and for other reasons in a seaway. This aforementioned resistance, caused by environmental conditions, is called an added resistance. Among the various types, the added resistance caused by water waves is investigated in this study.
Modularity in the design and construction of naval vessels is considered wherein modular installations that provide basic ship structure and services allowing various mission packages to be installed and interchanged as necessary are integrated in an otherwise conventional ship envelope. Consideration is given to providing a ship envelope from a primarily commercial shipbuilder, which could include such modules, but which is then transferred to a naval shipyard integrator for completion, including those modules which are purely naval mission oriented. In the context of such consideration the competitive practices of international commercial shipbuilders, particularly related to large passenger ships, suggest a potential application to naval vessels.
The resistance of ships is often dominated by friction between the hull and the water. This study explores possibilities of reducing skin-friction drag in a way inspired by dolphins. These possess a soft skin believed to diminish drag by delaying the transition from laminar to turbulent flow. The underlying mechanism builds on a stabilization of the laminar boundary layer by the compliant surface. To transfer this mechanism to ship hulls, coatings similar to dolphin skin have been designed numerically, made from polymeric materials, and tested in a water tunnel. For the best coating, a drag reduction by almost 3% has been predicted in the boundary layer along the hull model of a small search-and-rescue vessel. The trends of the numerical predictions have been confirmed in the experiments.
Dolphins are able to sustain a swimming speed of about 9 m/sec across long distances (Carpenter et al. 2000). This fascinating endurance has stimulated the hypothesis that the pliable dolphin skin interacts with the surrounding flow so as to maintain low-drag laminar flow via a delay of transition to turbulence (Gad-el-Hak 1996). Although this hypothesis is under debate (Fish & Lauder 2006), laboratory experiments have indeed demonstrated that soft coatings delay laminar-turbulent transition (Gaster 1987). According to boundary-layer linear stability theory (LST), compliant surfaces are able to mitigate the amplification of Tollmien-Schlichting (TS) waves, the forerunners of transition in low-disturbance environments (Carpenter & Garrad 1985). However, wall compliance may also promote transition in that the flow may excite instability waves borne by the soft coating material. These waves are known as fluid-induced surface instabilities (FISI) (Carpenter & Garrad 1985) or travelling-wave flutter (Gad-el-Hak 1996). FISI waves may in turn via nonlinear effects develop into quasi-steady surface corrugations (“divergence”) (Carpenter & Garrad 1986). This process is associated with an absolute instability mechanism (Tsigklifis & Lucey 2015) that rapidly triggers transition via the bypass route. The boundary-layer instability over a compliant coating is hence more complex than that over a rigid surface owing to the presence of two wave-bearing media. Compliant-wall boundary layers also support non-modal transient growth inducing bypass transition (Tsigklifis & Lucey 2015).
Kim, Hyun-Sung (Korea Research Institute of Ships and Ocean Engineering / University of Science and Technology) | Kim, Byoung Wan (Korea Research Institute of Ships and Ocean Engineering / University of Science and Technology) | Lee, Kangsu (Korea Research Institute of Ships and Ocean Engineering) | Sung, Hong Gun (Korea Research Institute of Ships and Ocean Engineering)
In case that a topside is transported to an installation site by using a deck transportation vessel, a topside could be fixed by using seafastening structures to be installed to a transportation vessel safely. Topside and seafastening structures behave in connection with the transportation vessel. Thus, to check the safety of the structure for the transportation period, the fatigue analysis of the seafastening structures in the coupled behavior of the transportation vessel and the topside is conducted in this work. Rainflow count algorithm is used to analyze a fatigue damage and the life of the seafastening structure. In this study, the number of environmental cases for the analysis is 14 and each case is analyzed to estimate each fatigue damage. And these damages of seafastening structures in each case are summed and fatigue life is obtained from the total fatigue damage. Because many calculation time is needed for all analysis cases, the average sea-state method is proposed. Expectation average values of significant wave height and peak period could be solved to use representative one for analysis cases. This average sea-state case is analyzed only once in the method. The fatigue damage and life of seafastening structure are estimated by using the result of the average sea-state method and compared with the results in common method.
The transportation method for an offshore structure becomes more important as offshore structures are getting larger and an installation depth becomes deeper. In case that a large offshore structure itself cannot be transported once, the structure is transported by splitting it into two parts that are lower support structure and topside. The lower support structure can float on the water surface by using its own buoyancy and thus, is transported by using tugboats. But the topside has not a buoyancy and also consists of equipment unfamiliar with water such as electrical, chemical, mechanical systems and so on. Thus the topside can be transported by using a deck transportation vessel (DTV) to avoid a direct contact with water. To be transported safely to an installation site, topside must be fixed to the transportation vessel by using the seafastening structures.
A literature study of existing methods for estimating the resistance of ships in ice is presented and a review of the influence of several ship particulars on the level ice resistance is made. The applicability of the Lindqvist method to vessels with conventional bow shapes is assessed, pointing out the strengths and weaknesses of the formulation. The concept of an improved method based on weighting factors is presented. Finally, recommendations for a model test campaign with an instrumented model are given in order to acquire sufficient knowledge to develop a revised method.
For typical icebreaker shaped vessels with an inclined bow and low flare angles the major components of the hull-ice interaction process are quite well understood. Analytical methods exist to predict the average resistance based on few inputs for the hull shape characteristic and ice properties. For non-typical icebreaking ships the interaction process includes many unknown phenomena like cracking, splitting and crushing, which are difficult to be described by straight forward approaches. Furthermore, the accumulation and clearing of the broken ice floes is completely different. Finally, the database (e.g. from model tests) of performance records for such vessels in solid ice is very limited.
The demand for a more profound understanding of ice interaction with non-icebreaker shaped vessels results from an increasing number of those ships accessing Arctic and Antarctic waters. Examples are cruise expedition vessels and government vessels with multiple missions (coast guard, rescue and salvage). Even if the sailing time of those vessels in ice is limited to few weeks in a year, a detailed assessment of their capabilities in ice is required to optimize their design and operational profile.
A study is proposed to investigate and understand the basic process of sea-ice interaction with ships of open-water or moderate icebreaking shape. The objective of the study is to identify the major process phenomena and to find correlations between parameters, especially those between the hull geometry, ice properties and motion characteristic of a vessel. The study is supported by the Office of Naval Research (ONR) and includes theoretic investigation and physical model tests conducted in the large ice model basin at the Hamburg Ship Model Basin (HSVA). The aims are as follows:
– improve principal understanding of the hull-ice interaction process, ice failure and the components contributing to the ice resistance
– find methods to evaluate the ice performance (ice resistance, attainable speed) as well as the factors of major influence
– enhance quantity and quality of ship-ice interaction observations
– provide a database of results obtained under controlled conditions
Strength-temperature relationships are presented for four categories of ice: first-year ice (FYI), second-year ice (SYI), young multi-year ice (yMYI) and thick multi-year ice (TkMYI). The equations are based upon the borehole strengths (BHS) measured during 876 tests in 162 boreholes. The strength of every type of sea ice decreases with increasing ice temperature. FYI and SYI are governed by nearly identical BHS-temperature relations for overlapping temperatures in the range −10°C to 0°C, but it is also important to note that SYI can be expected to deteriorate about one month later than FYI. The BHS-temperature relations for yMYI and TkMYI are similar over the temperature range −9°C to −2°C. Factors other than ice temperature affect ice strength, so it is to be expected that equations based solely upon ice temperature cannot reproduce the BHS exactly. The BHS was overestimated for 56.8 to 69.4% of tests performed at individual test depths and 61.1 to 72% of the depth-averaged BHS for individual boreholes, depending upon ice category. Cold ice produces the lowest relative errors in strength, and warm porous ice the highest relative errors in strength.
Multi-year ice (MYI) and second-year ice (SYI) exert the highest loads on offshore structures (Frederking and Sudom, 2006; Sudom and Frederking, 2010). MYI and SYI are not the same, yet they are usually grouped together as ‘old ice’, which the WMO (1985) defines as sea ice that has survived at least one summers’ melt. Differentiating MYI and SYI has become more pressing since the International Maritime Organization’s (IMO) Polar Code came into effect in January 2017. Two of the three Polar Ship categories will be permitted to transit regions of FYI that may contain old ice inclusions if the ship has (a) an appropriate ice class and (b) an approved methodology for determining the ship’s operational limitations in ice. One such methodology, POLARIS, permits mariners to differentiate between SYI, ‘light’ MYI, and ‘heavy’ MYI when the ice thickness can be determined confidently (IMO, 2014). That approach may seem reasonable since the WMO’s graduated classification system is based upon ice thickness, but it may not be appropriate for old ice because thickness can be an unreliable indicator for gauging the severity of old ice (B. Gorman personal communication; Johnston, 2012). The question that this study seeks to address is “does classifying sea ice incorrectly carry serious consequences for shipping and offshore activities?”. To help answer that question, we investigate whether different types of sea ice have different strengths, for comparable temperatures. That said, the temporal aspect (i.e. time of year) is also important because ice takes time to reach a given temperature. The temporal aspect is not examined here since it is discussed in Johnston (2017).
Ha, Yoon-Jin (Korea Research Institute of Ships & Ocean Engineering) | Nam, Bo Woo (Korea Research Institute of Ships & Ocean Engineering) | Kim, Kyong-Hwan (Korea Research Institute of Ships & Ocean Engineering) | Hwang, Sung-Chul (Korea Research Institute of Ships & Ocean Engineering) | Hong, Sa Young (Korea Research Institute of Ships & Ocean Engineering) | Kim, Hyun Jo (Samsung Heavy Industry)
Numerical simulations were carried out to investigate wave impact loads on bow flare of a FPSO under irregular conditions. In this study, the horizontal slamming and vertical slamming were surveyed through relation between the motions and the slamming forces. To do that, two time windows were selected from the experimental data. The horizontal and vertical slamming forces from the numerical results were directly compared with the model test results. From the results, physical phenomena of the horizontal and vertical slamming were discussed. It can be found that the horizontal slamming force as well as the vertical slamming force are significant as design parameter.
In sea, various environmental forces are existed and a structural damage happen to a ship and an offshore platform by the environmental forces. The wave force of various environmental forces is relatively strong and the wave induced force should be applied to design a ship and an offshore platform. The reason is that a local damage on the ship and the offshore platform can occur by the wave. Therefore, the structural safety as well as the hydrodynamic performance of a ship and an offshore platform should be confirmed at design phase. The wave force can be representatively divided to occurrence phenomena, such as the green water, the slamming, the sloshing, the wave-in deck and etc.. Of that, the slamming force is relatively important because the slamming force can frequently occur due to ever-present wave. So, the fatigue damage on a ship and an offshore platform can occur. The slamming forces can divided two types which are the horizontal slamming force and the vertical slamming force by the force action directions. However, most researches by the experiments were focused on the vertical slamming. Kim et al. (2014) studied the vertical slamming impact forces on symmetric and asymmetric wedges from the free drop model tests. The results of the model tests were directly compared with the analytic solutions. The vertical slamming model tests were performed not only simple structure but also ship-type structure. Kim et al. (2019) investigated the bow impact loading on a 10,000TEU containership. They used the segmented model and the slamming forces were measured in regular and irregular waves according to the heading angles. Also, they tried to estimate the slamming forces which the ship sections were simplified to wedge shapes. Not only the model test but also the CFD (Computational Fluid Dynamics) analysis are widely applying for the slamming study. Most researches using the CFDs were studied for the horizontal slamming on a fixed structure. Khayyer and Gotoh (2009) estimated the slamming impact pressures on a vertical wall using modified MPS (Moving Particle Semi-implicit). Interestingly, they considered the air compressibility for the estimation of the slamming impact pressure. The numerical results showed the more accurate and the stable pressure filed. Ha et al. (2018) showed the possibility for estimation of the slamming forces using CFD. The numerical simulations were performed for the slamming impact on a truncated circular cylinder by breaking waves. Seo and Jeong (2019) performed numerical simulations for bow flare slamming of a container ship in regular waves. They compared between the calculated results and estimated values by rules. As the fundamental study considering a moving body by CFD, numerical simulations were performed to survey the characteristics of the slamming phenomena on a FPSO model in this study. To do that, the 6-DoF motions of the model and 15 force measuring locations were considered in the numerical simulations. The results of the numerical simulations were directly compared with the existing model test results and the slamming phenomena in the horizontal and vertical directions were discussed from the numerical studies.
Park, Dong-Min (Seoul National University) | Lee, Jae-Hoon (Seoul National University) | Lee, Jaehoon (Seoul National University) | Kim, Beom-Soo (Seoul National University) | Kim, Byung-Soo (Seoul National University) | Yang, Kyung-Kyu (Seoul National University) | Kim, Yonghwan (Seoul National University) | Lee, Young-Gill (INHA University) | Kim, Taeyoung (Samsung Heavy Industries) | Yang, Jin-Ho (Hyundai Heavy Industries) | Song, Kang-Hyun (Korean Register of Shipping) | Jeong, Seung-Gyu (Lloyd's Register Asia) | Do, Hyung-Min (ABS Global Engineering -Busan) | Gerhardt, Frederik (SSPA Sweden AB)
This paper presents a comparative study on the motion responses and added resistance of a container ship. Eight institutions participated in the comparative study, and ten numerical results were compared with two experimental results. Two experimental results were obtained from Seoul National University towing tank and Sweden SSPA seakeeping basin. The results of two experimental institutions in head sea condition were compared and showed good agreement with each other. The difference in motion responses and added resistance according to the numerical analysis method were compared. Even though the same program was used, it was observed that different results were obtained depending on the users. The comparison of the motion response and the added resistance according to the change of wave slope showed that the added resistance greatly changed according to the wave slope. This tendency was the same in experimental results and CFD analysis results. From the comparative study, the influence of the experiment method on the added resistance, and the characteristics of numerical each code were identified.
Added resistance is the increased resistance due to waves and winds. A number of studies and projects have been conducted on added resistance since the Energy Efficiency Design Index (EEDI) regulation was presented by the International Maritime Organization (IMO). One of the projects is the Energy Efficient Safe Ship OPERAtion (SHOPERA, 2013∼2016) project in the European Union (EU). In the SHOPERA project, experiments were carried out in four experimental institutes for three types of ships. Similar project is underway in Korea (2016∼2019). This project is a four-year project supported by the Korean government, participated by eight institutions: Seoul National University, Inha University, Samsung Heavy Industries, Hyundai Heavy Industries, Daewoo Shipbuilding & Marine Engineering, Korean Register of Shipping, Lloyd’s Register Asia, ABS Global Engineering. The aim of this project is four; i) Development of highly accurate code to analyze added resistance, ii) Building added resistance database through experiments and numerical analysis, iii) Prediction of minimum power in adverse condition, iv) Hull form design considering added resistance. Experiments are planned for four ship types (LNG-carrier, VLCC, Container ship, Bulk carrier) over four years. In the first year, experiments were conducted at Samsung Heavy Industries and Seoul National University for a LNG-carrier (Kim, et al., 2018). In the second year, experiments were conducted at SSPA Sweden AB and Seoul National University for a VLCC (Park et al., 2018). In the third year, SSPA and Seoul National University conducted experiments for a container ship. This paper is about the third year experiments and numerical analysis.
Hong, Sa Young (Korea Research Institute of Ships & Ocean Engineering) | Ha, Yoon-Jin (Korea Research Institute of Ships & Ocean Engineering) | Nam, Bo Woo (Korea Research Institute of Ships & Ocean Engineering) | Kim, Kyong-Hwan (Korea Research Institute of Ships & Ocean Engineering) | Hwang, Sung-Chul (Korea Research Institute of Ships & Ocean Engineering) | Kim, Hyun Jo (Samsung Heavy Industries Co. Ltd.) | Kim, Jang Whan (Genesis Oil and Gas Consultants Ltd.) | Huang, ZhenJia Jerry (ExxonMobil Upstream Research Company)
Computational Fluid Dynamics (CFD) simulation methodologies for FPSO bow impact calculation were consolidated in a Joint Development Project (JDP). To validate the proposed simulation method, a series of model test performed for the bow wave impact problem by focusing wave was considered. First, wave generation performance was checked by applying the present CFD simulation method. In this case, the measured stroke signals of the wave maker in the model test were directly used as input of the inlet velocity boundary. Then, the numerical simulations results for wave impact forces were validated by comparing with the model test data. It is confirmed that FPSO bow impact prediction using the consolidated CFD simulation guideline is fairly good in overall physical process and wave impact forces.
Offshore structures are vulnerable to harsh environmental conditions during operation, which can result in critical wave impact loads during their lives. Depending on the impact direction, the wave impact can be divided into vertical and horizontal wave impacts. The vertical wave impact includes the bottom slamming of a ship-type offshore structure and the wave-in-deck impact of semi-submersible platform. On the other hand, the horizontal wave impact includes the column impact of the semi-submersible platform and bow flare impact of FPSO, where the large horizontal wave impact is generally caused by the breaking waves. It is known that the wave impact events can cause fatal damage on the offshore structures as well as the safety of operators. Thus, the accurate estimation of wave impact force is significant for the survivability of the offshore platform under the extreme environmental conditions.
In recent years, direct CFD simulation method is considered as a complimentary tool to estimate wave impact loads on offshore structure. Bredmose and Jacobsen (2010) analyzed the wave impact forces on a fixed monopile based on open source CFD solver (OpenFOAM). This study showed that peak wave loads on the fixed monopile can be changed depending on the impact location. Mo et al. (2013) presented large eddy simulation (LES) results about flow pattern and interaction between a breaking wave and a slender cylinder. Kamath et al. (2016) validated the CFD simulation results for wave impact forces by comparing existing model test results with breaking location effect. Peng (2014) also performed numerical simulations by using the VOF method to estimate the impact force on a circular cylinder. He suggested a new formula for the estimation of the slamming coefficient. Hong et al. (2018) presented a comparative study in which various CFD codes, such as OpenFOAM, STAR-CCM+, MPS, etc, give different results in wave impact problem.
This paper presents the development and application of an in-house manoeuvring method for the movement prediction of moored vessels. The method is based on a force model with force components for environmental and body forces. The components cover forces due to wind, waves and current. For the purpose of mooring system analysis an additional force component for the mooring line loads is introduced by using load-deflection curves. The results show the vessels trajectory during a loss of station keeping capability as a consequence of exceeded permissible mooring loads. In the presented paper the method is used for the analysis of a marine casualty due to harsh weather conditions.
Anchor dragging is a common problem in severe weather conditions. Recent examples are the heavy lift carrier Palmerton and the container ship MSC Vigo in January 2019 (Friedrich and Starke, 2019) as well as the bulk carrier Kuzma Minin in December 2018 (UK Government, 2018). The grounding of the bulk carrier Glory Amsterdam in October 2017 near the island Langeoog in the North Sea is also a well known example for the loss of station keeping capability in heavy weather (Kaspera, 2018).
In the following sections the manoeuvring method of the in-house ship design environment E4 is presented. The used force model is explained and the used force components are described. The routine for the calculation of mooring forces, which has been recently developed, is described in particular. Some exemplary results of the manoeuvring method are presented by means of the investigation of the Glory Amsterdam accident. All presented plots result from calculations carried out for Glory Amsterdam.
The calculations of the investigation are carried out with the body force manoeuvring model that is implemented in the ship design system E4, which is developed by the Institute of Ship Design and Ship Safety, among others. The model was developed by Soding (1984) and continuously enhanced by Kruger et al. (1998) on the basis of full scale measurements of ships during sea trials and operation. The model is used in the initial design stage for the layout of propulsion and manoeuvring devices as well as in the ship’s delivery stage for the preparation of documents such as manoeuvring booklets.