Bow Area Research Articles

Numerical analysis of wave slamming on the David Taylor Model Basin 5415 ship model

This paper employs the user-defined function method to define the boundary and analyzes the effects of various ship speeds, wave parameters, and bow structural loads on deck and hull motion responses. When the ship has a wave slamming phenomenon, the water body's height, its response to the slamming load on the deck and superstructure, and hull motion improve the seakeeping performance of the hull model. Analysis of simulation results reveals that peak slamming loads generally increase with higher speeds and wave heights. As speed increases, results oscillate irregularly, affecting the nonlinearity of the slamming load. Additionally, when the wave slamming occurs, the slamming load near the superstructure of the bow model is relatively small. Finally, the numerical modeling method is used to modify the bow area structure, and the simulation analysis is carried out under different incident waves and speeds. The influence of the drift angle on the superstructure is discussed, and beneficial suggestions are provided for the future studies of waves on deck.

Fatigue damage estimation of icebreaker ARAON colliding with level ice

This paper presents a methodology for precisely calculating the fatigue damage of an arctic vessel colliding with level ice. For accurate prediction of local ice loads acting on the external surface of the hull, focusing on the bow area, numerical simulation using the finite element method (FEM) was conducted first. The existing Drucker-Prager plastic model was combined with damage mechanics to simulate the icebreaking phenomenon. Furthermore, element erosion technology was considered to simulate crack formation and propagation through level ice that collides with a moving structure. Both dynamic drag and static buoyancy were applied to consider the dynamic behavior of submerged ice fragments. With this model, the ice resistance acting on rigid structures and a ship hull passing through level ice at multiple forward speeds were numerically calculated and compared with the test results. An additional simulation was performed in which ice fragments are removed immediately after being broken, with an attempt to decompose the total ice resistance into icebreaking resistance and the resistance of submerged ice fragments. Afterward, the spatial distribution of extreme values and frequencies of loads from the forefront to the vicinity of the hull shoulder area was derived. Finally, the ice load applied to the icebreaker ARAON at full scale under level ice conditions was calculated and then converted into stress at the target point using the influence coefficient method. Based on the converted stress information, the cumulative fatigue damage according to the speed was calculated, and the tendency of the cumulative fatigue damage was analyzed.

SLAM CHARACTERISTICS OF A HIGH-SPEED WAVE PIERCING CATAMARAN IN IRREGULAR WAVES

Slam characteristics of a 112m INCAT wave piercing catamaran in a range of realistic irregular sea conditions are presented in this paper. Towing tank testing of a 2.5 m hydroelastic segmented catamaran model was used to gather a database of slam events in irregular seas. The model was instrumented to measure motions, centrebow surface pressures and forces, encountered wave elevations and wave elevations within the bow area tunnel arches. From these measurements characteristics of the vessel slamming behaviour are examined: in particular relative vertical velocity, centrebow immersion, archway wave elevations and slam load distributions. A total of 2,098 slam events were identified over 22 different conditions, each containing about 80 to 100 slam events.
 The data, although inherently scattered, shows that encounter wave frequency and significant wave height are important parameters with regard to centrebow slamming. Relative vertical velocity was found to be a poor indicator of slam magnitude and slams were found to occur before the centrebow arch tunnel was completely filled, supporting the application of a two-dimensional filling height parameter as a slam indicator.

Investigations on the ship-ice impact: Part 2. spatial and temporal variations of ice load

The ship-ice glancing impact has been the governing scenario for the dimensional design of the bow structures for polar class ships. The present study aims to investigate the spatial and temporal variations of the impact loads by conducting model-scale ship-ice glancing impact tests in ice tank. The ship-ice impact loads were recorded by a matrix-based tactile sensor attached on the bow area of the model ship. To achieve a reasonable simulation on the design scenario described by the Unified Requirements for Polar Class Ships (UR I), a series of methodological validation tests were preliminarily carried out in the Part 1 of this study, and the standard procedures were proposed for the formal tests. The test results provided evidence on the global spatial migration of the ice load along the hull and presented the statistical characteristics of the parabola-shaped ice loading trail for glancing impact scenario. Also, various types of local ice failure processes including pure crushing, spalling and non-simultaneous crushing were classified based on the present tactile sensor data, and comparisons with published field observations were made. Furthermore, a combined approach to generating migrating and non-uniform ice loads was proposed based on Gaussian functions, and the limitations of the present tests were discussed.

Numerical prediction of ship motion and slamming load characteristics in cross wave

When waves from two weather systems converge at a certain sea area, cross waves can be produced. It is important to have a better understanding of the motion characteristics of ship in cross sea to ensure its navigation safety. In this paper, the motion responses of a S175 container ship hull in cross sea is first analyzed based on CFD technique using RANS method. VOF method is used to model and capture the free surface and overset grid technique is adopted to simulate ship motions in waves. Verifications on ship motion by the numerical method have been conducted for time step- and grid-independent studies. According to the motion results by numerical simulation, typical conditions are chosen for further investigation of slamming pressure on bow area and green water on deck. It is found that vertical motion responses of ship induced by cross waves can be quite large and the ship experienced obvious roll–pitch-coupled motion. Severe bow slamming and green water under cross sea state are also observed. The bow flare slamming pressure on the baseline can be quite large in symmetric cross wave. Asymmetrical slamming impacts occurred when the ship sails in an asymmetric cross wave field.

Calculation of the three-dimensional turbulent boundary layer in the vessel’s bow and midship area by the integral method

The quality of technical solutions applied in ship design and construction is substantially determined by the validity of viscous flow parameters, especially in the vicinity of thrusters. The influence of shapes on velocity, pressure and turbulence distribution can be assessed by physical experimentation. Along with undeniable advantages, physical modelling has a number of disadvantages: high labour input and cost, limited range of parameters variation (e.g. Reynolds numbers), difficulty in separating the influence of individual factors. Therefore, the development of mathematical models and numerical calculation schemes based on them is extremely relevant. Calculation of friction resistance and calculation of the velocity field in the vicinity of a vessel comes down to the calculation of its boundary layer and trace parameters. Current mathematical models with a planar representation, i.e. working with projections rather than real curves, do not give an accurate description. This has led to the need for a mathematical model that can address all of the required characteristics of a three-dimensional turbulent boundary layer. Both differential and integral methods are used to calculate three-dimensional boundary layers. The model is capable of calculating the characteristics of the spatial boundary layer in the stern and the viscous wake, in the bow and in the middle of the vessel. The model is quite versatile: it has been successfully used both for computing the boundary layer characteristics in the bow and midship area by the integral method based on the thick boundary layer concept, and for computing the turbulent flow in the stern and viscous wake by the differential method based on the partial parabolic concept using the k-ε turbulence model. In this paper we will elaborate on the integral method calculation.

Effect of Maneuvering on Ice-Induced Loading on Ship Hull: Dedicated Full-Scale Tests in the Baltic Sea

Maneuvers in level ice are common operations for icebreakers and polar supply vessels. Maneuvering exposes the midship and stern area to ice interaction, influencing the magnitude and frequency of ice-induced loading in these areas. However, full-scale measurements do not typically cover the midship and stern areas, as measurements have commonly focused on the bow area. Controlled maneuvering tests were conducted during the ice trials of S.A. Agulhas II in the Baltic Sea. During these tests, ice-induced loading at different hull areas was measured simultaneously with ship control, navigation, and ice condition data. This work studied the effect of maneuvers on the characteristics and statistics of ice-induced loading at different hull areas and compared the impact to ahead operations. The study showed that the maneuvers had minor impact to the magnitude, frequency, and duration of loading at the bow and bow shoulder. On the other hand, maneuvers had a clear effect on the load magnitude and frequency at the stern shoulder. Additionally, a statistical analysis showed that the load magnitude increased as a function of load duration in all hull areas. Furthermore, the analyzed measurement data are presented and made available with the paper.

Pathological evidence in Plicopurpura pansa associated with the stranding of a bulk carrier ship during Hurricane "Patricia" in the Mexican Central Pacific.

Due to the effects of Hurricane Patricia (2015), the bulk freighter "El Llanitos" ran aground in the rocky intertidal zone of Colima, Mexico. We assessed the impact of this ship's stranding on a population of the gastropod Plicopurpura pansa. Toxic elements, hydrocarbons, shell deformities, presence of tumors, imposex, and morphological relationships were analyzed. Two years after the stranding occurred, high cyanide concentrations (0.0363mg/l) and Ni concentrations above permissible limits (3.35mg/l) were found in surface seawater. Hydrocarbon concentrations were high in the aft zone of the ship and decreased towards the bow area of the freighter. The P. pansa specimens collected closest to the ship structure presented a high prevalence of tumorations in the structure of the foot and morphological anomalies in the shell structure; imposex was 32% and there was evidence of effects on the growth indicator. The evidence presented here supports the existence of a significant impact from the grounding of the ship on a protected gastropod species associated with the rocky intertidal zone on the coast of Colima. The potential of P. pansa as a bioindicator species of pollution caused by toxic elements and hydrocarbons associated with stranding events in the tropical Pacific is documented.

Investigations on the ship-ice impact: Part 1. Experimental methodologies

In the structural design of the Polar Class ships, glancing impact with ice has been considered as the governing load scenario for dimensioning the bow structure. At present, non-linear transient dynamic analysis has been reckoned as a fundamental requirement in the assessment of the structural strength of ships with higher ice classes. Under such requirement, understanding of the dynamic characteristics of the ship-ice impact load appears significant importance. The present study aims to investigate the spatial and temporal variations of the impact loads by simulating the glancing impact events between a polar research vessel and giant ice floes in ice tank. The ship-ice impact loads were recorded by a grid-based tactile sensor attached on the bow area of the model ship. To achieve a reasonable simulation on the design scenario described by the IACS Unified Requirements for Polar Class Ships (UR I), a series of methodological calibration tests were preliminarily carried out to determine the key parameters that should be carefully monitored and controlled, accompanying with thorough discussions on the ship-ice impact process. This paper provides detailed information on the preliminary methodological calibrations and the tactile data processing techniques, including the identification of the ship-ice contact area, the depiction of the ice loading trail and the outline of the spatial distributions of local ice pressures. A companion paper provides detailed analyses and discussions regarding the spatial and temporal variation of the ice impact loads from the formal tests based on the proposed testing procedures obtained by the methodological calibrations.

Analysis on improvement in resolution by excitation beam modulation in stimulated emission depletion nanoscopy

CW STED nanoscopy using illumination of continuous wave is considerably easy and less expensive to construct compared with the pulsed STED nanoscopy. In this study, to improve the resolution of CW STED nanoscopy, we analyzed the imaging characteristics of CW STED nanoscopy by amplitude modulation of incident light flux of the excitation beam illumination considering the polarization state and geometry of the pupil mask for amplitude modulation. We analyzed the imaging characteristics of STED nanoscopy by applying the characteristic, which shows an extremely confined electric field in transverse direction when the light waves with high spatial frequencies and with the same polarization direction are diffracted and interfered in the focal region. By applying linearly polarized illumination and the mixed-shaped aperture composed of the bow tie-shaped blocking area and the circular blocking aperture area, we analyzed that imaging resolution can be enhanced above 20% higher than the resolution of the conventional CW STED nanoscopy.

Model scale investigation of aspects influencing the ice resistance of ships sailing ahead in level ice

ABSTRACTFor a reliable prediction of the total resistance in ice in an early ship design stage, it is of great importance to have knowledge on the different influencing aspects. Three of the quite poorly investigated aspects of ship resistance in ice are evaluated for a contemporary common ice-breaking ship type with model tests in ice: The different components of the total resistance in ice are investigated by tests in pre-sawn ice. The additional resistance of a skeg in the bow area is analysed with model tests in ice with an instrumented skeg. The ship bottom ice coverage is determined by means of an underwater image analysis methodology. The results of these investigations are given and discussed.

PERANAN EKOLOGIS SHIPWRECK ATAU EXPOSED SHIPWRECK SEBAGAI MEDIA HIDUP KARANG DI PULAU BAWEAN DALAM UPAYA PERLINDUNGAN, PENGEMBANGAN DAN PEMANFAATAN SHIPWRECK ATAU EXPOSED SHIPWRECK

Metal salvage and theft activities have eliminated most shipwrecks at Nusa Island, and exposed shipwrecks in Gosong Gili, Bawean Island. In order to give recommendations for its conservation efforts, this study aims to identify the remaining shipwrecks or exposed shipwrecks at Nusa Island and Gosong Gili, and the types of corals and fishes in it. This study aims to prove that shipwrecks or exposed shipwrecks is not only having historical and economical value, but also ecological value for the survival of coral reef ecosystem. This is a descriptive-explorative research, data were gathered by underwater survey using GPS Map Sounder, and SCUBA diving. Shipwrecks at Nusa Island is only 30% left in fragmented form of mast, machine, boiler, propeller, ivory vessel, and bricks in the bow area. While the exposed shipwrecks at Gosong Gili is only 20% left in fragmented form boilers, machine, and ivory vessel that might be a cultural heritage according to the UU RI Number 11 of 2010 on Cultural Heritage. At Nusa Island, the corals are consisted of Poritidae and Acroporidae families, and various species reef fishes. While at Gosong Gili, there are more coral families including Merulinidae, Poritidae and Acroporidae, but their reef fishes species are fewer than Nusa island.

Improving container ship panel stress prediction, based on another highly correlated panel stress measurement

Operational safety requires that container ships are designed to endure extreme wave loads. This paper studies extreme panel stresses simultaneously measured at two different deck locations of a container vessel sailing in the North Atlantic between Canada and Europe. Ship panel stresses contain whipping part (transient vibratory response of the hull girder due to wave impacts occurring mainly in the bow area), the latter whipping phenomenon is inherently present in on-board stress measurements. It must be noted that measured hydroelastic vessel panel stresses include other complex non-linear effects as well, for example springing.In many practical situations it would be useful to improve accuracy of some statistical predictions extracted from a certain stochastic random process, given another synchronous highly correlated stochastic process that has been measured for a longer time, than the process of interest.The latter situation may happen if one on-board sensor malfunctioned, and it yielded data record much shorter than the neighboring well-functioning sensor. In this paper the latter issue of improving extreme value prediction has been addressed. In other words, this paper studies an efficient transfer of information between two synchronous highly correlated stochastic on-board stress processes. Two correlated ship panel stress processes at mid and aft deck locations were studied in order to test efficiency of the proposed technique of improving one process extreme prediction, based on the other. This paper intends to stimulate further research and fill the gap that is currently visible in the literature on the latter important topic.

Experiments on navigating resistance of an icebreaker in snow covered level ice

To investigate the ice resistance of an icebreaker under the influence of snow cover, two series of tests, i.e. normal level ice and snow covered level ice, were performed with different navigating speeds in the Ice Engineering Laboratory of Tianjin University. The model ship was mounted on a rigid carriage through a one-directional load cell to measure the total ice resistance. A tactile sensor covering the area from stem to bow shoulder on one side of the model vessel was used in measuring the spatial distribution and temporal variation of the ice pressure on the bow area. Different ice cusp patterns and ice channel shapes were observed in different test series. The measurements indicate that the presence of snow cover increases the ice resistance both in the breaking and submersion components. The measured results are also compared with the calculated results through Lindqvist method, and some improvements and important discussions are made in the paper.

The influence of the centre bow and wet-deck geometry on motions of wave-piercing catamarans

The effects of tunnel height and centre bow length on the motions of a 112-m wave-piercer catamaran with an above-water centre bow were investigated through model tests. Five alternative centre bow configurations were considered, and multiple series of model tests were conducted in regular head sea waves. The results showed that both heave and pitch increased over a wide range of wave encounter frequency as the wet-deck height of the catamaran model increased. However, increasing the length of the centre bow showed an increase in the pitch but a decrease in the heave for a limited range of wave encounter frequency near the heave and pitch resonance frequencies of the catamaran model. The positions of minimum vertical displacement were found to be aft of the longitudinal centre of gravity, between 20% and 38% of the overall length from the transom. Increase in the wet-deck height and consequently the archway clearance between the main hulls and centre bow also resulted in an increase in the vertical displacement relative to the undisturbed water surface in the centre bow area. The results also indicated the vulnerability to wet-deck slamming for the different bow and wet-deck designs.

Lithium and boron analysis by LA-ICP-MS results from a bowed PWR rod with contact

A previously published investigation of an irradiated fuel rod from the Ringhals 2 PWR, which was bowed to contact with an adjacent rod, identified a significant but highly localised thinning of the clad wall and increased corrosion. Rod fretting was deemed unlikely due to the adhering oxide covering the surfaces. Local overheating in itself was also deemed insufficient to account for the accelerated corrosion. Instead, an enhanced concentration of lithium due to conditions of local boiling was hypothesised to explain the accelerated corrosion. Studsvik has developed a hot cell coupled LA-ICP-MS (Laser Ablation Inductively Coupled Plasma Mass Spectrometer) equipment that enables a flexible means of isotopic analysis of irradiated fuel and other highly active surfaces. In this work, the equipment was used to investigate the distribution of lithium (7 Li) and boron (11 B) in the outer oxide at the bow contact area. Depth profiling in the clad oxide at the opposite side of the rod to the point of contact, which is considered to have experienced normal operating conditions and which has a typical oxide thickness, evidenced levels of ∼10–20 ppm 7 Li and a 11 B content reaching hundreds of ppm in the outer parts of the oxide, largely in agreement with the expected range of Li and B clad oxide concentrations from previous studies. In the contact area, the 11 B content was similar to the reference condition at the opposite side. The 7 Li content in the outermost oxide closest to the contact was, however, found to be strongly elevated, reaching several hundred ppm. The considerable and highly localised increase in lithium content at the area of enhanced corrosion thus offers strong evidence for a case of lithium induced breakaway corrosion during power operation, when rod-to-rod contact and high enough surface heat flux results in a very local increase in lithium concentration.

Discussion of assumptions behind rule-based ice loads due to crushing

Forecasts and trends indicate an increase in marine operations in polar waters. The design of new ships for severe polar conditions is usually solved via theoretical considerations that are combined with previous experience and engineering judgment. A deeper understanding of the theoretical considerations that underlie rule-based formulations is required for designing safe and efficient structures. This paper focuses on the assumptions that are hidden in the ice load formulations of the International Association of Classification Societies (IACS) Unified Requirements for Polar Ships (IACS, 2011) and of the Russian Maritime Register of Shipping (RMRS) Rules for the Classification and Construction of Sea-going Ships (RMRS, 2014), particularly the Daley ice load model and the Kurdyumov and Kheisin hydrodynamic model for ice crushing. A qualitative comparison of the two models is presented. The assumptions that underlie rule-based ice loads in the bow area are placed in the context of current understanding of ice–structure interaction process. The comparison of the models demonstrates that the underlying assumptions regarding the pressure–area relationship, ice edge spalling characteristics, dynamic viscosity and strength of the crushed ice are the most important assumptions, although they are highly contentious.

The Dor C shipwreck, Israel: metallurgical analysis and its contribution to the ship characterization

The Dor C shipwreck is the remains of a 60-t schooner that plied the Mediterranean during the last decades of the nineteenth century. The various building materials and ceramic ware found inside the shipwreck suggest an established commercial route between southern France and the Holy Land. Three metal objects were found in the bow area of the shipwreck: a lead pipe, an iron rigging hoop, and a brass wick housing. This study aims to understand their manufacturing processes, to propose possible dating and manufacturing locations, and to verify their use. The metallurgical investigation suggests that the objects were designated for marine use and manufactured using processes developed during the second half of the nineteenth century, probably post-1885, which supports the dating of the ship. The tonnage of the ship, the origin of her cargo, the provenance of some of the metal parts, and the location of the shipwreck, all suggest that her last voyage was a delivery of cargo from Marseilles to Dor.

Probabilistic Analysis of Local Ice Loads on a Lifeboat Measured in Full-Scale Field Trials

This paper presents an analysis of local ice loads measured during full-scale field trials conducted in 2014 with a totally enclosed motor propelled survival craft (TEMPSC) in controlled pack ice conditions. These data were collected as part of an ongoing research program that aims to identify the limitations of conventional TEMPSC operating in sea ice environments and to provide insight as to how these limitations might be extended. During the 2014 trials, local ice loads were measured at two locations on the TEMPSC's bow area. These loads were the most severe measured to date and corresponded to an average ice floe mass that was approximately 1.25 times the mass of the fully loaded TEMPSC. The event-maximum method of local ice pressure analysis was used to analyze these field data to improve understanding of the nature of ice loads for such interactions and to evaluate the suitability of this approach for design load estimation for TEMPSCs (i.e., lifeboats) in ice. The event-maximum method was adapted for the present application, so as to link exceedance probabilities with design load levels for a given scenario. Comparison of the 2014 results with a previous analysis of 2013 field trials data supports earlier conclusions that these interactions are highly influenced by kinetic energy, since more massive ice floes are observed to impart significantly higher loads on the lifeboats. Illustrative examples examining the influence of ice concentration and sail-away distance have also been provided. The work establishes links between extreme loads and the exposure of the lifeboat to ice for different operating conditions. Based on this work it is concluded that the event-maximum method provides a promising approach for establishing risk-based design criteria for lifeboats if field data are available which adequately represent ice conditions encountered during the design life of the lifeboat.

Design of a ship model for hydro-elastic experiments in waves

Large size ships have a very flexible construction resulting in low resonance frequencies of the structural eigen-modes. This feature increases the dynamic response of the structure on short period waves (springing) and on impulsive wave loads (whipping). This dynamic response in its turn increases both the fatigue damage and the ultimate load on the structure; these aspects illustrate the importance of including the dynamic response into the design loads for these ship types. Experiments have been carried out using a segmented scaled model of a container ship in a Seakeeping Basin. This paper describes the development of the model for these experiments; the choice was made to divide the hull into six rigid segments connected with a flexible beam. In order to model the typical feature of the open structure of the containership that the shear center is well below the keel line of the vessel, the beam was built into the model as low as possible. The model was instrumented with accelerometers and rotation rate gyroscopes on each segment, relative wave height meters and pressure gauges in the bow area. The beam was instrumented with strain gauges to measure the internal loads at the position of each of the cuts. Experiments have been carried out in regular waves at different amplitudes for the same wave period and in long crested irregular waves for a matrix of wave heights and periods. The results of the experiments are compared to results of calculations with a linear model based on potential flow theory that includes the effects of the flexural modes. Some of the tests were repeated with additional links between the segments to increase the model rigidity by several orders of magnitude, in order to compare the loads between a rigid and a flexible model.