Large scale physical model testing on the ultimate strength of a steel stiffened plate structure under cyclic compressive loading

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Large scale physical model testing on the ultimate compressive strength of a steel stiffened plate structure at cryogenic condition

Ship structures are typical examples of large plated structures which are made of large number of structural elements composed into system structures to be strong enough, while keeping the structural weight at minimum, to survive varying loads arising from cargo (e.g. weight and cryogenic condition due to LNG cargo), waves, winds or other environmental conditions (e.g. cold temperature due to Arctic operation). The design of ship structures are today designed based on limit states which are defined by the description of a condition for which a particular structural member or an entire structure would fail to perform the function designated beforehand. Four types of limit states are relevant, namely SLS (serviceability limit state), ULS (ultimate limit state), FLS (fatigue limit state) and ALS (accidental limit state). At the preliminary design stage, structural scantlings and materials of ship structures are determined based on the ULS, and ultimately other types of limit states are integrated to ensure so that the different parts of a ship structure will meet safety requirements and survive environmental and operational conditions during the life time period of some 25 years. \ua0The stiffened plate structures in the bottom, the deck and the side-shell are the most important parts of a ship in association with a ship’s integrity, safety and survivability. The design criteria for determining the scantlings of stiffened plate structures are the ultimate limit states (or ultimate strength). If applied loads exceed the ultimate strength then the stiffened plate structures fail to perform the function, leading to total loss of the ship. Therefore, it is of vital importance to accurately and efficiently compute the ultimate strength of stiffened plate structures. The behavior of stiffened plate structures until and after the ultimate strength is reached is highly nonlinear involving geometric nonlinearities (e.g. buckling and large deflection) and material nonlinearities (e.g. yielding, plasticity and material failure or fracture). Various types of collapse modes, including overall buckling collapse, beam-column type collapse, web buckling induced collapse and flexural-torsional buckling induced collapse, are relevant. Today\u27s large merchant ship structures are made of different grades of steel materials that should meet specific requirements for yield strength, ductility, brittleness, ultimate tensile strength resistance to corrosion in association with operational and environmental conditions.\ua0\ua0As of today, the ultimate strength of stiffened plate structures has been studied and applied in room temperature conditions. However, ships now operate in Arctic region at cold temperatures as climate change causes Arctic ice to melt at an alarming rate. A shipping company MAERSK recently navigates a 200m long container ship through the Arctic waters for the first time without the help of icebreakers. The average ambient temperature in Arctic region during winter season is -40 deg. C and the lowest temperature is reportedly -68 deg. C. Furthermore, the number of LNG-fueled ships is increasing in terms of resolving the issues associated with CO2 emissions. LNG-fueled ships need to have LNG fuel tanks in a large size, and hazards of LNG leakage always exist. The temperature of LNG is -163 deg. C. The collapse behavior of ship stiffened plate structures is vulnerable to cold temperatures or cryogenic condition in association with catastrophic failure, leading to total loss of ships that can affect personnel, assets and the environment, where brittle facture must be playing a significant role on the ultimate strength behavior. Theoretical methods are almost impossible to apply for computing such a highly nonlinear behavior of ship stiffened plate structures involving buckling, yielding and brittle fracture. Advanced computational models should be developed for that purpose. However, it is highly demanding to obtain physical model test database which shall be used to validate the accuracy and applicability of the advanced computational models.\ua0The purpose of the present study is to obtain physical model test database on the ultimate strength characteristics of ship stiffened plate structures subject to extreme loads and cold temperatures (due to LNG leakage). Physical model testing on a large scale ship stiffened plate structure is undertaken at cryogenic condition (-160 deg. C). Elastic-plastic large deflection behavior of the test model under axial compressive loads is measured until and after the ultimate strength is reached. Material properties at cryogenic temperature are tested in separate material experiments. Details of the test database are documented

Full-scale collapse testing of a steel stiffened plate structure under axial-compressive loading at a temperature of −80\ub0C

The aim of the paper was to develop a test database of the ultimate strength characteristics of full-scale\ua0steel stiffened plate structures under axial compressive loading at a temperature of −80\ub0C. This paper is a\ua0sequel to the authors’ articles (Paik et al. 2020a, https://doi.org/10.1016/j.istruc.2020.05.026 and Paik et al.\ua02020b, https://doi.org/10.1080/17445302.2020.1787930). In contrast to the earlier articles associated with\ua0room temperature or cryogenic condition, this paper investigated the effect of a low temperature at −80\ub0C\ua0which is within the boundary range of temperature of the ductile-to-brittle fracture transition for carbon\ua0steels. A material model representing the test conditions was also proposed to capture the characteristics\ua0of carbon steels at low temperatures both in tension and in compression, and it was used in finite element\ua0method simulations of the full-scale experiment. A comparison between numerical analyses and\ua0experiments showed that the proposed model could successfully predict the failure modes and\ua0ultimate strength characteristics at low temperatures for stiffened plate structures under axial\ua0compressive loading conditions

Thermal-Structural Characteristics of Multi-Layer Vacuum-Insulated Pipe for the Transfer of Cryogenic Liquid Hydrogen

As the world’s hydrocarbon supplies are gradually being depleted, the search for alternative energy sources with acceptably low emissions of environmentally harmful pollutants is a growing concern. Hydrogen has been proposed by numerous researchers as a fuel source for ships. Liquid hydrogen (LH2) has been shown to be particularly attractive as a ship fuel with respect to its ability to reduce pollution, density, high performance in engines, and high caloric value per unit mass. However, working with hydrogen in the liquid phase requires very low (i.e., cryogenic) temperatures. The design of a cryogenic LH2 pipeline is very different from the design of a normal fluid pipe due to the change between the liquid and gas states involved and the effect of thermal and structural characteristics on the cryogenic temperature during LH2 transportation through the transfer pipeline. This study investigated the material and thermal-structural characteristics of a multi-layer vacuum-insulated pipeline system through experiments and finite element analysis. The experimental and numerical results can be used as a database of material parameters for thermal-structural analysis when designing applications such as LH2 pipeline systems for hydrogen carriers and hydrogen-fuelled ships

The Supported Boro-Additive Effect for the Selective Recovery of Dy Elements from Rare-Earth-Elements-Based Magnets

Liquid metal extraction (LME) for recycling rare-earth elements from magnets is studied, in the present study, to examine its suitability as an environmentally friendly alternative for a circular economy. While Nd (neodymium) extraction efficiency can easily reach almost 100%, based on the high reactivity of Mg (magnesium), Dy (dysprosium) extraction has been limited because of the Dy–Fe intermetallic phase as the main extractive bottleneck. In the present paper, the boro-additive effect is designed thermodynamically and examined in the ternary and quinary systems to improve the selectivity of recovery. Based on the strong chemical affinity between B (boron) and Fe, the effect of excess boron, which is produced by the depletion of B in FeB by Mg, successfully resulted in the formation of Fe2B instead of Dy–Fe bonding. However, the growth of the Fe2B layer, which is the reason for the isolated Mg, leads to the production of other byproducts, rare-earth borides (RB4, R = Nd and Dy), as the side effect. By adjusting the ratio of FeB, the extraction efficiency of Dy over 12 h with FeB addition is improved to 80%, which is almost the same extraction efficiency of the conventional LME process over 24 h

Full-scale collapse testing of a steel stiffened plate structure under axial-compressive loading triggered by brittle fracture at cryogenic condition

This paper is a sequel to the authors’ earlier article (Paik et al. 2020a, Full-scale collapse testing of a steel stiffened plate structure under cyclic axial-compressive loading, Structures, https://doi.org/10.1016/j.istruc.2020.05.026).The aim of the paper was to present a test data on the ultimate compressive strength characteristics of a full-scale steel stiffened plate structure at cryogenic condition which may be due to unwanted release of liquefied gases. Steel plate panels of an as-built containership carrying 1,900 TEU were referenced for this purpose. The test structure was fabricated in a shipyard using exactly the same welding technology as used in today’s shipbuilding industry. It is observed that the test structure reaches the ultimate limit states triggered by brittle fracture, which is totally different from typical collapse modes at room temperature. Details of the test database are documented as they can be used to validate computational models for the structural crashworthiness analysis involving brittle fracture at cryogenic condition

Effect of solid rubber fenders on the structural damage due to collisions between a ship-shaped offshore installation and an offshore supply vessel

The effect of solid rubber fenders on the structural damage due to collisions between a ship-shaped offshore installation and an offshore supply vessel was investigated. An LS-DYNA computational modelling technique was developed to simulate the kinetic energy absorption behaviour of solid rubber fenders. Physical crushing testing was performed on rubber fender models to validate the computational model under different collision speeds. Traditional LS-DYNA computational models to simulate the structural crashworthiness of ship-shaped offshore hull structures colliding with an offshore supply vessel were combined with the developed rubber fender model. The computational models were applied to a hypothetical very-large-crude-oil-carrier (VLCC) class floating production storage and offloading unit (FPSO) hull that collides with an offshore supply vessel equipped with rubber fenders in the forecastle deck area, and the effects of rubber fenders on the collision energy absorption characteristics were examined in association with the structural damage of both striking OSV and struck FPSO hull structures. The findings and insights derived from the study were summarised

Full-scale collapse testing of a steel stiffened plate structure under cyclic axial-compressive loading

Plate panels of ships and floating offshore structures are likely subjected to cyclic loads arising from waves at sea.\ua0Depending on sea states, e.g., whipping in harsh sea states, the maximum amplitude of the cyclic loads may\ua0reach over 70% of ultimate loads. Of concerns is how the cyclic loads will affect the ultimate strength compared\ua0to a case of monotonically increasing loads. The aim of this paper is to experimentally investigate the ultimate\ua0strength characteristics of a steel stiffened plate structure under cyclic axial-compressive loading. A full-scale\ua0collapse testing in association with bottom structures of an as-built 1,900 TEU containership was conducted. It is\ua0concluded that the effects of cyclic loading on the ultimate compressive strength of steel stiffened plate structures\ua0are small as far as fatigue damages are not suffered due to the small number of load cycles and/or local\ua0structural members do not reach the ultimate strength during cyclic axial-compressive loading. Details of the test\ua0database are documented, which will be useful to validate computational models for the ultimate strength\ua0analysis

Numerical study of performance of flat and perforated radiant heat shields for offshore structures

Heat shields are an essential safety facility on offshore structures to protect the workers and the equipment on deck from the violent radiant heat flux and the high temperatures of the flare tower. In this study, a series of Computational Fluid Dynamics (CFD) simulations were performed to investigate the thermal characteristics of radiant heat shields on offshore structures in order to obtain a precise prediction of those reduction performances on heat flux and temperature. CFD methodologies for the radiant heat transfer simulation were suggested for grid, iteration, and time step with physical modelling methods of heat transfer considering the convection effect and the heat flux sensor, including the scaling method for the simulation of a perforated heat shield. The reduction ratios of the heat flux and temperature were obtained for the case without the heat shield and for a flat and perforated heat shield under the heat source of 25 kW/m2 for various distances from the heat shield, and the results were compared with the experimental results. Analytical estimation methods were included in the study of the radiant heat flux and temperature, and an empirical formula was provided for the performance of the heat shields based on the CFD results

Effect of pneumatic rubber fenders on the prevention of structural damage during collisions between a ship-shaped offshore installation and a shuttle tanker working side-by-side

This study investigated the effects of pneumatic fenders on the prevention of structural damage from collisions between a ship-shaped offshore installation and a shuttle tanker during side-by-side offloading operations. A nonlinear finite element modelling technique was developed to simulate the kinetic energy absorption behaviour of pneumatic fenders during collisions. Full-scale pneumatic fenders were physically tested to validate the computational model at various collision speeds. The developed pneumatic fender model was integrated with a conventional finite element model of a hull structure to simulate the crashworthiness of the hull structure in collisions with a shuttle tanker during side-by-side offloading. This integrated computational model was then applied to examine case studies involving a VLCC class ship-shaped offshore installation hull with and without pneumatic rubber fenders colliding with a Suezmax class shuttle tanker. The key findings and insights of these investigations, particularly the collision energy absorption characteristics are summarised