Marine Structures最新文献_第2页

Experimental investigation on live-bed scour development and protection of J-tube submarine cable

IF 4 2区工程技术

Marine Structures Pub Date : 2025-03-14 DOI: 10.1016/j.marstruc.2025.103807

Yangyang Gao , Peiyuan Zhou , Lizhong Wang , Lingzhi Jiang , Haojun Yang

{"title":"Experimental investigation on live-bed scour development and protection of J-tube submarine cable","authors":"Yangyang Gao , Peiyuan Zhou , Lizhong Wang , Lingzhi Jiang , Haojun Yang","doi":"10.1016/j.marstruc.2025.103807","DOIUrl":"10.1016/j.marstruc.2025.103807","url":null,"abstract":"<div><div>A series of experiments were conducted to investigate the live-bed scour development and protection of J-tube submarine cable under the current-only and current-wave conditions. The local scour development and final equilibrium scour depth around the monopile foundation and submarine cable under different wave and current conditions were analyzed. The results show that the maximum scour depth of the scour pit around the monopile increases with the increase of flow velocity and decrease of wave height. Under different current-wave conditions, the maximum scour depth of monopile on the side of J-tube cable is more than 10 % of that on the other side. Different protection methods including riprap protection, different bionic grasses protection and combination protections were examined. The dynamic response of J-tube submarine cable was investigated with different protection methods. The results show that the bionic grass can promote sediment deposition in the protection zone, reduce the suspended length of submarine cable. The concrete mattress can significantly reduce the motion amplitude of suspended submarine cable. The combined riprap-bionic grass 3-concrete mattress protection can reduce the local scour by 96.5 % and submarine cable motion amplitude by more than 80 % under current-wave conditions.</div></div>","PeriodicalId":49879,"journal":{"name":"Marine Structures","volume":"103 ","pages":"Article 103807"},"PeriodicalIF":4.0,"publicationDate":"2025-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143620758","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Ship collision model tests in a water tank

IF 4 2区工程技术

Marine Structures Pub Date : 2025-03-12 DOI: 10.1016/j.marstruc.2025.103791

Ling Zhu , Xiangbiao Wang

{"title":"Ship collision model tests in a water tank","authors":"Ling Zhu , Xiangbiao Wang","doi":"10.1016/j.marstruc.2025.103791","DOIUrl":"10.1016/j.marstruc.2025.103791","url":null,"abstract":"<div><div>This paper investigates the dynamic responses and energy distribution in perpendicular collisions using model tests, in which the three primary elements are involved simultaneously: fluid effects, global ship motions, and local elastoplastic responses. A novel in-tank ship collision testing system has been developed to simulate perpendicular ship collisions, where the struck ship is impacted at its central section. The dynamic process of ship motions, structural deformation, energy dissipation, and added mass during collision are analyzed. Three collision scenarios are examined: Perpendicular Collision (PC), Planar Perpendicular Collision (PPC), and Central Perpendicular Collision (CPC). The calculation of energy loss during collision based on PC gives a good fit to the experimental results. It is found that the energy dissipation in the collision test is approximately linearly correlated with the initial energy input to the system. On average, about 51% of the initial kinetic energy is dissipated in the collision, mainly absorbed by the side structure through plastic deformation. These experimental data can be used for benchmarking the theoretical and numerical methods, and useful insight is provided for assessing collision scenarios.</div></div>","PeriodicalId":49879,"journal":{"name":"Marine Structures","volume":"103 ","pages":"Article 103791"},"PeriodicalIF":4.0,"publicationDate":"2025-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143601245","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Comparisons on vibration reduction effect of two types of particle dampers for offshore wind turbine structures

IF 4 2区工程技术

Marine Structures Pub Date : 2025-03-12 DOI: 10.1016/j.marstruc.2025.103809

Xiaofeng Dong , Yuan Jia , Shencheng Ren , Jiale Li , Zhuo Miao

{"title":"Comparisons on vibration reduction effect of two types of particle dampers for offshore wind turbine structures","authors":"Xiaofeng Dong , Yuan Jia , Shencheng Ren , Jiale Li , Zhuo Miao","doi":"10.1016/j.marstruc.2025.103809","DOIUrl":"10.1016/j.marstruc.2025.103809","url":null,"abstract":"<div><div>Offshore wind power (OWP) is developing towards large capacity, high towers, and long blades, which causes offshore wind turbines (OWT) to bear more severe environmental loads and increase the risk of vibration and fatigue. Although dampers can effectively control vibration, they are mostly difficult to apply in practice due to the limited space in the nacelle and tower. To solve this problem, two types of particle dampers with strong robustness and flexible layout characteristics were introduced in this research, and their vibration reduction performance was compared. Firstly, considering the actual spatial layout inside OWT, two types of particle dampers, respectively, called the vibration reduction particle deck (VR-PD) and particle damping-tuned mass damper (PD-TMD), were proposed. Then, the finite-element method (FEM) and discrete-element method (DEM) were both used to establish the coupled FEM-DEM numerical model of OWT structure, and its effectiveness was demonstrated through a classic physical model experiment. Finally, the tuned mass damper (TMD) was installed on the numerical model of OWT structures and compared with two newly proposed dampers for vibration reduction effect under the seven conditions, including modal analysis, impact condition, extreme condition, seismic condition, vibration amplification condition, operation condition, and fatigue condition. It can be shown that VR-PD and PD-TMD can better control the vibration of OWT structures under the condition of large displacement and reduce the maximum displacement by 81.40 % and 81.05 %, respectively, under the vibration amplification condition. Simultaneously, VR-PD and TMD have good vibration reduction effects under operational conditions, which can reduce the root mean square (RMS) value of displacement by 30.1 % and 31.1 %, and the peak displacement by 30.95 % and 23.56 %, respectively. Additionally, VR-PD and TMD are more excellent in increasing the fatigue life of OWT structures.</div></div>","PeriodicalId":49879,"journal":{"name":"Marine Structures","volume":"103 ","pages":"Article 103809"},"PeriodicalIF":4.0,"publicationDate":"2025-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143609241","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Dynamic response analysis of the installation system during hoisting and mating phases using a floating vessel. Part Ⅰ: Model formulation and verification

IF 4 2区工程技术

Marine Structures Pub Date : 2025-03-06 DOI: 10.1016/j.marstruc.2025.103796

Li Yin , Dongsheng Qiao , Guoguang Sun , Pengfei Liu , Guoqiang Tang , Lin Lu , Jinping Ou

{"title":"Dynamic response analysis of the installation system during hoisting and mating phases using a floating vessel. Part Ⅰ: Model formulation and verification","authors":"Li Yin , Dongsheng Qiao , Guoguang Sun , Pengfei Liu , Guoqiang Tang , Lin Lu , Jinping Ou","doi":"10.1016/j.marstruc.2025.103796","DOIUrl":"10.1016/j.marstruc.2025.103796","url":null,"abstract":"<div><div>The blade installation system using the floating installation vessel comprises several parts, including the vessel equipped with the dynamic positioning system, the ship-mounted crane, and the double pendulum system. The interaction within the system will significantly impact the dynamic responses of the blade. To analyze the coupling responses of each part, the model-based design method is employed. The hydrodynamic analysis module of the installation vessel is built by the Cummins method, the kinematic module is constructed by the coordinate transformation and the double pendulum model, as well as the dynamic module is developed by the Lagrangian method. The aforementioned modules are integrated to develop the analysis program. By code-to-code comparison, the dynamic responses of the entire installation process can be accurately assessed by the program when the forces on the blade as well as the motion of installation vessel and ship-mounted crane are considered. In addition, the program can effectively improve calculation efficiency. In Part II of this paper, the dynamic responses of blade installation system are analyzed.</div></div>","PeriodicalId":49879,"journal":{"name":"Marine Structures","volume":"103 ","pages":"Article 103796"},"PeriodicalIF":4.0,"publicationDate":"2025-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143552054","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

A new finite joint element to model joint connections in offshore structures 用于模拟海上结构连接的新型有限连接单元

IF 4 2区工程技术

Marine Structures Pub Date : 2025-03-03 DOI: 10.1016/j.marstruc.2025.103797

A.R. Damanpack

{"title":"A new finite joint element to model joint connections in offshore structures","authors":"A.R. Damanpack","doi":"10.1016/j.marstruc.2025.103797","DOIUrl":"10.1016/j.marstruc.2025.103797","url":null,"abstract":"<div><div>In this paper, a novel approach is presented to improve the accuracy and reduce the computational time of the finite element analysis of massive lattice structures. To achieve these goals, the global structure is discretized based on the beam elements while joint connections are replaced with joint elements. Then, the proposed joint element matrices are formulated in the local model with solid elements and consequently formed according to the beam theory. The present formulation is able to impose the details of joint connections in the global matrices. To verify and evaluate the proposed model, the numerical results of various cases are compared with ANSYS and those reported in the open literature. Moreover, a special study on the real-life offshore jacket structure has been carried out subjected to static loads and free vibrations. The comparison study shows the consistency of joint elements in both mass and stiffness matrices by reducing errors significantly to 0 % and 5 % while the error of using only beam elements reaches up to 300 % in some cases. It is concluded that the present approach can be efficiently implemented for the modeling of 3D massive lattice structures with reasonable accuracy and computational time.</div></div>","PeriodicalId":49879,"journal":{"name":"Marine Structures","volume":"103 ","pages":"Article 103797"},"PeriodicalIF":4.0,"publicationDate":"2025-03-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143528964","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Experimental and numerical assessment of ultimate strength of a transversally loaded thin-walled deck structure

IF 4 2区工程技术

Marine Structures Pub Date : 2025-02-27 DOI: 10.1016/j.marstruc.2025.103793

Beatrice Barsotti , Carlo Battini , Marco Gaiotti , Cesare Mario Rizzo , Gianmarco Vergassola

{"title":"Experimental and numerical assessment of ultimate strength of a transversally loaded thin-walled deck structure","authors":"Beatrice Barsotti , Carlo Battini , Marco Gaiotti , Cesare Mario Rizzo , Gianmarco Vergassola","doi":"10.1016/j.marstruc.2025.103793","DOIUrl":"10.1016/j.marstruc.2025.103793","url":null,"abstract":"<div><div>Many studies have been conducted to determine the ultimate strength of axially loaded ship structures at different levels of complexity, considering grillages, stiffened panels, transverse ring frames as well as complete hull blocks, aimed at assessing progressive collapse analysis of the whole hull girder, both analytically and numerically. However, little research has been conducted on the effects that transversal loads can have on relatively thin shell plating, particularly sensitive to buckling phenomena even for rather low loading thresholds. Moreover, the more and more frequent use of higher and higher strength steels makes ship structures slender and, consequently, likely to be even more sensitive to buckling phenomena. In the framework of a research project funded by Fincantieri R&D Department, a full-scale experimental test is performed on a structure simulating a deck portion characterized by a relatively thin plating, such as to induce an early local elastic buckling with a wide post-buckling range, before the ultimate load is reached. Nonlinear finite element analysis is carried out to design the experiment, considering both the nominal and the actual geometry of the structure as obtained by laser scanning the plating and by 3D reconstruction of the stiffeners. The effect of initial plating imperfection and of welding residual stresses on the numerical models has been considered as well, verifying their impact both, on the load end-shortening curve and on the ultimate strength of the panel.</div></div>","PeriodicalId":49879,"journal":{"name":"Marine Structures","volume":"103 ","pages":"Article 103793"},"PeriodicalIF":4.0,"publicationDate":"2025-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143511820","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Derivation of design S-N curves for butt welds in support structures for wind turbines 风力涡轮机支撑结构对接焊缝设计 S-N 曲线的推导

IF 4 2区工程技术

Marine Structures Pub Date : 2025-02-17 DOI: 10.1016/j.marstruc.2025.103795

Inge Lotsberg

{"title":"Derivation of design S-N curves for butt welds in support structures for wind turbines","authors":"Inge Lotsberg","doi":"10.1016/j.marstruc.2025.103795","DOIUrl":"10.1016/j.marstruc.2025.103795","url":null,"abstract":"<div><div>The fatigue life of welded connections in structures is normally calculated from bi-linear S-N curves presented in design standards, one part S-N curve for the largest stress ranges that can be determined from constant amplitude testing to the left of the fatigue limit and one part S-N curve for stress ranges lower than the fatigue limit that can be determined from variable amplitude fatigue testing. The second curve is governing the calculated fatigue damage for typical long-term stress distributions for marine structures subjected to cyclic loads from wind and waves. In this study fracture mechanics analyses are performed in a relative way to reduce much of the uncertainties present in such analyses to estimate a second part of the S-N curve as function of fatigue crack growth parameters, threshold stress intensity factor, geometry functions and the long-term stress range distribution. The analysis methodology is calibrated to fatigue test data from constant amplitude loading. Based on the performed analyses it is shown that the second part of the design S-N curve for as-welded butt welds can be lifted to a higher level than presented in design standards of today. For structures supporting wind turbines where the Fatigue Limit State is governing design, this may result in reduction in steel weight as compared with existing design S-N curves in standards. This information may also be useful for lifetime extension of existing structures.</div></div>","PeriodicalId":49879,"journal":{"name":"Marine Structures","volume":"102 ","pages":"Article 103795"},"PeriodicalIF":4.0,"publicationDate":"2025-02-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143428685","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

State estimation method for deepwater drilling riser system based on monitoring information

IF 4 2区工程技术

Marine Structures Pub Date : 2025-02-12 DOI: 10.1016/j.marstruc.2025.103792

Zhaowei Liu , Xiuquan Liu , Guole Jia , Lumeng Huang , Yuanjiang Chang , Guoming Chen , Xiaoqiang Guo

{"title":"State estimation method for deepwater drilling riser system based on monitoring information","authors":"Zhaowei Liu , Xiuquan Liu , Guole Jia , Lumeng Huang , Yuanjiang Chang , Guoming Chen , Xiaoqiang Guo","doi":"10.1016/j.marstruc.2025.103792","DOIUrl":"10.1016/j.marstruc.2025.103792","url":null,"abstract":"<div><div>The state of the deepwater drilling riser system is critical for risk management. Monitoring is the most direct and accurate way to obtain the state. However, the large-scale deepwater drilling riser system makes it difficult to deploy global monitoring instruments, resulting in only local states that can be obtained by monitoring. Obtaining the global state of the deepwater drilling riser system has long been an engineering challenge. A state estimation methodology based on the locally monitored state and prior model of the drilling riser is proposed to solve the challenge. The locally monitored state includes the current state, floating drilling platform motion state, and riser string local acceleration state. The prior model includes the structural mechanics model of the drilling riser and various load models. A backpropagation model based on cross entropy and gradient descent method is established to modify the local prior model according to the locally monitored state. A global state estimation model is established by extending the modified local prior model with the proposed construction strategy. A drilling riser system with a water depth of 1000 m is selected to test the state estimation method. The results show that the proposed state estimation method can effectively estimate the global state of the deepwater drilling riser system. The estimation effect of the drilling riser state caused by the wave is relatively better than that caused by the current. The monitoring location has a significant effect on the estimation results of the drilling riser state caused by the current.</div></div>","PeriodicalId":49879,"journal":{"name":"Marine Structures","volume":"102 ","pages":"Article 103792"},"PeriodicalIF":4.0,"publicationDate":"2025-02-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143387625","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

An experimental study on the strain responses of blades and struts of a 5MW semi-submersible floating vertical-axis wind turbine

IF 4 2区工程技术

Marine Structures Pub Date : 2025-02-10 DOI: 10.1016/j.marstruc.2025.103794

Yingying Jiang , Zhengshun Cheng , Shi Deng , Peng Chen , Lei Liu , Longfei Xiao

{"title":"An experimental study on the strain responses of blades and struts of a 5MW semi-submersible floating vertical-axis wind turbine","authors":"Yingying Jiang , Zhengshun Cheng , Shi Deng , Peng Chen , Lei Liu , Longfei Xiao","doi":"10.1016/j.marstruc.2025.103794","DOIUrl":"10.1016/j.marstruc.2025.103794","url":null,"abstract":"<div><div>A blade and strut strain sensing system is utilized in this study for a floating vertical-axis wind turbine (VAWT) to monitor and measure dynamic strains in the wave basin model test. The floating VAWT concept consists of a 5MW H-type rotor with three straight blades and a semi-submersible platform. The strain sensing system combines the advantages of Fiber Bragg Grating (FBG) sensors and a fiber optic rotary joint (FORJ). Subsequently, a series of model tests are carried out to investigate the strain response characteristics of blades and struts under various environmental conditions. The results show that the strains on blades and struts are affected by wave, wind, and rotor rotational speed, among which the influence of waves is minor. Under combined wind, rotational speed, with/without wave conditions, the increasing wind speed and rotational speed can lead to increases in mean values and oscillations of blade and strut strains, as well as <em>n</em>P (<em>n</em> times per revolution) components. Besides, blade strain is primarily influenced by the 1P (once-per-revolution) component, while strut strain is mainly affected by the 2P (twice-per-revolution) component for the present FBG sensors arrangement. In summary, this study offers valuable insights into the dynamic strain characteristics of blades and struts of floating VAWT under different environmental conditions, contributing to the advancement of floating VAWT model test technology and the validation of future numerical models.</div></div>","PeriodicalId":49879,"journal":{"name":"Marine Structures","volume":"102 ","pages":"Article 103794"},"PeriodicalIF":4.0,"publicationDate":"2025-02-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143379329","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Evaluation of hull girder ultimate strength for dry cargo inland vessels

IF 4 2区工程技术

Marine Structures Pub Date : 2025-02-07 DOI: 10.1016/j.marstruc.2025.103790

Nemanja Ilić, Nikola Momčilović

{"title":"Evaluation of hull girder ultimate strength for dry cargo inland vessels","authors":"Nemanja Ilić, Nikola Momčilović","doi":"10.1016/j.marstruc.2025.103790","DOIUrl":"10.1016/j.marstruc.2025.103790","url":null,"abstract":"<div><div>Ultimate strength of sea-going ships is investigated in literature and addressed in the rules and regulations of classification societies, where detailed contemporary methods are defined. However, no systematic assessments or developed regulations for evaluating the ultimate strength of inland vessels have been introduced. This is concerning, considering that around 15,000 inland vessels navigate in Europe alone. These vessels are generally prone to longitudinal strength issues as they face specific design, operational and regulatory challenges, such as a large length-to-height ratio, shallow draught navigation, frequent grounding and overloading accidents, an older fleet and fewer regulatory requirements compared to sea-going ships. Therefore, this study presents a pioneering evaluation: it assesses ultimate strength of ten inland vessels, addressing this significant gap in literature. Five methods are employed for the calculation of ultimate strength: IACS defined progressive collapse analysis (PCA), three modified PCA methods according to different formulations for buckling of stiffeners, and a nonlinear finite element method. Moreover, maximum total bending moments are calculated in order to examine the margin between ultimate and service loads. Selected inland vessels are found to be particularly vulnerable to hull girder collapse, with some of them having extremely low or no margin with respect to hull girder collapse, largely due to the buckling of structural elements acting as a consequence of the selection of unique, dispersed and specific structural features. The research specifically emphasizes that vessels with longitudinal framing achieve higher ultimate strengths, offering greater structural safety against hull girder collapse.</div></div>","PeriodicalId":49879,"journal":{"name":"Marine Structures","volume":"102 ","pages":"Article 103790"},"PeriodicalIF":4.0,"publicationDate":"2025-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143349669","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0