Idealized Structural Unit Method for Dynamic Collapse Analysis of Plates

Dynamic ultimate strength analysis of stiffened plate based on Idealized Structural Unit Method

In advanced marine industry, the reduction in weight of hull structures for a very large object ship plays an important role as the economic efficiency is the most significant aspect. In this paper, we investigate the ultimate strength of structural ship stiffened-plates designed by International Association of Classification Societies (IACS) Common Structural Rules (CSR) methods of collapse state, by applying for ANSYS nonlinear finite element analysis (FEA). Specifically, the ultimate limit assessment methods for the outer bottom of ship structures, which have drawn a significant attention from industrial marine and offshore structures, are proposed to reduce the weight of ship structures. To solve this, we study the structures of a hypothetical Very Large Ore Carrier (VLOC) designed by pre-CSR and CSR methods. In particular, the stiffened-plates under the biaxial compression and lateral pressure loads with simply supported or/and clamped boundary condition(s), the results ultimate limit state assessment performance of Nonlinear FEA methods are shown and compared to various states.

Aging effect for the ultimate strength of offshore structure is studied in this paper. A frame model of offshore structure is used, which is simplified from an actual offshore structure of jacket type. As an aging effect, corrosion due to wave, wind, current, tide, etc is considered. The history of collapse and the ultimate strength of the frame model are analyzed by using the idealized structural unit method (ISUM), for the concentrated load such as collision by a ship or an iceberg, changing the angle of collision. The analyses are performed for the initial state in which the pipe members of the frame model have the original sizes, and for the deteriorated condition in which the members are corroded and their thicknesses are reduced.The collapse behaviors (collapse modes) and the characteristics are clarified for the above various conditions. They are different depending on the angle of the collision even if the location of collision is the same. They change with the reduction of thickness of the members due to corrosion. The ultimate strength decreases proportionally to the reduction of strength of the member which is the cause of the collapse of the model, if the collapse mode does not change. But, it is possible that the ultimate strength decreased largely, if the collapse mode changes due to corrosion. The reduction of strength of the member is almost proportional to the reduction of thickness of the member. The maximum and minimum ultimate strengths of the frame model after corrosion can be estimated, using the maximum and the minimum of the ratio of reduced thickness to the original thickness of all the members in the frame model.The next second report, the frame model very close to an actual offshore structure of jacket type will be used to verify widely the characteristics and the estimating method of the ultimate strength obtained in this study.

Since a few last decades in Vietnam, offshore structure engineering has been strongly developed to meet the demand of the oil and gas exploitation. This paper deals with some main research results performed by the authors as follows: (1) Wave loads acting on the jacket elements taking into account of the marine growth in Vietnam sea conditions; (2) Reliability of offshore steel jacket structures basing on the fatigue failure; (3) Reliability of offshore concrete gravity structures basing on the fatigue failure; (4) New concept for estimating the total reliability of offshore structures basing on the combination of the ULS and FLS; (5) Applying this new concept to designing offshore structures installed in Vietnam sea. This study is useful for installing offshore structures with better safety in harsh sea of a tropical country with many storms every year as Vietnam.

The optical fiber has been extensively used as a sensor in some special fields. Because the optical fiber exists crackles itself and also produce the micro-crack as well as local damage, the fatigue behavior of the optical fiber become the main problem we care about. This paper presents the experimental study on the fatigue performance of bare fiber under static, dynamic and cyclic load. The corresponding fatigue life index (Stress corrosion index) n can be obtained, which are 17.14, 11.83 and 5.88, respectively. The experiment data reveal that fatigue life index is related to loading mode and is treated as the indicator of crack propagation resistance of materials. Because dynamic and cyclic loads can induce additional damage, the fatigue life declines dramatically under the same stress levels.

Local scour around bridge foundations significantly impacts the stability and safety of marine structures. The development of scour holes adjacent to the pile foundations of sea-crossing bridges, influenced by tidal currents, involves multidimensional physical fields, multiscale coupling, and complex variations in marine loads. However, experimental models alone are inadequate for investigating the underlying mechanisms. Numerical simulation, a critical tool for studying local scour processes, faces the challenge of accurately modeling sediment transport, particularly under tidal flow conditions near pile foundations. To solve this challenge, this research considers the effect of reciprocating flow on sediment shear as well as its characteristic dissipation based on the immersed boundary method, introduces a reciprocating flow dissipation mechanism, and adds a momentum exchange term between the fluid and the sediment to derive a new controlling equation; a new tidal flow localized scour solver is ultimately constructed, termed TidalflowFOAM. The solver effectively simulates complex flow conditions under tidal currents, extending the modeling capabilities to more realistic three-dimensional bridge scour scenarios under combined wave and current conditions. Validation through cases reported in the literature and a series of controlled experiments, encompassing varying depths, flow velocities, and pile diameters, demonstrates the solver’s proficiency in capturing post-vortex data and accurately reflecting the influence of key factors on scour depth. However, the fidelity of the simulated scour hole morphology under tidal flow conditions behind the piles requires enhancement. The proposed numerical model for tidal flow conditions has high solution accuracy and can guide practical engineering applications.

This is one of the most definitive references available on marine construction. This comprehensive book covers all major aspects of the construction process for a variety of waterborne structures, including marine, offshore, coastal, riverine, and arctic engineering structures. The late Professor Gerwick has substantially revised the previous edition of his Construction of Marine and Offshore Structures book by extensively augmenting this third edition to include recent developments in these rapidly expanding engineering fields. With the added chapters and improvements, the third edition becomes a necessary reference book for all marine and civil engineers and corporations involved in planning, building, and maintaining structures in water environments. This book is an authoritative guide because it addresses many aspects of the current state of practice in easily understandable style, presenting the most comprehensive treatment of the construction process for marine and offshore structures. The author starts with design factors and planning considerations and describes many issues affecting the building of different types of structures in a marine environment. In addition, the book includes chapters on construction and maintenance of coastal and inland waterway structures and pays special attention to recent advances for ice-resistant structures, dams and locks, and bridge foundations. A number of the latest developments in materials and techniques are also described in this new edition that should be of great interest to engineers in the oil and service industries, as well as marine construction planners, designers, and contractors. To retain the volume’s standing as a complete authoritative resource, the author has incorporated into this edition many changes related to techniques, tools, and materials that have found their way into marine and offshore engineering practice. Topics with expanded coverage include construction equipment, marine operations, steel and concrete offshore platforms, cables and flexible or rigid pipelines and risers, tubes tunnels , walls, piles, rubble-mound breakwaters, precast armor units in coasts, repairs and strengthening existing structures, and removal and salvage. The author also provides new information on novel technologies, methods, materials, liquefaction of loose sediments, scour and erosion, ultra-high-performance concrete, H-piles and high-performance steel, cracking and corrosion, and construction in remote areas. He presents an interesting insight to archaeological concerns and damage from sabotage and terrorism, since these are important elements of the construction process. For marine construction planners, designers, contractors, ocean, coastal, and marine engineers involved in constructing waterborne structures, this book describes effec-

Fixed offshore structures in seismically active zones are likely to have deformations large enough to exceed the elastic limits of materials under strong ground motions. Therefore, investigation of nonlinear response of offshore structures under dynamic loadings is very interesting to structural engineers. Nonlinear behavior of structures is highly related with the soil properties and soil behavior. The main purpose of this study is to investigate and show the methodology for inelastic dynamic analyses of fixed-offshore structures under the 10,000-year earthquake loadings. The investigation in this study includes the effect of soil radiation damping, soil-pile gapping, and soil degradation on fixed offshore structures. Additionally, the effect of the direction of earthquake is included in this study. An offshore structure model ‘Platform A’ is modeled in CAPFOS. 10,000-year earthquake events are considered and for this purpose, two different earthquakes are used: Hector Mine Earthquake (1999) and Landers Earthquake (1992). These ground motion records are scaled to have a resulting earthquake that has a return period of 10,000-year. CAPFOS software is used to complete time-history analyses with these earthquakes. Results indicate that: (i) Considering the soil radiation damping negligible is not correct, because without the radiation damping, the total damping ratio is estimated as % 3, while including radiation damping raises the ratio to % 4.5, (ii) soil-pile gapping and soil radiation damping generate adverse effects on analyses outcome, and (iii) using high values of soil degradation factors is not always conservative.

A review of numerical modelling techniques for marine icing applications

PurposeThe safety assessment of engineering structures under repeated variable dynamic loads such as seismic and wind loads can be considered as a dynamic shakedown problem. This paper aims to extend the stress compensation method (SCM) to perform lower bound dynamic shakedown analysis of engineering structures and a double-closed-loop iterative algorithm is proposed to solve the shakedown load.Design/methodology/approachThe construction of the dynamic load vertexes is carried out to represent the loading domain of a structure under both dynamic and quasi-static load. The SCM is extended to perform lower bound dynamic shakedown analysis of engineering structures, which constructs the self-equilibrium stress field by a series of direct iteration computations. The self-equilibrium stress field is not only related to the amplitude of the repeated variable load but also related to its frequency. A novel double-closed-loop iterative algorithm is presented to calculate the dynamic shakedown load multiplier. The inner-loop iteration is to construct the self-equilibrated residual stress field based on the certain shakedown load multiplier. The outer-loop iteration is to update the dynamic shakedown load multiplier. With different combinations of dynamic load vertexes, a dynamic shakedown load domain could be obtained.FindingsThree-dimensional examples are presented to verify the applicability and accuracy of the SCM in dynamic shakedown analysis. The example of cantilever beam under harmonic dynamic load with different frequency shows the validity of the dynamic load vertex construction method. The shakedown domain of the elbow structure varies with the frequency under the dynamic approach. When the frequency is around the resonance frequency of the structure, the area of shakedown domain would be significantly reduced.Research limitations/implicationsIn this study, the dynamical response of structure is treated as perfect elastoplastic. The current analysis does not account for effects such as large deformation, stochastic external load and nonlinear vibration conditions which will inevitably be encountered and affect the load capacity.Originality/valueThis study provides a direct method for the dynamical shakedown analysis of engineering structures under repeated variable dynamic load.

Wind and gravity both impact trees in storms, but wind loads greatly exceed gravity loads in most situations. Complex behavior of trees in windstorms is gradually turning into a controversial concern among ecological engineers. To better understand the effects of nonlinear behavior of trees, the dynamic forces on tree structures during periods of high winds have been examined as a mass-spring system. In fact, the simulated dynamic forces created by strong winds are studied in order to determine the responses of the trees to such dynamic loads. Many of such nonlinear differential equations are complicated to solve. Therefore, this paper focuses on an accurate and simple solution, Differential Transformation Method (DTM), to solve the derived equation. In this regard, the concept of differential transformation is briefly introduced. The approximate solution to this equation is calculated in the form of a series with easily computable terms. Then, the method has been employed to achieve an acceptable solution to the presented nonlinear differential equation. To verify the accuracy of the proposed method, the obtained results from DTM are compared with those from the numerical solution. The results reveal that this method gives successive approximations of high accuracy solution.

Dynamic phenomena when a stand of drillpipe is run into the hole may result in pipe failure, either through exceeding the yield or through kicking the pipe off the slips. Two computer programs based on longitudinal wave propagation have been developed. Results are presented and recommendations are made.

The need for quality control in the ready-mixed concrete industry is increasingly emerging as a tool for ensuring the achievement of the highest possible quality in the produced concrete with the lowest practical price. In typical construction projects, the compressive concrete strength is the most important criterion in judging the acceptability of a produced concrete batch from a given plant. Variability in the compressive strength of the concrete batches of any plant is inevitable. Such variability has led researchers in the field of quality control to analyze the statistics of these results in order to draw conclusions about the quality of the concrete plant and ways to improve it. Ultimately, the goal of the owner of a structure being constructed, the engineer in charge of its construction, and hence the quality control professionals is the safety of the structure that the concrete is intended to be used for constructing. The quality of the concrete can be viewed as a means for the end goal, the structural safety. Therefore, a more informed decision could be made regarding the quality of the concrete if the structural safety is used as an indicator. Structural reliability theory and tools are commonly used nowadays for the quantification of structural safety under uncertainty. In this study, an approach for classifying the quality of ready-mixed concrete using structural reliability as a metric will be proposed. The influence of the statistical parameters of concrete on the structural reliability of the structural elements constructed with this concrete is investigated. Classification charts for classifying the quality of concrete based on the values of its statistical parameters and with reference to the attained structural reliability are proposed.

This research aims to develop principles for assessing the impact of mega-cyclic vibrodynamic loads on the reliability of construction structures. The relevance of the reasons for the development and improvement of algorithms for numerical modeling of multicycle dynamic loads on building structures is due to the steadily increasing intensity of such loads on buildings and structures in megacities, as well as the acute practical problem of significant differences in the dynamic characteristics of buildings and structures obtained as a result of mathematical modeling and determined by experimental methods. The article presents research materials on computational equivalent models of dynamic load sources for numerical modeling of the behavior of construction structures under their influence, using the method of vibroacoustic analogies. The article examines models of sources of dynamic impact on construction sites. Algorithms and final formulas for computational modeling of the simplest sources of dynamic load are developed using the method of vibroacoustic analogies. The dynamic properties of the simplest dynamic load sources were analyzed. A significant difference between the computational models of real and ideal dynamic load sources. The article presents research and development results intended for calculating the distribution of dynamic loads on elements of construction structures in industrial and civil engineering projects located in areas with high levels of transport vibrodynamic impacts. An important property of the proposed computational equivalent models of sources of dynamic impact on building structures is the possibility of computational verification of critical elements, points, or nodes of load-bearing structures of buildings and structures under dynamic overloads. The position of these critical elements, points, and nodes of load-bearing structures under dynamic loads can differ significantly from their position determined using static and quasistatic computational modeling methods.

Ambient and forced vibration tests were recently conducted on an offshore steel template platform in the Ekofisk complex of the North Sea. Valuable information about the dynamic characteristics of the structure was obtained. This paper focuses on the measurement and analysis of damping data for the platform. Modal damping values are very important in the dynamic analysis of offshore structures. Correct values of modal damping need to be utilized for the dynamic analysis to accurately predict the response of the structure. Little experimentally verified information of the modal damping characteristics of the fundamental and higher order modes of offshore structures is currently available. Damping values were calculated for the fundamental and higher order jacket modes which included natural frequencies up to approximately 5 Hz. Damping values are compared for forced and ambient vibration data, for bandwidth and response techniques, and for different excitation levels. The general results indicated that the fundamental modes important in fatigue had damping values of 1 to 3 percent of critical and the higher order modes had damping values of 2 to 3 percent of critical. Emphasis is placed on the apparent merits and limitations of the data presented. Response comparisons are also presented using an analytic model of the platform with various values of critical damping. INTRODUCTION Accurately predicting the dynamic behavior of offshore oil and gas production platforms to withstand the effects of earthquakes and environmental fatigue due to wind and wave loading is an essential part of the design of such structures. Research and development work currently being undertaken to apply integrity monitoring techniques to these platforms also requires an accurate interpretation of the structural dynamic behavior. These applications of vibration technology translate directly into cost effective design and increased reliability and safety of offshore structures. The complexity of these structures requires a high level of theoretical analysis in developing models which duplicate the dynamic behavior under design loading conditions. Current state-of-the-art modeling methods usually apply finite element techniques which discretize the structure into an assemblage of mass and stiffness matrices which mathematically define the structure. The complexity of these structures also implies the need for confirmation and improvement of the structural models by experimental techniques. Using system identification methods, both analytic and experimental results can be used to accurately define the dynamic behavior of structures. Structural damping is one of the least understood yet most vital design characteristics of dynamically loaded structures. An analytical model of a structure in which low critical damping values are used will respond much differently to environmental loads than one in which higher damping values are used. This paper presents values of critical damping obtained experimentally on an offshore platform and comparisons are made to an analytic model of the structure. The vibration tests were conducted on an offshore steel template platform in the Ekofisk complex of the North Sea. Both ambient and forced vibration test procedures were utilized.