Calculation of Extreme Wave Loads on Coastal Highway Bridges

Coastal bridges are exposed to severe wave, current and wind forces during a hurricane. Most coastal bridges are not designed to resist wave loads in such extreme situations, and there are no existing analytical methods to calculate wave loads on coastal highway bridges. This study focuses on developing a new scheme to estimate the extreme wave loads on bridges for designing purpose. In order to do this, a 2D wave velocity potential model (2D Model) is set up for the deterministic analysis of wave force on bridge decks. 2D Model is a linear wave model, which has the capability of calculating wave velocity potential components in time domain based on wave parameters such as wave height, wave period and water depth, and complex structural geometries. 2D Model has Laplace equation as general equation. The free surface boundary, incoming and outgoing wave boundary conditions are linearized, decomposed first, and then solved by the finite difference method. Maximum wave forces results calculated by the linear 2D Model are compared with results from CFD software Flow3D that is using Navier Stokes theory up to the 5th order; and 2D Model is validated by comparing results with experiment data. A case study is conducted for calculating extreme wave forces on I-10 Bridge across Escambia Bay, Florida during Hurricane Ivan in September 2004.SWAN model is adapted to investigate the parameters of wave heights and wave periods around bridge sites. SWAN model has the capability of predicting or hindcasting significant wave heights and wave periods as long as the domain and input parameters are given. The predicted significant wave heights are compared with measurements by Buoy Station 42039 and 42040 nearest to Escambia Bay. A new prediction equation of maximum uplift wave forces on bridge decks is developed in terms of wave height, wave period, water depth, bridge width, water clearance and over top water load. To develop the equations, the relationship is investigated between maximum uplift wave forces and wave parameters, water clearance, green water effects and bridge width. 2D Model is used for up to 1886 cases with difference parameters. Flow3D model is adopted to determine coefficients of water clearance and green water effects, which cannot be calculated by 2D Model

Numerical study on vibratory extraction of offshore wind turbine monopile foundations under sandy seabed condition

The wind industry has experienced a rapid growth in Europe over the last decades. The early generation turbines were designed for a life of 20–25 years. Decommissioning of offshore wind turbines is becoming more important since many of these installed assets are approaching their end of lifetime. In this study, using vibratory extraction of monopile foundations instead of current practice of cutting them is investigated numerically. Correct estimation of extraction force helps operators to choose suitable vibro-hammer and vessel (or crane-barge), which leads to reduction of decommissioning costs. A Coupled Eulerian-Lagrangian (CEL) approach of ABAQUS/Explicit combined with a modified Mohr-Coulomb (MMC) model are used to find the pile shaft resistance during total removal operation under saturated dense sand condition. The MMC model captures the nonlinear pre-peak hardening and post-peak softening of the dense sand which is not modelled by conventional Mohr-Coulomb model. The VUSDFLD subroutine, which is a user-defined framework, has been used to implement the MMC model into CEL analysis. A parametric study is conducted to analyze how the characteristics of the vibro-hammer, such as its frequency, eccentric moment, and the extraction rate influence the results. The present numerical results show that using proper frequency results in reduction of soil resistance to less than 25% of the initial resistance. However, appropriate hammer with enough eccentric moment and suitable extraction rate, are vital to ensure soil degradation. The results show that the proposed methodology is both robust and straightforward and it has the potential to reduce computational time which is efficient for engineering applications.publishedVersio

Assessment of Helical Anchors Bearing Capacity for Offshore Aquaculture Applications

Aquaculture in Maine is an important industry with expected growth in the coming years to provide food in an ecological and environmentally sustainable way. Accommodating such growth, farmers need more reliable engineering solutions, such as improving their anchoring systems. Current anchoring methods include deadweights (concrete blocks) or drag embedment anchors, which are of relatively simple construction and installation. However, in the challenge of accommodating larger loads, farmers have used larger sizes of the current anchors rising safety issues and costs during installation and decommissioning. Helical anchors are a foundation type extensively used onshore with the potential of adjusting the aquaculture growth demand, though research understanding their lateral and inclined capacity needs to be performed first. This study addresses such topic by performing 3D finite element simulations of helical anchors and studies their reliability for offshore aquaculture farming. Results obtained in this research indicate that the helical anchors capacity could be related to either pure vertical or horizontal resistances, depending on the load inclination angle. Reliability evaluation of helical anchors for inclined loading demand from an oyster aquaculture farm using the Hasoferd-Lind method, indicated these anchors are feasible for operational aquaculture loads

Geotechnical Response Models for Steel Compliant Riser in Deepwater Clays

The touchdown zone (TDZ) often proves to be a spot where cyclic bending stresses are the largest and is therefore a critical location for fatigue. Catenary steel compliant pipelines or risers (SCRs) are subject of much ongoing research, particularly with respect to their fatigue life, which is strongly influenced by seabed soil conditions in the TDZ. This chapter reviews the recent publications that might have an impact on the SCR-seabed interaction. The review starts by looking at the SCR general arrangement. Thereafter, the focus moves to the review of the recent research that studied the interactions between deepwater SCRs and the seabed. In addition, the review went over the analysis techniques of the SCR, including the modelling philosophy and models for geotechnical response. The research gap and the need for future research are identified

Reliability assessment of foundations for offshore mooring systems under extreme environments

textMooring systems for floating facilities that are used offshore to produce oil and gas, consisting of individual mooring lines and foundations, are currently designed on the basis of individual components and on a case-by-case basis. The most heavily loaded line and anchor are checked under extreme loading conditions (hurricane and loop current) with the system of lines intact and with one line removed. However, the performance of the entire mooring system depends more directly on the performance of the system of lines and foundations rather than on the performance of a single component. In this study, a floating production system design originally developed by the industry consortium, DeepStar, was chosen for study. The mooring system was designed for three different nominal water depths: 1000, 2000 and 3000 m. It is a classic spar with steel mooring lines in 1000 m of water and polyester mooring lines in deeper depths. Based on simulated results of loads on mooring lines and foundations using a numerical model, reliability analyses were conducted using representative probabilistic descriptions of the extreme met-ocean conditions, hurricanes and loop currents, in the Gulf of Mexico. The probability of failure of individual mooring line components during a 20-year design life is calculated first, followed by that of a complete mooring line which consists of top and bottom chains, a steel cable or polyester rope at the middle and a suction caisson foundation, and finally that of the mooring system. It is found that foundations have failure probabilities that are more than an order of magnitude smaller than those for lines under extreme loading. Mooring systems exhibit redundancy in that the failure of the most heavily loaded component during an extreme event does not necessarily lead to failure of the system. The system reliability and redundancy are greater for the taut versus semi-taut systems and is greater for designs governed by loop current versus hurricane events. Although this study concerns about the mooring systems of a classical spar, the methodology of the reliability analysis and the conclusions made in this study may have important implications to the other deepwater mooring systemsCivil, Architectural, and Environmental Engineerin

Effects of Internal Gas Explosion on an Underwater Tunnel Roof

An underwater reinforced concrete tunnel roof is subjected to an internal gas explosion. Dynamic analyses are performed for three cases, namely, (1) an uncoupled solution, (2) class II coupling analysis and (3) full model with class I and II couplings. Three load cases are considered, dead (gravity) load, uniformly distributed vertical loads from sand and water and finally an internal pressure gas explosion. Linear and non-linear constitutive relationships are considered for the materials constituting the gas explosion problem. Results include time deflection of tunnel roof, time histories of stresses in vertical reinforcing bars and contours of concrete stresses for tunnel roof. By conducting analyses from various models, the question whether the tunnel would be damaged to such an extent that its serviceability would be impaired is investigated

Pull-Out Capacity and Failure Mechanisms of Strip Anchors in Clay

ABSTRACT: Plate anchors are a well-established solution for supporting the efforts of floating platforms for wind and marine renewable energies. The behavior of ultrathin rigid plate anchors buried in purely cohesive soils under undrained and plane-strain conditions is analyzed. As already known, a dimensional analysis shows that the pull-out capacity of the anchor may be expressed using a weightless break-out factor (Nc0) that only depends on the ratio between the depth and the anchor width (H/B). Using finite element analyses, tabulated values of the weightless break-out factor are provided in this paper and three different failure mechanisms are identified, namely very shallow (quasi-vertical), shallow or intermediate (semi-vertical), and deep (rotational). For very shallow failure mechanisms, the studied problem is completely equivalent to the trapdoor problem because immediate breakaway at the bottom part of the anchor is considered (vented conditions). The existing analytical solutions for the very shallow (Nc0 = 1.956 H/B) and deep cases (Nc = 3? + 2) using the slip-line method are reviewed and an analytical limit is proposed for the first time for the very shallow mechanism (H/B = 1.314). For shallow (intermediate) cases, the failure mechanism is identified and the angle of the main slip lines is numerically evaluated

Physical Modeling of Suction Caissons Loaded in Two Orthogonal Directions for Efficient Mooring of Offshore Wind Platforms

Over the past decade a number of Federal and State policies and programs have promoted the development of the wind energy industry, including the establishment of offshore wind. A strategy by the Department of Energy set objectives of reducing cost and reducing time to deployment through specific deliverables such as innovative anchor and mooring design for floating offshore systems and hardware design concepts including turbine array grids. This research program proposes and investigates use of suction caissons as combined anchors to resist line loads from multiple platforms as an efficient solution for anchoring a network of wind turbine platforms. Suction caissons are a ‘mature’ anchor technology in the offshore oil and gas industry, yet there is minimal experience with application for offshore wind platforms. Established design methods, standards and recommended practices from the oil and gas industry, serve as a starting point for further adaptation. Considerations of the differences in conditions (e.g. loads, risk, failure and serviceability tolerances) between the two applications, is important for developing efficient anchor design suited to offshore wind platforms. A physical modelling program was developed to investigate the behaviour of caissons subjected to orthogonal cyclic and post-cyclic monotonic line loads, compared to the behaviour of single line loaded caissons. Modeling was performed in a geotechnical centrifuge in order to simulate in-situ stress profile at model scale, as stresses are critical to soil and foundation behavior. Load tests were performed on a model suction caisson anchor installed by jacking into normally consolidated kaolin clay (in-flight). Baseline tests were performed with single line loading for comparison to the multi-line loading tests. Line loads were applied in orthogonal directions for the multi-line load tests. The effect of varying cyclic mean load and cyclic load amplitude was also investigated. Comparison of test results was based on line displacement, applied line load, caisson rotation and internal pore pressure at the underside of the caisson cap. Centrifuge test results appear to indicate that the line load-displacement response during monotonic loading is similar for the multi-line and the single line loaded suction caisson anchors. The post-cyclic peak monotonic line load resistance provided by the caisson loaded in multiple directions was greater than the resistance provided by the caisson loaded in a single direction (accounting for the total resultant load applied). For all selected load cases, the accumulated permanent displacements during the cyclic loading did not result in a displacement (serviceability) failure of the suction caisson nor contribute significantly to the displacement correlating to the peak line load resistance of the caisson. Test results indicate that the resistance capacity of a given caisson is not reduced by applying line loads in multiple directions, when considering the resistance to the total resultant load. Test observations appear to support conceptualizations of a modified “zone of influence” (active/passive earth pressure wedges) due to the changing load orientation from resolving multiple out of phase line loads

Wave Interactions with Coastal Structures

Due to the ongoing rise in sea level and increases in extreme wave climates, which consequently change the wave climate, coastal structures such as sea dikes and seawalls are exposed to severe and frequent sea storms. Even though much research related to wave–structure interactions has been carried out, it remains one of the most important and challenging topics in the field of coastal engineering. The recent publications in the Special Issue “Wave Interactions with Coastal Structures” in the Journal of Marine Science and Engineering include a wide range of research, including theoretical/mathematical, experimental, and numerical work related to the interaction between sea waves and coastal structures. These publications address conventional coastal hard structures in deep water zones as well as those located in shallow water zones, such as wave overtopping over shallow foreshores with apartment buildings on dikes. The research findings presented help to improve our knowledge of hydrodynamic processes, and the new approaches and developments presented here will be good benchmarks for future work

Efficient Mooring Systems for Semisubmersible Floating Offshore Wind Turbines

This thesis examines critical components of the mooring system for Floating Offshore Wind Turbines including chain cables, anchors and soil. The mooring line is investigated using OrcaFlex models to assess the characteristics of both catenary and semi-taut mooring system. Then, the analysis is advanced to look into the effects of water depth variation on the performance of the mooring system. The continental shelf located at the northern California coastal area is selected as a study region. Based on the information of macro-scale study on the region, soil properties are developed to aid in understanding the performance of the mooring system. Combining the results from the mooring analysis and soil data base, considerations for appropriate anchor types are presented. The anchor types include: driven piles, drag embedment anchors, and direct embedment plate anchors. This study seeks to provide a novel mooring and anchor concept which can be used to design efficient mooring systems relevant to Floating Offshore Wind Turbines