A precise prediction of seabed stability involving the fluid-pipe-soil interaction can lead to significant cost reductions by optimising design. Unlike previous investigations, a three-dimensional numerical model for the wave-induced soil response around an offshore pipeline is proposed in this paper. The numerical model was first validated with 2-D experimental data available in the literature. Then, a parametric study will be carried out to examine the effects of wave, seabed characteristics and confirmation of pipeline. Numerical examples demonstrate significant influence of wave obliquity on the wave-induced pore pressures and the resultant seabed liquefaction around the pipeline, which cannot be observed in 2-D numerical simulation.
Nowadays, many offshore structures have been commonly constructed over the last few decades due to the growing engineering resource in the ocean. Submarine pipelines, as one of the popular offshore infrastructures, have been extensively used for transportation of natural gas and oil from offshore platform, and disposal of industrial as well as municipal waste. To ensure the safety of usage of such submarine pipelines, the coastal engineers have to consider the unexpected loads including the wave, current, and anchor dropping/dredging, which might cause the its stability and decrease its life span. Thus, it is customary to bury the pipeline by trenching and refilling soil whose cost is relatively high and time-consuming (FredsØ e, 2016).
As reported in the literature, two well-known main mechanisms of dynamic wave-induced seabed liquefactions are the momentary liquefaction and residual liquefaction, based on in the field measurements and laboratory experiments (Zen and Yamazaki, 1991). The fist mechanism, momentary liquefaction, can occur beneath wave troughs when the great seepage flow is upward directly. Since this kind of liquefaction may be happen within a short duration as the passage of wave trough, it is also called instantaneous liquefaction. The other mechanism, residual liquefaction, takes place as a result from a compacted and cyclic shearing process that the build-up of excess pore pressure in the seabed (Seed and Rahman, 1978). As mention previously, the waves also can induce shear stress in the soil when the waves propagate, which has been analytically investigated by Yamamoto et al (1978). Whereas the wave-induced shear stress has less impact on seabed instability compared to that caused by the previous two mechanism above. This study only focuses on the wave-induced seabed liquefaction incorporating both instantaneous mechanism.
Lin, Ming (CCCC HZMB Island and Tunnel Project General Office) | Lin, Wei (CCCC HZMB Island and Tunnel Project General Office) | Van Stee, Joel (Trelleborg B.V.) | Peng, Xiaopeng (CCCC HZMB Island and Tunnel Project General Office)
The immersed tunnel of Hong Kong-Zhuhai-Macao Bridge (HZMB) contains 219 segmented joints, 60% of which are placed at water depth over 40m and each segmented joint is of circumferential length of approximately 90 m. To ensure the watertightness, the improvement of using the injectable waterstop was attempted and no leakage was found in the 5.664 km long tunnel up to now. The ways of improvement were elaborated in this paper and the conclusion drawn is that the effectiveness of watersealing can be achieved by looking at the system covering the structure and foundation of each tunnel element. Further, the elongation of the injectable waterstop that may lead to water passage was controlled by using permanent prestressing tendons longitudinally to confine the opening of the segmented joint
The waterproofness of the segmented joint of HZMB immersed tunnel has been a challenge, for over 3 km long section is located in water depth of over 40m (maximum water depth is approximately 46 m). Further, the segmented joints amounts to 219 in total and the length of each joint is as long as 90m. Comparatively, other immersed tunnels in the world has either shallower water depth or smaller cross-section (Rasmussen and Grantz, 1997); some minor leakages were reported by (Grantz et al., 1997), and as per the third author's experience of over 20 immersed tunnel, leakage through segmented joint has always been a concern. Nevertheless, no leakage has ever occurred at the segmented joints in HZMB tunnel from the commencement of installation of tunnel element in May 2013 to the completion of all installation in March 2017, and to now (June 2018).
With the consideration of tunnel's large scale and risk of this project, four rounds of waterstops were initially made for the segmented joint in the beginning of works, namely, polyurea + injectable waterstop + water expansion adhesive belt + Omega gasket. As a matter of fact, the work of water expansive adhesive belt is hard to be executed and is thus cancelled. The polyurea layer is vulnerable to fall off under the wave effect during towing of tunnel element. Therefore, the two key rounds of waterstops are injectable waterstop and the Omega seal.
Of these two, the injectable waterstop (also named after rubber-metal waterstop) is positioned outside thus being the initial round of waterstop of the segmented joint. The waterstop product of Trelleborg B.V. has been selected and applied. This type of waterstop has been developed and applied in immersed tunnel for around 30 years (Janssen, 1978: Grantz et al., 1997). The Omega seal is the secondary waterstop; its function is to stop the possible seepage water. In HZMB tunnel to improve the water sealing effect of the injectable waterstop a series of attempts have been made; they were introduced in this paper.
Bravo, Cristobal Santiago (University of Science and Technology (UST)) | Hong, Seok Won (Korea Research Institute of Ships and Ocean Engineering (KRISO)) | Nam, Bo Woo (Korea Research Institute of Ships and Ocean Engineering (KRISO))
This paper aims to investigate the performance of a pusher-barge system in regular waves. The numerical simulation is carried out through the implementation of an in-house code for the evaluation of the first-order (linear) hydrodynamic properties. For the potential flow problem around the pusher-barge system, a higher-order boundary element method (HOBEM) with wave green function in frequency domain is implemented. For the pusher-barge system, six degrees-of- freedom (6DOF) motion are evaluated and discussed for three different heading angles in deep water conditions. In this study, a pusher tug is arranged and located at the stern notch of the barge in a linear combination connected with a well-proven coupling system. The coupling system configuration for the pusher-barge system using a connection pin is considered, allowing the system to work as a single unit. The chosen connection pin system allows an independent pitch motion while roll and yaw angular motions remain coupled. Furthermore, loads on the connecting pins are calculated for different wave periods. Finally, Response Amplitude Operators (RAOs) are compared and discussed.
A pusher-barge system is an alternative mode of sea and river transportation that is rapidly growing due to the expected development in processing, storage, and offloading facilities in deep water.
In recent years, many efforts have been made to study the significant advantages and disadvantages of the pusher-barge systems.
Compared to a towed barge configuration, the pusher-barge system offers several significant advantages including increased speed, reduced fuel consumption, ability to transit in higher sea states, access to the barge at any time, and the elimination of the vulnerable tow wire connection (Wolff, 2004). On the other hand, disadvantages are unavoidable. Severe discontinuities in the hull shape and induced turbulence at the notch area are some examples that should be considered.
So far, extensive research in model experiments has been conducted on pusher-barge systems. Valkhof et al. (2000) performed a series of experiments of a tug and barge system for sea and river services. Luo, Hu, and Zhou (2006) carried out a series of experiments where loads on the articulated connectors between a tug-barge in irregular waves were calculated. Finally, Koh and Yasukawa (2012) conducted a comparison study of a pusher-barge system in different water depth conditions where the course keeping ability of the system was evaluated.
The paper considers the technologies of the perspective marine industrial complex of aquaculture with energy supply from renewable sources. Technological schemes of structures and devices of the onshore plant for the cultivation of hydrobionts, a marine underwater farm and a supply vessel for working with marine plantations are presented. A universal autonomous mobile wave device is presented as a variant of using the energy of waves of the open ocean.
Currently, self-contained, civilian, volatile devices for navigational equipment of the seas, research submarine and surface autonomous devices, mainly receive power from batteries. The number of these facilities is more than one million and the priority task is to prevent adverse ecological consequences of energy supply for the world ocean, regardless of costs. For these purposes, separate developments are used for solar energy, wind energy, waves, currents, temperature differences and salinity of sea water. The optimal result will be the transfer of production and processing ships to hydrogen technologies. A more complex factor threatening the Earth's ecology is due to the rapid growth of industrial coastal marine aquaculture enterprises.
PERSPECTIVE COMPLEX OF MARICULTURE
A comprehensive program for the development of marine aquaculture technologies is required, taking into account the need for clean energy and the future creation of marine underwater plantations, while preserving the coastal environment and local aquatic organisms.Modular plant for breeding hydrobionts
The future network complex developed by Loshchenkov, Knyazhev (2014) for the coasts of the Far East of Russia can serve as a contribution to the development of the Program. The complex contains a coastal enterprise for the cultivation of hydrobionts, bottom plantations in the natural environment and underwater plantations in the water column in the shelf zone.
Coastal breeding plant, due to placement in remote, inaccessible ecologically clean areas of the coast, with valuable local species, is semi-automatic, in a modular design. The plant is located, after studying local geological, meteorological, hydrological and hydrobiological parameters in the places of maximum energy flows, Pool modules and energy modules are manufactured depending on the type of hydrobiont and local natural renewable energy sources. The scheme of the plant for the cultivation of hydrobionts on island of Popov of the Peter the Great Gulf developed for the mariculture enterprise is shown in Fig. 1.
International Maritime Organization (IMO)'s recent Energy Efficiency Design Index (EEDI) regulation for new ships has increased interests in ship efficiency. As a results ship added resistance is one of the key consideration in designing a highly efficient ship and many experiments and numerical methods are conducted to predict the added resistance. In this study the motion response and the added resistance of the LNG carrier in head waves were computed using the commercial computational fluid dynamics (CFD) code Star-CCM+. Unsteady Reynolds Averaged Navier-Stokes equation (RANS) was numerically solved and the volume of fluid (VOF) approach was used to simulate the flows. The wavelengths varied from half the ship length to twice the ship length and the design speed was selected for the velocity. The heave and pitch motions were calculated along with the added resistance and the wave contours were obtained. Several grid tests were conducted to achieve the converged motion and resistance values. The calculated results were compared and validated with the experimental results.
International Maritime Organizations (IMO) has released Energy Efficiency Design Index (EEDI) regulation recently. This regulation caused ship building companies to build more efficient ships and to achieve this goal, reducing added resistance became necessary. Accurate prediction of the added resistance of the ship is needed since it could give variety of information about the efficient hull shapes. As a results, predicting added resistance became one of the highly interested domain in seakeeping problems.
Traditionally, potential based numerical methods and experimental studies are applied to predict the added resistance more correctly. Seo et al. (2014) predicts the added resistance with potential based methods and Lee et al. (2016) investigated the added resistance by model tests. However, potential based methods have limitations since it has difficulty in considering the nonlinear effects and the viscosity effects. Experiments are desirable and needed, but the expenses are rather expensive than the computational methods.
Nowadays, development of computers gave rise to new field called Computational Fluid Dynamics (CFD). CFD has gained interests since it could consider nonlinear effects and viscous effects. Nonlinear effects are especially important for short wavelengths and the viscous effects are more realistic than the inviscid model. However, the computation time is still a major issue in CFD since most of the simulation still needs a lot of computation time compared to the potential based methods. Many studies have been made using CFD methods. Sadat-Hosseini et al. (2013) compared the motion and added resistance of the KVLCC2 and Tezdogan et al. (2015) estimated the added resistance of the KRISO Container Ship (KCS) by using full scale model with commercial code, Star-CCM+. Yang et al. (2015) applied Cartesian-grid-based method to the added resistance calculation. Also, Yang and Kim (2017) predicted added resistance in short waves for the hull with several different bow shapes using CFD and showed promising results.
In this study, CFD method was used to analyze the motion and the added resistance of a given ship with head sea conditions. As CFD results are very dependent on generated grids, several tests are done on mesh generations to show the convergence of the results. Also, calculated results are validated with the experimental results. Finally, wave contours and time signals obtained are shown and analyzed.
With the increase of human activities at sea, it is inevitable that anchors drop into the water due to operating errors, which may lead to failure of pipelines and cause economic damage and environmental pollution. Previous methods of related analysis are mostly based on the DNV-RP-F107 recommended method (hereinafter referred as DNV method). DNV method hardly considers the variation of anchor's size and weight. And it is insensitive to the pipeline geometry and material properties. Based on reliability theory, DNV method is improved to calculate failure probability under the consideration of the above relevant factors. The efficiency of the proposed method is verified by a practical case. Besides, analysis of the influence of various factors on pipeline failure probability is completed in this paper, including anchor weight, size, pipeline geometry and material properties, the distance from the anchor drop point. Meanwhile, considering the variability, the sensitivities of variables to the failure probability are discussed. Study results indicate that the failure probability calculated by DNV method is underestimated in some situations, which can probably cause a loss for pipeline projects. Whereas the proposed method is able to consider much more influences and leads to reasonable results consistent with the actual situation.
Submarine pipeline is seen as the ‘lifeline’ for offshore oil and gas industry. Pipeline safety is one of the most important problems for engineering practice. Recently, anchors dropping into the sea becomes more frequent due to the increasing human activities at sea. The dropped anchors are likely to impact on pipelines and lead to pipeline failures, which can cause economic damage and environmental pollution. In order to reduce the risk and provide safe design, considerable research efforts have been devoted to risk assessment and reliability analysis of pipelines. In general, methods of the relevant research mainly consist of two categories: one is qualitative analysis, which can study the main influence factors on pipeline failures. Among them, fault tree analysis (FTA) is the most popular methodology and has been extensively applied to pipeline failure analysis. (Wang et al., 2007; Dong et al., 2005; Lavasani et al., 2011). The other one is quantitative analysis, which can determine pipeline failure probability and provide reliable reference for safe design. Katteland et al. (1995) developed a model for risk calculation, and applied it to evaluate the risk of all the installations in the North Sea. Det Norske Veritas (2010) proposed a ubiquitously used method for pipeline risk assessment and failure probability calculation (DNV method). Based on statistics of crane accidents, Det Norske Veritas (2013) also gave the falling probability for typical loads and various objects, which provided abundant references for pipeline risk assessment. On the basic of the above research, Liu et al. (2005) proposed a model to calculate the probability of pipeline being impacted under various anchorage conditions. Ding et al. (2010) modified DNV method and made a risk assessment of pipelines due to third-party activities. Yan et al. (2014) proposed a procedure to estimate the pipeline failure probability caused by anchoring activities. Up to now, to the best of the author's knowledge, quantitative analysis methods are mainly based on DNV method. In some situations, this method is hardly to consider the effect of anchor size and weight on pipeline failure probability. What's more, it is insensitive to the effect of pipeline geometry and material properties, which is not consistent with practice and may cause errors. In order to give an insight into those effects, a method based on reliability theory to calculate pipeline failure probability is proposed.
Wind turbine, an efficient way to sustainably generate electricity, of which the noise problem would affect the living environment adversely. This paper presents the results of the aerodynamic and aero-acoustic calculation of a vertical axis wind turbine. The IDDES technique and FW-H acoustic analogy are adopted to conduct all simulations. The results indicate that the combination of thickness and loading noise are the dominant noise sources at tonal peak frequency, and quadrupole noise has negligible influence. Rotational speed and receiver distance will significantly affect noise level. This work can be exploited to design quieter vertical axis wind turbines.
In recent years, the demands of renewable energy have attracted more public attention. As a clean and sustainable renewable energy, offshore wind energy has been utilized by wind turbines to generate electricity. However, one offensive problem, noise pollution, would affect the living environment of nearby creatures. Especially in several offshore wind turbine farms, birds and other animals, have left for new habitats. Therefore, it is an important issue to simulate and evaluate wind turbine noise.
According to the direction of rotation, wind turbines can be divided into two major categories: horizontal axis wind turbines (HAWT) and vertical axis wind turbines (VAWT) (Borg, Collu and Brennan, 2012). Since the wind turbines require further performance optimization to be competitive with other energy devices, the geometrical design, aerodynamic performance and optimal solutions are continuing to be investigated. Bae et al. (Y.H. Bae, M.H. Kim and H.C. Kim, 2017) studied a floating offshore wind turbine with broken mooring line. The power production and structural fatigue life were checked respectively, and some risk assessments were conducted. Rezaeiha et al. (Rezaeiha, Kalkman and Blocken, 2017) conducted researches on the effects of pitch angle on power performance and aerodynamics of a vertical axis wind turbine. A 6.6% increase in power coefficient could be achieved using a pitch angle of 2 degree at a tip speed ratio of 4 was shown in the results. MirHassani and Yarahmadi( MirHassani and Yarahmadi, 2017) investigated the wind farm layout optimization under uncertainty. A mixed integer quadratic optimization model is developed based on the interaction matrix for multi-turbine wake effects considering different hub height wind turbines. Compared to the conventional HAWTs, the VAWTs show many superiorities, including universal wind exposure, relatively simple blade structure, lower maintenance costs and lesser aerodynamic noise (Tjiu, Marnoto, Mat, Ruslan and Sopian, 2015).Although the noise generated by VAWT is lesser than that caused by HAWT, VAWT's noise is not negligible. Noise generated by operating wind turbines can be divided into mechanical noise and aerodynamic noise. Mechanical noise is generated by different machinery parts. Aerodynamic noise is produced from the moving blades and is mainly associated with the interaction of turbulence with the blade surface (Ghasemian, Ashrafi, and Sedaghat, 2017). Mechanical noise can be decreased by some engineering methods, while the reduction of aerodynamic noise is still a problem.
Pile group is a commonly used structure in coastal and ocean engineering. The wave action on pile group structures has always been the focus of scholars' research. Because of the vortex shedding around the piles, small scale piles are different from large scale piles. Except inline force, transverse force of a small scale piles cannot be ignored. In order to explore the interaction between different piles, experimental investigations of the interaction of irregular waves with small scale, vertical bottom-mounted pile group which has 9 piles in side by side arrangement have been carried out. Considering the comprehensive influence of the relative pile diameter and KC1/3 number, a new parameter KCLD1/3 is proposed. The influence of relative spacing on the wave force of the pile group is analyzed. The change of pile group coefficient, inline force and resultant force with KCLD1/3 parameter and relative spacing are discussed.
Pile group structures are widely used in the area of coastal and offshore engineering such as crossing bridge and offshore wind turbine platform. However, there are many uncertain issues in the wave force of such piles. Accurate analysis of wave force is essential for designing pile group-supported marine structures. When the distance between the piles in the pile group structures is small, wave force on a single slender pile is significantly affected by the neighboring piles. The formula which is based on the concept of Morison et al. (1950) for calculating the wave force of a single isolated pile is not applicable.
So, a lot of laboratory tests had been conducted to study the interference effects of neighboring piles under the action of irregular waves. Chakrabarti (1981, 1982) measured inline forces on instrumented sections of the piles, the inertia and drag coefficients (Cmand Cd) are determined based on experimental data by applying for instance the least square fit. These coefficients are shown as functions of the KC number which is suggested by Keulegan (1958). The total forces on the piles were computed from the mean curves of the inertia and drag coefficients. The correlation between the maximum calculated forces and the corresponding measured maximum forces is good. However, any relationship with the Reynolds number could not be established primarily because of the small range of Reynolds number covered by the test. Sundar et al. (1998) found that the variations of Cd and Cm with KC for inclined cylinders are significantly wide. Boccotti et al. (2012, 2013) revealed that the inertia and drag coefficients are given as a function of KC number and Reynolds number Re for KC in (0, 20) and Re in (2*104, 2*105). Calculation of wave force of pile group by the Morison equation depends on inertia coefficient, Cm, and drag coefficient, Cd. However, the inertia and drag coefficients are not easy to be determined.
pang, Dan (Dalian University of Technology) | Tang, Guo-qiang (Dalian University of Technology) | Lu, Lin (Dalian University of Technology) | Gao, Rui (China Petroleum Bureau (CPP) No.6 Construction Company) | Zhu, Yan-shun (China Petroleum Bureau (CPP) No.6 Construction Company)
Numerical simulations are performed for the dynamic responses of two identical square cylinders in tandem arrangement oscillating separately in steady current. The results are presented based on a spacing ratio (L/B) ranging from 1.5 to 4 and a reduced velocity (Vr) ranging from 1 to 30 at a low Reynolds number (Re) of 180. The present numerical results show that the responses of both square cylinders are highly dependent on the spacing ratio and reduced velocity. When the spacing ratio is less than 2.5, a critical reduced velocity exists. The responses are dominated by vortex-induced vibration (VIV) when the reduced velocity is smaller than the critical reduced velocity and by galloping when the reduced velocity is larger than the critical reduced velocity. When the spacing ratio is 3.5, only VIV occurs for Vr is less than 20 while a response with combination of VIV and galloping appears for Vr over 20. Additionally, when the spacing ratio reaches 4, only VIV occurs. The results also show that the two square cylinders do not necessarily share the same synchronized mode. Moreover, besides the odd-number synchronized modes, an even-number synchronized mode is also identified.
VIVs of bluff bodies are of significance for both academic and practical applications, which have been widely investigated in recent several decades. In order to study the issue, the previous studies paid much attention to the fluid past an elastically-mounted circular cylinder. A typical phenomenon observed in the VIV of a circular cylinder is lock-in, characterized by the synchronization of vortex shedding frequency which synchronizes with the frequency of body oscillation (Williamson and Govardhan, 2004). Comprehensive investigations have been carried out in various aspects involving the VIV of circular cylindrical structures (e.g. Bearman, 1984; Sarpkaya, 2004; Gabbai and Benaroya, 2005; Williamson and Govardhan, 2008). In addition to circular cylinders, square-cross-section cylindrical structures have also been used in offshore engineering, for instance, the piers of bridges. However, less attention was focused on the dynamic responses of square cylinders in previous studies. Compared to the responses of circular cylinders, besides VIV, the dynamic response of a square cylinder presents another feature, i.e., transverse galloping, where the response amplitude increases with the reduced velocity. The transverse galloping is caused by the fluid force in phase with the body motion due to the change in the angle of attack (Zhao et al., 2014).
Sinusoidal motion of a cylinder in viscous flow has been extensively studied in the past decades. Distinction of flow patterns exists between cylinders in cross-flow freedom restricted and freely vibrating conditions when experiencing oscillatory flow. In this paper, a series of numerical simulations are carried out by the in-house CFD code naoe- FOAM-SJTU, which is developed basing on the open source code OpenFOAM with overset grid capability. The diameter of the cylinder is 0.02m and the KC numbers varies from 3 to 12 corresponding to the attached vortices regime and the transverse street regime. Results of vortex evolution, flow regimes and hydrodynamic force coefficients are compared.
In actual production, offshore floating structures subject to waves, currents or winds will cause the platform to move periodically in the water. Then relatively oscillatory flow is generated between the riser and the water. In recent decades, researches of the sinusoidal motion of a cylinder in viscous fluid have been extensively studied by Bearman (1984, 1985), Sarpkaya (1986,1995) and Williamson (1985).
Williamson (1985) conducted a series of experiments to investigate development of vortices around a single cylinder in relative oscillatory flow. And several vortex regimes were identified within particular ranges of Keulegan-Carpenter (KC) Numbers: the attached vortices regime (0 Kozakiewicz et al., (1996) conducted experiments of a cylinder exposed to oscillatory flow for two Keulegan– Carpenter numbers, KC=10 and 20. Then numerical simulations of a cylinder freely vibrating in the cross-flow direction were carried out at the same KC numbers. Comparisons showed that the number of vortices generated over one oscillating cycle increased when the cylinder was freely vibrating in the cross-flow direction. The vortex shedding direction changed to the opposite side of the cylinder in the transverse street regime when KC=10.
Kozakiewicz et al., (1996) conducted experiments of a cylinder exposed to oscillatory flow for two Keulegan– Carpenter numbers, KC=10 and 20. Then numerical simulations of a cylinder freely vibrating in the cross-flow direction were carried out at the same KC numbers. Comparisons showed that the number of vortices generated over one oscillating cycle increased when the cylinder was freely vibrating in the cross-flow direction. The vortex shedding direction changed to the opposite side of the cylinder in the transverse street regime when KC=10.