Chen, Ling (University of Chinese Academy of Sciences, Beijing) | Zhou, Jifu (Chinese Academy of Sciences, Beijing) | Wang, Xu (Chinese Academy of Sciences, Beijing) | Wang, Zhan (Chinese Academy of Sciences, Beijing)
A new type of bottom-fixed structure, the so-called high-rise pile cap foundation, has been proposed and used to support offshore wind turbines in the Donghai Bridge Wind Farm, China. Engineers are unaware of the wave load mechanisms for this new structure. Using the Navier–Stokes equations and volume of fluid technique, a fully nonlinear numerical wave tank is established to investigate free surface wave loads and moments for the new structure. The interaction between the cap and piles are discussed in detail. In the case of fully nonlinear waves, the maximum horizontal wave load on all the piles with the cap can increase by 30% compared with those without the cap, and the maximum horizontal wave load on a single pile is nearly doubled. The horizontal wave load on the cap with the piles can increase by about 15%, while the vertical wave load decreases slightly. The conventional Morison formula and diffraction theory generally underestimate the wave loads on the piles and the cap as well.
Hydraulic fracturing for shale gas production involves pumping large volumes of water; as a consequence of this, produced water management is an important topic to address in order to sustainably produce shale gas. It has been well documented that only approximately 10-40% of the pumped fluids will be produced back to the surface, and that there will be increased concentrations of various ions in the flowback water during this process. This flowback water, with high total dissolved solids and high concentrations of certain ions, presents a significant risk of mineral scaling (
In general, it can be very challenging to identify the
A further two-phase 3D flow model was developed to examine the scaling tendency due to the evolving produced brine composition over the lifetime of the well. It is based on the previously history matched model and includes the fracture fluid and formation water compositions to predict precipitation of minerals. Finally, scale inhibitor injection was simulated to examine the impact of inhibitor retention on well protection.
Internal solitary waves usually transform into an internal wave train when propagating through the continental shelf/slope. However, such phenomenon is rarely taken into account in previous design of marine structures. This paper aims to construct an evolution model to describe the evolution of internal wave trains. To be specific, in consideration of various influential factors, such as benthic topography, friction, dissipation, et al., a mathematical model is built to describe the evolution of wave trains and numerical experiments are carried out to validate the method by analyzing the leading internal wave and the induced velocity fields. It is shown that the numerical results of the wave train displacement and the velocity fields are in good agreements with the observational data in South China Sea. In the meantime, the sensitivity of dissipation and friction to the model is discussed.
Internal solitary waves propagating over underwater topography, such as a sill or continental shelf/slope can produce internal wave trains. Specific to South China Sea (SCS), these wave trains propagate westward across the Luzon Basin to South China Sea shelf break, and the corresponding surface expression has been detected with satellite synthetic aperture radar (SAR)(Liu et al., 1998). Many observations showed that internal wave trains occur frequently and exist widely, which has resulted in obvious impacts on the operation of offshore structures. For instance, the investigation of (Xu et al., 2013) has shown the impact of internal solitons on offloading system, and operations need to be assessed during the design of FLNG in soliton active area.
As the foundation for assessing the hydrodynamic action between internal wave trains and floating structures, the characteristics of internal soliton trains have been studied preliminarily by far (Liu et al., 1998). However, many issues are not yet clear. First, the factors such as dissipation, shoaling, and friction play a role during internal soliton evolution. But previous scholars have different opinions about which factor should be added into the Korteweg-de Vries (KdV) equation, which is one of the most popular equations to analytically describe internal solitary waves. Besides, the comparisons are very few between numerical results (especially induced velocity fields) and the observational data from actual sea areas. Finally, selecting the coefficients of dissipation and friction are often subjective due to the lack of clear criterions. Thus, it is necessary to discuss the sensitivity of numerical model to the two coefficients.
Chen, Ling (Chinese Academy of Sciences, University of Chinese Academy of Sciences) | Zhou, Jifu (Chinese Academy of Sciences, University of Chinese Academy of Sciences) | Wang, Xu (Chinese Academy of Sciences, University of Chinese Academy of Sciences)
High-rise pile cap foundation of offshore wind turbine is used in Donghai Bridge windfarm, East China Sea. The wave load characteristic of this new type of fixed structure has been paid close attention in engineering. In this investigation, based on Navier-Stokes equation, a fully nonlinear numerical wave tank was established for this high-rise pile cap foundation, and the wave loads and moments were obtained by integrating pressure over the surface of the structures. The effects of interaction between the cap and the piles are discussed in detail. In case of extreme wave height, the results indicate that the wave load on the piles with the cap increases by about 30 percent of those without it, and the maximum wave load is nearly doubled. The horizontal wave load on the cap with the piles increases by about 15 percent, while the vertical wave load decreases slightly. In addition, simply using Morison equation will seriously underestimate the wave loads of the piles.
A new type of fixed structure supporting offshore wind turbines is used in Donghai Bridge windfarm, East China Sea. It is a high-rise pile cap foundation, which consists of a circular platform of 14 m diameter and eight supporting piles of 1.7 m diameter. A high vertical tower is mounted to the platform with a 3.4 MW wind turbine fixed at its top end. This foundation has many advantages over other conventional supporting systems, such as high stiffness, controllable risk for construction, economical cost, anti-collision, etc. (Chen & Zhou, et. al., 2016). However, it serves at present as an in-situ test model for the new type of structure to support offshore wind turbines (Lin YF, 2007).
However, the wave load characteristics are still not very clear. Because of complexity of this structures, traditional methods (such as Morison equation, diffraction theory), are unable to estimate the wave loads accurately. Moreover, the ratio of the cap diameter to the wave length is about 0.2, and there is no specific approach to calculate wave loads for the structures of this scale in nonlinear wave conditions. What is more, the cap just pierces the still water surface so that it is sometimes exposed to air and sometimes submerged in case of large amplitude waves. Most standard engineering tools of today are not capable of accurately modelling these contributions, and the design load values are therefore often based on model test experience. CFD computation of wave impacts on these type of structure has been rarely undertaken. However, similar work of wave-in-deck loading have been achieved. Bredmose et al (2011) presented a numerical simulation of wave impacts on a monopile, and then showed a subsequent vertical impact on the inspection platform. Schellin et al (2011) demonstrated that a modern CFD technique was able to predict the loads on a typical jack- up platform, and the wave-in-deck load acting on the hull in freak wave is particularly taken into account.
Lu, Xiaolong (Harbin Engineering University) | Ren, Huilong (Harbin Engineering University) | Wang, Xu (Harbin Engineering University) | Feng, Guoqing (Harbin Engineering University) | Zhou, Xueqian (Harbin Engineering University)
Ship accidents occur most often to aged ships, and the main reasons obviously include corrosion and fatigue. Due to the special structural characteristics, the problem is more critical to catamarans’ corner spots. Based on Paik corrosion model and the spectrum analysis method for fatigue strength, this paper studies the influence of randomly distributed corrosion on the fatigue strength of a catamaran’s corner spots. According to the computation results, a prediction model for accumulated fatigue damage is proposed to guide ship construction.
Shipping plays, especially in this day and age, a role of cornerstone in the development of economic globalization and international trade. However, with the rapid increase of maritime transportation, ship accidents also happen more frequently than ever, causing losses of goods and assets. Statistics shows that ships older than fifteen years are much more prone to accidents. After a long time of operation, the strength of ship structure degrades due to corrosion and fatigue crack. For this reason, the fatigue problem of aged ships is attracting more and more attention.
There exists in the literature a good amount of works on the corrosion of structures. In most of them, the rate of corrosion is assumed to be constant, i.e., the thickness of the structure plate decreases linearly with time. But the data from the real sea corrosion tests show that the corrosion of metals in seawater is very complex, and nonlinear models are more suitable for dealing with problems of corrosion than linear corrosion models. Soares and Garbatov (1999) devised a model describing the growth of corrosion wastage by a non-linear function of time, in which the corrosion process is divided into three phases. In the first phase, it is assumed that there is no corrosion because the corrosion protection is effective. Failure of the protection will occur at a random point of time, which is defined as the second phase. While in the third, a non-linear process begins, and the corrosion wastage grows with time and finally asymptotically reaches a long-term value. In the revised version of this model (Soares et al. 2008), the corrosion depends only on time, and particularly, a number of environmental factors such as temperature, carbon dioxide concentration were introduced to account for their effects on the corrosion behavior, which facilitates the assessment of corrosion wastage.
Xu, Ning (National Marine Environmental Centre) | Wang, Xu (Liao Ning Hong Yan He Nuclear Power Co., Ltd) | Chen, Yuan (National Marine Environmental Centre) | Yan, Bizhong (Liao Ning Hong Yan He Nuclear Power Co., Ltd) | Xu, Peng (Liao Ning Hong Yan He Nuclear Power Co., Ltd) | Yuan, Shuai (National Marine Environmental Centre) | Chen, Weibin (Liao Ning Hong Yan He Nuclear Power Co., Ltd)
Sea ice is the dominant envirornnental factor to nuclear power plants in ice-covered region, especially for the cold source water intake. In order to monitor the sea ice risk of water intake to the only nuclear power plants in ice-covered region of China, Fiber Bragg Grating (FBG) strain sensors were used to directly measure the water intake coarse grids strain during May 2014 and Feb. 2015. Effective coarse grid strain data was obtained in and out of ice period. Analysis results show that the impact by submerged floe ice was not measured. This method could be used to monitor the sea ice risk condition of water intake by submerged floe ice, and then contribute to ensure the cold resource safety of nuclear power plant of cold regions during ice period.
Sea ice is the dominant envirornnental condition in the Bohai Sea of China (Yue and Bi, 1998). For the traditional business, such as oil exploration, harbor and navigation, sea ice action will induce the physical damage on ocean engineering structural (Zhang, et al., 2015), which is the main sea ice risk mode. For the purpose of the safety production during winters, research on sea ice risk mechanics and reduction method, management during ice period had been conducted since 1990's (Qu, Y., et al, 2006; Yue, Q.J., et al, 2009; Huang, Y, 2010, Zhang, D.Y., et al., 2006; Xu, N. and Yue, QJ, 2011). Nuclear power plant is one of the new kinds of industry in Bohai Rim Economic Circle; therefore the sea ice risk is a new challenge issue. Based on the accident of nuclear power plant (WIKIPEDIA, 2015), the possible influence to cold resource should be the primary issue effect when considering the sea ice risk.
Hong Yan He Nuclear Power Plant (LHNP) is the first nuclear power plant in ice covered region of china, which was llllder operation on Jlllle 2013. "While the mechanics for sea ice risk to cold source water intake is not clear. Either there is no recommendation on design or production to prevent sea ice. Water intake is the first position for water supply of cold resource in nuclear power plant. Since water intake is exposed to the natural sea water with low temperature, the sea ice floe or ice accumulation will reduce the effective area of water intake channels. Under distinct low tide level and serious wave, the appearance of submerge floe ice would act on the coarse grid. In one case, the coarse grid will be destroyed by significant ice impact, or the llllderwater ice block could be formed in the front of coarse impact, and then risk the safety of water intake.
Wang, Xu (CNPC USA) | Winterfeld, Philip (Colorado School of Mines) | Ma, Xu (Changqing Oilfield Company, Petrochina) | Ye, Dengsheng (Chuanqing Drilling Engineering Company) | Miao, Jijun (CNPC USA) | Wang, Yonghong (CNPC USA) | Wu, Yu-Shu (Colorado School of Mines)
Hydraulic fracturing combined with horizontal drilling has been the technology that makes it possible to economically produce natural gas from unconventional shale gas reservoirs. An efficient methodology to evaluate hydraulic fracturing operation parameters, such as different proppants, fraking liquids, injection rate and pressure, and so on is essential for the industry. Traditional numerical evaluation and optimization approaches are usually based on the simulated fracture properties like their efficient areas. In our opinion, the methodology based on the simulated production data is better, because the production is the direct goal and we can calibrate this approach with some production data already known. The core of this numerical methodology is a fully-coupled hydraulic fracture propagation and multi-phase flow model.
In this paper, we present a general fully-coupled numerical framework to simulate the hydraulic induced fracture propagation and post-fracture gas well performance. This three-dimensional, multi-phase simulator focuses on: (1) fracture width increases and fracture propagation occurs as slurry is injected into the fracture, (2) fracturing fluid erosion and leakoff, (3) proppants subside and flowback, and (4) multi-phase fluid flow through various-scaled anisotropic natural and man-made fractures. Mathematical and numerical details on how to fully couple the fracture propagation part and fluid flow part are discussed. Fracturing and production operation parameters, properties of formation, reservoir, fluid, and proppants are all taken into account of this model. The well in this model may be horizontal, vertical, or deviated and this well may also be open-hole or cemented. This simulator is verified based on benchmarks from literature survey. We will show its application to simulate the fracture network (hydraulic fracture and natural fracture) propagation and production data history matching of Sichuan Field in China. We will also conduct a series of real-data modeling studies with different combination of fracking parameters and present the methodology to design fracking operations with the feedback of simulated production data. This unified model could help on the optimization of hydraulic fracturing design, operation, and production.