A new model is established to estimate the reaction forces and torques on cutter head of cutter suction dredger in rock dredging. In our model, the cutting parameters of the teeth on cutter head are determined by numerically simulating the relative positions between the teeth and rocks, then those parameters are used for calculating the forces on the teeth. Summing up all the forces on all the teeth and the moments of all the teeth around the axis of the cutter head, the reaction forces and torques on cutter head can be obtained. The proposed model is effective for estimating dredging loads.
Cutter suction dredger is a highly efficient and core piece of dredging equipment, which is widely used in the waterway dredging, port construction, and reclamation and other projects. The loads on the cutter head have great effects on the design of bridge structure and mooring of the ship, because the loads are transferred to the ship body through the bridge and are resisted by the loads on the mooring system. It is essential for the accurate calculation of the dredging loads that are imparted onto the bridge structure while dredging for safety. Pan (Pan, Yang and Tang, 2009) and Yang (Yang, Zhu, Fan and Pei, 2012) analyzed the dynamic loads on the cutter head in dredging sediment based on two-dimensional cutting theory. Li (Li, Jiao, Huang, Jia, Wei, Liu, Ai and Lu, 2013) simulated the sediment dredging process of the cutter suction dredger. With the development of dredging industry, the cutter suction dredgers are now used for dredging soft rock or hard rock rather than just for sediment or soil. Gao (Gao, 2007) introduced the technicals related to the rock dredging with cutter suction dredger. Yao (Yao, 2011, Yao and Yang, 2011) and Chen(Chen, 2012, Chen and Yang, 2013) investigated the methods to estimate the dredging loads of the large cutter suction dredger with the theory from coal mining. Ma (Ma, 2015, Ma, Ouyang, Yang and Liu, 2014) built a model to estimate the dynamic loads on cutter heads. In Ma’s model, the two-dimensional rock cutting theory was used to calculate the cutting forces, and the effects of some dredging parameters were investigated. However, in all of the models for estimating the dredging loads, the effects of the breakout angle on the cutting forces for rock cutting have not been considered except two-dimensionally, which can result in underestimating the fluctuation of the dredging loads.
This paper investigates a method to determine the relative power production potential of a floating oscillating water column wave energy converter. This method focuses on determining the key characteristics of the parametric function relating the water column heave velocity to the structure heave velocity. The numerical investigation is undertaken using single frequency sinusoidal waves using WAMIT and OrcaFlex.
The paired velocities of the structure and the water column surface follow an elliptical function. The properties of this ellipse yields interesting information about the power produced by the OWC.
It has been determined through investigation into the length and gradient of the major (long) and minor (short) axes of the bisector of the ellipse that relates the vertical water column heave velocity to the structure heave velocity that the power production potential is linearly proportional to the magnitude of relative velocity between the water column and floating structure more so than a phase difference between these two velocities. It has also been determined that the lengths of both axes of the ellipse are maximised, and hence system efficiency, when the forcing frequency is equal to approximately 90-100% of the of natural frequency of the water column of the system in question.
An oscillating water column wave energy device usually consists of a chamber partially submerged, this chamber is open to wave excitation. Wave forces are used to move an air column within the chamber through a power takeoff device usually located at the top of the chamber. This power takeoff device is usually a turbine of some description. These devices can be fixed to the shore/sea bed or floating in the ocean. A two dimensional schematic of a floating system is seen in Figure 1 (Stappenbelt and Cooper, 2009).
Significant analytical investigation has been undertaken on fixed devices (Morris-Thomas, M. & Irvin, R. (2007); Mei (2011); Bull (2015)) and floating devices ((Sykes, R., Lewis, A. & Thomas, G. (2009); Szumko, S., (1989)).
Floating devices maintain one advantage over fixed devices, the structure is able to move. This additional degree of freedom can allow for an artificially longer chamber length and hence a larger volume. A longer chamber length will allow more air to be passed through the power takeoff device per cycle than a shorter chamber. Investigation into the relative movement of the structure and water column has not been extensively studied previously. Past studies have focused on achieving resonance of either degree of freedom with the forcing waves (Stappenbelt and Cooper (2009); Bayuomi et al. (2014)).
Understanding the complex hydrodynamic and morphodynamic processes associated with storm impact and subsequent recovery of barrier island systems is essential in developing appropriate coastal management strategies to protect these fragile resources. Measured morphology changes of the subaerial portions of a sediment-starved barrier island were analyzed using the process-based 2DH numerical morphodynamic model XBeach during hurricane impact, and LiDAR surveys covering five years of post-storm recovery. The recovered subaerial volume of the barrier island after five years exceeded prestorm volumes by up to 30%, suggesting that extreme events are necessary for barrier islands to sustain themselves in sediment-limited environments.
Background and Motivation
Along many of our coastlines barrier islands are the first line of defense against wave attack and damage from storm surge. Understanding the complex hydrodynamic and morphodynamic processes associated with storm impact and subsequent recovery of barrier island systems is essential in developing appropriate coastal management strategies to protect these fragile resources. While some pre- and post-storm topography and bathymetry data of barrier islands inundated during a storm exist, very little information is available to help understand the complex hydrodynamic and morphodynamic processes during storm impact (i.e. Sallenger, 2000; Houser et al., 2008). These processes are crucial to understanding sediment budgets, potential threats to infrastructure and best coastal management practices for specific locations. For this study, Follet’s Island (FI), a narrow, low-lying barrier island in a sediment-starved environment along the upper Texas coast (UTC) in the Gulf of Mexico was investigated. LiDAR and topographic surveys were collected before and after Hurricane Ike (2008) and on a yearly basis over the five years following the storm. The goal was to address how Hurricane Ike affected the sediment supply on the subaerial beach and foredune of FI, what physical processes governed the response of the island during the hurricane, and how the island recovered following the hurricane. The UTC is tentatively defined as the coastal region between the Sabine Pass and the Brazos River (Anderson, 2007) and is characterized by long, narrow barrier islands comprised of fine sand (less than 0.2 mm), and a microtidal wave-dominated hydrodynamic environment with a tidal range of 0.54 m between Mean-Lower-Low-Water (MLLW) and Mean-Higher-High-Water (MHHW). On average, approximately four hurricanes and four tropical cyclones make landfall per decade (Roth, 2010). Since the long term morphology of barrier islands is strongly influenced by the frequency of large scale episodic events, the UTC is particularly vulnerable to large scale erosion.
Xiao, Hong (Changsha Research Institute of Mining and Metallurgy Co. Ltd.) | Liu, Yuwei (Changsha Research Institute of Mining and Metallurgy Co. Ltd.) | Tang, Dasheng (Changsha Research Institute of Mining and Metallurgy Co. Ltd.) | Li, Xiaoyan (Changsha Research Institute of Mining and Metallurgy Co. Ltd.)
On the stage of pre commercial exploitation, the safety and economic cost become the main research content in the study of deep-sea mining pipeline transportation technical. The laboratory has been established to study on the deep-sea mining pipeline transportation for a long time. Based on the results of these research, the experimental study of different particle size and concentrations for artificial manganese nodules had been carried out in the test system. The following conclusions were obtained. 1. Resistance loss in different particle size and concentration, 2. The best ratio of particle size and concentration, 3. The Empirical formula of the optimal transport velocity.
On the stage of pre commercial exploitation, the safety and economic cost become the main research content in the study of deep-sea mining pipeline transportation technology. With deepening of the research on deep-sea mining transportation technology, more and more research institute start to study deep-sea mining and share the results of their research. But most of the results is the basic theory research and numerical simulation, and the test is carried out in the laboratory test, the effect is limited to deep sea mining commercial exploitation. The test should develop from laboratory to sea trial after years of research in deep-sea mining technology for commercial exploitation. We have made a professional multistage pump to take sea trial in the recent times, and Processing a set of multistage pump transportation test system before the sea trial, to exam the capability of multistage pump and motor which is the performance and the basis of deep-sea mining transportation, to test transmission efficiency of multistage pump in the condition of different slurry concentrations, flow velocities and particle sizes, find out the relationships between transportation conditions and the multistage pump efficiency, which provides necessary parameter for sea trials.
Jin S. Chung et al. (2001) presented particle size and concentration are the main factors influencing the pressure gradient with the result of the particle-water mixture flow test; Chi Ho Yoon et al.(1999) presented particle size, volume fraction and tube diameter is the main factors influencing the pressure drop and hydraulic gradient.
The paper focuses on a part of a large feasibility study conducted for Statoil ASA. The target of the study was a method for hyperbaric drying of a subsea welding chamber used in maintenance and repair operations of subsea pipelines. In order to verify the consistency of the numerical representation of convection and temperature distribution a welding chamber prototype was built and tested in atmospheric conditions. In this work we investigated conditions for heating and drying of the welding chamber prototype using methods of Computational Fluid Dynamics (CFD). Simulated convection patterns and temperature distributions are compared with the real world experiment performed by Statoil. The main goal of our research was to confirm that CFD can represent the real world phenomena and thus can conservatively be used for further investigations of the welding chamber.
Computational Fluid Dynamics is a powerful tool, which helps to reduce dramatically the cost of development, replacing real object with their computer models. In conjunction with modern computers CFD makes it possible to study a wide range of complex phenomena within a reasonable time span. In particular, it can be utilized for modeling of turbulent flow, fluid compressibility due to pressure and temperature variations, heat transfer due to fluid convection. For complex problems with industrial applications it is crucial to verify the accuracy of calculations. This can be done numerically by several means such as mesh metrics and mesh sensitivity test, monitoring the convergence of solution residuals and monitoring of important physical quantities. Ideally the results of a numerical study should be compared to a similar real world experiment. For a feasibility study, experimental data is invaluable, as it allows one to investigate, which parameters the solution is sensitive to, and whether a specific choice, such as e.g. mesh type and density, improves correspondence between simulation results and experimental data.
This paper focuses on a part of a large feasibility study conducted by Polytec for Statoil ASA. The target of the study was a method for hyperbaric (up to 100 bar) drying of a subsea remote welding chamber used in maintenance and repair operations of subsea pipelines. The chamber is lowered and placed on top of the pipe located at the seabed. Then the chamber is sealed off and flushed with argon gas, creating overpressure inside the chamber such that the sea water cannot leak in.
Welding operation requires that there is no free water in the welding zone and the wetness of the atmosphere inside the chamber is below a certain level. It was suggested to warm up the habitat such that all water is evaporated and consequently condensed in a cooler attached to the chamber. Thus it is important to set up stable circulation of fluids between the chamber and the cooler. Due to the specifications it was unreliable to use any sort of blowers with moving parts such as fans, while free convection due to fluid compressibility was an option.
It is widely recognized that seabed scour around offshore wind turbine foundation (OWTF) considerably influences performances of wind turbine such as bearing capability and dynamic responses. Thus a proper model is required to estimate seabed scour around OWTF. Some investigations have been conducted to predict scour around monopile, jacket and bucket foundation. However, scour around more-than-three-inclined- pile group OWTF is rarely investigated. Herein, Fluid is described with mass conservation law, momentum theorem, RNG turbulence closure model and VOF for free surface. Shields parameter is chosen as scour criterion. The transport of suspended sediment is governed by conservation law and momentum theorem. OWTF is simplified as wall boundary. The constructed model is used to estimate current-induced scour around eight-inclined-pile group foundation, scour topography is predicted and scour evolution with time is also estimated. Though the case study only takes current into account, model in this paper could be easily extended for wave-induced and wave-plus-current-induced scour around OWTF by changing the inlet and outlet boundaries.
Wind is one of the most popular new energies due to its environmental friendliness and large reserve in the world. Offshore wind is steadier with larger speed than land wind, so it is an important part of exploiting wind energy. However, some difficulties are confronted (Zhou and Lin, 2013) because of the complicated ocean environment such as wind, wave, current and soft seabed. One of the challenges is seabed scour around offshore wind turbine foundation (OWTF). Local scour around OWTF directly reduces the embedded length of pile(s). Consequently, the capacity, deformation, and dynamic responses of OWTF are changed. It was discovered that the scour depth has such a significant negative impact on dynamic responses of offshore wind turbine (OWT) that engineers must pay enough attention to it (Yan, Gu, Lu and Lin, 2011). According to Xue, Wang, and Yang (2012), scour may increase deformation and decrease bearing capacity of OWTF. With a small scale physical model test and a full scale FEM simulation. Prendergast, Gavin and Doherty (2015) found that wind turbines with loose sand seabed would show the largest relative reductions in natural frequency caused by scour. Additionally, some researchers put efforts on the scour protection for OWTF (Chen, Yang and Hwung, 2014; Matutano, Negro, López-Gutiérrez and Esteban, 2013; Whitehouse, Harris, Sutherland and Rees, 2011). Therefore, it is a wide recognition that seabed scour around OWTF considerably influences performances of wind turbine.
A fatigue analysis of the high-density polyethylene (HDPE) floating system of fish cage is presented. The fatigue analysis is based on the deterministic method and the finite element method combined with a hydrodynamic model. The stress of the floating collar is evaluated based on the joint use of the finite element method and hydrodynamic model. The fatigue life of the HDPE floating collar is about 20 years, which is using the deterministic method and evaluated by applying Palmgren-Miner cumulative damage theory and S-N curve of the material HDPE. Results indicate that the sensitivity of the fatigue life to the wave height is more important than that to the wave period.
Due to the growing domestic demand for seafood and the decline of fresh water resources available to the near-shore aquaculture, developing the marine cage net aquaculture in the open ocean is becoming a worldwide trend in the aquaculture industry. Unfortunately, the detrimental environment condition in the unprotected open ocean may lead to the collapse and fatigue failure of floating fish farms. Thus, ensuring the security and sustainability of marine cage becomes an important issue.
In the past decades, numerous studies were conducted to analyze the hydrodynamic characteristics of net cage system. Tsukrov et al. (2005) evaluated the performance of a tension leg fish cage and predicted the overall dynamics of the system in the open ocean environment, using a consistent finite element to model the net panels and nonlinear elastic components of mooring systems Fredriksson et al. (2003) analyzed the reactions of the net cages in waves by physical and numerical methods and compared the results with field observations. To investigate the dynamic properties of a flexible net sheet exposed to waves and currents, Lader and Fredheim (2006) conducted a series of experiments and developed a numerical model in which the super element concept was used to simulate the net sheet. Kristiansen and Faltinsen (2015) proposed a screen type force model for the viscous hydrodynamic load on nets, simulating the net by a system of trusses and investigated the mooring load on the net cage by experimental and numerical study. Shainee et al. (2014) examined the submergence characteristics of the single-point mooring (SPM) cage concept in random waves with following current using numerical simulations and experimental model tests. Decew et al. (2013) used an acoustic method to monitor the deformation of a small-scale fish cage deployed in currents. Zhao et al. (2014) and Bai et al. (2015) analyzed the deformations of the floating collar in waves using the curved beam method.
Inside an LNG floating tank as for LNG carriers, FLNGs, FSRUs or LNG fuel tanks, the possible phase change between LNG and its vapor during a wave impact might have an effect on the maximal pressure loads. Until now, this effect has been neglected in most of the sloshing studies.
In Ancellin et al. (2012), a non-equilibrium phase transition model embedded in Bagnold’s piston model was shown to have a damping effect on the pressure, in good accordance with the previous experimental results from Maillard and Brosset (2009).
This model is too limited to understand all the possible consequences of phase change on a real wave impact. To get a better understanding of this, we want now to simulate numerically a complete wave impact in a finite volume CFD code for two non-viscous compressible fluids including phase transition. We thus introduce a mathematical model of non-equilibrium interfacial liquid-vapor phase change and nucleation.
The numerical simulation of the piston problem allows us to retrieve the damping phenomena for gas pocket impacts. For a 2D liquid impact test case, a slight amplification of the maximal pressure has been found.
For any project of membrane Liquid Natural Gas (LNG) floating tank, the sloshing assessment relies on sloshing model tests, mostly at scale 1:40 with water and non-condensable gases. Despite the fact that sloshing and wave impacts inside LNG tanks involve liquid and vapor close to their thermodynamical equilibrium, the possible phase change is not directly modeled. Very few studies have tried to evaluate its effect on wave impacts loads.
During a 2007 sloshing experimental test study referred to in Maillard and Brosset (2009), it has been noticed that phase change has indeed an effect on the pressure signals at the wall of the tank. Pressure oscillations of any gas pocket impacts seems to be strongly damped, as illustrated by Figure 1. A statistical reduction of the pressure peaks has been noticed, which might be the consequence of this damping.
Reel-lay as an economical method for offshore pipeline installation is highly important. Pipes deform plastically when spooled and unspooled onto a large vessel. Buckling that occurs when spooling should be avoided by metallurgical design for pipeline steel. A low yield-to-tensile strength ratio makes it difficult for buckling to occur. In this paper, optimum chemical composition was investigated and discussed from the change in microstructure. The change in Y/T ratio can be explained by microstructural arrangement and precipitation.
Reel-lay is one of the installation methods for off-shore pipelines. Recently, the method has been become popular in the North Sea because it is more cost-effective than the other pipe laying methods, S-lay and J-lay (Denniel, 2011; Meissner, 2012). With the reel-lay method, short lengths of pipe are welded onshore under accurately controlled conditions to build a pipeline. After constructing the pipeline, it is spooled onto a large drum and mounted on a pipelay and construction vessels. After this, the spooled pipeline is unspooled to be laid subsea. This method has some advantages compared with the other pipelaying methods, i.e., laying speed, quality of the girth-weld portion because of onshore welding, and lower weather dependency (Recalde, 1990). During reel-lay, cyclic plastic strain by spooling and unspooling is introduced into the pipe. Under plastic bending, longitudinal buckling is likely to occur (Tsuru, 2015; Tkaczyk, 2011). In order to improve buckling resistance during this process, the pipes are required to have a low yield-to-tensile ratio (Y/T) in the longitudinal direction (Tkaczyk, 2011).
The underwater structure is always in a complex stress state caused by the hydrostatic pressure and the residual stress produced in machining and assembling. The complex stress has an influence on the structural vibration through changing structural stiffness matrix. Studying the vibration characteristics of this kind of structure is of great significance in engineering. In this paper, an analytical method for vibration analysis of structure with general stress distribution is presented. The analytical solution we obtained can be applied to a structure with arbitrary distributed stress, it has a wider range of applications than the previous methods. The accuracy and advantage of the current results is validated by comparison with the Finite Element Method (FEM) results, and numerical results for structures with different stress distributions are presented.
For some practical engineering structures, there is often stress in the structure already before undertaking the work loads, such as the artificial stress, like initial stress in the civil engineering; stress caused by manufacturing, like welding residual stresses and assembly stress; stress caused by the complex and special working environment, like submarine shell stress caused by hydrostatic pressure and tube stress caused by complex deep sea environment and so on. It is worth noting that, these kinds of stress could change some structural performances.
A large amount of research efforts have been devoted to study the influence of structural stress on the structural strength and fatigue [Khan, 2011; Paik, 2012; Masaoka, 2004; Gannon, 2011, 2012; Li, 2007; Tamagawa, 2010; Niemi, 1995]. In comparison, the influence of stress on the vibration characteristics is often ignored and the related researches are not so much. Annenakas and Herrmann [Herrmann, 1960] applied the variational principle to analyze an initial stress plate’s vibration and stability. Doong [Doong, 1987] applied high-order shear deformation theory to derive the initial stress thick plate vibration control equation, and compared this with reference data [Brunelle, 1976]. Fuller considered the pressure caused by the fluid filled in a cylinder and derived its free vibration equation [Fuller, 1982]. Liu and Zhang utilized the wave propagation method to study the effect of hydrostatic pressure fields on the vibration characteristics [Liu, 2010, 2011; Zhang, 2001, 2002]. Some researches about the influence of the stress concentration around holes on vibration have been done [Yahnioglu, 2007, 2009]. Gao performed an experimental comparison between a plate with and without welding stress [Gao, 2002, 2014].