Suspended sediment concentration (SSC) environment is analyzed based on the observed data during the period from 1985 to 1995, Jan. 2006, Jun. 2009 and Aug. 2009 and the remote sensing data from 1987 to 2005. Results from the study suggest that: (1)SSC has obvious seasonal, temporal and spatial change, which is controlled by tidal range; (2) SSC during the strong wind is 3-5 times the general weather, and the SSC peak has certain hysteresis with wave height peak; (3) in most cases, waves are the main power of sediment movement in the nearshore shallow waters, sediment movement by wave and tidal current plays an important influence on the Haizhou Bay terrain evolution.
SSC is an important indicator to reflect the sediment transport and resuspension processes, which are the important factors to study the condition of an estuary, its navigation environment and harbor construction (Zuo et al., 2012). SSC of the estuary or bay is controlled by multiple factors including freshwater and sediment discharges of the river, tides and waves (Li et al., 2010). Change of SSC can indicate the changes of sediment sources and transport processes or dynamic conditions.
Haizhou Bay is an open bay on the verge of Yellow Sea. Port development is still a blank in the bay at present. In order to develop the port resources of Haizhou Bay and the economic development of Jiangsu Province, Ganyu Harbor District of Lianyungang Port will be planned in northern sea area of Haizhou Bay, which is the adjacent area of Shandong Province and Jiangsu Province. In recent years, relative research achievements (i.e. geomorphic features, shoreline change, hydrodynamic and sediment) become abundant in response to the construction of Ganyu Harbor District (Fan et al., 1997; Sun et al., 2003; Zhao et al., 2008; Zhang et al., 2008). However, the characteristics of SSC distribution study of Haizhou Bay are rare.
The aim of this study is to contribute to understanding of the effects of submarine mass movement, ‘sliding block’, on tsunami amplitudes using basic source model. This study aims to see effect of movement as a block differently from pioneering studies that investigate submarine landslide and its effects on tsunami amplitudes. To define model, two sliding blocks moving with different velocities in different directions are considered. The differences of tsunami peak amplitudes among the sliding blocks’ movements in different depths and distances are compared. The interaction of near fiel tsunami amplitudes are discussed with different velocities, depths and distances. In the model, mass is conserved. Laplace and Fourier transform methods are used for the solution of equations and linearized shallow water wave theory is assumed.. The results show that during the source process, when the velocity of masses are much faster than velocity tsunami, the displacements on the free surface above the source resembles the displacement of the floor. Results for tsunami peak amplitudes are presented for mentioned parameters. The effects of sliding block slide as a kind of submarine mass movements on the tsunami amplitudes and the interaction of the tsunami wave forms are examined for specified parameters and illustrated.
Tsunami is one of the big disasters in the world. It can be generally created by the vertical motion of a fault under the sea bottom during the earthquake, submarine volcanic eruption, atmospheric conditions, submarine slides and slumps (Gutenberg, 1939). This gravity waves with long periods may have destructive effects along the shore. Due to this, it is important to recognize this disaster very well. Based on this necessity, many studies have investigated about tsunami models for years. Pioneering studies are especially about submarine slides-slumps and variable parameters that affect the tsunami amplitudes. This study is also an opportunity to see the similarities and differences between slides and sliding blocks. The ‘block slide’ could be used to represent the motion of the collapsed blocks at the Blake Escarpment, east of Florida. In this area, ‘’deep sea floor has enormous agglomeration of blocks, commonly 10 km across, that appear to have fallen from the face of the cliff’’ (Dillon et al.,1993). Other examples are the block slide at the base of Middle Canyon along the Beringian Margin in Alaska (Carlson et al.,1993) and the Sur submarine landslide, where ‘’intact sections of slope sediment as large as office buildings (≤ 25 m high) moved 5 km down the continental slope and as much as 20 km the gentle 0.5° incline of Monterey fan. Smaller, house-sized (≤ 10 m high) blocks were transported as 30 km further’’ (Gutmacher and normark, 1993). To define model, two sliding blocks moving with different velocities in different directions are considered in this study. The differences of tsunami peak amplitudes among the sliding blocks’ movements in different depths and distances are compared. As the velocity of tsunami wave is equal to square root of gravitational acceleration and the ocean depth, the depth effect on tsunami amplitude observed.
The perforated caissons are widely used to decrease wave force and reflection effectively in costal engineering. The nonlinear interactions between waves and partially perforated caissons are investigated using the weakly compressible Smoothed Particle Hydrodynamic (WCSPH) method. An improved algorithm based on the dynamic boundary particles (DBPs) is proposed to treat the solid boundary. The performance of the model is validated by the analytical solution of the surface elevations and wave pressures in front of the vertical wall. The SPH results of the reflection coefficients of the perforated caissons are compared with the available experiment data and good agreements are obtained. The wave pressures on the perforated front wall and the rear wall are analyzed. The effects of the relative wave chamber width B/Lc and the porosity of the perforated wall on the wave energy dissipation of the perforated caissons are discussed.
Perforated breakwaters are good alternatives to traditional non-permeable breakwaters and are used in offshore and coastal areas of circulation considerations. Compared with the conventional non-permeable caissons, the perforated caissons have such advantages as the reduced environmental impact and good performance of dissipating the wave energy. These positive effects enhanced the application of the perforated caissons of various opening types during the last decades. The knowledge of the forces acting on the caissons and the mechanism of wave dissipation are required for its design. There are few numerical studies for wave-perforated caisson interaction based on grid methods in the literatures because of the difficulties of dealing with strong nonlinear free surface and the opening pore.
Being a meshfree Lagrangian method, the Smoothed Particle Hydrodynamics model does not require the explicit surface capturing scheme in treating strong nonlinear flows with large free surface deformation and enables the easy modeling of coastal structures with complex geometrical boundaries. Recently SPH has attracted favorable attention in ocean and coastal engineering and been utilized to solve a variety of nonlinear problems involving wave slamming, liquid sloshing and fluid-structure interaction (Gao et al., 2012; Ren et al., 2015; Shao et al., 2012). Very recently Meringolo et al. (2015) used the diffusive weakly-compressible SPH to simulate wave loads and hydraulic characteristics of the perforated breakwaters.
Wave breaking is an important phenomenon in coastal protection due to the dissipated energy. Such phenomenon is also responsible for the nearshore sediment transport caused by the generated turbulence and currents.
The aim of this work is to apply two different CFD numerical codes to simulate accurately spilling and plunging wave breaking. Numerically simulated free surface elevations and velocities were compared with experimental data and also with numerical results published elsewhere.
In spite of the differences that were found between the performances of the numerical models, they reproduced well the experimental data.
Depth induced wave breaking is a rather complex process usually associated with energy dissipation, splash, air entrainment and an enhancement of turbulence. The type of wave breaking is of the utmost importance, especially because it determines the level of energy dissipation. On the other hand, the location of the wave breaking and the air entrained are crucial for, amongst other effects, the associated sediment transport and for the stability of maritime structures.
The wave breaking dynamics have been the subject of a number of studies. Svendsen (1987) analyzed the turbulence in the surf zone and the energy dissipation. Rivero and Arcilla (1995) developed a formulation to evaluate the vertical wave shear stress distribution in the surf zone. Recently, Zou et al. (2006) proposed a new approach to describe the vertical distribution of the wave shear stress in a variable water depth with breaking and non-breaking wave conditions. The theoretical predictions were compared with field measurements provided by Wilson et al. (2014).
Jiao, Jialong (Harbin Engineering University) | Ren, Huilong (Harbin Engineering University) | Sun, Shuzheng (Harbin Engineering University) | Li, Xin (Harbin Engineering University) | Wang, Zhenyu (Harbin Engineering University)
An alternative methodology to laboratory tank measurement for ship hydrodynamic tests is introduced in this paper. The hydrodynamic testing approach proposed in this paper is to perform large-scale models’ tests in actual sea conditions. The waves model encountered at sea are wind-generated short-crested waves, which are closer to the realistic condition compared with the waves generated in the in-house tanks. Moreover, the models are self-propelled and are equipped with their superstructures and appendages, by which the wind and current effects are taken into account during the measurements. To conduct the tests, a large-scale segmented free running model and the testing system are designed. The overall arrangement of the model and the testing system are presented in detail. The experimental campaign of the large-scale model carried at Huludao Harbour of China is described and typical testing results obtained are presented.
The traditional laboratory models for hydrodynamic performance are towed in calm waters or in two-dimensional rocker flap made waves. The disadvantages such as scale effects of the artificial environment are obvious. The waves are unidirectional, artificially generated and pseudo-random. Furthermore, the motion signals of the model are usually measured by seaworthiness instruments, which may restrict the model’s freedom motions in some sense. So there are some problems need to be addressed in terms of the testing technique of traditional tank model tests.
A new alternative to the laboratory measurement methodology is to conduct tests by large-scale models in actual sea conditions. The tests are conducted in short-crested, directional, wind-generated sea waves. The models are testing with their superstructures and the bilge keel so that wind as well as current effects can be taken into consideration. The tests are carried out at any arbitrary heading angle with less scale effects. In a word, this testing environment is definitely more realistic than the laboratory tank environment.
The present investigation concerns optimum wave absorption in numerical wave tanks. Recent developments have now established that (i) absorption controllers based on Infinite Impulse Response (IIR) filters are highly effective and (ii) cosh shaped wave board geometries offer significant potential in terms of active wave absorption due to their favourable added mass behaviour. While (i) and (ii) have been shown individually, their combination has never been demonstrated. To address this, a cosh shaped wavemaker is implemented in a time-domain numerical wave tank. Comparisons are presented between simple proportional controllers and the IIR approach, where the latter is demonstrated to offer excellent absorption performance over a very broad range of incident wave conditions. In excess of 90% amplitude (or equivalently 99% energy) absorption is demonstrated for the range 1 ≤ kh ≤ 8, where k is the wavenumber and h is the water depth. A broad-banded absorption performance of this type covers the vast majority of wave components present in practical offshore wave spectra. Test cases are presented for both regular and irregular seas, paving the way towards numerical simulations of long random sea states. This paper focuses on a two-dimensional description of the problem. The approach adopted can also be extended to three dimensions, where reduced domain sizes (no sponge layer requirements) offer orders of magnitude improvement in terms of computational cost.
Long random sea simulations are an essential part of laboratory model testing. This may, for example, concern the extreme wave crest statistics arising in steep sea states (Latheef & Swan 2013) or the loading of offshore structures (Rodríguez & Spinneken 2016). In either case, simulation times corresponding to 3 hours of real physical time are commonly adopted, particularly if storm conditions are of concern. In a laboratory context, this is possible by combining an efficient laboratory beach with actively absorbing wavemakers (Spinneken & Swan 2009a). The combination of these two measures eliminates the majority of the reflected wave content, and ensures a homogenous (and ergodic) sea state for a long testing duration.
For a special arrangement of multiple floating bodies, it is known that body-generated waves will be confined inside of the bodies due to hydrodynamic interactions; which is referred to as ‘cloaking’ phenomenon. In order to study this phenomenon in more detail and its application to engineering problems, we have developed an accurate computer code and an optimization scheme using GA (genetic algorithm) and presented some results for the diffraction problem. In the present paper, the floating body to be cloaked is assumed to be freely oscillating in regular waves and multiple bodies surrounding the central body are assumed to be controlled with an external dynamic system with damping and restoring forces. Study is made on the energy conservation relation and the scattered and radiation wave patterns when the cloaking is realized and also on the absorption of wave energy through the work done by the external force of damping installed in the surrounding cylinders.
In recent years, structures with complex shape or multiple floating bodies are increasing for the purpose of marine energy utilization. The wave drift force on these structures may increase by hydrodynamic interaction effects, and especially in the case of multiple floating bodies they may collide each other. Therefore the wave drift force should be calculated accurately and studied how to reduce it.
In general, the incident wave is disturbed by a floating body and thus the disturbance wave (consisting of scattered and radiation waves) is generated. In the cloaking phenomenon studied by Newman (2013), the disturbance wave could be zero and the incident wave was not disturbed by surrounding a central body with a finite number of smaller bodies and optimizing the location and size of those surrounding bodies. This phenomenon can be applied to reduce the wave drift force.
The case of non-isothermal, one-dimensional, unsteady, compressible pipe flow of natural gas is considered. The effect the different external heat transfer models have on the calculation of pipeline fluid pressures and temperatures in response to the annual ambient temperature cycle was studied. In the heat transfer model, the ambient temperature cycle is represented through the soil surface temperature having a time dependent periodic function. The results show that the pipeline pressures are not sensitive to the choice of external heat transfer model. For the base case, representing a typical natural gas export pipeline, the effect on the calculated gas temperatures is limited. The parameter sensitivity shows that with decreasing pipe diameter, increased soil thermal conductivity, and larger amplitude of the ambient temperature cycle, the heat transfer errors increase, resulting in larger gas temperature differences.
Correct modelling of external heat transfer in pipe flow is important in several areas of application. Examples are pipeline transmission of hydrocarbons or underground heat exchangers. In this paper, the case of non-isothermal, one-dimensional, unsteady, compressible pipe flow of natural gas is considered. The heat transfer between the gas inside the pipeline and the ambient is dependent on both the gas temperature fluctuations and the temperature variations at the upper soil boundary.
The main focus of this paper is the heat transfer across the pipe wall and the effect of soil heat storage due to the annual ambient temperature cycle at the soil surface boundary. In our study, generic pipeline models are used. The models describe full one-dimensional, unsteady, compressible flow, coupled to an external heat transfer model. The basic approaches for such models are discussed in Archer and O’Sullivan (1977), Thorley and Tiley (1987), Modisette (2002), Langelandsvik (2008), Chaczykowsky (2009) and Helgaker (2013). In this study, four external heat transfer models are used. The first is a 1D steady model representing pipe and soil thermal domain as an overall heat transfer coefficient. The second model is a steady periodic solution of the 1D heat transfer, presented by Barletta, Zanchini, Lazari, Terenzi (2008). The third model is a discretization of the one-dimensional (1D) heat conduction equation in radial coordinates. The fourth model represents the pipe and soil for each one-dimensional pipe calculation element as a two-dimensional (2D) cross-section in ANSYS Fluent.
Current codes and norms allow for structures to be operated in the transition between ductile and brittle behavior. Further, they often treat the Ductile to Brittle Transition Temperature as a constant even though it is well known to depend on a variety of factors, such as loading rate, constraint, and prior cold deformation. This paper proposes a method whereby the Beremin approach to cleavage modelling is used to shift the DBTT in the design process, thus allowing for the DBTT to be adjusted automatically based on the actual design condition of the structure.
Steels for use in maritime and offshore structures are designed and selected so that they are not used at temperatures in which they are brittle. This is typically done by selecting materials that have a specified Charpy value when tested at a temperature that is 0 to 300C below the lowest anticipated service temperature, depending on the code, location in the structure, severity of the consequences of failure, and other aspects. However, the practical implementation of this rule often allows for steels to be used in the transition between brittle and ductile – i.e. between upper and lower shelf behavior. For example, a typical minimum Charpy requirement is 27 J, which is low relative to the ductile Charpy energy for modern steels. While there is growing acknowledgement in standards development that operating a structure in the transition between brittle and ductile behavior is acceptable (Hauge et al., 2015), this acceptance is often left implicit in the minimum acceptable Charpy or CTOD requirements. Furthermore, many standards treat the Ductile to Brittle Transition Temperature (DBTT) as if it is a constant for the material; i.e. they give the same acceptance requirement regardless of the anticipated crack depth, loading mode, etc. However, it is well established that a number of factors affect the DBTT, such as strain rate (Corten and Shoemaker, 1967, Shoemaker and Rolfe, 1969, and others), prior cold deformation (Degenkolbe and Müsgen, 1973, Strassburger and Schauwinhold, 1967, and others), and constraint (Milne and Curry, 1982, Anderson, 1984, and many others). EN 1993-1-10 modifies the DBTT that is measured by Charpy testing by adding a number of shifts, depending on exposure to radiation, yield strength of the material, shape, strain rate, and prior cold deformation. However, these relationships are generally empirical fits from the literature, sometimes based on decades-old correlations, and there is an assumption that the temperature shift due to these various parameters is simply additive. ISO 27306 offers another approach. This standard assumes that the material fails in cleavage and offers a correction factor to account for the level of constraint experienced by the structure. The modified toughness level is then used in a standard Engineering Critical Assessment (ECA), e.g. like that of BS 7910. This particular approach has two key limitations. The first key limitation is that it scales the toughness without regard for what the upper-shelf toughness is. Therefore, the toughness could conceivably be scaled past the upper shelf toughness, leading to non-conservative results. The other limitation is that it treats just once contribution to the ductile to brittle shift (namely, constraint) without addressing other ones, such as strain rate or cold forming.
Using traditional method to disconnect the hang-off risers on offshore floating platform is very time consuming, if there are any new method which can reduce the time to do such work, it will bring very big economic benefit. With this purpose, creative scheme incorporate with power cable seal and riser over bend prevention technology have been introduced by the author. Using this new scheme to conduct riser disconnection work, the actual work time was reduced more than half comparing to traditional recovery method.
Dynamic cables and umbilicals are very important part of offshore floating production system. Suspended in sea water in various forms, they connect floating production platform and subsea production system by transferring power, signal, oil, water and gas in between. Dynamic cables and umbilicals (hereinafter referred to as cables) are hung off in position during normal production. But in some special circumstances, they need to be disconnected, such as drilling or workover operation, aged platform rejuvenation operations.
Normally, dynamic cable disconnection operation is very time consuming and costly. By using conventional method, a complete drill string needs to be deployed in order to retrieve the tree cap which connects to the lower end of the cable. The conventional method includes the following steps: deploy un-locking tool, un-lock the connector, retrieve un-locking tool, and retrieve the cable. It will take 2 days for each power cable and 5 days for each umbilical or service riser. There are total 25 of dynamic ESP cables, 4 control umbilical and 1 service riser hanging over the FPS moon pool (Fig.1). Conventionally, these 30 cables need to be recovered to the deck of the FPS one by one through winch operation and then store on reels. This work will take 90 days. If a time saving method can be found, it will reduce shut-down time largely and bring huge economic benefits (Yue, Liu, Mao and Yang, 2013).
In this paper, we will take LiuHua project as an example, and explore a quick disconnection method. After comparing several methods, a new efficient and reliable method was selected. This method has great reference value for deep water dynamic cables disconnection work.