This paper addresses the novel design of a biomimetic underwater vehicle (BUV) propelled by undulatory fins and its heading control problems. Inspired by the cuttlefish, which can perform flexible motions by undulatory propulsion in narrow spaces, our BUV with two undulatory fins is designed. The specific implementation of mechanical structure is elaborated. Moreover, a hybrid heading control which combines active disturbance rejection control (ADRC) with fuzzy strategy is proposed to achieve accurate heading control for this BUV. In the end, experimental results demonstrate the feasibility and effectiveness of the mechanism and control system.
Various autonomous underwater vehicles (AUVs) have been developed as ocean industries have grown rapidly (Blidberg, 2001; Ayutthaya, Tiaple, Laitongdee and Iamraksa, 2014). Nevertheless, operations in dangerous and worse environments are more complicated. To address increasing demands for high mobility, robustness and improved disturbance rejection, many researchers and engineers have attempted to design biomimetic AUVs. (Chu, Lee, Song, Han, Lee, Kim, Kim, Park, Cho and Ahn, 2012).
Recently, many BUVs propelled by undulatory fins have been built (Curet, Patankar, Lauder and MacIver, 2011; Hu, Low, Shen and Xu, 2012; Zhou and Low 2012; Rahman, Sugimori, Miki, Yamamoto, Sanada and Toda, 2013). However, most of researchers focus on undulatory fin control, but seldom consider precise heading control for those BUVs in underwater missions.
Heading control is a vital issue for the successful operation of a BUV. Although prior researchers have achieved satisfactory performance (Perez, 2006; Yu, Bao and Nonami, 2008), most heading controllers only aim to obtain the course stabilization of ships by steering the rudder angle, which is quite different from that of BUVs by coordinating the fins. Few researchers have presented some effective approaches to deal with heading control for BUVs (Wei, Wang, Wang, Zhou and Tan, 2015). They proposed a course controller to make a BUV rotate to a given angle in situ, while it’s more helpful to control the heading of BUVs at a certain swimming speed.
How to choose principal dimension is very important and difficult during conceptual design, especially for ice-going ships. This paper breaks through the traditional principle dimension to be rigidly adhere to parent ship or experience. Through research analysis of ice/no-ice dynamics, multidisciplinary optimization model of ice-going ships is built, three objective functions-EEDI (Energy Efficiency Design Index), relative turning diameter and ice-breaking sailing efficiency are integrated to optimize an ice-going oil tanker with Friendship- Framework software. The results show that principal dimensions have optimization space and optimized hull forms can satisfy conceptual design requirement roundly. The given optimization example demonstrates the practicability and superiority of the proposed multidisciplinary optimization method.
Ice-going ships research and design are paid more and more attention with Arctic route’s development. It takes big challenges to design icegoing ships. Different from general ships, ice-going ships design not only think about ice-breaking resistance and engine power in ice condition, but also think about good hydrodynamic performance in noice condition, ice/no-ice dynamic performance is very important .At the same time, ice-going ships require higher structure strength, and are confronted with more risk factor, such as low temperature, high latitude, polar night etc. In order to obtain principle dimensions in conceptual design stage, all above factors must be considered.
Traditional method to obtain principle dimensions is mainly to rely on parent ships, these bring many drawbacks if parent ship is not good. Based on above reasons, this paper will resolve these problems by use of multidisciplinary optimization model to look for optimum solution. Meanwhile, EEDI is introduced to solve powering performance in no ice condition. Ice-breaking sailing efficiency is introduced to judge icebreaking capability.
Hammer peening is widely adopted for steel structures in order to improve fatigue life of welded joints. The effect of hammer peening, under specific conditions, have been already confirmed in the previous experiments carried out by Morikage (2015). However, two main aspects need further investigations, since, in the current state of art, their contribution to the peening is still unclear. The first one is represented by the presence of a pre-load on the structure (referred as dead load in this paper) whereas the second one is the relaxation of the residual stress field induced by the peening process itself. The purpose of the present study will be the clarification of the interaction among all of this factors by investigating the stress distribution, and its relaxation, by means of FE analyses. The calibration of the material parameters, adopted in the numerical simulation, is done by comparison on the displacement field generated in an actual peening experiment carried out on a steel plate.
Many factors that are known to influence the fatigue life: residual stress, hardening, surface roughness, etc. (Jouno, 1995). Peening is one of the measures widely adopted with the intent to extend the components durability and their service life (Morikage, 2015). The application of this technique generally induces modifications on the geometrical shape, alters the material hardening, and induce a compressive residual stress field as consequence of the impact of the chisel with the surface. A specific form of this technique is the ultrasonic peening (Nose, 2008), easy to control, and well known to perform a uniformly distributed peening effect, however, it will not be treated in the present paper.
Hammer peening can be used directly on structures where the cracks are already opened in order to promote a partial closure and increase the material performances; experiments on this topic were already carried out by Kakiichi (2014). On the other hand, an undesired effect of the application of this process is the generation of a residual stress field inside the material, which can be relaxed through the application of fatigue loading as shown by (Miyashita, 2011). However, nowadays, the effect of the interaction among dead loads, peening and the following application of cyclic loading is still unclear.
Therefore, the present paper aims to investigate the interactions of these factors by means of numerical and experimental evidences. The Subloading Surface theory (Hashiguchi, 1989, 2009) is adopted in the FE analysis to model the elasto-plastic behavior of the material, due to its ability to catch a realistic ratcheting behavior induced by cyclic loads.
A number of coastal dykes were damaged by the 2011 off the Pacific coast of Tohoku Earthquake. The main cause of the failures is assumed as the local scour at the landward toe. Furthermore, liquefaction damage caused by the earthquake has been reported. When tsunami strikes and overtops a coastal dyke, there is a possibility that liquefaction occurs by earthquakes and promotes scour at the landward toe. Liquefaction is caused by a decrease in effective stress. Therefore, it is important to evaluate the influence of the effective stress on the scour due to overtopping. In the present study, flume experiments were conducted. The effective stress was controlled by upward seepage to reproduce liquefied ground. As a result, it is found that scour profile is influenced by the effective stress, and backfilling of the scour hole due to slope failure is observed at low effective stress.
The 2011 off the Pacific coast of Tohoku Earthquake generated massive tsunami in the northwestern Pacific Ocean. Giant tsunami damaged coastal dykes and seawalls. From field surveys by Kato et al. (2012), scour holes due to overtopping tsunami at the landward toe of coastal dykes were found in many places along the Pacific Coast in Tohoku region. The scour at the landward toe has been considered the main cause of the failure of coastal dykes. Furthermore, liquefaction damage caused by the earthquake has been reported. Fukumoto et al. (2012) showed from the hydraulic data that tsunami attacks and the largest aftershock might occur simultaneously. On the basis of these reports, there is a possibility that liquefaction occurs when tsunami strikes. It was confirmed that the ground liquefied before tsunami struck as shown in Fig. 1.
In the previous studies, experiments and analyses on relationship between variation of water level and liquefaction have been conducted (Nago and Maeno, 1987; Zen and Yamazaki, 1990; Sassa and Sekiguchi, 1999). Variation of water level leads to change in pore water pressure in the ground. The rapidly decreasing water level brings a decrease in the effective stress of the ground. It is predicted that the ground around a coastal dyke liquefy by rapidly decreasing water level when tsunami backwash comes, and overtopping tsunami backwash causes scour around a coastal dyke. Actually, Sawada et al. (2014) pointed out from the wave data that liquefaction could occur due to tsunami under the condition that amplitude of changes in sea level was large and the drawdown rapidly occurred.
Li, Lina (Offshore Oil Engineering Co., Ltd.) | Zhong, Wenjun (Offshore Oil Engineering Co., Ltd.) | Jiang, Ying (Offshore Oil Engineering Co., Ltd.) | He, Ningqiang (Offshore Oil Engineering Co., Ltd.) | Sun, Chenggong (Offshore Oil & Gas Research Center, China University of Petroleum (Beijing))
During the riser installation operation of S-lay vessels, such problems exist: tension conversion problem, complicated underwater operations, requiring a number of auxiliary vessels and so on. In order to solve these problems, taking S-lay vessel: Hai Yang Shi You 201(HYSY201) as target vessel and Liwan 3-1(LW3-1) as target project, a new installation system is developed. It is used for the installation of deepwater riser and subsea structure. This paper presents the design considerations and analysis methods of the new installation system. The ultimate strength analysis is performed and the results show that this system meets design requirements. Corresponding experimental verification is accomplished and results show the feasibility of the application.
The South China Sea is rich in oil and gas resources. In order to meet development requirements of oil and gas resources, China built its first 3,000 meters water depth S-lay pipelay vessel: HYSY201. With the continuous progress of the South China Sea deepwater oil and gas field development, more and more problems appear, including how to realize the S-lay pipelay vessel for riser and subsea structures installation.
The installation of risers and subsea structures is a complicated but essential operation in the development of deepwater oil and gas field. The vertical operation during J-lay is more suitable for deepwater installation, compared with the level operation during S-lay. It was originally planned to install J-lay tower on HYSY201 in the basic design, but ultimately did not come to integrate that. For the sake of economic/fast/effective installation of riser and subsea structures, HYSY201 needs to be partially modified and add some ancillary equipment. So a new installation system is developed.
This system is suitable for 1500m ~ 3000m depth of SCR installation or some subsea structures installation. It realizes directly riser lifting or subsea structures installing after completing pipeline laying, without the help of other large vessels. It avoids the mobilization and demobilization of large ships, and reduces the use of auxiliary vessels. And it also provides an important early knowledge accumulation for the future pipeline maintenance, and the integration of J-lay and so on.
Storm surge is a major cause of coastal flooding. Robust models have provided useful tools for storm surge forecasting and flood risk management. In this work, a finite volume shock-capturing shallow water equation model originally developed for flood simulation is improved and tested for storm surge modeling. For storm surge modeling, additional source terms are included to represent the wind stresses and atmospheric pressure variation. The performance of the improved model is validated and demonstrated through application to benchmark test cases.
Storm surges and the resulting coastal floods caused by hurricanes, cyclones and typhoons are a major type of natural hazards threatening many coastal cities worldwide. Nowadays, numerical modeling has provided an indispensible tool for forecasting storm surge and managing the resulting flood risk. Numerous models that can be used to simulate storm surge and the resulting flooding processes have been reported in literature in the last few decades. Most of these models are based on the solutions to the governing depth-average fluid equations using finite element, finite difference or finite volume numerical schemes.
Ip et al. (1998) presented a finite element Galerkin model for simulating tidal flooding and drying in shallow estuaries with applications to hypothetical embayment and to the Great Bay, New Hampshire estuary system. The ADvanced CIRCulation (ADCIRC) is a two-dimensional, depth-integrated, barotropic time-dependent long wave, hydrodynamic circulation model based on an unstructured finite element numerical scheme (Leuttich et al., 1992; Blain et al., 1994); it has been widely used for predicting coastal circulations and storm surges. However, due to the adoption of unstructured grids, the ADCIRC model is computationally too demanding to provide high-resolution ensemble forecasts in an efficient way. Westerink et al. (1992) reported another unstructured grid-based finite element model to calculate tides and hurricane driven storm surges in the Gulf of Mexico, in a region ranging from the South Mississippi to the northwest coast of Florida.
This paper presents a methodology for prioritisation of inspection by combining the probability of loss of the structure (which accounts for structural redundancy) and the probability of fatigue failure of joints. This process could also identify benefits arising from a monitoring plan. The method allows balancing of the initial cost of providing a stronger jacket, and/or long-life joints, with the future cost of monitoring and repair if a joint fails. The method identifies the joints most critical to the structural integrity, enabling inspection effort to be concentrated where it can be most effective.
The current industry practice requires the fatigue lives of inspectable joints (due to the environmental loads) to be twice the structure’s service life; and those of non-inspectable joints to be ten times the service life (e.g. ABS 2003 Table 1). Some Classification Societies have further subdivided joints into those failures that would, or would not, trigger progressive collapse and assigned different factors to the service life. Usually, if a joint is shown to have a fatigue life less than 10 times the design life of the structure, then it is assumed that the joint must be inspected for cracks at regular intervals while in-service.
The present practice for fatigue design uses S-N curves, the Miner rule together with the wave scatter diagram and the wave occurrence to size joints such that their fatigue lives are more than a prescribed multiple of the service life. The factor on the fatigue life is set so that the probability of failure is acceptably low.
In any given year, after installation, there is a possibility of no joint failure, one joint failure, two joint failures and so on, due to fatigue. It is assumed that failure of a joint makes the connecting member ineffective. Failure of a joint changes the stress distribution and hence the time to failure of all remaining joints may change. As a result, the previously calculated sequence of fatigue failures (calculated at the design stage, see Table 1 in Appendix) may no longer apply. However, for the illustration purposes, it is assumed that if the failure of a joint goes unnoticed, the time to failure for all joints does not change.
A numerical investigation of three-dimensional flow past an oscillating cylinder at Re = 400 was carried out to investigate the effects of oscillation mode on flow structure and forces. The cylinder is forced to oscillate with a frequency in the in-line direction twice that of the transverse frequency, thus following a figure-eight trajectory. It is found that the flow three-dimensionality and forces on the cylinder depend strongly on the direction in which the figure eight is traversed.
Bluff body wakes are characterized by very rich physics. Flow past a circular cylinder is the most representative bluff body wake. At very low Reynolds number, the flow is steady, characterized by a region of two counter-rotating standing vortices placed symmetrically in the wake. Bifurcation to oscillatory flow (Kármán street) occurs at Re˜49. Up to Re˜190, the oscillatory flow remains two-dimensional. Studies on the transition to three-dimensional flow have been initiated by Roshko (1954). It is now well assessed that the cylinder wake becomes three-dimensional for Re>190, as shown by experimental and numerical studies (Williamson, 1996; Barkley and Henderson, 1996). Three-dimensional wakes are characterized by the presence of spanwise Kármán rolls and streamwise vortex pairs. Two modes of vortex shedding have been identified as the dominant features of three-dimensionality in the wake, and are referred to as “Mode A” and “Mode B”. Mode A is associated with an instability with a spanwise wavelength of 3-4 cylinder diameters; see Williamson, 1996. On the other hand, Mode-B instability is characterized by a shorter wavelength (approximately one cylinder diameter). The presence of Mode A and Mode B in the wake of a circular cylinder has been reported by Williamson and Roshko (1988) and Williamson (1996a), and confirmed by several other studies (Zhang et al., 1995; Henderson, 1997; Brede et al.,1996; Thompson et al., 1996; Thompson et al., 2001).
Because of the dynamic nature of the lift and drag forces exerted by the flow, cylindrical structures undergo free oscillations, commonly characterized by a trajectory resembling a figure eight.
To shed light on the wake instabilities, several numerical studies of three-dimensional flow past a stationary cylinder have been performed. Studies relevant to Vortex Induced Vibrations (VIV) have considered the flow past a cylinder oscillating either in the transverse or the in the inline direction with respect to the incoming stream. However, computational studies considering a simultaneous oscillation in both directions are limited. The present study thus concerns the flow past an oscillating cylinder following a figure eight trajectory (commonly encountered in VIV), at a Reynolds number equal to 400, where the flow past the stationary cylinder is known to be three-dimensional. The approach is that of Direct Numerical Simulation (DNS) using a Spectral Element Method (SEM).
Coastal erosion caused by structures due to exploitation is a serious problem for coastal management in Taiwan. These structures disturb the continuity of the original littoral sediment transports, resulting in retreats of the shorelines in the downstream areas. This paper tries to assess the responsibilities of stakeholders regarding coastal defense and attempts to propose adequate remedies. Trend and mechanism analyses were used to assess the effects the coastal exploitation made on the coastal defenses. In the former, historical satellite images, maps, and bathymetric survey data were used to analyze the evolution of the coastlines. In the latter, we used numerical models to estimate the area where the marine mechanisms were changed by the constructions. Taoyuan, Yunlin and Chiayi coastal sectors were used as case studies. Based on the results, both engineering and non-engineering measures, such as sand bypass and land use control, respectively, were proposed for a sustainable usage of the coast. Using these results, the relative role of the governmental officials and land-users in the area was also investigated.
The total length of the coastal line around Taiwan is about 1,100 kilometers. According to their geotectonic structures, the coasts can roughly be categorized as rocky, sandy, and coral-reef coasts. In general, it could be said that, the morphology of a coast is governed by both natural and anthropogenic factors. The former includes sediment source, tidal and wave forcing; the latter can be activities such as channel dredging, land reclamation, seawall, or riverbank protection. Different geologic features cause the coasts in Taiwan to react differently to the impacts of these forcing.
In the years of 2005 - 2008, a project named “Dynamic monitoring of geological environment and resources – application of the FORMOSAT-2 Images” had been carried out by the ‘Central Geological Survey, MOEA’. The project analyzed the satellite images of FORMOSAT-2 for the developments of the coasts of northern and eastern Taiwan. According to a report of the project, in the preceeding three decades, the coasts of Sanchih (New Taipei City, NTC), Fulong (NTC), and Gichi (Hualien) have been retreating at rates of 1.77~2.86 m/year. In fact, almost all the coastlines in the northern part of Taiwan suffer from erosion. The report pointed out that, diminishing sediment sources in the upstream, erosion by marine forcing at the seaward side, and structures protruding coast lines are the main reasons for the receding coastlines in northern Taiwan.
Numerical simulations based on a simplified ship-ice collision model are implemented in LS-DYNA code. The ship structure is simplified as a rectangular plate and the ice floes are simplified as wedge blocks with different forepart widths. According to the ISO/CD19906 (2010) rules for ice loads in Abnormal Level Ice Event (ALIE), numerical simulation is implemented to test the material parameters. In this paper, two series of simulations are carried out for rigid steel and fragile ice collisions, respectively. Based on the numerical results, the Ice Influence Factor on Deflection (IIFD) and Damage Energy Reduction Ratio (DERR) are proposed. Besides, the critical forepart width of wedge that causes the maximum deflection is found, in the simulations of fragile ice collision.
During the ship-ice collision process, a lot of energy can be released in a very short time, and severe structural damage and deformation may occur. Particularly, the brittle feature of ice material enhances the complexity of ship-ice collision problems. Both the structure and ice floe dissipate strain energy by undergoing significant deformations. In this case, the shared-energy design strategy is proposed by the NORSOK code (NORSOK, 2004). In order to facilitate such analyses, a realistic ice model based on continuum mechanics is required, Liu et al. (2010) introduced a pressure-dependent and strain rate-independent ice material, in which the Tsai-Wu yield surface envelop was adopted and this material model was applied to integrated analysis of iceberg impacts for the Accidental Limit State. In addition, the yield surface shape in p-J2 space has been used to model ice mechanics by Riska and Frederking (1987). For simplicity, this type of ice material is always considered to be isotropic and temperature-independent in numerical studies. In order to obtain the reference data of ice strength in engineering application, some ice indentation tests have been implemented and the corresponding contact area-pressure curve has been mapped in a table (Masterson et al., 2007). These results are used for extreme ice load rules in ISO/CD 19906 (2010).