The AARI performed ice research work in the Barents Sea during the last 10 years (1996-2006). In the course of this work great amount of material was collected on flexural strength of drifting first-year sea ice (138 cantilever beam tests, many tests of small discs). Results of data analysis for level ice are presented in this report; this analysis was performed separately for the south-eastern and north-eastern regions of the Barents Sea. Influence of different ice characteristics exerted on the flexural strength is studied (temperature, salinity, brine volume etc.). Relation is analyzed between the full-scale flexural strength of ice cover determined by the results of the cantilever tests, and the strength corresponding to the tests of small specimens. As the most reliable method of ice flexural strength determination are the cantilever tests cut out of the entire ice thickness. However, these experiments are the most labor-intensive, so the trial was made to obtain empirical relations between the physical properties of ice, strength of small specimens and full-scale flexural strength of level ice. INTRODUCTION Over the last 10 years AARI conducted a number of comprehensive ice research expeditions in the Barents Sea. Oil and gas industries gave the main impetus for this work because the designers of shelf hydrotechnical structures such as ice-resisting platforms, underwater pipelines, terminals etc. need available data on environmental conditions (firstly on sea ice). The history of these expeditions as well as some results are given in various reports, publications and presentations delivered at international scientific conferences (Danilov et al, 2003, Naumov et al., 2003, Stepanov et al., 2003, Stepanov and Kubyshkin, 2003, Kubyshkin and Skutina, 2004). As a result a large amount of data concerning different sections of sea ice studies and polar oceanography including physical and mechanical characteristics of sea ice of the Barents Sea was collected.
Nishi, Yoshiki (Kyushu University) | Kashiwagi, Masashi (Kyushu University) | Koterayama, Wataru (Kyushu University) | Nakamura, Masahiko (Kyushu University) | Hua, Soo Zi (Kyushu University) | Yamamoto, Ikuo (Japan Agency for Marine-Earth Science & Technology) | Hyakudome, Tadahiro (Japan Agency for Marine-Earth Science & Technology)
To develop an underwater vehicle with better propulsion performance allowing long-time observations in the ocean, the resistance force acting on the vehicle is accurately estimated using computational fluid dynamics (CFD) and experiments in a towing tank. The flow around the body is simulated by a commercial CFD code (STAR-CD), and actuation of the thruster is modeled by a simplified propeller theory. The two-way coupling between the flow and the thruster is treated with an iteration scheme to satisfy the condition of equilibrium between the resistance and the thrust. For validation of the numerical method, the resistance computed is compared to the one measured by the experiment, which turns out to be good in agreement. In addition, the optimization of the body shape for less resistance is studied by considering several body shapes with their self-propulsion factors taken into account. INTRODUCTION The understanding of the ocean becomes increasingly important due to glowing global environmental problems such as the global warming. This requires us to obtain spatially and temporally denser in-situ observation data in the ocean. At present, moored devices (such as XBT: expendable bathythermograph, and CTD: conductivity temperature and depth profiling system) and drifting buoys are mainly used for in-situ observations. In addition, the remote sensing using satellites works well to widely investigate the surface of the ocean. Nevertheless, these tools do not always meet the demand mentioned above, since these can only provide information at limited observation sites and on two-dimensional surfaces. The AUV (autonomous underwater vehicle) is one of the promising devices to achieve a mission of three-dimensional and consecutive observation in the ocean, for AUVs are basically designed to travel in various directions and to stay stably at a certain location in the water. From this standpoint, various types of AUV have been developed, and recently high-resolution numerical works on biologically inspired underwater vehicles were conducted (e.g., Suzuki and Kato, 2005).
High pressure acid leach (HPAL) exposes low grade ore to very severe processing conditions in order to hydrometallurgically recover metals such as nickel, cobalt, and gold. Ball valves play a critical role in containing and directing the flow of the very hot acidic slurry within the autoclaves. A nanostructured titanium oxide (n-TiO2) coating has been developed with dramatically, superior abrasive and erosive wear resistance. Ball valves witH the n-Ti02 coating are currently being used in ten HPAL installations around the world. INTRODUCTION In 1996, United States Office of Naval Research''s (ONR''s) Dr. Lawrence T. Kabacoff initiated a program entitled, "Thermal Spray Processing of Nanostructured Coatings". This program generated a number of successful coatings with practical and economical values (Kabacoff, 2202). Coatings exhibiting enhanced toughness, superior wear, and increased adhesion, have been developed, qualified (MIL STD 1687A) and applied onto Navy components. The high-pressure acid-leach (HPAL) process is currently being used to extract nickel, cobalt, and gold from low-grade ore. The HF''AL technology relies on very severe processing environment to economically leach and extract metal: The current processing environment consists of very hot (- 260 °C) and corrosive (up to 95 % sulfuric acid) slurry (20 wt% solids) at high pressures (4,700 to 5,500 kPa). The severe conditions found in Ni/Co HPAL require the ball valves to have protection against abrasive wear, erosive wear, and extreme corrosion. To extend the life of the ball valves while meeting the general mechanical requirements of the components, titanium alloy balls and seats are treated with various surfacing techniques. Amongst the surfacing technologies available, thermal spray application of single- and multi-layer coatings is predominantly used. Past and present specifications use top coats of chromia-blend or titania on titanium balls and seats with or without a metallic bond coat.
Structural condition assessment and health monitoring of offshore structures in service are becoming essentially important. An offshore platform has exhibited unexpected excessive vibration under mildly hostile sea state in Bohai Bay, China. The Vibration behavior and condition assessment of the offshore platform were investigated through analysis of ambient field measurements. Modal analysis demonstrated that the fundamental frequency didn’t remain as a stable value and varied from 0.3Hz to 0.80Hz. In addition, the characteristics of impulsive responses (owing to impacts) are observed. Analysis revealed that the impact was most likely resulted from the collision between the jacket and the piles initiated by the wave loading. Engineering control measures were conducted to eliminate the potential unsafety by grouting the gap between the piles and the jacket legs. Treatment results indicated that the excessive vibration had been effectively reduced. INTRODUCTION Offshore structures, which have been working in harsh environmental conditions, are continuously exposed to wave action, corrosion, fatigue effect, etc. In general, the occurrence of damage during the lifetime of an offshore structure is inevitable. A feasible way to avoid or reduce the loss of capital, equipments or possible lives is to monitor the safety state of the structures and carry out remedies before disaster occurs. Among the commonly used inspection method such as manual, visual inspection, ultrasonic method, etc., structural condition assessment and health monitoring of offshore structures based on ambient vibration measurements in service are becoming extremely important; and have received much researchers’ close attention (Doebling, et al, 1996). For one thing, there is no easy way to measure the input excitations or alternatively, to externally excite the structures artificially, which is just critical for large-scale structures such as offshore platforms; and the interference of the normal operation process can be minimized. Furthermore, this process under ambient measurement makes it possible for a long term and online structural health monitoring.
Liao, Cheng-Jie (National Cheng Kung University) | Lin, Hung-Ming (Leader University) | Lee, Der-Her (National Cheng Kung University) | Chen, Po-Ying (National Cheng Kung University) | Liao, Jyh-Jong (National Chiao Tung University)
As slopes in the interbedded sandstone and mudstone formation are geologically characterized by proneness to landslides, past elaborations on the failure mechanism of such slopes were mostly confined to the fact that slope slides often occur after rainfalls when rainwater permeates through sandstone formation. Due to sharp difference in water permeability between sandstone and mudstone, the groundwater will accumulate on the interface of the interbedded formation, resulting in increased pore water pressures and reduced safety coefficients. In the process of slides with large displacement, however, change of mechanical properties on the sliding surface is a major factor that affects slope slides. For this purpose, the study aims to develop a ring shear test apparatus that can be applicable to weak rock materials to obtain their residual strength values under the condition of large displacement. The results show that ring shear tests are more effective in obtaining the actual residual strength of weak rock materials and complete post peak shear behaviors than direct shear tests. The results of this study also demonstrate that abrasion between grains of rock materials still continues till their residual strength values reach a stable condition, even though these rock materials are affected by the action of shear strength, and that the content of fine grained materials increases with the normal force in the shear zone. INTRODUCTION According to Skempton (1964), who proposed the concept of residual strength to long-term slope stability analysis, materials that have experienced a relatively large shear displacement on the sliding plane, shear strength of these materials would have been reduced to their residual strength due to strain weakening. In such cases, it is most appropriate to take the concept of residual strength when analyzing slope failures. Residual shear strength parameters generally used for slope stability analysis can be replaced by shear strength parameters c and φ, which can be obtained from direct shear tests, triaxial tests and field tests.
A refined dynamics model for the float-counterweight wave energy conversion system is presented here taking into account the previously unconsidered effects of the added mass and drag force on the behavior of float motion and energy gain. Computational results of the work rate, where the float was always in a partially submerged state were found to be in good agreement with the results obtained from wave tank tests. Comparative analysis of the results from the new and previous model has led to a better understanding of the effects of added mass and drag force on the system. Resonant frequency and the power output during resonance have been calculated for certain prototype designs. INTRODUCTION The importance of wave energy conversion need not be exaggerated especially in the context of today’s global environment which faces the problem of a massive increase in energy demand coupled with a rise in global warming. Various mechanisms for extracting wave energy have been developed but have not been fully utilized due to structural strength and economical problems. The OWC system seems to be considered a major one because it does not have serious problems of structural strength (Evans et. al. 1982, Malmo et. al. 1985, Folley et. al 2004, Suzuki et. al. 2006). However its practical use has not been attained due to economical reasons. The authors have proposed a movable body type in which the heaving motion of the partially submerged float causes the driving pulley and the shaft to rotate as shown in Fig. 1.The rotary converter rotates the shaft in a single direction independent of the direction of the float motion, i.e. up or down. The gearbox increases output shaft speed so that the size of the generator can be reduced depending upon the gear ratio.
Long-term evolution of a narrow-banded nonlinear wave train is investigated experimentally. The wavelet analysis providing information in both time and frequency domain is employed to examine the local evolutionary characteristics of wave modulation. The zero-crossing method, Hilbert transform and Fourier transform are utilized to compare and validate the results obtained from the wavelet analysis. Results show that the modulated wavetrain resulting from the sideband instability can be represented by the peak frequencies in the wavelet spectrum. The local evolutionary properties of asymmetric amplitude and frequency modulations are found. The local frequency downshift is evidenced to correlate to the wave breaking. It is manifested that the energy of the waves near the front of modulated wave group is originally concentrated near the upper sideband and then is downshifted to the lower sideband after the occurrence of wave breaking and the wave fusion. INTRODUCTION Wave modulation has been investigated by many researchers since Benjamin and Feir (1967). Lake et al. (1977) evidenced that the evolution of sideband instability of nonlinear wave train grows exponentially, which agrees with the theory proposed by Benjamin and Feir (1967). They also found a complete recurrence of modulated waves from a numerical solution of nonlinear Schrödinger (NLS) equation. Su (1982) investigated the evolution of a finite length wave packet experimentally. The downshift of the carrier frequency in their experiments follows fd =(1-k0a0)f0, where k0a0 is the initial wave steepness and f0 is the initial carrier frequency. Melville (1982) conducted a series of sideband evolution experiments containing wave breaking leaded by sideband instability. He found that the evolution of the spectrum is not restricted to a few discrete frequencies but also involves a growing continuous spectrum for k0a0<0.29. Tulin and Waseda (1999) observed a near recurrence of nonlinear wave group without downshift and breaking in a three-wave experiment.
Belibassakis, Konstandinos A. (Technological Educational Institute of Athens) | Gerostathis, Theodoros P. (National Technical University of Athens) | Athanassoulis, Gerassimos A. (National Technical University of Athens)
A phase-resolving, coupled-mode model is developed for the wave-current- seabed interaction problem, with application to wave scattering by steady currents over steep three-dimensional bottom topography. The vertical distribution of the wave potential is represented by a series of local vertical modes containing the propagating mode and all evanescent modes, plus an additional term accounting for the bottom boundary condition when the bottom slope is not negligible. Using the above representation, in conjunction with a variational principle, the problem is reduced to a coupled system of differential equations on the horizontal plane. If only the propagating mode is retained in the vertical expansion of the wave potential, and after additional simplifications, the above coupled-mode system is reduced to the mild-slope model derived by Kirby (1984) with application to the problem of wave-current interaction over slowly varying topography. The present system is discretized by using a second-order finite difference scheme and numerically solved by means of a parallel implementation, developed using the message passing programming paradigm on a commodity computer cluster. Thus, direct numerical solution is made feasible for realistic domains corresponding to areas with size of the order of several kilometers. The analytical structure of the present model facilitates its extension to treat non-linear waves, and it can be further elaborated to study wave propagation over random bottom topography and currents. INTRODUCTION The prediction of wave propagation in nearshore and coastal areas is critical to engineering applications associated with coastal management and harbour maintenance. In regions where ambient tidal and other currents are strong, their effect on wave transformation can be substantial. They create a Doppler shift and cause wave refraction, reflection, and breaking, which can completely change the wave energy pattern. In particular, the characteristics of surface gravity waves present significant variations as they propagate through non-homogeneous currents, in the presence of depth inhomogeneities in variable bathymetry regions.
Tsukioka, Satoshi (Japan Agency Marine-Earth Science and Technology) | Hyakudome, Tadahiro (Japan Agency Marine-Earth Science and Technology) | Sawa, Takao (Japan Agency Marine-Earth Science and Technology) | Yoshida, Hiroshi (Japan Agency Marine-Earth Science and Technology) | Yano, Yusuke (Japan Agency Marine-Earth Science and Technology) | Tahara, Jyunichiro (Japan Agency Marine-Earth Science and Technology) | Ashi, Jyuichiro (University of Tokyo) | Yamamoto, Fujio (University of Tokyo) | Morita, Sumito (Japan Agency Marine-Earth Science and Technology) | Kinoshita, Masataka (Japan Agency Marine-Earth Science and Technology) | Kasaya, Takafumi (Japan Agency Marine-Earth Science and Technology) | Ishikawa, Akihisa (The National Institute of Advanced Industrial Science and Technology)
This paper introduces one method to obtain super detailed sea floor acoustic image with an autonomous underwater vehicle and its result on the 2,000m depth mud volcanoes in Kumano Trough 50km offshore of Japan. Ocean going autonomous underwater vehicle “Urashima” was used as a platform to equip a high frequency side scan sonar system and its latitude, longitude and altitude was programmed and controlled keeping constant to unify the resolution of acoustical image. As the result, the vehicle was controlled successfully, and acoustic image of mud volcanoes was proved that the autonomous underwater vehicle has high capability for detailed deep seafloor scientific survey. INTRODUCTION The frequency of the sound wave for seafloor investigations by surface vessels are getting lower and even though narrow beams would be used, its footprints at seafloor are getting larger by becoming of depth is increasing, so that it is well known that the resolution of the acquisition data is decreasing by ocean depth. Recently, to obtain high resolution sea floor image, autonomous underwater vehicles have been developed by many institutions and companies instead of deep towing vehicles, because the vehicle motion is not restrained to its towing cable. Autonomous underwater vehicle “Urashima” (Hereafter, it is called ("AUV") shown in Table 1 by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) has been developing to research underwater engineerings as the energy storage system which composed from close polymer membrane fuel cell, metal hydride and cogeneration system, inertial navigation system with ring-laser gyro and acoustical digital telemetry system since 2000. The data obtained by sea tests is offered not only a technological research but also the science section of a precise inquiry in seafloor etc. is executed co-operation with Ocean Research institute of the Tokyo University (ORI), the National Institute of Advanced Industrial Science and Technology, Institute for Research Earth Evolution (IFREE) and Center for Deep Earth Exploration (CDEX) in JAMSTEC since 2005.
Grilli, Annette R. (University of Rhode Island) | Merrill, Jon (University of Rhode Island) | Grilli, Stéphan T. (University of Rhode Island) | Spaulding, Malcolm L. (University of Rhode Island) | Cheung, Jeffrey T. (Teledyne Scientific and Imaging)
We study free-floating point absorption wave generators, consisting of an assemblage of one or a few (mostly heaving) spar buoys, housing at least one short-stroke linear generator (SSLG), made of a magnet, suspended to a spring, and oscillating within a coil. This system is aimed at producing low and renewable wave power (up to Ο (1) kW) for marine coastal surveillance systems. Both scale model experiments and numerical modeling are performed in order to tune the system’s parameters and maximize its response for a target sea-state (i.e., operate near resonance in heave and magnet motion). We find that, for such buoy systems, viscous friction is the dominant damping mechanism near resonance and, hence, the buoy’s wet extremities must also be properly streamlined, and rolling must be minimized as it may significantly increase such damping. This can be achieved with a so-called trispar system, in which 3 spars buoys of identical diameter are mounted in an equilateral triangle configuration, one diameter apart from each other. Since the heave resonance period of a spar buoy is primarily a function of its draft, to lower this period and better match the resonance period of the SSLG, the draft of each buoy in the trispar is varied (in the scale model, to 25, 50 and 100 cm), with the longest spar buoy housing the SSLG, while simultaneously adjusting their dead weight. Experimental results in periodic waves, well supported by numerical modeling, show a significantly improved performance of the trispar vs. single spar design, both with respect to parasitic roll oscillations (almost none observed for the tripar) and power gene- ration. The good performance of the trispar, particularly in terms of “Capture Width Ratio”, is confirmed by preliminary numerical simulations in irregular waves. Future work will test the trispar in irregular waves and explore dynamic tuning strategies (e.g., latching) of the SSLG, in order to further improve power generation.