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ObjectiveAutonomous docking is the key to the cooperative operation of unmanned underwater vehicles (UUVs). However, due to environmental complexity and object characteristics, it is very difficult to achieve precise guidance and docking. In order to improve the accuracy and robustness of underwater docking, this study proposes a vision-guided docking scheme which encompasses vision processing and 3D trajectory tracking control. MethodsFirst, the overall vision-guided docking scheme is designed in combination with an analysis of task and object characteristics. Second, the YOLOv5 neural network is designed to complete the target detection of the underwater docking station, and the online measurement of the relative position and attitude relationship between the docking station and UUV is realized by an efficient perspective-n-point (EPnP) algorithm. Next, combined with the visual measurement results, an effective 3D robust trajectory tracking controller is designed on the basis of the 3D LOS guidance law, radial basis function neural network (RBFNN) and terminal sliding mode control (TSMC). Finally, the validity of the proposed scheme is verified through numerical simulation and a tank test. ResultsIn the tank test, the proposed vision-guided control algorithm can effectively complete the online detection and relative positioning of the underwater docking station, thereby achieving precise underwater docking. ConclusionThe results of this study show that the proposed vision-guided 3D trajectory tracking control scheme is reasonable and efficient, and can lay a good foundation for UUV docking.

In high-level radioactive waste geological repositories, compacted bentonite undergoes coupled thermo-hydraulic processes due to heat released from a central waste canister and groundwater imbibition from the surrounding host rock. An understanding of these processes is essential for long-term simulations of radionuclide migration and canister corrosion, which requires an understanding of temperature effects on the coupled thermo-hydraulic properties governing these processes. In this study, a tank-scale radial infiltration test was used to investigate water imbibition processes in compacted bentonite under a central heater temperature of 200 °C that simulates high thermal gradients in a repository. Interpretation of this test focuses on evaluation of the liquid water wetting front during hydration and the interpretation of the temperature-dependent transient soil water retention curve (SWRC), thermal conductivity function (TCF), and hydraulic conductivity function (HCF). The SWRC during imbibition follows a temperature-dependent wetting path. Temperature effects on the hydraulic conductivity of bentonite in saturated conditions had the greatest effect on the shape of the HCF, with minimal temperature effects at higher suctions. The transient thermal conductivity data matched well with a new TCF linked with the SWRC shape. Although the bentonite layer was restrained, local deformations during hydration may have affected the shapes of the TCF and HCF. [ABSTRACT FROM AUTHOR]

Marine current energy is recognized a promising energy source due to its inherent stability and high predictability. In the past decade, several milestones have been achieved in marine current turbine (MCT) research such as MeyGen and O2. However, compared with high-velocity currents, low velocity currents are more commonly distributed worldwide, which presents new challenges. The demand for low starting velocity and high efficiency necessitates some novel structure in the design of blade, power transmission, etc. To address these issues, taking a 50W MCT as research object, this paper firstly presents the MCT design of a new fan-shaped rotor configuration, a compact non-contact magnetic coupling, a low inertial power train and hollow-cup DC generator for easier starting. Furthermore, to realize the maximum power point tracking (MPPT) and sustainable power supply, the electrical system and its control strategy were designed. The hydrodynamic performance of the fan-shaped rotor was simulated and analyzed using CFD, and a simulation model of the electrical and control systems was constructed and tested to verify the performance. Finally, the tank and sea tests were respectively conducted to validate the performance of proposed MCT. The results indicate that the proposed MCT is capable of starting at velocities around 0.2 m/s and achieving a power coefficient (Cp) exceeding 0.4, making it well-suited for providing a continuous and stable power supply in areas with low flow velocities. • A comprehensive design of a marine current turbine (MCT) in low flow velocity was proposed. • The MCT was made and tank and sea tests were conducted. • The MCT can achieve a starting velocity of about 0.2 m/s, a power coefficient of above 0.4, showing good performance in low flow velocity areas. [ABSTRACT FROM AUTHOR]

Oyster farming rafts are traditionally constructed from bamboo, which are susceptible to damage during typhoons. To overcome this, a promising solution of farming rafts made of highly flexible polyethylene is proposed. Since there are only a few studies to understand the bending deformation of elastic deformable bodies in waves, the elasticity of the highly flexible polyethylene needs to evaluated quantitatively. Therefore, a time-domain analysis model for evaluating the motion characteristics and deformation performance of the polyethylene rafts is implemented. In addition, 1:6.75 model scale tests were conducted in a water tank under regular waves. Aluminum plates with similar bending rigidity as the real scale model were employed and bending strains were measured at three locations on the aluminum plates. It is found that the results in terms of displacements and bending strains predicted by the numerical model agree well with the model scale test results. A sensitivity analysis is conducted on the numerical model to elucidate the performance of the highly flexible polyethylene rafts for oyster farming. • A coupled numerical model of rigid and elastic deformable bodies is implemented. • The motion of a raft in waves was measured through numerical analysis and tests. • Bending strain of the elastic deformable body was accurately evaluated by time-domain analysis. [ABSTRACT FROM AUTHOR]

Wood ash is a complex mixture of inorganic and organic compounds. It is heterogeneous in composition, which can vary considerably. Ash is mainly disposed of in landfills, which creates a risk for air, soil and groundwater contamination by trace elements. In order for wood biomass ash to be used as a secondary raw material, it is necessary to perform leaching tests, to determine which microelements it contains, and which of them could be released into the environment during the ash disposal. Sequential extraction (SE) showed that in the exchangeable and carbonate fraction, the most volatile metals As, Cd, Zn and Pb are released the most from the ash of deciduous trees, while the leaching of ash from coniferous trees is significantly lower. The evaluation of risk assessment code (RAC) for the tested biomass ash samples, indicates that Pb is a high-risk leaching element due to its condensation on the ash particles. By performing toxicity characteristic leaching procedure (TCLP) and synthetic precipitation leaching procedure (SPLP) tests, it was established that the released concentrations of tested metals are below the maximum allowable concentration, given by the regulation. The leaching tests of composites, prepared from wood ash in combination with cement, indicate that the leaching of ash is reduced to a minimum, and that all heavy metals are bound in a cement matrix, which indicates the possibility of using wood ash for construction purposes.

Recently, shipyards have been booming in the product carrier (PC) market of the global shipbuilding industry. Due to the rising market conditions, orders for large container vessels and PCs are also steadily increasing. According to the industry, freight rates for LR tankers (70K) and MR tankers (50K) in the shipbuilding industry have rose to the highest level during the previous year. In order to secure the competitiveness of PCs, various core items are required, and Korean shipbuilders have been leading the market for a long time based on their knowledge of the design and production of low-fuel ships. In recent years, there have been frequent cases of coating cracks in the cargo hold after sea trial. All relevant rules presented by the classification so far are structural design, safety evaluation, and inspection standards, and coating cracks are considered a problem for coating makers. In other words, they must establish a standard coating measure agreed upon by all parties (owner, shipbuilder, and coating maker); therefore, solutions have been proposed by each shipping company. In this study, the causes of coating cracks occurring in the cargo hold of PCs during tank tests in sea trials were analyzed and measures to prevent them were studied. The main point of this study is assumed that coating crack are caused by mechanical load induced by structural behavior, and the numerical analysis methodology is newly introduced. Based on the results of the numerical analysis, it was confirmed that there is a high probability of coating cracks in the critical area where high stress occurs in the cargo hold. Therefore, the results obtained in this study will be useful to prevent coating cracks in future PC designs. [ABSTRACT FROM AUTHOR]

Numerous benchmark calculations have been performed on ship motions and loads in waves. However, there are usually significant differences between codes, even for programs based on the same theory, and it is often extremely difficult to identify the factors that cause such differences. In this paper, the authors present a formulation of the strip method and 3D method in such a way that the common parts between the two are emphasized, and then develop an integrated program that can handle the two methods (STFM and zero-speed Green's function method) based on this formulation. This approach enables the extraction of the differences in the ship response between the two methods caused by the pure difference in the hydrodynamic force of them, i.e., the 3D effect. A comparison using tank tests under a wide range of conditions is performed to clarify the estimation accuracy of the two methods and the tendency of the 3D effect for ship motion, hull-girder sectional force, and hydrodynamic pressure for a container ship and a VLCC. • We develop a program that can handle the strip method and 3D panel method based on an integrated formulation of them. • This eliminates uncertainties between codes and clarified difference in ship response due to 3D effects. • Tank test data under a wide range of conditions were compared with both calculation methods. • Trends in 3D effects of fluid forces on ship response in waves are summarized and discussed. [ABSTRACT FROM AUTHOR]

Floating wind power platforms are in constant motion due to waves when deployed at sea. This motion directly affects the stability and safety of the platform. Therefore, it is very important to study the laws governing the platform’s dynamic response. In this paper, the dynamic characteristics of an offshore floating wind power platform were analysed under nine different sets of operating conditions using a numerical calculation method. Following this, a scaled 1:50 platform model was tested in a tank. Model tests were carried out with different wave conditions, and dynamic response data for the platform were measured and analysed. The hydrodynamic variation rules of floating wind power generation platform in waves were obtained. Some effective measures for maintain the stability and safety of wind power platforms are put forward that can provide a reference for dynamic stability research and the design of floating wind power platforms in the future.

Recently, shipyards have been booming in the product carrier (PC) market of the global shipbuilding industry. Due to the rising market conditions, orders for large container vessels and PCs are also steadily increasing. According to the industry, freight rates for LR tankers (70K) and MR tankers (50K) in the shipbuilding industry have rose to the highest level during the previous year. In order to secure the competitiveness of PCs, various core items are required, and Korean shipbuilders have been leading the market for a long time based on their knowledge of the design and production of low-fuel ships. In recent years, there have been frequent cases of coating cracks in the cargo hold after sea trial. All relevant rules presented by the classification so far are structural design, safety evaluation, and inspection standards, and coating cracks are considered a problem for coating makers. In other words, they must establish a standard coating measure agreed upon by all parties (owner, shipbuilder, and coating maker); therefore, solutions have been proposed by each shipping company. In this study, the causes of coating cracks occurring in the cargo hold of PCs during tank tests in sea trials were analyzed and measures to prevent them were studied. The main point of this study is assumed that coating crack are caused by mechanical load induced by structural behavior, and the numerical analysis methodology is newly introduced. Based on the results of the numerical analysis, it was confirmed that there is a high probability of coating cracks in the critical area where high stress occurs in the cargo hold. Therefore, the results obtained in this study will be useful to prevent coating cracks in future PC designs.

Most previous experimental studies on the hydrodynamic and aerodynamic performances of an oscillating water column (OWC) wave energy converter were conducted in a wave flume. In this study, an experimental study on an isolated OWC plant is carried out in a wave tank. The interactions between the OWC system and incident regular and irregular waves are analyzed by measuring the surrounding wave fields using a wave gauge array. The wave distribution patterns and reflection ratios of the OWC model are presented. In addition, the free-surface elevation, air pressure varying amplitude, turbine torque output, and relative capture width ratios and efficiencies in regular and irregular wave scenarios are measured and analyzed. The operating performances of the OWC model are analyzed and compared to the results derived from the flume tests. An overall performance reduction of over 20% can be observed in the wave tank tests. In addition, the representative results of the overall capture width ratio of the OWC model derived from irregular wave tests are corrected from the scaling effects caused by the similarity contradiction. • An isolated OWC model was tested experimentally in a wave tank. • The wave field distribution patterns around the OWC device were presented. • The reflection ratios of the isolated OWC model were reported. • The operating performances in regular and irregular wave scenarios were analyzed. • The performance comparisons between wave tank and flume tests were conducted. [ABSTRACT FROM AUTHOR]

This paper proposed a compact design of the subsea cobalt-rich crust mining vehicle with a general purpose support vessel for subsea resource exploration, sample collection, and research. The necessary functions were considered in the concept design, including walk, crushing/mining, sample collection, cutter head adaptation, vehicle orientation, crust texture measurement, awareness, positioning, and navigation. The prototype was tested in both tank and subsea environment. The sea trials were carried out with the support of a general purpose support vessel. The track design worked well in both the tank and subsea environment and the mining vehicle walked smoothly in the sea trial. The crust was crushed to the size of 2 mm and 10 mm with different cutting parameters and successfully collected by the jet pump, 6 kg in total. The crust texture was measured by the onboard sonar successfully and can be used for cutting parameter selection. The cameras captured the images of the subsea environment, but the actions of crushing and sample collection produced plumes, which blocked the camera vision. In the situation, the front image sonar can be used to keep the vehicle away from big rocks. The mining vehicle is not limited to the mining and sampling of subsea cobalt-rich crust. Most of the subsea solid resources on the seabed can be considered to use the compact mining vehicle for sampling and related research. The only issues to be considered are the crushing ability and sample size required.

• The kinematic analysis and dynamic model of WDR are presented. • WDR has unique dynamic characteristics due to the unique multi-body joint structure. • Simulations of PID heading control demonstrate the unique control characteristic of WDR. Wave driven robots (WDRs) take ocean energies as the power sources and are often used for long-term monitoring of the marine environment. The unique multi-body joint structure and special operation mechanism of a WDR make the dynamics modeling problem unusual. The dynamic model of a WDR was put forward by taking the interconnection of forces and motions between the float body (float) and the submerged glider (glider) into account. Numerical simulation of longitudinal motion and the comparison between simulation and tank test of reciprocating steering motion of the "Ocean Rambler" WDR were carried out. The dynamic model proposed in this paper was consistent with the motion characteristics of "Ocean Rambler" WDR. Simulations of PID heading control demonstrated the unique control characteristics of the WDR, which proved the significance of the established dynamic model of the WDR in control algorithm design. [ABSTRACT FROM AUTHOR]

• The work gives a methodology to arrive at the optimal mixture for airbag gas generants using DSC-TGA, which will give better performance with minimum toxic residues. • The work depicts the major performance parameters to be evaluated for an effective airbag gas generant. • Tank testing using lower volumes and full-fledged 28.3 L vessels is done for NaN 3 /KNO 3 mixtures for the first time. • For the first time, the maximum pressure developed during decomposition of the fuel/oxidizer mixtures on a closed vessel test was compared with theoretically calculated maximum pressure. This paper reports the experimental methodology to arrive at an optimal weight composition of NaN 3 /KNO 3 airbag gas generants based on thermal studies using Differential Scanning Calorimetry/Thermogravimetry analysis. The residual analysis showed that the fuel oxidizer mixture of 62.5/37.5 by weight percentage can be used as the optimal composition for airbag gas generants, as it produced minimum residues after decomposition reaction. Spectroscopic studies using SEM-EDS showed that the optimal composition had zero residues of toxic NaN 3 compared to all other compositions tested. The heat energy released was found to be more in the air atmosphere due to the complete decomposition of mixtures compared to the nitrogen atmosphere. In this study, the ballistic properties such as time to peak pressure and peak pressure generated on ignition of the mixture were measured using the closed vessel test and the 28.3 lit full-fledged tank test. For the first time, the maximum pressure developed during decomposition of the fuel/oxidizer mixtures on the closed vessel test was compared with the theoretical maximum pressure value calculated using the ideal gas equation assuming that the process was adiabatic. The applicability of using the constant volume closed vessel test chamber for performance testing of auto airbag systems was also addressed. [ABSTRACT FROM AUTHOR]

This paper presents a study of the effect of model scale on the performance of a fixed Oscillating Water Column (OWC) type Wave Energy Converter (WEC). Tank tests at two different scales, including the effect of scaling of the test tanks to minimise the bias introduced by different wave blockage effects. CFD simulations based on Reynolds Average Navier Stokes (RANS) method were then carried out for both scaled OWCs to investigate whether CFD simulation is able to reproduce the scale effect. Comparison between the tank test results and the CFD simulation results suggests that CFD simulation is capable of reproducing the hydrodynamic scaling effect with a good accuracy. Results also suggest that the hydrodynamic scaling effect is mainly introduced by the Reynolds number effect for cases investigated in the current study. • Tank testing of two different scale OWC type wave energy devices. • Testing tanks are scaled accordingly to minimise the difference introduced by tank width. • CFD simulations suggest that CFD simulation is capable of reproducing the hydrodynamic scaling effect. [ABSTRACT FROM AUTHOR]

In this paper, seakeeping performance of vessels is comparatively investigated by means of improved 2.5D theoretical calculation, small-scale model towing tank test and large-scale free running model sea trial. This study also provides a scheme of ship vertical motion stabilization technique by using Semi-Submerged Bow (SSB) appendages. Firstly, an improved strip theory based 2.5D theoretical seakeeping algorithm, which considers the viscous flow effects attributed to bow appendages, is developed to estimate ship vertical motion responses in regular waves. Short-term predictions are also made on the basis of spectral analysis theory to predict ship motion responses in irregular waves. Then corresponding small-scale models are made and tested in a laboratory towing tank for both regular and irregular wave conditions to confirm the numerical results. The tank testing results between different ship schemes are also compared to experimentally investigate the effects of SSB and fin on hull vertical motion stabilization. Furthermore, large-scale model sea trials are conducted in coastal waves for a final validation of the ship seakeeping performance in short-crested sea waves. Finally, comparisons of the results by different testing approaches are systematically made and analyzed. [ABSTRACT FROM AUTHOR]

This paper addresses collapse behaviour of Very Large Floating Structure (VLFS) under extreme vertical bending moment. The study is performed as part of risk analysis to evaluate the consequence of a rare collapse event. Elastic and plastic deformation of VLFS develops under the extreme vertical bending moment while the deformation interacts with the fluid around VLFS. Therefore, hydro-elastoplasticity analysis need be developed taking account of these effects. In this study, the whole VLFS structure is modeled as two elastic beams with an elasto-plastic hinge embedded at the connection. The structural deformation is formulated by using finite element method (FEM). The hydrodynamic behaviour is modeled by using Rankine source panel method in time domain based on two-dimensional potential theory. The two models are coupled. A series of scaled model tests is performed for validation. Simulation and tank test results for the basic collapse behaviour of VLFS are presented and discussed. The numerical method is applied further to a realistic VLFS design to clarify its collapse behaviour. [ABSTRACT FROM AUTHOR]

This paper addresses nonlinear deflection waves traveling along a thin elastic plate floating at the water surface. The investigations are based on both the analytical and experimental aspects. A finite amplitude wave theory for the waves traveling on the plate developed by the present authors, in which, the nonlinear wave is formulated by a perturbation with respect to the wave height/wavelength ratio, is used. The behavior of the nonlinear wave traveling on the plate is like what the Stokes wave theory predicts for the free surface. However, for the waves traveling on the plate, there is an instability frequency at which the second order wave component grows considerably. The sign of the second order wave component is inverted at the instability frequency when the incident wave frequency is changed from low to high regions. These predictions are verified in a tank test in the two-dimensional flume using a long flexural plate that was newly designed. The spatio-temporal distribution of the deflection and bending strain on the plate was measured directly using the stereo Digital Image Correlation (DIC) technique with two high-speed CCD cameras. The measured results are compared with the predictions by analytical theory. The instability frequency is found in the tank test and the nonlinear wave properties are discussed. [ABSTRACT FROM AUTHOR]

Due to the abundant wind energy in deep water, floating offshore wind turbines (FWTs), especially for the semisubmersible FWTs, have attracted more attention these years. To reduce the heave motion of FWTs, heave plates are often attached at the bottom of the column. In this paper, experimental investigations of the hydrodynamic performance of the heave plates via the forced oscillation method are conducted. The impacts of the KC number (KC = 0.1–1.1), oscillation frequency (f = 0.4–1.43 Hz), diameter ratio- D d / D c (D d and D c are the diameter of the heave plate and column), thickness ratio- t d / D d (t d is the thickness of the heave plate), shapes of the heave plates, on the added mass, and damping coefficients are investigated. The results show that the added mass and damping coefficients are independent of oscillation frequencies, while the KC number influences significantly the hydrodynamic coefficients. Increase in the diameter ratios will decrease the added mass and damping coefficients. The thinner heave plates obtain larger damping coefficients. Comparison between the different shapes of the heave plates shows that the octagonal heave plate displays similar added mass and damping coefficients to the circular heave plate. However, square one obtains lower added mass coefficients compared to the other three shapes. And the hexagonal plate seems to have the highest damping force for different KC numbers. • Hydrodynamic performance of heave plates were investigated via an experimental approach. • The effects of the KC numbers and oscillation frequencies on the hydrodynamic coefficients were analyzed. • Diameter ratios and shapes effect of the heave plate on the hydrodynamic performance were also carried out. • KC numbers have great influence on the hydrodynamic coefficients of the heave plate. • The hexagonal plate obtains higher damping coefficients compared to other shapes. [ABSTRACT FROM AUTHOR]

This paper addresses the deflection waves traveling along a floating thin plate using a series of tank tests. A measurement system using stereo Digital Image Correlation (DIC) with two sets of high-speed cameras is adopted in the tests to find the instantaneous distribution of deflection and strain in a structure by taking the difference between the images before and after deformation. The model is made of rubber foam and its elastic modulus is found from four-point bending and free-vibration tests. The deflection waves traveling along a thin elastic plate at the water surface are identified in the tank tests. The measured results are compared with the numerical simulation results based on a linear potential flow theory. The agreement between the measurements and numerical results is found to be satisfactory in terms of deflection and strain distributions. Further, nonlinear components including the second and third harmonics, whose properties deviate slightly from the predictions by Stokes wave theory, are found and discussed. • The waves propagating along a long thin plate floating at the water surface are measured by using digital image correlation (DIC) method. The effectiveness of the measurement by the DIC is shown. • The tank test model is made of closed cell rubber foam. The material properties are measured by a static four-point-bending test and vibration test. The uncertanty with respect to the material properties is discussed. • The measured results are compared with numerical simulation results based on linear potential theory. The overall agreement is found good in terms of wave length, response amplitude, and distribution. • Nonlinearity of deflection waves on the floating plate, which is similar in some point to Stokes wave is identified for the first time by measurement. [ABSTRACT FROM AUTHOR]

The passenger side airbags (PAB) are usually larger than the driver airbags. Therefore, the inflator of PAB is more powerful with high mass rate. In this paper, an Arbitrary Lagrangian-Eulerian (ALE) method based computational method is developed to simulate the deployment of a PAB. The tank test is used to test the property of the inflator. Through comparison of numerical and experimental results, the ALE method is validated. Based on a failed airbag test, a smaller sub-airbag is placed inside PAB to disperse the gas flow to directions which are less damaging. By applying dynamic relaxation, the initial mesh corresponding to the experimental terms is obtained. The results indicate that the interior pressure and impact force coincide with the test data, and the method in this paper is capable of capturing airbag deploying process of the PAB module accurately. [ABSTRACT FROM AUTHOR]

Each year, millions of tonnes of waste are generated worldwide, partially through the construction and demolition of buildings. Recycling the resulting waste could reduce the amount of materials that need to be manufactured. Accordingly, the present work has analysed the potential reuse of construction waste in concrete manufacturing by replacing the natural aggregate with recycled concrete coarse aggregate. However, incorporating alternative materials in concrete manufacturing may increase the pollutant potential of the product, presenting an environmental risk via ground water contamination. The present work has tested two types of concrete batches that were manufactured with different replacement percentages. The experimental procedure analyses not only the effect of the portion of recycled aggregate on the physical properties of concrete but also on the leaching behaviour as indicative of the contamination degree. Thus, parameters such as slump, density, porosity and absorption of hardened concrete, were studied. Leaching behaviour was evaluated based on the availability test performed to three aggregates (raw materials of the concrete batches) and on the diffusion test performed to all concrete. From an environmental point of view, the question of whether the cumulative amount of heavy metals that are released by diffusion reaches the availability threshold was answered. The analysis of concentration levels allowed the establishment of different groups of metals according to the observed behaviour, the analysis of the role of pH and the identification of the main release mechanisms. Finally, through a statistical analysis, physical parameters and diffusion data were interrelated. It allowed estimating the relevance of porosity, density and absorption of hardened concrete on diffusion release of the metals in study. [ABSTRACT FROM AUTHOR]

Dynamic collapse behavior of a ship's hull girder in waves is investigated; post-ultimate strength behavior is the focus. Firstly, a simulation method is proposed. Assuming that a plastic hinge is formed during the collapse of the hull girder, the whole ship is modeled as two rigid bodies connected amidship via a nonlinear rotational spring. The post-ultimate strength behavior, such as the reduction of load carrying capacity due to buckling and yielding, is reflected in the model. Hydrodynamic loads are evaluated by using nonlinear strip theory to account for the effect of large plastic deformations on the loads. A scaled model for validation of the simulation is designed and fabricated. Then a series of tank tests is conducted using the scaled model to validate the simulation results. Post-ultimate strength behavior characteristics in waves are clarified by using the numerical and tank test results. It is shown that the hull girder collapses rapidly after reaching ultimate strength, and then the plastic deformation grows until unloading starts at the collapsed section. Finally, several parametric dependencies of the extent of the collapse behavior are discussed based on a series of the simulations. [ABSTRACT FROM AUTHOR]

In this paper, we investigated the effect of sloshing on the sway motions of two-dimensional rectangular cylinders in regular waves, bearing in mind possible applications for LNG-FPSO and LNG-FSRU. First, we carried out experiments for two models with different drafts, or the same draft but different filling ratios, in which the models were firmly connected to each other. The sway motion was measured with a noncontact video camera. This is an extension of Rognebakke and Faltinsen's work for a single model (J Ship Res 47(3):208-221, ). It was found that the sway motion became small when the incident wave frequency was close to the lowest natural frequency of each model. The sway motion greatly increased when the wave frequency was higher than this frequency. The measured data were compared with numerical results obtained by a single-dominant multi-modal method; relatively good agreement was noted. However, the numerical results deviated from the experimental results near the lowest natural frequency of the smaller model, which was believed to be due to overturning waves, as observed during the experiment. Since this is out of the valid range for the single-dominant multi-modal method, other, more appropriate, methods such as the multi-dominant modal method must be applied instead. [ABSTRACT FROM AUTHOR]

This paper proposed a compact design of the subsea cobalt-rich crust mining vehicle with a general purpose support vessel for subsea resource exploration, sample collection, and research. The necessary functions were considered in the concept design, including walk, crushing/mining, sample collection, cutter head adaptation, vehicle orientation, crust texture measurement, awareness, positioning, and navigation. The prototype was tested in both tank and subsea environment. The sea trials were carried out with the support of a general purpose support vessel. The track design worked well in both the tank and subsea environment and the mining vehicle walked smoothly in the sea trial. The crust was crushed to the size of 2 mm and 10 mm with different cutting parameters and successfully collected by the jet pump, 6 kg in total. The crust texture was measured by the onboard sonar successfully and can be used for cutting parameter selection. The cameras captured the images of the subsea environment, but the actions of crushing and sample collection produced plumes, which blocked the camera vision. In the situation, the front image sonar can be used to keep the vehicle away from big rocks. The mining vehicle is not limited to the mining and sampling of subsea cobalt-rich crust. Most of the subsea solid resources on the seabed can be considered to use the compact mining vehicle for sampling and related research. The only issues to be considered are the crushing ability and sample size required. [ABSTRACT FROM AUTHOR]

Abstract: Container ship structures are characterized by large hatch openings. Due to this structural property, they are subject to large diagonal deformations of hatch openings and warping stresses under complex torsional moments in waves. This necessitates torsional strength assessment of hull girder of container ships in their structural design stage. In this paper, a practical method for torsional strength assessment of container ship structures with transparent and consistent background is discussed based on the results from up-to-date analyses. In order to estimate the torsional response characteristics as accurately as possible, three-dimensional Rankine source method, after being validated by tank tests, is employed for estimation of wave loads on a container ship, and FE analyses are conducted on the entire-ship model under the estimated loads. Then, a dominant regular wave condition under which the torsional response of the container ship becomes maximum is specified. Design loads for torsional strength assessment that give torsional response equivalent to the long-term predicted values of torsional response are investigated based on the torsional moments on several container ships under the specified dominant wave condition. An appropriate combination of stress components to estimate the total hull girder stress is also discussed. [Copyright &y& Elsevier]

• To test leaching during construction phase, a tank test for fresh concrete was developed. • The new test allows a more accurate assessment of the environmental compatibility for relevant applications. • Ba, Cr, Cu, V release was higher at young age. • Pb release was higher from pre-stored, hardened cementitious materials. Investigations concerning the release of potentially harmful substances are carried out on hardened concrete only and just in a few countries (e. g. Netherlands and Germany). However, in some applications, cementitious material can be exposed to water in a fresh state during the construction phase. Therefore, a tank test for fresh concrete has been developed. In contrast to common leaching tests, e. g. the European dynamic surface leaching test (DSLT, CEN/TS 16637–2) , water is applied on the fresh concrete surface rather than on a hardened, monolithic specimen. This paper summarizes the results of several research projects on this topic conducted during the last 20 years. For the parameters Ba, Cr, Cu, Pb and V, the leaching of fresh cementitious materials (concrete and cement grouts) including the subsequent leaching of the hardening materials are compared with DSLT results. For Ba, Cr, Cu, V, the release of fresh materials is significantly higher than that of hardened materials, which can be explained by the decreasing diffusion coefficient with progressing hydration. However, for Pb, the leaching of hardened materials is higher. [ABSTRACT FROM AUTHOR]

The use of mineral additives from the power and metallurgy industries in the production of building materials still raises questions about the ecological safety of such materials. These questions are particularly associated with the release of heavy metals. The article presents research related to the leaching of chromium from concretes made of Portland cement CEM I and slag cement CEM III/B (containing 75% of granulated blast furnace slag). Concrete was evaluated for leaching mechanisms that may appear during tank test over the long term (64 days). It has been presented that the dominating process associated with the leaching of chromium from both types of concrete is surface wash-off. Between the 9th and 64th day of the test, leaching of Portland cement concrete can be diffusion controlled. It has been proven that the participation of slag in the composition of concrete does not affect the level of leaching of chromium into the environment from concrete. [ABSTRACT FROM AUTHOR]

Large floating structures, such as liquefied natural gas (LNG) ships, are subject to both internal and external fluid forces. The internal fluid forces may also be detrimental to a vessel's stability and cause excessive loading regimes when sloshing occurs. Whilst it is relatively easy to measure the motion of external free surface with conventional measurement techniques, the sloshing of the internal free surface is more difficult to capture. The location of the internal free surface is normally extrapolated from measuring the pressure acting on the internal walls of the vessel. In order to understand better the loading mechanisms of sloshing internal fluids, a method of capturing the transient inner free surface motion with negligible affect on the response of the fluid or structure is required. In this paper two methods will be demonstrated for this purpose. The first approach uses resistive wave gauges made of copper tape to quantify the water run-up height on the walls of the structure. The second approach extends the conventional use of optical motion tracking to report the position of randomly distributed free floating markers on the internal water surface. The methods simultaneously report the position of the internal free surface with good agreement under static conditions, with absolute variation in the measured water level of around 4 mm. This new combined approach provides a map of the free surface elevation under transient conditions. The experimental error is shown to be acceptable (low mm-range), proving that these experimental techniques are robust free surface tracking methods in a range of situations. [ABSTRACT FROM AUTHOR]