Showing papers in "Journal of Marine Science and Technology in 2013"

EFD and CFD for KCS heaving and pitching in regular head waves

Abstract: The KCS container ship was investigated in calm water and regular head seas by means of EFD and CFD. The experimental study was conducted in FORCE Technology’s towing tank in Denmark, and the CFD study was conducted using the URANS codes CFDSHIP-IOWA and Star-CCM+ plus the potential theory code AEGIR. Three speeds were covered and the wave conditions were chosen in order to study the ship’s response in waves under resonance and maximum exciting conditions. In the experiment, the heave and pitch motions and the resistance were measured together with wave elevation of the incoming wave. The model test was designed and conducted in order to enable UA assessment of the measured data. The results show that the ship responds strongly when the resonance and maximum exciting conditions are met. With respect to experimental uncertainty, the level for calm water is comparable to PMM uncertainties for maneuvering testing while the level is higher in waves. Concerning the CFD results, the computation shows a very complex and time-varying flow pattern. For the integral quantities, a comparison between EFD and CFD shows that the computed motions and resistance in calm water is in fair agreement with the measurement. In waves, the motions are still in fair agreement with measured data, but larger differences are observed for the resistance. The mean resistance is reasonable, but the first order amplitude of the resistance time history is underpredicted by CFD. Finally, it seems that the URANS codes are in closer agreement with the measurements compared to the potential theory.

Turn and zigzag maneuvers of a surface combatant using a URANS approach with dynamic overset grids

Abstract: Unsteady Reynolds averaged Navier–Stokes (URANS) computations of standard maneuvers are performed for a surface combatant at model and full scale. The computations are performed using CFDShip-Iowa v4, a free surface solver designed for 6DOF motions in free and semi-captive problems. Overset grids and a hierarchy of bodies allow the deflection of the rudders while the ship undergoes 6DOF motions. Two types of maneuvers are simulated: steady turn and zigzag. Simulations of steady turn at 35° rudder deflection and zigzag 20/20 maneuvers for Fr = 0.25 and 0.41 using constant RPM propulsion are benchmarked against experimental time histories of yaw, yaw rate and roll, and trajectories, and also compared against available integral variables. Differences between CFD and experiments are mostly within 10 % for both maneuvers, highly satisfactory given the degree of complexity of these computations. Simulations are performed also with waves, and with propulsion at either constant RPM or torque. 20/20 zigzag maneuvers are simulated at model and full scale for Fr = 0.41. The full scale case produces a thinner boundary layer profile compared to the model scale with different reaction times and handling needed for maneuvering. Results indicate that URANS computations of maneuvers are feasible, though issues regarding adequate modeling of propellers remain to be solved.

Ship underwater noise assessment by the acoustic analogy. Part I: nonlinear analysis of a marine propeller in a uniform flow

Abstract: The aim of this work is to analyze the hydroacoustic behavior of a marine propeller through the acoustic analogy and to test the versatility and effectiveness of this approach in dealing with the many (and relatively unexplored) issues concerning the underwater noise and its numerical prediction. In particular, a propeller in a noncavitating open water condition is examined here by coupling a Reynolds averaged Navier–Stokes hydrodynamic solver to a hydroacoustic code implementing different resolution forms of the Ffowcs Williams–Hawkings (FWH) equation. The numerical results suggest that unlike the analogous aeronautical problem, where the role played by the nonlinear quadrupole sources is known to be relevant just at high transonic or supersonic regime, the pressure field underwater seems to be significantly affected by the flow nonlinearities, while the contribution from the linear terms (the thickness and loading noise components) is dominant only in a spatially very limited region. Then, contrary to popular belief and regardless of the low blade rotational speed, a reliable hydroacoustic analysis of a marine propeller cannot put aside the contribution of the nonlinear noise sources represented by the turbulence and vorticity three-dimensional fields and requires the computation of the FWH quadrupole source terms.

A coupled FDM–FEM method for free surface flow interaction with thin elastic plate

Abstract: A partitioned approach by the coupling finite difference method (FDM) and the finite element method (FEM) is developed for simulating the interaction between free surface flow and a thin elastic plate. The FDM, in which the constraint interpolation profile method is applied, is used for solving the flow field in a regular fixed Cartesian grid, and the tangent of the hyperbola for interface capturing with the slope weighting scheme is used for capturing free surface. The FEM is used for solving structural deformation of the thin plate. A conservative momentum-exchange method, based on the immersed boundary method, is adopted to couple the FDM and the FEM. Background grid resolution of the thin plate in a regular fixed Cartesian grid is important to the computational accuracy by using this method. A virtual structure method is proposed to improve the background grid resolution of the thin plate. Both of the flow solver and the structural solver are carefully tested and extensive validations of the coupled FDM–FEM method are carried out on a benchmark experiment, a rolling tank sloshing with a thin elastic plate.

A novel tracking control approach for unmanned underwater vehicles based on bio-inspired neurodynamics

Abstract: A novel hybrid control approach is presented for trajectory tracking control of unmanned underwater vehicles in this paper. The kinematic and dynamic controllers are integrated by the proposed control strategy. The paper has two objectives. Firstly, an improved backstep method is proposed to generate the virtual velocity using a bio-inspired neurodynamics model in the kinematic controller. The bio-inspired neurodynamics model is intended to smooth the virtual velocity output to avoid speed jumps of the unmanned underwater vehicle caused by tracking errors and to meet the thruster control constraints. Secondly, a new sliding-mode method is added to the dynamic controller, which is robust against parameter inaccuracy and disturbances. The combined kinematic–dynamic control law is applied to the trajectory tracking problem of two different types of unmanned underwater vehicle. Finally, simulation results illustrate the performance of the proposed controller.

Probabilistic modelling of the ultimate strength of ship plates with non-uniform corrosion

Abstract: This paper presents the results of a parametric study of probabilistic modelling of the ultimate strength of ship plates with non-uniform corrosion represented by random fields. The load-shortening behaviour of the plates with non-uniform reduction of thickness due to corrosion under longitudinal compression is obtained using a general-purpose nonlinear finite element analysis program. A nonlinear time-dependent corrosion model is used to define the probabilistic characteristics of the random fields based on corrosion data measured in plate elements at different locations of bulk carriers. Based on the probabilistic models derived by Monte Carlo simulation, equations to predict the mean and the 5 % characteristic value of the ultimate strength of plates with non-uniform corrosion are developed. Finally a regression equation is proposed to take into account the effect of non-uniform corrosion patterns in the predictions of the ultimate strength of plates with uniform corrosion.

Estimation and prediction of effective inflow velocity to propeller in waves

Abstract: A free running test using a container ship model clarified properties of effective inflow velocity to propellers in waves. The analysis assumes that thrust and torque vary keeping their relation to the effective inflow velocity as represented by open-water characteristics of a propeller in a steady calm water condition. Measurement in regular waves confirmed the variation of average values of the effective wake coefficient and ship speed depending on wavelength and wave encounter angle. Comparison with the longitudinal flow velocity measured at the sides of the propeller using an onboard vane-wheel current meters confirmed that one can estimate the effective inflow velocity based on thrust or torque data. Theoretical estimates in regular waves based on a strip method are provided and compared with the experimental data. A prediction model of the future inflow velocity is proposed to cope with a time delay of a propeller pitch controller for higher propeller efficiency in waves.

Application of a Support Vector Machine for Liquefaction Assessment

Abstract: This study presents a support vector machine (SVM)-based approach for predicting earthquake liquefaction. The SVM model database includes five indexes: earthquake magnitude, total overburden pressure, effective overburden pressure, qc values from cone penetration tests (CPT), and peak ground acceleration. The proposed model was trained and tested on a dataset comprising 466 field liquefaction performance records and CPT measurements. A grid search method with k-fold cross-validation was also used to verify the feasibility. Compared with an artificial neural network (ANN)-based method, the SVM-based method has the advantage of increased accuracy and simpler operation. Experimental results show that the proposed SVM approach can increase the classification accuracy rate to a standard of 98.71%.

PIV study of the effect of piston position on the in-cylinder swirling flow during the scavenging process in large two-stroke marine diesel engines

Abstract: A simplified model of a low speed large two-stroke marine diesel engine cylinder is developed The effect of piston position on the in-cylinder swirling flow during the scavenging process is studied using the stereoscopic particle image velocimetry technique The measurements are conducted at different cross-sectional planes along the cylinder length and at piston positions covering the air intake port by 0, 25, 50 and 75 % When the intake port is fully open, the tangential velocity profile is similar to a Burgers vortex, whereas the axial velocity has a wake-like profile Due to internal wall friction, the swirl decays downstream, and the size of the vortex core increases For increasing port closures, the tangential velocity profile changes from a Burgers vortex to a forced vortex, and the axial velocity changes correspondingly from a wake-like profile to a jet-like profile For piston position with 75 % intake port closure, the jet-like axial velocity profile at a cross-sectional plane close to the intake port changes back to a wake-like profile at the adjacent downstream cross-sectional plane This is characteristic of a vortex breakdown The non-dimensional velocity profiles show no significant variation with the variation in Reynolds number

Ship underwater noise assessment by the acoustic analogy, part III: measurements versus numerical predictions on a full-scale ship

Abstract: The acoustic analogy represents a powerful and versatile approach, able to numerically predict the noise generated by a body moving in a fluid. It is widely used to provide essential indications about the aeroacoustic behavior of aircraft and helicopters (even at a design stage) and, eventually, to pursue effective strategies aimed at desirable reduction and/or control of noise. Nevertheless, applications in the area of hydroacoustics and in the prediction of ship underwater noise are very rare. In this paper, the potential of the acoustic analogy is directly tested on a large ferry, for which a measurement campaign at sea was performed. In spite of the complexity of the tested configuration [the ship mounts two contracted and loaded tip (CLT) propellers located ahead of two rudders, and its hull is characterized by a rather elongated skeg] and the many variables not taken into account in the numerical simulation (such as the contribution from machinery noise and the probable occurrence of tip vortex cavitation), the agreement between the measured and computed noise spectra is quite satisfactory. The analysis suggests many interesting features of the ship hydroacoustic field: the dominant role played by nonlinear sources far from the body and the relevance of scattering effects from the hull surface. Furthermore, the scattered pressure seems to contribute to alter the frequency content of the resulting signatures with respect to the blade passage frequencies. Finally, an overview of future developments and applications of this numerical approach for marine/maritime problems is presented.

Investigation of water depth and basin wall effects on KVLCC2 in manoeuvring motion using viscous-flow calculations

Abstract: The objective of the NATO AVT-161 working group is to assess the capability of computational tools to aid in the design of air, land and sea vehicles. For sea vehicles, a study has been initiated to validate tools that can be used to simulate the manoeuvrability or seakeeping characteristics of ships. This article is part of the work concentrating on manoeuvring in shallow water. As benchmark case for the work, the KVLCC2 tanker from MOERI was selected. At INSEAN, captive PMM manoeuvring tests were conducted with a scale model of the vessel for various water depths. Several partners in the AVT group have conducted RANS calculations for a selected set of manoeuvring conditions and water depths for the bare hull. Each partner was asked to use their best practice and own tools to prepare the computations and run their flow codes. Specific instructions on the post-processing were given such that the results could be compared easily. The present article discusses these results. Detailed descriptions of the approach, assumptions, and verification and validation studies are given. Comparisons are made between the computational results and with the experiments. Furthermore, flow features are discussed.

An experimental investigation by towing tank on VIV of a long flexible cylinder for deepwater riser application

Abstract: In this study, the dynamic response of a vertical flexible cylinder vibrating at low mode numbers with combined x−y motion was investigated in a towing tank. The uniform flow was simulated by towing the flexible cylinder along the tank in still water; therefore, the turbulence intensity of the free flow was negligible in obtaining more reliable results. A lower branch of dominant frequencies with micro vibration amplitude was found in both cross-flow and in-line directions. This justifiable discrepancy was likely caused by an initial lock-in. The maximum attainable amplitude, modal analysis and x−y trajectory in cross-flow and in-line directions are reported here and compared with previous literature, along with some good agreements and different observations that were obtained from the study. Drag and lift coefficients are also evaluated by making use of a generalized integral transform technique approach, yielding an alternative method to study fluid force acting upon a flexible cylinder.

Computational fluid dynamics (CFD) prediction of bank effects including verification and validation

Abstract: Restricted waters impose significant effects on ship navigation. In particular, with the presence of a side bank in the vicinity of the hull, the flow is greatly complicated. Additional hydrodynamic forces and moments act on the hull, thus changing the ship's maneuverability. In this paper, computational fluid dynamics methods are utilized for investigating the bank effects on a tanker hull. The tanker moves straight ahead at a low speed in two canals, characterized by surface piercing and sloping banks. For varying water depth and ship-to-bank distance, the sinkage and trim, as well as the viscous hydrodynamic forces on the hull, are predicted by a steady state Reynolds averaged Navier–Stokes solver with the double model approximation to simulate the flat free surface. A potential flow method is also applied to evaluate the effect of waves and viscosity on the solutions. The focus is placed on verification and validation based on a grid convergence study and comparisons with experimental data. There is also an exploration of the modeling errors in the numerical method.

Planning vessel air emission regulations compliance under uncertainty

Abstract: In this paper we consider the reduction of air emissions from vessels when uncertainty is taken into account. Uncertainty in the reduction effects of the different existing air emission controls is currently high and makes their selection for vessel emission regulations compliance a challenging process. We develop a two-stage stochastic optimization model that addresses this uncertainty. The model’s objective is to plan the installation of air emission controls over a specified time horizon for a vessel to comply in the most cost-efficient way with the air emission regulations. The uncertain reduction effects of the controls are modelled by a set of scenarios. The approach is applied to a case study with real data. The solution exposes the important impact of uncertainty on this problem, especially on the SO X reduction, while the CO2 reduction plan seems in this case not affected by uncertainty.

Numerical analysis of ducted propeller performance under open water test condition

Abstract: This paper investigates the open water performance of the Ka-series propellers at various pitch and expanded area ratios in combination with the 19A duct by employing the panel method panMARE and the RANSE code ANSYS-CFX. An efficient method, Caly, is developed in order to generate the 3D-geometry and the surface numerical grid of the ducted propellers. Caly can be coupled with ANSYS-TurboGrid to automatically produce 3D-grids for the RANSE solver. The numerical results are compared with published experimental data and the flow details are concluded and compared. The influences that the grid resolution, the panel arrangements of duct and blade, and the flow in gap between inside wall of the duct and blade tip on the numerical results are studied. Grids verification, turbulence model dependency analysis and Reynolds number scantling are also discussed.

Numerical investigation on the ultimate strength of stiffened cylindrical shells considering residual stresses and shakedown

Abstract: In this paper, the effects of residual stresses on the ultimate strength of stiffened cylinders are numerically investigated with an emphasis on shakedown which might occur during the service of these structures Residual stresses caused by two types of actions, namely, cold bending and welding, are simulated with simplified approaches in numerical analysis Cold bending stresses are simulated by simulating cold rolling and elastic springback until the desired curvature for cylindrical shell is obtained Welding is simulated by applying cooling down to a certain temperature on the elements adjacent to stiffener-shell joints to obtain weld-shrinkage with realistic magnitudes Six small-scale externally pressurized ring-stiffened cylinder models are utilized to evaluate the appropriateness of the method for inclusion of welding residual stresses in numerical analysis by comparing the experimental and numerical results Ultimate strength analyses are then performed for a reference ring-stiffened cylinder model under radial pressure and stringer-stiffened cylinder under axial loading To assess the effect of shakedown, after applying cyclic compressive loading to the ring-stiffened cylinder model, the level of stress relief and the change in the ultimate strength are evaluated

On the probability of underwater glider loss due to collision with a ship

Abstract: The demonstrated utility of underwater gliders as measurement platforms for the open ocean has sparked a growing interest in operating them in shallow coastal areas too. Underwater gliders face additional challenges in this environment, such as strong (tidal) currents and high shipping intensity. This work focuses on the probability of losing a glider through a collision with a ship. A ship density map is constructed for the German Bight from observed ship movements derived from automatic identification system data. A simple probability model is developed to convert ship densities into collision probabilities. More realistic—but also more computationally expensive—Monte Carlo simulations were carried out for verification. This model can be used to generate geographic maps showing the probability of glider loss due to collisions. Such maps are useful when planning glider missions. The method developed herein is also applicable to other types of AUVs.

Black-box modeling of ship manoeuvring motion based on feed-forward neural network with Chebyshev orthogonal basis function

Abstract: Based on polynomial interpolation and approximation theory, a novel feed-forward neural network, the feed-forward neural network with Chebyshev orthogonal basis function, is proposed for black-box modeling of ship manoeuvring motion. The neural model adopts a three-layer structure, in which the hidden layer neurons are activated by a group of Chebyshev orthogonal polynomial activation functions and the other two layers’ neurons use identity mapping as activation functions. Weight update formulas are derived by employing the standard back-propagation (BP) training method. With the simulated 15o/15o zigzag test data as input and calculated values of the hydrodynamic forces and moment as output, the feed-forward neural network with Chebyshev orthogonal basis function and the BP neural network are applied to identify the nonlinear functions in the nonlinear hydrodynamic model of ship manoeuvring motion. With the simulated 20o/20o zigzag test data and 35o turning test data as input, the hydrodynamic forces and moment are predicted by using the identified nonlinear functions. Comparison between the calculated and predicted hydrodynamic forces and moment shows that the feed-forward neural network with Chebyshev orthogonal basis function is superior to the BP neural network in identifying the nonlinear functions of the nonlinear hydrodynamic model of ship manoeuvring motion and is an effective method to conduct the black-box modeling of ship manoeuvring motion.

Vortex-induced vibration (VIV) dynamics of a tensioned flexible cylinder subjected to uniform cross-flow

Abstract: This paper presents the experimental results of a study on the effects of axial applied tension on the vibration amplitude, the suppression of vibration, hydrodynamic force coefficients and in-line (IL) and cross-flow (CF) frequency responses during vortex-induced vibration of a horizontally mounted flexible cylinder with a low mass ratio (cylinder’s mass/mass of displaced water), low bending-stiffness, and high aspect ratio (length/diameter 200) in the subcritical Reynolds number regime (Re = 1000–16000). The effect of tension is studied by applying four different tensions. It was revealed that higher applied tensions, which reduce the vibration amplitude, could significantly raise the hydrodynamic lift force coefficient. In addition, higher applied tensions generate narrower lock-in bandwidths. After the highest vibration amplitude and during the region of lower vibration amplitudes, within the first lock-in region (in the first mode of vibration), power spectral densities show broad bandwidth, while within other regions and higher modes they appear narrow-banded. The ratio of the dominant IL to CF frequency is approximately equal to 2.0, except for the lower reduced velocities, where the ratio values reach 3.83 for the highest tension accompanied by widening of the region in which this ratio is over 2.0. This ratio is 2.76 for the lowest applied tension with a narrower region.

Solving Inhomogeneous Problems by Singular Boundary Method

Abstract: This study makes the first attempt to extend the singular boundary method (SBM) to inhomogeneous problems in conjunction with the dual reciprocity method (DRM). The SBM is a new boundary-type meshless method and utilizes the fundamental solution to calculate the homogeneous solution of the governing equation of interest, where the inverse interpolation technique is designed to evaluate the origin intensity factor while overcoming the singularity of the fundamental solution at the origin. In this study, the DRM is employed to evaluate the particular solution of Poisson equation with multiquadratic functions. The efficiency and accuracy of the proposed SBM-DRM scheme are tested to the three benchmark inhomogeneous Poisson problems. We also demonstrate the stability of the SBM-DRM scheme in dealing with noisy boundary data.

The Influence of Mixture Variables for the Alkali-Activated Slag Concrete on the Properties of Concrete

Abstract: In this study, the influence of three mixture variables named Sand/Aggregate ratio, Liquid/Binder ratio and Paste/Aggregate ratio on the concrete properties were studied. The properties of fresh concrete including the slump, air content and unit weight were examined. In addition, the mechanical properties such as the compressive strength, elastic modulus and splitting tensile strength were studied. Results showed that the alkali-activated slag concrete has superior strength. The 28-day compressive strength can reach 80% of the 90-day compressive strength. In addition, the influence of the Liquid/Binder ratio on the 28-day compressive strength is not as apparent as the water/cement ratio is for the ordinary Portland cement concrete. The trends of influences on the concrete properties for these three mixture variables are similar to those for the ordinary Portland cement concrete. It means that the experiences for making the ordinary Portland cement concrete should be able to be used for the alkali-activated slag concrete. This paper also provides substantial fresh-concrete and mechanical properties results for future development of the alkali-activated slag concrete mix design.

Carbonation service life prediction of existing concrete viaduct/bridge using time-dependent reliability analysis

Abstract: This paper examines the predicted carbonation life of an existing concrete viaduct/bridge in the atmospheric environment based on probability and reliability indices. The probability is dependent upon the carbonation rate, carbonation remainder, concrete quality, and concrete cover. The carbonation life is defined as the service life of reinforced concrete (RC) or prestressed concrete (PC) structure at the beginning of time of steel corrosion when concrete cover surfers from carbonation and loses the protection function to steel. The carbonation life is equivalent to the initiation time of corrosion of reinforcement. Both the Chorng-ching viaduct and Wannfwu bridge were offered as illustrative examples for verifying the analytical method and carbonation life prediction. Thepredicted carbonation life results for the Chorng-ching viaduct and Wann-fwu bridge are 55 and 55, 40 and 17, and 18 and 0 years at βc = 0, 0.5, and 1.25 reliability indices, respectively. The results show that both structures are serviceable and reliable comparing the initiation time calculated using Fick's second law, Guirguis, and AJMF methods. The results can provide a basis for repair, strengthening, and demolition of existing RC and PC viaducts or bridges.

Purification and characterization of acidic protease from aspergillus oryzae bcrc 30118

Abstract: The acidic protease was purified from 4-day cultivation of Aspergillus oryzae BCRC 30118 by DEAE Sephacel and Sephacryl S-200 HR chromatographs. The specific activity, yield and purification fold were 117.62 kU/mg, 15.1% and 6.6, respectively. The molecular weight (M) was 41.0 kDa, while the optimal pH and temperature were 3.0 and 60°C, respectively. It was stable at pH 3.0-6.0 and 4-35°C. However, it was inhibited by Fe^2+, Hg^2+, Fe^3+ and pepstatin A, and slightly by leupeptin and TPCK. According to substrate specificity and inhibitor study, it was a cysteine protease with activation energy of 37.5 kcal/mol. Its Km, Vmax, Kcat and Kcat/Km for the hydrolysis of hemoglobin were 0.12 mM, 14.29 μmol/min, 14.55 sec^(-1) and 125.80 (sec^(-1) mM^(-1)), respectively.

Bayesian-network-based hydro-power fault diagnosis system development by fault tree transformation

Abstract: Currently, fault diagnosis of reservoir facilities relies mostly on check-list evaluation. The results and qualities of evaluation are limited by experience and ability of the evaluators, which may not achieve the goal of systematic assessment in a consistent manner. To overcome the limitation of the traditional approach, this research develops a fault diagnosis and evaluation system for reservoir facility by utilizing multi-state Fault-Tree Analysis (FTA) technique, in conjunction with Bayesian Networks (BN) which incorporate expert experiences through lateral linkages among BN nodes and weighting factors. The system has been used to analyze and verify against three hydro-power systems currently in operation. It was found that through BN analysis the fault trend is consistent to that from historical data analysis via Weibull distribution. This indicates that the transformation of a multi-state Fault-Tree (FT) and BN is reasonable and practical. Based upon the analysis of BN by inputting prior information of the hydro-power systems, the probabilities of fault occurrences are effectively computed based on which proper preventive maintenance strategies can be established.

Free and forced vibration analyses of ship structures using the finite element method

Abstract: With increases in ship size and speed, shipboard vibration becomes a significant concern in the design and construction of vessels. Excessive ship vibration is to be avoided for passenger comfort and crew habitability. In addition to the undesired effects on humans, excessive ship vibration may result in the fatigue failure of local structural members or malfunctioning of machinery and equipment. The propeller induces fluctuating pressure on the surface of the hull, which induces vibration in the hull structure. These pressure pulses acting on the ship hull surface above the propeller are the predominant factor for vibrations of ship structures are taken as excitation forces for forced vibration analysis. Ship structures are complex and may be analyzed after idealization of the structure. Several simplifying assumptions are made in the finite element idealization of the hull structure. In this study, a three-dimensional finite element model representing the entire ship hull, including the deckhouse and machinery propulsion system, has been developed using solid modeling software for local and global vibration analyses. Vibration analyses have been conducted under two conditions: free–free (dry) and in-water (wet). The wet analysis has been implemented using acoustic elements. The total damping associated with overall ship hull structure vibration has been considered as a combination of the several damping components. As a result of the global ship free vibration analysis, global natural frequencies and mode shapes have been determined. Moreover, the responses of local ship structures have been determined as a result of the propeller-induced forced vibration analysis.

An analytical investigation of two-dimensional and three-dimensional biplanes operating in the vicinity of a free surface

Abstract: In the present article, the classical two- and three-dimensional lifting theories are generalized to the biplane operating in proximity to a free surface. The singularity distribution method is employed to calculate the lifting force for a two-dimensional biplane subjected to wing-in-ground effect in the vicinity of a free surface, and the three-dimensional correction is carried out by the aid of the Prandtl lifting line theory. The essential techniques lie in finding the three-dimensional Green’s function for the system of horseshoe vortices operating above a free surface and ensuring numerical implementation. Extensive numerical examples are carried out to show the lift coefficient for the two- and three-dimensional biplanes in the vicinity of a free surface with the variation of the clearance-to-chord ratio and the height-to-chord ratio. Incidentally, the induced (inviscid) drag coefficients as well as the lift-to-drag ratio for a three-dimensional biplane are also computed. Good agreement can be found among results obtained from this study and the experiment.

The Correlation between Air-borne Salt and Chlorides Cumulated on Concrete Surface in the Marine Atmosphere Zone in North Taiwan

Abstract: In this study, the improved Japanese salt sampler was adopted for the air-borne salt sampling tests in coastal areas of northern Taiwan. Thirty-five collection stations were set up in the northern coastal areas to collect air-borne salt data monthly from 2006 to 2009. As the exposure of structures in the natural environment, the chloride on the concrete surface of RC structures would be washed away by the precipitation. Therefore, a two-phase collection method was used to get the total air-borne salt ”Cair” and the adhesive air-borne salt ”Cadh”. The statistic results showed that the percentage of Cadh/Cair has a high correlation with the volume of effective precipitation. Conclusively, the concentration of chloride ion on the concrete surface can be inferred a linear empirical formula according to the regional climatic characters to indicate the total air-borne salt and the adhesive air-borne salt on concrete surface respectively.

Model experiment reproducing an incident of fast ferry

Abstract: A model scale experiment at a new basin reproduced a phenomenon occurring for a fast ferry; large roll motion and subsequent cargo shift in a quartering sea. Wave generators surrounding the whole periphery of the basin realized a designated directional sea. A carriage system tracked a free-running model ship and a movable weight simulated the cargo shift. Measuring the directional wave field in the basin confirmed the all-around wave generator successfully reproduced the intended wave field that was estimated for the location and the time of the incident. The encounter wave spectrum analyzed using measured data agree well with the theoretically predicted one. The reproduced ship motion, triggered by a small concentrating wave, tells how the ship responded in the successive large quartering waves and the validity of the procedure to reproduce the incident. Repeated measurements of the model ship’s extreme motion confirm a high repeatability of the experiment.

Optimization of shipyard space allocation and scheduling using a heuristic algorithm

Abstract: In this article we describe the development of a tool that allows planners to efficiently and effectively plan space within valuable areas of a shipyard. Traditionally, space is considered as resource; however, it is difficult to accurately account for and plan its consumption with the currently available planning software’s. The spatial scheduling tool described in this article can be used by planners to manually or automatically reserve space within the shipyard for construction of large blocks over the entire erection period of the ship. The software is coupled with a heuristic optimization solver inspired by an algorithm used for "3D bin-packing problems." The result is the ability to efficiently generate and compare multiple space allocation alternatives in a reduced time with the ultimate goal of maintaining the critical ship erection schedule. A better solution than manual or semi-automatic allocation of blocks can be obtained through the optimization module.

Experimental and numerical study of the effects of heave plate on the motion of a new deep draft multi-spar platform

Abstract: The heave motion of a floating structure is critical, as a favorable heave characteristic permits dry tree systems, amongst other benefits. The heave response can be suppressed by installing heave plates. However, the associated hydrodynamic effects, which include viscous damping and added mass, are very complicated. Moreover, there are limited experimental investigations to understand the heave plate effects on actual platform designs. This paper aims to study the abovementioned issue based on a novel deep draft multi-spar (DDMS) platform, for four different configurations (with/without upper and lower heave plates). A set of experiments (free decay, regular and irregular wave tests) are conducted, and compared with time domain and linearized frequency domain analyses. Amongst other things, the investigations and discussions include the added mass and damping coefficients for the platform and heave plates, comparison of experimental and numerical results, and the influence of the heave plates on the surge, heave and pitch motions.