Main Deck Research Articles

Operational modal analysis of a catamaran using a limited set of accelerometers

ABSTRACT Experimental modal analysis tests were performed during the catamaran’s normal operation and using only 06 accelerometers on the main deck. This work focuses on estimating and comparing modal parameters using experimental (time and frequency domain techniques) and numerical analyses. Ten (10) experimental natural frequencies and (incomplete) mode shapes were estimated, in the range of 4–50 Hz, using Balance Realisation, Frequency-Spatial Domain Decomposition and Enhanced Frequency Domain Decomposition techniques. As only 06 accelerometers had been used for modal testing, a finite element (FE) model was used to augment the spatial resolution of the experimental mode shapes. Experimental and numerical natural frequencies showed good correlation with only the 3rd bending mode shape exhibiting 13.5% deviation. It was concluded that the experimental techniques can: (i) identify natural frequencies in the presence of harmonic components and, (ii) estimate mode shapes using a limited set of accelerometers, aided by a FE model.

Load-Carrying Capacity of Bailey Bridge in Civil Applications

The paper presents an extensive study aimed to determine the applicability of the demountable Bailey bridge (BB) system on construction sites or in other temporary conditions while meeting the regulations for the design and assessment of steel bridges. The analysis is focused on whether and to what extent the BB system with spans between 12 and 36 m is usable for on-site freight transport with conventional lorries with a total weight of up to 22–28 tons. At the same time, the BB system within these spans should be utilized for construction vehicles with a total weight of up to 32–40 tons. To calculate the load-carrying capacity, spatial numerical models were analysed using FEM and procedures of actual design codes were utilized. In the case of the main girders, analysis is focused on the out-of-plane stability of their compressed chords. Recommendations for the use of this bridge system in different arrangements of the main girder and bridge deck are then summarized and discussed.

Investigations of air cushion effect on the slamming load acting on trimaran cross deck during water entry

The cross-sectional shape of a trimaran is more complex than that of a monohull and consists of a main hull, side hull, and cross deck. When a trimaran moves downward in a severe sea state, air trapped between the main and side hulls forms a cushion under the cross deck, and this has a significant effect on the slamming pressure on the structure. In this work, laboratory experiments are performed on a scale-model trimaran section to gain deeper insight into the dynamic interactions between hull structure, water, and air and to investigate the effects of the air cushion on slamming loads. The air–water–structure interactions are investigated through particle image velocimetry, the accelerations of the ship section are measured by inertial motion units, and the slamming loads are obtained from pressure sensors. To enhance the influence of the air cushion, two plates are installed, one on each side of the ship section, to restrain the escape of air during the experiments. In addition, to eliminate the influence of the air cushion, numerical simulations of water entry are conducted with air replaced by hydrogen, whose density is much lower. The experimental and numerical results confirm that the air cushion under the cross deck can significantly reduce the slamming pressure.

Comparative analysis between co-curing and adhesive bonding of glass-epoxy composite laminates and AA5083 aluminium sheets for Maritime application: effect of surface pattern

Co-curing and secondary bonding are effective techniques to join not only composite structures but also dissimilar materials such as metals and composites whose combined use is increasing in several industrials fields where lightness is strategic to reduce fuel consumption and, consequently, greenhouse emissions (i.e. transports). In particular, the aim of this research is to investigate the effect of different patterns both on co-cured glass-epoxy composite/aluminium joints and on the same joints made with adhesive as third material to bond the aluminium and the laminate preliminary realized by vacuum infusion. These configurations and the materials to join were used typically in maritime applications, i.e. the composite can be used for the main deck and the aluminium for the superstructures. The patterns were made with a controlled milling machine equipped with an engraver with a 45° cutting angle. In both cases, the results showed that the mechanical treatment affected the mechanical properties, i.e. the joint with the best pattern had a higher mechanical strength than the joint where the surface was not treated. Moreover, this influence was more significant for co-curing. Finally, a statistical analysis was performed to evaluate the significance of both the selected factors: i.e. joining process and treatment, and their interaction. The novelty of the work lay both in the materials used to make the joints, which are employed in marine applications, in the use of macroscopic pattern to treat the metal surface for co-cured joints, and in the manufacturing process, which used a CNC milling machine.

A STUDY ON THE AIR RESISTANCE OF AN LNG TANKER BY EMPIRICAL AND CFD METHOD

Air resistance has a significant effazqect on ships with large main deck structures such as container ships, liquefied natural gas (LNG) tanker, and large cruise ships. This paper presents a method to determine the air resistance for LNG tankers model by doing the experimental test in the wind tunnel. In addition, the author also calculates the air resistance by computational fluid (CFD) and compares the calculated results with experimental results.

Modification of the Main Deck of Pc40 Using the Sandwich Plate System to Support Marine Defense Operations

Indonesia is the largest archipelagic maritime country in the world, it should strengthen its ability to secure a very wide territorial waters, in order to ensure the security and safety of shipping in Indonesian jurisdictional. PC 40 ship is a reliable TNI-AL patrol ship with relatively small dimensions and will be easy to operate in archipelagic areas. In general, structural construction on conventional PC 40 ships, along with the times, the Sandwich Plate System material has been found to have characteristics that provide advantages in terms of strength and a simpler structure compared to conventional construction. the construction structure uses conventional aluminum using the Sandwich Plate System material with an aluminum-elastomer-aluminum configuration in the flat plate structure on the main deck of the TNI-AL PC 40 Ship. Analysis based on finite element on main deck construction with load loading. From the simulation results, the maximum stress for aluminum material is 17 MPa using stiffeners, while the construction with sandwich plate material system produces a maximum stress of 15 MPa reducing the use of 15 stiffeners, with maximum deformation for conventional aluminum.

Modification of the Main Deck of Pc40 Using the Sandwich Plate System to Support Marine Defense Operations

Indonesia is the largest archipelagic maritime country in the world, it should strengthen its ability to secure a very wide territorial waters, in order to ensure the security and safety of shipping in Indonesian jurisdictional. PC 40 ship is a reliable TNI-AL patrol ship with relatively small dimensions and will be easy to operate in archipelagic areas. In general, structural construction on conventional PC 40 ships, along with the times, the Sandwich Plate System material has been found to have characteristics that provide advantages in terms of strength and a simpler structure compared to conventional construction. the construction structure uses conventional aluminum using the Sandwich Plate System material with an aluminum-elastomer-aluminum configuration in the flat plate structure on the main deck of the TNI-AL PC 40 Ship. Analysis based on finite element on main deck construction with load loading. From the simulation results, the maximum stress for aluminum material is 17 MPa using stiffeners, while the construction with sandwich plate material system produces a maximum stress of 15 MPa reducing the use of 15 stiffeners, with maximum deformation for conventional aluminum.

Optimization of Space Under Main Deck on Landing Craft Utility (LCU) Ships to Increase Loading Capacity

Optimization of Space Under Main Deck on Landing Craft Utility (LCU) Ships to Increase Loading Capacity

Two new bridges over the River Vardar in Skopje

This paper presents some aspects of the design of two new bridges over the River Vardar in Skopje. "Mihajlo Apostolski" is an integral bridge, consisting of two separate structures (22.05 + 50.50 + 21.05 m = 93.6 m length and 15.3 m width). The bridge deck is made up of a two-cell prestressed cast-in-situ box girder with a parabolically variable cross section. The abutments and the piers are wall-shaped and supported on single and double row piles, respectively. The side spans, together with the approaching structures, were proposed to be built on traditional scaffolding, while the middle span over the minor riverbed was built with a free cantilever method. The extradosed bridge at Ljubljanska Street is 27.5 + 56 + 27.5 m = 111 m long and 24.1m wide. The ribbed deck (two post-tensioned main girders, cross girders, and deck slab) is supported from above by 32 parallel stay cables. The 12.6 m high pylons are located at the intermediate supports. In the base, the four piers have a rectangular cross section that has been rotated 45 degrees. The superstructure is supported by pot bearings. A deep foundation on piles was chosen. Cast-in-place construction of the superstructure was foreseen. The design of the bridges was done according to Eurocodes and respecting the fib and PTI recommendations. Detailed numerical analysis was carried out in the FEM software SOFiSTiK and additional auxiliary software.

Endurance Time Analysis of Bridges with Unbonded Prestressed Piers

The endurance time method (ETM) is a novel dynamic seismic analysis, which employs intensified artificial earthquakes as the input. This method can ensure both the structural dynamic effect and the computation efficiency when conducting the seismic evaluation of complex structural systems. Based on these advantages, this study investigated the applicability of ETM in the self-centering bridges incorporating prestressed concrete-filled steel tube (CFST) piers. A 3D finite-element model of a typical four span continuous-beam bridge which adopted prestressed CFST piers was established by OpenSees software. Compared with the incremental dynamic analysis (IDA) results, the feasibility of ETM to predict the seismic response of self-centering bridges was validated. Also, the effect of prestressing force in piers on the seismic performance of self-centering bridge systems was studied by ETM. Numerical results show that ETM can be used in the seismic evaluation of bridges with prestressed self-centering piers. The seismic response, such as PT force and residual displacement, can be predicted using this method. In addition, the influence of prestressing force on the seismic response of bridges is related to the type of bearings and the intensity of earthquakes. For the superstructure, the displacement of the main deck can be reduced by increasing the prestressing force, but the shear force of fixed bearings increases accordingly. For the substructure, the piers with sliding bearings are less influenced by the prestressing force, while the seismic internal force of fixed piers increases with the occurrence of prestressing force. Therefore, it is necessary to comprehensively consider the structural system arrangement and seismic basic intensity of the site during the seismic design of such bridges.

Experimental Study on the Spanwise Correlation of Vortex-Induced Force Using Large-Scale Section Model

To investigate the spanwise correlation of vortex-induced forces (VIF) of a typical section of a streamlined box girder, wind tunnel tests of simultaneous measurement of force and displacement responses of a sectional model were conducted in a smooth flow. The spanwise correlation of VIF and pressure coefficients on the measurement points of an oscillating main deck were analyzed in both the time domain and frequency domain, respectively. The research results indicated that the spanwise correlation of VIF and pressure coefficients on the measurement points were related to the amplitudes of vortex-induced vibration (VIV), both of them weakened with the increase of spanwise distance; the maximum value of spanwise correlation coefficient is situated at the ascending stage of the lock-in region, rather than at the extreme amplitude point. The amplitudes of VIV showed different impacts on the spanwise correlation of pressure coefficients on the measurement points of the upper and lower surfaces, for which the maximum value of the spanwise correlation coefficients is located at the extreme amplitude point and the ascending stage of the lock-in region, respectively. Furthermore, the spanwise correlation of the pressure coefficients decreases continually from the upstream to downstream of the main deck; large coherence of vortex-induced forces and pressure appears around the frequency of vortex shedding, and the coherence of VIF and pressure becomes smaller with the increase in the spanwise distance.

An Approach to Ship Deck Arrangement Optimization Problem Using an Improved Multiobjective Hybrid Genetic Algorithm

Ship deck arrangement design is about determining the positions and dimensions of arranged objects. This paper presents the mathematical model for the ship deck arrangement optimization problem statement and how the individual’s objective and constraint functions are computed. Moreover, an improved multiobjective hybrid genetic algorithm is redesigned to solve this complex nondeterministic problem and generate a set of diverse and rational deck arrangements in the early stage of ship design. An adaptive crossover operator and a novel topological replace operator invoked in this algorithm are described. Finally, the proposed algorithm is tested on a main deck arrangement optimization of an underwater detection ship. In the validation tests, the proposed algorithm is compared to the standard NSGA-II to determine its ability to produce a set of diverse and rational deck arrangements. Subsequently, the performance tests are used to determine the ability of the algorithm to work with the highly constrained arrangement problems and the efficiency of the adaptive crossover and topological replace operators.

Ferry M/V Kramer noise mitigation

The Motor Vessel (M/V) Edward V. Kramer is an aluminum vessel that operates as a small passenger ferry, which is owned and operated by the Department of Homeland Security (DHS) and used to transport DHS personnel and materials to Plum Island, NY. It was placed in service in 2018 and right from the start the sound levels inside the Main Deck compartment were found to be excessive. The original vessel specification included a noise limit of 75 dBA in the Main Deck Passenger Lounge and measured levels were as high as 87 dBA. A ship survey of sound and vibration was performed. Noise predictions to determine the controlling sound paths was also performed based on engine sound and vibration source levels. Recommendations for mitigation were presented and carried out by another shipyard. Mitigation included vibration isolation of the main engines and sound attenuation improvements to the Main Deck Passenger Lounge. After completion of the modifications, another survey was performed in 2021 and results show a reduction by as much as 11 dB in the Main Deck Passenger lounge. Noise estimation methods and details on the noise control treatments are given in the paper.

Improvement of the Ship Emergency Response Procedure in Case of Collision Accident Considering Crack Propagation during Salvage Period

Specialized procedures to help in the emergency response situations following ship accidents have been under development by the Classification Societies. Such procedures consider the hull-girder collapse as the most important failure mode, without the possibility of crack propagation caused by fluctuating wave loads. In the present study, the fatigue crack propagation in the main deck of the oil tanker damaged in collision during salvage is investigated. The shape and size of the damage are modelled using the realistic bow shape of the striking ship and historical data of ship accidents. The stress intensity factor (SIF) across the main deck of the struck ship is calculated numerically and by the method based on the available experimental results of the crack propagation in the stiffened panel. Fluctuating wave–induced stresses in short-term sea conditions during salvage are obtained by Monte Carlo simulation (MC) based on Rayleigh distribution. Cycle-by-cycle crack propagation is calculated using Paris law. Many salvage simulations are performed to cover different possible time-histories of the fatigue loading. Results of the analysis are presented as histogram of the crack increase during salvage. Parametric analysis is performed to investigate the influence of the sea state severity, initial crack size, and towing duration on the final crack size. The proposed procedure can be considered as a part of a software tool for emergency response action during salvage of damaged ship.

Neptune's Spatial Brightness Temperature Variations from the VLA and ALMA

Abstract We present spatially resolved (0.″1–1.″0) radio maps of Neptune taken from the Very Large Array and Atacama Large Millimeter/submillimeter Array between 2015 and 2017. Combined, these observations probe from just below the main methane cloud deck at ∼1 bar down to the NH4SH cloud at ∼50 bar. Prominent latitudinal variations in the brightness temperature are seen across the disk. Depending on wavelength, the south polar region is 5–40 K brighter than the mid-latitudes and northern equatorial region. We use radiative transfer modeling coupled to Markov Chain Monte Carlo methods to retrieve H2S, NH3, and CH4 abundance profiles across the disk, though only strong constraints can be made for H2S. Below all cloud formation, the data are well fit by 53.8 − 13.4 + 18.9 × and 3.9 − 3.1 + 2.1 × protosolar enrichment in the H2S and NH3 abundances, respectively, assuming a dry adiabat. Models in which the radio-cold mid-latitudes and northern equatorial region are supersaturated in H2S are statistically favored over models following strict thermochemical equilibrium. H2S is more abundant at the equatorial region than at the poles, indicative of strong, persistent global circulation. Our results imply that Neptune's sulfur-to-nitrogen ratio exceeds unity, as H2S is more abundant than NH3 in every retrieval. The absence of NH3 above 50 bar can be explained either by partial dissolution of NH3 in an ionic ocean at GPa pressures or by a planet formation scenario in which hydrated clathrates preferentially delivered sulfur rather than nitrogen onto planetesimals, or a combination of these hypotheses.

Research on the dynamic buckling of a typical deck grillage structure subjected to in-plane impact Load

The dynamic buckling of the main deck grillage would result in the total collapse of the ship hull subjected to a far-filed underwater explosion. This dynamic buckling is mainly due to the dynamic moment of the ship hull when the ship hull experiences a sudden movement under impact load from the explosion. In order to investigate the ultimate strength of a typical deck grillage under quasi-static and dynamic in-plane compressive load, a structure model, in which the real constrained condition of the deck grillage was taken into consideration, was designed and manufactured. The quasi-static ultimate strength and damage mode of the deck grillage under in-plane compressive load was experimentally investigated. The Finite Element Method (FEM) was employed to predict the ultimate strength of the deck grillage subjected to quasi-static in-plane compressive load, and was validated by comparing the results from experimental tests and numerical simulations. In addition, the numerical simulations of dynamic buckling of the same model under in-plane impact load was performed, in which the influences of the load amplitude and the frequency of dynamic impact load, as well as the initial stress and deflection induced by wave load on the ultimate strength and failure mode were investigated. The results show that the dynamic buckling mode is quite different from the failure mode of the structure subjected to quasi-static in-plane compressive load. The displacements of deck edge in the vertical direction and the axial displacements are getting larger with the decrease of impact frequency. Besides, it is found that the dynamic buckling strength roughly linearly decreased with the increase of initial proportion of the static ultimate strength P0. The conclusions drawn from the researches of this paper would help better designing of the ship structure under impact loads.

Analysis of the Root Causes of Damage to the Edges of Tank Manholes on the Main Deck of Handy-Size Bulk Carriers.

This study analyzes the root causes of cracks in the deck plating around tank manholes. Four handy-size bulk carriers built in one shipyard were analyzed. In all cases, deck cracks were found near manholes, and the average time from the commencement of operation until the occurrence of cracks was 1356 days. Due to this short wear-life of the vessel’s structural material, the authors believed that it was unlikely to be caused by corrosion fatigue. The authors hypothesized that main decks cracked around manholes because of very poor-quality welded joints and poor-quality steel (large amounts of non-metallic impurities) used to make the manholes. In order to verify this hypothesis, on each of the vessels, material samples were collected from near the cracks and then examined thoroughly. Each sample was subjected to the macroscopic examination of the natural surfaces of cracks and their vicinity, microscopic examination of the material, mechanical property tests, and scanning electron microscope fractography for samples obtained after impact tests. The examination and test results were used to draw detailed conclusions for each case study. The general conclusions based on examination of the whole damage population validated the authors’ hypothesis that main decks cracked around manholes because of very poor-quality welded joints and poor-quality steel used to make the manholes.

Viaducto mixto en el acceso al Hospital Universitario Central de Asturias

El puente forma parte del nuevo enlace entre la AS-II y el Hospital Universitario Central deAsturias. Se trata de un puente pantalón de siete vanos y luz máxima 61.75 m en el troncoprincipal curvo al que se incorpora un ramal también curvo de dos vanos y luz máxima 48,00metros. La estructura presenta cuatro zonas:En los tres primeros vanos del tronco principal el tablero es de anchura 17.65 metros, compuestopor una viga cajón mixta con costillas a cada lado.En los dos primeros vanos del ramal el tablero está formado por una única viga cajón metálicacurva.Tras la confluencia de las losas de los dos cajones se desarrolla una zona de anchura variablehasta su convergencia a una sección constante de 21.30 metros. En esta zona la vinculacióntransversal de los cajones es potente, ya que se disponen cinco riostras transversales.Finalmente, la estructura continua con anchura constante de 21.30 metros hasta el estriboopuesto con sección con doble cajón.En la comunicación se comentarán los aspectos más singulares de la respuesta estructural delpuente, como el diseño de las costillas y riostras transversales, y el acoplamiento en la respuestade los dos cajones en la zona pantalón, así como los aspectos constructivos más significativos.

Crashworthiness characteristic of longitudinal deck structures against identified accidental action in marine environment: a study case of ship–bow collision

Rising demand for transportation safety during their operation has become public awareness these days which leads to massive development in navigation and mitigation technologies. However, accidents for various transportation modes, including ship, are still occurring despite this progress. The numbers of involved parameters make accidental phenomena in the maritime environment, namely collision to be the latest concern as its influence on remarkable casualties. This paper aims to analyze ship collision incident which involves cargo carrier and passenger vessel. Structural crashworthiness as the main subject accounting for accidental limit state design and safety assessment is performed using a finite element approach to observe both global and local behaviors of the target ship under the bow impact. Initial prediction indicates that major collision energy is dedicated to destroying the main deck and outer shell. The tendency of the force during the collision period explicitly hints that progressive failure on the deck will continue to take place even if the accidental limit is extended. The behavior of the local member/component of the target ship is also to be presented in the discussion.

CFD-based simulation of accidental fuel release from LNG-fuelled ships

ABSTRACT Liquefied natural gas (LNG) exhibits significant environmental advantages. However, the hazards of LNG-fuelled ships need to be investigated in their early design stages, particularly with regard to accidental fuel leakage. In this study, a hypothetical oil tanker model was used with a fuel gas supply system installed on the main deck; the objective was to establish a critical zone for natural gas dispersion. A probabilistic approach was applied to determine credible scenarios, and leak size, location, and direction were considered as parameters along with environmental parameters such as wind direction and speed. Computational fluid dynamics was used to present the critical zone in terms of the contours of the natural gas concentration. The simulation results indicated that the leak size and wind speed significantly influence the size of the critical zone.