Hull Segment Research Articles

Experimental study on the drop test on wet deck slamming for a SWATH segment model

Wet deck slamming is a serious issue for high-speed catamarans if the relative vertical motions are higher. In this study, a drop test on wet deck slamming is conducted for a small waterplane area twin hull segment model, and the vertical water-entry model test is performed under different drop heights and speeds. The slamming pressure under the wet deck and the acceleration are measured. The flow field is obtained through particle image velocimetry measurement. A high-speed camera observation during wet deck slamming shows that air is pressed into water, and a water–gas mixture is formed due to the air compressibility effect. The slamming pressure shows an oscillating property with multiple frequency components, which is due to the air cushion effect caused by the volume variation of the water–gas mixture and the acoustic wave oscillation with the air pocket. The effects of the drop height variation and the constant-drop speed on the slamming load are analyzed. The results show that the pressure peak appears during the demihull's bottom slamming and wet deck slamming. The acceleration time record produces two peaks, one for the demihull's bottom slamming and another for the wet deck slamming. In conclusion, the air cushion effect can reduce the wet deck slamming pressure.

Experimental determination of interaction between the radiation fields of Dragonfly's MMRTG and Titan's environment II: Gamma induced atmospheric conductivity

The apparatus described in part I of this investigation was filled with various blends of ultra high purity nitrogen and a mixture of 95% nitrogen/5% methane, simulating Titan's atmosphere with up to 50% relative methane humidity, as well as an Earth atmosphere for comparison, with a source of gamma rays suspended therein. Readings were taken from a plate immersed in the atmosphere at the top of the chamber connected to a conductivity probe, with the source at various distances from the plate. Gamma-induced conductivity was not found to be significant at a distance from the source equivalent to that on the surface of the hull segment on Dragonfly containing the radioisotope generator when gamma ray energies and field geometry were corrected for, however ion buildup in the experiment chamber indicated the possibility of similar buildup within the hull segment itself. The effect of methane in the atmosphere was statistically indeterminate, reflecting earlier simulation results, however molecular ions were shown more likely to be the predominant carriers of charge than the free electrons measured in the simulation.

Ultimate local strength of a submarine structure considering the influence of localized reduction of thickness

Commonly, failures that occur in a submarine's structure could be caused by the high external hydrostatic pressure which may first take it to an unstable condition influenced by its geometry. In these vessels, reduction of thickness can develop because of corrosion or similar causes, which leads to reduction of structure's strength. The objective of this work is to determine the ultimate load that a cylindrical part of a submarine structure can support, considering the influence of localized thickness reduction. For this purpose, firstly the ultimate response of a 50 cm steel square plate of 3 mm in thickness, intact and considering local thickness reduction was analyzed using experimental tests and numerical approach. Then, the ultimate response of a high strength steel cylinder is numerically analyzed, intact condition and with localized thickness reduction. For this analysis typical submarine hull segment including three circular frames is modelled with solid finite elements subjected to external pressure and axial load, simultaneously. Buckling occurs in the elastic range of the material and the circular plate thickness reduction considering a diameter of 78% of the space between frames and 30% of the thickness, reduces only in 6% the collapse external load on the cylinder.

Research on Lean Shipbuilding and Its Manufacturing Execution System

Abstract Based on the work breakdown structure theory, the lean shipbuilding method guided by intermediate products is proposed in this article. The hull segment task package is divided according to the content of the shipbuilding operation. Considering the constraints of resources and personnel at the production site, the scheduling strategy of the task package is formulated. Moreover, a virtual flow production system of the shipbuilding workshop is established. On this basis, a lean shipbuilding manufacturing execution system for small and medium-sized shipbuilding enterprises is developed to achieve lean production in a shipbuilding workshop. The application results indicate that implementation of the lean shipbuilding method and manufacturing execution system can significantly reduce the ship production cycle and the number of operators, as well as improve the production efficiency. Introduction In recent years, to resist strong international competition, manufacturers are under great pressure to develop products more efficiently and economically (Nam et al. 2016). The ship manufacturing industry, which faces fierce market competition, helps many nations’ economic systems (Rahman & Karim 2015). For example, the shipbuilding industry contributed over $37 billion of the Gross Domestic Product (GDP) to the U.S. economy in 2013 (MARAD 2015). Currently, China’s shipbuilding industry is in a downturn. If the shipbuilding enterprises want to survive and improve their competitiveness, they must reduce labor costs and shorten the production cycle. Lean production is a type of management philosophy born in Toyota Motors. One of the lean thinking goals is to eliminate waste, which can increase work satisfaction and turn waste into value. It should be emphasized that lean thinking must go beyond the company. In other words, lean thinking has to be employed from the product design to the set of activities delivered to the end customer (Barbosa 2014). Lean manufacturing technology focuses on eliminating all types of waste in the manufacturing process and reducing the lead time (Zhu et al. 2019).

A Knowledge Acquisition Method of Ship Coating Defects Based on IHQGA-RS

Coating defects are caused by a series of factors such as the improper operation of workers and the quality of the coating itself. At present, the coating process of all shipyards is inspected and recorded at a specific time after construction, which cannot prevent and control defects scientifically. As a result, coating quality decreases, and production costs increase. Therefore, this paper proposes a knowledge acquisition method based on a rough set (RS) optimized by an improved hybrid quantum genetic algorithm (IHQGA) to guide the ship-coating construction process. Firstly, the probability amplitude is determined according to the individual position of the population, and the adaptive value k is proposed to determine the rotation angle of the quantum gate. On this basis, the simulated annealing algorithm is combined to enhance the local search ability of the algorithm. Finally, the algorithm is applied to rough set attribute reduction to improve the efficiency and accuracy of rough set attribute reduction. The data of 600 painted examples of 210-KBC bulk carriers from a shipyard between 2015 and 2020 are randomly selected to test the knowledge acquisition method proposed in the paper and other knowledge acquisition methods. The results show that the IHQGA attribute approximate reduction algorithm proposed in this paper is the first to reach the optimal adaptation degree of 0.847, the average adaptation degree is better than other algorithms, and the average consumption time is about 10% less than different algorithms, so the IHQGA has more vital and more efficient seeking ability. The knowledge acquisition result based on the IHQGA optimization rough set has 20–50% fewer rules and 5–10% higher accuracy than other methods, and the industry experts have high recognition. The knowledge acquisition method of this paper is validated on a hull segment. The obtained results are consistent with the expert diagnosis results, indicating that the method proposed in this paper has certain practicability.

Analysis of Data Point Cloud Preprocessing and Feature Angle Detection Algorithm

Background: The two main stages are utilized for feature extraction, from which the first stage consists of a penalty weight to the neighbor graph’s edges. The edge penalty weights are minimized by the neighbor sub-graph extraction to produce the set of feature patterns. For noisy data, the second stage is helpful. Methodology: In order to realize the measurement of the geometric dimensions of the ship block, this paper uses the theory of computer vision and reverse engineering to obtain the data of the segmented- hull with the method of digitizing the physical parts based on the vision, and processes the data by using the relevant knowledge of reverse engineering. Result: The results show that the efficiency of the edge extraction algorithm based on mathematical morphology is 30% higher than that of the mesh generation method. An adaptive corner detection algorithm based on the edge can adaptively determine the size of the support area and accurately detect the corner position. Conclusion: According to the characteristics of the point cloud of ship hull segment data, an adaptive corner detection algorithm based on the edge is adopted to verify its feasibility.

Trajectory Clustering Of Segmented Field Operations Logistics Process

It has become a new research direction to use process mining technology to mine and analyze all kinds of data generated during shipbuilding. The classification of hull segments into different clusters according to some properties in advance can make the excavation results more specific. In this paper, the process examples in ship construction are divided into different clusters based on the cohesive hierarchical clustering algorithm. Firstly, this paper introduces the advantages and disadvantages of several main clustering algorithms, selects the clustering algorithm most suitable for segmented outfield logistics, establishes the mathematical model of segmented outfield logistics process trajectory clustering, and defines the appropriate feature vectors. Euclidean distance, Hamming distance, Jekard distance and cosine distance were used to calculate the similarity distance between process instances, and the concepts of chain, single chain and group average were added to select the appropriate similarity distance between clusters. An evaluation method of clustering results based on coutour coefficient is introducedwhich can effectively evaluate the clustering results of the logistics process trajectory during segmented remote operations. Finally, the feasibility and effectiveness of the proposed algorithm are verified by experiments.

Simulation and Optimization Scheme of Hull Segment Manufacturing Planning Management

Simulation and Optimization Scheme of Hull Segment Manufacturing Planning Management

Research on hull segment workshop scheduling based on simulated annealing genetic algorithm

Research on hull segment workshop scheduling based on simulated annealing genetic algorithm

MapReduce Based Parallel Bayesian Network for Manufacturing Quality Control

Increasing complexity of industrial products and manufacturing processes have challenged conventional statistics based quality management approaches in the circumstances of dynamic production. A Bayesian network and big data analytics integrated approach for manufacturing process quality analysis and control is proposed. Based on Hadoop distributed architecture and MapReduce parallel computing model, big volume and variety quality related data generated during the manufacturing process could be dealt with. Artificial intelligent algorithms, including Bayesian network learning, classification and reasoning, are embedded into the Reduce process. Relying on the ability of the Bayesian network in dealing with dynamic and uncertain problem and the parallel computing power of MapReduce, Bayesian network of impact factors on quality are built based on prior probability distribution and modified with posterior probability distribution. A case study on hull segment manufacturing precision management for ship and offshore platform building shows that computing speed accelerates almost directly proportionally to the increase of computing nodes. It is also proved that the proposed model is feasible for locating and reasoning of root causes, forecasting of manufacturing outcome, and intelligent decision for precision problem solving. The integration of bigdata analytics and BN method offers a whole new perspective in manufacturing quality control.

CFRP-Aluminium Structures Realized by Laser Beam Joining Process

Modern lightweight structures containing hybrid materials allow an improvement of the weight-specific properties. However, to exploit the potential as far as possible novel joint concepts are necessary, enabling an economic structure manufacturing. The DFG-researcher group Schwarz-Silber (FOR 1224) at the University of Bremen aims to explore and develop interface structures for advanced FRP-Al compounds. Considering textile, welding and casting techniques novel joint concepts are under development, in five interdisciplinary projects. Within their work the researcher group focuses on three concepts realizing the transition structures: the usage of wires (titanium), foils (titanium) and fibres (glass fibre) as transition elements between CFRP and aluminium. Typical examples for such hybrid structures can be found in products from the aerospace industry (e.g. hull segments), the car industry (e.g. CFRP roof structures), but also in general mechanical engineering (e.g. rotor blade elements). In this paper, the joint configuration based on titanium wires and a laser beam conduction welding process will be presented. As beam source a lamp pumped Nd:YAG laser (HL4006D) was used. First specimens obtained will be discussed with respect to their properties. It will be shown that the novel approach is in principle suitable to produce load-bearing CFRP-aluminium structures. The wire concept represents a parallel arrangement of miniaturized loop connections. It is characterized by joining a CF-Ti-textile to an aluminium sheet. A carbon fibre loop is threaded through a titanium wire loop by textile technologies on one side. On the side opposite to the CF, the titanium wire loops of the CF-Ti-textile are joined to an aluminium component by welding or casting. A double-sided laser beam heat conduction welding process was applied, for both concepts. During processing, the laser beam was travels along the aluminium edge. The titanium-aluminium structure is welded in two steps. During the first step (i.e. the first weld pass) the aluminium and titanium are heated by the defocused laser beam simultaneously on both sides. An aluminium melt pool is formed, supported by the action of gravity and a certain amount of pre-heating of the titanium-wire or the titanium-foils by the laser beam and by heat conduction through the aluminium melt pool. In the second, immediately subsequent step (i.e. the second weld pass), due to a pre-heating of the materials by the first pass and an increased heat transfer between both materials, a complete wetting of the titanium structures in the joining zone is achieved.

A Fast Convex Hull Algorithm of Planar Point Set

In this paper ,a new algorithm is proposed for improving speed of calculating convex hull of planar point set .The algorithm creates a square mesh to manage points ,when eliminating points which are obviously in convex hull ,selecting or eliminating of points can be converted to that of grid , work of calculation depends on points near edges of convex hull and density of grid but not the number of points ;at the meantime ,remainder points are sorted roughly .When calculating convex hull of remainder points ,a method is presented which can take advantage of order of remainder points ,it calculates boundaries of convex hull segment by segment ,then ,combines the boundaries to form convex hull.

Contemporary Trends in General Insurance Industry

The paper presents a theoretical framework on ever changing competitive dynamics of Indian General Insurance Industry. The insurance sector is highly concentrated with the large number of private and government insurance companies in India. The growth of the insurance sector in India has been phenomenal, offering a diversified product portfolio and excellent services. The main theme of this paper is to expose the ever changing approach of general insurance industry in the era of LPG and especially after detariffing. The de-tariffing of Indian general insurance industry has occurred in three phases, - in 1994 marine cargo, personal accident, health, aviation; in 2006 - marine hull segment and in 2007 - Fire, engineering and motor own damage (OD) segments. The general insurance industry is facing many challenges, particularly in terms of profitability. Profitability pressures are arising from the pricing, claims fronts, and changes that are happening because of motor third-party provisions.

Evaluation of added resistance of kvlcc2 in short waves

The added resistance of KVLCC2 in short and regular head waves has been studied theoretically and experimentally. Model tests are performed to determine how well the asymptotic formula (Faltinsen et al. 1980) predicts the typical level of added resistance in short waves. Because the asymptotic formula neglects the effects of ship motions, it is combined with theoretical methods to calculate the added resistance in long waves using an R function to predict the added resistance in the intermediate wavelength region where both ship motions and wave reflection are important. A unique feature of this experiment is that the ship model is divided into three segments to explore the added resistance distribution with respect to hull segment. This paper discusses the sensitivity of experimental results to the quality of the incident regular head waves. Moreover, a novel procedure for analyzing added resistance is described. Finally, the experimentally determined added resistance of KVLCC2 is compared with theoretical results. It is shown that the added resistance from the combined theoretical methods agrees well with experimental results in both the intermediate and short wave regions. The use of hull segments shows that added resistance is concentrated primarily at the bow.

Experimental investigation of a fast monohull in forced harmonic motions

The paper presents the results of an experimental investigation of added masses and damping coefficients of a model of a fast monohull. A model of 4.5 m length between perpendiculars was constructed of fiber glass reinforced plastic (FRP) with four segments connected by a backbone. The backbone was instrumented with load cells at the positions of the cuts. This configuration, combined with load cells measuring the force exerted by the forced motion actuators, made it possible to obtain the hydrodynamic coefficients for each of the four hull segments. The investigation focused on the vertical motions. Thus, the experimental program included forced harmonic heave and pitch motions in calm water (no incident waves). Subtracting inertial and restoring forces from total measured forces, one obtained the hydrodynamic component, which then resulted in the hydrodynamic coefficients. The effects of steady forward speed on the radiation forces were investigated by conducting model tests at four forward speeds. Finally, nonlinear effects were assessed by conducting model tests for three amplitudes of forced heave and forced pitch motions.

Aerodynamic estimation techniques for aerostats and airships

A semi-empirical steady-state model of a finned axisymmetric body is developed and used to compute hull -fin mutual interference factors and cross flow drag coefficients from wind tunnel data on five aerostats and airships. The results are in general agreement with expectations from theory and provide a b asis for predicting aerodynamic coefficients. The model is extended to unsteady motion by considering the local flow on finite hull segments and the fins. This dynamic model is applicable to non-linear simulations and the computation of rotational stability derivatives for which equations are derived. For one zerostat, rotational stability derivatives calculated from static wind tunnel data are compared with experimental results from a whirl ing-arm tow tank.