Hull Deformation Research Articles

Systems Errors Identification Method of Hull Deformation Data Based on Total Variation Constrained

Based on the analysis of influence factors for hull deformation data, physical models including hull curve deformation, hull torsion deformation and hull athletics deformation were established according to mechanical principle. Considering characteristics of the space instrumentation ship, systems errors identification method based on total variation constrained was provided. First order differential coefficient of deformation data was joined in a constrained equation in the method. Systems errors coefficient and exact value of deformation data were solved through alternating iterations. The simulation result of deformation measured data indicated that identification errors were in consistent with plus errors, and systems errors coefficient was also estimated accurately. This demonstrated that the proposed method is suitable for systems errors identification of hull deformation data.

Model Reference Robust Control for Marine Propulsion Systems with Model Uncertainty Caused by Hull Deformation

A marine propulsion system can be strongly coupled with the hull deformation in a large-scale ship. The interaction of this coupling dynamics increases the nonlinearity and complexity of the control model. Traditional control method based on the empirical PID (proportion-integration-differentiation) parameters has difficulty in dealing with the model uncertainty caused by the hull deflection. However, up to date, limited work has been done to address the model uncertainty problem of the marine propulsion system. It is therefore imperative to develop feasible and effective control systems that take the model uncertainty into account. In this study, a new method based on the model reference adaptive system (MRAS) has been proposed for the active and accurate control of the marine propulsion system coupling with the hull deformation. A finite element model of the ship shaft line was established to investigate the uncertainty boundaries of the propulsion system. Moreover, the sea trial was carried out on the hydraulic dredge named ”Changjing 2” to measure the main engine power loss under hull deformation. The finite element analysis (FEA) and shipboard measurement results showed a fiducial interval of [0.1% 10%] for the model uncertainty of the marine propulsion system. These uncertainty boundaries were added into the ship speed control system model, and the MRAS controller was designed based on the Lyapunov theory to mitigate the adverse effects of model uncertainty. The stability of the MRAS has been proven by the Lyapunov stability criterion. Numerical evaluations using MATLAB®/ Simulink® software for the ”Changjing 2” ship engine parameters have showed high effectiveness of the MRAS structure for speed tracking under the hull deflection coupling. This study has demonstrated that the newly proposed control system can work stably with various ship operating conditions, and its performance is superior to the traditional PID controller.

MONITORING SYSTEM OF EXTREME LOADINGS OF PROPULSION SYSTEM’S FOUNDATION. DESIGN ASSUMPTIONS

Project of on-line diagnostic (monitoring) system of marine propulsion system working parameters is the authors' general target. Proper propulsion system’s foundation is one of the most important parameters for its reliable operation. Different types of quasi-static loadings and dynamic excitations can be observed during ships exploitation. Presented research has been limited to extreme loadings. Underwater explosions or ship groundings are considered examples of extreme foundation loadings. Analysis of the physical parameters of the extreme forces has been presented in the first part of the paper. Water pressure spatial and non-spatial (time) distribution during underwater explosion has been analysed as an example. Short overview of the dynamic mathematical models of underwater explosions is presented. Time function of vibrations acceleration of ship construction is important design assumption of planned Structural Health Monitoring (SHM) system. Propulsion system's foundation loading measurements should take into account general ship hull deformation (in the aft part of the ship) as well as reactions changes of main engine and shaft line bearings. Ship hull deformation should be monitored as quasi-continuous measurements, along whole propulsion system. Optical Time-Domain Reflectometer method (OTDR) is planned for hull deformation monitoring. Propulsion system bearings' reactions are a source of local foundation pads' strain changes. Fibre Bragg Grating (FBG) sensors are the best for that kind of measurements, in authors opinion. Both techniques (OTDR and FBG) have been shortly described in the paper. Scheme of monitoring system of marine propulsion systems foundation's loadings are proposed in the end of the article.

Compensation of Ship Hull Deformation in Transfer Alignment

By building the velocity plus attitude matching mode for ship transfer alignment, we analyze the impact of different hull deformation angles to the performance of transfer alignment and give simulation results. The theoretical accuracy of GPS attitude determination network applied for ship hull deformation monitoring is proposed. According to the simulation results, the performance of transfer alignment after hull deformation compensation by the monitoring network is effectively improved compared to the one without compensation.

Finite element method analysis of pipe material temperature changes influence on line expansion loops in hydraulic installations on modern tankers

Finite element method analysis of main lines of hydraulic central loading system installation expansion loops mounted on product and chemical tankers has been presented in the paper. The axial forces problem in installations mounted along the ship?s open decks executed from hull deformations on waves and thermal stresses is given. Use of ?U? type expansion loops is described. Results of forces in anchor points and stresses of Mises due to expansion loop deformations are shown. Calculations were made by ABAQUS Ver.6.7 FEM computer program.

Research on shafting alignment considering ship hull deformations

Ship hull deformation is one of the most significant influences on propulsion shafting alignment. Based on the calculation fundamentals of ship hull deformations, a new method of shafting alignment considering ship hull deformations is proposed in this paper. Ship loadings, wave loads and environment temperature differences in some extreme conditions, as well as elastic constraints, are simulated and applied to the finite element model of 76,000 DWT product oil tanker, so that ship hull deformations can be solved. Then, the deformations of the double bottom are converted to bearing offsets, which behave as boundary constraints for shafting alignment calculations. Taking the condition of light ship in calm water as a reference, the impact of hull deformations on shafting alignment is analyzed and optimized shafting alignment considering ship hull deformations is realized.

Strongly coupled fluid–structure interaction method for structural loads on surface ships

A method to compute structural loads on surface ships coupling a CFD solver with rigid or elastic representations of the ship hull is presented. One-way and two-way coupling approaches were used for the cases when the ship was considered elastic, in which the forces obtained from the CFD solver were used to compute the structural loads. In the two-way coupling method the hull deformation influenced the CFD solution, while in the one-way coupling method this feedback was not needed. The flow field around the ship was calculated with the URANS/DES overset solver CFDShip-Iowa version 4, with the structural response obtained using modal superposition. Predictions of ship motions and structural loads were compared with available experimental data for the S175 containership, obtained from a segmented elastic model. Predicted heave and pitch transfer functions in regular waves matched well with the experimental values. The computations showed that slamming events greatly affected the vertical bending moment amplitude, showing sharp peaks for the rigid model. The elastic models predicted well the ringing of the structure and showed that the ringing was mainly triggered by bow flare slamming. The one-way coupled approach with a virtual mass correction provided a solution that in some aspects had almost the same quality as the two-way coupled solution, at a fraction of the cost.

Non-linear finite element analysis for the mating procedure of a large offshore structure

Simulation techniques for complicated offshore structures are presented in this article by conducting a non-linear finite element analysis (FEA) to simulate the mating procedure of a semisubmersible offshore platform. The main part of the offshore structure is a hull structure that is initially supported by a truss. In the mating procedure, supporting of the hull is gradually taken over by four column structures during the mating procedure. The interactions between hull and truss, and between hull and columns are implemented with contact algorithms. The mating procedure is accompanied with variations of contact zones and redistribution of contact stress as well as variation of the hull deformation. The analysis provided accurate prediction of stress and deformation that are vital for the designers to build up confidence on sufficient structural strength and high assembly quality.

비선형 베어링 요소를 이용한 탄성 추진 축계정렬에 관한 고찰

The effects of hull flexibility on shaft alignment are growing as ship sizes are increased mainly for container carrier and LNG carrier. In order to consider hull flexibility on a propulsion shafting system, standardization of ship service conditions is necessary because hull deformation is continuously variable according to ship service conditions. How to summarize ship service conditions is suggested based on practically applicable four viewpoints : hull, engine, loading and sea status. Effects of the external forces acting on a ship propulsion shafting system are generally commented. Several design criteria regulated by classification societies are pointed at issue which seems to have Insufficient technical background. A qualitative verification is carried out to point out the invalidity of the assumption of effective supporting position. In this work, an elastic nonlinear multi-supporting bearing system is introduced as a key concept of the elastic shaft alignment. Hertz contact theory is proved to be more proper one than projected area method in calculation of the nonlinear elastic stiffness of the bearing, The squeezing and oil film pressure calculations in the long journal bearing like an after stern tube bearing are recognized as a necessary process for elastic shaft alignment design.

Shaft line alignment analysis taking ship construction flexibility and deformations into consideration

Proper shaft line alignment is one of the most important actions during the design of the propulsion system. Usually, a beam model of the power transmission system is isolated from the ship hull. Therefore, determining the correctness of the boundary conditions is one of the most important and difficult issue during the marine shaft line alignment calculations. In the author's opinion stiffness and damping characteristics of the journal bearings’ oil film, ship hull and bearings frame should be taken into account. Ship hull deformations, under different load conditions and regular sea waves, are also analysed. The presented numerical analysis method is compared and verified by measurements on real ships.

Study on Crack Resistance Performance of Continuous Glassfiber Reinforced Polyurethane Foam (1st Report)

Rigid PUF (polyurethane foam) is one of materials for in-ground LNG storage tanks which have been successfully constructed since 1970. For LNG carriers, however, it is necessary to use a material having sufficient strength to withstand cyclic load and impact load caused by hull motion in waves and hull deformation etc., and having excellent resistance to crack propagation as well. To meet this requirement, reinforced PUF consisting of continuous glassfiber uniformly dispersed in rigid PUF has been developed especially for TGZ Mark III cargo containment system.The present paper aims at making a quantitative evaluation of the reinforcing effect of glassfiber in reinforced PUF from a viewpoint of increased crack resistance performance. In this report, crack extension behavior and fracture toughness of reinforced PUF have been examined in detail in comparison with those of rigid PUF under a three-point bending test on notched beam specimens at room temperature. Acoustic emission analyses and finite element simulations have been shown to be successful in comparing the fracture behavior of reinforced PUF with that of rigid PUF.

A Study on the Collapse of Ship Structure in Collision with Bridge Piers

The present paper gives the results of static tests on the fracture of simplified models of the bow and the side of ships, which were carried out for the purpose of examining the extent of fracture developed in a ship hull in collision with a bridge pier and estimating the amount of collision force. The models simulate the structures of somewhat small ships, ranging from 500 tons to 4, 000 tons in gross tonnage. We assume a bow collision in which a ship strikes in a right angle encounter with the flat plane of a bridge pier. It is assumed in a ship-side collision that a ship hits the corner parts of a bridge pier.The test results show that the buckling of hull plate is dominant in the strength of the bow of a ship. The load-penetration curves of the side of a ship show a distinct difference between transversely-framed side structures and longitudinally-framed ones. The collision force and the hull deformation calculated by a simple theoretical expression are graphically presented, for a range of gross tonnage of ships, in an attempt to derive general information on buffer equipments designed for the protection of both ship hulls and bridge piers.

Deformability of the hull steel-work and deformations of the engine-room of large tankers

Convinced of the actuality and importance of the Phenomena related to the deformability of the steel-work and encouraged by the interest raised up by these phenomena, it can be considered as useful to draw up the inventory of the above mentioned phenomena and to present the most recent results of the studies and researches obtained by the use of the most sophisticated investigation means. So in what follows the authors: (1) present their point of view on the appearance of the phenomena related to the flexibility of the steel-work and their importance, (2) analyze thoroughly various questions connected with the deformations of the various parts of the steel-work, questions which are often not in accordance with the classical theory, (3) present the results of the recent theoretical studies related mainly to the deformations of the engine room of large tankers, by calling for the calculations using the finite element technique.

Deflection of Engine Room Double Bottom in Large Tankers

Increase of tanker size may be accompanied with the problem that hull deformation will affect alignment of shafting and turbined gear in various conditions.We investigated deformation of hull structure by FEM calculation and measurement of 270, 000 & 410, 000 DWT turbine tankers. The results of FEM calculation agree rather well with the measurement of actual ship (270, 000 DWT tanker).In this paper, we would report some results as reference for structural design. The summary is as follows.(1) Shear rigidity of hull girder affects the response of double bottom deflection. Therefore, 3-dimensional calculation is useful for checking the bouble bottom design.(2) In way of narrower breadth of double bottom, vertical deflection is much affected by bending moment carried from pressure on side shell than by vertical pressure from bottom shell.(3) Variation of loading weight in engine room, and L. O. temperature seem to give some effects on hull deformation and alignment of shafting.(4) Reverse deflection in (2) due to side pressure works good effection on shafting as a cancellation factor of upward deflection of double bottom due to bottom pressure.

MEASURING OF SQUAT IN THE FAIRWAY TO THE PORT OF LULEA, NORTH SWEDEN

The importance of knowledge of squat and expected underkeel clearance for ships passing a fairway is essential to the navigational safety and the economy of a harbour. In order to check the squat of ships in the fairway to the port of Lulea a photographic measuring method has been evolved and used in measurements on three different ships. Determining of squat is made by levelling the position of vessels in relation to water level at the berth before sailing and en route at measuring points along the fairway. The accuracy of measurements was determined by observations on reference staffs. The order of standard deviation is 1/2 inch, at 2,400 feet distance. Observations indicate squat ranging from 1 foot 5 inches at speeds of 9 knots to 2 inches at 3>7 knots. The measured squat corresponds rather good to tneoretically calculated values according to Woltiger and Shell/Sogreah. The measuring method used has reduced the field work. The greatest advantage is that adequate values of squat will be directly recorded with only a few corrections including irregular factors such as turbulent flow, hull deformations and variable channel sections. A condition is however sheltered water and possioilities of solid foundation for instrument arrangement. 1499