Hull Model Research Articles

Structural characteristics and strength analysis of main hull of cylindrical FPSO

In this paper, a cylindrical FPSO is analyzed. Firstly, the structural characteristics and structural layout principles are introduced. The overall structural model of the main hull of the cylindrical FPSO is established by using the three-dimensional finite element design software. According to the actual situation in the operation process, the boundary conditions and load cases are determined. Finally, the yield strength of the main hull is checked. This paper has a certain guiding significance for the design of cylindrical FPSO.

Research and development of 3D hull modeling and stability calculation system

Objectives To realize the visualization and fast modeling and stability calculation of hulls and compartments, and extend the application scope to complex ship forms such as multi-body and combined hull, a three-dimensional hull modeling and stability calculation system is developed. Methods Model-View-Controller mode is used to build the system framework; 3D visualization, object pick-up, feature point snap, command stream, reference expression-linkage update, undo-redo, intelligent table and other functional elements are integrated to realize the 3D interactive modeling of ships and compartments for general users, and command stream rapid modeling for skilled users; moreover, a 3D surface grid integration algorithm is used to realize static hydraulic and stability calculation without the limitation of hull shape, and multiple regulation criteria are implemented for users to select from based on the technology of the derived classes. Results Real ship tests and a large number of engineering applications show that this system can realize the fast 3D modeling and accurate stability calculation of hulls and compartments, covering complex ship forms such as multiple stern, bulbous bow, head up, tail up and convex deck, as well as special ship types such as floating dock, catamaran, trimaran and assembled combined ship. Conclusions This system has reference value for the design and development of ship engineering software.

A front‐fixing method for American option pricing on zero‐coupon bond under the Hull and White model

A new efficient numerical method is proposed for valuation of American option on zero‐coupon bond using Hull and White model. By applying the front‐fixing transformation suggested by Holmes and Yang, the original free boundary problem is transformed into a new fixed boundary partial differential equation (PDE) problem, where the optimal stopping boundary is one of the unknowns of the problem. The numerical finite difference scheme for the transformed problem is constructed. Stability and convergence rate is studied empirically. Numerical simulation of the computation of both the option price and the optimal stopping boundary are illustrated with examples and the comparison with the Hull and White tree method.

Interest rates forecasting: Between Hull and White and the CIR#—How to make a single‐factor model work

AbstractIn this work, we present our findings of the so‐called CIR#, which is a modified version of the Cox, Ingersoll, and Ross (CIR) model, turned into a forecasting tool for any term structure. The main feature of the CIR# model is its ability to cope with negative interest rates, cluster volatility, and jumps. By considering a dataset composed of money market interest rates during turmoil and calmer periods, we show how the CIR# performs in terms of directionality of rates and forecasting error. Comparison is carried out with a revamped version of the CIR model (denoted ), the Hull and White model, and the exponentially weighted moving average (EWMA) which is often adopted whenever no structure in data is assumed. To confirm the analysis, testing and validation is performed on both historical and ad hoc data with different metrics and clustering criteria.

Assessing the sustainability of supply chains by dynamic network data envelopment analysis: a SCOR-based framework.

The objective of this paper is to assess the sustainability of supply chains by proposing a dynamic network data envelopment analysis (DNDEA) model in the presence of interval data, due to the fact that in many real-world applications, the condition of convexity in the production technology might be violated. To prevent this issue, a DNDEA model based on the free disposal hull (FDH) approach is developed. For the first time, this paper develops a DNDEA version of the free disposal hull (FDH) model in the context of the SCOR framework. It is also shown that this model always presents a finite efficiency score for assessing the sustainability of supply chains. Moreover, using this model, real benchmarks can be calculated to improve the sustainability of unsustainable supply chains. A case study in print industry is given. The results validate our proposed model.

An Approximation Scheme for Value at Risk under Mean Reverting Stochastic Volatility Model

AbstractIn this paper, a stochastic differential equation is provided for the stock price in which not only the volatility of returns is stochastic same as Hull and White model but also, it has the mean-reverting property. Then, to analyze the probability distribution of this model, the Fokker--Plank equation is applied and the resulting problem is solved numerically. The well known numerical scheme, q-method is applied to approximate the solution of the resulting equation. Finally, a practical application of the provided model in financial aspects is shown within a numerical example. In this example, the proposed model and numerical results are used to approximate the Value at Risk (VaR) of the Tehran stock exchange total index.

A novel algorithm of ship structure modeling and target identification based on point cloud for automation in bulk cargo terminals

Achieving port automation of machinery at bulk terminals is a challenging problem due to the volatile operation environments and complexity of bulk loading compared to the situations in container terminals. In order to facilitate port automation, we present a method of hull modeling (reconstruction of hull’s structure) and operation target (cargo holds under loading) identification based on 3D point cloud collected by Laser Measurement System mounted on the ship loader. In the hull modeling algorithm, we incrementally register pairs of point clouds and reconstruct the 3D structure of bulk ship’s hull blocks in details through process of encoder data of the loader, FPFH feature matching and ICP algorithm. In the identification algorithm, we project real-time point clouds of the operation zone to spherical coordinate and transforms the 3D point clouds to 2D images for fast and reliable identification of operation target. Our method detects and complements four edges of the operation target through process of the 2D images and estimates both posture and size of operation target in the bulk terminal based on the complemented edges. Experimental trials show that our algorithm allows us to achieve the reconstruction of hull blocks and real-time identification of operation target with high accuracy and reliability.

Hydrodynamic Analysis of KVLCC2 Ship Sailing near Inclined Banks

The hydrodynamic forces of KVLCC2 ship sailing near inclined banks are calculated by using CFD based on RANS equation. Corresponding CFD uncertainty analysis is conducted according to the procedure recommended by ITTC. An unstructured grid, tetrahedral grid, is employed for discretization. To control the number of grids, global element scale factor is selected as the same as refinement ratio. In numerical simulation, straightforward and oblique navigation conditions are investigated. The variation of transverse force and yaw moment with the ship-shore distance, bank angle, water depth, and drift angle are analyzed. Both hull model and hull-propeller-rudder model are considered in numerical simulation. The simulation results show the hydrodynamic characteristics of ship sailing near inclined banks.

Experimental Study on Motion Behavior and Longitudinal Stability Assessment of a Trimaran Planing Hull Model in Calm Water

In this study, a high-speed planing trimaran hull form is designed, and the effects of different displacements and gravity longitudinal layouts on the performance of the trimaran planing hull in calm water are experimentally investigated in the towing tank of the China Special Vehicle Research Institute. Based on previous work, an innovative inner tunnel appendage hydroflap is mounted in the inner aft tunnel, located 1/8 L from the transom in the longitudinal direction with attack angles of 0° and 4°, respectively. Furthermore, a regular stern flap is mounted on the transom close to the chine. The towing test results show that, as the gravity center moves forward, the high-speed region resistance of the planing trimaran increases and the longitudinal stability is also strengthened. Further, the total resistance of the planing trimaran with a heavier displacement is larger while the average mass resistance declines; i.e., the resistance efficiency is improved. The results also indicate that the inner tunnel hydroflap and stern flap enhance the aft hull hydrodynamic lift and tunnel aerodynamic lift. As a result, mounting aft hull lift enhancement appendages can affect the bottom and inner tunnel pressure distribution and then cause a slight resistance decrease in the low-speed region. The value relationship of resistance between groups of appendages for the attached hull and bare hull is reversed at a speed of about Froude number 3.0. Although the aft hull lift enhancement appendages result in a higher resistance cost in the high-speed region, the longitudinal stability is effectively promoted and the occurrence speed of porpoising results in a delay of 1 to 2 m/s.

High Froude Number Experimental Investigation of the 2 DOF Behavior of a Multihull Float in Head Waves

Dynamic Velocity Prediction Programs are taking an increasingly prominent role in high performance yacht design, as they allow to deal with seakeeping abilities and stability issues. Their validation is however often neglected for lack of time and data. This paper presents an experimental campaign carried out in the towing tank of the Ecole Centrale de Nantes, France, to validate the hull modeling in use in a previously presented Dynamic Velocity Prediction Program. Even though with foils, hulls are less frequently immersed, a reliable hull modeling is necessary to properly simulate the critical transient phases such as touchdowns and takeoffs. The model is a multihull float with a waterline length of 2.5 m. Measurements were made in head waves in both captive and semi-captive conditions (free to heave and pitch), with the model towed at constant yaw and speed. To get as close as possible to real sailing conditions, experiments were made at both zero and non-zero leeway angles, sweeping a wide range of speed values, with Froude numbers up to 1.2. Both linear and nonlinear wave conditions were studied in order to test the limits of the modeling approach, with wave steepness reaching up to 7% in captive conditions and 3.5% in semi-captive ones. The paper presents the design and methodology of the experiments, as well as comparisons of measured loads and motions with simulations. Loads are shown to be consistent, with a good representation of the sustained non-linearities. Pitch and heave motions depict an encouraging correlation which confirms that the modeling approach is valid.

Model scale prediction of seakeeping and global bending moment on a high speed craft

Estimating the forces acting on a high speed craft for structural assessment purposes is challenging due to the complex combination of hydrodynamic loads. These include wave pressures, slamming pressures and their load effects at a global ‘hull girder’ level. An experimental approach to validate the use of established strip theory methods for predicting the hydrodynamic wave pressure loads is presented here. A series of regular wave seakeeping tests on a small scale segmented hull model of a high speed craft were completed and compared to equivalent seakeeping calculations. Experiments were conducted with a 1:13.5 scale hull model of a 17-metre all weather lifeboat, which is typical of a high speed watercraft capable of operating in severe weather at exposed locations. The model is segmented into four sections, rigidly held together by an instrumented backbone beam which can measure shear force and bending moments at the segmentation points. The model was tested over a full range of operating speeds and wave encounter frequencies. Results are compared with two strip theory calculations, the first using a zero speed Green function and the second using a Rankine source method with a forward speed correction term. It is shown that the Green function strip theory provides better correlation at lower speeds (up to a Froude number of 0.4) and the Rankine source method is more appropriate at higher speeds. The experiments generally show good equivalence to calculations and demonstrate that strip theory gives reasonable predictions of the global bending moment assuming linearity with the wave height. Equivalently, this suggests that strip theory is an appropriate method to predict the hydrodynamic wave induced load component in displacement and semi-planing regimes. This unlocks the potential for strip theory to be used as part of a complete assessment of the seakeeping loads on a high speed craft by combining the wave induced loads with the other significant load components, which include the local hydrodynamic wave pressures and the transient loads caused by slamming impacts. This may be applied as part of an analysis to determine a craft’s safe operating envelope or for interpreting component loads within full scale trial data.

A practical method for stability assessment of a damaged ship

Reliable onboard stability assessment for a damaged ship is of great importance to ship operators. This paper presents a practical method to calculate ship's damage stability directly from the full three-dimensional (3D) geometric models, in which the method of lost buoyancy is used. First, the computational database is established by cutting the 3D models of hull and compartments in transverse direction according to ship's frame distance table; Then, trapezoidal rule integration method is adopted to calculate ship's volumetric data; After that, the centre of gravity of liquid loads is calculated using Newton's iterative method; Finally, ship's equilibrium state of balanced trim and draft for a given heel angle is determined using a successive linear method, and the right level could be obtained. Lloyd's Register (LR) test cases for IACS UR L5 Type 1, 2 and 3 are used to verify the proposed method. In every stage of the test program, the method achieves a high-accuracy result, and thus can be used onboard to calculate intact stability and damage stability of ships by direct application of preprogrammed damage cases, especially for bulk carriers and tankers.

Comparison between Model Test and Three CFD Studies for a Benchmark Container Ship

An alternative to experiments is the use of numerical model tests, where the performances of ships can be evaluated entirely by computer simulations. In this paper, the free surface viscous flow around a bare hull model is simulated with three Computational Fluid Dynamics (CFD) software packages (FINE Marine, ANSYS CFD and SHIPFLOW) and compared to the results obtained during the experimental tests. The bare hull model studied is the Duisburg Test Case (DTC), developed at the Institute of Ship Technology, Ocean Engineering and Transport Systems (ISMT) for benchmarking and validation of the numerical methods. Hull geometry and model test results of resistance, conducted in the experimental facility at SVA Postdam, Nietzschmann, in 2010, are publicly available. A comparative analysis of the numerical approach and experimental results is performed, related to the numerical simulation of the free surface viscous flow around a typical container ship. Further, a comparative analysis between the results provided by NUMECA, ANSYS and SHIPFLOW is performed. Regarding the solution obtained, a satisfactory agreement between the towing test results and the computation results can be noticed. The minimum mean error was obtained through the SHIPFLOW case, 2.011%, which proved the best solution for the case studied.

Optimizing the working performance of a boat-type tractor using central composite rotatable design and response surface method

Optimization of the structural and working parameters for a boat-type tractor is essential to improve the working performance and reduce the energy consumption of the agricultural machinery. To apply the central composite rotatable design and response surface method, the individual and interactive impacts of grounding pressure (X1), sliding speed (X2), depth of surface water (X3), curvature radius of the bow (X4), and grounding angle (X5) on the sliding resistance and subsidence depth of a self-designed boat-type tractor were assessed. An analysis of variance test indicated that the sliding resistance and subsidence depth were significantly sensitive to all independent variables except X4, and the contribution rates of a single factor on the sliding resistance and subsidence depth were ordered as X1 > X5 > X2 > X3 > X4. The terms X4X5 and X1X5 were the only significant factors (p < 0.05) that affected the sliding resistance and subsidence depth, respectively. Subsequently, the optimal combination of the structural and working parameters for the boat-type tractor on a specific soil was determined. The results suggested that the minimal sliding resistance was 150.71 N, which was obtained when X1, X2, X3, X4, and X5 were 265.2 kg m2, 0.52 m s−1, 2.35 cm, 454.01 mm, and 28.88°, respectively. To verify the working performance of the boat-type tractor with the optimized parameters, laboratory tests were performed on the hull model in soil bins. Using the original working parameters, the sliding resistance and subsidence depth were 165.2 N and 7.1 cm, respectively, which were accordingly optimized to 159.8 N and 6.7 cm with the optimal parameters. Consequently, the sliding resistance was reduced by 5.4 N (3.3%), and the subsidence depth was decreased by 0.4 cm (5.6%), indicating that the working performance of the boat-type tractor was greatly improved.

Performance of Rescue Boat Operation when Operated in Waves

Search and rescue operations, especially in ship accidents, require speed and reliability from the rescue vessels in facing the challenges of extreme weather and sea waves. A rescue boat hydrodynamic performance study is very important to do to determine the ship’s ability to withstand dangerous conditions while operating. Therefore, a rescue boat design is needed that is capable of high acceleration and can penetrate various extreme sea condition. Three rescue boat hull models have been developed to obtain the hull model with the best seakeeping performance. A numerical arrangement based on computational fluid dynamics (CFD) techniques is used to predict seakeeping behaviour from three rescue boat hull model in wave. Three-dimensional diffraction panel method uses as a CFD solver method to predict the seakeeping performance of rescue boat high-speed operation in wave. From the study results, it was found that the first rescue boat hull model had a good seakeeping performance compared to other hull models.

Modification and Analysis of Twin Screw Ship Stern for Optimizing Propulsive Coefficient Values in Propulsive System

Twin-screw ship has the advantage of being able to reduce the diameter of propeller by using the same rotation and engine power as a single-screw ship. With the result that twin-screw ship can be operated in areas with lower water depth. However, the type of twin-screw ship has a deficiency in the value of hull efficiency ( ) and the relative rotative efficiency ( ). This occurs because of the propeller position which is far from the field of the flow of the ship’s hull speed (V). So that the value of the water flow to the propeller (advance velocity/) becomes low. Various studies have been conducted to increase wake fraction (w) and reduce the thrust deduction factor (t) values some of which are by modifying the shape of the ship’s stern parts bossing to increase the water speed to the propeller (advance velocity/) which will have a large effect on the wake fraction (w) and thrust deduction factor (t). Among them is by modifying the shape of the ship’s stern bossing so that it can increase the speed of water to the propeller (advance velocity/) which will greatly affect the value of the wake fraction (w) and thrust deduction factor (t) to increase the propulsive coefficient (PC). In this study, it is known that the QPC value for the ship model tested in the Hydrodynamics Laboratory Indonesia (LHI) is 0.54 while for the four models tested using the CFD method is model one 0.63, model two 0.55, model three 0.63, and model four amount 0.51. Based on the above test it can be concluded that the third hull model has the highest QPC. be in ALARP compared to acceptance criteria.

Effect of Non-Convective Zone Thickness on Thermal Efficiency of Salt Gradient Solar Ponds

An improved radiation transmission and thermal efficiency model for solar ponds has been proposed based on both the Hull Model and Wang/Seyed-Yagoobi Model in this paper. The new model is more accurate to actual measured conditions because multiple reflections and turbidity effects are included. Absorption penetration, thermal conductivity loss and thermal efficiency under different Non-Convective Zone thicknesses are numerically analyzed and thoroughly discussed. The results show that ΔT/I0 plays a critical role for the thermal efficiency of solar pond. Furthermore, it is found through calculation that there is an optimum thickness of the Non-Convective Zone. When the Non-Convective Zone thickness is less than this critical threshold, both temperature and thermal efficiency are decreased with increasing turbidity. However, when the Non-Convective Zone thickness is greater than this critical threshold, the increasing turbidity within a certain range will be beneficial to improve the thermal efficiency of solar pond. In addition, optimum Non-Convective Zone thickness is also related to the temperature, turbidity, salinity variation and bottom reflectivity.

Parametric optimization of FPSO hull dimensions for Brazil field using sophisticated stability and hydrodynamic calculations

In this study, hull dimensions of an FPSO were optimized to maximize its operability at Brazil field. In contrast with the previous works which have used simplified models to evaluate some indicators related to stability and hydrodynamic performances of FPSOs for its own optimal design, we developed a generic hull and compartment modeler and sophisticated stability and hydrodynamic calculation modules. With the aid of the developed tools, the hull optimization was performed with initial dimensions of an FPSO originally designed for west Africa field. The optimization results indicated the relative importance of hydrodynamic performances compared with stability performances for the FPSO hull dimensioning by showing that there were 3 active constraints related to them, which were the natural periods of heave and roll and the maximum pitch angle under 1-year return period waves at full load condition. To the author's knowledge, this study is the first attempt to combine altogether the hull and compartment modeling and full set of stability and hydrodynamic calculations precisely to optimize an FPSO's hull dimensions within 30 min. Also, it is worthwhile to mention that the developed methods are generic enough to be applied to all types of ship-shaped offshore platforms.

Application of Pendulum Theory to a Model of Overturning of a Rectangular Hull

This paper reports an experimental study on application of pendulum theory to determine the possibility of overturning of a rectangular hull model. The model was not a hull of a self-propelling ship but was a pontoon used as a non-self-navigating work vessel. The model begins to list when an unbalanced load is applied. It can then either stabilize in an inclined state or continue to overturn, throwing the unbalanced load midway, and finally stabilizing in the inverted position. In a mid-air experiment, this correlation was observed for two motion scenarios: pendulum and rotational motion. The two motions were reproduced by changing the mass of the load. The experimental results closely match those of analysis performed using the Runge-Kutta method. In an experiment in a water tank, the change in the mass of the load applied to the model hull and the effect of buoyancy were considered for analysis. Both experimental results and analytic results exhibited the same tendency for overturning. The validity of our analytical method using pendulum theory was confirmed by the consistency between these relationships.

An algorithm for the anchor points of the PPS of the FRH models

In this paper we deal with a variant of non-convex data envelopment analysis, called free replication hull model and try to obtain their anchor points. This paper uses a variant of super-efficiency model to characterize all extreme efficient decision making units and anchor points of the free replication hull models. A necessary and sufficient conditions for a decision making unit to be anchor point of the production possibility set of the free replication hull models are stated and proved. Since the set of anchor points is a subset of the set of extreme units, a definition of extreme units and a new method for obtaining these units in non-convex technologies are given. To illustrate the applicability of the proposed model, some numerical examples are finally provided.