Multi-fidelity optimization of a high-speed foil-assisted semi-planing catamaran for low wake

The wakes of high-speed passenger-only ferries that operated through Rich Passage, on the Seattle-Bremerton ferry route, caused beach erosion and damage to habitat. A task was initiated to design a low-wake high-speed vessel using multi-fidelity CFD based design optimization by using low-fidelity potential flow solvers for initial global design optimization and by using URANS solvers for high-fidelity tuning of the optimized design. This simulation based design process involved a close collaboration between ship designers, and hydrodynamics and CFD specialists, whose collective expertise guided the evolution of the design based on both hydrodynamic and structural aspects. The initial hull shape optimization using potential flow code was carried out by blending three different initial concepts provided by the designers. Subsequently, URANS was used to evaluate the potential flow optimized hull and to further optimize the hull configuration parameters, namely, the centre-of-gravity, demihull spacing, foil location, foil angle and slenderness ratio at different displacement conditions. The URANS based configuration optimization also took into account the far field wakes’ energy spectrum with an objective of reducing the energetic, low frequency far field wakes which are associated with beach flattening on the mixed sand and gravel beaches. Calculation of the far field wake using URANS would require an unfeasibly large domain size; therefore, a Havelock code with a source distribution matching the URANS calculated near field wave elevation was used to propagate the wakes into the far field. The end result of the optimization was a design with significantly reduced far field wake, which is currently being built for experimental testing.     

The effect of sloshing on the sway motions of 2D rectangular cylinders in regular waves

In this paper, we investigated the effect of sloshing on the sway motions of two-dimensional rectangular cylinders in regular waves, bearing in mind possible applications for LNG-FPSO and LNG-FSRU. First, we carried out experiments for two models with different drafts, or the same draft but different filling ratios, in which the models were firmly connected to each other. The sway motion was measured with a noncontact video camera. This is an extension of Rognebakke and Faltinsen’s work for a single model (J Ship Res 47(3):208–221, 2003). It was found that the sway motion became small when the incident wave frequency was close to the lowest natural frequency of each model. The sway motion greatly increased when the wave frequency was higher than this frequency. The measured data were compared with numerical results obtained by a single-dominant multi-modal method; relatively good agreement was noted. However, the numerical results deviated from the experimental results near the lowest natural frequency of the smaller model, which was believed to be due to overturning waves, as observed during the experiment. Since this is out of the valid range for the single-dominant multi-modal method, other, more appropriate, methods such as the multi-dominant modal method must be applied instead.     

Modelling multiple yacht sailing interactions between upwind sailing yachts

An approach for enhancing the realism of yacht fleet race simulations based on a lifting line method is developed. The wake of an upwind sailing yacht is represented as a single heeled horseshoe vortex and image system. At each time step, changes in vortex strength are convected into the wake as a pair of vortex line elements. These subsequently move in accordance with the local wind, the self-induced velocity and the velocity induced by the presence of the wakes of other yachts. In addition, the lifting line model has a model for the viscous wake due to the drag associated with the yacht and its sails superimposed on it. A synthesis of sail yacht wake representations based on detailed 3D Reynolds-averaged Navier–Stokes computational fluid dynamics calculations with wind tunnel test results is used to capture the initial strength of the combined main-jib vortex system and its vertical height. The implementation of the lifting line algorithm within Robo-Race, a real-time yacht race strategy analysis tool, is described. Two upwind race interaction case studies are presented, and these show that the newly implemented wake model makes an important contribution to enhancing the realism of the sailing simulation.     

The Maritime Labour Convention, 2006—reflections on challenges for flag State implementation

This paper begins by providing a brief overview of the International Labour Organization’s Maritime Labour Convention, 2006 (MLC, 2006), noting that this Convention, often called the “Seafarers’ bill of rights”, seeks to achieve both social and labour rights (“decent work”) for seafarers and fair competition (achieving a level-playing field) for shipowners. It has been described as the “fourth pillar” of the international maritime regulatory regime complementing the major International Maritime Organization conventions. The paper provides a brief update on international efforts to achieve the 30/33 formula needed to bring the Convention into force [at present, the tonnage element, 33% has been achieved already with coverage now at 54% of the world fleet (by gross tonnage), with 18 ratifications]. It then explores challenges faced by flag States in connection with capacity to implement the ship inspection and certification system under the MLC, 2006 and other difficulties with respect to legal implementation by the flag States. The paper also comments on some challenges in connection with port State, coastal State and labour-supplying State responsibilities. The paper points out that the MLC, 2006 is a comprehensive code that covers diverse issues and a wider range of both ships and seafarers than previous conventions. It often requires interdepartmental cooperation to implement its requirements at the national level. The paper concludes that, despite the slower pace of ratification in some regions, largely because of the recent economic and other crises, it appears that many actors in the maritime sector are already actively engaged in MLC, 2006 implementation, often ahead of governments. The question is not “if” but “when” the formula will be achieved to allow the MLC, 2006 to enter into force.     

Experimental investigation of TARMAX model for modeling of hydrodynamic forces on cylinder-like structures

A new approach that models lift and drag hydrodynamic force signals operating over cylindrical structures was developed and validated. This approach is based on stochastic auto regressive moving average with exogenous (ARMAX) input and its time-varying form, TARMAX. Model structure selection and parameter estimation were discussed while considering the validation stage. In this paper, the cylindrical structure was considered as a dynamic system with an incoming water wave and resulting forces as the input and outputs, respectively. The experimental data, used in this study, were collected from a full-scale rough vertical cylinder at the Delft Hydraulics Laboratory. The practicality of the proposed method and also its efficiency in structural modeling were demonstrated through applying two hydrodynamic force components. For this purpose, an ARMAX model is first used to capture the dynamics of the process, relating in-line forces provided by water waves;secondly, the TARMAX model was applied to modeling and analysis of the lift forces on the cylinder. The evaluation of the lift force by the TARMAX model shows the model is successful in modeling the force from the surface elevation.     

Experimental and numerical investigation of fuel mixing effects on soot structures in counterflow diffusion flames

Experimental and numerical analyses of laminar diffusion flames were performed to identify the effect of fuel mixing on soot formation in a counterflow burner. In this experiment, the volume fraction, number density, and particle size of soot were investigated using light extinction/scattering systems. The experimental results showed that the synergistic effect of an ethylene-propane flame is appreciable. Numerical simulations showed that the benzene (C₆H₆) concentration in mixture flames was higher than in ethylene-base flames because of the increase in the concentration of propargyl radicals. Methyl radicals were found to play an important role in the formation of propargyl, and the recombination of propargyl with benzene was found to lead to an increase in the number density for cases exhibiting synergistic effects. These results imply that methyl radicals play an important role in soot formation, particularly with regard to the number density.     

Lubrication characteristics of spiral groove liquid seals for use in the carrier of a vane-type external LPG fuel pump

We analyzed the lubrication characteristics of a design-selected spiral groove liquid seal for the critical component, the carrier, of a rotary vane-type fuel pump developed for external installation on fuel tanks for liquid phase LPG (liquefied petroleum gas) injection (LPLi) vehicles, with the aim of fundamentally improving lubrication performance and so protecting the carrier from early frictional wear damage at its suction face. The main reason for selecting a spiral groove pattern was because the viscosity of liquid LPG is very low, comparable to that of air, and current commercial dry gas seals adopting spiral grooves have been successfully employed in completely noncontacting applications. Utilizing the Galerkin finite element lubrication analysis method, a detailed lubrication characteristic analysis of the seal was performed, and lubrication performance optimization was performed by systematic parameter analyses of the design variables. Compared to the initial reference design, the final optimized spiral groove seal design had a groove depth increased by 66.7% and an equilibrium seal clearance increased by 65.3%. Our model also predicted that under a condition of equilibrium between the closing force of the pumping pressure and the seal opening force, the optimally designed carrier spiral groove liquid seal was capable of maintaining a stable lubricating film with sufficient axial stiffness and thereby demonstrated successful noncontact operation; in addition, leakage through the seal was minimal.     

Finite-element analysis of quasistatic fracture in CV joints under full-turn and full-throttle conditions

Quasistatic fractures at high joint angles constitute a chronic quality problem in CV joints. This type of fracture occurs when a driver unintentionally depresses the brake and accelerator simultaneously under a full-turn retreat condition. In general, the cage in a ball joint can be broken only at these high joint angles. Here we present a flexible quasistatic simulation model developed to simulate fracture in a CV joint. The cause and process of the quasistatic fracture were analyzed using simulations and physical tests. Static fracture simulations and tests at high joint angles showed that, initially, only one of the six cage posts was damaged. In a simulation of one revolution at constant torque, we found that an imbalance in ball loads generated an excessive cage load. Moreover, if this high cage load was applied when the cage protruded outward, the cage post was subjected to severe shear loading. The cage post was damaged in this specific rotational range. Quasistatic fracture simulations and tests at high joint angles showed that all six cage posts were damaged sequentially. Because entire cage posts were damaged, the quasistatic fracture torque was approximately half of the static torque. The plastic strain in each cage post displayed one step-like jump per revolution in the quasistatic simulations. The ball indentation created by a high ball load was interrupted by the cage-window edges as the ball joint rotated. This hindrance by ball indentation triggered the final breakage of the cage, although it was not the major cause of cage fractures.     

Dynamic correction of the steering-characteristic curve and application to an EPS control system

The steering torque of an electric-power steering (EPS) motor is interrelated with the performance of the EPS control system, therefore calculating an exact steering torque is critical in this application. This study presents a dynamic correction method that greatly decreases the calculated error in the steering torque; the PID controller demonstrated here is therefore suitable for the demands of this system. Based on an analysis of the detection process of the steering torque sensor, we first deduced that the variation of the system resistance torque equals the difference between the measured value of the steering torque and the ideal one in the previous cycle. Based on this result, we then proposed a dynamic correction method. Finally, a comparison of the simulated and experimental results for several vehicles evidenced the effectiveness of this dynamic correction method.     

Sensorless adaptive speed control of a permanent-magnet dc motor for anti-lock brake systems

An adaptive control algorithm was developed for the sensorless speed control of a permanent-magnet DC motor directly connected to the hydraulic pump of an antilock brake system. Due to the severe cost and reliability constraints of the application, the motor speed was controlled by a very simple on-off switching method, in which the only measurement required is the voltage across the control switch. The motor speed was calculated solely from the back-EMF voltage during the period of the control cycle when the switching controller is in the switch-off mode. The stability of the developed adaptiveswitching control algorithm was proven mathematically and confirmed experimentally in several vehicle tests over a wide range of target speeds and pump-load conditions. The accuracy and the response time of the controller can easily be tuned by adjusting a single tuning parameter. The switching frequency of the controller can also easily be tuned by adjusting the over-and undershoot thresholds independently from the accuracy of the speed-tracking control.