Risk factors and theory building: a study to improve passenger vessel safety

Given the inherent complexity of the maritime transportation system, developing effective policy can be challenging. Using risk factors identified by an elicitation and aggregation of expert judgment, a relative-risk rating scheme was developed in the theory-building tradition of the social sciences. The model was empirically evaluated using 18 months of data from the US small passenger vessel sector. The model identified that the top 10% of relatively highest risk vessels accounted for 50% of all marine casualties during the period of examination. A policy for deploying the model nationally is proposed.     

Design of the lines of underwater vehicles based on collaborative optimization

A generalized collaborative optimization (CO) framework is proposed to the optimization design of the lines of an underwater vehicle. The resistance and maneuvering performances are concerned about and taken as the optimization objectives in the optimization framework. The resistance, lateral force and yaw moment are calculated by RANS method. To improve the optimization efficiency, an automatic integration optimization platform is constructed in which a surrogate model is adopted. A SUBOFF model is taken as the verification model. The optimal results demonstrate the validity of the optimization strategy proposed.     

Shift of reference point and implications on behavioral reaction to gains and losses

It is widely recognized that individual decision-making is subject to the evaluation of gains and losses around a reference point. The estimation of discrete choice models increasingly use data from stated choice experiments which are pivoted around a reference alternative. However, to date, the specification of a reference alternative in transport studies has been fixed, whereas it is common to observe individuals adjusting their preferences according to a change in their reference point. This paper focuses on individual reactions, in a freight choice context, to a negative change in the reference alternative values, identifying the behavioural implications in terms of loss aversion and diminishing sensitivity. The results show a significant adjustment in the valuation of gains and losses around a shifted reference alternative. In particular, we find an average increase in loss aversion for cost and time attributes, and a substantial decrease for punctuality. These findings are translated to significant differences in the willingness to pay and willingness to accept measures, providing supporting evidence of respondents’ behavioural reaction.     

Experimental study and 3D CFD analysis on the optimization of throttle angle for a convergent vortex tube

Seven adjustments of convergent-type Vortex Tube (VT) with different throttle angles were applied. The adjustments were made to analyze the influences of such angles on cold and hot temperature drops as well as flow structures inside the VTs. An experimental setup was designed, and tests were performed on different convergent VT configurations at injection pressures ranging from 0.45 to 0.65 MPa. The angles of the throttle valve were arranged between 30° to 90°, and the numbers of injection nozzles ranged between 2 and 6. Laboratory results indicated that the maximum hot and cold temperature drops ranged from 23.24 to 35 K and from 22.87 to 32.88 K, respectively, at four injection nozzles. Results also showed that temperature drop is a function of hot throttle valve angle with the maximum hot and cold temperature drops depending on the angle applied. We used graphs to demonstrate the changes in the cold and hot temperature drops with respect to hot throttle angle values. These values were interpreted and evaluated to determine the optimum angle, which was 60°. The CFD outputs agreed very well with the laboratory results. The proposed CFD results can help future researchers gain good insights into the complicated separation process taking place inside the VTs.     

Imprecise reliability assessment for heavy numerical control machine tools against small sample size problem

Small sample size problem is one of the main problems that heavy numerical control (NC) machine tools encounter in their reliability assessment. In order to deal with the small sample size problem, many indirect reliability data such as reliability data of similar products, expert opinion, and engineers’ experience are used in reliability assessment. However, the existing mathematical theories cannot simultaneously process the above reliability data of multiple types, and thus imprecise probability theory is introduced. Imprecise probability theory can simultaneously process multiple reliability data by quantifying multiple uncertainties (stochastic uncertainty, fuzzy uncertainty, epistemic uncertainty, etc.) together. Although imprecise probability theory has so many advantages, the existing natural extension models are complex and the computation result is imprecise. Therefore, they need some improvement for the better application of reliability engineering. This paper proposes an improved imprecise reliability assessment method by introducing empirical probability distributions to natural extension model, and the improved natural extension model is applied to the reliability assessment of heavy NC machine tool spindle to illustrate its effectiveness.     

Optimal thrust allocation logic design of dynamic positioning with pseudo-inverse method

This article presents a method named pseudo-inverse to solve the optimal thrust allocation of dynamic positioning (DP) system, proposes to optimally determine the azimuth angle of thrusters instead of man-control or semi-auto control, and combines with the pseudo-inverse methods to get the optimal solutions for dynamic positioning control system. It is able to greatly reduce the risk of manual mode. Three different kinds of modes are proposed and detailedly illuminated, and can be used to solve much more complex nonlinear constraint problems, such as typical forbidden vector boundary. Several illustrative examples are provided to demonstrate the effectiveness and correctness of the proposed thrust allocation modes.     

Sealed v/s open bids for certificates of entitlement under the vehicle quota system in Singapore

The Vehicle Quota System manages vehicle ownership in Singapore by making the procurement of a Certificate of Entitlement (COE) a prerequisite for the registration of a new vehicle. The procurement is done during uniform price auctions of quotas of COEs currently held on a twice-a-month schedule. The auction format which started out as sealed bids in May 1990 changed to open bids in July 2001. This paper uses a regression model framework to investigate if this shift in auction format has resulted in lower COE premium volatility and a better reflection of demand and supply forces. The empirical results are pertinent to transport policy analysis. A suggestion in the form of incentives for early bids is also made to improve the efficiency of the open bids auction.     

Mathematical model for takeoff simulation of a wing in proximity to the ground

Aircraft flying close to the ground benefit from enhanced efficiency owing to decreased induced drag and increased lift. In this study, a mathematical model is developed to simulate the takeoff of a wing near the ground using an Iterative Boundary Element Method (IBEM) and the finite difference scheme. Two stand-alone sub-codes and a mother code, which enables communication between the sub-codes, are developed to solve for the self-excitation of the Wing-In-Ground (WIG) effect. The aerodynamic force exerted on the wing is calculated by the first sub-code using the IBEM, and the vertical displacement of the wing is calculated by the second sub-code using the finite difference scheme. The mother code commands the two sub-codes and can solve for the aerodynamics of the wing and operating height within seconds. The developed code system is used to solve for the force, velocity, and displacement of an NACA6409 wing at a 4° Angle of Attack (AoA) which has various numerical and experimental studies in the literature. The effects of thickness and AoA are then investigated and conclusions were drawn with respect to generated results. The proposed model provides a practical method for understanding the flight dynamics and it is specifically beneficial at the pre-design stages of a WIG effect craft.     

Properties and electronic structure of iron under pressure up to 30GPa

The properties and electronic structure of Fe under pressures of 0–30GPa have been studied by first principles employing the density functional theory (DFT), the ultra-soft pseudo-potentials (USPP) and the generalized gradient approximation (GGA). The calculating results show that there is a structural transition from magnetic body-centered cubic (bcc) to nonmagnetic hexagonal-close-packed (hcp) structure for Fe around 11GPa pressure. There is a pseudogap both in the density of states (DOS) for bcc and hcp Fe. The pseudogap of bcc Fe is deeper and wider than that of hcp Fe. The elastic modulus is obtained by Voigt-Reuss-Hill averaging scheme. The results indicate that the elastic properties of bcc Fe enhance with pressure except for elastic stiffness constant C ₁₁, shear modulus G and elastic modulus E at the transition pressure, while the elastic properties of hcp Fe increase linearly with pressure. Magnetic bcc Fe is ductile, and hcp Fe becomes ductile from brittle around 25GPa.