Investigation of ship waves in a narrow channel

This paper presents a discussion of the characteristics of ship waves in a narrow channel restricted by vertical walls, based on observed data and the results computed by a 2-D model. In the numerical model, the propagation of waves generated by a moving ship is simulated by solving 2-D depth-integrated Boussinesq equations. To get the boundary conditions at the location of the ship, the slender-ship approximation is employed. A field observation was carried out at a straight length of navigation channel. The ships targeted in the observations are two kinds of waterbuses with lengths of 28 and 24 m. The relative depth Froude number for the river current, an appropriate parameter for assessing the influence of the current on ship wave characteristics in a navigation channel, ranged from 0.47 to 0.76. The observed maximum wave height varied between 0.13 and 1.26 m. The maximum wave height of the wave train is sharply increased when the relative depth Froude number exceeds 0.6. The results computed by the present model agree fairly well with the observed data.     

Trip generation of vulnerable populations in three Canadian cities: a spatial ordered probit approach

This paper provides an analysis of trip generation of three vulnerable groups: single-parent families, low income households, and the elderly. It compares the mobility of these groups to that of the general population in three Canadian urban areas of Hamilton, Montreal and Toronto, based on data from large-sample metropolitan transport surveys. An ordered probit model with spatially expanded coefficients is used for the analysis. Spatial expansion shows that there are spatial mobility trends for elderly populations and low-income populations even after socio-economic attributes are accounted for. Such spatial differences are not generally found for single parent families. This novel spatial analysis provides clues as to where vulnerable populations may experience greater degrees of social exclusion. It provides information to help prioritize transportation infrastructure projects or other social programs to take into account the needs of vulnerable populations with the lowest levels of mobility.     

基于SPH方法的波浪对水平板冲击的数值模拟(英文)

A numerical model was established for simulating wave impact on a horizontal deck by an improved incompressible smoothed particle hydrodynamics (ISPH). As a grid-less particle method, the ISPH method has been widely used in the free-surface hydrodynamic flows with good accuracy. The improvement includes the employment of a corrective function for enhancement of angular momentum conservation in a particle-based calculation and a new estimation method to predict the pressure on the horizontal deck. The simulation results show a good agreement with the experiment. The present numerical model can be used to study wave impact load on the horizontal deck.     

An investigation of the performance of an electronic in-line pump system for diesel engines

WIT Electronic Fuel System Co., Ltd. has developed a new fuel injector, the Electronic In-line Pump （EIP） system, designed to meet China＇s diesel engine emission and fuel economy regulations. It can be used on marine diesel engines and commercial vehicle engines through different EIP systems. A numerical model of the EIP system was built in the AMESim environment for the purpose of creating a design tool for engine application and system optimization. The model was used to predict key injection characteristics under different operating conditions, such as injection pressure, injection rate, and injection duration. To validate these predictions, experimental tests were conducted under the conditions that were modeled. The results were quite encouraging and in agreement with model predictions. Additional experiments were conducted to study the injection characteristics of the EIP system. These results show that injection pressure and injection quantity are insensitive to injection timing variations, this is due to the design of the constant velocity cam profile. Finally, injection quantity and pressure vs. pulse width at different cam speeds are presented, an important injection characteristic for EIP system calibration.     

Optimal tolls for multi-class traffic: Analytical formulations and policy implications

This paper puts together an analytical formulation to compute optimal tolls for multi-class traffic. The formulation is comprised of two major modules. The first one is an optimization component aimed at computing optimal tolls assuming a Stackelberg game in which the toll agency sets the tolls, and the equilibrating traffic plays the role of the followers. The optimization component is supported by a set of cost models that estimate the externalities as a function of a multivariate vector of traffic flows. These models were estimated using Taylor series expansions of the output obtained from traffic simulations of a hypothetical test case. Of importance to the paper is the total travel time function estimated using this approach that expresses total travel time as a multivariate function of the traffic volumes. The formulation presented in the paper is then applied to a variety of scenarios to gain insight into the optimality of current toll policies. The optimal tolls are computed for two different cases: independent tolls, and tolls proportional to passenger car equivalencies (PCE).The numerical results clearly show that setting tolls proportional to PCEs leads to lower values of welfare that are on average 15% lower than when using independent tolls, though, in some cases the total welfare could be up to 33% lower. This is a consequence of two factors. First, the case of independent tolls has more degrees of freedom than the case of tolls proportional to PCEs. Second, tolls proportional to PCEs do not account for externalities other than congestion, which is likely to lead to lower welfare values.The analytical formulations and numerical results indicate that, because the total travel time is a non-linear function of the traffic volumes, the marginal social costs and thus the optimal congestion tolls also depend on the traffic volumes for each vehicle class. As a result of this, for the relatively low volumes of truck traffic observed in real life, the optimal congestion tolls for trucks could indeed be either lower or about the same as for passenger cars. This stand in sharp contrast with what is implied in the use of PCEs, i.e., that the contribution to congestion are constant. This latter assumption leads to optimal truck congestion tolls that are always proportional to the PCE values.The comparison of the toll ratios (truck tolls divided by passenger car tolls) for both observed and optimal conditions suggests that the tolls for small trucks are about the right level, maybe a slightly lower than optimal. However, the analysis of the toll ratio for large trucks seems to indicate a significant overcharge. The estimates show that the average observed toll ratio for large trucks is even higher than the maximum optimal toll ratio found in the numerical experiments. This suggests that the tolls for large trucks are set on the basis of revenue generation principles while the passenger car tolls are being set based on a mild form of welfare maximization. This leads to a suboptimal cross-subsidization of passenger car traffic in detriment of an important sector of the economy.     

Creep Life Prediction of Alloy 718 for Automotive Engine Materials

This study was carried out to investigate the creep life at the high temperature of the Alloy 718 for automotive engine components using the initial strain parameter method (ISPM). Creep tests have performed at elevated temperatures in the range of 550 oC to 700 oC in this work. We also carried out constant stress creep tests. The initial strains were measured during 1 minute after loading. Both the creep stress and rupture time depend on the initial strain. We calculated the creep life of Alloy 718 by using the creep life prediction equations obtained from the ISPM. Then, we compared the creep life predicted by the ISPM to the Larson-Miller parameter (LMP). The experimental rupture time and the calculated rupture time by using the ISPM agreed with a confidence level of 95 %. The creep life predicted by using the ISPM was in very good agreement with the creep life predicted using the LMP method.     

Mathematical model validated by a crash test for studying the occupant’s kinematics and dynamics in a cars’ frontal collision

The aim of the paper was to determine the kinematic parameters that influence the occupant injury risk through a mathematical model. The developed model is a 2D model composed of 4 bodies (2 vehicles, thorax and head). The head and thorax are interconnected with a rotation joint and a torsion spring meant to stiffen the relative movement between the bodies. The thorax is connected with the vehicle body by a linear spring meant to simulate the seatbelt stiffness. The model was solved using Lagrange principle and the validation of the model was made through a crash test performed using the same initial conditions and comparing the obtained values of the displacement, velocity and acceleration parameters with the ones obtained with the mathematical model. The head and torso were chosen due to the fact that they are the common parts of the body that get injured, especially the head with the change of 80 % to cause fatal injury in car’s frontal collision. Once the model was validated, the stiffness of the seatbelt was modified in order to determine the behavior of the occupant in case of car frontal collisions. When the seatbelt stiffness was reduced, the occupant displacement and velocity increased, while by increasing the stiffness, these parameters decreased. The values of the developed model presented a high degree of similarity with the results obtained from the crash test with an error of 10 %. This model can be used by engineers to easily asses the occupant injury risk in case of vehicle frontal collisions.     

Flexural gravity wave generation by initial disturbances in the presence of current

The effect of uniform current on the generation of flexural gravity waves resulting from initial disturbances at a point was analyzed in two dimensions. The problem was formulated as an initial boundary value problem under the assumptions of the linearized theory of water waves. By direct application of the Laplace transform and then the Fourier transform, explicit expressions for the velocity potential and free surface elevation were obtained in integral forms; these were evaluated asymptotically for large distances and times by the application of the method of the stationary phase to obtain the far field behavior of the surface elevations in specific cases. Simple numerical computations were performed to illustrate the effect of uniform current on the surface elevation, wavelength, phase velocity, and group velocity of the flexural gravity waves and on the far field behavior of the progressive waves in two different cases, namely, when there is an initial depression concentrated at the origin and an initial impulse concentrated at the origin.     

The external cost of speed at sea: An analysis based on selected short sea shipping routes

According to the mid-term review of the EU White Paper on Transport, Short Sea Shipping (SSS) is expected to grow at a rate of 59% (metric tonnes) between 2000 and 2020. If we consider that the overall expected increase in both freight exchanges and volume is 50%, sea transport is one of the most feasible alternatives to reduce traffic congestion on European roads. Maritime transportation may compete with road transport as far as certain traffics are concerned, but only when assuming external costs. This paper analyzes several intermodal transport chains involving a sea leg by comparing the effect of pollutant emissions from different ship types and road transport in terms of potential external cost savings. The translation of these emissions into environmental costs shows, for certain conditions, savings in the case of sea transport that would justify the use of an environmental bonus to promote the sea option.     

Design optimization of a torpedo shell structure

An optimized methodology to design a more robust torpedo shell is proposed. The method has taken into account reliability requirements and controllable and uncontrollable factors such as geometry, load, material properties, manufacturing processes, installation, etc. as well as human and environmental factors. The result is a more realistic shell design. Our reliability optimization design model was developed based on sensitivity analysis. Details of the design model are given in this paper. An example of a torpedo shell design based on this model is given and demonstrates that the method produces designs that are more effective and reliable than traditional torpedo shell designs. This method can be used for other torpedo system designs.