Estimation of wave-induced ship hull bending moment from ship motion measurements

A time-domain technique for estimating wave-induced ship hull bending moment from ship motion measurements is presented. This technique is developed to improve hull response monitoring systems. Artificial neural networks are used to model the time-domain relationship between the wave-induced vertical bending moment and the coupled heave and pitch motions. The application of the proposed technique is validated using experimental data.     

Dynamite Fishing in a Marine Protected Area in Tanzania: Why Youth Perceptions Matter

Young men in coastal Tanzania are often blamed for damaging marine habitats by engaging in unsustainable and destructive fishing practices, including dynamite fishing, but their perceptions have not been sufficiently documented. While marine scientists, international environmental NGOs, and activists have called attention to the destructive fishing practices’ devastating impacts, insights into the contextual factors that motivate those who engage in dynamite fishing are limited. Additionally, risk perceptions and concerns regarding the environmental impact and dangers of dynamite fishing among the youth are also understudied. This paper provides ethnographic insights into the historical and contextual factors underlying dynamite fishing in rural coastal Mtwara. It draws on ethnographic data gathered through participant observation, focus group discussions and in-depth interviews with residents from two neighboring coastal villages – one located inside a marine protected area (MPA), and another located outside the MPA’s boundary. The paper first examines the views of elderly men and women to provide the historical context of dynamite fishing in coastal Mtwara. It then juxtaposes youth perceptions regarding marine conservation and dynamite fishing in the two villages, vis-à-vis ongoing efforts to curb destructive fishing practices and to enhance marine biodiversity and ecotourism in the region. Results of the study reveal that unresolved tensions between the MPA authorities and local fishers surrounding enforcement practices and unfulfilled gear-exchange-related promises, and allegations of poor governance, are important contextual factors in the persistence of dynamite fishing. The paper concludes by articulating possible remedial measures to mitigate the tensions between youth concerns about their livelihoods, and the goals of marine biodiversity conservation as a way forward in preventing dynamite fishing.     

Numerical Simulation of Vehicle Behavior during Straight Line Keeping on Undulating Road Surfaces

Numerical design of vehicles having optimal straight line stability on undulating road surfaces requires an accurate vehicle model based on knowledge of the relevant phenomena. Therefore, vehicle behavior on undulating straight roads has been analyzed and modeled. Measurements on a flat road surface have shown that the dedicated vehicle model yields accurate simulation results of the steering response to medium steering wheel angle inputs. In addition, the model has been validated by measuring two vehicle responses during normal driving on an undulating straight road: viz. the responses to the small steering wheel angle input and to the input by the global inclination of the road surface.     

带功率因数补偿的单相半控桥整流器(二)

介绍了绘制正弦线电流的开关模式单相半控桥整流器,用它来获得功率因数补偿并保持直流环节电压的恒定.在该整流器中使用4个有源开关,以便在交流端电压上产生单极脉宽调制(PWM)电压波形.与中性点箝位变流器(NPC)相比,该整流器没有箝位二极管也能实现三点式PWM控制.控制电路采用两个控制回路:外部控制回路用比例积分电压控制器调整直流环节电压,采用相位闭环电路产生与电源电压同相的正弦波形来实现功率因数补偿.在内部控制回路中,用基于载波的电流控制器跟踪线电流信号.为补偿由于负载变化所引起的中点电压,控制电路采用中点电压补偿器.该整流器的交流侧可产生3个电压电平,并用计算机仿真与试验结果验证了控制算法的有效性.     

A study of the dynamic response of submerged rectangular flat plates

The dynamic response of flat horizontal plates vibrating in air and under water has been investigated experimentally and analytically. The effect of the boundary conditions and the depth of submergence of the plates has been studied. Excellent agreement was obtained between the analytical solution and the experimental results. An approximate expression for the evaluation of the modal added masses for rectangular plates has been derived. This can be used to estimate the natural frequencies of plating constituting the internal structure within the cargo spaces in tankers and liquid cargo carriers.     

Airline industry deregulation and changes in systematic risk

Deregulation of U.S. Airline Industry may have lowered systematic risk because pricing freedom and route flexibility improved airline management reaction to various economic conditions. Reduced systematic risk offers lower cost of equity capital for the industry as a whole as well as for individual carriers. Previous research has had mixed results in identifying a relationship between deregulation and airline industry cost of capital. This study plots airline industry Beta coefficients across the years 1963 to 1987 and clears up previously conflicting research findings. Beta coefficients had been falling since the fuel crisis of 1974 and continued to fall through 1980. Fluctuations since deregulation have been relatively minor and systematic risk has leveled off at a significantly lower value than before deregulation. Studies which concentrate on the fluctuation in Beta since 1978 are dependent on the exact time period of analysis, and their conclusions that deregulation raised or lowered systematic risk are likewise suspect. A broader view of systematic risk changes in the deregulatory era shows airline Betas peaking from 1971 to 1973 and a gradual decrease as deregulation was being discussed, implemented, and legally mandated. This gradual decline from 1974 to 1980 may be attributed to such factors as fuel prices, interest rates, general inflation as well as deregulation. In any case systematic risk of the U.S. Airline industry has been lower since deregulation than in decades before.     

Grade measurement with an instrumented car

Grade information may be needed for route surveys and is important when fuel consumption is studied. An instrumented car was used to measure acceleration along the road surface by double differentiating accumulated pulses generated off the drive train. A second acceleration measure included the component due to gravity relative to the car body. The difference between these acceleration measures contains grade information but it also influenced by suspension dynamics and pitch of the car body. The effect of suspension dynamics was removed by filtering which limited the minimum wavelength to 160 m. The effect of pitch was removed by a correction based on acceleration, jerk and the square of vehicle speed. The correction was computed from data collected on a level airfield runaway. The method is verified for a high capacity arterial road. Grade is measured to within 0.001 rad (95% confidence limits). Elevation derived from the grade data was consistent with road construction drawings to the same limits.     

The effects of marine cargo delays in law and commerce

With the development of door-to-door intermodal services and the advent of just-in-time supply systems, punctual delivery of cargoes is more than ever a priority both for shippers and for shipowners. This paper is about the incidence of delay in transportation, particularly in the marine mode, and its legal and commercial consequences.

The fundamental legal obligations of marine carriers have always included delivery with dispatch. Thus the law would seem to support the commercial expectations of shippers for reliable performance. The authors discuss the nature of these obligations, investigate their adequacy under modern conditions of trade and report on a survey of Canadian shippers and consignees.

The authors conclude that there appears to be a divergence in the toleration of delay, but that few of the Canadian companies suffering unacceptable delays received, or even sought, financial compensation and none of them planned to do more. The authors speculate about their reasons for absorbing the losses incurred through unacceptable delays. The evidence from the survey is that shippers, in spite of their dissatisfaction with the resolution or outcome of incidents of unacceptable delay, are loath to seek compensation through legal means, but instead prefer to resort to a range of commercial actions.