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Risto Laulajainen 《Maritime Policy and Management》2013,40(5):447-461
Trade flows subjected to a major upheaval are followed by a reorganized freight rate structure. Rate functions developed under the old regime are unlikely to perform well because they are implicitly based on the circulation of tonnage which no longer applies, for example fronthauls and backhauls. A gravity-type static model capable of estimating route-specific rate levels from trade matrix data is developed and tested with historical data. The rates are in index form which makes it possible to integrate data from several ship size segments (large capesize, small capesize, panamax, handysize) and years. 相似文献
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《中国远洋航务公告》2010,(3):43-43
今年和明年,运力极度过剩将是令较大船型船东痛苦的事情。另一方面,轻便型船注定要赚得盆满钵溢。本文打算探讨一下2010年亚洲船东的经营前景问题。 相似文献
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The world bulk shipping market has been in a peak period since 2003, and this has lasted an incredibly long time considering that the markets are much more complex than before. This paper investigates the characteristics of volatility in dry bulk freight rates of different vessel sizes (capesize, panamax and handysize). The daily returns of freight rate indices of three different types of bulk vessel in the sample period have been examined. The sample period ran from 1 March 1999 to 23 December 2005, and applying the GARCH (generalized auto regressive conditional heteroskedasticity) model showed that the shocks will not decrease but have the tendency to strengthen for all the daily return series. Further, external shocks on the market have a different magnitude of influence on volatility in different types of vessels due to their distinct flexibility. To examine the asymmetric characters of daily return volatility in different bulk shipping sectors and different market conditions, the sample was divided into two periods: one is from 1 March 1999 to 31 December 2002, the other is from 1 January 2003 to 23 December 2005; the EGARCH (exponential generalized auto regressive conditional heteroskedasticity) model was then applied to investigate the asymmetric impact between past innovations and current volatility. The results show that the asymmetric characters are distinct for different vessel size segments and different market conditions. The reasons for the results are discussed and it is considered that the main reasons may be the different flexibility and different commodity transport on different routes. The results from this investigation will be useful for the operators and investors in the dry bulk shipping market to increase profitability and reduce investment risk. 相似文献
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文章提出了基于参考点的随机子空间船舶模态参数识别方法.该方法直接根据环境激励下测得的输出响应来构建Hankel矩阵,并通过QR分解技术对数据进行精简,再对投影矩阵进行奇异值分解(SVD)来剔除噪声,最后识别出结构的模态参数.它不受FFT(傅立叶变换)的影响,识别速度快,精度高.对于需快速识别船舶结构的模态参数,检测其可能存在的损伤,建立起预警及适时维修机制提供了有效手段. 相似文献
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Turbulence has a strong influence on plankton contact rate, which is a crucial parameter for plankton ecology. In the field of particle-turbulence interactions, it is now well known that fully developed turbulence does not always homogenise particle distributions, but instead creates, in some well-defined conditions, preferential concentrations of heavy particles. Many studies have considered the influence of this type of preferential concentration on particle contact rate. We consider here the possible application of these results to copepods, assuming that some results obtained for heavy particles are still valid for light particles. Using parameter values representative of copepod species in coastal waters and open ocean, we numerically estimate the possible enhancement of copepod contact rates due to the preferential concentration by turbulence. The assessment is done by using data from a laboratory experiment: we find from the trajectory analysis of small neutrally buoyant particles, that the preferential concentration effect increases the contact rate up to 140%. We argue that this effect may be more pronounced for higher Reynolds numbers, and may have important ecological applications. 相似文献
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对于复杂载荷作用下的船舶及海洋工程结构物,至今仍没有一个统一的疲劳寿命预报模型能够很好地解释载荷次序效应的影响.单峰过载下的疲劳裂纹扩展问题是研究变幅载荷疲劳问题的基础,伴随单峰过载将出现疲劳裂纹扩展迟滞现象.课题组所提出的广义疲劳裂纹扩展模型能够定量地预报出过载迟滞这一现象,通过确定过载参数β的大小,能够有效地衡量出过载迟滞的程度.在此基础上,文章将广义的疲劳裂纹扩展模型进行了进一步的修正,通过引入一个幂指数项,使得模型能够更好地反映出过载后疲劳裂纹扩展速率由迟滞的最低点逐渐恢复到过载前的水平.文中将课题组所发展的广义疲劳裂纹扩展率模型应用于实际的单峰过载疲劳问题中,并引用铝合金D16Cz的单峰过载试验数据与模型预报结果进行了比较,结果发现,经修正的广义疲劳裂纹扩展模型能够更好地反映出单峰过载后的疲劳裂纹扩展情况. 相似文献
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The purpose of this paper is to investigate the dynamics of forward freight rate dynamics. We specify our model in a Heath-Jarrow-Morton framework. This model was originally developed for interest rate markets and, in subsequent work, the model has been applied to various commodity markets. We analyse ten years of weekly time charter (TC) rates for a Panamax 65,000 dwt bulk carrier. Our data set consists of 6-, 12- and 36-month TC rates. We use this data to construct, each day, a forward rate function using a smoothing algorithm. We use the smooth data to investigate the factors governing the dynamics of the forward freight rate curve. We find a strange volatility structure in the data. Out results show that the volatility of the forward curve is bumped, with volatility reaching a peak for freight rates with roughly one year to maturity. Also, correlations between different parts of the term structure are in general low and even negative. 相似文献
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The purpose of this paper is to investigate the dynamics of forward freight rate dynamics. We specify our model in a Heath–Jarrow–Morton framework. This model was originally developed for interest rate markets and, in subsequent work, the model has been applied to various commodity markets. We analyse ten years of weekly time charter (TC) rates for a Panamax 65,000?dwt bulk carrier. Our data set consists of 6-, 12- and 36-month TC rates. We use this data to construct, each day, a forward rate function using a smoothing algorithm. We use the smooth data to investigate the factors governing the dynamics of the forward freight rate curve. We find a strange volatility structure in the data. Out results show that the volatility of the forward curve is bumped, with volatility reaching a peak for freight rates with roughly one year to maturity. Also, correlations between different parts of the term structure are in general low and even negative. 相似文献
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《船舶与海洋工程学报》2015,(3)
Submerged arc welding(SAW) is advantageous for joining high thickness materials in large structure due to high material deposition rate. The non-uniform heating and cooling generates the thermal stresses and subsequently the residual stresses and distortion. The longitudinal and transverse residual stresses and angular distortion are generally measured in large panel structure of submerged arc welded fillet joints. Hence, the objective of this present work is to quantify the amount of residual stress and distortion in and around the weld joint due to positioning of stiffeners tack. The tacking sequence influences the level of residual stress and proper controlling of tacking sequences is required to minimize the stress. In present study, an elasto-plastic material behavior is considered to develop the thermo mechanical model which predicts the residual stress and angular distortion with varying tacking sequences. The simulated result reveals that the tacking sequence heavily influences the residual stress and deformation pattern of the single sided fillet joint. The finite element based numerical model is calibrated by comparing the experimental data from published literature. Henceforth, the angular distortions are measured from an in-house developed experimental set-up. A fair agreement between the predicted and experimental results indicates the robustness of the developed numerical model. However, the most significant conclusion from present study states that tack weld position should be placed opposite to the fillet weld side to minimize the residual stress. 相似文献
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Civil infrastructure systems such as bridge piers, navigational guide walls, and protection structures that are located near navigable waterways are inherently at risk for being impacted by cargo vessels such as barges and ships. To safely design such systems to possess adequate vessel impact resistance, structural loads associated with potential vessel-structure collision conditions must be quantified in a conservative manner. While high-resolution finite element impact simulations may be employed to compute such loads, care must be exercised in defining the material characteristics of the vessel if conservative structural design loads are to be obtained. Importantly, constitutive relationships assigned to steel components in the vessel model must be capable of accounting for strain rate sensitivities and large-scale plastic deformations.In the present study, strain rate sensitive constitutive models were developed for two types of steel commonly utilized in marine construction in the United States—ASTM A36 and ASTM A1011. Tension tests were conducted over a wide range of strain rates (7.00 × 10−5 s−1 – 250 s−1) spanning from quasi-static to intermediate and high rates that are typically associated with vessel-structure impact events. A novel testing apparatus—employing an impact pendulum as an energy supply mechanism—was designed for this study to conduct intermediate to high-rate material testing. Features of the apparatus, discussed in this paper, overcome key problems encountered in other studies that have employed impact loading for tensile material testing. From the testing program, representative stress–strain relations and Cowper–Symonds strain rate sensitivity parameters were developed for the materials tested. Rate sensitivities of the two steel grades tested were found to be very similar to each other. Additionally, rate sensitivities from the present study agreed well with ultimate stress data measured in past studies of mild steel, but were found to be less rate-sensitive than yield stress data measured in past studies. 相似文献
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Submerged arc welding (SAW) is advantageous for joining high thickness materials in large structure due to high material deposition rate. The non-uniform heating and cooling generates the thermal stresses and subsequently the residual stresses and distortion. The longitudinal and transverse residual stresses and angular distortion are generally measured in large panel structure of submerged arc welded fillet joints. Hence, the objective of this present work is to quantify the amount of residual stress and distortion in and around the weld joint due to positioning of stiffeners tack. The tacking sequence influences the level of residual stress and proper controlling of tacking sequences is required to minimize the stress. In present study, an elasto-plastic material behavior is considered to develop the thermo mechanical model which predicts the residual stress and angular distortion with varying tacking sequences. The simulated result reveals that the tacking sequence heavily influences the residual stress and deformation pattern of the single sided fillet joint. The finite element based numerical model is calibrated by comparing the experimental data from published literature. Henceforth, the angular distortions are measured from an in-house developed experimental set-up. A fair agreement between the predicted and experimental results indicates the robustness of the developed numerical model. However, the most significant conclusion from present study states that tack weld position should be placed opposite to the fillet weld side to minimize the residual stress. 相似文献
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Hang Tuah. Salim 《水道港口》2010,31(5):321-321
Belawan is the largest port serving North Sumatra for the import and export.Port has facilities for handling container,CPO liquid bulk cargo,Oil,and other agriculture products.Its location is at the river mouth which is subjected to the heavy sedimentation especially after many deforestation activities in its catchment area. The numerical modeling was developed for predicting the rate of sediment caused by erosion in the catchment area for several scenarios.This predicted rate of sediment was applied as input to model of sedimentation in the ocean.Present condition of sedimentation data was used as calibrated data.This integrated model was used to simulate the sedimentation in Belawan access channel and harbor basin for several development plans. 相似文献
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Mathematical model of single-propeller twin-rudder ship 总被引:1,自引:1,他引:0
Donghoon Kang Vishwanath Nagarajan Kazuhiko Hasegawa Masaaki Sano 《Journal of Marine Science and Technology》2008,13(3):207-222
A mathematical model of a single-propeller twin-rudder ship has been developed from captive and free running model experiments.
An open water rudder experiment was carried out to figure out the characteristics of the rudder. Captive experiments in a
towing tank were carried out to figure out the performance of a single-propeller twin-rudder system on a large vessel. Interactions
between the hull, propeller and twin rudders, including mutual interactions between the twin rudders, were expressed with
several coefficients that were calculated from the experimental results at various ship speeds. In the analysis, the unique
characteristics of a single-propeller twin-rudder ship, which affects rudder forces, were explained and formulated in the
mathematical model. The captive model tests were conducted with zero ship’s yaw rate, so the interaction coefficients, which
are influenced by the yaw rate, are determined from free running model experiments. Validation of the mathematical model of
a single-propeller twin-rudder system for a blunt body ship is carried out with an independent set of free running experiments,
which were not used for determining the interaction coefficients. The validated numerical model is used for carrying out simulations.
Based on simulation results, some recommendations have been proposed for installing a single-propeller twin-rudder system. 相似文献
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苏通大桥主桥钢箱梁安装几何测量与监测技术 总被引:1,自引:0,他引:1
苏通大桥为主跨1 088 m的世界第一跨距双塔双索面斜拉桥。主桥钢箱梁安装过程中,因风、温差等引起钢箱梁较大变形及振动,为此,进行了测量机器人自动监测软件系统的开发,同时采用高采样率GPS,研究开发实时无线数据采集传输系统,克服了斜拉桥传统测量、监测方法的弊端,该研究系统在钢箱梁安装局部测量与全局测量中取得了较理想的效果及应用价值,确保了苏通大桥主桥钢箱梁线形几何控制准确,合龙精度为轴线0.5 mm、高程1.5 mm。 相似文献