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01 December 2017, Volume 22 Issue 6 Previous Issue    Next Issue

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Model Testing for Ship Hydroelasticity: A Review and Future Trends JIAO Jialong1,2 (焦甲龙), REN Huilong2 (任慧龙), CHEN Chaohe1* (陈超核) 2017, 22 (6):  641-650.  doi: 10.1007/s12204-017-1886-5 Abstract ( 812 )   Conducting model experiments is an effective and reliable way in the investigation of ship hydrodynamic and hydroelastic behaviors. A survey of model testing techniques for ship hydroelasticity and its prospect are presented in this paper. The research highlights with respect to ship hydroelasticity and key points in model testing are summarized at first. Then testing techniques including laboratory tank test and full-scale sea trial are reviewed, and both their advantages and disadvantages are analyzed comprehensively. Based on the conventional testing approaches, a state-of-the-art testing approach which includes performing tests using large-scale model at sea is proposed. Furthermore, recommendations towards the further development of ship hydroelasticity tests are forecasted and discussed. References | Related Articles | Metrics

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Experimental Study on Performance of Combined Cambered-Type Wave Absorbing Beach LI Jun* (李俊), YANG Jianmin (杨建民), PENG Tao (彭涛) 2017, 22 (6):  651-656.  doi: 10.1007/s12204-017-1887-4 Abstract ( 784 )   Wave simulation performance and its quality are key factors to reflect the overall capacity and level of an ocean engineering basin. They include wave simulating and absorbing capacity of reflected waves. In order to reduce the influence of reflected waves, various wave absorbing devices are equipped in ocean engineering basins across the world. The experimental investigation into the performance of combined cambered-type wave absorbing beach (CCTWAB) with damping bars equipped in Deepwater Offshore Basin is conducted. The experiment adopts the two-point method. The reflection coefficients are calculated by the method, in which the incident and reflected waves can be separated from the physically simulated composite waves with different periods and wave heights in the time domain. The experimental results indicate that in the range of normal wave heights and periods for model tests, the CCTWAB with damping bars is excellent in eliminating the reflected waves. References | Related Articles | Metrics

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Minimum Resistance Ship Hull Uncertainty Optimization Design Based on Simulation-Based Design Method HOU Yuanhang* (候远杭), YOU Yuan (游园), LIANG Xiao (梁霄) 2017, 22 (6):  657-663.  doi: 10.1007/s12204-017-1882-9 Abstract ( 713 )   In the ship hull optimization design based on simulation-based design (SBD) technology, low precision of the approximate model leads to an uncertainty form of optimization model. In order to enable the approximate model with finite precision to maximize the effectiveness, uncertainty optimization method is introduced here. Wave resistance coefficient approximation model, built by back propagation (BP) neural network, is represented as a form of interval. Afterwards, a minimum resistance optimization model is established with the design space constituted by principal dimensions and ship form coefficients. Double-level nested optimization architecture is proposed: for outer layer, improved particle swarm optimization (IPSO) algorithm with learning factor improvement strategy is used to generate design variables, and for inner layer, modified very fast simulated annealing (MVFSA) algorithm is used to solve the objective function interval with uncertainty region. Cases calculation proves the effectiveness and superiority of uncertainty optimization method for ship hull SBD optimization design, thus providing a good way for finding optimal designs. References | Related Articles | Metrics

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Optimal Allocation of Fleet’s Spare Parts for System Reliability WANG Hongdonga (王鸿东), LI Danb* (李丹), YI Honga (易宏) 2017, 22 (6):  664-671.  doi: 10.1007/s12204-017-1888-3 Abstract ( 769 )   Allocation of fleet’s spare parts is rarely studied due to its complexity. However, this task is extremely important because the warship’s service level highly relies on the maintenance logistics’ level. In this study, the readiness ratio is proposed as a critical index in measuring the system’s reliability. A well-established mathematical model adopting the optimization method of spare part allocation is also introduced. The objective is to minimize the number of each spare part while satisfying the fleet’s system reliability. The fault tree analysis (FTA) is applied to analyze the system’s failure logic and stratify the units on ship. As a result, the strategy of spare part sharing can be introduced in detail. The solution algorithm is developed, and the simulation experiments to obtain the key parameters are conducted. The proposed model and algorithm are applied to an actual fleet of two warships, and results show that the method above is feasible and can be directly applied into practice. References | Related Articles | Metrics

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Uncertainty Analysis of Value for Money Assessment for Public-Private Partnership Projects LIANG Qingxue (梁晴雪), HU Hao* (胡昊) 2017, 22 (6):  672-681.  doi: 10.1007/s12204-017-1889-2 Abstract ( 853 )   In recent years, private sectors are encouraged to take an active part in franchising of urban infrastructure investments and operations, which promotes the rapid development of public-private partnership (PPP) in infrastructure and public service supply. Value for money (VFM) assessment has been officially proposed to provide a reference for selection of projects planning to adopt PPP. Based on the bottlenecks of VFM application in China and the uncertainties for urban infrastructure PPP projects, a discounted cash flow (DCF) model is established for VFM of infrastructure PPP projects. Then, a Monte Carlo simulation model is established on the basis of uncertainty factors for VFM. Through the analysis of Huai’an trams PPP project, coping strategies of uncertainties for VFM are put forward. Findings of the research may propel the establishment of a complete VFM evaluation system for PPP projects. Key instructional functions of VFM during the process of decision-making can be brought into full play and PPP may develop orderly. References | Related Articles | Metrics

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Analyzing Behavior Differences of Occupied and Non-Occupied Taxi Drivers Using Floating Car Data NIAN Guangyue1,2 (年光跃), LI Zhe2,3 (李喆), ZHU Weiquan4 (朱伟权), SUN Jian1,2* (孙健) 2017, 22 (6):  682-687.  doi: 10.1007/s12204-017-1890-9 Abstract ( 789 )   As the travel purpose of non-occupied taxies is to find new passengers rather than to arrive at the destination, large differences exist in the route choice behavior between the occupied and non-occupied taxies. With the assistance of geographic information system (GIS) and taxi-based floating car data (FCD), this paper investigates the behavior differences between occupied and non-occupied taxi drivers with the same origin and destination. Descriptive statistical indexes from the FCD in Shenzhen, China are explored to identify the route choice characteristics of occupied and non-occupied taxies. Then, a conditional logit model is proposed to model the quantitative relationship between drivers’ route choice and the related significant variables. Attributes of the variables related to non-occupied taxies’ observed routes are compared with the case of occupied ones. The results indicate that, compared with their counterparts, non-occupied taxi drivers generally pay more attention to choosing arterial roads and avoiding congested segments. Additionally, they are also found less sensitive to fewer traffic lights and shorter travel time. Findings from this research can assist to improve urban road network planning and traffic management. References | Related Articles | Metrics

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Pedestrian Crosswalk Overflow Violation in China: Characteristics and Countermeasure CAO Ningbo (曹宁博), CHEN Yongheng* (陈永恒), QU Zhaowei (曲昭伟),ZHAO Liying (赵利英), BAI Qiaowen (白乔文), DENG Xiaolei (邓晓磊) 2017, 22 (6):  688-696.  doi: 10.1007/s12204-017-1891-8 Abstract ( 790 )   The phenomenon that pedestrians do not walk in the crosswalk during pedestrian green is defined as overflow violation, which is illegal but common. Broadly varying crossing positions at far-side cross-section may result in widely distributed conflict points with left-turning and right-turning vehicles, which may cause the occurrence of severe conflicts. This paper proposes a model to estimate the overflow pedestrians’ crossing positions at the far-side cross-section of signalized crosswalk, which enables us to better understand pedestrian overflow violation behavior and finally facilitate their safety. After analysis, the intersection geometry and destination are determined as the critical factors causing pedestrians to overflow. And then, Weibull distribution is employed to describe the stochastic characteristics of overflow pedestrians’ crossing position distribution at the far-side cross-section. A crossing position distribution model which takes the crosswalk length, width and distance between crosswalk and destination into account is developed. The established model is validated by comparing the observed pedestrian crossing positions with the estimated crossing positions. The validation results suggest that the established model is capable of being adopted to estimate the overflow pedestrians’ crossing positions at far-side cross-section. Based on the model, countermeasure for overflow violation can be put forward to prevent pedestrians from walking outside the crosswalk. References | Related Articles | Metrics

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An Improved General Bidirectional Progression Model for Arterial GUO Yajuan1,2 (郭亚娟), YANG Licai1* (杨立才), HAO Shenxue1 (郝慎学), GAO Jun3 (郜军) 2017, 22 (6):  697-704.  doi: 10.1007/s12204-017-1892-7 Abstract ( 618 )   Optimal control of arterial signals is critical for the effective operation of urban road network. With the goal of providing reasonable allocation of bidirectional green time while maximizing general bidirectional traffic progression along the arterial, this paper develops an improved general bidirectional coordinated progression model for arterial based on Maxband model. In the model, a proportional coefficient of bidirectional bandwidth demands is introduced and calibrated by adopting average link queue occupancy. The calibration method takes full account of actual traffic volume and capacity of each link, which helps to provide optimal control performance. Additionally, new constraints are added into the model and enable the model with two features: it can automatically select two-way or one-way progression, and the involved intersection unit can be either one-phase-one-approach or bidirectional symmetric release mode. The results of extensive simulation studies indicate that the improved model outperforms existing methods, markedly increasing the utilization of available bidirectional green time. References | Related Articles | Metrics

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Responses of the Strata and Supporting System to Dewatering in Deep Excavations XIAO Xiao (肖潇), ZHANG Yangqing (张扬清), LI Mingguang* (李明广), WANG Jianhua (王建华) 2017, 22 (6):  705-711.  doi: 10.1007/s12204-017-1884-7 Abstract ( 643 )   In order to prevent the inrushing caused by deep excavations, dewatering measure has to be adopted to decrease the confined water level. In this study, the responses of the strata and supporting system to dewatering in deep excavations are investigated through numerical simulations and case studies. Coupled fluid-mechanical analyses are performed by the use of the numerical software, FLAC3D. The responses of the ground settlement, base heave and interior columns to the excavation and dewatering are analyzed. Numerical results indicate that the dewatering measure can effectively reduce the uplift of the subsurface soil in the excavation, and decrease the vertical displacement of the supporting system. In addition, field data of two case histories show the similar responses and confirm the validation of the numerical results. Based on the analyses, dewatering in the confined aquifer is recommended as a construction method for controlling the vertical displacement of the strata and supporting system in deep excavations. References | Related Articles | Metrics

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Microstructure Evolution During Remelting of High Solid Fraction ZL101 Alloy LUO Shuai (罗帅), YU Huping* (于沪平), QIU Haiyuan (邱海渊), SHEN Yu (申昱) 2017, 22 (6):  712-718.  doi: 10.1007/s12204-017-1885-6 Abstract ( 752 )   This work deals with the reheating process for semi-solid thixoforming of ZL101 (AlSi7Mg) alloy. The semi-solid state can decrease the viscosity and the resistance while sheared because of the evolutional behavior, which is characterized by a solid-like behavior at rest and a liquid flow during shearing. The microstructure evolution of ZL101 alloy at different temperatures from 540 to 580 ?C has been studied. Results show that the eutectic temperature can affect the transformation speed of semi-solid structure. Semi-solid microstructures with high solid fraction can be obtained by controlling the reheating time in less than 20min, while at the temperature lower than the eutectic temperature it needs more than one hour. Another character of semi-solid ZL101 alloy is the segregation of microstructures in semi-solid state, in which the liquid phase between the solid phases can flow freely and lead to the shrinkage of the sample during the heating process. As the holding time goes on, more shrinkage holes appear and change the surface of the specimen. These shrinkage holes are replenished by the liquid phase during compression deformation, resulting in the segregation of the components. References | Related Articles | Metrics

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Application of Digital Image Correlation Method to In-Situ Dynamic Strain Measurement LIN Liexiong (林烈雄), LU Hao* (陆皓), XU Jijin (徐济进),CHEN Junmei (陈俊梅), YU Chun (余春) 2017, 22 (6):  719-725.  doi: 10.1007/s12204-017-1864-y Abstract ( 807 )   Application of digital image correlation (DIC) method to determination of in-situ dynamic strain is presented in this study. Firstly, an integrative software is programmed based on the DIC algorithms and pointwise least-squares fitting technique. Then, simulated speckle images are generated to study the computational accuracy of this software. The experimental setup and procedures for measuring in-situ dynamic strain through both DIC and strain gauge are proposed. The DIC results are close to those measured by strain gauge. This fact reveals that DIC is a practical and effective tool for in-situ dynamic strain measurement. Finally, the full-field in-situ dynamic strain of another specimen is measured by DIC, and the overall distribution of the strain in the measurement area is clearly shown. References | Related Articles | Metrics

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Experimental Simulation on Dynamic Variation of the Permeability of High-Rank Coal Reservoirs HE Ye1,2* (何也), FU Xuehai1 (傅雪海), LIU Aihua3 (刘爱华) 2017, 22 (6):  726-732.  doi: 10.1007/s12204-017-1893-6 Abstract ( 572 )   In terms of the coal reservoir permeability of effective stress, coal matrix shrinkage and gas slippage, we conduct the tests of gas permeability under constant confining pressure and effective stress, as well as illustrate the cumulating method of permeability increment caused by the effects of gas slippage and coal matrix shrinkage. The results show that under the constant confining pressure, gas slippage affecting coal permeability changes to effective stress affecting it mainly. The change point increases with the increase of the confining pressure. The gas slippage effect leads to high permeability under low confining pressure, but coal matrix expansion results in the low value as confining and gas pressures increase. Combined with the drainage process of coalbed methane (CBM) well, the permeability is divided into four change stages based on the above analysis about the three effects, which can improve the change regulation understanding. Four stages are the downward phase under effective stress, the conversion phase of effective stress-coal matrix contraction effect (mainly based on effective stress), the rising stage of the effective stress-coal matrix contraction effect (mainly based on coal matrix contraction effect) and the rising phase of coal matrix contraction-slippage effect (mainly based on slippage effect). Permeability of coal reservoir during the process of drainage and production goes through four stages. References | Related Articles | Metrics

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Integration of Learning Algorithm on Fuzzy Min-Max Neural Networks HU Jing* (胡静), LUO Yiyuan (罗宜元) 2017, 22 (6):  733-741.  doi: 10.1007/s12204-017-1894-5 Abstract ( 944 )   An integrated fuzzy min-max neural network (IFMMNN) is developed to avoid the classification result influenced by the input sequence of training samples, and the learning algorithm can be used as pure clustering, pure classification, or a hybrid clustering classification. Three experiments are designed to realize the aim. The serial input of samples is changed to parallel input, and the fuzzy membership function is substituted by similarity matrix. The experimental results show its superiority in contrast with the original method proposed by Simpson. References | Related Articles | Metrics

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Trade-off in Optimizing Energy Consumption and End User Quality of Experience in Radio Access Network XU Yuemei1* (徐月梅), WANG Zihou2 (王子厚), LI Yang3 (李杨), CAI Lianqiao1 (蔡连侨) 2017, 22 (6):  742-751.  doi: 10.1007/s12204-017-1895-4 Abstract ( 665 )   To reduce network access latency, network traffic volume and server load, caching capacity has been proposed as a component of evolved Node B (eNodeB) in the ratio access network (RAN). These eNodeB caches reduce transport energy consumption but lead to additional energy cost by equipping every eNodeB with caching capacity. Existing researches focus on how to minimize total energy consumption, but often ignore the trade-off between energy efficiency and end user quality of experience, which may lead to undesired network performance degradation. In this paper, for the first time, we build an energy model to formulate the problem of minimizing total energy consumption at eNodeB caches by taking a trade-off between energy efficiency and end user quality of experience. Through coordinating all the eNodeB caches in the same RAN, the proposed model can take a good balance between caching energy and transport energy consumption while also guarantee end user quality of experience. The experimental results demonstrate the effectiveness of the proposed model. Compared with the existing works, our proposal significantly reduces the energy consumption by approximately 17% while keeps superior end user quality of experience performance. References | Related Articles | Metrics

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Optimal Inspection and Replacement Strategy for Systems Subject to Two Types of Failures with Adjustable Inspection Intervals MA Xiaoyang1* (马晓洋), WANG Wenbin1,2 (王文彬), LIU Xuejuan1 (刘学娟), PENG Rui1 (彭锐) 2017, 22 (6):  752-755.  doi: 10.1007/s12204-017-1896-3 Abstract ( 675 )   The inspection activities are often carried out to detect possible indication of failures in plant systems. This paper considers a single unit system subject to two types of failures, where one failure mode is the traditional 0-1 logic failure and the other failure mode is described by a two-stage failure process. Adjustable inspections are used to detect the defective stage of the latter. We assume that the inspection duration gets shorter and shorter with a constant ratio. At the same time, preventive replacement is used to avoid the possible failure due to the former failure mode. The renewal process of this system is analyzed and the expected long-run cost per unit time (ELRCUT) is derived. The optimal inspection period and the preventive replacement interval to minimize ELRCUT are studied. At last, a numerical example is presented to illustrate the proposed model. References | Related Articles | Metrics

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CT Reconstruction with Priori MRI Images Through Multi-Group Datasets Expansion WANG Qihui (王齐辉), XI Yan (奚岩), CHEN Yi (陈毅),ZHANG Weikang (张伟康), ZHAO Jun* (赵俊) 2017, 22 (6):  756-762.  doi: 10.1007/s12204-017-1897-2 Abstract ( 775 )   Computed tomography (CT) reconstruction with a well-registered priori magnetic resonance imaging (MRI) image can improve reconstruction results with low-dose CT, because well-registered CT and MRI images have similar structures. However, in clinical settings, the CT image of patients does not always match the priori MRI image because of breathing and movement of patients during CT scanning. To improve the image quality in this case, multi-group datasets expansion is proposed in this paper. In our method, multi-group CT-MRI datasets are formed by expanding CT-MRI datasets. These expanded datasets can also be used by most existing CT-MRI algorithms and improve the reconstructed image quality when the CT image of a patient is not registered with the priori MRI image. In the experiments, we evaluate the performance of the algorithm by using multi-group CT-MRI datasets in several unregistered situations. Experiments show that when the CT and priori MRI images are not registered, the reconstruction results of using multi-group dataset expansion are better than those obtained without using the expansion. References | Related Articles | Metrics