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01 August 2018, Volume 23 Issue 4 Previous Issue    Next Issue

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Multi-Objective Optimization of Torsion Springs for Solar Array Deployment YANG Lili (杨丽丽), WANG Deyu (王德禹) 2018, 23 (4):  465.  doi: 10.1007/s12204-018-1969-y Abstract ( 477 )   For solar array deployment, most existing studies mainly focus on modeling method of deployment dynamics, characteristics of hinges, and synchronization mechanisms. However, torsion springs, which work as the drive mechanisms, have hardly attracted people’s attention. In this study, the influence of the parameters of torsion springs on the deployment behavior of a solar array system with clearance joint is investigated by simulation experiments. The experimental results indicate that the deployment performances are very sensitive to the parameter values of the torsion spring. Suitable torsion springs are highly needed to improve the deployment dynamics of solar array system. Therefore, a multi-objective optimization method for the design of torsion springs is proposed. The objective of the optimization is to make the contact-impact force in revolute joint and the mass of the torsion spring minimum under the constraints of deployment time and structure strength. Finally, the effectiveness of the multi-objective optimization method is verified by an optimization example of solar array system. References | Related Articles | Metrics

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Numerical Simulation of Focused Wave and Its Uncertainty Analysis BAI Junli (柏君励), MA Ning (马宁), GU Xiechong (顾解忡) 2018, 23 (4):  475.  doi: 10.1007/s12204-018-1970-5 Abstract ( 508 )   On the basis of the transient water wave (TWW) theory, focused wave is generated in the circulating water channel. Numerical simulation of the focused wave is carried out by solving the Reynolds averaged Navier- Stokes (RANS) equations. The dynamic grid technique is adopted to simulate the motion of the wave maker, and the volume of fluid (VOF) method is used to capture the free surface of the wave. The simulation results are compared with the measured data, and good agreement is obtained. For quantitative estimation of the numerical simulation error and uncertainty, the uncertainty analysis method recommended by the International Towing Tank Conference (ITTC) procedure is performed for the simulation results of the surface elevations at different positions. Both grid-convergence and time-step-size convergence studies are conducted using three types of grids and time step sizes. The simulation results are all monotonously convergent in the verification procedure, and the validations of the simulated surface elevations with the positions at 3.5, 4.0 and 4.5m are all achieved by comparing with the validation uncertainty. It is found that the numerical simulation errors caused by the grid and time-step-size in the convergence studies have the same order of magnitude. In addition, the numerical errors and uncertainties for the surface elevations at different positions are compared and discussed in detail. This paper presents the first attempt to carry out the uncertainty analysis of the simulation of focused wave, and the effectiveness of the proposed verification and validation procedures in the uncertainty analysis is demonstrated. References | Related Articles | Metrics

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Field Tests for Investigating the Extraction Rate of Piles Using a Vibratory Technique QIN Zhaohui (秦朝辉), CHEN Longzhu (陈龙珠), SONG Chunyu (宋春雨), ZHANG Jingyi (张敬一) 2018, 23 (4):  482.  doi: 10.1007/s12204-018-1971-4 Abstract ( 420 )   Factors directly affecting the extraction rate of the piles pulled out by a vibratory pulling system are summarized and classified into five categories (excitation force, resistance, vibration amplitude, pile plumbness keeping, and slowing down at the later stage) from the mechanics and engineering practice. Field tests on steel sheet piles extracted by vibratory technique in different soil conditions are conducted to ascertain how these factors affect the extraction rate of a pile with regard to three major actors of vibratory pile pulling: the pile to be extracted, the selected pulling system, and the imposed soil conditions. The extraction rates of three different sheet pile types (having up to four different lengths) pulled out by two different vibratory pulling systems are documented. The piles with different lengths and types, pulled out with or without a clutch, have different extraction rates. The working parameters governing the vibratory hammer, such as excitation force and vibration amplitude, exert significant influences on the rate of pile extraction, especially in the early stages of up-lift process. The extraction rate of the piles driven in different soil conditions is uniform because different extraction resistances mainly refer to shaft friction. The properties of the pile-soil interface influence the extraction rate of the piles, and the extraction rate decreases with the time for which the piles have been buried in the earth. References | Related Articles | Metrics

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Protection of Historical Buildings in Metro Line Construction: A Case Study in Shanghai, China FAN Fan (范凡), CHEN Jinjian (陈锦剑), WANG Jianhua (王建华) 2018, 23 (4):  490.  doi: 10.1007/s12204-017-1883-8 Abstract ( 493 )   his research presents a holistic approach to the protection of historical building group adjacent to metro line construction, in which health investigation, protection criterion determining, numerical simulation analyses, corresponding protection measures and field monitoring analyses are incorporated as main procedures. A case relating to the conservation of a seven-storey brick-wood pagoda, Longhua Pagoda, adjacent to the construction of Shanghai Metro Lines 11 and 12 in China, is presented. A reasonable protection criterion is determined rationally by means of numerical simulation based on the health investigation results combined with related standards, which can help to achieve a fine balance between system safety and cost constraints in protection measures determining. A full numerical model is developed to analyze the effect of dewatering, excavation, tunneling, and shield departure/reception, and corresponding measures are adopted to ensure the safety of the pagoda. Especially a brand new method, steel jacket method, is introduced in detail, which has a good performance on decreasing the amount of dewatering and maintaining a stable working face. Results demonstrate the application potential of the proposed approach, as well as its feasibility. The proposed approach can be used in the industry by practitioners to provide positive guidelines on the conservation of historical building group against metro line constructions. The reliable and detailed data in this case can also provide verification for subsequent research. References | Related Articles | Metrics

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Research on Dynamic Response Characteristics of 6MW Spar-Type Floating Offshore Wind Turbine MENG Long (孟龙), HE Yanping (何炎平), ZHOU Tao (周涛), ZHAO Yongsheng (赵永生), LIU Yadong (刘亚东) 2018, 23 (4):  505.  doi: 10.1007/s12204-018-1972-3 Abstract ( 525 )   A 6MW spar-type floating offshore wind turbine (FOWT) model is put forward and a fully coupled aero-hydro-servo-elastic time domain model is established in the fatigue, aerodynamics, structures and turbulence (FAST) code. Influence rules of wind load and wave load on the characteristics of 6MW spar-type FOWT are investigated. Firstly, validation of the model is carried out and a satisfactory result is obtained. The maximal deviations of rotor thrust and power between simulation results and reference values are 4.54% and ?2.74%, respectively. Then the characteristics, including rotor thrust, rotor power, out-of-plane blade deflection, tower base fore-aft bending moment, and mooring line tension, are researched. The results illustrate that the mean value of dynamic response characteristics is mainly controlled by the wind-induced action. For characteristics of tower base fore-aft bending moment and platform pitch motion, the oscillation is dominated by the wave-induced action during all conditions considered. For characteristics of out-of-plane blade tip deflection and mooring line tension, the oscillation is commanded by combination effect of wave and wind loads when the wind speed is lower than the rated wind speed (hereinafter referred to as below rated wind speed) and is controlled by the wave-induced action when the wind speed is higher than the rated wind speed (hereinafter referred to as above rated wind speed). As to the rotor thrust and power, the oscillation is dominated by the wind induced action at below rated wind speed and by the combination action of wind and wave loads at above rated wind speed. The results should be useful to the detailed design and model basin test of the 6MW spar-type FOWT. References | Related Articles | Metrics

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Tool for Predicting the Ultimate Bending Moment of Ship and Ship-Shaped Hull Girders VU Van Tuyen, YANG Ping(杨平) 2018, 23 (4):  515.  doi: 10.1007/s12204-018-1973-2 Abstract ( 377 )   The present paper presents a historical review associated with the research works on hull girder strength of ship and ship-shaped structures. Then, a new program is developed to determine the ultimate vertical bending moment of hull girder by applying direct method, stress distribution method, and progressive collapse analysis method. Six ships and ship-shaped structures used in the benchmark study of International Ship and Offshore Structures Congress (ISSC) in 2012 are adopted as examples. The calculation results by applying the developed program are analyzed and compared with the existing results. Finally, the roles of the developed program and its further development are discussed. References | Related Articles | Metrics

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Multi-Objective Optimization of Rail Pre-Grinding Profile in Straight Line for High Speed Railway ZENG Wei (曾威), QIU Wensheng (丘文生), REN Tao (任涛), SUN Wen (孙文), YANG Yue (杨岳) 2018, 23 (4):  527.  doi: 10.1007/s12204-018-1974-1 Abstract ( 370 )   In order to modify the rail pre-grinding profile smoothly, non-uniform rational B-spline (NURBS) curve with weight factors is used to establish a parameterized model of the profile. A wheel-rail contact stochastic finite element model (FEM) is constructed by the Latin hypercube sampling method and 3D elasto-plastic FEM, in which the wheelset’s lateral displacement quantity is regarded as a random variable. The maximum values of nodal accumulated contact stress (NACS) and nodal mean contact stress (NMCS) in different pre-grinding profiles with differential weight factors are calculated and taken as the training samples to establish two Kriging models. A multi-objective optimization model of pre-grinding profile is established, in which the objective functions are the NACS and NMCS Kriging models. The optimum weight factors are sought using a non-dominated sorting genetic algorithm II (NSGA-II), and the corresponding optimum pre-grinding profile is obtained. The contact stress calculation before and after optimization indicates that the maximum values of NACS and NMCS decline significantly. References | Related Articles | Metrics

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Structural Optimization of Hatch Cover Based on Bi-directional Evolutionary Structure Optimization and Surrogate Model Method LI Kai (李楷), YU Yanyun (于雁云), HE Jingyi (何靖仪), ZHAO Decai (赵德财), LIN Yan (林焰) 2018, 23 (4):  538.  doi: 10.1007/s12204-018-1975-0 Abstract ( 356 )   Weight reduction has attracted much attention among ship designers and ship owners. In the present work, based on an improved bi-directional evolutionary structural optimization (BESO) method and surrogate model method, we propose a hybrid optimization method for the structural design optimization of beam-plate structures, which covers three optimization levels: dimension optimization, topology optimization and section optimization. The objective of the proposed optimization method is to minimize the weight of design object under a group of constraints. The kernel optimization procedure (KOP) uses BESO to obtain the optimal topology from a ground structure. To deal with beam-plate structures, the traditional BESO method is improved by using cubic box as the unit cell instead of solid unit to construct periodic lattice structure. In the first optimization level, a series of ground structures are generated based on different dimensional parameter combinations, the KOP is performed to all the ground structures, the response surface model of optimal objective values and dimension parameters is created, and then the optimal dimension parameters can be obtained. In the second optimization level, the optimal topology is obtained by using the KOP according to the optimal dimension parameters. In the third optimization level, response surface method (RSM) is used to determine the section parameters. The proposed method is applied to a hatch cover structure design. The locations and shapes of all the structural members are determined from an oversized ground structure. The results show that the proposed method leads to a greater weight saving, compared with the original design and genetic algorithm (GA) based optimization results. References | Related Articles | Metrics

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Adaptive Multi-Objective Optimization of Bionic Shoulder Joint Based on Particle Swarm Optimization LIU Kai (刘凯), WU Yang (吴阳), GE Zhishang (葛志尚), WANG Yangwei (王扬威), XU Jiaqi (许嘉琪), LU Yonghua (陆永华), ZHAO Dongbiao (赵东标) 2018, 23 (4):  550.  doi: 10.1007/s12204-018-1958-1 Abstract ( 417 )   To get the movement mode and driving mechanism similar to human shoulder joint, a six degrees of freedom (DOF) serial-parallel bionic shoulder joint mechanism driven by pneumatic muscle actuators (PMAs) was designed. However, the structural parameters of the shoulder joint will affect various performances of the mechanism. To obtain the optimal structure parameters, the particle swarm optimization (PSO) was used. Besides, the mathematical expressions of indexes of rotation ranges, maximum bearing torque, discrete dexterity and muscle shrinkage of the bionic shoulder joint were established respectively to represent its many-sided characteristics. And the multi-objective optimization problem was transformed into a single-objective optimization problem by using the weighted-sum method. The normalization method and adaptive-weight method were used to determine each optimization index’s weight coefficient; then the particle swarm optimization was used to optimize the integrated objective function of the bionic shoulder joint and the optimal solution was obtained. Compared with the average optimization generations and the optimal target values of many experiments, using adaptive-weight method to adjust weights of integrated objective function is better than using normalization method, which validates superiority of the adaptive-weight method. References | Related Articles | Metrics

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Research on Motion Estimation Algorithm of Star Point Based on Nonlinear Gaussian Fitting WANG Chaoran (王超然), BAO Qilian (鲍其莲), ZHENG Xunjiang (郑循江), SUN Shuodong (孙朔冬) 2018, 23 (4):  562.  doi: 10.1007/s12204-018-1943-8 Abstract ( 485 )   The energy distribution model of motion blurred star point is analyzed. The distribution of the star point approximates to a two-dimensional (2D) Gaussian distribution under degeneration. Two multi-parameter nonlinear Gaussian fitting methods (GFMs) are proposed, and the relationship between fitting parameters and motion blur parameters is analyzed. Estimation of the parameters of motion blur by fitting parameters is calculated to realize the error compensation of the motion blur. The simulation results show the effectiveness and accuracy. References | Related Articles | Metrics

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Querying Linked Data Based on Hierarchical Multi-Hop Ranking Model LI Junxian (李俊娴), WANG Wei (汪卫), WANG Jingjing (王晶晶) 2018, 23 (4):  568.  doi: 10.1007/s12204-018-1976-z Abstract ( 466 )   How to query Linked Data effectively is a challenge due to its heterogeneous datasets. There are three types of heterogeneities, i.e., different structures representing entities, different predicates with the same meaning and different literal formats used in objects. Approaches based on ontology mapping or Information Retrieval (IR) cannot deal with all types of heterogeneities. Facing these limitations, we propose a hierarchical multi-hop language model (HMPM). It discriminates among three types of predicates, descriptive predicates, out-associated predicates and in-associated predicates, and generates multi-hop models for them respectively. All predicates’ similarities between the query and entity are organized into a hierarchy, with predicate types on the first level and predicates of this type on the second level. All candidates are ranked in ascending order. We evaluated HMPM in three datasets, DBpedia, LinkedMDB and Yago. The results of experiments show that the effectiveness and generality of HMPM outperform the existing approaches. References | Related Articles | Metrics

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An SNN Ontology Based Environment Monitoring Method for Intelligent Irrigation System LI Shuoming (李硕明), CHEN Lei (陈磊), CHEN Shihong (陈世鸿) 2018, 23 (4):  577.  doi: 10.1007/s12204-018-1959-0 Abstract ( 437 )   In order to realize high precision of environment parameters detection in irrigation applications, a sensor and sensor network (SSN) ontology based data fusion method is proposed. An SSN sub-ontology for soilstate monitoring is revised, which includes the sensing devices hierarchies and measurement properties selection according to the detection feature interests. As for sensor data processing, a tuning data method by data pool filtering and clustering is adopted, as well as a useful data fusion method for multi-sensor system. The testing results show that both the accuracy and efficiency of the proposed method are higher after related filtering and clustering process, which enables a thorough monitoring for intelligent irrigation systems and can be extended into environment monitoring and control applications. References | Related Articles | Metrics

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Automatic Multi-Document Summarization Based on Keyword Density and Sentence-Word Graphs YE Feiyue (叶飞跃), XU Xinchen (徐欣辰) 2018, 23 (4):  584.  doi: 10.1007/s12204-018-1957-2 Abstract ( 378 )   As a fundamental and effective tool for document understanding and organization, multi-document summarization enables better information services by creating concise and informative reports for large collections of documents. In this paper, we propose a sentence-word two layer graph algorithm combining with keyword density to generate the multi-document summarization, known as Graph & Keywordρ. The traditional graph methods of multi-document summarization only consider the influence of sentence and word in all documents rather than individual documents. Therefore, we construct multiple word graph and extract right keywords in each document to modify the sentence graph and to improve the significance and richness of the summary. Meanwhile, because of the differences in the words importance in documents, we propose to use keyword density for the summaries to provide rich content while using a small number of words. The experiment results show that the Graph & Keywordρ method outperforms the state of the art systems when tested on the Duc2004 data set. References | Related Articles | Metrics