Abstract:The space grid structure is mostly adopted to the sector lock gate of ship lock,and the sector lock gate is the first time to be adopted in the design for 34 m ship lock. To improve the design rationality and safety reliability of gate structure,we combine with the design example of the sector lock gate of the expansion and reconstruction project of Yuxi first ship lock on Heyu line,analyze the key technical difficulties in the design of sector lock gate of the large entrance ship lock from four aspects including the main structure of the gate,the supporting and moving parts,the anti-collision system and the water sealing system,perform finite element simulation analysis of the spatial gate structure for two design water level combinations,design top and bottom pintle structures specifically,and propose solutions in the aspects of surface strengthening technology of moving parts,structural type of anti-collision system and water sealing design. The results show that the stresses of all parts of the gate are within the allowable range,and the moving parts are safe and reliable,the water sealing system has good adaptability. Overall,all of them meet the requirements of use.

Abstract:Taking the 34 m gate of the expansion and reconstruction project of Yuxi first ship lock as the research object,we propose a new type of anti-collision structure system of triangle gate,which is composed of aluminum honeycomb panel and rigid supporting bars. We establish the finite element model of the new anti-collision structure system,carry out the impact simulation,and compare the new anti-collision structure system with the traditional rigid anti-collision structure system. The results show that the new anti-collision structure system works well under the calculation condition,and there is no plasticity. Compared with the traditional rigid anti-collision structure,it has good advantages in energy dissipation,lightweight,and replacement.

Abstract:The expansion and reconstruction project of the Yuxi first-line ship lock increased the width of the sector gate to 34 m for the first time. To improve the operation efficiency of the ship lock and give full play to the advantages of the opening and closing of the dynamic water of the sector gate,an experimental study on the water conveyance condition of the large sector gate joint is carried out. Based on the hydrodynamic characteristics of the sector gate and the safety of ship berthing,the study puts forward the operating conditions of the large triangular gate of the Yuxi new ship lock. The conditions are as follows:1）The water conveyance of the sector gate should be opened within 1 m head difference as far as possible. 2）The opening degree of the gate should be controlled within 1 m. 3）With the decrease of the head difference,the opening degree of the gate can be further increased.

Abstract:Taking the bottom pivot’s mushroom head and shaft of 34 m-entrance wedge gate in Yuxi first-line ship lock expansion and reconstruction project as a study case,we carry out comparative research on different base materials and laser cladding powders from the macroscopic metallography,microstructure,X-ray diffractometer,the surface hardness of the cladding layer, and the corrosion resistance of the specimen tested by the salt spray test machine. The results show that Ni40 powder and Co40 powder have high hardness and excellent corrosion resistance,which can meet the performance requirements of laser cladding. Compared with the other two materials,Fe40 has different properties and is not suitable for laser cladding powder.

Abstract:At present,the research on waterstop is mostly in the layout,design,and construction,while that on the stress capacity and deformation performance of waterstop under the working state of the gate is less. Moreover,most of the research on the waterstop performance is only for the waterstop itself. In actual engineering,the waterstop is fixed on the ship lock and is jointly affected by the water head. Therefore,it is necessary to consider the force when the waterstop is connected to the ship lock. Taking the 34 m-entrance triangular gate in the Yuxi ship lock expansion and reconstruction project as an example,we select two actual working conditions and two additional working conditions to conduct finite element simulation on the waterstop and the gate as a whole and analyze the working state,stress and deformation performance under each working condition. The result shows that the strength of the waterstop meets the requirements. The bottom waterstop and the side horn waterstop are in a compressed state,and the deformation performance is favorable. The middle horn waterstop plays a positive role in restraining the expansion of the gap.

Abstract:The metallization modification method is a new method of rubber concrete modification. We use compressive strength,flexural strength,and load-deflection tests to study the modification effect of mechanical,bending,and deflection properties of rubber concrete by the metallization modification method,and compare and analyze the modification effect between the metallization modification method and the traditional modification methods such as styrene-butadiene latex and coupling agent. The results show that the metallization modification method can greatly improve the bending toughness of concrete. The mid-span deflection of metallization modification rubber concrete grows 530% than that of unmixed rubber concrete,compares to the unmodified rubber concrete 28 d compressive strength increases by 40%,and flexural strength increases by about 25%. The metallization modification method in the mechanical property of concrete,bending deformation,and other aspects of the modification is better than the butyl rubber latex,coupling agent,and other traditional modification methods. The mid-span deflection increases by up to 320%,28 d compressive strength decay rate decreases by about 50% to 75%.

Abstract:To probe into the development of the LNG market and provide reference for the scientific layout of the LNG terminals in the Yangtze River Delta region,this paper analyzes the current situation and development trend of natural gas consumption in the area. Natural gas demand is forecasted after carding the factors that affect the development of the natural gas market. According to the co-ordination of supply and demand,there is still a large growth space for the volume of imported LNG by LNG terminals in the Yangtze River Delta region. The next two to three years will be an upsurge of constructing LNG terminals. Based on the analysis of the development trend,this paper puts forward suggestions on promoting the development of LNG terminals in the Yangtze River Delta from the aspects of planning layout,functional orientation,and marketization.

Abstract:With the Guangdong-Hong Kong-Macao Greater Bay Area becoming a national strategy,new changes in the development focus of the regional economy will have an important impact on the development of Shenzhen Port. We systematically sort out the development goals and strategic deployment of the Greater Bay Area,select five important indicators such as regional GDP,industrial structure,ecological environmental protection,fixed asset investment,and distribution system,analyze the impulse response of port throughput by a two-variable VAR model,and propose the development advice of Shenzhen Port. The results show that the regional GDP,industrial structure,and distribution system can have a long-term positive impact on port throughput,ecological environmental protection has a long-term negative impact on port throughput,and fixed asset investment has a weak impact. Optimizing the layout of the port area,focusing on ecological and environmental protection,and strengthening the construction of channels can accelerate the construction of Shenzhen Port into a new port that meets the development characteristics of the greater bay area.

Abstract:For insufficient wind and wave-resistant of the existing traditional floating wharf,the causes are analyzed. This paper puts forward a new type of anti-wind and anti-wave floating wharf scheme. The design idea is to divide the existing process of the floating wharf into two states：normal working stage and wind and waves-resistant stage. The key measures such as the wind and waves-resistant sliding trough,working restriction,and herringbone anchor system are taken to ensure its normal working requirements and high resistance to wind and wave. The model test is carried out to verify the design scheme,and principle and method for determining the key parameters are provided,which provides a solution and technical support for effectively improving the adaptability and viability of the floating wharf in the marine environment and giving full play to the technical advantages of the floating wharf.

Abstract:Aiming at the problem that it is difficult to determine the design wave data of the rear revetment works sheltered by the offshore high-piled wharf,this paper combines the actual project with the 2D wave physical model and 3D wave physical model tests,and studies the design wave,overtopping and cross-section stability of the revetment under the influence of the wharf. The results show that the superstructure of a high-piled wharf has a good shelter effect on the rear revetment works,especially at the high water level has a good effect on wave attenuation. The embankment top elevation of the rear sheltered revetment is controlled by the high water level,and the embankment top elevation can be appropriately reduced. The stability of the revetment structure,especially the bottom protection and foot protection,is mainly controlled by the lower water level,but wave height reduction is limited because of the bad sheltered by the wharf when the lower water level.

Abstract:The horizontal stability of the pontoon in the floating wharf is related to the operation safety of the tourist wharf and the personal safety of tourists. Before the issuance of JTS 165-7—2014 Code for design of marinas,the calculation principle of the floating stability of the pontoon in the engineering design was based on the calculation principle of the floating stability of the gravity caisson. Based on combing the calculation principles of caissons and pontoons,this paper uses the research methods of theoretical analysis,formula derivation and engineering case verification to verify that it is reasonable and feasible to calculate the floating stability of pontoons by using gravity caisson floating stability calculation principles. The research results of this paper have important reference value for the follow-up research and design work.

Abstract:Floating breakwater has the advantages of environmental protection,economy,and mobility,and the constraints of reliability and wave dissipation effect exist at the same time. Many types of research focus on improving its better wave dissipation performance. We take single,double,flexible,floating,and other types of floating breakwater as the principal line,summarize the research achievements,means,and progress of floating breakwater,induce the hydrodynamic characteristics of various types of floating breakwaters using physical model test and numerical simulation,and give the practical engineering cases,which can guide further research and exploration of floating breakwater.

Abstract:This paper discusses the butterfly oil terminal which is popular in port engineering. Combining with relevant domestic and foreign codes,three main points,i.e. terminal length,mooring dolphin location， and breasting dolphin location are researched by comparative analysis. Among them,the location of the breasting dolphin is the most important design issue,due to the asymmetry of the flat body area relative to the amidship. Unreasonable mooring dolphin’s location will only quantitatively affect the uniformity of mooring line tension and vessel movement,while the unreasonable breasting dolphin location will affect the berthing security. Therefore,the key points of breasting dolphin position design are elaborated through an overseas oil terminal of 50,000 to 300,000 DWT for designers’ reference.

Abstract:In order to systematically study the design method of the control system of a floating LNG terminal project in Pakistan,we focus on the special requirements of mooring,berthing,and operation for floating LNG terminals,draw the suitable control system framework,and introduce the relationship and configuration of subsystems including ship-shore linkage system,fire control system and auxiliary berthing system. Based on the layout condition of a floating LNG terminal in Pakistan,we study the relevant provisions of national standards and combine them with the current domestic control system design standard,and summarize an idea and solution for a control system different from normal LNG terminals. The results show that compared with control system establishment for normal LNG terminal,there are further optimizations space in data transmission,reasonable cable arrangement,and control object selection for floating LNG terminal.

Abstract:In view of the problem that how hydraulic structural designers can quickly obtain the cross-sectional dimensions of gravity concrete block quay,we apply the linear programming model to establish constraint equations,program under certain assumptions to solve the minimum ratio of width and height of the wall structure,and form a table of calculation results. The designers can look up the values of key variables in the calculation results table,use interpolation and other methods to obtain the minimum ratio coefficient,and get the minimum width of the wall structure of gravity concrete block quay. The results show that the method can realize the rapid design and improve work efficiency effectively.

Abstract:In some bulk cargo terminal projects,the location of the quay is far away from the storage area,and it is necessary to use long-distance belt conveyors to transport the materials from the quay to the storage yard. Considering the large cost of the marine approach bridge due to the conventional horizontal transportation option,we probe into the way of optimizing the layout of belt conveyors and reducing the construction cost of the whole terminal. By the double-layer design option,i.e. ordinary belt conveyor for the lower layer and the pipe belt conveyor for the upper layer,the width of the approach bridge can be reduced under the prerequisite of ensuring the effective transportation of different materials. The actual operation proves that the double-layer belt conveyor system can operate safely and reliably.

Abstract:Including transportation by sea,the multi-modal system is the future direction of spent fuel transportation. In the early stage of construction,coastal nuclear power plants have planned,designed and built heavy cargo wharf for large equipment transportation. Spent fuel can be transferred from the heavy cargo wharf in the multi-modal system. In order to satisfy the requirement of transferring spent fuel,we combine with the berthing and unberthing conditions of ships to carry out the comprehensive evaluation,sort out the modification content of nuclear power plant wharf after investigation and analysis. The results show that nuclear power plants should focus on physical protection of nuclear materials and ship berthing conditions and package loading technology to carry out modification of wharf by centering on wharf plane scale and structure,operation technology,auxiliary production facilities,and management system. To ensure that spent fuel can be shipped out on time in the future.

Abstract:To summarize and promote the design and construction experiences of a super large offshore island-type jetty,taking the design of the 300,000-ton-class jetty of Sinochem Quanzhou as an example,several key technical problems to be solved in the project are proposed,such as coordination of work ship berths and operation standards of large oil tankers,the structural design of the 450,000-ton terminal with large waves and large geological changes,the fixation of submarine pipelines,and fire protection water safety guarantee. By analyzing the wave geological conditions,optimizing the layout of the wharf,calculating the load,and innovating the structure,the above problems have been effectively solved.

Abstract:The axis layout of the newly-built navigation buildings of the built high dam junction in mountainous area is limited by conditions such as the narrow river channel,high water heads，the discharge of power station ,and existing buildings. In view of the problems,based on the new navigation building project of Baishi hydropower station in Qingshui River,Guizhou Province，using the technical means of 1:100 normal integral hydraulic model and self navigation remote control ship model,the navigation water flow conditions and ship navigation research and optimization of the multiple axis layout schemes are carried out. The test results show that the navigable flow condition and ship navigation state of the right bank axis layout scheme are good,which is the recommended scheme. The research results have solved the key problems of the project,which can be used for reference for the new or expanded navigation building projects of similar high dam water conservancy projects.

Abstract:The determination of the width of the regulation line in the channel regulation is one of the key factors for the success or failure of regulation. In this paper，the calculation formula of the regulation width is improved on the basis of considering the stability of the navigation channel and the capacity of ships ascending rapids. Also，a formula for calculating the regulation width of the sand-pebble shoal in mountainous rivers is put forward. A mathematical model is established to verify and optimize the regulation width calculated by the formula in this paper through an engineering example. The calculation of regulation width is systematic work，the regulation widths calculated by the traditional formula，and the formula in this paper can only be used as reference values. To achieve a good regulation effect，the regulation width needs to be further modified by the mathematical model and physical model experiment.

Abstract:Aiming at the expansion of the first 300，000 DWT artificial channel in China，this paper expounds on the necessity of channel expansion from the aspects of navigation saturation，increasing trend of ship flow in core port area，upsizing of ships，and berthing demand，etc. Based on the analysis of the adaptability of extending the duration of tide and navigation capacity of the extended channel，the expansion scale and scheme of the channel are determined，and the effects of channel expansion，such as the improvement of flow conditions，sediment siltation，channel scale simulation，and the matching of the ships entering channel and berthing wharf time，are systematically studied. The proposed expansion scheme of deepening to -23.5 m and widening to 440 m is reasonable and has a good navigation effect，the expansion scheme can meet the navigation requirements of ships’ safe passing through the channel and berthing at one tide.

Abstract:The single-well tower structure greatly improves the synchronicity of water level vertical shaft of the hydro-floating ship lift，but with the increase of the lifting height，the greater the water depth in the vertical shaft is，and the more prominent the problems of lateral wall displacement and the excessive bending moment become. Taking the 150-meter-class single well tower column as an example，this paper puts forward the assumption of opposite-tensile cable arrangement in the shaft and simplified cable arrangement scheme. Based on the optimization method of the weight allocation coefficient of cable tension，the optimal solution of the density distribution of cable equal stress is obtained，and the solution is discretized into the equivalent equal load arrangement scheme，which can be applied in practical engineering. The results of the finite element model show that the maximum displacement can be reduced by 47.44% in the equal-load layout compared with the simplified scheme，and there is little difference between the extreme values of the longitudinal and longitudinal bending moments. Compared with the cable-free scheme，the maximum displacement，longitudinal moment and vertical moment can be reduced by 93.5%，74.36%，and 75.84%，respectively. The prestressing scheme of high strength steel cable deserves further study.

Abstract:The second-line ship lock of Jinweizhou Junction in Xiangjiang is an upgrade and reconstruction project. There is no choice of location and axis. The navigational flow conditions in the entrance area of the downstream approach channel can only be improved by optimizing the opening method or constructing a diversion pier. Using 1:100 fixed-bed normal river physics model test，on the basis of fully understanding the water flow conditions of the downstream approach channel entrance area of the conventional gate discharge method，through a combination of multiple-gate discharge methods and diversion pier layout optimization experiments such as number，spacing，angle，etc.，we propose the conventional way of opening gate + side hole supplementary discharge，or the arrangement of three diversion piers with a single pier length of 20 m，a direction parallel to the route，and a spacing of 20 m. Both can be opened to the traffic flow increased to a flood in 2 years.

Abstract:To systematically evaluate the implementation effect of maintenance dredging in the upper Yangtze River waterway in 2018 and provide technical reference for future waterway maintenance projects，based on the systematic analysis of the water situation，we evaluate the dredging project from the dredging scheme design，construction timing，dynamic management of construction process，as well as sustainability of the channel. The results show that the selection of beach section and the design of dredging scheme basically adapt to the river evolution law. The time and frequency of dredging are basically reasonable，which reduce the contradiction with navigation to the greatest extent. However，since the maintenance dredging has not significantly changed the river flow characteristics and riverbed boundary，the sustainability of shallow channel in the natural reach is poor，so it is still necessary to strengthen observation or take other regulation measures.

Abstract:The Paihekou ship lock is an important part of the Paihekou hub for diversion project from the Yangtze River to the Huaihe River. It is located at the entrance of the Paihe River into the Chaohu Lake and has complex construction conditions. Based on the existing engineering，river boundary，and related planning，a preliminary plan for the layout of the double-track ship lock is proposed.A detailed study of the navigable flow conditions in the downstream approach channel and the entrance area of the ship lock is carried out using the technical means of the fixed-bed river engineering model test. The longitudinal and transverse surface velocity and flow pattern characteristics of the downstream navigable water area when the check-gate releases flood water are analyzed. The reasons why the conditions do not meet the requirements of the specification are pointed out，and they could be improved by measures such as smoothing coastline，newly opened flood diversion channels，and control of critical and safe flood discharge. The optimized scheme can help meet the design requirements and provide technical support for engineering design and operation and management in the future.

Abstract:The lock capacity is one of the core concerns for the Pinglu Canal. This paper analyzes the factors influencing the lock capacity. Through computer simulation，three main indicators，i.e. the average total tonnages per lockage，the average vessel number per lockage，and the occupancy rate of the lock chamber，are acquired，and according to which，the lock capacities of the two operation modes including separate operation of large and small locks with a reasonable scale and random operation of the double-lane lock are compared. Moreover，the lock capacity and ship’s freight tonnage under the separate operation mode are adjusted. The result shows that double-lane locks shall be built at the same time，the separate mode provides a bigger capacity when the 1 000 DWT vessel accounts for a larger proportion，and some 1 000 DWT vessels have to pass through the big lock to ensure that the small lock’s capacity meets the transport demand.

Abstract:In view of the problem that the actual maximum navigable flow after the construction of the navigation and power junction in mountainous rivers can’t meet the requirement of the code，we study the maximum navigable flow after the arrangement of the navigation and power junction in mountainous rivers. Based on the Dongfengyan navigation power junction，we analyze the flow and navigation conditions of the entrance area and the connecting section of the upper and lower approach channels of the ship lock by means of physical model test and ship model test，and put forward suggestions on the maximum navigation flow for safe navigation of Dongfengyan navigation power junction，and come to the conclusion that the maximum navigable flow of the medium-low-head hydro junction in the mountainous river should not be lower than the forbidden flow of the natural river. The research results may serve as a reference in the determination of the maximum navigable flow of the middle-low-head hydro junction in mountainous rivers.

Abstract:Since the scheduling of the Xijiang River navigation ship locks is mainly based on experience management and lack of effective quantitative analysis，a multi-stage ship locks joint scheduling chain of the Xijiang River shipping line is proposed based on the factors of lock congestion coefficient，daily ship overstock loss，and channel safe water level. Based on the natural leaf vein distribution characteristics of the Xijiang River shipping line，a dynamic binary tree model of the Xijiang River multi-stage ship locks chain is proposed. The results show that the reasonable diversion of ships can effectively alleviate the lock stagnation and reduce the accident rate. The model has been applied to the shipping management department to effectively optimize the lock chain scheduling and ensure the safety of shipping materials.

Abstract:At present，the operation mode of the North-South two lines of the Three Gorges ship lock is a centralized and semi-automatic mode，and the human factor accounts for a relatively high proportion in the operation safety of the lock. In order to avoid the risk of human factors in lock operation and improve the reliability and safety of lock operation，we probe into the method of intelligent and automatic operation of the continuous multi-level lock. The intelligent automatic operation mode of ship lock is mainly composed of three parts，i.e. the confirmation of shipowner，the monitoring of the lock chamber，and the centralized monitoring. The implementation method of the intelligent operation mode of the ship lock and selection of the three parts are discussed.

Abstract:To solve the problem of complex structural style，vast investment，difficult investment control in the construction of lock engineering，BIM technology is introduced to assist investment management. This article summarizes the construction experience including design optimization，engineering quantity statistics，as well as measurement and disbursement of the progress payment. BIM-5D is developed based on BIM technology and earned value theory to assist project investment management，which provides a comprehensive and intuitive new model of investment management for lock engineering. It is found that BIM technology can improve design quality and reduce the cost of rework. Component-level engineering measurement payment and BIM-5D investment management technology based on BIM technology innovate investment management means，improve the efficiency and management level of engineering investment management，and control effectively the project investment.

Abstract:Given the shortcomings of the traditional high-piled wharf two-dimensional design process，combined with the practical application of BIM technology in Yancheng Port’s heavy-duty wharf project，this paper elaborates the BIM collaborative design method from three aspects：collaborative server construction，family library construction，and multi-disciplinary collaboration，and puts forward the application points of BIM design stage of component parameterized design，detailed statistics of engineering quantities，parameterized design of complex nodes，and standardization of engineering drawings. Studies have shown that the application of BIM technology has realized the linkage and sharing of model element information，and has improved the participation of multi-disciplinary collaboration，and the accuracy of engineering design expression and collaboration efficiency have also been improved.

Abstract:Due to the economics of composite pile foundations，it has received more and more attention in recent years，but it has been less used in waterway revetment projects. The reason is that the force of composite pile foundations with low pile caps on waterway revetments is more complicated and technically difficult.By analyzing the vertical bearing capacity and horizontal bearing capacity of the composite pile foundation of low pile caps retaining wall of waterway revetments，the design control principle of the composite pile foundation is proposed：1） Vertical overall safety K≥2，fulfilled rate of subsoil bearing capacity ψ≥0.5. 2） Pile and soil jointly bear horizontal force. The design method and procedures of the composite pile foundation of waterway revetments is formulated to provide a reference for similar projects.

Abstract:For investigating the effect of cyclic loading waveforms on deformation of structural soft soil，we take the marine soft soil of Lingang industrial area in Tianjin Binhai new area as the research object，carry out the cyclic loadings with varying waveforms and amplitudes to the samples，research the dissipated energy curves of structural soft soil are researched under cyclic loadings with varying waveforms and amplitudes，and propose the evolution equations in two cases. The results show that when the effect of the loading waveform is considered，the cumulative plastic strain develops slowly，and the change of the waveform has little effect on the development trend of plastic strain when the loading amplitude is below the threshold stress，for example，30 kPa. When the amplitude is much higher than the threshold，for example，40 kPa，60 kPa，and 80 kPa，the cumulative plastic strain increases rapidly，the rate of deformation for the square wave is fastest，and the sinusoidal wave comes the second，while the triangular wave is the last.

Abstract:In the JTS 190-2018 Design Code for Maritime Structures and Services in Shipyard，the stability of sheet piled dock wall should be checked in accordance with the relevant provisions of sheet piled wharf in JTS 167-2018 Design Code for Wharf Structures. However，the water pressure for piled wharf is smaller than that of the dock wall. Thus，the rationality of directly using partial factor format and factor values for the stability of sheet piled wharf should be verified. Through the calibration of reliability for the stability of sheet piled dock wall，which is designed by the old code JTJ 252-1987 Code for Design of Dry Dock（Hydraulic Structures） ，the target reliability index is determined，and reliability indexes for wall designed by current practice are determined. The results show that the target reliability index of stability for sheet piled dock wall should be 4.0，while the average value of reliability index for wall designed by the new code is slightly larger than 4.0，which validates the rationality of factor values utilized in the current code.

Abstract:It is difficult to ensure the design service life of the concrete square pile of suspended jetty constructed in the early years by conventional repair and reinforcement methods. For the problem，based on the distribution of chloride ion content in the pile，the pile concrete cover and the calculation results of the remaining service life of the pile，this paper studies the durability evaluation of the pile foundation of the old jetty. By cutting and casting of the pile head of the square pile of the old jetty，and innovative application of the installation of sacrificial anode to prevent the continuous corrosion of square pile reinforcement，the durability requirements are ensured. The construction of this project proves that this method is feasible，which not only avoids demolishing of all the old structure and cost saving，but also successfully applies the sacrificial anode technology to the anti-corrosion of concrete square piles.

Abstract:The original structure of 1#to 3#berths of a hydraulic reconstruction and expansion project in Tanzania is a gravity block，and the new-build expansion part is a pier structure with 11.54 m width. We carry out the displacement monitoring of the old gravity square block of 1#and 2#berths in the PHC pile driving process and summarize the pile sinking laws. The results show that after dredging the coral reef cushion under the gravity block，the PHC pile is driven，and the displacement of the original gravity wharf structure has a greater impact，and cracks appear on the old wharf surface and nearby buildings ground. During the pile driving process，the horizontal displacement of the interface between the different structural forms of the block is the largest. With the outer convex cross-tip pile boots，the PHC pile has the strongest penetration performance，the original horizontal displacement of the square structure of the dock is minimum，and the dock is more stable.