OMPUTER-AIDED M ODEL CONSTRUCTION AND DATABASE DESIGN OF RAILWAY YARD INFORMATION

Railway yard is the basic composition unit of railways, therefore, the efficiency and quality of railway yard design have a crucial effect on the construction and operation of railways. Plane design is the basis and core of railway yard design, consequently, it is significant to research plane design of railway yard. In this study, through analysis and summary of the research status as well as integrated application of computer technology and railway yard plane design methods, we researched and developed railway yard plane design system based on AutoCAD platform. According to the characteristics of railway yard plane design, we constructed the information model based on which we established specialized database, with the information data organized and managed efficiently; moreover, we put forward methods of constructing geometric models of the plane equipment, meanwhile, we did a focused research on associated design of yard equipment and preliminarily realized linkage design of planar yards.


Introduction
As the bond of the frontier and the back of stations, railway yard plays a key role (Peng et al., 2014).The efficiency and quality of railway yard design have a vital effect on the construction and operation of railways (Yuan et al., 2014), and the design quality directly affects railway engineering, operational indicators and transport capacity.As the basis and core of railway yard design (Zhu, 2008), plane design directly affects the follow-up profile design, cross-sectional design, 3D visual design and calculation of engineering quantity, therefore, it is of great significance to research on the theories of railway yard plane design (Yang, 2006).Since 1960s, a large number of scholars and R&D institutions have carried on thorough researches on the theories and methods of railway yard plane design, and developed a series of computer-aided design software (Liu et al., 2012).Overall, the software systems mentioned above improve the efficiency of railway yard design to some extent, however, some software are short of professional database and independent organization and management mechanism, with mass data completely under the management of AutoCAD platform; even if there is database, the simple and rough design makes it difficult to complete a mass of editing and modification; and most software neglect associated constraint design.In brief, with limited functions, the existing software fail to fundamentally solve the problems in digital design of railway yard, and software development is still in a relatively low level (Krishnapillai & Zeid, 2006;Zhou, 2013).In this study, to begin with, we constructed scientific and reasonable railway yard information models, followed by the design of data models of equipment in railway yard plane; then, we established specialized database of railway yard plane, and researched on various associated design methods; furthermore, we set up behavioral models of railway yard plane design; with AutoCAD adopted as the development platform, we developed new railway yard plane design system which can greatly improve the efficiency, quality and level of railway yard design.

Overall design of the system 2.1. Overall goal of the system
The overall goal of developing railway yard plane design system is to achieve functional maturation, process clearness, accurate calculation, standard graphical representation, simple operation, and meet the requirements of digital plane design (in the phases of pre-feasibility study, preliminary design and construction documents design) of railway yard (of mixed passenger and freight railway and high speed railway).By establishing the plane scheme database and storing the plane design data information of railway yard, along with the application of spatial index technology, efficient organization and management of railway yard data can be achieved.With man-machine interactive design method adopted, railway yard plane scheme can be generated and modified.The design process and graphic output are mutually independent; once the design is completed, design result output can be implemented rapidly by means of graphs and forms.

Overall structure and function design of the system
According to the overall goal, the system is divided into four modules-project management, database, plane design and diagram output.There is business logic connection between project management, plane design and diagram output, and system can conduct unified management on the three modules through database.Overall structure of the system is shown in figure 1.

Operation and data process of the system
Operation and data process of the system is shown in figure 2. In the flow chart railway yard plane design data mainly include normal data, basic data, input data and result data (Roanes-Lozano et al., 2002;Thuraisingham, 2007).

Development tools of the system
This system adopts a variety of development tools, such as C++, ObjectARX and database, at the same time, AutoCAD is developed based on ObjectARX2012.As a fully object-oriented development tool of computer-aided design, ObjectARX allows developers to use objectoriented C++ language to customize entity objects for AutoCAD so as to meet practical needs.The entity objects are similar to the internal entity of AutoCAD and reflect the object-oriented design concept.In this study, on account of the moderate data size, and data relations in the railway yard plane design system were not very complex, we chose a small-scale database management system.The small-scale relational database management system (RDMS) Access is easy to operate, with full functions, friendly interface and simple configuration, in addition, it is completely compatible with Windows.(2) Information of railway yard equipment This paper gave systematic analysis and induction of various equipment in railway yard.The equipment can be divided into line equipment, turnout, signal equipment, passengers and freight equipment and other accessory equipment.It is necessary to describe the data model of each equipment accurately and express its behavioral model.The information of railway yard equipment is shown in table 1.

Plane design system of railway yard
(3) Information of railway structures Site selection and plan design of railway yard are usually completed on condition that the railway structures (route, bridge and tunnel) have been determined (Kardas-Cinal, 2014).This paper constructed the information model of railway structures (route, bridge and tunnel).

Other accessory equipment
To describe the basic attributes, location, size and associated information of the road, drainage ditch, fence and etc.
To import, create, edit and save the road, drainage ditch, fence and etc.
Plane design of railway yard is based on the design data of route profession which provides route database file for yard profession; based on the file, railway yard profession creates planar baseline entity.
Plane design of railway yard also requires the information of bridge and tunnel; the given railway yard technology standards from users as well as the beginning and end of the bridge and tunnel can be offered as reference for yard profession so that the settings meet the requirements.
(4) Associated constraint information There are plenty of associated constraints in the plane design of railway yard.In this study, based on the analysis and summary of associated constraints between various equipment in the railway yard plane, we constructed associated constraint information model so as to achieve effective organization and management of complex association and constraint relations.The association diagram of railway yard plane equipment is shown in figure 3.

Database design (1) Data structures
In the data structures, the basic attributes (type, location and size) of railway yard plane equipment are described, moreover, associated information between the equipment is recorded to meet the requirements of associated constraint design.Therefore, data structures of railway yard plane equipment include basic attributes and associated attributes.
(2) Database design In this system, the plane scheme is named as *.mdb file.The information of each plane equipment is saved in database in the form of table.Table structure is determined according to data structure so as to make it convenient for plane scheme and each equipment to implement rapid import and storage, which sets the foundation for result output.Turnout plane data (the basic attributes and associated attributes) are stored in turnout table, as shown in table 2.  In order to describe the information of these line elements, we adopted two-dimension XYAiTay for encoding.

Baseline
(2) Baseline design As the foundation of railway yard plane design, baseline is generally absolute alignment, while station track is relative baseline alignment.
Therefore, baseline design is the top priority.
According to actual project requirements, baseline design is supposed to be able to import, create and add line elements along with the functions of editing, deleting and saving; it can generate baseline with centerline data; and it also has the functions of mileage and coordinate transformation.
(3) Station track design Station track design is an important part of railway yard plane design and the foundation of subsequent design work.In view of the actual project requirements, we formulated detailed design methods (figure 4).

Turnout design (1) Geometry model of line elements
The main line of lateral turnout is straight line, while the lateral line branches out to the left or right side of main line, in the form of left-lateral and right-lateral (Qing- Yuan, 2003).In practice, in order to meet design requirements, the center line of the two lines at turnout and the intersection denote turnout, which is a more simple and convenient drawing method (Gao et al., 2011).Based on the model above, we adopted onedimensional array (XYArray) in program coding to describe the attributes of turnout.In this study, we aimed at the association of turnout and line equipment as well as the association of turnout and signal equipment.Turnout design is implemented through creating, editing and moving turnout.

Design of station track
(3) Junction line design Junction line (including single junction line, shortened junction line and crossed junction line) refers to the equipment that leads rolling stock from a line into another.With turnout and station track involved, junction line has complex structure.In order to facilitate the editing and modification functions of junction line, the system turns it into user-defined entity, and integrates turnout and station track line elements.

Coordinates of fouling post and semaphore
Coordinate positions of fouling post and semaphore are affected by the following factors: turnout frog angle, geometry elements of the line connected with turnout, whether out-of-gauge goods train can go through (Gamon, 2015).According to these factors, we can form the path lines where fouling post or semaphore is set up along the line of turnout and derivative line, and intersection of the two path lines is the theoretical coordinate position.For example, the turnout (whose frog angle is ) connects line 1 and line 2, turnout center O is the origin, back tangent of line 1 is in the direction of axis X, thus the rectangular plane coordinate system is established, and then, the limit path lines of line 1 and line 2 are located.When the two dotted lines intersect, the intersection is obviously the theoretical position of fouling post or semaphore, and y values of the dotted lines are the same.

Design of passengers and freight equipment (1) Passenger traffic equipment
The ground of passengers' station buildings should be on the same height (or on slightly different height) as basic platform.Passengers' platforms include basic platform and intermediate platform.
In general, the length of passenger platform is 400 m to 500 m.As to the platforms designed for short distance or suburb passenger trains, the platform length (no less than 300 m) is determined according to the actual lengths of the trains, and the width of platform is no less than 6 m.
Crossing equipment (including flat corridor, overbridge and tunnel) refer to the passageways between station buildings and platform or between platforms.This study focused on the design principles of over-bridge and tunnel.
(  5, on descending route, the effective length of track 1 starts from the departure semaphore to the fouling post on the other end; on ascending route, the effective length starts from the departure semaphore to the stock rail joint on the other end. As for track 2 and track 3, the effective length starts from departure semaphore in corresponding direction to the fouling post on the other end.In the figure, departure semaphore in each turnout is located on the left side (in departure direction); when there are fouling posts on both sides, the closer one is taken as the control marker.

Ascending route Descending route
Fig. 5. Sketch map of effective track length

Conclusion
In this study, according to the characteristics of railway yard plane design, we constructed railway yard information model which involved information of geographical environment, railway yard equipment, railway structures and associated constraints; then, we summarized and analyzed the data models and behavioral models of the information; based on railway yard information model, professional database was set up with database management technologies which offered efficient organization and management of all kinds of information data; through efficient spatial index, rapid access to the required data and information output could be achieved; to some degree, establishment of database guaranteed associated constraint design, linkage design of graphics and data; moreover, we put forward the methods for building geometric models of railway yard plane equipment; through user-defined entity technology, we implemented the customization and modular encapsulation of the equipment entity in railway yard plane; in the process of designing, we also did a focused research on associated design of equipment in railway yard, and preliminarily realized linkage design of plane railway yard.
For example, Li et al. (2015) put forward practical railway yard design mode along with the requirements of target, function, overall structure, data flow and the key technology; Durmuş et al. (2010) researched on computer-aided railway yard design; Liang et al. (2013) carried out simulation system design of railway yard based on J2EE technology.

Fig. 3 .
Fig. 3.The association diagram of railway yard equipment

Table 1 .
Information of railway yard equipment

Table 2 .
Table of turnouts

. Calculation of station line length
Station line length includes total track length, railway length and effective track length.Total track length refers to the length between the stock rail joints at both ends.Railway length is obtained by subtracting the length of all turnouts from total track length.Control marks of effective track length include departure semaphore, fouling post, point of switch and bumper post.Effective track length is calculated separately according to ascending route and descending route.As shown in figure