单塔起重机位置优化的外文翻译(编辑修改稿)

单塔起重机位置优化的外文翻译(编辑修改稿)内容摘要：

ansportation times incurred. Emsley (1992) proposed several improvements to the Choi and Harris model. Apart from these algorithmic approaches, rulebased systems have also evolved to assist decisions on crane numbers and types as well as their site layout。 Assumptions Site managers were interviewed to identify their concerns and observe current approaches to the task at hand. Further, operations were observed on 14 sites where cranes were intensively used (four in China, six in England, and four in Scotland). Time studies were carried out on four sites for six weeks, two sites for two weeks each, and two for one week each. Findings suggested inter alia that full coverage of working area, balanced workload with no interference, and ground conditions are major considerations in determining group location. Therefore, efforts were concentrated on these factors (except ground conditions because site managers can specify feasible location areas). The following four assumptions were applied to model development (detailed later): 1. Geometric layout of all supply (S) and demand (D) points, together with the type and number of cranes, are predetermined. 2. For each SD pair, demand levels for transportation are known, ., total number of lifts, number of lifts for each batch, maximum load, unloading delays, and so on. 3. The duration of construction is broadly similar over the working areas. 4. The material transported between an SD pair is handled by one crane only. MODEL DESCRIPTION Three steps are involved in determining optimal positions for a crane group. First, a location generation model produces an approximate task group for each crane. This is then adjusted by a task assignment model. Finally, an optimization model is applied to each tower in turn to find an exact crane location for each task group. Initial Location Generation Model Lift Capacity and ‘‘Feasible’’ Area Crane lift capacity is determined from a radiusload curve where the greater the load, the smaller the crane’s operating radius. Assuming a load at supply point (S) with the weight w, its corresponding crane radius is r. A crane is therefore unable to lift a load unless it is located within a circle with radius r[Fig. 1(a)]. To deliver a load from (S) to demand point (D), the crane has to be positioned within an elliptical area (a) . Feasible Area of Crane Location for Task FIG. 2. Task “Closenness” enclosed by two circles, shown in Fig. 1(b). This is called the feasible task area. The size of the area is related to the distance between S and D, the weight of the load, and crane capacity. The larger the feasible area, the mor e easily the task can be handled. Measurement of ‘‘Closeness’’ of Tasks Three geometric relationships exist for any two feasible task areas, as illustrated in Fig. 2。 namely, (a) one fully enclosed by another (tasks 1 and 2)。 (b) two areas partly intersected (tasks 1 and 3)。