水利水电翻译.doc

Design of SpillwaysSpillways are ordinarily classified according to their most prominent feature .Commonly referred to types can be listed as follows. 1. Free Overall (Straight Drop) SpillwaysA free overfall or straight drop spillways is one in which the flow drops freely from the crest. This type is suited to a thin arch or deck overflow dam or to a crest is which has a nearly vertical downstream face. Occasionally the crest is extended in the form of an overhanging lip to direct small discharges away from the face of the overfall section. Where no artificial protection is provided at the base of the overfall, scour will occur in most streambeds and will form a deep plunge poll. The volume and depth of the hole are related to the range of discharges, the height of the drop, and the depth of tailwater.A free overfall spillways is not adaptable for high drops on yielding foundations, because of the large impact forces which must be absorbed by the apron at the point of impingement of the jet. Vibrations incident to the impact might crack or displace the structure, with danger from failure by piping or undermining. Ordinarily, the use of this structure for hydraulic drops from head pool to tailwater in excess of 20 feet should not be considered.2. Ogee (Overflow) SpillwaysThe ogee spillways has a control weir which is ogee or S-shaped in profile. The upper curve of the ogee ordinarily is made to conform closely to the profile of lower nappe of a ventilated sheet falling from a sharp-crested weir. Flow over the crest is made to adhere to the face of the profile by prevening access of air to the under side of the sheet. For discharges at designed head, the flow glides over the crest with no interference from the boundary surface and attains near maximum discharge efficiency. The profile below the upper curve of the ogee is continued tangent along a slope to support the sheet on the face of the overflow. A reverse curve at the bottom of the slope turns the flow onto the apron of a stilling basin or into the spillway discharge channel.An ogee crest and apron may comprise all entire spillway, such as the overflow portion of a concrete gravity dam, or the ogee crest may only be the control structure for some other type of spillway. Because of its high discharge efficiency, the nappe-shaped profile is used for most spillway control crests.3. Side Channel SpillwaysThe side channel spillway is one in which the control weir is placed along the side of and approximately parallel to the upper portion of the spillway discharge channel. Flow over the crest falls into a narrow trough opposite the weir, turns an approximate right angle, and then continues into the main discharge channel.Discharge characteristics of a side channel spillway are similar to those of an ordinary overflow and are dependent on the selected profile of the weir crest. The discharge constriction may be a point of critical flow in the channel, an orifice control, or a conduit or tunnel flowing full. Although the side channel is neither hydraulically efficient nor inexpensive, it has advantages which make it adaptable to certain spillway layouts.4. Chute (Open Channel or Trough) SpillwaysA spillways, whose discharge is conveyed from the reservoir to the downstream river level through an open channel, placed either along a dam abutment or through a saddle, might be called a chute, open channel, or trough type spillway. These designations can apply regardless of the control device used to regulate the flow. Thus, a spillway having a chute-type discharge channel,though controlled by an overflow crest, a gated orifice, a side channel crest, or some other control device, might still be called a chute spillway. However, the name is most often applied when the spillway control is placed normal or nearly normal to the axis of an open channel, and where the streamlines of flow both above and below the control crest follow in the direction of the axis.The chute spillway has been used with earth fill dams more often than any other type. Factors influencing the selection of chute spillways are the simplicity of their design and construction, their adaptability to almost any foundation condition, and the overall economy often obtained by the use of large amounts of spillways excavation in the dam embankment.Chute spillways ordinarily consist of an entrance channel, a control structure, a discharge channel, a terminal structure, and an outlet channel. The simplest form of chute spillway has a straight centerline and is of uniform width. Often, either the axis of the entrance channel or that of the discharge channel must be curved to fit the alignment to the topography. In such cases,the curvature is confined to the entrance channel if possible, because of the low approach velocities. Where the discharge channel must be curved, its floor is sometimes superelevated to guide the high-velocity flow around the bend, thus avoiding a piling up of flow toward the outside of the chute.5. Conduit and Tunnel SpillwaysWhere a closed channel is used to convey the discharge around or under a dam, the spillway is often called a tunnel or conduit spillway, as appropriate. The closed channel may take the from of a vertical or inclined shaft, a horizontal tunnel through earth or roke, or a conduit constructed in open cut and backfilled with earth materials. Most forms of control structures,including overflow crest,vertical of inclined orifice entrances, drop inlet entrances, and side channel crests, can be used with conduit and tunnel spillways.With the drop inlet or orifice control, the tunnel or conduit size is selected so that it flows full for only a short section at the control and thence partly full for its remaining length. To guarantee free flow in the tunnel, the ratio of the flow area to the total tunnel area is often limited to about 75 percent. Air vents may be provided at critical points along the tunnel or conduit to insure an adequate air supply which will avoid unsteady flow through the spillway.Tunnel spillways may present advantages for dam sites in narrow canyons with steep abutments or at sites where there is danger to open channels from snow or rock slides. Conduit spillways may be appropriate at dam sites in wide valleys, where the abutments rise gradually and are at a considerable distance from the stream channel. Use of a conduit will permit the spillway to be located under the dam near the streambed.6. Drop Inlet (Shaft or Morning Glory) SpillwaysA drop inlet or shaft spillway, as the name implies, is one in which the water enters over a horizontally positioned lip, drops through a vertical or sloping shaft, and then flow to the downstream river channel through a horizontal or near horizontal conduit or tunnel. The structure may be considered as being made up of three elements; namely,an overflow control weir, a vertical transition,and a closed discharge channel. Where the inlet is funnel-shaped, this type of structure is often called a morning glory or glory hole spillway.Discharge characteristics of the drop inlet spillway may vary with a range of head. For example, as the heads increase on a glory hole spillway, the control will shift from weir flow over the crest to tube flow in the transition and then to full pipe flow in the downstream portion. A drop inlet spillway can be used advantageously at dam sites in narrow canyons where the abutments rise steeply or where a diversion tunnel or conduit is available for use as the downstream leg. Another advantage of this type of spillway is that near maximum capacity is attained at relatively low heads.7. Siphon SpillwaysA siphon spillway is a closed conduit system formed in the shape of an inverted U, positioned so that inside of the bend of the upper passageway is at normal reservoir storage level. The initial discharges of the spillway, as the reservoir level rises above normal, are similar to flow over a weir. Siphonic action takes place after the air in the bend over the crest has been exhausted. Continuous flow is maintained by the suction effect due to the gravity pull of the water in the lower leg of the siphon.The principal advantage of a siphon spillway is its ability to pass full capacity discharges with narrow limits of headwater rise. A further advantage is its positive and automatic operation without mechanical devices or moving parts.设计溢洪道溢洪道设计溢洪道通常分类根据其最突出的特征。通常称为类型可以列出如下。1。自由溢洪道整体（直线下降）自由溢流式溢洪道或直线下降是一种自由流滴从嵴。这种类型是适合薄拱坝溢流坝或甲板或一个波峰是具有接近垂直，下游面。偶尔波峰是扩展的形式，悬垂的嘴唇直接小放电远离面对溢流段。在没有人工提供保护，在该基地的溢流，冲刷将大多数发生在河床，将形成一个深插民意调查。体积和深度的孔是与该范围的放电，高度的下降，和深度的尾。自由溢流式溢洪道是不适合高滴在高产的基础，因为大的冲击力，必须吸收围裙在撞击点的飞机。振动的影响，裂缝或事件可能会取代结构，从失败的危险或破坏管道。通常，使用这种结构的液压滴头池尾超过20英尺，不应被视为。2。坝顶溢洪道（溢出）溢洪道控制堰的边缘有是形或S -简介。上的椭圆曲线通常是由符合密切的简介下覆的通风板从一个薄壁堰。流动的波峰是坚持面对的配置防止空气进入到下片方。排放在设计水头，流量滑过嵴无干扰的边界表面和达到最大放电效率。简介低于上曲线的切线斜率S继续沿着一个支持表的脸上溢出。反向曲线在坡底转流到停机坪的消力池或进入溢洪道泄洪通道。一个反弧顶和围裙可以包括所有整个溢洪道，如溢出的部分混凝土重力坝，或边缘嵴可能只是控制结构的一些其他类型的溢洪道。由于其放电效率高，nappe-shaped的配置文件是用于大多数溢洪道控制徽章。3。侧槽式溢洪道侧槽溢洪道控制堰是一种放置沿一侧大致平行的上半部分的溢洪道泄洪通道。流动的嵴落入一个窄槽对面的堰，变成一个近似直角，然后继续到主放电通道。放电特性的一个侧槽溢洪道是类似于那些普通的溢出和依赖于选定的剖面堰顶。放电收缩可能是一个临界点流动的渠道，一个孔控制，或一个管道或隧道流满。虽然侧通道没有液压效率也不便宜，它的优点，使它能适应一定的溢洪道设计。4。陡槽溢洪道（开放通道或槽）一个溢洪道，其放电转达了水库下游河道的水平，通过一个开放的通道，无论是沿坝肩或通过鞍，可以被称为一个降落伞，打开通道，或槽式溢洪道。这些名称可以适用，无论控制装置用来调节流量。因此，一个溢洪道具有chute-type放电通道，通过控制溢流顶，门孔，侧沟嵴，或其他控制装置，可能仍然被称为陡槽溢洪道。然而，这个名字是最常应用在溢洪道控制在正常或接近正常的轴，一个开放的通道，并在流动简化的上方和下方的控制顶在轴方向。槽溢洪道已用于土坝多于任何其他类型。影响因素的选择陡槽式溢洪道简单的设