Plane layout of breakwater

Under the combined action of waves and tidal currents, the sediment in sandy coast and muddy coast is active and often accumulates in port channels and berths. In this case, the construction of breakwater needs not only wave prevention, but also sand prevention. For sandy coast, breakwater can intercept sediment-laden flow and change the position of sediment deposition. For the muddy coast, the breakwater can be used to guide the sediment-laden flow and try not to change the original balance of scouring and silting on the beach. The intensity of sediment deposition in port directly affects the depth of harbor basin and waterway. In addition to using breakwater to prevent and reduce sediment, dredging measures should be taken to maintain water depth when necessary. When building breakwaters in ports with ice, we should also consider reducing the impact of floating ice on navigation channels and berths to facilitate ice discharge.

The plane layout of breakwater, especially the position, direction and size of the entrance, plays a decisive role in the water surface stability and sediment deposition in the harbor waters. Generally, the entrance is arranged at the deepest part of the port area, and the entrance axis (i.e. the vertical line connecting the embankment) should make an angle of 45 ~ 60 with the gale direction, and the entrance width should be 65,438+0 ~ 65,438+0.5 captain, and the entrance of military port and fishing port can be widened appropriately. Some waves propagate inward through the entrance, and the wave height distribution in the harbor waters is the main index to judge the effect of wave cover. The calculation of wave height distribution in harbor is usually based on the wave elements at the entrance (regular wave method) or the directional spectrum of waves (irregular wave method). When the wave meets the pier head at the entrance, it diffracts, the peak line of the diffracted wave diffuses into the harbor, the wave energy diffuses, and the wave height decreases continuously, forming a stable water surface.

When arranging breakwater, it is required to cover the required water area with the shortest breakwater line, and the plane outline is generally composed of straight lines to avoid the bad phenomenon of local wave energy concentration. In the plane layout, attention should also be paid to avoid the occurrence of port vibration, that is, periodic waves outside the port invade from the entrance, causing forced vibration of long-period standing waves in the waters of the port. Port vibration, also known as false tide, will seriously affect the stability of water areas, and may cause collision accidents between ships and docks, forcing operations to stop. Port vibration is a kind of low-frequency water fluctuation, which is mainly related to the geometric shape of the port water boundary. When determining the scale of the water area, the natural frequency of the water area should be as far as possible outside the frequency spectrum of the long-period waves in the port area, and a smaller port should be adopted on the premise of meeting the navigation needs.

Physical model test or mathematical model calculation is usually used to verify and compare the schemes of breakwater and select the best scheme.