Experimental Study on Influence of Arrangement and Shape of Wave-dissipating Blocks to Flow Characteristics

In recent years, performance design has been introduced for the design of marine structures.

There are few things that showed the difference in performance depending on the shape in calculation formulas.

Clarifying the effects of wave-dissipating block shape on the flow around the block is one of the effective ways to consider the shape characteristics of block in the performance-based design.

In this study, hydraulic model experiments of flow around a block with the different shapes, installed in an open channel, was conducted for examining the shape effects of the block such as round shape, square shape and hollow shape, by measuring surrounding flow characteristics by the particle image velocimetry (PIV).

In this study, a straight water channel made of glass was used for the side wall and the bottom surface of 6.0 m in length, 0.2 m in width and 0.2 m in depth, and the wave-dissipating block model placed in a group was fixed on the side.

The wave-dissipating blocks to be used is the T block with many examples, the A block and R block which can expect the wave-elimination effect, and the K block with the recessed hole of the R block.

In order to confirm the influence due to the difference in cross section, measurements were made on two cross sections, the upper part and the central part of the model.

Two types of analysis of the entire photographed image (wide analysis, number of meshes: 104 × 38) and analysis of a narrow range between blocks (Narrow analysis, number of meshes: 107 × 91) were performed.

Based on the results of the experiment, we found out the following three.

The flow characteristics around each block has been clarified by the dimensionless turbulence strength and the spatial distribution of the Reynolds stress.

As for the Reynolds stress between blocks, it was found that the influence of the concave shape on disturbance becomes larger.

Because turbulence inside the block occurs and energy is consumed, the Reynolds stress decreases in the downstream region.