Yu Shu Kuo

Minimum embedded length of cyclic horizontally loaded monopiles

Monopiles are used as foundation structures for offshore wind energy towers. To ensure stable behavior of the monopile under cyclic loading conditions, a minimum embedded length is usually required. For this, different design criteria are used, some of which result in very large embedded depths for large-diameter monopiles. The suitability of these criteria is tested by means of numerical simulations. To account for cyclic loading, a new approach called the stiffness degradation method is applied. The results of a parametric study show that the design criteria used can indeed ensure optimum pile performance under static and cyclic loads. It is recommended that the requirement of a critical pile length, which leads to the minimum pile deflection under extreme load, is used as a design criterion. For the cases considered, this requirement results in only slightly greater cyclic deformations compared to the optimum case of very long piles. A further optimization of the required monopile length with respect to cyclic loading is possible, but requires specific consideration of cyclic behavior, as is done in this paper. DOI: 10.1061/(ASCE)GT.1943-5606.0000602.

Rapid geometry analysis for earthquake-induced and rainfall-induced landslide dams in Taiwan

Stability analysis of the dam is important for disaster prevention and reduction. The dam’s geometry plays an important role in understanding its stability. This study develops a rapid landslide dam geometry assessment method for both earthquake-induced and rainfall-induced landslide dams based on nine real cases collected in Chinese Taipei and 214 cases collected worldwide. For simplification purposes, a landslide dam is classified into triangular or trapezoidal. The rapid landslide dam geometry assessment method in this paper uses only satellite maps and the topographic maps to get landslide area, and then analyze the dam geometry. These maps are used to evaluate the area of the landslide and the slope of the river bed. Based on the evaluation information, the proposed method can calculate dam height, the length of the dam, and the angles of the dam in both upstream and downstream directions. These geometry parameters of a landslide dam provide important information for further dam stability analysis. The proposed methodology is applied to a real landslide dam case at Hsiaolin Village. The result shows that the proposed method can be used to assess the landslide dam geometry.

Wave loading distribution of oscillating water column caisson breakwaters under non-breaking wave forces

Wave energy is one of the most potential marine energy resources in Taiwan, especially in the northeast and east coast of Taiwan. There are numerous existing wave energy devices. Among them Oscillating Water Column (OWC) caisson breakwater is very suitable for the harbors in Taiwan. This multiple function structure can generate the electric power and protect the harbor. To evaluate the stability of OWC caisson breakwater, the loadings induced by wave acted on the OWC caisson breakwater are analyzed. Experiments of a small scale physical model of OWC caisson breakwater is presented in this study. The model is fixed in the wave flume and the wave pressures acting on the structure are recorded. It is found that wave pressure at oscillating water column caisson breakwaters is smaller than the wave pressure at vertical wall. The wave loadings calculated with the suggestion of Sainflou and Goda are compared with the test results. The applicability of the empirical formulas is also discussed. Under the selected wave condition, the Sainflous formula overestimates the wave pressure acting on the OWC caisson breakwater. Godas formula provides good estimation for the force estimation but tends to underestimate the momentum and could possibly result in structure overturning.

On waves propagating over two submerged closely spaced poroelastic breakwaters

In this paper, the problem of wave interactions created by two submerged closely spaced poroelastic breakwaters is investigated theoretically. An existing analytical solution is extended so as to be able to consider the problem subject to appropriate boundary conditions. The study domain is divided into seven sub-regions. Using general solutions for each region and matching kinematic and dynamic boundary conditions combined with an orthogonality condition, a set of simultaneous equations is developed; the individual equations being solved numerically. The analytical solutions are in agreement with the simplified cases of a submerged rigid breakwater, submerged permeable rigid breakwater and submerged poroelastic breakwater. Changes in the width of the two adjacent breakwaters, the effect of the permeability coefficient on wave profile, and the effect of materials and configurations of the breakwater on wave variation are the focus of the present paper. The presented results show that a large amount of energy is lost when the adjacent structures both have the same widths for a layer of a soft material with a high permeability. Different materials and shapes of structures can significantly influence the reflection coefficient.

An extended analytic solution of combined refraction and diffraction of long waves propagating over circular island

An analytic solution of long waves scattering by a cylindrical island mounted on a permeable circular shoal was obtained by solving the linear long wave equation (LWE). The solution is in terms of the Bessel function expressed by complex variables. The present solution is suitable for arbitrary bottom configurations described by a power function with two independent parameters. For the case of the paraboloidal shoal, there exists a singular point () which can be removed using Frobenius series, where α is a real constant. The present solution is reduced to Yu and Zhang’s (2003) solution for impermeable circular shoal. The numerical results show some special features of the combined effect of wave refraction and diffraction caused by a porous circular island. The effect of key parameters of the island dimension, the shoal slope, and permeability on wave scattering was discussed based on the analytic solution.

Turbidity reduction in Taiwan reservoir environment using bio-based polymer—Chitosan

AbstractWater derived from storm events in Taiwan is a critical issue because of its high turbidity, which could be larger than 100,000 Nephelometric Turbidity Units (NTU), due to the fragile geology and steep topography of the island. The high turbidity water lowers the efficiency of a water treatment plant or can even shut down the facility resulting in a loss of water supply. Commonly used coagulants, such as aluminum salt, iron salt, and polymers, have dosage limitations and application restrictions due to health concerns. This study provides a new method for turbidity reduction, which can be applied both inside and outside of a water treatment plant. This method then provides a more stable, safe, and environment-friendly water supply by using Chitosan as bio-based polymer for extremely high turbidity water. Representative samples are used to evaluate the effectiveness of Chitosan: (1) the collected sample from Chengqing Lake Reservoir in southern Taiwan; (2) Kaolin soil (or Kaolinite clay), and (3) O...