A Comparative Study of Piers with DSCT and Steel Piles

Because of climate changes, the demand for securing marine space is increasing owing to problems such as sea level rise, design wave height increase, and lack of land and space, and research on the development of a new high-performance pier has been conducted. In the existing pier supported by steel piles, buckling failure and corrosion problems may lead to a risk of structural safety, and maintenance is difficult owing to a narrow span. The new type of double-skinned composite tubular (DSCT) structure, which has been extensively studied recently, is filled with concrete between the inner and outer tubes, increasing the strength of concrete because of the three-axis confined effect. In addition, it is advantageous in terms of ductility. Furthermore, owing to the hollow cross-section, it is economical because it weighs less than the concrete-filled steel tubular (CFT) structure, effectively saving materials. In this study, the performance of a pier with 30 steel piles and that of a pier supported with 20 DSCT piles was compared under the same external force through finite element analysis. Consequently, it was confirmed that the pier with DSCT piles showed higher performance in displacement and stress than the existing pier with steel piles.

Wave transformation around breakwater (case study: tourism harbour, Eastern Bali, Indonesia)

An essential aspect in the sustainable design of breakwater is the determination of the design wave condition. It is predicted by utilizing severe wave conditions of the past 10 to 20 years. The tourism harbor at eastern Bali, Indonesia, is located where extreme wave condition occurs. Therefore, this research studies the wave height before and after constructing a breakwater in the harbor area. The wave height was simulated using numerical modeling. The methodology was performed by using the coastal modeling software of the SMS-CGWAVE model. The result shows the highest design wave height value of 3.9 m in the direction from the southeast. The design breakwater can reduce wave height up to 0.9 m or a 75.5% reduction. Further study is needed to simulate the extension of breakwater length to meet the criterion design of wave height in the harbor basin.

Proposal on Hybrid Design Method of Outer Port Facilities Using Failure Probability

Lately, many efforts have been made to address the problem concerned with deterministic design using reliability-based design, and the research results are significant. However, there is considerable confusion in the design practice regarding how to use failure probability, the main output of reliability-based design. In this rationale, this study aims to develop a robust hybrid deterministic design method for outer port facilities using the failure probability. To this end, we first reviewed the design process of Eulleungdo East Breakwater, some of which were recently damaged. It was revealed that the exceeding probability of design wave height of 5.2 m was merely 0.65, which corresponds to a return period of 1.53 years, showing that the outer port facilities of Ulleungdo were considerably underdesigned. In an effort to find an alternative that can overcome the limitations of the deterministic design method, which is highly likely to involve subjective judgment, a Level III reliability design was carried out. In doing so, tri-modal Gaussian wave slope distribution was used as a probabilistic model for wave slope. Numerical results show that failure probability was excessively estimated in the Gaussian distribution, and even if the TTP size was slightly reduced, the failure probability increased rapidly. Although failure probability is sensitive to the change in nominal diameter, there is a gradually increasing zone where the failure probability change rapidly decreases when the nominal diameter is larger than the critical value. The presence of a Gradually Increasing Zone mentioned above implies that it is uneconomical and has no physical background to adjust the nominal diameter to be larger than the critical value. Therefore, it can be easily conceived that outer port facility design should be performed using a failure probability provided by Level III reliability-based design.

Design Wave Height Parameter Estimation Model Reflecting the Influence of Typhoon Time and Space

Typhoon storm surge disasters are one of the main restrictive factors of sustainable development in coastal areas. They are one of several important tasks in disaster prevention and reduction in coastal areas and require reasonable and accurate calculations of wave height in typhoon-affected sea areas to predict and resist typhoon storm surge disasters. In this paper, the design wave height estimation method based on the stochastic process and the principle of maximum entropy are theoretically advanced, and it can provide a new idea as well as a new method for the estimation of the return level for marine environmental elements under the influence of extreme weather. The model uses a family of random variables to reflect the influence of a typhoon on wave height at different times and then displays the statistical characteristics of wave height in time and space. At the same time, under the constraints of the given observations, the maximum uncertainty of the unobtainable data is maintained. The new model covers the compound extreme value distribution model that has been widely used and overcomes the subjective interference of the artificially selected distribution function—to a certain extent. Taking the typhoon wave height data of Naozhou Observatory as an example, this paper analyzes the probability of typhoon occurrence frequency at different times and the characteristics of typhoon intensity in different time periods. We then calculate the wave height return level and compare it with traditional calculation models. The calculation results show that the new model takes into account the time factor and the interaction between adjacent time periods. Furthermore, it reduces the subjective human interference, so the calculated results of the typhoon’s influence on wave height return level are more stable and accurate.

TEGAL BESAR BEACH REHABILITATION WITH SCALLOPED CONCRETE BLOCK REVETMENT

Klungkung has a coastline of 113 km out of a total of 5780.06 km2 the coastline in the province of Bali, but about 25 km is eroded. One of the critical areas occurs in Tegal Besar beach which caused erosion of 0.08875 to 3.0915 m/yr. Revetment with scalloped concrete blocks is expected to protect land from the wave attack. Concrete blocks have uniform size and shape, showing the aesthetic aspect so as not damage the beauty of the beach. Analysis of wind, tidal, bathymetry and soil data are carried out to obtain the structure and stability of the revetment. The results of this design can be used to rehabilitate the condition of the Tegal Besar beach. From the analysis, the design wave height with a return period of 25 years (H25) = 0.891 m, while the height with the breaking wave (Hb) = 1.003 m and the breaking wave depth (db) = 1.068 m and the design water level elevation (DWL) = 2.061 m calculated from MSL. The revetment structure has a height of 4.00 m, a peak width of 1.50 m, the weight of the first layer of protection is 300 kg and the second is 30 kg with a thickness of 1.00 m. Toe protection are 1.25 m high, 3.00 m wide and weigh 150 kg. The results showed that the revetment was stable against overturning, shearing, and the bearing capacity of the soil was declared safe with the results of overturning stability 22,075 > 2, slidding stability 2.249 > 1.5 and the bearing capacity of the soil 57,993 > 3 so that the revetment can be eligible to be applied at the site.

The problem of determining the threshold for statistical analysis by the POT method: Application to wave data on the Moroccan Atlantic coast

In a study of extreme waves by the Peak Over Threshold (POT) method, the determination of the threshold of data censoring is an essential step. A wrong choice of the threshold can lead to erroneous results of the wave height design and consequently a bad design of maritime structures such as breakwaters for deep sea ports. In this study, we analyzed the influence of the threshold variation on the results of the hundred-year return period waves, generally considered for the design of maritime structures. The sensitivity study allowed us to confirm that the exponential model is the best probability distribution to describe wave data in two points on the Moroccan Atlantic coast for the wave data period from 1958 to 2019. This study also confirmed that a wrong choice of the statistical distribution and a wrong choice of the threshold lead to significant errors in the estimation of design wave height.

Double Entropy Joint Distribution Function and Its Application in Calculation of Design Wave Height

Wave height and wave period are important oceanic environmental factors that are used to describe the randomness of a wave. Within the field of ocean engineering, the calculation of design wave height is of great significance. In this paper, a periodic maximum entropy distribution function with four undetermined parameters is derived by means of coordinate transformation and solving conditional variational problems. A double entropy joint distribution function of wave height and wave period is also derived. The function is derived from the maximum entropy wave height function and the maximum entropy periodic function, with the help of structures of the Copula function. The double entropy joint distribution function of wave height and wave period is not limited by weak nonlinearity, nor by normal stochastic process and narrow spectrum. Besides, it can fit the observed data more carefully and be more widely applicable to nonlinear waves in various cases, owing to the many undetermined parameters it contains. The engineering cases show that the recurrence level derived from the double entropy joint distribution function is higher than that from the extreme value distribution using the single variables of wave height or wave period. It is also higher than that from the traditional joint distribution function of wave height and wave period.

UPGRADING BREAKWATERS IN RESPONSE TO SEA LEVEL RISE: PRACTICAL INSIGHTS FROM PHYSICAL MODELLING

Coastal structures in many parts of the world are typically designed for depth-limited breaking wave conditions. With a projected sea level rise of up to 90 cm by 2100 (Church et al., 2013), the design wave height for these structures is expected to increase. Many of these structures will require significant armour upgrades to accommodate these new design conditions (for example, a 25% increase in wave height will require the mass of similar density armour to be doubled).