Recent Innovations on Some Coastal Structures

Abstract

This article discusses the technical, economical and environmental aspects of three different novel coastal structures used as wave dampers for different applications. One is floating breakwater with skirt walls; other one is vertical porous walls with an impervious back wall used for the construction of Ports, Harbors and marinas and the third one is on vertical porous slotted wave barrier as a substitute or for replacing offshore rubble mound breakwaters. The knowhow of these three US patents are revealed. The merits and demerits are also described. It is proved that these inventions are economical when compared to the conventional solution used for wave damping applications. It is encouraging to see that some of these products are better in terms of wave damping performance compared to rubble mound wave barriers. It is strongly believed that the clients from around the world would use these innovations for their future coastal infrastructure developments.

1 Introduction

Out of 257 countries in the world, 213 countries have coastline and sea fronts [1]. The total coastline of the world is about 620,000 km. A country with a coast is considered economically blessed because of its beneficial ecological services for the socio-economic development of the country. Coastal and offshore area attracts more development because of the following reasons:

• The sea is rich in protein and provides many varieties of Fish/Crabs/Shrimps/Oysters etc.

• Sea is the source of water for desalination and cooling of power plants

• Coastal space is widely used for the construction of ports and harbors for international trade and marinas for local economic activities

• Coast and quality beaches are the main attractions for tourism and entertainment

• Coastal area provides many different types of nonliving resources

• The climate near the coast is mostly moderate due to the presence of a cool breeze from the sea

• Ocean space acts as a sink for treated waste water

• Ocean is the source for future energy and for a wide range of life-saving medicines

The Ocean Conference, United Nations, New York, 5–9 June 2017 reveals that more than 600 million people (around 10% of the world’s population) live in coastal areas that are less than 10 m above mean sea level. Nearly 2.4 billion people (almost 40% of the population of the world) live within 100 km of the coast. The ocean economy, which includes employment, ecosystem and cultural services provided by the ocean, is estimated at between US$ 3–6 trillion/year.

Most of the ocean and coastal countries are working at a fast phase to improve the blue economy [2], which demands high investment for different types of marine structures for sustainable exploitation of different kinds of living and nonliving resources. It is essential to innovate marine structures with the following strategies: a. It must be economically viable; b. Environmentally acceptable; c. Easy to build; d. Appear elegant; e. Do better performance than the conventional marine structures. This article reveals three different types of marine structures, which almost fulfill these requirements for modern infrastructure development in the coastal area. Three US patents are obtained for the innovations [3, 4] and [5].

This article provides the brief technical, economic and environmental aspects of three innovative coastal structures from these three US patents, and the knowledge is believed to be useful for the coastal space development around the world. Further details for commercialization of these inventions can be obtained from the Scientific and Technical Innovations Department (STID), Commercialization Division (CD), Kuwait Institute for Scientific Research (KISR), Tel: +965-24989955, Mob: +965-99014472, E-mail: ahaji@kisr.edu.kw. This is an attempt to market these products to the world.

2 Technical, Economic and Environmental Aspects of Three Different Coastal Structures

First, the technical, economic and environmental aspects of Floating breakwater [3] will be discussed. Next similar aspect for the Method of Dissipating Water Wave Energy [4] will be revealed. Finally, these aspects from Method for Damping Ocean Waves in Coastal Area [5] will be elaborated.

2.1 Technical, Economic and Environmental Aspects of Floating Breakwater

Technical Aspects.

Floating breakwaters (FBW) are typical marine structures used for wave damping applications. A typical floating breakwater is shown in Fig. 1.

Fig. 1.

A typical floating breakwater with pontoon and a single slotted barrier.

FBW is technically suitable for marine locations with moderate wave climates, especially when the wave periods are less than 6 s and wave heights are less than 1.0 to 2.0 m [6]. It is more suitable in locations with no severe cyclone and Tsunami activities. They are suitable for wave damping in deep waters such as open sea oil and gas loading stations, offshore fish farms etc. The floating breakwaters are moored with the sea bed. Studies on many different types of floating breakwaters are available [7]. The wave transmission performance of FBW is mainly a function of its dimensions, such as its width along the direction of wave propagation (B), water depth (d) and a draft of the breakwater (∆). Pontoon type floating breakwaters (Fig. 2) are used at the beginning. The width of this breakwater should be about 50% of the design wave length to reduce 50% wave energy transmission, and hence it is expensive.

Fig. 2.

A pontoon type floating breakwater with width ‘W’ and draft ‘∆’.

Hence, it is felt that modification of its cross-sectional shape is required to reduce wave transmission. Hence, few cross-sections, as shown in Fig. 3a to 3d are selected, and detailed physical model studies were carried out at Kuwait Institute for Scientific Research, Kuwait. 29 different FBW configurations are tested. Tests are also carried out on a fixed pontoon without any skirt wall. The details of these configurations are provided in Table 1. The wave transmission, reflection, mooring forces, dynamic responses of these models were measured and assessed for a wide range of wave conditions [8]. For 3a, different depths of skirt walls, ‘h’ were used, as shown in Table 1. Porosities are introduced in the skirt wall and vary from 0% to 20%. Porosity in the skirt wall helps to change the hydrodynamic performance due to a change in energy dissipation during wave interaction.

Fig. 3.

Pontoon floating breakwater with different number of skirt walls.

Table 1. Details of different floating breakwater configurations

A typical comparison of the hydrodynamic performance of these different FBW configurations is shown in Fig. 4. Here, K_t, K_r and K_l are called transmission coefficient (H_ts/H_s), reflection coefficient (H_rs/H_s) and dissipation coefficient (K_l = (1 − K_t² − K_r²)^1/2) respectively for a typical wave condition (B/L_p = 0.646 and H_s/d = 0.214), where H_s is the significant incident wave height, H_ts is the significant transmitted wave height, H_rs is the significant reflected wave height, and L_p is the wave length corresponds to peak wave period. It can be seen that wave transmission can be changed by introducing skirt walls of varying numbers and porosity. The user can select the configuration, which provides minimum wave transmission for this wave condition, which is 0.23 for configuration 29 (pontoon with five skirt walls and 20% porosity, as shown in Table 1).

Fig. 4.

Effect of the Floating Breakwater Configuration on K_t, K_r, and K_l for B/L_p = 0.646 with H_s/d = 0.214.

For the same input condition, the normalized seaside and leeside mooring forces are provided in Fig. 5 for all configurations. It is to be noted that the seaside mooring force is always higher compared to the leeside force, and the mooring force value increases with more number of skirt walls.

Fig. 5.

Effect of the floating breakwater configuration on normalized mooring forces for B/L_p = 0.646 with H_s/d = 0.214.

More information is available in [6] and [8].

Economics and Environmental Analysis.

A detailed economic and environmental analysis was carried out. For this analysis, an open sea marina is considered. The marine location is assumed with a tidal variation of 3 m, waves of moderate conditions (H_s = 1.0 m, T_p = 4.0 s). The water depth at the location of the offshore breakwater is considered as 6 m (Fig. 6).

Fig. 6.

Marina configuration for economic analysis.

For economic analysis, two different options of the offshore breakwater are considered. Option 1 is a rubble mound offshore breakwater with concrete armor. The seaside slope is 1 V: 2 H, and the leeside slope is 1 V: 1.5 H. The top level of the breakwater is at 5 m, and the sea bottom is at-6 m. For option 2, a floating BW with 5 skirt walls is considered. Each FBW is 8 m wide × 12 m long and 5 m deep. Skirt walls are 2 m deep and 20 cm thick. The FBW bottom thickness is 0.4 m, and all vertical wall thickness is 0.3 m. The details of material quantity, unit costs, economics and environmental issues are described in Table 2. For the economic analysis, the currency of Kuwait, Kuwaiti Dinar (KD) is used (1 KD = 3.32 US $).

Table 2. Material estimate, cost and environmental analysis for rubble mound and floating breakwater

It is found that floating breakwater of suitable configuration can be elected and designed economically compared to a conventional rubble mound breakwater. It also offers better environmental benefits.

2.2 Technical, Economical and Environmental Aspects of Designing Port, Harbor and Marina Using Vertical Porous Walls Instead of Rubble Mound Breakwaters

Motivation and Technical Details.

The volume of rubble mound required to build breakwaters for Port, Harbor or marina are usually very high. The motivation for replacing rubble mound breakwater for Port, Harbor or marina is because of a few important reasons: a. to reduce the volume of stones needed for construction; b. Increase the area of boat mooring space; c. Elegance; d. Environmental aspects and e. Economics.

Normally, when a sloped wave barrier is used inside the marina, it occupies significant space as shown in Fig. 7. The breakwater here is for damping the waves.

Fig. 7.

Inner part of a typical marina with sloped rubble mound breakwaters for dissipating the wave energy.

A detailed study is carried out by Al-Salem et al. [9] and the promising results of this study is available in Neelamani et al. [10]. It is found that the conventional sloped rubble mound breakwater can be replaced by an array of slotted vertical barriers (Fig. 8) with the same or better wave energy dissipation characters (Neelamani et al. [10]).

Fig. 8.

A comparison of the inner part of a marina built using the slotted vertical barrier and conventional rubble mound breakwater.

A 3D view of a marina built using this innovative solution is shown in Fig. 9.

Fig. 9.

Marina to be built using the slotted vertical barrier.

The main advantage of this innovation is the significant reduction in the volume of materials compared to rubble mound breakwater. The details about the volume of material required for the slotted barrier type wave barrier compared to conventional rubble mound breakwater are provided in Table 3.

Table 3. The percentage volume of material required for different number of slotted wall and porosity combination, when compared to the volume required for 0.9 m V: 1.2 m H sloped rubble mound breakwater

The performance of the present wave barrier is explained by its wave reflection characteristics for different d/L_p values and for H_s/d = 0.214, which is provided in Fig. 10. X-axis represents the type of wave barrier. (1,0%) means a single vertical wall with 0% porosity. RM-1 is a rubble mound breakwater with the slope of 0.7 V: 1.2 H. Seabee-1 and Dolos-1 are breakwater with Seabee and Dolos as armour, respectively, with 0.7 V:1.2H slopes. Similarly, RM-2, Seabee-2, Dolos-2 are similar structures with 0.9 V: 1.2H slope. (1,10%) means single vertical porous barrier with 10% porosity and similar meaning is applicable for others. Smaller the reflection coefficient, the better it is for application. From this plot, one can select the needed number of slotted barriers and the porosity for a selected wave reflection. More information is available in Al-Salem et al. [9].

Fig. 10.

The effect of different wave barriers on wave reflection for different d/L_p values and H_s/d = 0.214.

The main merits of slotted vertical barrier type breakwaters are a. the volume of material needed is only 3.5% to 21% (depends upon the number of slotted walls and porosity) when compared to a sloped rubble mound sea wall; b. If used, it will create more space for berthing; c. With proper design, the top level of the barrier can be used as a berthing facility, as shown in Fig. 8 or 9; d. It is easy to prefabricate and quickly install in a short span of time; e. High-strength polymer materials can be used for its construction, and hence, it offers relief from corrosion of reinforced concrete panels and f. The load on the seabed is less, and the effect on benthic life is also less.

This experimental study is carried out for a wide range of wave conditions. Kuwait Institute for Scientific Research (KISR) can provide solutions for two types of clients: Client 1, mainly from economically strong countries, who wish to invest more at the beginning with less risk and Client 2, the one from developing countries, who wish to spend less for initial construction and wish to take a bit more risk than client 1, but willing to spend more for annual maintenance and any future partial failures. KISR can provide optimized configuration (minimum number of porous walls, optimized porosity), which performs better than sloped sea walls in terms of wave energy dissipation. It is found from this study that a slotted barrier is a better wave energy dissipator for long waves [9, 10], which is very attractive for coastal engineers.

Economics and Environmental Analysis.

The marine conditions assumed for the floating breakwater are considered for the economic analysis for this structure also. Option 1 is the rubble mound breakwater, and option 2 is the wave barrier with porous vertical walls. The cross-section and plan view of each unit can be as shown in Fig. 11a and 11b. Each unit can be 14.7 m wide × 8 m long; 25 units is required to cover the 200 m width of the coastal length. This type of structure can be prefabricated and assembled quickly. For its construction, a floating barge with fabrication and crane facilities are needed.

Fig. 11.

a. Typical cross section of the breakwater with slotted wall. b. Typical plan view of the breakwater with slotted wall.

Table 4 provides the details of material estimate, economic and environmental analysis.

Table 4. Material estimate, cost analysis and environmental issues

The knowhow, scientific results, economic analysis and the merits and demerits can be considered for appropriate design of this new type of breakwater with slotted walls, which can be used for construction of new Ports, Harbors and marina. Significant savings can be achieved with attractive environmental merits and elegance.

2.3 Technical, Economical and Environmental Aspects of Method for Damping Ocean Waves in Coastal Area

Motivation and Technical Details.

The main difference between the previous wave barrier and this one is that in the previous case, the waves were not allowed to transmit since the rear side was provided with an impervious vertical wall. In the present case, waves are allowed to transmit. This study is aimed as an alternative for rubble mound offshore breakwater by using a vertical slotted barrier. The motivation is to reduce or save materials during construction, improve the hydrodynamic performance, add more environmental benefits compared to rubble mound offshore breakwater. The complete scientific details of the experimental study is available in [11]. The results of wave pressures on the panels are available in [12]. From this study, it is possible to select the number of slotted wave barriers and their porosity for any required wave transmission coefficient. This is an important merit of the slotted vertical barrier, which is not easily possible if a rubble mound offshore breakwater is selected. The typical conventional rubble mound offshore breakwater used is as shown in Fig. 12.

Fig. 12.

Typical rubble mound offshore breakwater.

The motivation is to replace the rubble mound offshore breakwater with slotted wave barrier as shown in Fig. 13.

Fig. 13.

Typical slotted wave barrier.

Figure 14 provides the characteristics of wave transmission coefficient for different d/L_p values and for H_s/d = 0.214. From this plot, the user can select a suitable slotted wave barrier configuration for the required wave transmission conditions.

Fig. 14.

The wave transmission coefficient for different d/L_p values and H_s/d = 0.214.

Similar to the other patents, KISR can provide the needed design information for both the type of clients as discussed in the previous section. The information needed for optimized design are the optimized configuration (No. of porous walls, optimized porosity), which performs better than rubble mound offshore breakwater in terms of wave transmission; design wave forces, moments and wave pressures on the barrier plates.

3 Conclusions

Innovation on marine structures is a key and critical issue today and in the future. The focus is required on reducing the volume of materials used for construction (overall cost saving); Improved performance; more positive environmental impact; improved aesthetic value; reduction in the construction time, and improvement in the intended functions. Three different US patents are secured on three different coastal structures, which fulfills these requirements. The detailed knowhow can be obtained from the final reports and publications as provided in the reference section.