Armor Units Research Articles

Numerical Simulation of Random Wave Overtopping of Rubble Mound Breakwater with Armor Units

Based on the open source code OpenFOAM, a three-dimensional model is presented for simulation of the interaction between waves and rubble mound breakwater with armor units. The armor units with their real geometries are depicted through computational grids. The volume-averaged RANS equation and the seepage equation containing nonlinear term are used to describe the percolation in the core and underlayer of the breakwater. Grids independence analysis are carried out, the horizontal and vertical grid size are recommended to take as one-fifteenth of the mean nominal diameter D50 of the armor units and one-fifteenth of the wave height respectively. Random wave overtopping of rubble mound breakwater with armor units is simulated through the proposed model. The results show good agreement between the simulated and measured overtopping discharge rates for different types of armor units. The developed numerical model can be used to evaluate the random wave overtopping in design of rubble mound breakwater with artificial armor blocs.

Monte Carlo Simulation for Reliability Hydraulic Stability of Rubble Mound Breakwater Armour at Sudimoro Power Plant, Pacitan

In breakwater design, the conventional deterministic methods are commonly used. This method based on the concept of load, where the design load should not exceed the carrying capacity of the structure. However, the design load itself can be identified using statistics analysis, such as the average value of a 60-years return period of wave. Most of the available design formulas only provide a link between wave characteristics and some structural responses, such as run up, overtopping, or armor layer damage. In this paper, a reliability analysis of the breakwater hydraulic stability of Sudimoro Power Plant, Pacitan is performed with Monte Carlo simulation. The formulas used in hydraulic stability calculations were Hudson and Van der Meer formulas. The analysis shows that the breakwater structure in Pacitan Power Plant already meets the hydraulic stability design with reliability of 98,8% for Hudson and 95,12% for Van der Meer formula. This paper also presents the reliability of breakwater armour units proposed by authors.

Virtual Level Analysis Applied to Wave Flume Experiments: The Case of Waves-Cubipod Homogeneous Low-Crested Structure Interaction

This paper presents the use of virtual level (VL) probes as an alternative image-based approach to investigate the interaction of waves with coastal structures in wave flume experiments. These probes are defined as regions of interest located at specific positions along the horizontal domain of the images, in which edge interfaces are detected and, thus, their vertical motions can be obtained. To demonstrate the use of the methodology, a critical condition of breaking waves interacting with a Cubipod homogeneous low-crested structure (HLCS) in a two-dimensional framework was selected. With the video recorded from the experiments, image calibration, processing, and analysis stages were implemented to analyze the performance of the HLCS in reducing wave elevations and to study the stability of the armor units. The present approach can be extended to a wide range of coastal structures applications where the interface detection between components of the scene is useful to observe the behavior of coastal structures, increasing effectiveness and alternatives to acquire precise data in 2D experimental tests.

Risk-based assessment of breakwater armour units including effect of epistemic uncertainty on wave hazard

A formulation to assess a breakwater damage probability and to select the optimal maintenance strategy is presented and illustrated with a case study in Mexico. The formulation includes the calculation of annual and lifetime exceedance damage probabilities, the cost of damage/failure consequences, epistemic uncertainty and information on port logistics. The limit-state corresponds to the stability of the breakwater core (armour) units and the cost of failure consequences includes the explicit consideration of costs of fatalities, loss of armour units, damage and loss of property to port facilities, and economic loss due to business interruption in the port. The Van der Meer approach is followed to describe the damage state and the number of waves is modelled as lognormal instead of normal. A curve of tetrapod’s weight versus wave height is proposed as an approximation to the tetrapod’s fragility. FOSM (First Order Second Moments) and MCS (Monte Carlo simulation) techniques are implemented. The wave height is identified, through the calculation of gradients, as the most sensitive parameter for epistemic uncertainty. The optimal maintenance is selected after assessing three maintenance alternatives by balancing costs and safety. A breakwater located in Mexico called Tampico Port is used as case study to illustrate the formulation.

CFD/DEM coupled approach for the stability of caisson-type breakwater subjected to violent wave impact

Wave impacts on vertical caissons may cause breakwaters failures. This paper focuses on the analysis of the stability of breakwaters under violent wave impacts by using a triple-coupled Fluid-Porous-Solid model. The fluid model is described by the Volume-Averaged Reynolds-Averaged Navier-Stokes equations in which the nonlinear Forchheimer equations for the porous medium are added to the inertia terms. The solid model, based on the DDA method which is an implicit DEM method, has been used to analyze the movement and the stability of the caisson and armour units by taking into account the shapes of the armor units, as well as the contact between blocks. The developed model has been used for multiple purposes. Firstly, to estimate the variation of the maximum height of the impacting wave with the breakwater slope. A new formula has then been established for this purpose. Secondly, to analyze the influence of the porosity and of the thickness of the porous layer on the Turbulence Kinetic Energy (TKE) distribution around the breakwater structure. The results show that the higher the thickness, the lower the TKE intensity will be. Finally, the model has been used to analyze the stability of shaped armour units placed behind the caisson.

Hydrodynamic Performance of A‐Jacks Concrete Armor Units in Riverbeds around Downstream in Flip Buckets

The jet flipped from flip buckets hits the dam’s downstream side as a free jet with an immense amount of energy, leading to bed erosion. Erosion of river bed materials downstream of dams could affect the performance of dams or power plants by altering the tailwater depth, rendering proper designs of controlling structures or erosion reduction methods highly indispensable in this regard. Hence, the hydrodynamic performance of A‐Jacks concrete armor units in controlling scour was examined in this study. A‐Jacks armors are applicable as a flexible protection without environmental risks often for bed erosion control. The desirable functionality of A‐Jacks armors depends on the flow hydrodynamic parameters such as velocity profile variations (U/UB), the Reynolds stresses ( and τv′w′), and the skin friction coefficient (Cf) created as a consequence of using A‐Jacks armors on beds. The size of A‐Jacks elements can have a role in increasing the flow turbulence to a certain depth so that after the impact of the flow with A‐Jacks armor, the vortices’ intensity as well as the shear stress affecting the bed gradually decreases. The results of the numerical model suggest that the surge in the flow turbulence energy dissipation downstream of flip buckets significantly mitigates the underlying conditions of scouring phenomena, which is evidence of A‐Jacks armors’ acceptable performance in scaling down scour depths.

Stability Number of Additionally Placed Armor Unit (Tetrapod) Covered on Existing Two-Layered Tetrapod Rubble Mound Structures: Pattern Placing Condition

항만구조물의 ë ¸í›„í™”ê°€ 가속화되면서 상향된 설계파 조건에 대응하기 위한 연구가 필요한 상황이다. 특히 피복재가 거치되는 경사식구조물의 경우, 상향된 ì„¤ê³„íŒŒê³ ì— ì•ˆì •ì¤‘ëŸ‰ì„ 확보하기 위해서는 피복재의 중량 증가가 필요하다. ê·¸ë ‡ì§€ë§Œ 그와 ê´€ë ¨ëœ 연구는 진행된 사례가 없다. 본 연구에서는 기존 피복재가 거치된 경사식구조물에 추가 피복재를 거치하는 경우, 추가 피복재의 ì•ˆì •ì¤‘ëŸ‰ ì‚°ì •ì„ 위한 수리모형실험을 수행하였다. 피복재로는 콘크리트 이형블록인 í ŒíŠ¸ë¼í¬ë“œë¥¼ ì ìš©í•˜ì˜€ë‹¤. 실험결과에 의하면 비월파 조건에서 기존 피복재(í ŒíŠ¸ë¼í¬ë“œ)가 ì •ì  ê±°ì¹˜ì´ê³ ì‚¬ë©´ê²½ì‚¬ì˜ 변화가 거의 없는 경우 실험조건 내에서 추가피복재(í ŒíŠ¸ë¼í¬ë“œ)의 ì•ˆì •ê³„ìˆ˜(Kd)는 ì¼ë°˜ì ì¸ í ŒíŠ¸ 라포드 ì•ˆì •ê³„ìˆ˜(Kd = 8)에 비하여 주기별로 차이가 있으나 최대 10% 증가하는 것으로 나타났다. 핵심용어: ê²½ì‚¬ì œ, 피복재, ì•ˆì •ê³„ìˆ˜, 수리실험, í ŒíŠ¸ë¼í¬ë“œ, 추가 거치

Physical model studies on damage and stability analysis of breakwaters armoured with geotextile sand containers

Harnessing the advantages of geotextile sand containers (GSCs), numerous submerged breakwaters and shoreline protection structures have been constructed worldwide. But an emerged breakwater structure with geotextile armour units, capable of replacing the conventional structures, is rarely discussed. A 1:30 scaled physical experimentation is chosen as a preliminary investigation to test the feasibility of using GSCs as breakwater armour units. Structural design is evolved based on a comprehensive literature survey. The paper focuses on the stability parameters and damage characteristics of the proposed structure. Four different configurations are subjected to waves, confining to Mangaluru's wave parameters. Effect of armour unit size and sand fill ratio on the stability of the structure is analysed and it is concluded that changing sand fill ratio from 80% to 100% shot up the structural stability to a maximum of 14%. Increasing bag size also resulted in the increased stability up to 8%. Experiments revealed that the best performing configuration could withstand wave heights up to 2.7 m. Stability curves for all tested configurations are discussed and can serve as an effective guideline for designing GSC breakwaters.

STABILITY OF XBLOCPLUS ARMOUR LAYERS AFTER INITIAL DAMAGE

XblocPlus is an interlocking single layer armour unit that is placed with uniform orientation. The unit is applied with a large safety margin. Physical model test were performed without damage up to stability numbers of Hs/dDn=5.5 whereas a design stability number of Hs/dDn=2.5 has been adopted. The behaviour of an XblocPlus armour layer after initial damage is has been investigated by physical model tests with broken and manually removed model units. XblocPlus armour layers (with uniform orientation) respond differently to initial damage than interlocking armour units with random orientation. The latter are moving and re-arranging in order to bridge a gap in the armour layer (de Rover et al., 2008). XblocPlus units in contrast hardly move and nonetheless maintain the hydraulic stability of the damaged section. Details of the experiments and findings as well as implications for design and maintenance of breakwater armour layers will be discussed in the final paper.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/izwm60IBx-4

XBLOC-PLUS: THE INTERLOCKING, PATTERN PLACED AND EFFICIENT ARMOUR UNIT

Most breakwaters are built with randomly placed single layer armour units as these are most cost-efficient. Most single layer blocks require random unit orientations, which requires the crane operator to assess the orientation of each individual unit during placement. DMC noticed the desire for an interlocking block which can be placed in a regular pattern as many crane operators find it easier to place units uniformly, which requires less intuition. Fifteen years after the introduction of Xbloc, DMC introduces a new interlocking breakwater armour unit called XblocPlus which is placed with uniform block orientations.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/oEb1vsYfjL8

Enhanced massivity index based on evidence from case studies: Towards a robust pre-design assessment of early-age thermal cracking risk and practical recommendations

Tensile stresses resulting from a combination of thermal volumetric changes, due to the heat of hydration and ambient conditions, autogenous deformations and boundary restraints, often induce a significant intrinsic load on massive concrete structures. Whenever such stresses attain the concrete tensile strength, cracking occurs, which may in turn impair the serviceability and durability of the structure. This study is an output of Working Group 7 of RILEM Technical Committee 254-CMS: Thermal cracking in massive concrete structures and is presenting case studies of early-age thermal cracking in massive concrete structures where internal restraining conditions often prevail, such as thick blocks, armour units, footings, dams and spillways, and large-sized columns. It covers the analysis of causes of this type of cracking together with the lessons learned from the collected evidence along with best mitigation practices (often resulting from forensic investigations by means of computer-based simulations). Based on the evidence retrieved from the analysed case studies, the concept of massivity used to indicate potential thermal crack proneness in massive concrete structures is significantly improved to account for binder type and content as well as casting and fresh concrete temperature, in addition to the geometrical characteristics of the element under investigation. The use of such an indicator may lead to a more robust pre-design assessment of the likelihood for thermal cracking occurrence in massive concrete elements, advising designers and contractors dealing with such structures whether more complex analyses should be performed already at the design stage.

High-density geopolymer concrete for Port Kembla breakwater upgrade

Marine environments can pose continuous threats to coastal infrastructure, especially during episodic storm events. Thus, monitoring and maintenance of rock or concrete units-armoured coastal breakwaters are required, especially under present climate change scenarios, where changes in wave behaviour are anticipated and coastal structures are likely to be exposed to even greater wave energy resulting in higher rates of damage. A possible pathway towards the upgrading of existing breakwaters is to introduce high-density armour units, suggested by theoretical estimates and physical model test findings. In this project, a unique, sustainable high-density geopolymer concrete (GPC) mix was developed and trialled in fabricating armour units for upgrading existing coastal breakwaters. The system developed in laboratories was upscaled for field applications and is being tested at the Northern breakwater of NSW Ports’ Port Kembla Harbour. The concrete uses steel furnace slag (SFS) aggregate in an alkali-activated blended fly ash-blast furnace slag binder proportioned to facilitate the elimination of delayed expansion of the aggregate. The concrete properties were measured and microstructural analyses undertaken. The results show that SFS aggregate offers higher bulk density to the concrete alongside satisfactory strength in on-site curing and can reduce armour mass requirements at the same level of structural stability. Microstructural analyses confirm the elimination of SFS aggregate free-lime expansion. This important result provides a novel approach to both repair of existing structures and construction of new structures with reductions to both cost and carbon footprint.

Stability of berm type breakwater with cube blocks in the lower slope and berm

In this study, the stability of cube armour units in the lower slope and berm of rubble mound breakwaters with a berm was investigated for irregular and regular placement methods. Cubes are simple and cheap in production. However, the design conditions for the upper slope and lower slope may differ depending on the water level of the dominant storm conditions. For the upper slope, relatively higher water levels are dominant. The berm has a reducing effect on the wave loading on the upper slope and therefore, it may be relevant to use cubes in the lower slope, in combination with rock in the upper slope. In this study, a regular placement technique named “the double pyramid placement method” was applied for cubes placed on the lower slope and the berm. This placement technique was compared with the irregular placement technique by performing experiments in a wave flume. As a result of this investigation, the regular placement method was found to be superior for the stability of cubes in the lower slope and berm of rubble mound breakwaters with a berm.

BPPT-lock Armor Unit Implementation for Improving Breakwater Sustainability at the Pacitan Power Plant

BPPT-lock was developed by the Agency for The Assessment and Application of Technology (BPPT) and was awarded patent in 2012. The hydraulic stability (KD) of BPPT-lock armor unit was compared to Tetrapod, Dolos and Xbloc armor units. The results indicate that, BPPT-lock performs far better KD in comparison to each of these armor units. A comparative analysis on the economical use of material was also carried out among BPPT-lock, Dolos, Tetrapod and rough stone and rounded stones for similar design condition, the armor unit weight is 4.68ton, 4.97ton, 9.95ton, 19.89ton, and 39.79ton respectively, means that BPPT-lock is more efficient in this comparison. Considering its feasible performance, BPPT-lock is designed as the armor units for the maintenance and reparation of the existing rubble mound breakwater of Pacitan Coal Fired Power Plant port. The 110 m parts of the existing breakwater was hardly damaged and the new structure is designed to stand against a 30 yrs RP waves of Hs = 7m. BPPT-lock armor unit of W = 11 ton on the breakwater slope 1:1,5 is implemented. The first phase construction works was completed in December 2018 and visual observation has shown the great integrity and stability of BPPT-lock armor units.

Image-Based Measurement of Wave Interactions with Rubble Mound Breakwaters

Over the past decade, the use of imaging devices to perform quantitative measurements has seen wide-scale adoption and has become integral to the emerging fields of research, such as computer vision and artificial intelligence. Recent studies, published across a wide variety of fields, have demonstrated a vast number of ways through which image-based measurement systems can be used in their respective fields. A growing number of studies have demonstrated applications in coastal and ocean research. Edge detection methods have been used to measure water surface and bedform elevation from recorded video taken during wave flume experiments. The turbulent mixing of air and water, induced by the breaking waves and the runup processes, poses a particular problem for the edge-detection methods, since they rely on a sharp contrast between air and water. In this paper, an alternative method for tracking water surface, based on color segmentation, is presented. A set of experiments were conducted whereby the proposed method was used to detect water surface profiles for various types of breaking waves interacting with a rubble mound breakwater. The results were further processed to compute the surface velocity during runup. The time-history of surface velocity is shown to closely parallel the point measurements taken nearby the instrumented armor unit. These velocities can potentially serve as boundary conditions for determining the dynamic loads exerted on the armour units. Further, the image processing results are used to remove the time-varying buoyant force from the measured force acting on an individual armour unit, providing additional insight into how the forces develop over time.

Stability of Composite Breakwaters under Tsunami Attack

Breakwaters are effective structures for mitigating tsunami-induced damage. However, pieces of the breakwater can be displaced by the turbulent tsunami flow, which undermines the stability of the breakwater and reduces its mitigation effectiveness. Assessing the damage to breakwaters in tsunami-prone coasts is, therefore, valuable for the port authority, cargo owners, and coastal residents. Physical experiments were conducted to assess potential damage to a typical composite breakwater in New Zealand due to tsunamis. Higher breakwaters can resist a stronger bore impact and experience delayed initiation of the same damage. A new parameter is proposed to assess the damage in the armor layer, which takes into account the size and density of armor units, the height of the breakwater, and the tsunami bore depth.

Ceramic Armour for Armoured Vehicles Against Large-Calibre Bullets

Modelling the armour-piercing bullets B-32 calibre 12.7 mm penetration into the double-layer ceramic-composite armour has been performed for the armour blocks of two designs. The first one is a layer of ceramic square tiles supported by the glass or polyamide fabric. Modelling and subsequent ballistic tests have shown that the conical Hertz crack localized in the ceramic tile is formed. The tile is destroyed from the spread of radial cracks, and the entire armour unit becomes unable to sustain the repeated hit of the bullet. In the second case, the armour block consists of the discrete epoxy-filled cylindrical ceramic elements with spherical ends. The advantage of this "discrete" armour is localization of the damage zone and thus an ability to sustain the multiple bullet hits. The ballistic tests of the compared armour units have shown that both provide effective additional protection of light-armoured vehicles against the normal impact of the calibre 12.7 mm bullet.

Development of high-density geopolymer concrete with steel furnace slag aggregate for coastal protection structures

Anticipated changes in coastal wave conditions due to various climate change impact scenarios along coastlines may expose coastal protection structures to greater wave energies and higher damage rates than designed for, especially during episodic storm events. Some existing coastal breakwaters need upgrading to withstand the projected conditions. Breakwater armour unit design equations and physical model tests predict a large gain in stability with a modest increase in the armour material density and indicate reduced armour unit size requirements when utilising high-density concrete. In this study, a high-density geopolymer concrete mix with steel furnace slag (SFS) aggregate was developed based on several trials; the material properties were evaluated for on-site applications under ambient curing conditions. The use of SFS aggregate offers higher bulk density to concrete and mixes were proportioned to achieve good workability and setting time. Most importantly, the fly ash-blast furnace slag blended binder used in this study leads to adequate strength gain in ambient curing and allows the diffusion of the free lime associated with the SFS aggregate into the geopolymer matrix to eliminate the delayed hydration and expansion of the aggregate. This research provides a pathway to both upgradings of existing breakwaters and construction of new structures with a reduction to the carbon footprint in breakwater construction.

2D water-wave interaction with permeable and impermeable slopes: Dimensional analysis and experimental overview

The main objective of this research is to characterize and quantify the prevalent physical processes in the energy transformation of a regular wave train when it interacts with permeable and impermeable breakwaters. Two sources of experimental data are considered: (a) numerical experiments on an undefined impermeable rigid slope, using the numerical model (IH–2VOF), and (b) physical experiments on a non-overtoppable permeable breakwater with a cube armor layer and a porous core of finite width in a 2D wave flume. A revised dimensional analysis reveals that the relative water depth, h/L, and the incident wave steepness, H/L, at the toe of permeable and impermeable breakwaters are the key factors to define and optimize the experimental space (HI/L, h/L). Moreover, the product of (h/L) (HI/L) can be applied to identify the type of wave breaking and the domains of wave energy transformation, and to quantify the reflected and transmitted energy coefficients and the dissipation rate (KR2,KT2,D∗). Fitting an experimental curve (i.e. a sigmoid function) to the impermeable data, the slope is a plotting parameter. The same conclusion is obtained for a permeable breakwater; in addition the wave energy coefficients depend on the relative breakwater width B*/L, and the relative core grain size and D50,p/L, and armor unit diameter, Da/L. Because the range of the design factors spans several orders of magnitude, a log-transformation provides a well behaved experimental space [ln(h/L), ln(H/L)] which is likely of benefit to verify the wave breaker type and the related dissipation-reflection-transmission on slopes. Finally, this study shows that there is not a biunivocal relationship between the Iribarren number, Ir, and the type of breaker, the reflection and transmission coefficients and the bulk dissipation. Therefore, Iribarren's number is not a sufficient similarity parameter for the analysis of wave breaking, and related flow characteristics on slopes.

Evaluation of force exerted by tetrapods displaced by tsunami on caisson breakwater return wall

ABSTRACT Tsunamis can cause large damage to breakwaters and other protection structures placed along the coastline. The strong flows generated by such waves can move the armor units of composite breakwaters, leading to large impact forces on the caissons behind them. In the present work laboratory experiments were carried out in a flume to determine the forces that can result from such impacts. Then, an empirical equation that would allow the estimation of these forces was proposed, with the aim of facilitating the construction of returning walls and parapets situated on top of caissons.