Wave Barrier Research Articles

Medium-scale resonant wave barrier for seismic surface waves

In this work, we design an experimental campaign to assess the attenuation performance of a medium-scale resonant wave barrier operating within the frequency range of 50–100 Hz. In particular, the dispersive properties of (i) bare soil, (ii) a configuration of “dead masses” placed over the soil surface, and (iii) a locally resonant barrier, also known as metabarrier, are compared numerically. The resonant barrier introduces a significant amplitude reduction of the surface waves in a narrow frequency range around the resonant frequency of the resonators. Multiple-frequency barriers are designed with increasing and decreasing resonant frequencies to enlarge the attenuation frequency band.

EPS Geofoam as a Wave Barrier for Attenuating High-Speed Train-Induced Ground Vibrations: A Single-Wheel Analysis

Vibrations induced by high-speed trains in the ground are a common cause of concern in the urban railway lines due to construction of buildings and inhabitation of residents close to railway lines. The present study aims to evaluate the potential use of geofoam as an in-fill material for passive trenches to reduce the vibrations generated by railways. Considering the higher frequencies of railway vibrations in comparison with earthquake excitations, characterization of vibration attenuation efficiencies of geofoam in-filled trenches is done in the scale of peak particle velocities (PPV). A comprehensive study is conducted on the effects of buffer stiffness, geofoam density, and dimensions and location of the in-filled trench away from the railway track. Results indicate that having low buffer stiffness for the geofoam in-filled trenches are efficient in reduction of railway-induced ground vibrations. Grades of geofoam with smaller densities are observed to have better vibration attenuation characteristics as well. It is also characterized that the location of the trench close to the railway embankment results in an overall reduction in the vibration levels in the ground. A higher depth of in-filled trench is requisite, if the trench is located at higher distance from the track. It is ascertained that geofoam in-filled trenches are highly suitable for attenuating the train-induced vibrations in the native sub-soil.

Vertical wave barriers for vibration reduction

Earthquakes generate a series of waves that penetrate the Earth. Depending on proximity to the epicenter of an earthquake, different types of seismic waves dominate at the surface of the Earth. Distinct kinds of seismic waves shake the ground in various ways. Love and Rayleigh waves both produce ground shaking at the surface of the Earth, which exponentially attenuates with depth. Surface waves can often constitute the most important component of ground shaking far from the epicenter due to the fact that the decrease in their amplitude diminishes less rapidly with distance; thus, these waves can be dangerous and destructive. Hereinafter, the concept of a seismic barrier in soil protecting the area from seismic waves of the Rayleigh type is considered. The main idea behind this type of protection is to prevent seismic waves from transmitting wave energy into the protected zone, decreasing the amplitudes of displacements, velocities and accelerations at the points behind the barrier. In this article, numerical simulations on planar and spatial models are presented and discussed for the cases of horizontal and vertical barriers using different mechanical and geometrical parameters of the barriers. Additionally, an algorithm for a multi-parametric optimization of the barrier geometry and material is presented and adopted for specific soil conditions.

An Optimal Design Procedure of Wave Barriers for Mitigation of Underground and Above-Ground Railway Vibrations

In this paper, a robust parallel finite-element/genetic-algorithm (FE/GA) procedure is presented for finding the optimal layout of wave barriers in the ground alongside the underground or above-ground railways. The proposed FE/GA procedure is capable of optimizing the topology of the wave barriers by altering the FE model geometry and mesh at each optimization step to cope with the excitations by underground, above-ground, and simultaneous under- and above-ground loadings. The results obtained show that this coupled procedure is effective for the analysis and design of different types of wave barriers subjected to dynamic transient loadings. Three different types of wave barriers are studied including wave impeding blocks (WIBs), jet-grouted columns, and trenches. It is found that the open trenches have the largest mitigation capacity and if they cannot be used, the WIBs perform better than the jet-grouted columns. Although the wave barriers can notably reduce the ground vibrations induced by underground trains, they perform more effectively when the source of vibrations is located at the ground surface.

MITIGATION OF SHOCK WAVE EFFECT PRODUCED BY AN EXPLOSION IN MINES BY CHANGING SAFETY BARRIER PENETRABILITY

Shock wave travel in a roadway with impermeable safety barriers is modeled numerically in the equilibrium and non-viscous formulation. Inclined and arched barriers are studied at the varied porosity in a range from 0 to 0.8. The inclined and arched barriers decrease the load exerted on the barrier structure by the shock wave owing to formation of a reflected wave which is oblique, or radial in case of the arched barrier. An increase in porosity of the barrier can additionally weaken the shock wave effect but barriers with high penetrability make the defensive screen inefficient, which is confirmed by the higher differential pressure at the shock wave front after passing the barrier.

Topology optimization of periodic barriers for surface waves

Dispersion engineering is always the important topic in the field of artificial periodic structures. In particular, topology optimization of composite structures with expected bandgaps plays a key role. However, most reported studies focused on topology optimization for bulk waves, and the optimization for surface wave bandgaps (SWBGs) is still missing. In this paper, we develop a topology optimization framework based on the genetic algorithm and finite element method to design periodic barriers embedded in semi-infinite space for reducing surface waves on demand. The objective functions for SWBGs are proposed based on the energy distribution properties of surface waves. The numerical results show that the optimization framework has stable convergence for this problem and is effective to optimize SWBGs. Considering large SWBGs and low filling fraction of solids, we investigate single- and multi-objective optimizations, respectively, and obtain novel wave barriers with good performance. The beneficial configuration features and mechanism of broadband SWBGs from the optimized results are explored. The results indicate that for the first-order SWBG, most optimized structures consist of a main scatterer at the center and some subsidiary scatterers near the surface. The rigid body resonance of the main scatterer determines the lower edge of SWBG, and the subsidiary scatterers can regulate the upper edge. Higher-order SWBGs are generated from the interaction of multiple scatterers, whose relative distance has a great influence on the position of SWBGs. The optimized structures can make the surface waves propagate far away from the surface within the frequencies of bandgaps, leading to a strong attenuation of surface vibration. In practice, our topological optimization framework is promising in designing high-performance surface wave devices and novel isolating structures for earthquake or environmental vibration in civil engineering.

Oblique Wave Scattering by a Floating Bridge in the Presence of a Vertical Permeable Flexible Barrier

Abstract The interaction between oblique water waves and floating bridge in the presence of a vertical partial flexible permeable barrier is studied under the assumption of the linear water wave theory in finite water depth. The associated mathematical problem is handled for a solution using the least-squares approximation method. The reflection and transmission coefficients, free surface elevation, wave force acting on the bridge and barrier are computed to study the effects of various wave and structural parameters for three different edge conditions. The study reveals that wave reflection decreases with an increase in porosity, and a reverse pattern is found in the case of wave transmission. As the normalized spacing between the barrier and the floating bridge increases, the reflection coefficient follows a periodically oscillatory pattern. Furthermore, it is noticed that regardless of the barrier configurations, the wave reflection increases for an increase in the angle of incidence. It is also found that the surface-piercing barrier is more efficient than the bottom-standing barrier as a wave barrier. Moreover, the results indicate that by placing a porous flexible barrier at an appropriate position, the wave force on the bridge can be reduced significantly.

Decorated membrane resonators as underground seismic wave barriers against high magnitude earthquakes

We report a framework of underground barriers against seismic waves from high-magnitude earthquakes, which consist of the deep subwavelength decorated membrane resonators (DMR's) modeled as a type of artificial soil, the meta-soil, which is buried in the host soil. The meta-soil has the same elastic properties as the host soil but with a dynamic effective mass density that mimics the functionality of the DMR's mixed with the host soil. Metallic membrane DMR's with multiple working frequencies down to 7 Hz are experimentally demonstrated. Transmission attenuation exceeding 20 dB and absorption above 98% are numerically demonstrated for the 1 Hz Rayleigh waves using about 12 rows of underground meta-soil columns. The findings obtained from the meta-soil are validated by using discrete generic tuned mass dampers buried in the soil. A scaling law similar to the mass density law for acoustic waves that relates the meta-soil mass density to the wave frequency for a given transmission attenuation has been analytically derived and numerically verified. The main mechanism for the wave attenuation is the resonant enhancement of scattering and dissipation by the resonators in the meta-soil. The findings for attenuating the 1 Hz seismic waves serve as a benchmark and design platform for the broadband seismic wave barriers due to the following findings. (1) It is a representative frequency for high magnitude earthquakes. The practical lower frequency limit is about 0.5 Hz, so the dimension and weight of the dampers for 0.5 Hz will be comparable to that for 1 Hz, while the dampers for higher frequencies will be smaller in size and lighter in weight. (2) The length of the wells will be comparable to that of the 1 Hz ones and proportionally shorter for higher frequency waves. Our findings provide a viable solution that could fill the gap between the maximum earthquake resistance capability of most modern buildings and infrastructures (∼seventh magnitude) and the need to resist the highest (∼eighth) magnitude earthquakes recorded in human history, and remedy one of the main shortcomings in the literature on the local resonators for underground seismic wave barriers, which is the gross over-estimation of the seismic wave blocking power of the barriers due to the omission or unrealistic under-estimation of the intrinsic dissipation of the elastic components of the local resonators.

An Experimental and Theoretical Study of Wave Damping due to the Elastic Coating of the Sea Surface

Flexible plates or membranes located on the sea surface can be effective for attenuation waves approaching the beach. The most efficient structures should be found through comprehensive research using developed experiments and theory. Our experimental work was focused on the wave propagation and attenuation passing through floating elastic structures. The experiments were conducted at the wave flume of Tainan Hydraulics Laboratory, National Cheng Kung University, Taiwan. The experiment mainly analyzes the reflection coefficient, transmission coefficient and energy loss of the regular wave of intermediate water depth after passing through the elastic structure under different wave steepness and other different wave conditions. Our experiments also explore the comparison of energy dissipation effects and the differences in motion characteristics between different elastic plates and different plate fixing methods. Three elastic materials were tested in the experiments: Latex, cool cotton and polyvinyl chloride (PVC). A model of a thin elastic plate covering the sea surface was used to evaluate the effectiveness of the structure of the wave barrier. The results of experiments carried out in the wave flume were compared with theoretical predictions in a wide range of generated waves.

Gravity wave interaction with a submerged wavy porous plate

ABSTRACT A numerical model based on multi-domain boundary element method (BEM) is developed to study the gravity wave interaction with a horizontally submerged wavy porous plate. The boundary condition on the porous barrier is considered a quadratic pressure drop to incorporate the effect of wave height on the wave energy dissipation directly. The performance characteristics of the wavy porous plate are studied by analysing the hydrodynamic coefficients of the breakwater for different physical parameters. Numerical results demonstrate that wavy porous plate improves the energy dissipation and reduce wave transmission compared against the conventional flat plate. The increase in wave energy dissipation is governed by the ripple amplitude and the number of ripples. The proposed model is expected to act as an effective wave barrier in the attenuation of wave energy for the creation of a tranquillity zone in the marine environment for water depths ranging from intermediate to deep waters.

Gravity wave interaction with a wave attenuating system

In the present study, gravity wave interaction with a wave attenuating system (WAS) comprised of a series of surface piercing thin vertical porous plates fixed on a fully submerged rigid pontoon is analyzed. For the wave past porous barriers, a quadratic pressure drop is considered to account for the energy dissipation due to changes in wave steepness. A numerical model based on iterative multi-domain boundary element method is developed under the assumption of a small amplitude water wave theory. The scattering coefficients (reflection and transmission) and wave force coefficients (horizontal, vertical and moments) are computed for different wave and structural parameters such as the number of plates, relative plate width, the relative depth of submergence, plate porosities, and relative wave steepness. The results demonstrate that with the creation of trap zones through multiple porous plates on a submerged rigid pontoon, it is possible to reduce wave transmission by 60–70%. For optimum performance across all water depths, it is suggested for the WAS to have 1 ≤ B/h ≤ 1.5 and h1/h ≤ 0.3. Also, interestingly there is a 25–30% reduction in the vertical wave forces which reduces the load acting on the ancillary equipment. The WAS is found to perform well for porosity μ=20%, above which the wave transmission increases gradually. The study results can be useful in the cost-effective design of this type of special wave barrier for a range of coastal engineering field applications.

Coupled eigenfunction expansion–boundary element method for wave scattering by thick vertical barrier over an arbitrary seabed

Wave structure interaction problem having thick vertical barrier over an arbitrary seabed is analysed for its solution. The associated boundary value problem is handled using a coupled eigenfunction expansion–boundary element method. This method converts the boundary value problem into integral equation over the physical boundaries. The physical boundaries are discretised into a finite number of elements and hence the integral equation give rise to a system of linear algebraic equations. Finally, the system of equations is solved to obtain the physical quantities, namely, the reflection and transmission coefficients. For ensuring the correctness of these physical quantities, the energy balance relation is derived and verified. The present results are also verified by comparing the results available in the literature. The present study reveals that the width and height of the structure along with the undulated seabed play an important role to construct an effective wave barrier to protect various marine facilities from wave attack and also helpful to create the tranquility zone on the lee side of the structure.

Vibration isolation of over-track buildings in a metro depot by using trackside wave barriers

More and more cities consider to build superstructures over metro depots to comprehensively exploit the air space. However, metro train operations into and out of depots can generate excessive vibration and noise within the over-track buildings, which hampers the performance of vibration sensitive equipment and adversely affects the living quality of building occupants. This paper explores a systematic numerical investigation on the use of trackside wave barriers to isolate vibration transmission from the track into over-track buildings. A numerical model composed of a train-track dynamics sub-model and a track-soil-building finite element sub-model was developed to study the vibration isolation efficiency of various wave barriers including trenches and concrete walls. Utilizing this model, which was validated by previous field measurement results, parametric studies were further conducted to investigate the vibration isolation sensitivities of geometrical (depth, width and distance) and infilling material properties of trenches. Results showed that the open trenches performed best in building vibration isolation, and its isolation efficiency depended on the normalized depth. Geofoam trenches, i.e. soft material infilled trenches, were proved to be more effective than lightweight aggregate concrete trenches, i.e. hard material infilled trenches, in the dominant frequency range of 16–40 Hz. Concrete walls offered even worse vibration isolation performance than the hard material infilled trenches. These results can be used as a guideline in designing the geometry of wave barriers or the infilling materials of trenches in metro depots with over-track buildings.

Effects of water table on ground-borne vibration screening effectiveness by using open trenches

The seasonal variations in groundwater table would significantly change the dynamic responses of the ground and the screening performances of wave barriers. This paper develops a two-dimensional finite element model based on COMSOL to describe the propagation of waves in a layered ground with open trenches. This layered ground is modelled as a dry layer resting on a saturated half-space. The influence of the moving groundwater table on isolation efficiency of barriers is then investigated, considering the infiltrated water in trenches. The effects of soil hydraulic properties and geometrical parameters of the trench are also analyzed respectively. Results show that a low value of the permeability coefficient of saturated half-space may have a significantly detrimental effect on the screening performance due to the low frequency behaviors of the medium. Placing a trench in vibration-strengthening (weakening) zones results in a better (worse) isolation effect, and with a critical water table (Hw,c), increasing trench depth and width can hardly achieve a satisfactory screening efficiency (75% reduction) due to the occurrence of resonance in the dry layer. In addition, a multiple trench isolation system is simulated in the condition of high water levels and its shielding performance is compared to the single trench barrier. A triple trench barrier is found to be a preferred alternative because it can achieve a much better screening efficiency. Specially for Hw,c, a multiple trench barrier can effectively eliminate the adverse effect of the resonance and achieve more than 75% reduction of ground vibration.

Experimental studies on surface-wave isolation by periodic wave barriers

Periodic structures often fabricated at the micro/nano-scale have opened new vistas in acoustic and electromagnetic wave manipulations due to band-gap properties. This study shows theoretically and experimentally that the propagation of destructive surface waves can also be controlled artificially using periodic wave barriers that modify the global properties of the background soil. To depict the attenuation property of surface waves, this study provides a complete dispersion analysis, the complex dispersion relation. Results show that, remarkably, the attenuation zone for surface waves includes not only the band gap but also other evanescent surface modes. This result agrees well with that in the experimental transmission spectra for both periodic trench barriers and periodic pile barriers. Due to their broadband attenuation performance, periodic wave barriers are expected to apply to vibration isolation in a wide range of systems.

Concrete wave barriers to mitigate ground vibrations induced by railway traffic: a three-dimensional numerical study

Continuous wave barriers are mitigation measures to reduce vibrations induced by railway traffic which have been well studied in technical literature. Nevertheless, there are not many studies about discontinuous concrete wave barriers. By this reason, in this paper continuous and discontinuous concrete wave barriers are studied and compared. With this objective, two theoretical cases with discontinuous barriers have been analysed and the results have been compared with those from both continuous barriers and without barriers cases. The study has been carried out with a dynamic numerical 3D FEM model formulated in the space/time domain, which has previously been validated by authors on the Lisbon-Oporto (Portugal) railway line. The numerical results show the discontinuous barriers with a small separation between axles (less than twice the thickness of the continuous barrier) are an efficient measure in the reduction of vibrations, reaching values of insertion loss of up to 13 dB. So, these could be a very interesting alternative to continuous barriers, in order to conjugate a somewhat lower level of reduction of vibration at a considerable lower cost.

A Flexible Membrane Breakwater with a Piezoelectric Layer for Providing Harborage and Wave-Energy Conversion

Liu, C. and Huang, Z., 2020. A flexible membrane breakwater with a piezoelectric layer for providing harborage and wave-energy conversion. Journal of Coastal Research, 36(1), 148–156. Coconut Creek (Florida), ISSN 0749-0208.Integration of wave-energy converters with coastal structures provides a way to make wave-energy utilization economically viable. This theoretical study examines a piezoelectric membrane system that serves as a breakwater and a wave-energy harvester. The system is in the form of a piezoelectric layer built into a flexible membrane wave barrier. Series resistor-inductor-capacitor electric circuits are used to obtain electrical output power from ocean waves through the piezoelectric layer. This type of piezoelectric membrane system is proposed for providing harborage and wave-energy extraction at marinas and small boat harbors. Use of an eigenfunction expansion method, solutions to the wave-scattering problem, the calculation of the deflection of the piezoelectric membrane, and an analytical expression for the electric-power output per unit surface area of the piezoelectric layer (output power density) are described. The output power density can reach its maximum value at an optimum resistance, which increases with the thickness and surface area of the piezoelectric layer and decreases with wave frequency. At the optimum resistance, the maximum power output density and the minimum transmission coefficient occur at the same critical frequency, which is controlled by the dimensions and initial tension of the piezoelectric membrane. The surface area and the inductance of the piezoelectric layer have little effect on the output power density, which increases with the thickness of piezoelectric layer nearly linearly.

PERIODIC BARRIERS WITH CRUCIFORM TRENCHES FOR SEISMIC SURFACE WAVES

Seismic surface waves with large amplitudes, long distances of propagation and low frequencies can cause great damage to structures. To isolate the seismic Rayleigh surface waves, periodic barriers with cruciform trenches distributed in a homogeneous semi-infinite soil substrate in a square lattice are designed and investigated. By using finite element method, numerical simulations were carried out on the band structures and the frequency responses of the surface wave barriers. The effects of the structure parameters on the complete band gaps were discussed. As an application example, the time-history responses to the Oroville seismic waves were analyzed. The results show that the periodic barriers with cruciform trenches present effective attenuation zones for lower frequencies, and exhibit good performance on the isolation of Oroville seismic surface waves.

Scattering of Surface Gravity Waves by a Pair of Floating Porous Boxes

A numerical model is developed based on multidomain boundary element method (MBEM) to investigate the scattering of surface gravity waves by a pair of floating porous boxes. This study reveals that there is a significant reduction in wave forces acting on the boxes with the introduction of structural porosity. Moderate porosity is highly effective for shallow and intermediate water depth for dissipating wave energy, while high porosity is more suitable in case of deep water. A major part of the wave energy is trapped by the porous boxes when the widths of the boxes are close to half of the wavelength of the incident waves. Apart from wave reflection and energy dissipation, a pair of floating porous boxes traps a part of wave energy, which helps in the wave attenuation on the lee side of the porous box. Horizontal and vertical forces of the seaside porous box are 180 deg out of phase, while they are in-phase in case of the box located on the lee side. Optima in the horizontal and vertical forces are attained when the distance between the boxes are at periodic intervals of half the wavelength. This study will be of immense help in the design of box-type porous structures as effective wave barriers for the creation of tranquility zone in the marine environment.

Design of wave barriers for mitigation of train–induced vibrations using a coupled genetic-algorithm/finite-element methodology

Train-induced ground vibrations can cause major problems in structures that accommodate sensitive apparatus or located in densely populated districts. Wave barriers are used extensively in practice to mitigate the detrimental effects of these vibrations. Many factors have influence on the efficacy of the wave barriers, and a robust procedure is required for an appropriate design that can consider the effect of these factors. This paper describes a coupled genetic-algorithm/finite-element methodology for design of wave barriers. In this methodology, all of the important geometrical and material parameters associated with the performance of wave barriers are considered collectively. Therefore, the combined effect of all parameters and their interdependency is acknowledged. These parameters include the shape, dimensions, position, number, and material properties of the wave barriers. In addition, the uncertainties associated with the nature of transient train-induced loading are taken into account. The results of this study show that open trenches have much higher mitigation capacities when compared with the in-filled trenches, and importantly using double-trench barriers instead of single-trench, enhances the mitigation capacity by as much as 20%. However, such a great boost in the mitigation level is not observed for triple-trench barriers.