Reduction In Heave Research Articles

Power and dynamic performance of a floating multi-functional platform: An experimental study

Hybrid platforms which integrate a floating offshore wind turbine and a wave energy converter are a promising technology as the wave energy converter can lead to a more stable platform and potentially lower costs. In the present work, a semi-submersible floating offshore wind turbine platform integrating with an array of wave energy converters (WECs) in the form of an oscillating water column (OWC) is presented and tested experimentally. The hydrodynamic properties of the multi-functional platform were investigated under a series of regular and irregular wave tests considering both operational and survival sea states. The influence of various parameters (including incident wave directions and chamber opening ratios) on the dynamic responses and the wave energy capturing were systematically studied. The introduction of the oscillating water column can not only capture wave energy but also reduce the heave, roll and pitch responses, especially for long waves kh ≤ 2.0, kh ≤ 1.4 and kh ≤ 1.76 respectively. The maximum reduction in heave, roll and pitch are 35 %, 55.4 % and 13.8 %, respectively. The chamber air orifice size was analyzed and optimized. From the survival sea state tests, it is found that the introduction of the OWC WECs decreases the maximum amplitudes of the platform motions in all five freedoms and the nacelle acceleration.

Experimental evaluation of heave characteristics in sand bed reinforced with closely woven rattan mats

The restrictions imposed on infrastructural development in a country due to the scarcity of structurally sound and stable earthen base can be resolved by means of suitable ground improvement methods. Soil reinforcement using natural fibers like coir, jute, sisal and bamboo have attracted our recent attention due to the achievement of promising results in the field of geotechnical engineering. The present study investigates the potential benefits of using rattan for reinforcing sand beds as an alternative to geosynthetic products. Rattan being an eco-friendly and easily available material has been decided to be used in the form of rattan strips to fabricate closely woven rattan mats. Series of plate load tests were carried out to study the load settlement behavior of square model footing resting on sand bed reinforced with closely woven rattan mats. The paper presents the results obtained after varying the parameters like top layer spacing, number of reinforcement layers and width of reinforcement. A considerable reduction in heave was observed after placing rattan mats of width 3B at an optimum spacing of 0.3B. The experimental investigations indicates that the heave has reduced to 97 % after incorporating four layers of planar rattan mats at optimum spacings when compared to unreinforced sand.

The efficiency of granular pile anchor foundation system in reducing heave of Irbid expansive clayey soil: An experimental investigation

This study is devoted to investigate the efficiency of granular pile anchor (GPA) in controlling heave of shallow foundations constructing over expansive soils. In this study heave measurements were made on laboratory model footings reinforced with GPAs having different diameter (3 cm, 4 cm and 5 cm) and embedded length (20 cm, 30 cm and 40 cm). The GPAs foundation system was constructed on expansive clay compacted in a steel box 60 cm in diameter and 70 cm in height. The measured percent reduction in heave was found to increase with increasing embedded length and diameter of GPA. The experiments conducted in this study showed that the percent reduction in heave when using GPAs may reach as high as 93 %. A theoretical formulation for the prediction of the percent reduction in heave was developed in this study. A comparison of the predicted percent reduction in heave using the developed formulation with the measured values in this study indicated good agreement and suggested that the proposed formulation in this study can be used to estimate the percent reduction in heave of shallow foundations constructing over expansive soils reinforced with GPAs.

Effect of lime-stabilised copper slag cushion on swelling behaviour of highly plastic clay

Clay soil is prone to seasonal volume change due to variation in water content. The use of waste materials in civil engineering, especially in road construction, has been in vogue all over the world due to the development of road infrastructure. Copper slag is one such waste material available abundantly from the copper industry in India. This paper discusses the heave and swelling of copper slag–cushioned clayey subgrade prepared in a model test tank. The results revealed that the methodology adopted is effective in reducing the swelling of clay. The thickness ratios of the stabilised copper slag cushion and clayey subgrade bed adopted are 0.25, 0.5, 0.75 and 1.0. The copper slag cushion is stabilised with lime content varying from 2 to 10%. A reduction in heave of clayey soil subgrade bed is observed with an increase in the percentage of lime and the thickness of the copper slag cushion. For a cushion–clay soil subgrade thickness ratio h c/h s = 1, the reduction in the heave of a clayey subgrade bed is 84.4%. The swell potential observed from the present study follows well the trend obtained from the rectangular hyperbolic model.

NUMERICAL INVESTIGATION OF INTERCEPTOR EFFECT ON SEA KEEPING BEHAVIOUR OF PLANING HULL ADVANCING IN REGULAR HEAD WAVES

In this paper an attempt has been made to assess the capability of numerical algorithm based on Reynolds Averaged Navier Stokes (RANS) for predicting the motion characteristics of the planing hull in calm water and regular waves. The focus of the present study is the impact of interceptors on the sea keeping quality of a planing vessel investigated through the application of numerical methods. The wave properties such as wavelength and wave height are taken into consideration to investigate the effect of wave steepness on vessel response. It is found that numerical data can efficiently simulate the motion attitude and the hydrodynamic characteristics of planing craft in regular head waves. The planing hull with and without interceptor fitted at the transom is simulated in numerical wave tank. The results show reduction in heave and pitch motions which gave favorable sea keeping behavior for the hull fitted with interceptor. The numerical solution is useful for the preliminary prediction of navigation safety during sailing.

Effect of Geofoam under Strip Footing Rested on Swelling Soil

ABSTRACT Swelling soils are considered a highly problematic soil due to the volume change actions. The cyclic heave and settlement of expansive soils could be the main reason for considerable damages to the structures, roads, and highways. Many available methodologies are followed to combat these problems of the swelling soils. This paper presents the results of experimental research which performed to show the efficiency of the (EPS) geofoam layers system as a new technique for controlling the upward movement of structures over swelling soils. The performance of the geofoam layer under the footing at different positions is studied. Geofoam layer has two configurations; flat and ribbed cross-section. Different densities and thicknesses of geofoam are considered in the study. Sand with different thicknesses is placed above swelling soil as a partial replacement under the footing. Their effectiveness of the performance is analyzed and discussed. Test results show a noticeable reduction in heave as a result of using the ribbed geofoam layer and partial replacement by sand above the swelling soil.

WITHDRAWN: Effect of polypropylene fibre on swelling behaviour of black cotton soil

Abstract This paper discusses the laboratory study of performance on expansive soil reinforced with polypropylene fiber and demonstrates that discrete and randomly distributed polypropylene fiber is useful in restraining the swelling tendency of expansive soils. Swelling characteristics of remoulded expansive soil specimens reinforced with varying fiber content (f = 0.2%, 0.3%, 0.4% and 0.5%) and aspect ratio (l/b = 15, 30 and 45) were studied. One dimensional swell-consolidation tests were conducted on consolidometer specimens. Reduction in heave and swelling pressure was the maximum at low aspect ratios at both the fibers contents of 0.2%, 0.3%, 0.4%, and 0.5%. Finally, the mechanism by which discrete and randomly distributed polypropylene fiber restrain swelling of expansive soil is explained with the help of soil-fiber interaction.

Incorporation of a nanotechnology-based product in cementitious binders for sustainable mitigation of sulphate-induced heaving of stabilised soils

Sulphate-induced heaving in soils is a common problem caused mostly by the use of calcium-based binders in the stabilisation of sulphate-bearing soils. Sulphate-induced heaving is attributed to precipitation and growth of ettringite minerals in a high alkaline environment. A sustainable means of reducing sulphate-induced heaving by the addition of an additive called “RoadCem” (RC) to soils stabilised by calcium-based cementitious products has not been studied. RoadCem (RC) is an additive that is manufactured based on nanotechnology and comprises synthetic zeolite, alkaline metals and some complex activators as some of its constituents. This research is therefore concerned with the performance of a sulphate-bearing soil stabilised by partially substituting cement (CEM I) with ground granulated blast furnace slag (GGBS) and incorporation of marginal quantities of RC. Laboratory studies including oedometer free swelling testing, unconfined compressive tests and microstructural analyses of the phases of hydration in the stabilised soils were carried out. Results indicated a reduction in heave by about 67% when 1% of RC was included in the cementitious mix with 50% of the CEM I replaced by a combination of GGBS and RC. The use of RC in the stabilised soil was even more promising than that in which only GGBS was utilised to replace half of the CEM I proportion in the stabilised soil with the result indicating almost a 30% difference in heave reduction. Results also indicated an increase in the unsoaked strength of stabilised soil with RC inclusion compared to the stabilised mix without RC. Scanning electron micrograph studies revealed almost a complete elimination of heave-causing ettringite minerals under a 28-day hydration phase of the stabilised soil when using RC.

Efficacy of Geopile–Anchors in Controlling Heave of Expansive Clay Beds

This paper presents the efficacy of a new technique in the form of geopile–anchors in arresting heave of expansive soils. Heave behaviour of a remoulded expansive clay reinforced with vertical cylindrical cells made of geogrid and filled with geomaterials (geopiles) with a central anchor inside is presented. A geogrid cylinder installed vertically in an expansive soil (forming a geopile), with an anchor inside is a geopile–anchor. In a geopile–anchor, foundation is anchored to an anchor plate at the bottom of the geopile with the help of an anchor rod. The upward movement of foundation due to swelling of clay is resisted by anchorage and by friction mobilized at the interface formed by the fill material (expansive soil)–geogrid–expansive soil. Filling the geopile with granular material can augment uplift resistance. Tests were conducted on expansive clay beds reinforced with geopile–anchors varying geopile diameter and type of geopile-fill material. In the case of group of geopile–anchors, spacing was varied and its effect on heave studied. The experimental results indicated that geopile–anchors reduced heave of expansive clay beds. With expansive clay fill, a maximum reduction in heave of 78.50% was obtained. When gravel fill was used, a percentage reduction of 92.50% was obtained. At a radial distance of 60-mm the reduction in heave obtained was 50%, 58%, 67% and 73% for single geopile–anchor, and 69%, 73%, 81% and 88% for two group geopile–anchors installed at a spacing of 2d when the fill materials were clay, fine sand, coarse sand and gravel respectively.

Experimental analysis of wave energy converters concentrically attached on a floating offshore platform

This paper presents an initial experimental study of wave energy converters concentrically arranged and attached on a floating offshore platform model. The 1:27 scale model, has been designed, built and tested, in two main situations, without and with twelve cone shape wave energy converters. To simulate the power take-off system in each wave energy converter, rotational friction dampers have been installed on the joints of the floaters arms to the platform deck. The experimental results show that the interaction between buoys and platform have a positive effect on the platform heave and pitch motions. However, the reduction in heave and pitch motions of the platform, after installing the wave energy converter array, depends on the damping of the equivalent power take-off system. Thus, the effect of dampers in the motion of buoys is presented to allow an initial understanding of the required damping range of the power take-off system and related control strategies.

Study of Swelling Potential of Copper Slag Cushion Laid Over Expansive Soil Bed

Expansive soils are subjected to changes in volume with seasonal water content variations. Techniques like sand cushion and cohesive non-swelling cushion have been tried to minimize the heave of expansive soils. But, they have inherent limitations. Utilization of waste materials in civil engineering has been in vogue all over the world in recent times and is primarily needed because of the problems associated with their disposal. Copper slag is one such waste material. Research carried out by the authors using lime-stabilized and cement-stabilized copper slag as cushioning material over expansive soil beds was found effective in minimizing heave of expansive clay beds. Heave studies were conducted using the stabilized cushions over expansive clay beds with thickness ratios of the cushion to the soil bed varying as 0.25, 0.50, 0.75 and 1.00. Percentage of lime and cement was also varied from 2 to 10%. The present paper discusses the experimental results of the swelling studies conducted on the cushion-soil system. It was noticed that, with an increase in the percentage of lime or cement, there is an increased reduction in heave.

Turret location impact on global performance of a thruster-assisted turret-moored FPSO

The change of the global performance of a turret-moored FPSO (Floating Production Storage Offloading) with DP (Dynamic Positioning) control is simulated, analyzed, and compared for two different internal turret location cases; bow and midship. Both collinear and non-collinear 100-yr GOM (Gulf of Mexico) storm environments and three cases (mooring-only, with DP position control, with DP position+heading control) are considered. The horizontal trajectory, 6DOF (degree of freedom) motions, fairlead mooring and riser tension, and fuel consumptions are compared. The PID (Proportional-Integral-Derivative) controller based on LQR (linear quadratic regulator) theory and the thrust-allocation algorithm which is based on the penalty optimization theory are implemented in the fully-coupled time-domain hull-mooring-riser-DP simulation program. Both in collinear and non-collinear 100-yr WWC (wind-wave-current) environments, the advantage of mid-ship turret is demonstrated by the significant reduction in heave at the turret location due to the minimal coupling with pitch mode, which is beneficial to mooring and riser design. However, in the non-collinear WWC environment, the mid-turret case exhibits unfavorable weathervaning characteristics, which can be reduced by employing DP position and heading controls as demonstrated in the present case studies. The present study also reveals the plausible cause of the failure of mid-turret Gryphon Alpha FPSO in milder environment than its survival condition.

Surface Heave Behavior of Geogrid Reinforced Sand Bed

This paper studies the surface heave phenomena of geogrid reinforced sand bed. Laboratory plate load test were conducted on square footing initially without geogrid and then with the inclusion of geogrid at various depth and spacing. It is observed that the heave is considerably reduced by the inclusion of geogrid. The heave behavior is depended on placement depth, spacing and number of layers of geogrid. The magnitude of reduction in heave is represented by a non-dimensional parameter called heave reduction factor (HRF)..

Effect of polypropylene tape fibre reinforcement on swelling behaviour of an expansive soil

ABSTRACT: The objective of this study was to examine the influence of discrete and randomly distributed fibres on heave of an expansive soil. One-dimensional swell tests were conducted on a remoulded expansive soil with and without fibres. In this study, fibre content was varied as 0.25 and 0.5% and fibre length as 30, 60 and 90 mm. A twin semi-circular-shaped fabricated mould with a front Perspex sheet was developed for testing. Digital imaging technique was used to observe heave of the soil in both unreinforced and fibre-reinforced conditions. Displacement profiles obtained from image analysis were used for interpreting swell or upward movement profiles of the specimens. Heave observed in the digital image analysis was compared with that obtained from dial gauge readings. Reduction in heave was directly proportional to fibre content and fibre length. Reduction in heave was the maximum at low aspect ratios at both fibre contents of 0.25 and 0.5%. Test results revealed that fibre length is a key factor that influences the reinforcing effect of fibre. Discrete and randomly distributed fibres were found efficacious in reducing heave.

Small-scale micropiles to control heave on expansive clays

The main purpose of this study was to examine the effectiveness of using micropiles as a technique to control upward movement of lightweight structures over expansive soils. For this purpose, smooth and roughened steel laboratory small-scale micropiles surrounded by dense sand were inserted in predrilled holes of larger diameter made in highly expansive clay. The expansive clay was compacted in a steel box (50 cm × 50 cm × 35 cm) to a final height of 20 cm. Steel plates (25 cm × 25 cm × 1 cm) were used to model footings. The heads of the model micropiles were fastened to the steel plate. Footings with zero, one, two or four micropiles were prepared then the compacted clay in the laboratory box was flooded with water then upward movement of the model footings due to compacted clay swelling was monitored with time. The results showed that the percentage reduction in heave due to micropile reinforcement was larger for roughened micropiles and increased with increasing number and diameter of micropiles. The maximum measured percentage reduction in heave was 87·2% obtained when four 18 mm diameter roughened micropiles were used. A comparison between measured and predicted percentage reduction in heave using the proposed method of Nusier and Alawneh (Geotechnical and Geological Engineering Journal, 2004, 22, No. 1, 89–104) was made, and the results of the comparison showed acceptable agreement.

Swelling behaviour of a geofiber-reinforced expansive soil

This paper reports the results of laboratory study performed on expansive soil reinforced with geofibers and demonstrates that discrete and randomly distributed geofibers are useful in restraining the swelling tendency of expansive soils. Swelling characteristics of remoulded expansive soil specimens reinforced with varying fiber content ( f = 0.25% and 0.50%) and aspect ratio ( l/ b = 15, 30 and 45) were studied. One-dimensional swell-consolidation tests were conducted on oedometer specimens. Reduction in heave and swelling pressure was the maximum at low aspect ratios at both the fiber contents of 0.25% and 0.50%. Finally, the mechanism by which discrete and randomly distributed fibers restrain swelling of expansive soil is explained with the help of soil–fiber interaction.