The Experts below are selected from a list of 1452 Experts worldwide ranked by ideXlab platform
B. Mutlu Sumer - One of the best experts on this subject based on the ideXlab platform.
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Sinking of Armour Layer around a vertical cylinder exposed to waves and current
Coastal Engineering, 2015Co-Authors: Anders Nielsen, Thor Ugelvig Petersen, Thomas Probst, B. Mutlu SumerAbstract:Abstract The mechanisms of the sinking of a scour protection adjacent to a monopile are described in this paper, together with the determination of the equilibrium sinking depth in various wave and combined wave and current conditions based on physical model tests. Sinking of the rocks may ultimately lead to failure of the scour protection. It may cause exposure and free-span of cables, and possibly change the natural frequency of the wind turbine in an unfavourable manner. For these reasons it is important to consider the possible effects of sinking in the scour protection design, and to understand the mechanisms that could lead to unacceptable sinking of the scour protection. The study showed that the sinking is controlled by two mechanisms: removal of sediment adjacent to the pile (destabilizing) and infilling of sediment into the scour protection from the surrounding seabed (stabilizing). The latter mechanism is found to be the strongest, but it might take some time to fill the pores of the scour protection with sediment and during the time delay considerable sinking might take place. This means that the larger the scour protection, the larger the sinking will be (for a given KC-number smaller than approximately 15). The magnitude of the sinking of the scour protection adjacent to a monopile exposed to waves, and combined waves and current, was found to be similar to the current case.
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Pressure-induced forces and shear stresses on rubble mound breakwater Armour Layers in regular waves
Coastal Engineering, 2014Co-Authors: Bjarne Jensen, Erik Damgaard Christensen, B. Mutlu SumerAbstract:Abstract This paper presents the results from an experimental investigation of the pressure-induced forces in the core material below the main Armour Layer and shear stresses on the Armour Layer for a porous breakwater structure. Two parallel experiments were performed which both involved pore pressure measurements in the core material: (1) core material with an idealized Armour Layer made out of spherical objects that also allowed for detailed velocity measurements between and above the Armour, and (2) core material with real rock Armour stones. The same core material was applied through the entire structure i.e. no additional filter Layers were applied. For both experiments, high-speed video recordings were synchronised with the pressure measurements for a detailed investigation of the coupling between the run-up and run-down flow processes and the measured pressure variations. Outward directed pressure gradients were found which exerted a lift force up to ≈ 60% of the submerged weight of the core material. These maximum outward directed pressure gradients were linked to the maximum run-down event and were in general situated at, or slightly below, the maximum run-down level. Detailed velocity and turbulence measurements showed that the large outward directed pressure gradients in general coincide, both in time and space, with the maximum bed-shear stresses on the Armour Layer based on the Reynolds-stresses. The bed-shear stresses were found to result in a Shields parameter in the same order of magnitude as the critical value for movement of the Armour stones.
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WAVE INTERACTION WITH LARGE ROUGHNESS ELEMENTS ON AN IMPERMEABLE SLOPING BED
Coastal Engineering Proceedings, 2012Co-Authors: Bjarne Jensen, Erik Damgaard Christensen, B. Mutlu SumerAbstract:The present paper presents the results of an experimental and numerical investigation of the flow between large roughness elements on a steep sloping impermeable bed during wave action. The setup is designed to resemble a breakwater structure. The work is part of a study where the focus is on the details in the porous core flow and the Armour Layer flow i.e. the interaction between the two flow domains and the effect on the Armour Layer stability. In order to isolate the processes involved with the flow in the porous core the investigations are first carried out with a completely impermeable bed and successively repeated with a porous bed. In this paper the focus is on the impermeable bed. Results are obtained experimentally for flow and turbulence between the roughness elements on the sloping bed. Numerical simulations have reproduced the experimental results with good agreements and can hereby add more details to the understanding of the fluid-structure interaction.
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Sinking of Armour Layer around a cylinder exposed to a current
Proceedings of the Institution of Civil Engineers - Maritime Engineering, 2011Co-Authors: Anders Wedel Nielsen, B. Mutlu Sumer, Jørgen Fredsøe, Erik Damgaard ChristensenAbstract:The flow processes in a scour protection around a monopile in steady current are described in relation to transport of sediment in the scour protection based on physical model tests. The scour protection consisted of uniformly distributed coarse stones without filter Layer. Transport of sediment in the scour protection may cause sinking of the scour protection. This may reduce the stability of the monopile and change for instance the natural frequency of the dynamic response of an offshore wind turbine in an unfavourable manner. The most important flow process with regard to transport of sediment and sinking of the scour protection is found to be the horseshoe vortex. It is found that a larger pile diameter relative to the size of the protection stones will cause a larger sinking and that two Layers of stones will decrease the sinking relative to one Layer of stones with the same size.
Annette M. Harte - One of the best experts on this subject based on the ideXlab platform.
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a global local fretting analysis methodology and design study for the pressure Armour Layer of dynamic flexible marine risers
Tribology International, 2020Co-Authors: Sinead M Ohalloran, Adrian Connaire, Annette M. Harte, Sean B. LeenAbstract:Abstract In this paper, a global-local fretting design methodology for the pressure Armour Layer of flexible marine risers is outlined. This includes global dynamic riser analysis, geometrical and analytical sub-models and local nub-groove contact finite element analysis. Furthermore, a fretting test rig is developed and utilised to quantify coefficient of friction and wear coefficient under representative nub-groove loading conditions. The combination of the global-local computational methodology and experimental characterisation of pressure Armour wire material allows for the development of running condition fretting maps. This identifies design criteria for critical riser global curvatures that are associated with minimum number of cycles to failure. The design methodology presented in this paper is applied to a realistic riser design study, using extreme sea-state loading conditions. In this case study, the predicted pressure Armour fretting fatigue lives are found to be in the same range as the plain fatigue lives of the tensile Armour Layer.
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a combined wear fatigue design methodology for fretting in the pressure Armour Layer of flexible marine risers
Tribology International, 2017Co-Authors: Sinead M Ohalloran, Sean B. Leen, Philip H. Shipway, Adrian Connaire, Annette M. HarteAbstract:This paper presents a combined experimental and computational methodology for fretting wear-fatigue prediction of pressure Armour wire in flexible marine risers. Fretting wear, friction and fatigue parameters of pressure Armour material have been characterised experimentally. A combined fretting wear-fatigue finite element model has been developed using an adaptive meshing technique and the effect of bending-induced tangential slip has been characterised. It has been shown that a surface damage parameter combined with a multiaxial fatigue parameter can accurately predict the beneficial effect of fretting wear on fatigue predictions. This provides a computationally efficient design tool for fretting in the pressure Armour Layer of flexible marine risers.
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The Prediction of Fretting Fatigue in the Pressure Armours of Dynamic Flexible Pipes
Day 4 Thu May 05 2016, 2016Co-Authors: Sinéad O'halloran, Annette M. Harte, Adrian Connaire, Sean B. LeenAbstract:Abstract This paper presents a combined experimental and computational framework for the design of flexible marine risers against fretting and fatigue. The framework is based on: (i) a suite of laboratory experimental methods for fretting and fatigue tests, and (ii) a global-local methodology for flexible riser analysis including dynamics and frictional contact mechanics. The effect of coefficient of friction on the predicted substrate stress distributions and fatigue life of the nub-groove region of flexibles has been investigated. It is shown that coefficient of friction has a significant effect on predicted trailing-edge tensile stresses in the pressure Armour Layer and, hence on fretting crack initiation in risers. The framework should assist in the design of pressure Armour Layers in flexible marine risers against fretting wear and fatigue.
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Modelling of fretting in the pressure Armour Layer of flexible marine risers
Tribology International, 2016Co-Authors: Sinéad O'halloran, Annette M. Harte, Adrian Connaire, Sean B. LeenAbstract:Abstract This paper presents a computational methodology for frictional contact mechanics of the pressure Armour Layer in flexible risers. This will allow, for the first time, quantification of key fretting variables, such as contact pressure, relative slip and sub-surface stresses in this complex geometry, under representative loading conditions. Fatigue lives are calculated using the 3-dimensional critical plane Smith–Watson–Topper multiaxial fatigue parameter. It is shown that COF has a significant effect on predicted trailing-edge tensile stresses in the pressure Armour Layer and, hence on fretting crack initiation in risers. It is also shown that operating pressure and bending-induced axial displacement significantly affect predicted crack initiation. These results will facilitate representative fretting wear and fretting fatigue testing of pressure Armour Layer material.
Bambang Agus Kironoto - One of the best experts on this subject based on the ideXlab platform.
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Efek Tegangan Geser Dasar Yang Terjadi Pada Lapisan Pelindung Terhadap Karakteristik Kemiringan Dasar Saluran
Jurnal Teknik Sipil, 2016Co-Authors: Cahyono Ikhsan, Djoko Legono, Adam Pamudji Raharjo, Bambang Agus KironotoAbstract:Abstrak . Armouring adalah suatu proses terbentuknya lapisan pelindung (Armour Layer) di dasar sungai yang diawali dari pergerakan sedimen dasar (bedload) sampai terjadinya erosi permukaan dasar (eroded surface) sehingga tercapai lapisan dasar yang stabil atau kondisi equilibrium yaitu tidak ada lagi sedimen dasar (bedload) yang terangkut. Armour Layer merupakan jenis gravel dengan susunan gradasi butir yang hampir seragam terletak di permukaan dasar dan menghambat gerak bedload yang melintas di atasnya. Penelitian dilakukan di laboratorium Hidraulika PS-IT UGM, menggunakan perangkat utama sediment recirculacy flume pada dinding terbuat dari plexiglass dengan dimensi panjang 10,00 m, lebar 0,60 m, tinggi 0,45 m. Kemiringan dasar saluran yaitu 1%, 1.4%, 1,8%, 2,2%, dan 2,6%. Debit aliran konstan pada kapasitas 25 l/s, 30 l/s, 40 l/s dan 45 l/s. Material berupa pasir dan gravel dicampur merata, dengan 5 variasi grain size yang berbeda. Pada tiap running terdapat 2 fase kejadian yaitu fase eroded surface dan fase equilibrium. Instrumen yang digunakan pada saat running adalah digital currentmeter, point gauge, sediment traps. Pada saat proses eroded surface, struktur Armour Layer nampak semakin kokoh di permukaan karena tegangan geser yang dimiliki butir Armour lebih besar dari tegangan geser dasar, jadi butir Armour merupakan struktur butir sedimen yang memiliki critical shear stress lebih besar dari bed shear stress. Abstract . Armouring is one of the development processes of Armour Layer on the base of a river, started from the movement of the transported base sediment of eroded surface reaching to stabile base Layer condition or equilibrium, where there is no more transported base sediment. Armour Layer is a type of gravel with almost uniform composition of granule gradation in surface base position which hampers the sediment moving above it. This research was carried out at the Hydraulic Laboratory of PS-IT UGM, using the main infrastructure of sediment recirculacy flume on the wall made from plexiglass in 10.00 m length, 0.60 m width, and 0.45 m height. The base slopes were 1%, 1.4%, 1.8%, 2.2%, and 2.6%. The flow debit was constant at 25 l/s, 30 l/s, 40 l/s and 45 l/s capacities. The material consisted of sand and gravel which was evenly mixed within 5 different variations of grainsize. At each running, there were two phases of eroded surface and equilibrium. The instruments used during the running were digital current meter, point gauge, sediment traps. Within the eroded surface process, the Armour Layer structure looked standing out in the base surface due to the granule critical shear stress of Armour that was larger than the base shear stress, thus the Armour Layer was the structure of sediment granule with larger critical shear stress than bed shear stress.
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pengaruh tegangan geser dasar terhadap karakteristik Armour Layer
2014Co-Authors: Cahyono Ikhsan, Djoko Legono, Adam Pamudji Raharjo, Bambang Agus KironotoAbstract:The study presents the analysis of bedload transport, changes in the structure Armour Layer and topography of the sediments during the degradation process. In the analysis of variations in channel slope and bedload composition of actively moving. The study focused on observations of shear stress on the condition of passive and active conditions on the formation of armor Layer at a constant discharge. Hydraulics Lab studies using the main sediment-recirculating flume of plexiglass dimensionless width 0.60 m, length of 10.00 m, a depth of 0.45 m and a channel slope of 1% to 3%. Constant discharge capacity of 40 l / s. Granular material is mixed with a composition of 70% gravel, 30% sand. Running on low flow two phases which phase equilibrium and armor. The instruments used between digital currentmeter, point gauge meter, sediment feeder, trap sediment, and surfer software version 8.0. The results illustrate the change in the slope of the channel Armouring impact on increasing shear stress. Conditions are shown armor Layer structure changes and changes in surface topography. While the grain size profile armor Layer more upright, this condition indicates that the formation of armor Layer effect on the stability of the channel. Penelitian menyajikan tentang analisis angkutan bedload, perubahan struktur Armour Layer dan topografi sedimen dasar selama proses degradasi berlangsung. Pada analisis tersebut membahas variasi pada kemiringan dasar saluran dan komposisi bedload yang bergerak aktif. Penelitian ini lebih memfokuskan pada pengamatan terhadap besarnya tegangan geser dasar yang terjadi pada kondisi pasif kepada suatu kondisi aktif dalam pembentukan Armour Layer akibat kecepatan aliran pada debit konstan. Penelitian ini dilakukan di laboratorium Hidraulika menggunakan perangkat utama sediment-recirculating flume dari plexiglass berdimensi lebar 0,60 m, panjang 10,00 m, tinggi 0,45 m serta dengan kemiringan dasar yang dimulai dari 1% sampai 3%. Debit konstan pada kapasitas 40 l/s. Material granular yang dipakai dicampur dengan komposisi 70% gravel, 30% pasir. Running dilakukan pada debit aliran low flow pada 2 fase yaitu fase equilibrium dan fase Armour. Instrumen yang digunakan antara lain digital currentmeter, point gauge meter, sediment feeder, sediment trap, dan dibantu software surfer 8.0. Hasil penelitian tersebut dapat menggambarkan Armouring didasarkan pada perubahan kemiringan dasar yang berdampak pada peningkatan tegangan geser. Kondisi tersebut diperlihatkan pada perubahan struktur lapisan dasar dan perubahan topografi permukaan. Sedangkan profil grain size pada Armour Layer semakin tegak, kondisi tersebut menunjukkan terbentuknya Armour Layer yang berpengaruh pada stabilitas dasar saluran.
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Effect of Bed Shear Stress on Static Armour Layer.
2013Co-Authors: Cahyono Ikhsan, Adam Pamudji Rahardjo, Djoko Legono, Bambang Agus KironotoAbstract:The movement of water over a bed of sediment results in the entrainment of pal1icles. The finer sediment will be entrained earlier than the larger particles or Armour Layer. Basic questions regarding Armour Layers need to be resolved is mechanism am-lour Layers and the relevant properties of Armour Layer can they be predicted. The study focused on observations of shear stress on the condition of passive and active conditions on the formation of armor Layer at a constant discharge. Hydraulic laboratorium studies using the main sediment-recirculating flume of plexiglass dimensionless width 0.60 m, length of 10.00 m, a depth of 0.45 m and a channel slope of 1 % to 2,6%. The flume experiments created Armoured beds testing 5 sediment mixtures with a composition of 70% gravel. 30% sand, and 4 flow rates constant discharge capacity of 25 l/s, 30 l/s, 40 lis and 45 lis. Running on low flow 3 phases which phase graded, phase equilibrium and phase Armour The instruments used between digital currentmeter, point gauge meter, sediment feeder, trap sediment, and surfer software version 8.0. The results are shown Armour Layer structure changes and changes in surface topography. While the grain size profile Armour Layer more upright, this condition indicates that the formation of annour Layer effect on the stability of the channel.
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Effect of Bed Shear Stress on Armour Layer Characteristics That Sloof Channel
2012Co-Authors: Cahyono Ikhsan, Adam Pamudji Rahardjo, Djoko Legono, Bambang Agus KironotoAbstract:The study presents the analysis of bedload transport, changes in the structure Armour Layer and topography of the sediments during the degradation process, In the anaiysis of variations in channel slope and bedload composition of actively moving, The study focused on observations of shear stress on the condition of passive and active conditions on the formation of armor Layer at a constant discharge, Hydraulics Lab studies usir'6 the main sediment-recirculating flume of plexiglass dimensionless width 0,60 m, length of 10,00 m, a depth of OA5 m and a channel slope of 1 % to 3%, Constant discharge capacity of 40 l/s, Granular material is mixed with a composition of 70% gravel, 30% sand, Running on low flow two phases which phase equilibrium and armor. The instruments used between digital current meter, point gauge meter, sediment feeder, trap sediment, and surfer software version 8,0, The ;esults illustrale the change in the ,iope of the channel Armouring impact on increasing shear stress, Conditions are shown armor iayer structure changes and changes in surface topography_ While the grain size profile armor Layer more upright, this condition indicates that the formation of armor Layer effect on the stabil;!y of the channel
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CHARACTERIZED BY A COARSER SURFACE Layer OF SEDIMENT ArmourKARAKTERISTIK KEKASARAN LAPISAN DASAR SEDIMEN Armour
2011Co-Authors: Cahyono Ikhsan, Djoko Legono, Adam Pamudji Raharjo, Bambang Agus KironotoAbstract:The static armored bed condition exists as a result of an extended period of flows over a mixed gravel bed. The flows generate shear stresses less than that needed to entrain the largest particles but large enough to transport the fines and over time the fines sediment is winnowed from the bed surface. A coarse surface Layer forms on the bed surface, effectively sheltering the finer substrate grains from entrainment. The presence of an Armour Layer on the bed surface is a common phenomena in rivers. The flume experiment was 0.6 m wide by 10 m long and inclined at a slope of 1% and 1,5%. The channel bed and feed were composed of a moderately to poorly sorted, lognormally distributed mixture of sand and gravel. The feed rate was 100 g/min for the initial experimental runs. Digits to the right of the decimal refer to irregular intervals (0 min-440 min) during the same feed rate between times when the experiment was temporarily halted and measurements of the bed were made.). Water discharge was held constant at 40 It/s. The paper presents a relatively has been applied to replicate bedload transport measured during static Armouring flume experiments. The model proved to be able to simulate well the vanishing sediment transport due to both slope reduction and surface coarsening. Key words: Armour Layer, degradation, sediment transport, coarser
Sean B. Leen - One of the best experts on this subject based on the ideXlab platform.
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a global local fretting analysis methodology and design study for the pressure Armour Layer of dynamic flexible marine risers
Tribology International, 2020Co-Authors: Sinead M Ohalloran, Adrian Connaire, Annette M. Harte, Sean B. LeenAbstract:Abstract In this paper, a global-local fretting design methodology for the pressure Armour Layer of flexible marine risers is outlined. This includes global dynamic riser analysis, geometrical and analytical sub-models and local nub-groove contact finite element analysis. Furthermore, a fretting test rig is developed and utilised to quantify coefficient of friction and wear coefficient under representative nub-groove loading conditions. The combination of the global-local computational methodology and experimental characterisation of pressure Armour wire material allows for the development of running condition fretting maps. This identifies design criteria for critical riser global curvatures that are associated with minimum number of cycles to failure. The design methodology presented in this paper is applied to a realistic riser design study, using extreme sea-state loading conditions. In this case study, the predicted pressure Armour fretting fatigue lives are found to be in the same range as the plain fatigue lives of the tensile Armour Layer.
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a combined wear fatigue design methodology for fretting in the pressure Armour Layer of flexible marine risers
Tribology International, 2017Co-Authors: Sinead M Ohalloran, Sean B. Leen, Philip H. Shipway, Adrian Connaire, Annette M. HarteAbstract:This paper presents a combined experimental and computational methodology for fretting wear-fatigue prediction of pressure Armour wire in flexible marine risers. Fretting wear, friction and fatigue parameters of pressure Armour material have been characterised experimentally. A combined fretting wear-fatigue finite element model has been developed using an adaptive meshing technique and the effect of bending-induced tangential slip has been characterised. It has been shown that a surface damage parameter combined with a multiaxial fatigue parameter can accurately predict the beneficial effect of fretting wear on fatigue predictions. This provides a computationally efficient design tool for fretting in the pressure Armour Layer of flexible marine risers.
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The Prediction of Fretting Fatigue in the Pressure Armours of Dynamic Flexible Pipes
Day 4 Thu May 05 2016, 2016Co-Authors: Sinéad O'halloran, Annette M. Harte, Adrian Connaire, Sean B. LeenAbstract:Abstract This paper presents a combined experimental and computational framework for the design of flexible marine risers against fretting and fatigue. The framework is based on: (i) a suite of laboratory experimental methods for fretting and fatigue tests, and (ii) a global-local methodology for flexible riser analysis including dynamics and frictional contact mechanics. The effect of coefficient of friction on the predicted substrate stress distributions and fatigue life of the nub-groove region of flexibles has been investigated. It is shown that coefficient of friction has a significant effect on predicted trailing-edge tensile stresses in the pressure Armour Layer and, hence on fretting crack initiation in risers. The framework should assist in the design of pressure Armour Layers in flexible marine risers against fretting wear and fatigue.
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Modelling of fretting in the pressure Armour Layer of flexible marine risers
Tribology International, 2016Co-Authors: Sinéad O'halloran, Annette M. Harte, Adrian Connaire, Sean B. LeenAbstract:Abstract This paper presents a computational methodology for frictional contact mechanics of the pressure Armour Layer in flexible risers. This will allow, for the first time, quantification of key fretting variables, such as contact pressure, relative slip and sub-surface stresses in this complex geometry, under representative loading conditions. Fatigue lives are calculated using the 3-dimensional critical plane Smith–Watson–Topper multiaxial fatigue parameter. It is shown that COF has a significant effect on predicted trailing-edge tensile stresses in the pressure Armour Layer and, hence on fretting crack initiation in risers. It is also shown that operating pressure and bending-induced axial displacement significantly affect predicted crack initiation. These results will facilitate representative fretting wear and fretting fatigue testing of pressure Armour Layer material.
Cahyono Ikhsan - One of the best experts on this subject based on the ideXlab platform.
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DEVELOPMENT OF STATIC Armour
Jurnal Riset Rekayasa Sipil, 2018Co-Authors: Cahyono IkhsanAbstract:Armour Layer is the type of gravel bed composed on the bed surface with pores between the composing grains as the place of sand to stay and lock the pores. This research was carried out in the Hydraulic Laboratory by using the main infrastructure of sediment flume from Plexiglas in 0.60 m width, 10.00 m length, and 0.45 m height dimension. The base gradients used was parallel to the water surface gradients, which were 1%, 1.4%, 1.8%, 2.2%, and 2.6%. The constant flow debit was at 25 l/s, 30 l/s, 40 l/s and 45 l/s capacity. The materials consisted of sand and gravel and were evenly mixed in 5 different grain size variations. At each running, there were 2 phases of occurrence: eroded surface and equilibrium. The instruments used during the running were digital current meter, point gauge, and sediment traps.The results of this research indicated Armour Layer formula stated in un-dimensional number with an average bedload limit of 0.8 mm to 2.9 mm, uniformity coefficient of 2.5 to 5, and critical shear stress of 0.61 N/m 2 to 2.7 N/m 2. and with minimum base shear stress of 6 N/m 2 .
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Efek Tegangan Geser Dasar Yang Terjadi Pada Lapisan Pelindung Terhadap Karakteristik Kemiringan Dasar Saluran
Jurnal Teknik Sipil, 2016Co-Authors: Cahyono Ikhsan, Djoko Legono, Adam Pamudji Raharjo, Bambang Agus KironotoAbstract:Abstrak . Armouring adalah suatu proses terbentuknya lapisan pelindung (Armour Layer) di dasar sungai yang diawali dari pergerakan sedimen dasar (bedload) sampai terjadinya erosi permukaan dasar (eroded surface) sehingga tercapai lapisan dasar yang stabil atau kondisi equilibrium yaitu tidak ada lagi sedimen dasar (bedload) yang terangkut. Armour Layer merupakan jenis gravel dengan susunan gradasi butir yang hampir seragam terletak di permukaan dasar dan menghambat gerak bedload yang melintas di atasnya. Penelitian dilakukan di laboratorium Hidraulika PS-IT UGM, menggunakan perangkat utama sediment recirculacy flume pada dinding terbuat dari plexiglass dengan dimensi panjang 10,00 m, lebar 0,60 m, tinggi 0,45 m. Kemiringan dasar saluran yaitu 1%, 1.4%, 1,8%, 2,2%, dan 2,6%. Debit aliran konstan pada kapasitas 25 l/s, 30 l/s, 40 l/s dan 45 l/s. Material berupa pasir dan gravel dicampur merata, dengan 5 variasi grain size yang berbeda. Pada tiap running terdapat 2 fase kejadian yaitu fase eroded surface dan fase equilibrium. Instrumen yang digunakan pada saat running adalah digital currentmeter, point gauge, sediment traps. Pada saat proses eroded surface, struktur Armour Layer nampak semakin kokoh di permukaan karena tegangan geser yang dimiliki butir Armour lebih besar dari tegangan geser dasar, jadi butir Armour merupakan struktur butir sedimen yang memiliki critical shear stress lebih besar dari bed shear stress. Abstract . Armouring is one of the development processes of Armour Layer on the base of a river, started from the movement of the transported base sediment of eroded surface reaching to stabile base Layer condition or equilibrium, where there is no more transported base sediment. Armour Layer is a type of gravel with almost uniform composition of granule gradation in surface base position which hampers the sediment moving above it. This research was carried out at the Hydraulic Laboratory of PS-IT UGM, using the main infrastructure of sediment recirculacy flume on the wall made from plexiglass in 10.00 m length, 0.60 m width, and 0.45 m height. The base slopes were 1%, 1.4%, 1.8%, 2.2%, and 2.6%. The flow debit was constant at 25 l/s, 30 l/s, 40 l/s and 45 l/s capacities. The material consisted of sand and gravel which was evenly mixed within 5 different variations of grainsize. At each running, there were two phases of eroded surface and equilibrium. The instruments used during the running were digital current meter, point gauge, sediment traps. Within the eroded surface process, the Armour Layer structure looked standing out in the base surface due to the granule critical shear stress of Armour that was larger than the base shear stress, thus the Armour Layer was the structure of sediment granule with larger critical shear stress than bed shear stress.
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pengaruh tegangan geser dasar terhadap karakteristik Armour Layer
2014Co-Authors: Cahyono Ikhsan, Djoko Legono, Adam Pamudji Raharjo, Bambang Agus KironotoAbstract:The study presents the analysis of bedload transport, changes in the structure Armour Layer and topography of the sediments during the degradation process. In the analysis of variations in channel slope and bedload composition of actively moving. The study focused on observations of shear stress on the condition of passive and active conditions on the formation of armor Layer at a constant discharge. Hydraulics Lab studies using the main sediment-recirculating flume of plexiglass dimensionless width 0.60 m, length of 10.00 m, a depth of 0.45 m and a channel slope of 1% to 3%. Constant discharge capacity of 40 l / s. Granular material is mixed with a composition of 70% gravel, 30% sand. Running on low flow two phases which phase equilibrium and armor. The instruments used between digital currentmeter, point gauge meter, sediment feeder, trap sediment, and surfer software version 8.0. The results illustrate the change in the slope of the channel Armouring impact on increasing shear stress. Conditions are shown armor Layer structure changes and changes in surface topography. While the grain size profile armor Layer more upright, this condition indicates that the formation of armor Layer effect on the stability of the channel. Penelitian menyajikan tentang analisis angkutan bedload, perubahan struktur Armour Layer dan topografi sedimen dasar selama proses degradasi berlangsung. Pada analisis tersebut membahas variasi pada kemiringan dasar saluran dan komposisi bedload yang bergerak aktif. Penelitian ini lebih memfokuskan pada pengamatan terhadap besarnya tegangan geser dasar yang terjadi pada kondisi pasif kepada suatu kondisi aktif dalam pembentukan Armour Layer akibat kecepatan aliran pada debit konstan. Penelitian ini dilakukan di laboratorium Hidraulika menggunakan perangkat utama sediment-recirculating flume dari plexiglass berdimensi lebar 0,60 m, panjang 10,00 m, tinggi 0,45 m serta dengan kemiringan dasar yang dimulai dari 1% sampai 3%. Debit konstan pada kapasitas 40 l/s. Material granular yang dipakai dicampur dengan komposisi 70% gravel, 30% pasir. Running dilakukan pada debit aliran low flow pada 2 fase yaitu fase equilibrium dan fase Armour. Instrumen yang digunakan antara lain digital currentmeter, point gauge meter, sediment feeder, sediment trap, dan dibantu software surfer 8.0. Hasil penelitian tersebut dapat menggambarkan Armouring didasarkan pada perubahan kemiringan dasar yang berdampak pada peningkatan tegangan geser. Kondisi tersebut diperlihatkan pada perubahan struktur lapisan dasar dan perubahan topografi permukaan. Sedangkan profil grain size pada Armour Layer semakin tegak, kondisi tersebut menunjukkan terbentuknya Armour Layer yang berpengaruh pada stabilitas dasar saluran.
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Effect of Bed Shear Stress on Static Armour Layer.
2013Co-Authors: Cahyono Ikhsan, Adam Pamudji Rahardjo, Djoko Legono, Bambang Agus KironotoAbstract:The movement of water over a bed of sediment results in the entrainment of pal1icles. The finer sediment will be entrained earlier than the larger particles or Armour Layer. Basic questions regarding Armour Layers need to be resolved is mechanism am-lour Layers and the relevant properties of Armour Layer can they be predicted. The study focused on observations of shear stress on the condition of passive and active conditions on the formation of armor Layer at a constant discharge. Hydraulic laboratorium studies using the main sediment-recirculating flume of plexiglass dimensionless width 0.60 m, length of 10.00 m, a depth of 0.45 m and a channel slope of 1 % to 2,6%. The flume experiments created Armoured beds testing 5 sediment mixtures with a composition of 70% gravel. 30% sand, and 4 flow rates constant discharge capacity of 25 l/s, 30 l/s, 40 lis and 45 lis. Running on low flow 3 phases which phase graded, phase equilibrium and phase Armour The instruments used between digital currentmeter, point gauge meter, sediment feeder, trap sediment, and surfer software version 8.0. The results are shown Armour Layer structure changes and changes in surface topography. While the grain size profile Armour Layer more upright, this condition indicates that the formation of annour Layer effect on the stability of the channel.
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Effect of Bed Shear Stress on Armour Layer Characteristics That Sloof Channel
2012Co-Authors: Cahyono Ikhsan, Adam Pamudji Rahardjo, Djoko Legono, Bambang Agus KironotoAbstract:The study presents the analysis of bedload transport, changes in the structure Armour Layer and topography of the sediments during the degradation process, In the anaiysis of variations in channel slope and bedload composition of actively moving, The study focused on observations of shear stress on the condition of passive and active conditions on the formation of armor Layer at a constant discharge, Hydraulics Lab studies usir'6 the main sediment-recirculating flume of plexiglass dimensionless width 0,60 m, length of 10,00 m, a depth of OA5 m and a channel slope of 1 % to 3%, Constant discharge capacity of 40 l/s, Granular material is mixed with a composition of 70% gravel, 30% sand, Running on low flow two phases which phase equilibrium and armor. The instruments used between digital current meter, point gauge meter, sediment feeder, trap sediment, and surfer software version 8,0, The ;esults illustrale the change in the ,iope of the channel Armouring impact on increasing shear stress, Conditions are shown armor iayer structure changes and changes in surface topography_ While the grain size profile armor Layer more upright, this condition indicates that the formation of armor Layer effect on the stabil;!y of the channel