Recent Submissions

  • Implementation relations and testing for cyclic systems: adding probabilities

    Nunez, M.; Hierons, R.M.; Lefticaru, Raluca (Elsevier, 2023-07)
    This paper concerns the systematic testing of robotic control software based on state-based models. We focus on cyclic systems that typically receive inputs (values from sensors), perform computations, produce outputs (sent to actuators) and possibly change state. We provide a testing theory for such cyclic systems where time can be represented and probabilities are used to quantify non-deterministic choices, making it possible to model probabilistic algorithms. In addition, refusals, the inability of a system to perform a set of actions, are taken into account. We consider several possible testing scenarios. For example, a tester might only be able to passively observe a sequence of events and so cannot check probabilities, while in another scenario a tester might be able to repeatedly apply a test case and so estimate the probabilities of sequences of events. These different testing scenarios lead to a range of implementation relations (notions of correctness). As a consequence, this paper provides formal definitions of implementation relations that can form the basis of sound automated testing in a range of testing scenarios. We also validate the implementation relations by showing how observers can be used to provide an alternative but equivalent characterisation.
  • Comparative analysis of granule properties in continuous granulators

    Sekyi, Nana; Kelly, Adrian L.; Rahmanian, Nejat (2023)
    Several contributions in answering granulation challenges including the use of computer simulation and well thought out experimental analyses are being researched. Using a twin screw granulator (TSG) by design of experiments (DoE), comparisons on 1) equipment similarities i.e., continuous and 2) shear forces, are made to previous literature on continuous equipment and a Cyclomix. This study proposes that equipment specific DoE, better explains the contribution of parameters than investigating an identified parameter from the experimental findings from a specific equipment. Granule strength and structure are presented together with the contribution of process parameters, speed, temperature, and binder content. Seeded structures are present in all but the Extrudomix. Longer residence times within the Cyclomix facilitates seeded structures. Granule crushing strengths are higher in TSG than all other continuous equipment. Optimum condition for the formation of stronger granules with least variation is around 65.4 °C.
  • Demountable reinforced concrete structures - a way forward to minimize energy and waste in construction industry

    Ashour, Ashraf F.; Figueira, Diogo; Almahmood, H.; Yildirim, Gurkan; Aldemir, A.; Sahmaran, M. (SpringerNature, 2023)
    In the current practice, at the end of life of a reinforced concrete struc-ture, it is destructively demolished, and the demolition waste is limited to downcycling and low-tech applications, while the remaining is being landfilled. A recent report showed that construction and demolition waste (CDW) is the big-gest waste stream in the EU by weight, accounting for over 800 million tons in 2018, i.e. around 32% of the total waste generated. This approach is clearly wasteful of energy, jeopardizing the health of individuals and environments and at high cost. However, design for deconstruction (DfD) of reinforced concrete structures would facilitate the future reuse of structural elements at the end of their life, potentially achieving a significant reduction in embodied energy of structures and CO2 emission as well as giving the owners the benefit of retaining the value of their assets. In this paper, recent research developments and practical applications of DfD of reinforced concrete structures are reviewed and key technical issues are dis-cussed. The focus is on connections that should be designed in such a way to al-low demounting of precast reinforced concrete structural elements, including beam/column, wall/wall, column/column and segmental slab connections. The main achievements and progress to date are outlined for each type of dry connec-tions, along with the aspects that still need to be developed. The paper concludes with an outline of challenges in the application of DfD in concrete structures.
  • An Investigation into Durability Aspects of Geopolymer Concretes Based Fully on Construction and Demolition Waste

    Ozcelikci, E.; Yildirim, Gurkan; Alhawat, Musab M.; Ashour, Ashraf F.; Sahmaran, M. (SpringerNature, 2023)
    The focus of the construction industry has shifted towards the development of al-ternative, eco-friendly and green construction materials due to the energy-inefficient and carbon-intensive nature of Portland cement (PC) production and aggregate quarrying. Meanwhile, increased number of repetitive re-pair/renovation/maintenance activities and demolition operations for the end-of-life buildings generate significant amounts of construction and demolition waste (CDW). For the purposes of sustainability and upcycling wastes into high-value-added materials with improved greenness, components from CDW streams can be used in producing geopolymer concretes without using PC and natural aggre-gates, given the rich aluminosiliceous nature of CDW components. The focus of current work is therefore on the analysis of durability of aspects (i.e., drying shrinkage and resistance against sulfate attack, cyclic freezing-thawing, and chlo-ride penetration) of geopolymer concretes made entirely of CDW. Different types of bricks, tile, concrete, and glass were used in mixed form as precursors for ge-opolymerization while different-size grains of waste concrete were used as recy-cled aggregates. As alkali activators, sodium hydroxide, calcium hydroxide and sodium silicate were used. In a companion mixture, CDW-based precursors were replaced with slag and class-F fly ash. Results showed that sulfate and cyclic freeze-thaw exposure did not cause any noticeable weight and compressive strength loss in CDW-based geopolymer concretes, while chloride penetration was found comparable to PC-based concrete. While drying shrinkage was found high in entirely CDW-based geopolymer concrete and resulted in surface mi-crocracks, it was possible to lower the drying shrinkage substantially via substi-tution of CDW-based precursors with fly ash and slag.
  • Digital capabilities in the construction industry

    Atuahene, Bernard T.; Kanjanabootra, S.; Gajendran, T. (Taylor and Francis (Routledge), 2023-05)
    Digitalization is transforming the way of doing business, and the construction industry is experiencing its fair share. It has necessitated the influx and growth of digital technologies application on construction projects and, to a larger extent, construction firms. In as much as this is a great initiative, early adopters in construction are still exploring, experimenting, and exploiting the potential of these digital transformations in their projects. There appears to be a gap in the digital capabilities needed in the construction life cycle and how these should be developed. A systematic review approach was used to identify digital technologies used in the construction industry. Literature on organization and digital capabilities was used to identify these capabilities and supported with examples from the UK and Australia to explain the capabilities. A case was made for how developing countries can develop digital capabilities in the construction industry from geographical distribution analysis from the systematic review and inference from the identified capabilities and the enabling approaches. Three main digital capabilities (digital mindset, digital infrastructure/investment and digital skillset) with sub-capabilities and two main approaches (firm and external) to developing these capabilities are discussed in this chapter. By implication, these capabilities are also useful in the construction industry in developing countries
  • Development of Concrete Mixtures Based Entirely on Construction and Demolition Waste and Assessment of Parameters Influencing the Compressive Strength

    Yildirim, Gurkan; Ozcelikci, E.; Alhawat, Musab M.; Ashour, Ashraf F. (2023-06)
    Demolition and reconstruction of degrading structures alongside with the repetitive repair, maintenance, and renovation applications create significant amounts of construction and demolition waste (CDW), which needs proper tackling. The main emphasis of this study has therefore been placed on the development of concrete mixtures with components (i.e., aggregates and binder) coming entirely from CDW. As the binding phase, powdered CDW-based masonry units, concrete and glass were used collectively as precursors to obtain geopolymer binders, which were then incorporated with CDW-based fine and coarse concrete aggregates. Together with the entirely CDW-based concretes, designs were also proposed for companion mixtures with mainstream precursors (e.g., fly ash and slag) occupying some part of the CDW-based precursor combination. Sodium hydroxide (NaOH), sodium silicate (Na2SiO3) and calcium hydroxide (Ca[OH]2) were used at various concentrations and combinations as the alkaline activators. Several factors that have impact on the compressive strength results of concrete mixtures, such as mainstream precursor replacement rate, al-kaline molar concentrations, aggregate-to-binder ratios and curing conditions, were considered and these were also backed by the micro-structural analyses. Our results showed that through proper optimiza-tion of the design factors, it is possible to manufacture concrete mix-tures entirely out of CDW with compressive strength results able to reach up to 40 MPa under ambient curing. Current research is believed to be very likely to promote more innovative and up-to-date techniques to upcycle CDW, which are mostly downcycled through basic practices of road base/sub-base filling, encouraging further research and increas-ing the awareness in CDW issue.
  • Hydration characteristics, hydration products and microstructure of reactive powder concrete

    Ge, W.; Zhang, Z.; Ashour, Ashraf F.; Li, W.; Jiang, H.; Hu, Y.; Shuai, H.; Chuanzhi, S.; Li, S.; Liu, W. (Elsevier, 2023-06)
    Reactive Powder Concrete (RPC) is a new type of cementitious materials with a complex hydration mechanism, and active admixtures greatly influence the hydration reaction, formation of hydration products, and evolution of microstructure. In order to comprehensively study the quantitative effects of active admixtures contents, namely silica fume, slag and fly ash, on hydration characteristics, hydration products, and microstructure of RPCs, tests of workability, setting time, electrical conductivity, bound water and mechanical properties were conducted. Furthermore, a series of properties including morphology and micro-structure characteristics of RPCs were analyzed by thermogravimetric (TG) analysis, X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), mercury intrusion porosimetry (MIP), Brunauer-Emmet-Teller (BET), and scanning electron microscope (SEM). The results indicate that the initial hydration reaction rate of RPCs is reduced by partly replacing cement with active admixtures. The pozzolanic effect created by the active admixtures enhances hydration and improves RPC's compressive and flexural strength. RPCs made of cement-silica fume mixture exhibit the best macroscopic properties. The adoption of silica fume promotes the production of C-S-H gel during hydration and exerts pozzolanic and crystal nucleation effects to promote cement hydration. RPCs made of pure cement exhibit 15.3% porosity after 28 days of hydration, with the largest proportion of less harmful pores in the microstructure. The porosity is reduced to 5.2% when cement is partially replaced with silica fume, and the microstructure is dominated by harmless pores. When replacement of silica fume is kept at 25%, using slag powder or fly ash substitute part of cement also reduces the number of less harmful pores. It is beneficial to add slag powder to increase the number of gel pores, whereas fly ash reduces the number of gel pores. The investigation presented in this paper would contribute to the production of low cost and environmentally-friendly RPCs, and accelerate the wider applications of ultra-high performance concrete (UHPC) in engineering structures.
  • Flexural performance of prefabricated U-shaped UHPC permanent formwork - concrete composite beams reinforced with FRP bars

    Ge, W.; Zhang, Z.; Ashour, Ashraf F.; Li, W.; Jiang, H.; Hu, Y.; Shuai, H.; Sun, C.; Qiu, L.; Yao, S.; et al. (2023-04-06)
    Finite element (FE) analysis of fiber-reinforced polymer (FRP) reinforced concrete beams cast in U-shaped ultra-high performance concrete (UHPC) permanent formworks is presented in this paper. Concrete damage plasticity (CDP) and FRP brittle damage models were used to simulate the damage behavior of concrete and FRP bars. The results of FE simulation are in good agreement with the experimental results. Furthermore, parametric studies were conducted to investigate the effect of concrete and UHPC strengths, yield strength of steel bars, elastic modulus of FRP bars, ultimate tensile strength of FRP bars, types of UHPC normal strength concrete (NSC) interface and thickness of UHPC under different reinforcement conditions. Flexural performances, in terms of cracking, yield, ultimate loads and corresponding deflections, failure mode, energy dissipation and ductility, were investigated. Traction-separation model was used to describe the bonding degradation and the maximum slip of two types of bonding interfaces (smooth surface and medium-rough surface). Both flexural capacity and resistance to deformation of composite beams are significantly improved by the utilization of hybrid FRP/steel reinforcement. The UHPC formwork can also delay the occurrence and development of cracks. By appropriately increasing the strength of UHPC or elastic modulus of FRP bar, the flexural capacity of composite beams is effectively improved. It is expected that the results presented in this paper can guide the design and construction of U-shaped UHPC permanent formwork-concrete composite beams reinforced with FRP bars.
  • Micro-nano scale pore structure and fractal dimension of ultra-high performance cementitious composites modified with nanofillers

    Wang, J.; Wang, X.; Ding, S.; Ashour, Ashraf F.; Yu, F.; Xinjun, L.; Han, B.; National Science Foundation of China (51978127, 52178188 and 51908103), the China Postdoctoral Science Foundation (2022M720648 and 2022M710973) and the Fundamental Research Funds for the Central Universities (DUT21RC(3)039). (2023-08)
    The development of ultra-high performance cementitious composite (UHPCC) represents a significant advancement in the field of concrete science and technology, but insufficient hydration and high autogenous shrinkage relatively increase the pores inside UHPCC, in turn, affecting the macro-performance of UHPCC. This paper, initially, optimized the pore structure of UHPCC using different types and dimensions of nanofillers. Subsequently, the pore structure characteristics of nano-modified UHPCC were investigated by the mercury intrusion porosimeter method and fractal theory. Finally, the fluid permeability of nano-modified UHPCC was estimated by applying the Katz-Thompson equation. Experimental results showed that all incorporated nanofillers can refine the pore structure of UHPCC, but nanofillers with different types and dimensions have various effects on the pore structure of UHPCC. Specifically, CNTs, especially the thin-short one, can significantly reduce the porosity of UHPCC, whereas nanoparticles, especially nano-SiO2, are more conducive to refine the pore size. Among all nanofillers, nano-SiO2 has the most obvious effect on pore structure, reducing the porosity, specific pore volume and most probable pore radius of UHPCC by 31.9%, 35.1% and 40.9%, respectively. Additionally, the pore size distribution of nano-modified UHPCC ranges from 10-1nm to 105nm, and the gel pores and fine capillary pores in the range of 3-50nm account for more than 70% of the total pore content, confirming nanofillers incorporation can effectively weaken pore connectivity and induce pore distribution to concentrate at nanoscale. Fractal results indicated the provision of nanofillers reduces the structural heterogeneity of gel pores and fine capillary pores, and induces homogenization and densification of UHPCC matrix, in turn, decreasing the UHPCC fluid permeability by 15.7%-79.2%.
  • Developing a sustainable ultra-high performance concrete using seawater and sea-sand in combination with super-fine stainless wires

    Yu, F.; Dong, S.; Li, L.; Ashour, Ashraf F.; Ding, S.; Han, B.; Ou, J. (ASCE, 2023)
    Utilizing seawater and sea-sand for producing ultra-high performance concrete (UHPC) can substantially reduce raw materials costs and alleviate the current freshwater and river sand resources shortage in coastal and marine areas. However, the corrosion risk to reinforcing fibers inside UHPC caused by chlorides in seawater and sea-sand cannot be ignored. In this study, a new type of sustainable UHPC composed of seawater and desalinated sea-sand (UHPSSC) reinforced with stainless profile, super-fine stainless wire (SSW) was developed. Its mechanical properties and chloride content were studied. The research results show that SSWs do not rust after immersion in seawater. The flexural and compressive strengths of UHPSSC incorporating 1.5% SSWs are 13.8MPa and 138.6MPa, respectively, and the flexural toughness of UHPSSC is increased by 428.9%, reaching the basic mechanical requirements of UHPC. The high specific surface area of SSW and enrichment of silica fume on its surface enhance the interfacial bond between fiber and matrix, further promoting the full play of the SSWs’ reinforcing mechanisms as proved by the decrease of the Ca/Si ratio at the SSW surface. The C-S-H gels with a high Ca/Si ratio within the ITZ as well as Friedel’s salt are conducive to immobilize chlorides, blocking the migration of chlorides through the matrix and further mitigating the risk of long-term chloride corrosion of SSWs. Overall, utilizing seawater and desalinated sea-sand in combination with SSWs can produce UHPC with improved strength and toughness, making it a suitable choice for applications where high durability and long-term mechanical performance is required.
  • High pressure adsorption of hydrogen sulfide and regeneration ability of ultra-stable Y zeolite for natural gas sweetening

    Rahmani, M.; Mokhtarani, B.; Rahmanian, Nejat (2023-07-01)
    Adsorbents are developing in the various separation industries; these adsorbents can use to sweeten natural gas and remove hydrogen sulfide. Many commercial adsorbents are not regenerable when exposed to hydrogen sulfide because hydrogen sulfide is highly reactive. For removal, the main challenge when using surface adsorbent, is the dissociation adsorption of and non-regenerability of adsorbent. In this study, ultra-stable Y (USY) zeolite, was chosen to adsorb hydrogen sulfide due to its unique physical and chemical properties. To accurately model the adsorption isotherms, experimental adsorption data were measured in high pressure up to 12 bar for hydrogen sulfide and 21 bar for carbon dioxide, methane, and nitrogen as other natural gas components. The experiments were performed at three temperatures of 283, 293 and 303 K. Toth model fitted the experimental data very well, and the capacity of hydrogen sulfide adsorption on USY at the temperature of 283 K and pressure of 12 bar is 4.47 mmol/g that is noticeable. By performing ten cycles of adsorption and regeneration of hydrogen sulfide on USY, the regenerability of the adsorbent was investigated and compared by conducting a similar test on commercial 13X adsorbent. USY is found to be completely regenerable when exposed to hydrogen sulfide. The Isosteric adsorption heat of hydrogen sulfide on the adsorbent is 18.1 kJ/mol, which indicates physical adsorption, and the order of adsorption capacity of tested compounds on USY is H2S > CO2≫CH4 > N2.
  • 5th Annual Innovative Engineering Research Conference: Book of Abstracts

    Cooke, Kavian O.; Lefticaru, Raluca; Sheehan, Therese (University of Bradford, 2022-06)
  • Development of ambient-cured geopolymer mortars with construction and demolition waste-based materials

    Yildirim, Gurkan; Ashour, Ashraf F.; Ozcelikci, E.; Gunal, M.F.; Ozel, B.F.; Alhawat, Musab M. (2023-02)
    Degrading infrastructure and applications of structural demolition create tremendous amounts of construction and demolition waste (CDW) all around the world. To address this issue in an effective way, recycling CDW in a most appropriate way has become a global concern in recent years. To this end, this study focused on the utilization of CDW-based materials such as hollow brick (HB), red clay brick (RCB), roof tile (RT), glass (G) and concrete (C) in the production of geopolymer mortars. These materials were first collected from an urban transformation area and then subjected to an identical two-step crushing-milling procedure to provide sufficient fineness for geopolymerization. To investigate the influence of blast furnace slag (S) addition to the CDW-based mixtures, 20% S substituted mixture designs were also made. Fine recycled concrete aggregates (FRCA) obtained from crushing and sieving of the waste concrete were used as the aggregate. A series of mixtures were designed using different proportions of three distinct alkali activators such as sodium hydroxide (NaOH), sodium silicate (Na2SiO3) and calcium hydroxide (Ca[OH]2). To improve their applicability, the mixtures were left to cure at room temperature rather than the heat curing which is frequently applied in the literature. After 28 days of ambient curing, the 100% CDW-based geopolymer mortar activated with three different activators reached a compressive strength of 31.6 MPa, whereas the 20% S substituted geopolymer mortar achieved a compressive strength of 51.9 MPa. While the geopolymer mortars activated with only NaOH exhibited poor performance, it was found that the use of Na2SiO3 and Ca(OH)2 improved the compressive strength. Main geopolymerization products were related to NASH, CASH, and C(N)ASH gel formations. Our results demonstrated that mixed CDW-based materials can be employed in the manufacturing geopolymers, making them potential alternatives to Portland cement-based systems by being eco-friendly, energy-efficient, and comparable in compressive strength.
  • A comprehensive study on the compressive strength, durability-related parameters and microstructure of geopolymer mortars based on mixed construction and demolition waste

    Ozcelikci, E.; Kul, A.; Gunal, M.F.; Ozel, B.F.; Yildirim, Gurkan; Ashour, Ashraf F.; Sahmaran, M. (Elsevier, 2023-04)
    As a viable option to upcycle construction and demolition waste (CDW) into value-added materials, geopolymer technology is emerging. Most studies investigate CDWs in a separated form or in combination with mainstream pozzolanic/cementitious materials focusing only on fundamental properties of geopolymer pastes, not considering to scale such materials to the level of their application in the forms of structural mortars/concretes or to characterize long-term performance/durability. This study investigated the development and characterization of ambient-cured mortars with mixed CDW-based geopolymer binders and untreated fine recycled concrete aggregates (FRCA). Mixture of CDW-based roof tile (RT), red clay brick (RCB), hollow brick (HB), concrete (C), and glass (G) was used as the precursor, while ground granulated blast furnace slag (S) was used in some mixtures to partly replace CDW precursors. Compressive strength, durability-related parameters including drying shrinkage, water absorption, and efflorescence, microstructure and materials sustainability were evaluated. Results showed that 28 d compressive strength results above 30 and 50 MPa is achievable with the entirely CDW-based and slag-substituted mortars, which were found improvable to have entirely CDW-based structural concretes. Drying shrinkage of the mortars is slightly higher than that of conventional cementitious/geopolymeric systems although it can be minimized significantly through mixture optimization. Water absorption values remain comparable with the literature. CDW-based geopolymer mortars outperform Portland cement mortars in terms of CO2 emission and energy requirement. Our findings show that via utilizing CDW-based constituents in mixed form as precursor and waste aggregates, it is possible to develop greener construction materials with acceptable strength and long-term performance.
  • Process simulation of twin-screw granulator: The effect of screw configuration on size distribution

    Arthur, T.B.; Sekyi, Nana; Rahmanian, Nejat; Pu, Jaan H. (2023-06)
    The effect of screw configuration on granule size distribution (GSD) using gPROMS FormulatedProduct (gFP) software to perform optimization, estimation of complex processes, and analyses is evaluated. Twin-screw granulation modeling was used to investigate the contribution of screw configuration and liquid-to-solid (L/S) ratio on GSD. Lactose and Avicel were the granulating materials. Twelve different configurations were investigated under three feed rates as consistent with literature and at various L/S ratios. Results indicate that kneading elements promote the recovery of 100–1000 µm granules while reducing the production of oversized granules. Higher feed rates support the production of fines and agglomerates, while a low feed rate produces 100–1000 µm granules.
  • Use of gene-expression programming to estimate Manning's roughness coefficient for a low flow stream

    Chaplot, B.; Peters, M.; Birbal, P.; Pu, Jaan H.; Shafie, A. (2021-12)
    Manning’s roughness coefficient (n) has been widely used to estimate flood discharges and flow depths in natural channels. Therefore, although extensive guidelines are available, the selection of the appropriate n value is of great importance to hydraulic engineers and hydrologists. Generally, the largest source of error in post-flood estimates is caused by the estimation of n values, particularly when there has been minimal field verification of flow resistance. This emphasizes the need to improve methods for evaluating the roughness coefficients. Trinidad and Tobago currently does not have any set method or standardised procedure that they use to determine the n value. Therefore, the objective of this study was to develop a soft computing model in the calculation of the roughness coefficient values using low flow discharge measurements for a stream. This study presents Gene-Expression Programming (GEP), as an improved approach to compute Manning’s Roughness Coefficient. The GEP model was found to be accurate, producing a coefficient of determination (R2) of 0.94 and Root Mean Square Error (RSME) of 0.0024.
  • The urban fluvial and hydro-environment system

    Pu, Jaan H.; Li, J.; Satyanaga, A.; Kundu, S.; Pandey, M.; Hanmaiahgari, P.R.; Shao, S. (Frontiers Media SA, 2022-12)
    With the rapid urbanization of cities around the world, water security, flood control, and urban hydro-environmental management have become important tasks to tackle. The majority of large to megacities are located in delta regions surrounded by river networks, due to their historical development. They are not only threatened by floods from upstream river basins, but also endangered by the challenges of urban hydro-environmental governance. Fast urbanization causes interference and fragmentation of the river system and impedes its hydrodynamic potential, which is a primary driver of flooding, pollution, and sediment deposition. Consequently, water security and environmental problems are major issues for sustainable urban development. The purpose of this Research Topic (RT) is to examine the latest advances and developments in addressing the challenges in urban fluvial and freshwater systems as well as to discuss the opportunities they create for improvement in modelling, management practices and governance. This RT consists of twenty research articles from 99 authors under three different research themes, which feature contributions on urban space management, water pollution mitigation and urban watercourse behavioural sciences to strengthen resilience. The RT includes the following themes: • State-of-the-art numerical models, • Urban environmental and hydrological advances, and • Sustainable cities implementation.
  • Editorial: The urban fluvial and hydro-environment system

    Pu, Jaan H.; Pandey, M.; Li, J.; Satyanaga, A.; Kundu, S.; Hanmaiahgari, P.R. (2022-11)
  • Semi-analytical solution of solute dispersion model in semi-infinite media

    Taghvaei, P.; Pourshahbaz, H.; Pu, Jaan H.; Pandey, M.; Pourshahbaz, V.; Abbasi, S.; Tofangdar, N. (2022-12)
    The advection–dispersion equation (ADE) is one of the most widely used methods for estimating natural stream pollution at different locations and times. In this paper, variational iteration method (VIM) is utilized to obtain a semianalytical solution for 1D ADE in a temporally dependent solute dispersion within uniformsteady flow. Through a computational validation, the effect of different parameters such as uniform flow velocity and dispersion coefficient on the solute concentration values has been investigated. Results show that the change in velocity has a strong effect on fluid density variation. However, when the diffusion coefficient has been increased, the change in flow and velocity behaviors is negligible. To verify the proposed semianalytical solution, the results were compared to analytical solutions and errors were found to be <0.7% in all simulations.
  • Wake flow field of a wall-mounted pipe with spoiler on a rough channel bed

    Devi, K.; Mishra, S.; Hanmaiahgari, P.R.; Pu, Jaan H. (2023)
    This research work focuses on the wake flow region of a cylinder with a spoiler on a rough bed under steady flow conditions. The acoustic Doppler velocimetry was used for the measurement of three-dimensional velocity data for two Reynolds numbers in a fully developed turbulent flow around the cylinder with a spoiler. The mean flow velocities, second-order turbulence structures, and conditional statistics were investigated in the wake region of the spoilered cylinder. The flow was separated from the spoiler with the formation of two shear layers between free surface flow and recirculating flow. It is observed that the flow is reattaching to the bed at 11D irrespective of the Reynolds number. Downstream of the cylinder, the mean velocity distributions are asymmetric due to the wall–wake effect, and the point of inflection is observed for each velocity profile at z = 0.40ẟ. The turbulence intensities, Reynolds stresses, and TKE are highly enhanced in the wake region of the cylinder as compared to their respective upstream values for both runs. The turbulence intensities, Reynolds normal stresses, Reynolds shear stresses, and turbulent kinetic energy are attaining peaks at z = 0.4 ẟ for all the streamwise locations, and the peaks are found to be highest at x = 10D. The quadrant analysis results indicate that the sweeps are dominating bursting events in the inner and intermediate layers, while ejections are dominating in the outer layer of the wake region. As the hole size, H increases ejections stress fraction rises as compared to that of the sweeps in the wake region for z = 0.2–0.7 h.

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