OpenMETU (Middle East Technical University)
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Insight into greenhouse gas emission in freshwater aquaculture ponds in Jiangsu Province: Variation due to species used and ponds management practice
No full textAquaculture ponds have emerged as a significant contributor to greenhouse gas (GHG) emissions. We measured methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) emissions in ponds, all located in Jiangsu Province, with different fish and management practices over an entire cycle. All ponds emitted these gases, with higher CH4 and N2O levels during fish growth than stocking period. The highest CH4 and N2O fluxes were found in the Crucian carp (Carassius auratus) pond with up to 16,512 +/- 3015 mu mol/(m(2)h) and 5.54 +/- 0.31 mu mol/(m(2)h), respectively. CH4 was the primary contributor to the global warming potential in traditional earthen ponds, accounting for an average contribution rate of 87.7 %. The dissolved oxygen (DO) concentration was the water quality parameter that most significantly influenced the CO2 flux, while pH acted as its primary regulator. The GHG emission intensity per unit of fish production in traditional earthen ponds was 197 times higher than that in-pond raceway systems. Largemouth bass (Micropterus salmoides) and Crucian carp ponds exhibited CH4 diffusion fluxes at the sediment-water interface, which were > 20 times higher than those at the water-air interface. Our results further suggest that stocking density and feed amount significantly influence the variations in GHG emissions among the ponds with the in-pond raceway system having low carbon emissions and being high yield aquaculture system compared to traditional earthen ponds. The water depth and DO concentration can be manipulated to reduce GHG emissions across the various interfaces
Pulse sequence analysis-based characterization of corona and surface discharges under DC voltages
No full textPartial discharge (PD) measurement under direct current (DC) stress has been receiving increasing attention due to the increasing prevalence of medium voltage (MVDC) and high voltage (HVDC) systems and cable technologies. Since PD patterns differ significantly under DC voltage from those under alternating current (AC) stress, this work presents a comprehensive investigation of the PD pattern under DC voltage by considering both corona and surface discharge scenarios. Surface discharges were simulated on glass dielectric samples, while corona discharges were built in needle-plane geometry under both positive and negative polarities. Pulse sequence analysis and statistical evaluations of discharge characteristics revealed different behaviors under positive and negative polarities as well as other factors like the level of threshold used to detect PD pulses, the number of pulses used to construct a pattern, noise levels and multisource PDs. The findings emphasize the robustness of various PD patterns under these conditions and the suitability of each pattern for analyzing PD data
Strut and tie models with the dual use of the finite element method and the lattice networks
No full textStrut and tie modelling (STM) is widely recognized as a prominent design method for the design of disturbed (D) region reinforced concrete structural elements. The paramount initial step in conducting optimized reinforcement designs lies in the establishment of strut and tie geometry. In this study, a novel dual modelling approach is proposed, combining two distinct models, namely the continuum model (specifically, a finite element model) and the lattice network (comprising overlapping truss elements interconnected at every two nodes). The approach involves the application of a novel element removal algorithm based on the computed internal forces and stresses for the two lattice and finite element models working in tandem while sharing information. The iterative process continues until the convergence of the internal energy of the reduced lattice network. To evaluate the accuracy and efficacy of the proposed approach, a comprehensive demonstration is conducted employing the 20 most extensively studied design examples documented in the literature. The findings indicate that the dual system is a viable alternative method for STM design by satisfying the minimum energy requirements and without conducting laborious nonlinear finite element analysis. Furthermore, objective designs are possible from the derived STM models which can used in automated design flows
Nonlinear vibrations and modal interactions in rotating pre-twisted blades with thickness and chord variations using high-fidelity models with DICFs and PA
No full textThis study presents a high-fidelity investigation into the coupled in-plane and out-of-plane nonlinear vibration characteristics and modal interactions of rotating pre-twisted blades with variable thickness and chord length. A geometrically nonlinear structural model is developed based on first-order shear deformation theory, with all nonlinear terms of the Green's strain tensor retained to accurately capture large deformation effects. The formulation is constructed within a surface-based framework that incorporates pre-set, pre-twist, spanwise and chordwise cross-sectional variation, and chord tapering. Two centrifugal stiffening strategies, i.e., Direct Integration of Centrifugal Forces (DICFs) and Pre-Stressed Analysis (PA), are systematically compared to evaluate their influence on both free and forced vibration responses. The spatial domain is discretized using the Spectral Chebyshev Technique (SCT), allowing a high number of modes to be retained across complex geometries. An enhanced reduced-order modeling framework is employed to preserve key nonlinear restoring forces and multi-mode interactions. The resulting equations are solved using the harmonic balance method with arc-length continuation to compute steady-state solutions and nonlinear frequency response curves. Numerical results reveal significant differences in resonance behavior and internal modal couplings under different centrifugal stiffening assumptions. This comprehensive approach offers new insights into the nonlinear dynamics of rotating blades, highlighting the critical influence of modeling strategy and model order on accurately capturing the full spectrum of nonlinear dynamics
An integrated qualitative farm-to-fork approach to rank foodborne pathogens associated with mastitis-affected raw milk from Irish dairy farms to the consumer
No full textA qualitative microbial risk assessment (MRA) framework was applied to evaluate the potential introduction of foodborne pathogens from bovine mastitis raw milk into the dairy chain. In a survey between January and December 2024, 588 raw milk samples were obtained from mastitis affected cows across 66 Irish dairy farms. Following guidelines from the International Dairy Federation and National Mastitis Council, samples were analysed for mastitis pathogens, where 337 positive samples (55.3 %) were further tested for seven foodborne microbial pathogens using a hierarchical testing strategy with ten culture-based methods. A qualitative MRA guided by the FAO/WHO and EFSA framework was developed in this study. Incorporating stages of the risk assessment paradigm that include hazard identification, hazard characterisation, exposure assessment, and risk characterisation through a structured decision-tree approach. For the survey, Streptococcus spp. was most frequently isolated (n = 123), followed by Escherichia coli (n = 76), Staphylococcus aureus (n = 67), and coagulase-negative staphylococci (CNS) (n = 39). Less frequently detected pathogens included Enterococcus spp. (n = 15), Salmonella spp. (n = 4), and Bacillus cereus (n = 1). Exposure assessment and risk characterisation identified S. aureus, E. coli, and Salmonella spp., as high risk, necessitating targeted interventions within dairy chain systems, including processing failures. This study provides novel insights into the risks posed by mastitisassociated foodborne pathogens, facilitating evidence based recommendations for improving dairy safety management in the dairy chain
A local correlation-based algebraic transition model in k-ω SST formulation
No full textA new correlation-based algebraic transition model using local variables is proposed. Instead of solving an additional transport equation for intermittency, the model employs an intermittency function that controls the source terms of the turbulence model used. Thus, the model reduces the number of constants and functions needed, and achieves to solve problems by using less computational power compared to one-or two-equation transition models. The intermittency function of the present model is a more sophisticated modified version of that in the SA-BCM transition model, and it is coupled with the k-w SST turbulence model to eliminate the shortcomings in the SA-BCM model. The present model involves only four calibration constant, which are calibrated against the cases other than validation cases. The model is validated against a series of common flat plate experiments and four airfoil test cases. The results show a good agreement with the experiments and that the new model provides comparable success with more complicated transition models. Therefore, the present model provides an alternative means to include boundary layer transition effects in CFD simulations by reducing the number of constants and functions needed compared to that in other transition models
Fast investigation of control interaction risks in PV parks using eigenvalue analysis in Modelica
No full textThis paper contributes to the fast detection of control interaction risk in a PV park using the eigenvalue analysis in Modelica. The entire PV park and its interconnected network are represented by time-domain equations in Modelica, then linearized state space equations are extracted directly by leveraging the Modelica features. This constitutes an advantageous approach for fast finding eigenvalues and extracting potential instability conditions. The presented approach is verified with electromagnetic transient (EMT) simulation and impedance-based stability analysis (IBSA) that uses EMT-type impedance scanning methods. The results show an outstanding improvement in the simulation time and accuracy
Evaluating confidence in geometric matching between 3D point clouds and BIM models by integrating coverage, distance, and distribution metrics
Full text linkAccurate and objective assessment of the matching of a Building Information Model (BIM) with 3D point cloud data (PCD) is critical to Scan-to-BIM and Scan-vs-BIM workflows. However, existing methods for PCD-BIM matching evaluation do not fully and robustly account for geometric accuracy and spatial completeness. This paper introduces a statistically-grounded method that combines three indices that complementarily assess matching Coverage, Distribution, and Distance. The proposed method also accounts for inter-element occlusions when calculating each element's theoretically visible surface, which increases the metrics' reliability. Validation is conducted across 46 PCD-BIM pairs, encompassing 4000+ elements from ISPRS, CV4AEC, BIMNET and custom datasets, as well as a residential building case study comparing manual and automated BIM model reconstructions, and demonstrating the applicability of the method to any type of element. Results show practical value for both Scan-to-BIM and Scan-vs-BIM practice and enable quantitative assessment of benchmark dataset quality via the proposed indices
Mechanical properties and displacement capacity of welded-plate flexural yielding dampers
No full textReplaceable hysteretic steel dampers can be installed at the ends of diagonal braces to provide passive energy dissipation in frame-type structures. These dampers must satisfy both strength and displacement requirements. Previous studies have primarily focused on small-scale component testing, with limited investigation into the performance of large-scale dampers, particularly through sub-assemblage testing. This paper presents the findings of a combined experimental and numerical study on the mechanical properties and displacement capacity of welded-plate flexural yielding dampers. The experimental program was carried out in two phases: the first involved component testing of five specimens, while the second involved sub-assemblage testing of two specimens. Key variables included the number of yielding plates, plate length, plate thickness, and steel grade. Results from the first phase demonstrated that welded-plate flexural yielding dampers can achieve yield and ultimate resistances of 626 kN and 891 kN, respectively, with deformation capacities exceeding 40 mm. In the second phase, sub-assemblage tests showed that braces equipped with welded-plate flexural yielding dampers could accommodate story drifts of 2.63 % with single dampers and 5.5 % with dual dampers. Finite element analysis was used to simulate the behavior of the specimens and to develop a failure criterion for damper design. An expression was developed to calculate displacement capacity based on geometric variables. Both experimental and numerical results confirm the suitability of welded-plate flexural yielding dampers for seismic applications, offering a reliable and efficient energy dissipation mechanism for braced frame structures
Terahertz frequency-domain characterization of UHMW-PE ballistic armor plates
Full text linkUltra-high molecular weight polyethylene (UHMW-PE) fiber-based ballistic armor plates are analyzed in the terahertz (THz) frequency region to better understand their structural properties. Various thickness plates are produced by hot pressing 5, 10 and 15 layer four-ply cross-weaved UHMW-PE fiber sheets whose refractive index and absorption characteristics are then examined for three different frequencies using time-domain imaging techniques. The obtained transmission images reveal significant structural information, including surface texture and potential defects, such as air bubbles or voids. It is found that with an increasing number of layers in each plate there is an increase in the refractive index approaching the value of the UHMW-PE fiber sheet. The change in the effective refractive index is attributed to inhomogeneities such as bunching up of the fibers as well as voids because of the manufacturing processes with a larger inhomogeneity in the 5-layer plates as compared to the 10-and 15-layer plates. Furthermore, a significant change in refractive index is observed for different orientations of the armor plate with respect to the input beam polarization due to the presence of periodic surface ridge formations. A detailed analysis of the extinction coefficient with respect to the refractive index shows groupings in the range of values for different thickness plates which can serve as an indicator of the inhomogeneities inside the structures. The purely frequency domain analysis performed here suggests that such methods in the THz region can offer a new, rapid way for non-destructive analysis of ballistic armor plates