Simplified analytical method for the robustness assessment of precast reinforced concrete structural systems

The article presents the simplified implementation of alternative load path method based on the energy balance approach. This method should be used to check the global resistance of a damaged structural system after the occurrence of an accidental event. Basic assumptions of simplified analytical models for modelling resistance of horizontal ties in a damaged structural system, taking into account the membrane (chain) effects, were presented. An approach to modelling the dynamic resistance of a damaged structural system based on the energy balance method is described. Calculated dependencies for checking the robustness of a prefabricated multi-storey building with hollow-core slabs after the loss of the central column are proposed and considered using an example. On the considered example, a comparison of the required tie sections area with the dynamic resistance designed using the energy balance method (EBM) and according to the current standards, and a statistical assessment of the reliability of the load-bearing capacity models are carried out. In the end, a brief algorithm for the simplified calculation of the dynamic resistance of a damaged structural system is proposed.

Theoretical Estimation of Energy Balance Components in Water Networks for Top-Down Approach

The energy balance calculation for pressurized water networks is an important step in assessing the energy efficiency of water distribution systems. However, the calculation generally requires mathematical modelling of the water networks to estimate three important energy components: outgoing energy through water loss (El), friction energy loss (Ef) and energy associated with water loss (EWL). Based on a theoretical energy balance analysis of simplified pipe networks, a simple method is proposed to estimate El, Ef and EWL with minimum data requirements: input energy, water loss (WL) and head loss between the source and the minimum energy point (ΔH). By inclusion of the head loss in water networks into the estimation, the percentages of El and EWL are lower and higher, respectively, than using only the percentage of WL. The percentage of Ef can be a function of the percentage of ΔH. By demonstrating our analysis with the simulation results from the mathematical models of 20 real water networks, the proposed method can be used to effectively estimate El, Ef and EWL as a top-down energy balance approach.

Analytical Investigation into Effects of Capillary Force on Condensate Film Flowing over Horizontal Semicircular Tube in Porous Medium

A theoretical investigation is performed into the problem of laminar filmwise condensation flow over a horizontal semicircular tube embedded in a porous medium and subject to capillary forces. The effects of the capillary force and gravity force on the condensation heat transfer performance are analyzed using an energy balance approach method. For analytical convenience, several dimensionless parameters are introduced, including the Jakob number Ja, Rayleigh number Ra, and capillary force parameter Boc. The resulting dimensionless governing equation is solved using the numerical shooting method to determine the effect of capillary forces on the condensate thickness. A capillary suction velocity can be obtained mathematically in the calculation process and indicates whether the gravity force is greater than the capillary force. It is shown that if the capillary force is greater than the condensate gravity force, the liquid condensate will be sucked into the two-phase zone. Under this condition, the condensate film thickness reduces and the heat transfer performance is correspondingly improved. Without considering the capillary force effects, the mean Nusselt number is also obtained in the present study as N u ¯ | V 2 ∗ = 0 = 2 R a D a / J a 1 / 2 ∫ 0 π 1 + cos θ 1 / 2 d θ .

Modelling mass changes of Dokriani (Central Himalaya) and Chhota Shigri (Western Himalaya) glaciers, India using energy balance approach

<p>Processes controlling the glacier wastage in the Himalaya are still poorly understood. In the present study, a surface energy-mass balance model is applied to reconstruct the long-term mass balances over 1979-2020 on two benchmark glaciers, Dokriani and Chhota Shigri, located in different climatic regimes. The model is forced with ERA5 reanalysis data and calibrated using field-observed point mass balances. The model is validated against available glacier-wide mass balances. Dokriani and Chhota Shigri glaciers show moderate wastage with a mean value of –0.28 and –0.34 m w.e. a<sup>-1</sup>, respectively over 1979-2020. The mean winter and summer glacier-wide mass balances are 0.44 and –0.72 m w.e. a<sup>-1</sup> for Dokriani Glacier and 0.53 and –0.85 m w.e. a<sup>-1</sup> for Chhota Shigri Glacier, respectively, showing a higher mass turn over on Chhota Shigri Glacier. Net radiation flux is the major component of surface energy balance followed by sensible and latent heat fluxes on both the glaciers. The losses through sublimation is around 10% to the total ablation. Surface albedo is one of the most important drivers controlling the annual mass balance of both Dokriani and Chhota Shigri glacier. Summer mass balance (0.76, p<0.05) mainly controls the annual glacier-wide mass balance on Dokriani Glacier whereas the summer (0.91, p<0.05) and winter (0.78, p<0.05) mass balances together control the annual glacier-wide mass balance on Chhota Shigri Glacier.</p>

Brayton-Moser Passivity Based Controller for Electric Vehicle Battery Charger

In this paper Brayton-Moser passivity-based control (BM-PBC) methodology is developed for an on-board battery charger for plug-in electric vehicles(PHEVs). The main features of this electric vehicle (EV) charger include improved power quality, reduced filter size and voltage stress across the switches and fast dynamic response. In this paper, a dynamic model of the three-level (TL) boost power factor correction (PFC) converter is developed using the Brayton-Moser formulation. Then, the Brayton-Moser based control technique is designed by injecting a virtual resistor in series with the input inductor. Further, the stability analysis of the proposed controller is also carried out using energy balance approach. To improve the dynamic performance and reduce the steady state error, a PI controller is integrated with the aforesaid controller. Therefore, the controller comprises of BM-PBC and the PI controller is implemented for the TL boost PFC converter as a battery charger and its performances are investigated under various operating modes with the help of MATLAB/Simulink. Furthermore, power quality of charger is assessed by monitoring source current total harmonic distortion (THD) under different operating conditions. It is also observed that the proposed system provides THD less than 5% in source current which satisfies IEC 61000-3-2 Class C standard. The performance of the aforesaid controller is also compared with the conventional PI controller. In order to validate the proposed controller, a prototype model of same specifications is tested in hardware in loop and obtained test results are also presented.

The challenges of an in situ validation of a nonequilibrium model of soil heat and moisture dynamics during fires

With the increasing frequency and severity of fire, there is an increasing desire to better manage fuels and minimize, as much as possible, the impacts of fire on soils and other natural resources. Piling and/or burning slash is one method of managing fuels and reducing the risk and consequences of wildfire, but the repercussions to the soil, although very localized, can be significant and often irreversible. In an effort to provide a tool to better understand the impact of fire on soils, this study outlines the improvements to and the in situ validation of a nonequilibrium model for simulating the coupled interactions and transport of heat, moisture and water vapor during fires. Improvements to the model eliminate the following two important (but heretofore universally overlooked) inconsistencies: one that describes the relationship between evaporation and condensation in the parameterization of the nonequilibrium vapor source term, and the other that is the incorrect use of the apparent thermal conductivity in the soil heat flow equation. The first of these made a small enhancement in the stability and performance of the model. The second is an important improvement in the physics underpinning the model but had less of an impact on the model's performance and stability than the first. This study also (a) develops a general heating function that describes the energy input to the soil surface by the fire and (b) discusses the complexities and difficulties of formulating the upper boundary condition from a surface energy balance approach. The model validation uses (in situ temperature, soil moisture and heat flux) data obtained in a 2004 experimental slash pile burn. Important temperature-dependent corrections to the instruments used for measuring soil heat flux and moisture are also discussed and assessed. Despite any possible ambiguities in the calibration of the sensors or the simplicity of the parameterization of the surface heating function, the difficulties and complexities of formulating the upper boundary condition and the obvious complexities of the dynamic response of the soil's temperature and heat flux, the model produced at least a very credible, if not surprisingly good, simulation of the observed data. This study then continues with a discussion and sensitivity analysis of some important feedbacks (some of which are well known and others that are more hypothetical) that are not included in the present (or any extant) model, but that undoubtedly are dynamically influencing the physical properties of the soil in situ during the fire and, thereby, modulating the behavior of the soil temperature and moisture. This paper concludes with a list of possible future observational and modeling studies and how they would advance the research and findings discussed here.

Utilization of sugarcane factories’ wastes as inexpensive source of nutrients and CO2 for microalgal biomass production: process coupling and potential evaluation

One approach for the viable production of algal biomass is to couple its production with wastewater treatment plants, power and/or industrial plants. This is intended towards the utilization of the nutrients and the CO2 in the wastewater and in the flue gases of the industry respectively by the microalgae during their growth. In the present study microalgal biomass production was conceptually coupled with a sugar factory. The potential of the wastewater and the flue gas of the factory to support the growth of the microalgae was evaluated. Likewise the possible reduction of pollution by the microalgae was studied. The outputs from the coupled process were determined using the material and energy balance approach with a spread sheet. The cultivation model shows that 12 mg of total nitrogen (TN) and 7.4 mg of total phosphorus (TP) per liter of wastewater could be transferred to the algal growth ponds. It was found that there is a nitrogen deficit in the wastewater. With the supply of makeup nutrient, 120.5 tons/year microalgal biomass could be produced from the coupled process. Application of the assumptions resulted in the reduction of chemical oxygen demand (COD) (mg O2/L) from 2200 to 447, biological oxygen demand (BOD5) (mg O2/L) from 1200 to 207, TN (mg/L) from 15 to 0.6 and, TP (mg/L) from 10 to 1.5 in the wastewater. Integration of the sugarcane processing factories with algal biomass production is important for both biomass production and bioremediation.

Modeling Air Aspiration in Steel Continuous Casting Slide-Gate Nozzles

Air aspiration is an important cause of nozzle clogging and inclusions in final products of continuous casting of steel due to the presence of metal oxides (such as alumina) which occur through the reoxidation of molten steel. This problem is most likely to occur when the flow control system (slide-gate or stopper rod) causes the pressure inside the nozzle to drop below atmospheric pressure, drawing gas into the system through possible cracks or gaps in the refractory walls. In this work, a 1-D pressure-energy model of the complete metal delivery system from the tundish to the mold is developed to predict the pressure distribution and throughput under dynamic operating conditions and varying clogging conditions. The energy balance approach includes pressure losses in the slide-gate, wall friction, and nozzle geometry variations, including the effects of multiphase flow due to argon gas injection. The model also predicts air aspiration, oxide inclusion formation, and the time for clogging shutdown. The predicted pressure distribution is verified with a three-dimensional numerical simulation of multiphase turbulent flow, and is validated with plant measurements. Parametric studies with different submerged entry nozzle (SEN) designs revealed that a smaller SEN diameter may lessen negative pressure by redistributing the pressure loss from the slide-gate to the entire nozzle through increased friction losses. Under negative pressure, a submillimeter-thin gap was shown to cause considerable air aspiration. Clogging shutdown times were evaluated for several scenarios under static and dynamic operating conditions.