Energy Balance Principle Research Articles

Deformation mode and energy absorption of polycrystal-inspired square-cell lattice structures

Lattice structures are widely used in many engineering fields due to their excellent mechanical properties such as high specific strength and high specific energy absorption (SEA) capacity. In this paper, square-cell lattice structures with different lattice orientations are investigated in terms of the deformation modes and the energy absorption (EA) performance. Finite element (FE) simulations of in-plane compression are carried out, and the theoretical models from the energy balance principle are deve-loped for calculating the EA of these lattice structures. Satisfactory agreement is achieved between the FE simulation results and the theoretical results. It indicates that the 30° oriented lattice has the largest EA capacity. Furthermore, inspired by the polycrystal microstructure of metals, novel structures of bi-crystal lattices and quad-crystal lattices are developed through combining multiple singly oriented lattices together. The results of FE simulations of compression indicate that the EA performances of symmetric lattice bi-crystals and quad-crystals are better than those of the identical lattice polycrystal counterparts. This work confirms the feasibility of designing superior energy absorbers with architected meso-structures from the inspiration of metallurgical concepts and microstructures.

Analytical Model and Experimental Verification of the Interfacial Peeling Strength of Electrodes

The interfacial peeling strength of lithium-ion battery electrodes is a very important mechanical property that significantly affects the electrochemical performance of battery cells. To characterize the interfacial peeling strength of an electrode, an analytical model based on the energy balance principle is established by considering the state of charge (SOC), the energy release rate, the tensile stiffness, and the peeling angle. Uniaxial tensile tests and 180-degree peeling tests are conducted to determine the Young’s modulus and the interfacial peeling strengths of electrodes at different SOCs, respectively. The experimental data serve as a validation of the accuracy of the analytical model. The interfacial peeling strength of the electrode shows a strong reliance on many factors. Specifically, the interfacial peeling strength increases with the SOC and the energy release, and decreases with the peeling angle. When the tensile stiffness of the active layer equals that of the current collector, the interfacial peeling strength has a maximum value. By comparing with experimental data of the 180-degree peeling test, the model prediction shows excellent agreement at different SOCs, and the analytical model established in this paper can be used to guide and assess the interfacial properties of electrodes for industry.

A New Decision Method of Filling Ratio Based on Energy Matching of Surrounding Rock and Backfill

In order to simplify the ratio decision process of cemented backfill in underground mines and achieve fine decision of filling ratio, the research on the energy matching between surrounding rock and cemented backfill in underground mines was conducted in this study. Based on the cubic function strength model of cemented backfill, the peak specific energy equation of backfill was improved by inversion analysis of the data of filling ratio experiment, and the functional relationship between the peak specific energy and the filling ratio was obtained by regression analysis. Then, based on the energy balance principle between the deformation energy released by the excavation of the underground rock mass and the peak specific energy of the cemented backfill, considering the physical and mechanical parameters of the surrounding rock of the goaf, including bulk density, elastic modulus, and burial depth, a ratio decision model of cemented backfill is established. The application results suggested that the calculation result of the model is reliable, and it can realize the rapid and accurate decision of the ratio of cement backfill in underground mines.

Serious analytical inconsistencies challenge the validity of the energy balance theory

Energy metabolism theory affirms that body weight stability is achieved as over time the average energy intake equals the average energy expenditure, a state known as energy balance. Here it is demonstrated, however, that weight stability coexists with a persistent energy imbalance. Such unexpected result emerges as a consequence of the answers to three fundamental problems: 1. Is it possible to model body weight fluctuations without the energy balance theory? And if so, what are the benefits over the energy balance strategy? 2. During energy balance, how the oxidized macronutrient distribution that underlies the average energy expenditure is related to the macronutrient distribution of the average energy intake? 3. Is energy balance possible under a low-fat diet that simultaneously satisfies the following conditions? (a) The fat fraction of the absorbed energy intake is always less than the oxidized fat fraction of the energy expenditure. (b) The carbohydrate fraction of the absorbed energy intake is always greater or equal to the oxidized carbohydrate fraction of the energy expenditure. The first of these issues is addressed with the axiomatic method while the rest are managed through analythical arguments. On the whole, this analysis identifies inconsistencies in the principle of energy balance. The axiomatic approach results also in a simple mass balance model that fits experimental data and explains body composition alterations. This model gives rise to a convincing argument that appears to elucidate the advantage of low-carbohydrate diets over isocaloric low-fat diets. It is concluded, according to the aforementioned model, that weight fluctuations are ultimately dependent on the difference between daily food mass intake and daily mass loss (e.g., excretion of macronutrient oxidation products) and not on energy imbalance. In effect, it is shown that assuming otherwise may caused unintended weight gain.

Evapotranspiración del cultivo de granado por balance de energía

Evapotranspiration is a key element in calculating the surface energy balance, wáter balance and crop water stress and crop yield determination. However, it´s direct measurement or estimation is frequently complicated, since the diversity and complexity of the factors acting in this physical process. (morphological, physiological and soil factors). SEBAL (Surface Energy Balance Algorithm for Land) estimates ET based on satellite images, using the principles of surface energy balance producing excellent results as reported in several studies of different scientist authors; minimizing the cost and time for the ET determination for large vegetation zones. The objective of this research work was to estimate the potential evapotranspiration for the pomegranate crop in a commercial farm, located in Gomez Palacio, Durango, Mexico, by SEBAL using Landsat 8 satellite images during the crop cycle 2016. The results were validated with estimates of ET by the FAO 56 method, obtaining a Willmott concordance index of 0.96, which means good estimation precision.

The characteristics of high speed crack propagation at ultra high loading rate

It is important to understand the characteristics of high speed crack in brittle materials under ultra high loading rate forming through impact loading condition, which is important for understanding the impact damage evolution of ceramics and solid explosives. In this paper, a lattice spring model, which can accurately show the mechanical properties of brittle materials, is used to study the evolution law and mechanism of crack path and crack velocity in brittle materials under ultra high loading rate. This model uses the quantitative parameter mapping method proposed by Gusev to solve the spring stiffness coefficient of the model accurately, and the fracture criterion of the model based on the energy balance principle of Griffith is set up. Simulations show that the path of high speed crack behave the evolution process of a single crack and then micro-branching crack and bifurcation crack finally under the influence of ultra high loading rate. The crack propagation distance between the beginning and the bifurcation decreases with the increase of the loading rate; the crack bifurcation is not immediately after the crack initiation, but as the crack propagation speed reaches the critical value, the expansion path produces more secondary cracks, and then the crack is bifurcated. With the increase of loading rate, the average velocity of cracks gradually increases in three stages, but it shows a different variation after reaching the stable value. In the single crack stage, the steady average velocity is 0.584 times the Rayleigh wave velocity (CR), and there exists only a very small velocity oscillation; the steady value of the average crack velocity corresponding to the differential fork phase is 0.5 times the Rayleigh wave velocity, accompanied by a certain oscillation; The average speed of the stable crack corresponding to the bifurcation stage is much higher than the value of the first two stages, and it can reach 0.638 times the Rayleigh wave speed. It is also accompanied by obvious speed oscillation. The study of the propagation of cracks under different loading rates can predict the internal crack growth rate, propagation direction, and extension distance of brittle materials such as ceramics and rocks.

Estimation of optimal drilling efficiency and rock strength by using controllable drilling parameters in rotary non-percussive drilling

Fundamental rock-drilling studies are aimed at optimizing the drilling efficiency by identifying the optimal drilling conditions and rock drillability. In this study, a field-drilling test is performed using a rotary non-percussive drilling machine equipped with a new drilling-monitoring system to investigate the effects of drilling parameters on the specific energy (SE) and rate of penetration (ROP). During the drilling test, different thrusts (8.5–70 kN) and rotation speeds (40–400 r/min) are applied on a predrilled borehole re-injected with pure concrete. The magnitudes of the thrust, torque, ROP, and rotation speed are measured simultaneously by the new drilling-monitoring system to calculate the changes in SE. A modified SE model, which only includes a few controlled drilling parameters, is then proposed to determine the optimal drilling conditions. The results first show that torque has a linear relationship with thrust but shows no obvious changes with respect to the rotation speed. According to the energy balance principle in rock drilling and the relationship between SE and ROP, the optimal drilling efficiency with the maximum attainable ROP is then innovatively identified around the lower point of the second reduction in SE. In conclusion, the slope of the linear relationship between the thrust and penetration rate per revolution is only related to the rock properties and can be used to define the strength parameters of stratification by using the measured drilling parameters.

Radiation Controls the Interannual Variability of Evaporation of a Subtropical Lake

AbstractDoes lake evaporation increase or decrease under the scenario of climate warming? This paper aims to answer this question by investigating the controlling mechanism of interannual variations in lake evaporation at a subtropical lake. The research methodology is based on continuous eddy covariance measurement over >7 years and a diagnostic analysis using the surface energy balance principle. The results indicate that lake evaporation was enhanced mainly by increasing energy inputs including solar radiation and incoming longwave radiation and was weakened by surface feedback through outgoing longwave radiation. The incoming longwave radiation was positively correlated with cloud cover. Bowen ratio and surface albedo had slight effect on the change of lake evaporation. The annual lake evaporation can be predicted by the Priestly‐Taylor model using a larger coefficient of 1.39 than the original value of 1.26, suggesting that advection or entrainment in the atmospheric boundary layer may play a role in lake evaporation.

Lisähuomioita energiataseiden käytöstä virtauslaskennassa

Artikkeli on täydennys tämän lehden aikaisempaan energiataseiden käyttöä koskevaan artikkeliin. Mekaanisen energian taseen periaatteessa kokoonpuristuvassa virtauksessa esiintyvä niin sanottu kokoonpuristumistermi otetaan mukaan tarkasteluun. Eräs havainnollistava esimerkkitapaus käydään yksityiskohtaisesti läpi. Lisäksi esitetään kritiikkiä virtauslaskennan esityksissä ilmeneviin epätäsmällisyyksiin, joita saattaa esiintyä energiatarkastelujen yhteydessä.

IoT Based Root Stress Detection for Lettuce Culture Using Infrared Leaf Temperature Sensor and Light Intensity Sensor

Root stress is a big problem for lettuce farming in tropical climates, especially temperature root stress. Black root rot, a final stage of the temperature root stress, leads to huge production loss. This paper presents the IoTs based root stress detection system for lettuce cultures. The proposed detection algorithm is based on the leaf energy balance and transpiration patterns. Unlike image sensors based detection methods, leaf energy balance principle and transpiration patterns measured from a lettuce leaf are considered as the key features to address the lettuce root stress conditions. The challenge of detecting lettuce stress by using a leaf sensor is to estimate the non-linear function of stomatal conductance. This paper has clarified the concept of detecting lettuce root stress using the transpiration patterns as well. Graphically, the combination of infrared temperature and light intensity sensors is appropriate to deal with the lettuce root stress detection. The proposed detection algorithm has been designed to detect three conditions of root stress problems: normal, root stress, and black root rot conditions. The infrared sensors are very suitable for the sensitive leaf like lettuce. To evaluate the proposed leaf sensor, the experiments are set up to show that the proposed detection algorithm can accurately detect the temperature root stress in different conditions. Moreover, the detection algorithm based leaf area index (LAI) has been discussed to the proposed detection algorithm. In addition, the performance of the proposed detection algorithm has been compared to the LAI based algorithm. The detection accuracy of the proposed detection method is 95% with different root stress conditions.

A non-isothermal thermodynamically consistent phase field model for damage, fracture and fatigue evolutions in elasto-plastic materials

This paper presents a general thermodynamically consistent non-isothermal phase field framework to model effects of damage, fracture and fatigue evolutions in elasto-plastic materials under the hypothesis of small strains. The proposed methodology is obtained from the principle of virtual power, energy balance and second law of thermodynamics in the form of a generalized Clausius–Duhem inequality for entropy. Aspects of the energy degradation functions are thoroughly investigated for an isotropic elasto-plastic material with viscous dissipation and constant specific heat. A new combined degradation function is proposed to degrade both elastic and plastic energy densities as an alternative to the classical degradation functions. Our conceptual framework leads to thermodynamically consistent models that may include contributions not usually considered in the literature, as temperature and inertia effects as well as time-rate dependent processes. The governing nonlinear transient equations obtained are solved adopting a semi-implicit time integration scheme combined with the classical Newton–Raphson iterative procedure. Results for an I-shaped specimen made of 7075-T7351 aluminum alloy under different conditions are presented. The proposed model is able to reproduce qualitative and quantitatively the ductile fracture and the fatigue phenomena. In particular for fatigue, both the S–N experimental data and the Paris crack growth curve over cycles are recovered. In addition, the cycle jump strategy reduces four times the CPU time for fatigue simulations.

Energy efficiency of membrane distillation: Simplified analysis, heat recovery, and the use of waste-heat

Membrane distillation (MD) is a thermal desalination process that is advantageous due to its ability to harness low-grade waste heat to separate highly saline feedstock. However, like any thermal desalination process, the energy efficiency depends on the ability to recover latent heat from condensation in the distillate. In direct contact MD (DCMD), this can be achieved by integrating a heat exchanger (HX) to recover latent heat stored in the distillate stream to preheat the incoming feed stream. Based on the principle of equal heat capacity flows, we derive a simple and intuitive expression for the optimal flow rate ratio between the feed and distillate streams to best recover this latent. Following the principle of energy balance, we derive simple expressions for the specific thermal energy consumption (SECth) and gained output ratio (GOR) of DCMD with and without a coupled HX for latent heat recovery, revealing an intuitive critical condition that indicates whether DCMD should or should not be coupled with HX. As MD is attractive for its ability to use low-grade waste heat as a heat source, we also evaluate the energy efficiency of DCMD powered by a waste heat stream. A waste heat stream differs fundamentally from a conventional constant-temperature heat source in that the temperature of the waste heat stream decreases as heat is extracted from it. We discuss the implication of this fundamental difference on energy efficiency and how we should analyze the energy efficiency of DCMD powered by waste heat streams. A new metric, namely specific yield, is proposed to quantify the performance of DCMD powered by waste heat stream. Our analysis suggests that, for a single-stage DCMD powered by a waste heat stream, whether implementing latent heat recovery or not only affects conventional metrics for energy efficiency (e.g. SECth and GOR) but not the specific yield. Overall, this analysis presents an intuitive and important framework for evaluating and optimizing energy efficiency in DCMD.

Real-Time Determination of Overall Heat Transfer Coefficient from the Seebeck Effect by Using Adaptive Learning-Rate Optimization

It is challenging to determine the actual overall heat transfer coefficient under thermal conditions during processes. In a conventional approach, they are obtained as a constant with the empirical formula for the given conditions. In this study, the Adaptive moment estimation (Adam) technique is investigated for adaptive learning-rate optimization in the real-time determination of the overall heat transfer coefficient via the Seebeck effect in the thermoelectric modules. Two thermoelectric modules detect heat transfer as solid surfaces exposed to the outdoor air. The principle of energy balance and the Seebeck effect determine the overall heat transfer coefficients over time. The heating/cooling process of a copper plate is considered with exposure to the outdoor air. The overall heat transfer coefficient is determined with the proposed methodology over time. The temperature of the copper plate is numerically determined by the mathematical models with the obtained values of the overall heat transfer coefficient. It is confirmed that the calculated values of temperature are close to the measured values, with RMSE = 0.07 °C.

Quantifying configuration-entropy change during plastic flow of metallic glasses

Based on the energy balance principle for a serrated shear event, the configuration entropy change of a plastic flow within a shear band in metallic glasses is precisely quantified. With this method, we successfully investigated the evolution of entropy change with the plastic displacement/strain. It was found that the evolution of entropy changes for various metallic glasses follows a unified linear relation. The experimental result is consistent with the thermodynamic deduction from the free volume theory, corroborating the nature of shear-induced dilation for the plastic flow of metallic glasses.

Micro indentation fracture of cement paste assessed by energy-based method: The method improvement and affecting factors

This paper reported an improved energy-based method to assess the fracture properties of a hardened cement paste (HCP) by using micro indentation technique. The model was initiated by the additionally generated fracture energy that is assumed to be averagely distributed during indentation, and only involves the load–displacement curves that follow power functions. An explicit equation for estimating the plastic energy considering the effect of holding procedure that has not been considered before was established, which, together with the principle of energy balance, allows us to assess the fracture energy, energy release rate and fracture toughness of the HCP. The accuracy, reliability and robustness of the model were validated by the experimental data with changing the maximum load, loading speed and holding time. Overall, the micro fracture testing method developed here provides an efficient way to assess the fracture properties of cement-based materials in micro scale.

Nutrition-Related Mobile Apps in the China App Store: Assessment of Functionality and Quality.

BackgroundThere are an increasing number of mobile apps that provide dietary guidance to support a healthy lifestyle and disease management. However, the characteristics of these nutrition-related apps are not well analyzed.ObjectiveThis study aimed to evaluate the functionality and quality of nutrition-related apps in China.MethodsMobile apps providing dietary guidance were screened in the Chinese iOS and Android app stores in November 2017, using stepwise searching criteria. The first screening consisted of extracting information from the app descriptions. Apps that (1) were free, (2) contain information on diet and nutrition, and (3) were last updated after January 1, 2016, were downloaded for further analysis. Nutritional functionalities were determined according to the Chinese Dietary Guidelines framework. Market-related functionalities were developed from previous studies and tailored to downloaded apps. The quality of apps was assessed with the user version of the Mobile App Rating Scale (uMARS).ResultsOut of 628 dietary guidance apps screened, 44 were nutrition-related. Of these, guidance was provided on diet exclusively (11/44, 25%), fitness (17/44, 39%), disease management (11/44, 25%), or maternal health (5/44, 11%). Nutritional functionalities included nutritional information inquiry (40/44, 91%), nutrition education (35/44, 80%), food record (34/44, 77%), diet analysis (34/44, 77%), and personalized recipes (21/44, 48%). Dietary analysis and suggestions mainly focused on energy intake (33/44, 75%) and less on other factors such as dietary structure (10/44, 23%). Social communication functionalities were available in 42 apps (96%), user incentives were supported in 26 apps (59%), and intelligent recognition technology was available in 8 apps (18%). The median score for the quality of the 44 apps, as determined on a 5-point uMARS scale, was 3.6 (interquartile range 0.7).ConclusionsMost nutrition-related apps are developed for health management rather than for dietary guidance exclusively. Although basic principles of energy balance are used, their nutritional functionality was relatively limited and not individualized. More efforts should be made to develop nutrition-related apps with evidence-based nutritional knowledge, comprehensive and personalized dietary guidance, and innovative technology.

Combined velocity and position control of large inertial hydraulic swing mechanism considering energy balance of supply and demand

Abstract The position of a conventional large inertial hydraulic swing system is controlled by the operator-in-loop, the production efficiency of which is poor, and the repetitive positioning precision is low owing to slow human reactions. To address this problem, this study proposes a combined velocity and position control strategy based on the independent metering control system. In this method, it is not necessary to change the conventional operation mode. If the required rotary angle is the same in each swing process, a precise desired position is provided as the input signal for closed-loop position control. If the required rotary angle is random, in order to be compatible with the handle operation mode used in mobile machines, a handle signal integral control method is proposed. Moreover, velocity feedback is used to improve the control accuracy, while differential pressure feedback is used to reduce the position overshoot. Meanwhile, to improve the system dynamic characteristics during the braking process, an energy balance principle is applied. The proposed strategy is verified with simulation and a 6 t hydraulic excavator. The simulation and experimental results demonstrate that a higher positioning accuracy can be achieved with different desired angular displacements. Furthermore, the position overshoot, and velocity and pressure fluctuation are avoided, while the dynamic characteristics are clearly improved.

Phenomenology of droplet collision hydrodynamics on wetting and non-wetting spheres

In this study, the spreading characteristics of water droplets impacted on a solid spherical target have been investigated experimentally and theoretically. Droplet impact and postimpact feature studies have been conducted on hydrophilic and superhydrophobic spherical surfaces. Effects of the impact Weber number and target-to-drop diameter ratio on the spreading hydrodynamics have been discussed. Postcollision dynamics are explored with side and top views of impaction phenomenon using a high speed imaging technique. The morphological outcome of this impingement process has been quantitatively discussed with three geometric parameters, namely, liquid film thickness at the north-pole of the target surface, spread factor, and the maximum spread angle. Observations revel that spread factor and the maximum spread angle increases with the decrease in the size of the spherical target, whereas opposite of this is true for liquid film thickness at the north-pole of the target surface. Temporal variations of liquid film thickness at the north pole of the target have been plotted and found in agreement with the theoretical predictions made in the earlier studies. Finally, a mathematical model based on the energy balance principle has been proposed to predict the maximum spread angle on spherical targets. The theoretical values are found in good agreement with the experimental results for a wide range of spherical diameters studied. The findings may have implications toward a better understanding of fluid wetting, spraying, and coating behavior of complex shapes and geometries.

Stability Research Considering Non-Linear Change in the Machining of Titanium Thin-Walled Parts.

Aiming to solve the problem whereby the damping process effect is significant and difficult to measure during low-speed machining of titanium alloy thin-walled parts, the ploughing coefficient of the flank face is obtained based on the frequency-domain decomposition (FDD) of the measured vibration signal and the energy balance principle, and then the process-damping prediction model is obtained. Aiming to solve the problem of non-linear change of dynamic characteristics of a workpiece caused by the material removal effect in the machining of titanium alloy thin-walled parts, a prediction model of dynamic characteristics of a workpiece is established based on the structural dynamic modification method. Meanwhile, the effect of material removal on the process-damping coefficient is studied, and the internal relationship between the process-damping coefficient and the dynamic characteristics of the workpiece is revealed. The stability lobe diagram is obtained by the full discretization in the titanium alloy milling process. The correctness of the model and stability prediction is verified by experiments under different working conditions. It is found that the coupling characteristics of process-damping and workpiece dynamic characteristics control the stability of the milling process. The research results can provide theoretical support for accurate characterization and process optimization of titanium alloy thin-walled workpiece milling.

Dynamic modeling of a dielectric elastomeric spherical actuator: an energy-based approach

ABSTRACT The present work is concerned with the dynamic modeling of a dielectric elastomeric spherical actuator subjected to an inflation pressure and an electrical DC step voltage across the actuator wall. Herein, we report an alternative method to obtain the static and dynamic instability parameters based on establishing the energy balance principle at the point of maximum stretch in an oscillation cycle. Additionally, we proposed a new energy density function, which accounts the electrostriction phenomenon for a class of an incompressible isotropic dielectric elastomeric material. We first deduce an explicit analytical Lagrange equation of motion based on the Hamiltonian principle of least action for a dielectric elastomeric spherical actuator. Further, a quantitative comparison is presented between the static and dynamic instability parameters. Finally, the numerical results obtained from the developed equation of motion are discussed in line with the parallel results presented in the literature. In summary, the present study brings out the effect of an inflation pressure on the onset of dynamic response in a dielectric elastomeric spherical actuator. In addition, the proposed method is so versatile, and can also be used in other systems of interest.