Energy Conservation Method Research Articles

Convection linearization of energy conservative implicit method for incompressible turbulence simulations

Time accurate implicit methods for unsteady turbulent flows are proposed based on the energy conservative finite difference method of the incompressible Navier-Stokes equations with convection linearization. The standard and Runge-Kutta type high-order temporal linearizations are introduced for the convective term. The time increment independent solution of turbulence is explored for the linearized coupled governing equations. Coupled and uncoupled (splitting) algorithms are then considered to isolate the effect of splitting error. The simulation examples are periodic inviscid, Taylor-Green vortex, and DNS of turbulent plane channel flows. These are test cases for the energy conservation property, the order of accuracy, and the time increment independence of turbulence statistics, respectively. The second order accurate two-stage convection linearized semi-implicit Runge-Kutta (SIRK2L) method works very well and has almost the same conservation property as the fully (spatio-temporally) conservative nonlinear method based on the implicit midpoint (IM) time marching. The second place is the standard third order convection linearization (IM3L) method. The second order convection linearization method (IM2L) is not recommended, although it may be preferred by the point of view of formal accuracy. The effect of splitting error is significant, and the numbers of coupling iteration of 5 and 10 are required for SIRK2L and IM3L methods with the uncoupled (splitting) algorithm, respectively, for the turbulent plane channel flow simulation. Finally, the DNS of forward-facing step flow is carried out as an example of practical problems.

Energy-preserving methods for non-smooth nonlinear Schrödinger equations

In this paper, we propose energy-preserving methods for nonlinear Schrödinger equations (NLSEs) with delta potentials. We reformulate the prototype model equation into an infinite-dimensional Hamiltonian system (IDHS), apply the average vector field (AVF) method to the time, and obtain the corresponding temporal semi-discrete system which possesses exact energy preservation properties. Then we apply the immersed interface method (IIM) to discretize the space of the semi-discrete system and get a scheme of full-discrete systems. The scheme preserves the discrete total energy precisely and admits, however, just first-order local accuracy. In order to improve the accuracy, we give some modifications for the scheme and get a second-order method as desired. The precise preservation of the discrete energy is rigorously proved for the modified scheme. Extensive numerical experimentation for cases of single- and double-delta potentials is examined and discussed, and different comparisons are made to validate the theoretical analyses. Together with the normalization conservation law and some convergence behaviours, it demonstrates that our methods are considerably good in the long-term calculations, especially the superiorities of preserving the energy conservation laws.

Screening, identification, and degradation characteristics of 3-methylindole degrading bacteria

3-Methylindole is a major component of organic pollutants in livestock compost, which can contribute to the deterioration of the environment in livestock farms and their surrounding areas. This study demonstrates that using microorganisms to degrade 3-methylindole is an effective method for energy conservation and environmental protection. The microbe capable of efficiently degrading 3-methylindole was isolated and screened from fecal samples. The isolated bacteria were identified as Acinetobacter oleivorans after morphological characterization and 16S rRNA sequencing. This project demonstrated that 3-methylindole was completely degraded under optimal conditions (initial concentration of 3MI: 100 mg/L, 30°C, pH8.0, and shaking at 160 rpm for 48 h). N2-Acetyl-L-ornithine, Phenylacetaldehyde, Phenylacetic acid, Indole-3-carboxylic acid, and Indole-3-carboxaldehyde were the primary metabolites of this degradation process. This study provides a theoretical foundation for other microbe-mediated environmental remediation approaches as well as a basis for future work to apply bacteria that degrade 3-methylindole for the purification of polluted environments. It has a promising application in the control of malodorous gas pollution in the large-scale livestock and poultry breeding industries.

Hydrogen production from methane via liquid phase microwave plasma: A deoxidation strategy

In this paper, in order to improve hydrogen production, the effect of dissolved oxygen (DO) on methane (CH4) reforming was studied by liquid phase microwave discharge firstly. DO was reduced by deducing pressure and gas replacement, and the reaction mechanism was researched by radical detection. It was revealed that reducing DO can improve hydrogen (H2) yield and H2 selectivity and energy efficiency of hydrogen production. When microwave power was 900 W and the DO was decreased from 4.82 mg/L to 0.65 mg/L, the production and selectivity of H2 increased by 21.3 % and 22.6 % respectively, and the energy efficiency of hydrogen production increased by 33.1 %. Through the study on the characteristics of discharge radicals, it was concluded that ∙H extraction and ∙H coupling reaction and ∙OH oxidation ∙CHX are the main ways to produce hydrogen. The existence of DO affects the formation of H2 by limiting the decomposition of water molecules. In addition, the reduction of DO can improve the stability of discharge. These results indicate that reducing the DO can be a simple, effective and energy conservation method to increase the selectivity of target products in the liquid phase discharge reforming of CH4.

Explicit exactly energy-conserving methods for Hamiltonian systems

For Hamiltonian systems, simulation algorithms that exactly conserve numerical energy or pseudo-energy have seen extensive investigation. Most available methods either require the iterative solution of nonlinear algebraic equations at each time step, or are explicit, but where the exact conservation property depends on the exact evaluation of an integral in continuous time. Under further restrictions, namely that the potential energy contribution to the Hamiltonian is non-negative, newer techniques based on invariant energy quadratisation allow for exact numerical energy conservation and yield linearly implicit updates, requiring only the solution of a linear system at each time step. In this article, it is shown that, for a general class of Hamiltonian systems, and under the non-negativity condition on potential energy, it is possible to arrive at a fully explicit method that exactly conserves numerical energy. Furthermore, such methods are unconditionally stable, and are of comparable computational cost to the very simplest integration methods (such as Störmer-Verlet). A variant of this scheme leading to a conditionally-stable method is also presented, and follows from a splitting of the potential energy. Various numerical results are presented, in the case of the classic test problem of Fermi, Pasta and Ulam and for nonlinear systems of partial differential equations, including those describing high amplitude vibration of strings and plates.

Robust adaptive filtering algorithms based on the half‐quadratic criterion

Recently, robust adaptive filtering algorithms have attracted the interest of researchers and have been extensively studied. However, most of these methods suffer from the non-convexity of their performance surfaces, which results in reduced convergence rate and filtering accuracy. To address this problem, we present a novel robust half-quadratic criterion (HQC) adaptive filtering algorithm by utilizing a convex cost function. In contrast with conventional methods, the proposed HQC can introduce a more effective performance surface, allowing a gradient-based strategy to provide significant performance improvements in convergence speed and robustness against impulsive noise. Furthermore, to enhance the performance of the HQC adaptive filter, a variable step-size (VSS) version, the VSS-HQC algorithm, has also been introduced. Using the energy conservation method, the theoretical expressions for the transient, steady-state, and tracking performance analysis of the proposed HQC algorithm are studied under the Gaussian noise assumption. Then, we examined the theoretical analysis of the HQC using various numerical simulations for system identification to validate the findings. Finally, we compared the performance of the HQC and VSS-HQC algorithms to their competitors in both Gaussian noise and non-Gaussian noise scenarios through numerical experiments.

A new freezing model of sessile droplets considering ice fraction and ice distribution after recalescence

In this work, a new three-dimensional sessile droplet freezing model, involving the ice fraction and ice distribution after the droplet recalescence, is established based on the many-body dissipative particle dynamics with the energy conservation method for the first time. The proposed model is verified by comparing it with experimental results, and the accuracy of this model increases as the ice distribution becomes more non-uniform after recalescence. Furthermore, the effects of surface contact angle, droplet volume, surface temperature, and droplet supercooling degree on the freezing process are investigated in detail. The numerical results demonstrate that the angle of ice tips maintains a constant under various conditions. The upper and lower limits of solidification time under specific conditions are derived, and the droplet solidification time decreases linearly with the increase in supercooling. In addition, the average droplet solidification rate decreases with the increase in droplet volume, contact angle, and surface temperature, and the surface temperature is demonstrated to have the greatest influence on the solidification rate. Emphatically, we put forward an empirical formula, as a function of droplet volume, contact angle, droplet supercooling degree, and surface temperature, to predict the freezing time of a sessile supercooled droplet.

The successful integration of anammox to enhance the operational stability and nitrogen removal efficiency during municipal wastewater treatment

The anaerobic ammonium oxidation (anammox) process is a promising method for carbon reduction and energy conservation. However, the advantages of its application in municipal wastewater treatment have not been completely revealed. Stable nitrogen removal was successfully achieved in the anaerobic/aerobic/anoxic (AOA) process by directly integrating stable anammox. Over a 200 + day operating period, the abundance of anammox bacteria (3.1 ± 0.9 × 108 copies/gSS) and anammox activity (0.32 ± 0.07 mgN/(gSS·h)) remained high, despite a temperature decrease (27.8–17.2 °C) and fluctuating carbon-nitrogen (C/N) ratio (1.6–5.0). A stable nitrogen removal efficiency of 87.1 ± 2.5 % was successfully maintained, because the anammox activity compensated for the effect of low temperatures and low C/N ratios on the nitrification and denitrification. Further analysis found that anammox accounted for 52.6 %-57.5 % of N2 production, and the rest was through nitrification–denitrification. The stable anammox reaction was mainly due to the limitation of oxygen and carbon sources and the stable supply of nitrite by endogenous denitrification. Overall, these findings confirmed that the stability and efficiency of nitrogen removal from municipal wastewater could be increased by integrating anammox under appropriate conditions.

A multi-scale analysis on reinforcement origin of static and dynamic mechanics in graphene-elastomer nanocomposites

The graphene reinforced nanocomposites have been attracting considerable attention owing to their excellent mechanical and physical properties. Herein we systematically develop a multiscale scheme of graphene-polyisoprene nanocomposites, in which the effective coarse-grained potentials of polyisoprene (PI), graphene, interface derived from the all-atom models using inverse Boltzmann iteration along with pressure correction, strain energy conservation and energy matching method during graphene pull-out testing respectively. Graphene dispersion, PI entanglement network and PI-graphene network structures are quantitively characterized by the interlayer distance distributions of graphene sheets, conformity of PI chains with the entanglement theory and the conformation of polymer chains adjacent to graphene surfaces respectively. Particularly, there are three regimes of reptation dynamics, chain confinement, sufficient network of PI chains in terms of various graphene loading correspond to the dispersion, percolation and aggregation of graphene. In the rubbery region the initial high reinforcement of shear modulus is caused by trapped conformation at high frequency, while at low frequencies, the gained conformational freedom leads a relatively low reinforcement, which increases exponentially with a reduced weight fraction. Generally, our multi-scale strategy may be readily extended to other kinds of filling models, and this work could guide the rational design and preparation of nanocomposites.

A Conservative and Energy Stable Discontinuous Spectral Element Method for the Shifted Wave Equation in Second Order Form

In this paper, we develop a provably energy stable and conservative discontinuous spectral element method for the shifted wave equation in second order form. The proposed method combines the advantages and central ideas of the following very successful numerical techniques: the summation-by-parts finite difference method, the spectral method, and the discontinuous Galerkin method. We prove energy stability and the discrete conservation principle and derive error estimates in the energy norm for the (1+1)-dimensions shifted wave equation in second order form. The energy-stability results, discrete conservation principle, and the error estimates generalize to multiple dimensions using tensor products of quadrilateral and hexahedral elements. Numerical experiments, in (1+1)-dimensions and (2+1)-dimensions, verify the theoretical results and demonstrate optimal convergence of $L^2$ numerical errors at subsonic, sonic and supersonic regimes.

Long-Time Oscillatory Energy Conservation of Total Energy-Preserving Methods for Highly Oscillatory Hamiltonian Systems

Long-Time Oscillatory Energy Conservation of Total Energy-Preserving Methods for Highly Oscillatory Hamiltonian Systems

Arbitrary high-order methods for one-sided direct event location in discontinuous differential problems with nonlinear event function

In this paper we are concerned with numerical methods for the one-sided event location in discontinuous differential problems, whose event function is nonlinear (in particular, of polynomial type). The original problem is transformed into an equivalent Poisson problem, which is effectively solved by suitably adapting a recently devised class of energy-conserving methods for Poisson systems. The actual implementation of the methods is fully discussed, with a particular emphasis to the problem at hand. Some numerical tests are reported, to assess the theoretical findings.

Energy saving and high efficiency production oriented forward-and-reverse multidirectional turning: Energy modeling and application

The energy modeling has been recognized as an effective analytical methodology and management tool that helps to predict the energy consumption and to manage the efficiency and performance of energy utilization. With a wide distribution and large amount of energy consumption at a low efficiency, the mechanical manufacturing industry has considerable energy saving potential. In this study, a new method of energy conservation and high efficiency production oriented multidirectional turning is proposed to overcome the performance deficiencies of traditional turning in the mechanical manufacturing industry. Based on energy and production performance analysis, the energy consumption model of the forward-and-reverse multidirectional turning is established through the process stage-oriented modeling method. Besides, the case study indicates the high (more than 97%) accuracy of the proposed energy consumption model for forward-and-reverse multidirectional turning. This study contributes to a new production method and energy models to reduce energy consumption and improve production efficiency.

Outdoor PM<sub>2.5</sub> air filtration: optimising indoor air quality and energy

Human inhalation exposure to fine particulate matter (PM_2.5), including the PM_2.5 of outdoor origin, predominantly occurs indoors. To limit outdoor PM_2.5 penetration into buildings, ventilation standards often require the filtration of outdoor air with a minimum efficiency. Nevertheless, the PM_2.5 filter selection recommended by the standards is based on the annual average outdoor concentrations without considering seasonal or diurnal fluctuations. This could result in a waste of energy or elevated indoor PM_2.5 exposures. Representative outdoor PM_2.5 data from 37 cities worldwide in conjunction with a simulated office building are used to examine the impact of filtration strategies on indoor PM_2.5 levels and the fan’s energy consumption. Two energy-saving methods are tested: (1) the optimum filter selection that maintains the indoor PM_2.5 below the World Health Organization’s (WHO) air quality guidelines; and (2) the baseline filter recommended by standards in combination with a filter bypass. Relative to a standard recommended baseline case, the two applied methods could reduce energy demand by between 4% and 17%. This indicates that the outdoor air is over-filtered in the majority of the investigated cities. In cities with low-to-moderate outdoor PM_2.5 levels, using a filter bypass can be an effective energy conservation method without compromising PM_2.5 exposures indoors. <em><strong>Practice relevance</strong></em> Protecting building occupants from outdoor originating PM_2.5 without a high energy penalty is not a simple task. The majority of recommendations for ventilation system design typically do not consider temporal variation in outdoor PM_2.5. This study’s data suggest that outdoor air filtration efficiencies required by building standards are not sufficient to protect the building occupants living in severely polluted areas. In these areas, outdoor air filtration should be supplemented with other measures to limit outdoor PM_2.5 penetration. In areas with low or intermittent outdoor PM_2.5 levels, bypassing the filter can significantly reduce the energy consumption from fans without compromising indoor air quality. The energy-saving potential increases with the increase of outdoor air quality. This study suggests that improved outdoor air filtration can be achieved by a stronger reliance on continuous outdoor air quality data recorded on site.

Arbitrarily high-order energy-conserving methods for Poisson problems

In this paper, we are concerned with energy-conserving methods for Poisson problems, which are effectively solved by defining a suitable generalization of HBVMs, a class of energy-conserving methods for Hamiltonian problems. The actual implementation of the methods is fully discussed, with a particular emphasis on the conservation of Casimirs. Some numerical tests are reported, in order to assess the theoretical findings.

Energy-preserving methods for guiding center system based on averaged vector field

We propose a family of energy-preserving methods for guiding center dynamics by perceiving its Hamiltonian nature based on the averaged vector field. The energy conservation, symmetric property, and algebraic order of these methods are studied. Furthermore, higher order energy-preserving methods are systematically introduced by using a composition technique. Two second order and two fourth order symmetric energy-preserving methods are constructed and applied to simulate the guiding center motion in both the dipole magnetic field and the tokamak magnetic field. Numerical results show that these methods have significant superiorities in energy conservation compared with the existing canonicalized symplectic methods of the corresponding orders. The numerical case of the guiding center motion in the toroidal acceleration electric field exhibits favorable long-term conservative properties of the new methods to the particle-field system, while the kinetic energy of guiding centers keeps increasing. These energy-preserving methods based on the averaged vector field can be applied to any non-canonical Hamiltonian system.

Novel resonance stability criterion for the 2D magnetically levitated servo-proportional valve

The leakage of the pilot stage of the 2D valve mainly depends on the size of its initial opening. According to the Routh criterion, the pilot stage of the two-dimensional magnetically levitated servo-proportional valve (2D-MSP valve) needs to be designed to have certain positive values to increase the damping ratio to improve valve stability, which leads to the leakage flow representing a non-negligible power loss. In order to reduce leakage flow and achieve goal of energy saving, this paper presents a novel resonance stability criterion by considering nonlinear characteristics of the fluid dynamic system. First, the 2D-MSP valve is regarded as a three-way valve-controlled differential cylinder system. Based on the frequency response of the resonance state, the energy conservation method is used to solve the flow “backfilling” area, the motion equation of the cylinder piston (valve spool displacement) and the pressure waveform of the sensing chamber under different opening and pressure amplitude ratio. Then, the analytical expression of the resonance peak amplitude is obtained and the resonance stability criterion is deduced. The result is compared with the Routh stability criterion, which illustrates that the positive openings of the pilot stage can be reduced to one-third of the original value. The prototype valve is then designed and manufactured based on the resonance stability criterion. The dynamic and static characteristics under different system pressures are measured. Experimental results show that the prototype valve is an over-damped system without any overshoot, which has excellent working stability, and its static and dynamic performance can meet the demands of the industry servo-proportional control system. The research work validates the effectiveness of the proposed resonance stability criterion.

Impact of climate change on fruit and vegetable crops and its mitigation strategies

The biggest challenge to humanity in the twenty-first century is global warming and climate change. Climate change reduces production and efficiency, while also increasing environmental stress on fruit and vegetable crops. Increased temperature, decreased irrigation water supply, flooding, and salinity are thought to be the limiting factors in improving fruit and vegetable productivity. The melting of the Himalayan ice cap would minimise the cooling effect needed for the flowering of many horticultural crops such as apples, saffron, rhododendrons, and orchids, among others. Commercial horticulture plant development especially that grown in open fields will be severely harmed. Integrated approaches such as fertiliser and tillage, residue management, water management, mulching, enhanced pest management, and breeding approaches such as production of genotypes resistant to high temperatures, salinity, modification of current horticultural practices, and increased use of greenhouse technology are to be adopted. Conservation agriculture, renewable energy, forest and water conservation, reforestation, and other methods are the most important.

Construction of the Energy-Preserving Methods for the Conservative System and Unconditional Energy Stable Methods for the Dissipative System

Construction of the Energy-Preserving Methods for the Conservative System and Unconditional Energy Stable Methods for the Dissipative System

Precision improvement method for onsite performance measurement of variable refrigerant flow system

With the widespread use of variable refrigerant flow (VRF) systems in various commercial and residential buildings, the performance and efficiency of VRF systems have attracted considerable attention in recent years. Although the compressor set energy conservation (CSEC) method exhibits a high accuracy in most cases of VRF performance measurement, several problems limit its accuracy. To improve the accuracy of the CSEC method for performance measurement, two methods are proposed to resolve the measurement difficulty of two-phase suction. The accuracies of the proposed methods are experimentally validated using three VRF configurations. In the experiments, the relative errors for the compressor isentropic efficiency-based method range from ±15%, ±17%, and ±18% for the three configurations. For the compressor volumetric efficiency-based method, the relative errors of the three configurations range from ±15%, ±16%, and ±16%, respectively. The capacity distribution and heat loss of the VRF system are measured and analyzed in the experiment. Heat losses from closed indoor units range from 0% to 21.5% in different cases in the cooling mode and from 0% to 31.1% in the heating mode. Additionally, an estimation method for the temperature measurement deviation is proposed to improve the precision of performance measurement.