A mechanistic model for simulating methane emissions from unstirred liquid manure storages

2010 ◽  
Vol 90 (3) ◽  
pp. 507-516 ◽  
Author(s):  
Q. Huang ◽  
O. Wohlgemut ◽  
N. Cicek ◽  
J. France ◽  
E. Kebreab
Keyword(s):  
Mechanistic Model ◽  
Correlation Coefficients ◽  
Methanogenic Bacteria ◽  
Integration Step ◽  
State Variables ◽  
Liquid Manure ◽  
Step Size ◽  
Intergovernmental Panel ◽  
Manure Storage ◽  
Time Courses

The objective of the study was to develop a mechanistic model of methane (CH4) producing processes in unstirred conditions with potential application for estimating CH4 emissions from anaerobic manure storage facilities. Although models for describing anaerobic digestion processes are available, they largely relate to anaerobic digesters, and do not directly apply to the prediction of CH4 emissions from liquid manure storage. Based on extant models, six biochemical steps were described: hydrolysis, acetogenesis, hydrogenogenesis, homoacetogenesis, hydrogenous methanogenesis and acetic methanogenesis, performed by five bacterial groups. The model contains six state variables, and mass flow is mostly generated and quantified using bacterial kinetics. The model was coded in acslX and a fourth-order Runge-Kutta method with an integration step size of 0.05 d was used for numerical integration. The time courses of CH4 production and volatile fatty acid (VFA) concentration of two laboratory-scale liquid manure storage tanks, both filled with liquid sow manures and running in unstirred and constant 25°C conditions, were well predicted, with correlation coefficients over 0.90. Discrepancies between predicted and measured CH4 production and VFA concentration were mainly due to random variation of observed data. The model was sensitive to parameters describing hydrolysis and the kinetics of acetogenic and acetate methanogenic bacteria. Simulations based on the Intergovernmental Panel on Climate Change model (Tier II) predicted 260 g CH4 kg-1 volatile solids (VS, assuming maximum CH4 producing capacity of 0.48 and methane conversion factor of 80%), whereas the measured value was 78.3 g CH4 kg-1 VS after 146 d and the mechanistic model predicted 74.8 g CH4 kg-1 VS. The model developed in this study appears to be better suited to batch manure storage than the IPCC model.

Stability and Accuracy Analysis of Baumgarte’s Constraint Violation Stabilization Method

1995 ◽  
Vol 117 (3) ◽  
pp. 446-453 ◽  
Author(s):  
S. Yoon ◽  
R. M. Howe ◽  
D. T. Greenwood
Keyword(s):  
Equations Of Motion ◽  
Integration Step ◽  
State Variables ◽  
Stabilization Method ◽  
Lagrange Equations ◽  
Step Size ◽  
Constraint Violation ◽  
Truncation Errors ◽  
Numerical Stability Analysis ◽  
Stability And Accuracy

When Baumgarte’s Constraint Violation Stabilization Method (CVSM) is used in the simulation of Lagrange equations of motion with holonomic constraints, it is shown that, with suitable assumptions on the integration step size h and the eigenvalues (λ’s) of the linearized system, the constraint variables are effectively integrated by the same algorithm as that used for the state variables. A numerical stability analysis of the constraint violations can be performed using this so-called pseudo-integration equation. A study is also made of truncation errors and their modeling in the continuous time domain. This model can be used to determine the effectiveness of various constraint controls and integration methods in reducing the errors in the solution due to truncation errors. Examples are presented to illustrate the use of a higher-order truncation error model which leads to an accurate quantitative steady-state analysis of the constraint violations.

scholarly journals The Effect of Diet and Farm Management on N2O Emissions from Dairy Farms Estimated from Farm Data

Agriculture ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 654
Author(s):  
Simona Menardo ◽  
Giacomo Lanza ◽  
Werner Berg
Keyword(s):  
Diet Composition ◽  
Predictive Power ◽  
Emission Inventory ◽  
Dairy Farms ◽  
Farm Management ◽  
Mitigation Strategies ◽  
N2o Emissions ◽  
Intergovernmental Panel ◽  
Manure Storage ◽  
Animal Diet

The N2O emissions of 21 dairy farms in Germany were evaluated to determine the feasibility of an estimation of emissions from farm data and the effects of the farm management, along with possible mitigation strategies. Emissions due to the application of different fertilisers, manure storage and grazing were calculated based on equations from the IPCC (Intergovernmental Panel of Climate Change) and German emission inventory. The dependence of the N2O emissions on fertiliser type and quantity, cultivated crops and diet composition was assessed via correlation analysis and linear regression. The N2O emissions ranged between 0.11 and 0.29 kg CO2eq per kilogram energy-corrected milk, with on average 60% resulting from fertilisation and less than 30% from fertiliser storage and field applications. The total emissions had a high dependence on the diet composition; in particular, on the grass/maize ratio and the protein content of the animal diet, as well as from the manure management. A linear model for the prediction of the N2O emissions based on the diet composition and the fertilisation reached a predictive power of R2 = 0.89. As a possible mitigation strategy, the substitution of slurry for solid manure would reduce N2O emissions by 40%. Feeding cows maize-based diets instead of grass-based diets could reduce them by 14%.

Wastewater modification processes assessment in a stabilization reservoir

2008 ◽  
Vol 57 (7) ◽  
pp. 1037-1045 ◽  
Author(s):  
G. Mannina ◽  
G. Mancini ◽  
M. Torregrossa ◽  
G. Viviani
Keyword(s):  
Organic Matter ◽  
Performance Optimization ◽  
Flow Reactor ◽  
Batch Reactor ◽  
Mechanistic Model ◽  
Resource Planning ◽  
Treated Wastewater ◽  
State Variables ◽  
Factors Affecting ◽  
Effluent Quality

A semi-empirical mechanistic model able to simulate the dynamics of a stabilization reservoir was developed incorporating both settling of particulate components and chemical/biological processes. Several factors affecting the reservoir effluent quality were taken into account: hydraulics and hydrology, solar radiation, atmospheric reaeration, algae, zooplankton, organic matter, pathogen bacteria, and sediment-water interaction. The model quantifies the specific influence of each factor on effluent quality, evaluating the correlation between the different considered factors. State variables included in the model were: algae, dissolved oxygen, organic matter, zooplankton and indicator bacteria. The model was transferred into a computational code in order to provide a useful and versatile tool for water resource planning management issues. The model was verified by comparing simulated results with full-scale data collected from a small reservoir (Sicily, IT) filled with partially treated wastewater. The reservoir has a volume of 11,000 m3, a maximum depth of 6.3 m and a mean depth of about 5 m. The monitoring period lasted four months during which the reservoir operated in different hydraulics conditions: as a standard batch reactor and as a continuous flow reactor. The model was able to reproduce the behaviour of the principal simulated parameters thus representing a potential tool for the management and performance optimization of these peculiar storage/treatment systems.

Newmark-Beta Method in Discrete Elastic Rods Algorithm to Avoid Energy Dissipation

2019 ◽  
Vol 86 (8) ◽  
Author(s):  
Weicheng Huang ◽  
Mohammad Khalid Jawed
Keyword(s):  
Energy Dissipation ◽  
Time Integration ◽  
Integration Scheme ◽  
Integration Step ◽  
Elastic Rods ◽  
Computationally Efficient ◽  
Step Size ◽  
Time Step ◽  
Time Step Size ◽  
Time Integration Scheme

Discrete elastic rods (DER) algorithm presents a computationally efficient means of simulating the geometrically nonlinear dynamics of elastic rods. However, it can suffer from artificial energy loss during the time integration step. Our approach extends the existing DER technique by using a different time integration scheme—we consider a second-order, implicit Newmark-beta method to avoid energy dissipation. This treatment shows better convergence with time step size, specially when the damping forces are negligible and the structure undergoes vibratory motion. Two demonstrations—a cantilever beam and a helical rod hanging under gravity—are used to show the effectiveness of the modified discrete elastic rods simulator.

scholarly journals Correlation of Primate Caudate Neural Activity and Saccade Parameters in Reward-Oriented Behavior

2003 ◽  
Vol 89 (4) ◽  
pp. 1774-1783 ◽  
Author(s):  
Hideaki Itoh ◽  
Hiroyuki Nakahara ◽  
Okihide Hikosaka ◽  
Reiko Kawagoe ◽  
Yoriko Takikawa ◽  
...  
Keyword(s):  
Neuronal Activity ◽  
Time Window ◽  
Correlation Coefficients ◽  
Saccade Latency ◽  
Major Type ◽  
Projection Neurons ◽  
Saccade Velocity ◽  
Trial Basis ◽  
The Mean ◽  
Time Courses

Changes in the reward context are associated with changes in neuronal activity in the basal ganglia as well as changes in motor outputs. A typical example is found in the caudate (CD) projection neurons and saccade parameters. It raised the possibility that the changes in CD neuronal activity contribute to the changes in saccade parameters. To examine this possibility, we calculated the correlation coefficients (CORs) of the firing rates of each neuron with saccade parameters (peak saccade velocity and latency) on a trial-by-trial basis. We then calculated the mean CORs separately for two CD populations: reward-enhanced type neurons (RENs) that showed enhanced activity and reward-depressed type neurons (RDNs) that showed depressed activity when reward was expected. The activity of RENs was positively correlated with the saccadic peak velocity and negatively correlated with the saccade latency. The activity of RDNs was not significantly correlated with the saccade parameters. We further analyzed the CORs for RENs, a major type of CD neurons. First, we examined the time courses of the CORs using a moving time window (duration: 200 ms). The positive correlation with the saccade velocity and the negative correlation with the saccade latency were present not only in the peri-saccadic period but also during the pre- and postcue periods. Second, we asked whether the CORs with the saccade parameters were direction-selective. A majority of RENs were more active before contralateral saccades (contralateral-preferring neurons) and their activity was correlated more strongly with contralateral saccades than with ipsilateral saccades. A minority of RENs, ipsilateral-preferring neurons, showed no such preference. These results are consistent with the hypothesis that CD neuronal activity exerts facilitatory effects on contralateral saccades and that the effects start well before saccade execution. Furthermore, a multiple regression analysis indicated that changes in activity of some, but not all, CD neurons could be explained by changes in saccade parameters; a major determinant was reward context (presence or absence of reward). These results suggest that, while a majority of CD neurons receive reward-related signals, only some of them can make a significant contribution to change saccadic outputs based on expected reward.

Simulating Maximum and Residual Displacements of RC Structures: II. Sensitivity

2011 ◽  
Vol 27 (4) ◽  
pp. 1203-1218 ◽  
Author(s):  
Ufuk Yazgan ◽  
Alessandro Dazio
Keyword(s):  
Damping Ratio ◽  
Time Integration ◽  
Integration Step ◽  
Discretization Scheme ◽  
Hysteretic Model ◽  
Step Size ◽  
Shake Table Tests ◽  
Rc Structures ◽  
Residual Displacements ◽  
Response History Analysis

The simulated response of a structure subjected to seismic excitation is sensitive to the idealizations made to model its response. This paper examines critical idealizations and assumptions that have a strong influence on the accuracy of the maximum and residual displacements predicted by response-history analysis. A set of shake table tests are numerically reproduced for this purpose. The investigated idealizations include the discretization scheme, the axial load, the steel hysteretic model, the viscous damping ratio, and the time-integration step size. The results indicate that the simulated residual displacements are significantly more sensitive to the model idealizations than the maximum displacements. It is found that the adopted discretization scheme and the utilized steel hysteresis model have very large influences on simulated residual displacements.

scholarly journals Analysis of Orbital Dynamic Equation in Navigation for a Mars Gravity-Assist Mission

2012 ◽  
Vol 65 (3) ◽  
pp. 531-548 ◽  
Author(s):  
Xin Ma ◽  
Xiaolin Ning ◽  
Jiancheng Fang
Keyword(s):  
Navigation System ◽  
Dynamic Equation ◽  
Autonomous Navigation ◽  
Impact Factors ◽  
Integration Step ◽  
Step Size ◽  
Gravity Assist ◽  
Efficient System ◽  
Numerical Integrator ◽  
The Impact

Gravity Assist (GA) is a kind of transfer orbit technology widely used in interplanetary missions, which highly depends on navigation performance to succeed. The Orbital Dynamic Equation is an essential component in the navigation system, affected by factors including the numerical integrator, perturbing planets, integration step size, gravitational constant and planet ephemerides. To analyse the impact factors mentioned above and investigate an efficient system model, the propagation and navigation results are carried out in a Mars-assist explorer scenario; a specific case study is also provided in this paper. The results indicate that the planetary ephemeris uncertainty and integration size are the dominant error sources, and the integration step size is the dominant impact factor on the real-time performance. In this specific case, the ‘Orbital Dynamic Equation’ considering Sun and Mars perturbation is suggested for integration by RK4 with 60 s integration step size. The conclusions drawn by this study are particularly useful in the design, construction, and analysis of an autonomous navigation system for a GA explorer.

Metabolism of the lactating cow: II. Digestive elements of a mechanistic model

1987 ◽  
Vol 54 (1) ◽  
pp. 107-131 ◽  
Author(s):  
R. Lee Baldwin ◽  
John H. M. Thornley ◽  
David E. Beever
Keyword(s):  
Mechanistic Model ◽  
Mass Action ◽  
State Variables ◽  
Fatty Acid Production ◽  
Mass Action Kinetics ◽  
Lactating Cows ◽  
Dietary Nutrients ◽  
Overall Stability ◽  
Feeding Regimes ◽  
Continuous Feeding

SummaryThe structure and characteristics of a model suitable for estimating digestion within the rumen and rates and patterns of nutrient entry in lactating cows are presented. The model consists of 12 state variables comprising a large particle pool, small particle pools representing insoluble dietary nutrients, soluble pools representing soluble dietary nutrients, and fermentation intermediates and end products. The model was constructed assuming continuous feeding, using Michaelis–Menten or mass action kinetics. The computer program was written in ACSL to run on a VAX computer. A fourth-order Runge–Kutta procedure was used for numerical integration.Sensitivity and behavioural analysis demonstrated that overall stability and sensitivity of the model to individual parameters was generally satisfactory, but the need to improve the description and parameterization of aspects such as particle size in relation to availability, rate and affinity constants for amino acid degradation and rate constants for particle outflow from the rumen was established. Adjustments of the model to examine discontinuous feeding regimes were undertaken and initial results with respect to changes in fermentation rates, rumen acetate levels and microbial metabolism were considered realistic.Comparisons with experimental data were considered satisfactory on forage-based and medium concentrate-containing diets, but with diets comprising 90% cereal, some inconsistencies, especially with respect to predictions of volatile fatty acid production rates, were observed. Reasons for this are put forward and suggestions for improvements in the model are discussed.

scholarly journals Caged Layer Performance in Pens with Oxidation Ditches and Liquid Manure Storage Tanks

1971 ◽  
Vol 50 (2) ◽  
pp. 501-505
Author(s):  
J.P. Walker ◽  
H.L. Orr ◽  
J. Pos
Keyword(s):  
Storage Tanks ◽  
Liquid Manure ◽  
Manure Storage

scholarly journals An improved mechanistic model for ammonia volatilization in Earth system models: Flow of Agricultural Nitrogen version 2 (FANv2)

2020 ◽  
Vol 13 (9) ◽  
pp. 4459-4490 ◽  
Author(s):  
Julius Vira ◽  
Peter Hess ◽  
Jeff Melkonian ◽  
William R. Wieder
Keyword(s):  
Process Model ◽  
Mechanistic Model ◽  
Earth System Model ◽  
System Model ◽  
Mineral Fertilizers ◽  
Earth System ◽  
Community Earth System Model ◽  
Manure Storage ◽  
Significant Pathway ◽  
Global Emissions

Abstract. Volatilization of ammonia (NH3) from fertilizers and livestock wastes forms a significant pathway of nitrogen losses in agricultural ecosystems and constitutes the largest source of atmospheric emissions of NH3. This paper describes a major update to the process model FAN (Flow of Agricultural Nitrogen), which evaluates NH3 emissions interactively within an Earth system model; in this work, the Community Earth System Model (CESM) is used. The updated version (FANv2) includes a more detailed treatment of both physical and agricultural processes, which allows the model to differentiate between the volatilization losses from animal housings, manure storage, grazed pastures, and the application of manure and different types of mineral fertilizers. The modeled ammonia emissions are first evaluated at a local scale against experimental data for various types of fertilizers and manure, and they are subsequently run globally to evaluate NH3 emissions for 2010–2015 based on gridded datasets of fertilizer use and livestock populations. Comparison of regional emissions shows that FANv2 agrees with previous inventories for North America and Europe and is within the range of previous inventories for China. However, due to higher NH3 emissions in Africa, India, and Latin America, the global emissions simulated by FANv2 (48 Tg N) are 30 %–40 % higher than in the existing inventories.

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