Explicit Dynamic Model Research Articles

Does replacing coal with wood lower CO2 emissions? Dynamic lifecycle analysis of wood bioenergy

Bioenergy is booming as nations seek to cut their greenhouse gas emissions. The European Union declared biofuels to be carbon-neutral, triggering a surge in wood use. But do biofuels actually reduce emissions? A molecule of CO2 emitted today has the same impact on radiative forcing whether it comes from coal or biomass. Biofuels can only reduce atmospheric CO2 over time through post-harvest increases in net primary production (NPP). The climate impact of biofuels therefore depends on CO2 emissions from combustion of biofuels versus fossil fuels, the fate of the harvested land and dynamics of NPP. Here we develop a model for dynamic bioenergy lifecycle analysis. The model tracks carbon stocks and fluxes among the atmosphere, biomass, and soils, is extensible to multiple land types and regions, and runs in ≈1s, enabling rapid, interactive policy design and sensitivity testing. We simulate substitution of wood for coal in power generation, estimating the parameters governing NPP and other fluxes using data for forests in the eastern US and using published estimates for supply chain emissions. Because combustion and processing efficiencies for wood are less than coal, the immediate impact of substituting wood for coal is an increase in atmospheric CO2 relative to coal. The payback time for this carbon debt ranges from 44–104 years after clearcut, depending on forest type—assuming the land remains forest. Surprisingly, replanting hardwood forests with fast-growing pine plantations raises the CO2 impact of wood because the equilibrium carbon density of plantations is lower than natural forests. Further, projected growth in wood harvest for bioenergy would increase atmospheric CO2 for at least a century because new carbon debt continuously exceeds NPP. Assuming biofuels are carbon neutral may worsen irreversible impacts of climate change before benefits accrue. Instead, explicit dynamic models should be used to assess the climate impacts of biofuels.

Experimental study and FEM analysis of forward hot dieless spinning

In this study, the forward hot dieless spinning method is employed in order to fabricate conical tubes using thick aluminum. The process is first examined numerically and then verified by an experimental work. In the numerical study, a 3-D dynamic explicit model is used to solve a common problem in the modeling of the spinning process, the tube is fixed and the roller rotates around the tube. The strain distribution in the tube at various forming passes is studied. The numerical results show that the circumferential strain distribution in different positions of the tube has a negative value whose value increases toward the free end of the tube. Besides, the results indicate that the hardness of the sample increases by about 18% due to the hot dieless spinning process and such a hardness augmentation is obvious along the thickness of the formed tube.

Numerical and experimental study of wheel-rail impact vibration and noise generated at an insulated rail joint

As essential track components for rail connections and signal transmission and control, insulated rail joints (IRJs) have been widely used in traditional and high-speed railways. However, the IRJ is considered as one of the weakest parts of railway track structures due to the significant discontinuities in stiffness and geometry. When a train runs over an IRJ, a wheel-rail impact occurs and it increases with train speed. The impact consequently leads to vibration and noise and accelerates track deterioration in the vicinity of the IRJ. This paper establishes an explicit finite element wheel-IRJ dynamic interaction model to simulate high-frequency impact vibration and noise generated at a typical IRJ in the Dutch railway network, and validates the model against a comprehensive hammer test and a pass-by measurement. Good agreements between the simulation and measurements indicate that the proposed model can effectively reproduce high-frequency impact vibration and noise up to 10 kHz. This paper also connects the dominant frequencies of wheel-IRJ impact vibration and noise with the dynamic behaviour of the target IRJ, which may contribute to the mitigation of impact vibration and noise at IRJs as well as to train-borne detection of deterioration types of IRJs.

Development of the method for creating explicit integral dynamic models of measuring transducers

Increasing requirements to measuring transducers lead to the need to improve and propose alternatives of their mathematical description. The application in this case of differential equations of various types testifies to great computational complexity of the given problem statement. In this regard, constructively relevant are the methods for creating integral dynamic models of measuring transducers that enable expansion of the tools for computer simulation. The method considered in present paper implies determining a pulse transient characteristic and leads to the formation of the operators (cores) of measuring transducers in the form of integral mathematical dependences, that is, explicit integral dynamic models. The method of obtaining an analytic expression of the pulse transition function of measuring transducers with lumped parameters is represented as a solution to the homogeneous differential equation that corresponds to the specified non-homogeneous differential equation. This technique is easily illustrated on the examples of measuring transducers of the first and second order. The principle of determining a pulse transient characteristic for measuring transducers with distributed parameters by the assigned equations in partial derivatives is the same as for the case with lumped parameters.

Understanding water-energy-food and ecosystem interactions using the nexus simulation tool NexSym

The water-energy-food (WEF) nexus concept highlights the importance of integrative solutions that secure resource supplies and meet demands sustainably. There is a need for translating the nexus concept into clear frameworks and tools that can be applied to decision making. A simulation and analytics framework, and a concomitant Nexus Simulation System (NexSym) is presented here. NexSym advances the state-of-the-art in nexus tools by explicit dynamic modelling of local techno-ecological interactions relevant to WEF operations. The modular tool integrates models for ecosystems, WEF production and consumption components and allows the user to build, simulate and analyse a “flowsheet” of a local system. This enables elucidation of critical interactions and gaining knowledge and understanding that supports innovative solutions by balancing resource supply and demand and increasing synergies between components, while maintaining ecosystems. NexSym allowed assessment of the synergistic design of a local nexus system in a UK eco-town. The design improved local nutrient balance and meets 100% of electricity demand, while achieving higher carbon capture and biomass provisioning, higher water reuse and food production, however with a remarkable impact on land use.

Non-Gaussian data assimilation of satellite-based leaf area index observations with an individual-based dynamic global vegetation model

Abstract. We developed a data assimilation system based on a particle filter approach with the spatially explicit individual-based dynamic global vegetation model (SEIB-DGVM). We first performed an idealized observing system simulation experiment to evaluate the impact of assimilating the leaf area index (LAI) data every 4 days, simulating the satellite-based LAI. Although we assimilated only LAI as a whole, the tree and grass LAIs were estimated separately with high accuracy. Uncertain model parameters and other state variables were also estimated accurately. Therefore, we extended the experiment to the real world using the real Moderate Resolution Imaging Spectroradiometer (MODIS) LAI data and obtained promising results.

Explicit Dynamic Modeling of a 3SPS+1PS Parallel Manipulator with Joint Friction

Explicit Dynamic Modeling of a 3SPS+1PS Parallel Manipulator with Joint Friction

Static and dynamic analyses of insulated concrete sandwich panels using a unified non-linear finite element model

Insulated concrete sandwich panels are comprised of two outer concrete wythes and an inner layer of foam insulation. They have been increasingly used because of their advantages of light weight and energy efficiency. Various shear connectors can be used to connect the two outer concrete wythes. More recently, Fiber-Reinforced Polymer (FRP) shear connectors have been used, which can eliminate thermal bridging and improve the thermal performance. Typical approaches to Finite Element (FE) analysis treat static and dynamic analyses separately. However, due to the flexibility of the FRP shear connectors and the cracking of the concrete in insulated concrete sandwich panels, a nonlinear static analysis model would often diverge early based on a preliminary FE study conducted by the authors. To address this issue, a nonlinear explicit dynamic FE model using ABAQUS© was developed, which can study both the panels’ static behavior under typical flexural loading and dynamic behavior under blast loading. Nonlinear material properties were incorporated and damaged plasticity model was used to model concrete in both compression and tension. In order to simulate the static behavior, the time loading control was applied to the FE model to slow down the rate of loading to smoothly capture the response. For dynamic analysis under blast loading, a verification study was conducted first using the developed FE model, where good correlations can be obtained between the FE and test results on a panel tested in a previous study. The FE model was further used to study the dynamic behavior of two panels under blast loading: one is a solid concrete panel and the other is an insulated concrete sandwich panel. It can be concluded that, although the insulated concrete sandwich panel is lighter, it still performs relatively well compared to the solid panel under blast loading. Therefore, it is promising to use insulated concrete sandwich panels for both conventional and blast-resistant structures.

The effect of branching angle on adaptive growth in patchy environments

In clonal plants, the genetic individual (genet) develops via the production of multiple physiological individuals (ramets). The branching angle between the ramets can significantly influence the shape of the developing clone. We investigated the adaptive significance of this phenomenon by means of a spatially explicit dynamic model of clonal growth. We studied the effect of the branching angle on the efficiency of filling habitat patches, varying the sizes and shapes of the patches. Two growth forms were compared: the Narrow Range (NR) versus Wide Range (WR) form. In the NR plant, the branching angle was always acute, while in the WR plant, both acute and wide angles could occur. We hypothesized that the NR plant would be less successful, as narrower branching constrained the plant’s ability to turn. The simulations revealed an opposite trend: the NR plant occupied more space in most of the simulated habitats. However, the effect was weak in general. We conclude that the branching angle between ramets is likely to be a neutral trait in terms of natural selection.

A Multi-Body Dynamic Model for Analysis of Localized Track Responses in Vicinity of Rail Discontinuities

Rail discontinuities are one of the main sources of wheel impact causing high levels of noise, vibration and stresses in railway track. Even though various multi-body train–track interaction models have been developed in the past decade, accurate modeling and analysis of the track dynamic behavior in the vicinity of rail discontinuities is rare in the literature. In this paper, formulation of a new explicit multi-body dynamic (MBD) model incorporating detailed wagon, wheel–rail subsystems and track containing a rail discontinuity (rail joint) is reported. The predictions of the localized track responses are validated using the data from two gapped rail joints in the field test. The validated model accurately determines the impact forces and dynamic responses. The simulation results provide valuable insight on the behavior of track in vicinity of a rail discontinuity, the sensitivity of the design parameters to the impact forces and the track dynamic responses currently unavailable in the literature.

Periodic Filtering as a subgrid-scale model for LES of laminar separation bubble flows

ABSTRACTLaminar separation bubbles develop over many blades and airfoils at moderate angles of attack and Reynolds numbers ranging from 104 to 105. More accurate simulation tools are necessary to enable higher fidelity design optimisation for these airfoils and blades as well as to test flow control schemes. Following previous investigators, an equivalent problem is formulated by imposing suitable boundary conditions for flow over a flat plate which allows to use a high accuracy spectral solver. Large eddy simulation (LES) of such a flow were performed at drastically reduced resolution to assess the accuracy of several LES modelling approaches: the explicit dynamic Smagorinsky model, implicit LES, and the truncated Navier–Stokes approach (TNS). To mimic dissipation that occurs in implicit LES, the solution on a coarse mesh is filtered at every time step and two different filter strengths are used. In the TNS approach, the solution is filtered periodically, every few hundred time steps. The performance of each approach is evaluated against benchmark direct numerical simulation (DNS) data focusing on pressure and skin friction distributions, which are critical to airfoil designers. TNS results confirm that periodic filtering can act as an apt substitute for explicit subgrid-scale models, whereas filtering at every time step demonstrates the dependence of implicit LES on details of numerics.

Closed-form dynamics of a 3-DOF spatial parallel manipulator by combining the Lagrangian formulation with the virtual work principle

Dynamic modeling of spatial multi-degree-of-freedom (multi-DOF) parallel motion system is a challenging research because of its multi-closed-loop configuration, in contrast to serial manipulator. This study readdresses the issue of deriving explicit closed-form dynamic equations in the actuation space of non-redundant parallel mechanisms through the Lagrange modeling approach. Due to the complex relationship between passive joint variables and active joint variables, the application of the Lagrangian formulation for dynamic modeling of parallel mechanisms is considered nearly impossible. In this paper, the utilization of the virtual work principle makes the application of the Lagrangian formulation for parallel mechanisms possible and efficient. A closed-loop parallel mechanism is divided into several serial open-loop subchains. Explicit dynamic equations of each subchain can be derived by using the Lagrangian formalism straightforwardly with respect to their own local generalized coordinates. The principle of virtual work is used to combine the differential dynamic equations of the subsystems into an explicit dynamic model of the full parallel manipulator with respect to robot’s active generalized coordinates. The Jacobian and Hessian matrices play a crucial role in the transformation of the dynamic equations with respect to different generalized coordinates due to the application of the virtual work principle. The introduction of the cubic Hessian matrices makes the dynamic equations more compact. The procedure of modeling for a 3-DOF spatial parallel manipulator is taken as an application example of the proposed approach. The efficiency of the proposed approach and the correctness of the dynamic model are demonstrated by simulations and experiments.

Impacts of land use and infrastructural changes on threatened Little Bustard Tetrax tetrax breeding populations: quantitative assessments using a recently developed spatially explicit dynamic modelling framework

SummaryWith the combination of worldwide landscape changes and the uncertainty about the impact on species abundance and distribution, the value of spatio-temporal modelling tools is increasingly obvious. The Little Bustard Tetrax tetrax breeds on low-intensity arable cultivation and pastoral land and is currently threatened by diverse landscape modifications. The aim of this research was to predict Little Bustard population trends in the face of realistic scenarios of land use and infrastructure changes, applying a recently developed spatially explicit framework, based on the stochastic dynamic methodology (StDM). The application of this approach provided some basis to analyse the responses of breeding populations’ spatial distribution and abundance to the scenarios implemented. Since some of these scenarios represent local and/or regional risks to the viability of Little Bustard breeding populations, the results obtained demonstrate the potential of the proposed framework for landscape planning in the scope of the conservation of this threatened species. This approach also provides a promising baseline to support ecological risk assessments for other species, derived from ecological models with increased predictive power and intuitiveness to decision makers and environmental managers.

Invasiveness of plant pathogens depends on the spatial scale of host distribution

Plant diseases often cause serious yield losses in agriculture. A pathogen's invasiveness can be quantified by the basic reproductive number, R₀. Since pathogen transmission between host plants depends on the spatial separation between them, R₀ is strongly influenced by the spatial scale of the host distribution. We present a proof of principle of a novel approach to estimate the basic reproductivenumber, R₀, of plant pathogens as a function of the size of a field planted with crops and its aspect ratio. This general approach is based on a spatially explicit population dynamical model. The basic reproductive number was found to increase with the field size at small field sizes and to saturate to a constant value at large field sizes. It reaches amaximum in square fields and decreases as the field becomes elongated. This pattern appears to be quite general: it holds for dispersal kernels that decrease exponentially or faster, as well as for fat-tailed dispersal kernels that decrease slower than exponential (i.e., power-law kernels). We used this approach to estimate R₀ in wheat stripe rust(an important disease caused by Puccinia striiformis), where we inferred both the transmission rates and the dispersal kernels from the measurements of disease gradients. For the two largest datasets, we estimated R₀ of P. striiformis in the limit of large fields to be of the order of 30. We found that the spatial extent over which R₀ changes strongly is quite fine-scaled (about 30 m of the linear extension of the field). Our results indicate that in order to optimize the spatial scale of deployment of fungicides or host resistances, the adjustments should be made at a fine spatial scale. We also demonstrated how the knowledge of the spatial dependence of R₀ can improve recommendations with regard to fungicide treatment.

Linking landscape futures with biodiversity conservation strategies in northwest Iberia — A simulation study combining surrogates with a spatio-temporal modelling approach

The most prominent factors inducing landscape change in the rural regions of south west Europe are depopulation and the associated socio-ecological modifications. The aim of this work was to assess the future implications of these processes on land use/land cover and biodiversity in northwest Iberia. To achieve our goal, we developed a virtual spatially explicit dynamic model to simulate regional socio-ecological dynamics. For the period between 1960 and 2040, we tested four different environmental scenarios ranging from small decreases in conifer forest and a stabilization of agricultural areas and shrublands to more radical shifts, substantial decreases in agricultural areas and massive expansion of eucalyptus stands. The model considers also fire, whose role increased significantly in the scenarios of expanded forests. Bird assemblages, which we used as a surrogate for biodiversity, showed complex patterns although with overall decreases in richness and abundance. Species with narrow niche and from Mediterranean open habitats were particularly sensitive to the ongoing changes simulated. Our results suggest that landscape management actions and planning assessments designed for conserving biodiversity should focus on the maintenance of the traditional agricultural mosaic combined with a regulatory legislation limiting the expansion of fast growing tree forests (e.g Eucalyptus stands). This strategy can contribute to maintaining a diversity of land use/land cover in a heterogeneous landscape and the prevention of the occurrence of large wildfires, fundamental for the implementation of national biodiversity strategies and action plans.

Model‐based evaluation of impact of soil redistribution on soil organic carbon stocks in a temperate hedgerow landscape

AbstractAgroforestry systems are promoted for providing a number of ecosystem services and environmental benefits, including soil protection and carbon sequestration. This study proposes a modelling approach to quantify the impact of soil redistribution on soil organic carbon (SOC) storage in a temperate hedgerow landscape. Evolution of SOC stocks at the landscape scale was examined by simulating vertical and horizontal SOC transfers in the 0–105 cm soil layer due to soil redistribution by tillage and water processes. A spatially explicit SOC dynamics model (adapted from RothC‐26.3) was used, coupled with a soil‐redistribution model (LandSoil). SOC dynamics were simulated over 90 years in an agricultural hedgerow landscape dedicated to dairy farming, with a mix of cropping and grasslands. Climate and land use were simulated considering business‐as‐usual scenarios derived from existing information on the study area. A net decrease in SOC stocks was predicted at the end of the simulation period. Soil redistribution induced a net SOC loss equivalent to 2 kg C ha−1 yr−1 because of soil exportation out of the study site and an increase in SOC mineralization. Hedgerows and woods were the only land use in which soil redistribution induced net SOC storage. Soil tillage was the main process that induced soil redistribution within cultivated fields. Soil exportation out of the study area was due to erosion by water, but remained low because of the protective role of the hedgerow network. These soil transfers redistributed SOC stocks in the landscape, mostly within cultivated fields. Copyright © 2016 John Wiley & Sons, Ltd.

Collapse Failure of Prestressed Concrete Continuous Rigid-Frame Bridge under Strong Earthquake Excitation: Testing and Simulation

AbstractIn recent years, increasing attention has been paid to the collapse failures of long-span continuous rigid-frame bridges under strong earthquake excitations. This paper presents the results of a study in which a 1:15 scaled two-span prestressed concrete continuous rigid-frame bridge model with box-type piers was tested using the shake-table array test system to investigate the seismic response characteristics. Two nonlinear finite-element (FE) models were constructed. The first was a single-girder model that was used to simulate the seismic response under weak seismic waves. The second was an explicit dynamic FE model that was used to simulate the collapse and failure mechanisms of the scaled bridge under strong earthquakes. Testing revealed that the response of the central pier of the prestressed concrete continuous rigid-frame bridge was the largest under seismic excitation, and the damage first appeared at the lower end of the central pier in all cases. The numerical simulations revealed that t...

Dynamic research on single-row slewing bearing with local spalling of inner ring

The working state of equipments such as wind turbines, cranes, and excavators is directly affected by the damage of the slewing bearing. Condition monitoring system is a good method to identify the defects; however, the measuring range and distribution of the sensors have important influence on the monitoring efficacy. Due to the thin-wall and cyclic structure characteristics of a slewing bearing, the defect characteristic response is unusual and unknown. To solve this problem, a finite element model for local defect on the raceway of a slewing bearing was established by ABAQUS, and the operating process of the slewing bearing was simulated based on the explicit dynamic finite element algorithm. The pulse waveforms of vibration responses under different defect sizes are obtained, and the influencing mechanism of the damage sizes on the slewing bearing was studied. The simulation results show that the increase in defect length is the dominant influence on the operation of a slewing bearing and the effect of height is negligible under the same conditions. Furthermore, the explicit dynamic finite element analysis model was reasonable by comparing the simulation results with the test results. Therefore, the localized defect on the raceway surface of a slewing bearing can be reflected by finite element simulation analysis, and the analytical results can help develop the raceway damage monitoring system of a slewing bearing.

Applying ecological model evaludation: Lessons learned with the forest dynamics model Samsara2

Ecological models are increasingly used as decision-making tools and their reliability is becoming a key issue. At the same time, the sophistication of techniques for model development and analysis has given rise to a relative compartmentalization of model building and evaluation tasks. Several guidelines invite ecological modelers to follow an organized sequence of development and analysis steps and have coined the term “evaludation” for this process. The objective of this paper is to assess the feasibility and the value of a structured evaludation process, based on the working example of the Samsara2 model, a spatially explicit individual-based forest dynamics model. We implemented the six steps of model design, process level calibration, qualitative evaluation, quantitative evaluation, global sensitivity analysis, and partial recalibration using approximate Bayesian computing. We then evaluated how the evaludation process revealed model strengths and weaknesses, specified the model's conditions of use, clarified how the model works, and provided insights into forest ecosystem functioning. Finally, the efficiency/cost ratio of the process and future improvements are discussed.

Modelling and predicting the spatial distribution of tree root density in heterogeneous forest ecosystems.

In mountain ecosystems, predicting root density in three dimensions (3-D) is highly challenging due to the spatial heterogeneity of forest communities. This study presents a simple and semi-mechanistic model, named ChaMRoots, that predicts root interception density (RID, number of roots m(-2)). ChaMRoots hypothesizes that RID at a given point is affected by the presence of roots from surrounding trees forming a polygon shape. The model comprises three sub-models for predicting: (1) the spatial heterogeneity - RID of the finest roots in the top soil layer as a function of tree basal area at breast height, and the distance between the tree and a given point; (2) the diameter spectrum - the distribution of RID as a function of root diameter up to 50 mm thick; and (3) the vertical profile - the distribution of RID as a function of soil depth. The RID data used for fitting in the model were measured in two uneven-aged mountain forest ecosystems in the French Alps. These sites differ in tree density and species composition. In general, the validation of each sub-model indicated that all sub-models of ChaMRoots had good fits. The model achieved a highly satisfactory compromise between the number of aerial input parameters and the fit to the observed data. The semi-mechanistic ChaMRoots model focuses on the spatial distribution of root density at the tree cluster scale, in contrast to the majority of published root models, which function at the level of the individual. Based on easy-to-measure characteristics, simple forest inventory protocols and three sub-models, it achieves a good compromise between the complexity of the case study area and that of the global model structure. ChaMRoots can be easily coupled with spatially explicit individual-based forest dynamics models and thus provides a highly transferable approach for modelling 3-D root spatial distribution in complex forest ecosystems.