Dynamic simulation of forest fires

1988 ◽  
Vol 18 (6) ◽  
pp. 807-814 ◽  
Author(s):  
Wolfgang Von Niessen ◽  
Alexander Blumen

In this article we present the results of a simplified dynamic model for forest fires. We consider isotropic situations with different ignition mechanisms and different types of trees, models of crown and surface fires, and anisotropic cases that account for the influence of wind. We calculate the probabilities for a fire to become critical and characterize the temporal evolution and the spatial extent of the fire.

Author(s):  
T. M. Robinson

This article argues the following five claims: 1. Plato’s description of the origins of cosmos in the Timaeus is not a myth, nor something unlikely: when he called it an eikos mythos or eikos logos, he meant a likely or trustworthy account on this very subject. 2. Among the details in this account, the following are prominent and surprising: a) the world was fashioned in time, in that precise point that was the beginning of time; b) several kinds of duration can be distinguished in cosmology (mainly eternity, sempiternity, perpetuity and time); and c) space is an entity characterized by movement and tension. 3. In the Statesman, Plato repeats much the same thing, adding this time the strange notion that the universe’s circular movement is periodically reversed. 4. In spite of the important differences in detail, there is a striking similarity between Plato’s account of the origins of the world and the explanation adopted by much of modern cosmology. 5. What Plato shares with so many instances of recent thought is here termed “cosmological imaginativity”. A first section of the paper deals exclusively with the Timaeus. Claims 1 and 2a are supported by a revision of the meanings of mythos and logos, followed by brief reference and discussion of the argument at Timaeus 27d, leading to the conclusion that Plato affirms that the ever-changing world has indeed had a beginning in time. Claim 2b describes five different types of duration, corresponding to Forms, the Demiurge, Space, the [empirical] world and its contents, physical objects. The second section is concerned with the myth in the Statesman, discussing it as a parallel and describing its peculiar turn to the Timaeus’ cosmology and cosmogony, a complex spheric and dynamic model. After digressing into some important ideas in modern cosmology, touching especially on affinities of some of Einstein’s ideas with of Plato’s own, the paper closes with a discussion of cosmological imaginativity, oriented to recover and recognize fully Plato’s greatness as a cosmologist.


2014 ◽  
Vol 945-949 ◽  
pp. 1421-1425
Author(s):  
Xiu Qing Hao

Take typical parallel mechanism 3PTT as research subject, its inverse kinematic analysis solution was gotten. Dynamic model of the mechanism was established by Newton-Euler method, and the force and torque equations were derived. Dynamic simulation of 3PTT parallel mechanism was done by using ADAMS software, and simulation results have verified the correctness of the theoretical conclusions.


2014 ◽  
Vol 11 (03) ◽  
pp. 1450020 ◽  
Author(s):  
John Fasoulas ◽  
Michael Sfakiotakis

This paper presents a general dynamic model that describes the two-dimensional grasp by two robotic fingers with soft fingertips. We derive the system's kinematics and dynamics by incorporating rolling constraints that depend on the deformation and on the rolling distance characteristics of the fingertips' material. We analyze the grasp stability at equilibrium, and conclude that the rolling properties of the fingertips can play an important role in grasp stability, especially when the width of the grasped object is small compared to the radius of the tips. Subsequently, a controller, which is based on the fingertips' rolling properties, is proposed for stable grasping concurrent with object orientation control. We evaluate the dynamic model under the proposed control law by simulations and experiments that make use of two different types of soft fingertip materials, through which it is confirmed that the dynamic model can successfully capture the effect of the fingertips' deformation and their rolling distance characteristics. Finally, we use the dynamic model to demonstrate by simulations the significance of the fingertips' rolling properties in grasping thin objects.


2020 ◽  
Vol 55 ◽  
pp. 65-87
Author(s):  
Laura Gilabert Sansalvador

Over more than ten centuries, Maya vaults had great technical developments that allowed to achieve constructive and structural advanced systems and increasingly improved forms. One of the key factors to consider when studying its temporal evolution and the different regional variants is the stone vaults shape. This work is based on data collected during fieldwork and comparative analysis of a wide sample of vaults from different geographical zones and chronological periods, and as a result proposes a classification of the Maya stone vaults. The study of the influence of stereotomy on its form and the analysis of the use of different types of stone vaults by zones offer new data to understand the technological evolution of vaulted Maya architecture and the transfers of building knowledge.


Author(s):  
Z. Liu ◽  
X. Han ◽  
Y. F. Liu

A nonlinear dynamic model of a large flow solenoid is presented with the multi-physics dynamic simulation software called SimulationX. Validation is performed by comparing the experimental results with the simulated ones. The dynamic characteristics of the large flow solenoid valve are analyzed. Different structural parameters are modified in this research and the diameter of the orifice is proved to be one of the most important parameters which influences the pressure response most.


Author(s):  
Clifford S. Bonaventura ◽  
Joseph W. Palese ◽  
Allan M. Zarembski

A real-time dynamic simulation system designed to identify sections of track geometry that are likely to cause unsafe rail vehicle response is discussed. Known as TrackSafe, this system operates onboard a track geometry vehicle where the geometry measurements are passed as inputs to the dynamic model of one or more rail vehicle types. In order to comprehensively analyze the effect of the existing geometry on rail vehicle behavior, the system is capable of simultaneously simulating the response of several vehicle models, each over a range of traveling speeds. The resulting response predictions for each modeled vehicle and each simulated traveling speed are used to assess the track geometry condition and to identify locations leading to potentially unsafe response. This paper presents the latest work in the development of TrackSafe, specifically, the development and testing of eight new vehicle models is presented. The new car types modeled include a box car, flat car, and both a long and short tank car. Each can be simulated in a fully loaded or empty condition. Accuracy of the models is discussed in detail.


2012 ◽  
Vol 518-523 ◽  
pp. 1062-1071 ◽  
Author(s):  
Margaret Chan Kit Yok ◽  
Yap Bee Wah ◽  
Ting Siew King ◽  
Wong Mui Hung ◽  
Elly Lawai

The Third Principle which is pertaining to the right to development in Agenda 21 of the Rio Declaration or Earth Summit asserts that it must be fulfilled so that development must be sustainable which has been defined as development that meets the needs of the present without compromising the ability of future generations to meet their own need. Among the various models of environmental sustainability comparative studies was the Environmental Performance Index (EPI) model. Malaysia was ranked 54 recording a score of 65 and ranked 10 among the Asia and Pacific Countries behind two ASEAN countries: Singapore and Philippines. The environmental indicators from 2010 EPI was therefore used to develop the System Dynamics Simulation Model to provide the framework and procedure for qualitative and quantitative description, exploration and analysis of the systems in terms of their processes, information boundaries and strategies, facilitating quantitative simulation modeling for policy evaluation and predictions pertinent to sustainability. The System Dynamic Simulation Model developed for the EPI of Malaysia changed the static presentation to a dynamic scenario. Two very important components were considered: the contribution and the impact of population and the industrial activities indicated as the Industrial Productivity Index. The simulated EPI of 66.51 was shown to differ slightly from the EPI 2010 of 65 attributed to the inclusion of the population and the industrial production factors in the system dynamic model, in which the later study did not compute the EPI with respect to the two factors. Thus, the System Dynamic Simulation Model developed has shown to be reliable and be used for any country to simulate EPI for future trends.


2003 ◽  
Vol 84 (6) ◽  
pp. 767-776 ◽  
Author(s):  
V. A. Rakov

Characteristics of lightning discharges that transport either positive charge or both positive and negative charges to the ground are reviewed. These are termed positive and bipolar lightning discharges, respectively. Different types of positive and bipolar lightning are discussed. Although positive lightning discharges account for 10% or less of global cloud-to-ground lightning activity, there are five situations that appear to be conducive to the more frequent occurrence of positive lightning. These situations include 1) the dissipating stage of an individual thunderstorm, 2) winter thunderstorms, 3) trailing stratiform regions of mesoscale convective systems, 4) some severe storms, and 5) thunderclouds formed over forest fires or contaminated by smoke. The highest directly measured lightning currents (near 300 kA) and the largest charge transfers (hundreds of coulombs or more) are thought to be associated with positive lightning. Two types of impulsive positive current waveforms have been observed. One type is characterized by rise times of the order of 10 μs, comparable to those for first strokes in negative lightning, and the other type is characterized by considerably longer rise times, up to hundreds of microseconds. The latter waveforms are apparently associated with very long, 1–2 km, upward negative connecting leaders. The positive return-stroke speed is of the order of 108 m s−1. Positive flashes are usually composed of a single stroke. Positive return strokes often appear to be preceded by significant in-cloud discharge activity, then followed by continuing currents, and involve long horizontal channels. In contrast to negative leaders, which are always optically stepped when they propagate in virgin air, positive leaders seem to be able to move either continuously or in a stepped fashion. The reported percentage of bipolar flashes in summer storms ranges from 6% to 14% and from 5% to 33% in winter storms. Bipolar lightning discharges are usually initiated by upward leaders from tall objects. It appears that positive and negative charge sources in the cloud are tapped by different upward branches of the bipolar-lightning channel.


Author(s):  
Ying-Ju Yu ◽  
Chin-Hsiang Cheng

Dynamic simulation of a beta-type Stirling engine with cam-drive mechanism has been performed. A dynamic model associated with the cam-drive mechanism has been developed. Upon obtaining the gas pressure inside the chambers, the derived dynamic model is used to evaluate the transient rotational speed of the engine before the steady-state regime is reached. The torque of the engine can be calculated as long as the gas force, the inertia torque, the friction torque, and the load torque are evaluated. In this study, the mass moment of inertia of the flywheel is firstly calculated. The friction torque is assumed to be proportional to the time-varied rotational speed which is obtained by experiments. The weight of the individual parts of the engine has also been considered. An extensive parametric study of the engine under different geometrical and operating conditions has been performed and results are presented.


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