Effects Of Terrain Roughness Research Articles

Computational fluid dynamics study of CO2 dispersion with phase change of water following the release of supercritical CO2 pipeline

Accidental release of pressurized CO2 pipeline in carbon capture and storage involves the interaction of phase change and heavy-gas dispersion. However, the effect of the phase change of water vapor in air on the performance of cold CO2 dispersion is usually neglected. In this study, a three-dimensional two-phase computational fluid dynamics (CFD) model is developed to evaluate the cold CO2 dispersion by considering the phase change of water. A phase-change model based on the homogeneous relaxation model is used to describe the evaporation and condensation of water. The effects of terrain roughness, atmospheric stability, and turbulence models on the dispersion are also considered. The numerical results show that the model that uses the k–ω turbulent equations is superior to the other models. The results in which the phase change of water is considered exhibit a better agreement with the data from the experiments than those that do not consider it. The model is subsequently used in urban areas, which results in over-predicted CO2 concentration in the near field and under-predicted CO2 concentration in the far field when the phase change of water vapor is considered than that when it is neglected. Therefore, we proposed that the phase change of water vapor in the atmosphere should not be overlooked in the more accurate modeling of cold CO2 dispersion.

Pilot workload investigation for rotorcraft operation in low-altitude atmospheric turbulence

This paper aims to investigate pilot workload for rotorcraft operations in low-altitude atmospheric turbulence. A novel low-altitude turbulence model derived through the pre-warped Tustin transformation is used to modify the classic distributed turbulence model. The distributed model is then validated against the von Kármán spectra and is integrated into a flight simulation environment that consists of a high-fidelity nonlinear flight dynamics model and a multi-loop compensatory pilot model. The simulation responses and pilot controls in turbulence have been compared against flight test data for operations in bluff-body and freestream turbulence conditions. The effect of terrain roughness on pilot workload is analyzed. The results show that low-altitude turbulence becomes more intense and has smaller length scales over rougher terrain for the same conditions of the reference wind speed and altitude. Moreover, the effect of terrain roughness can increase pilot workload with increasing airspeed and decreasing flight altitude.

Исследование процесса распространения вредных примесей в атмосфере с учетом влияния типов наземного покрова на характеристики ветра

Исследование процесса распространения вредных примесей в атмосфере с учетом влияния типов наземного покрова на характеристики ветра

Evaluation of Peak Transmission Line Conductor Reactions Under Downburst Winds Using Optimization and Simplified Approaches

Transmission line structures, though designed per code provisions, suffered several failures worldwide in the past. As reported in the body of the available literature, more than 90% of those failures are due to sever localized wind events such as downbursts. Several recent studies emphasised on the importance of the conductor loads and how their forces contribute to the failure of the towers. The velocity profile and loads associated with a downburst wind field vary significantly with the change in its configuration. Previous studies, focused on identifying the critical transmission tower members that are likely to fail during a downburst event and the associated critical downburst configurations. In all these studies, a smooth terrain was assumed where the effect of terrain roughness is not considered. In the current study, an evolutionary optimization algorithm is coupled with a semi-closed form solution technique to predict the maximum conductor’s reactions under downburst wind field and the associated critical downburst configurations. A Large Eddy Simulation (LES) model of downbursts impinging on various exposure conditions, developed in a previous study, has been incorporated to predict wind forces acting on the conductor line. It is believed that the current study is the first of its kind to provide critical downburst configurations that lead to maximum conductors’ reactions while considering the effect of terrain exposure (open, countryside, suburban, and urban). Based on the optimal downburst configuration identified for each type of terrain roughness, a simple and practical approach in the form of simple equations and a set of charts to evaluate maximum reactions has been developed and validated. The simplified approach is suitable for practitioner engineers to accurately and rapidly evaluate maximum conductor reactions under downburst events considering multiple terrain conditions.

Terrain-Referenced Navigation using an Interferometric Radar Altimeter

This paper addresses measurement models in a particle filter for application in terrain-referenced navigation using an interferometric radar altimeter (IRA). We propose a novel method for utilizing an IRA in a terrain-referenced navigation system based on the fact that an IRA provides accurate three-dimensional measurement of the closest target point on the ground. The proposed measurement model searches for the closest point on an on-board digital elevation model and constructs an estimated measurement to calculate the measurement residual. Comparative simulation analysis with an existing method shows the proposed method provides outstanding navigation performance in terms of root mean square position error. The proposed method yields positioning solutions with an average root mean square error less than 3 m whereas that of the existing method is more than 11 m using a virtual digital elevation model fulfilling the HRTI-3 specification. Simulation results on the effects of terrain roughness, cruising altitude, sampling frequency, and magnitudes of inertial navigation system/barometer biases are also presented.

Effect of Terrain Roughness on the Roll and Yaw Directional Stability of an Articulated Frame Steer Vehicle

Compared to the vehicles with conventional steering, the articulated frame steer vehicles (ASV) are known to exhibit lower directional and roll stability limits. Furthermore, the tire interactions with relatively rough terrains could adversely affect the directional and roll stability limits of an ASV due to terrain-induced variations in the vertical and lateral tire forces. It may thus be desirable to assess the dynamic safety of ASVs in terms of their directional control and stability limits while operating on different terrains. The effects of terrain roughness on the directional stability limits of an ASV are investigated through simulations of a comprehensive three-dimensional model of the vehicle with and without a rear axle suspension. The model incorporates a torsio-elastic rear axle suspension, a kineto-dynamic model of the frame steering struts and equivalent random profiles of different undeformable terrains together with coherence between the two tracks profiles. The simulations are performed to determine the stability limits of the ASV models while operating on different terrains, namely: a perfectly smooth surface, plowed field, pasture, gravel road, and the MVEE random course. The directional stability limits are defined in terms of the static and dynamic rollover thresholds, rearward amplification ratio, and critical speed corresponding to snaking instability under steady and transient steering inputs. The results suggest that the tire interactions with the rough terrains affect the stability limits of both the unsuspended and suspended vehicles in a highly adverse manner. The suspended vehicle responses, however, show less sensitivity to variations in the road roughness profile.

On the Effective Low-Grazing Reflection Coefficient of Random Terrain Roughness for Modeling Near-Earth Radiowave Propagation

An investigation on the effects of terrain roughness on near-ground radiowave propagation is featured. In spite of the fact that a variety of analytical and numerical routines have been proposed by many workers for the general treatment of the scattering properties of rough surfaces, much disagreement remains in the solution of the problem for near-grazing scenarios. In striving to analytically describe the near-grazing propagation of signals from 2D and 3D radiators, an existing volumetric polarization current-based perturbation approach is exploited in this work to formulate closed-form expressions for the coherent rough surface reflection coefficients. Although the perturbation approach was originally intended for analyzing the scattering coefficients of a ground with scale of roughness much smaller than the wavelength, it is shown through Monte Carlo simulations that the effective reflection coefficients reported herein are applicable for near-ground path-loss prediction even when the surface variation (rms height) is on the order of a wavelength or more.

Characteristics of wind and rainfall induced by typhoons from the viewpoint of building damage

Meteorological data during typhoons, measured at 46 JMA meteorological observatories in Japan from 1975 to 1997, are analyzed from the viewpoint of building damage. The number of typhoons used for the present analysis ranges from 29 at Sapporo to 110 at Okinawa. Special attention is paid to the gust factor and the intensity and amount of precipitation at and after the occurrence of the maximum peak gust. Based on the results, a simple model of the gust factor is provided, in which the effect of terrain roughness is considered. Furthermore a stochastic model is proposed for the amount of precipitation as a function of the shortest distance between the typhoon center and the observation site. These models can be incorporated into a prediction model of typhoon-induced building damage, which the authors are now developing.

Introduction of terrain roughness effects into a Gaussian dispersion model

The Gaussian dispersion model is used to predict the concentration field created by a plume during the dispersion phase. Roughness effects are introduced using a differential method for the calculation of the vertical dispersion coefficient. An estimate of terrain roughness is obtained by inspection of topographical land maps. This information is digitalized as proposed by Hosker and stored in topographical files. The present paper stresses the need to consider the effects of terrain roughness on the transport of air pollutants even when described through Gaussian models; the results show an increase of 60% in SO 2 peak concentrations over rough terrain.