Complex Geometric Environments Research Articles

PTFE-Based Circular Terahertz Dielectric Waveguides

This paper presents the transmission characteristics of flexible solid circular dielectric waveguides in the terahertz frequency band. In this paper, we measured the electrical properties of certain polymers within 325–500 GHz. Through simulation and measurement, the transmission loss, bending loss, and electric field distribution of solid-core polymer dielectric waveguides were analyzed and discussed. Additionally, we considered the surrounding cladding of the dielectric waveguide, the signal-feeding mode transmitter, and the interconnection of the dielectric waveguide. Ultimately, in the operating frequency range of 325–500 GHz, we selected PTFE rods with diameters of 0.5 mm and 1 mm as the dielectric waveguides, with measured transmission loss of less than 30 dB/m and 33 dB/m, respectively, and bending loss of less than 1 dB/m. The described dielectric waveguide has engineering significance for short-distance connections in complex geometric environments and provides a reference for subsequent research.

UAV Intelligent Coverage Navigation Based on DRL in Complex Geometrical Environments

Unmanned aerial vehicle (UAV) is one of the preferred tools for coverage detection missions, because of its maneuverability and flexibility. It is challenging for the UAV to decide a track by itself in a complex geometrical environment. This paper presents a UAV intelligent navigation method based on deep reinforcement learning (DRL). We propose using geographic information systems (GIS) as the DRL training environment to overcome the inconsistency between the training environment and the test environment. We creatively save the flight path in the form of an image. The combination of the knowledge-based Monte Carlo tree search method and local search method can not only effectively avoid falling into local search, but also ensure learning the optimal search direction under the limitation of computing power. Experiments show that the trained UAV can find an excellent flight path by intelligent navigation, and able to make effective flight decisions in a complex geometrical environment.

Dispersion-limited versus power-limited terahertz communication links using solid core subwavelength dielectric fibers

Terahertz (THz) band (0.1–10 THz) is the next frontier for ultra-high-speed communication systems. Currently, most of communications research in this spectral range is focused on wireless systems, while waveguide/fiber-based links have been less explored. Although free space communications have several advantages such as convenience in mobility for the end user, as well as easier multi-device interconnectivity in simple environments, fiber-based communications provide superior performance in certain short-range communication applications such as multi-device connectivity in complex geometrical environments (ex., intra-vehicle connectivity) and secure communications with low probability of eavesdropping, as well as secure signal delivery to hard-to-reach or highly protected environments. In this work, we present an in-depth experimental and numerical study of the short-range THz communications links that use subwavelength dielectric fibers for information transmission and define the main challenges and trade-offs in the link implementation. Particularly, we use air or foam-cladded polypropylene-core subwavelength dielectric THz fibers of various diameters (0.57–1.75 mm) to study link performance as a function of the link length of up to ∼ 10 m , and data bit rates of up to 6 Gbps at the carrier frequency of 128 GHz (2.34 mm wavelength). We find that depending on the fiber diameter, the quality of the transmitted signal is mostly limited either by the modal propagation loss or by the fiber velocity dispersion (GVD). An error-free transmission over 10 m is achieved for the bit rate of 4 Gbps using the fiber of smaller 0.57 mm diameter. Furthermore, since the fields of subwavelength fibers are weakly confined and extend deep into the air cladding, we study the modal field extent outside of the fiber core, as well as fiber bending loss. Finally, the power budget of the rod-in-air subwavelength THz fiber-based links is compared to that of free space communication links, and we demonstrate that fiber links offer an excellent solution for various short-range applications.

Numerical Simulation of Mud-Filtrate Invasion in Deviated Wells

Summary Understanding the spatial distribution of fluids in the near-borehole region caused by mud-filtrate invasion is necessary for the accurate petrophysical interpretation of wireline measurements acquired in deviated wells. This paper provides a sorely needed petrophysical and fluid-flow template that can be used to integrate several wireline measurements into a unique model of petrophysical parameters in the near-borehole region of deviated wells. We simulate numerically the physics of mud-filtrate invasion in vertical, horizontal, and highly deviated overbalanced wells. The numerical algorithm is adapted from a general 3D multiphase-fluid-flow simulator that is widely used in large-scale reservoir applications. Checks of numerical consistency and accuracy are performed against one commercial reservoir simulator. Emphasis is placed on describing the influence of mudcake buildup on the mud-filtration process. We approach the latter problem by introducing an effective-flow-rate function that describes the evolution in time of the rate of invasion of mud filtrate into rock formations. Parametric representations of the flow-rate function are derived on the basis of previously published laboratory experiments of mud circulation. A sensitivity analysis quantifies the influence of several geometrical and petrophysical parameters on the spatial distribution of mud-filtrate invasion away from the borehole wall. These parameters include relative permeability, capillary pressure, permeability anisotropy, dipping layers, and degree of hydraulic communication between adjacent layers. Our simulations reveal the character of invasion profiles in complex geometrical environments taking place under realistic petrophysical conditions. We show that standard pistonlike descriptions of mud-filtrate invasion, commonly used in well-log interpretation, can lead to inaccurate interpretations of wireline measurements. An example is presented of the use of our simulation technique by calculating the sensitivity of borehole electromagnetic induction measurements to specific conditions of mud-filtrate invasion in a vertical well.

A numerical method to estimate time-varying values of diffuse irradiance on surfaces in complex geometrical environments

The estimation of diffuse irradiance that impinges on a window or photovoltaic panel is of major importance for the determination of their performance. The present paper introduces the concept of angular shading factors (ASF) for the calculation of time-varying diffuse irradiances to be performed without the need to repeat time consuming intereflection calculations at every time step. For the calculation of ASF, a Monte Carlo backward ray tracing technique was used. As a result, geometrically complex scenes consisting of surfaces with diffuse and specular reflectances, while transparent and translucent surfaces can be modeled as well. After that, the calculation of diffuse irradiance can be performed in a dynamic way, by taking into consideration the sky radiance distribution variability.

Distributed Algorithms for Multi-Robot Observation of Multiple Moving Targets

An important issue that arises in the automation of many security, surveillance, and reconnaissance tasks is that of observing the movements of targets navigating in a bounded area of interest. A key research issue in these problems is that of sensor placement—determining where sensors should be located to maintain the targets in view. In complex applications involving limited-range sensors, the use of multiple sensors dynamically moving over time is required. In this paper, we investigate the use of a cooperative team of autonomous sensor-based robots for the observation of multiple moving targets. In other research, analytical techniques have been developed for solving this problem in complex geometrical environments. However, these previous approaches are very computationally expensive—at least exponential in the number of robots—and cannot be implemented on robots operating in real-time. Thus, this paper reports on our studies of a simpler problem involving uncluttered environments—those with either no obstacles or with randomly distributed simple convex obstacles. We focus primarily on developing the on-line distributed control strategies that allow the robot team to attempt to minimize the total time in which targets escape observation by some robot team member in the area of interest. This paper first formalizes the problem (which we term CMOMMT for i>Cooperative Multi-Robot Observation of Multiple Moving Targets) and discusses related work. We then present a distributed heuristic approach (which we call A-CMOMMT) for solving the CMOMMT problem that uses weighted local force vector control. We analyze the effectiveness of the resulting weighted force vector approach by comparing it to three other approaches. We present the results of our experiments in both simulation and on physical robots that demonstrate the superiority of the A-CMOMMT approach for situations in which the ratio of targets to robots is greater than 1/2. Finally, we conclude by proposing that the CMOMMT problem makes an excellent domain for studying multi-robot learning in inherently cooperative tasks. This approach is the first of its kind for solving the on-line cooperative observation problem and implementing it on a physical robot team.