Obstacle Geometry Research Articles

Non-radiating sources in elastodynamics and their applications in the exterior cloaking

In this work, we develop a mathematical framework on constructed general non-radiating sources of elastic waves governed by the Navier equation via the approach of Helmholtz decomposition and potential theory in elastodynamics. Our study offers a rather comprehensive analysis. We first provide a rigorous justification of the general non-radiating sources. Based on the complete destructive interference of external elastic fields generated by specific radiating sources, a general non-radiating elastic source is derived and shown to possess a hidden interior wave field. For an incident wave, targets remain invisible within non-radiating source regions, and the geometry and boundary conditions of obstacles can be very general, which holds significant practical implications. Moreover, we introduce an effective novel method for designing such generalized non-radiating sources. To avoid the complex structure, we propose to use radiating source overlay construction on specific nodes at the boundary of non-radiating regions construction and derive sharp error estimates to evaluate the cloaking performance. The proposed scheme is capable of nearly cloaking arbitrary obstacles with a high accuracy. Numerical verifications validate the precision of our analytical findings.

Application of the material point method (MPM) to characterise the impact forces of granular landslides on rigid obstacles

This study deploys the Material Point Method (MPM) to investigate the soil pressures exerted on a 3D rigid obstacle partially obstructing a dry granular flow; a configuration not previously addressed in the literature on a numerical modelling basis. A 2D simulation is first developed and validated against a flume experiment that monitors the interaction of dry granular flows with retaining structures under varying flume angles. The model is then extended to 3D, enabling the adjustment of the obstacle's geometry to observe the impact of granular flows on impermeable rigid obstacles partially obstructing the soil material. The trend in the recorded soil forces exhibits an initial peak that occurs simultaneously with the first impact, followed by a steep degradation branch as the soil deposits in front of the structure, thus reducing the flow's dynamics. The numerical simulation is subsequently upscaled to ensure that macroscopic dimensional analysis adequately interprets small-scale numerical observations to mimic prototype conditions using the MPM approach. Simplified factors are finally derived to represent the response characteristics of large-scale simulations based on the original findings.

Shading impact on the electricity generated by a photovoltaic installation using “Solar Shadow-Mask”

Abstract Solar energy is an excellent source of renewable power, but designing photovoltaic (PV) systems can be challenging without proper knowledge of solar radiation. The amount of energy received at the installation site plays a crucial role in determining the number of panels required to meet the electrical demand. For a given electrical demand, higher levels of received energy imply a reduced number of panels required, and vice versa. Hence, having knowledge of this irradiance is of paramount importance in the design and sizing of solar energy systems. The primary objective of this article is to provide an accurate estimation of electricity production in a PV installation when it is affected by shading. To achieve this, we performed calculations of the irradiation (direct and diffuse) received by our installation using the “Hottel” method, which integrates relevant local site parameters for our study. Subsequently, we study the impact of shading by conducting shade mask measurements on our installation. This enables us to obtain an accurate estimation of the irradiance received by the PV panels. The measurements include surveys of the geometry of obstacles and shade measurements taken at various times of the day. Additionally, a practical study of shading effects will be conducted using “close shading masks.” This method was applied to a 1.44 kWp PV installation located at the Faculty of Science and Technology of Settat (Morocco), where the output energy of PV panels was calculated. Finally, the effect of shading on the PV installation was quantified.

Obstructed swelling and fracture of hydrogels.

Obstructions influence the growth and expansion of bodies in a wide range of settings-but isolating and understanding their impact can be difficult in complex environments. Here, we study obstructed growth/expansion in a model system accessible to experiments, simulations, and theory: hydrogels swelling around fixed cylindrical obstacles with varying geometries. When the obstacles are large and widely-spaced, hydrogels swell around them and remain intact. In contrast, our experiments reveal that when the obstacles are narrow and closely-spaced, hydrogels fracture as they swell. We use finite element simulations to map the magnitude and spatial distribution of stresses that build up during swelling at equilibrium in a 2D model, providing a route toward predicting when this phenomenon of self-fracturing is likely to arise. Applying lessons from indentation theory, poroelasticity, and nonlinear continuum mechanics, we also develop a theoretical framework for understanding how the maximum principal tensile and compressive stresses that develop during swelling are controlled by obstacle geometry and material parameters. These results thus help to shed light on the mechanical principles underlying growth/expansion in environments with obstructions.

MODELLING EVACUATION STRATEGIES UNDER DYNAMIC CONDITIONS DUE TO OBSTACLE LOCATIONS BASED ON A SEMANTIC 3D BUILDING MODELS

Abstract. The evacuation path from inside a building to safe point outside becomes highly unpredictable due to changes in the local geometry or presence of obstacles during a disaster like a fire. During emergencies, Evacuees need appropriate information and hence prediction of an unobstructed path, as it emerges, needs to be computed well. Understanding the exits with its allowable people flow rate; the type - door or alternative exit such as windows, balconies, etc.; and its role as a node in the graph network is important to ensure safe and timely evacuation from a building. The study here evaluates how obstacles present in the evacuation route affect the removal of the last person. These obstacles, such as furniture, decrease the flow rate at which evacuees can escape. A subspace model is proposed for geometric spaces or carpet areas containing obstacles and is used to compute the shortest obstacle-free paths. The occupancy is considered within the subspaces containing obstacles. The proposed method clearly shows that a graph-based path generation using a subspace model improves the computation time, can be dynamically adapted, and can be scalable across geometric spaces. The results clearly show the impact of the obstacles, with a 2× to 6× rise when compared to obstacle-free scenarios.

Optimization study of obstacles in T–T mixing channel at low Reynolds numbers

AbstractIn this study, numerical simulations were conducted to optimize obstacle geometry for improving mixing in T–T mixers at low Reynolds numbers (2 < Re < 100). The study considered obstacles of cylindrical and prismatic shapes and optimized their pitch and geometrical parameters for enhanced mixing. For cylindrical obstacles, the optimized configuration resulted in symmetrical recirculation zones at Re > 30, which led to larger mixing qualities of 80% and 85% for Re values above 30 and 50, respectively. However, the pressure drop increased in the optimized T–T mixer due to the larger size of the obstacles. On the other hand, in the case of prismatic obstacles, the mixing qualities of 80% and 85% were achieved only at relatively higher Re values of 70 and 90, respectively. The recirculation zone formed behind the obstacle was asymmetric due to the asymmetrical shape of the optimized prism. At higher Re, the optimized cylindrical obstacle configuration resulted in better mixing than the prismatic configuration. However, the choking effect in the former increased the pressure drop.

Numerical study of Newtonian fluid flow characteristics in triangle enclosure considering various obstacle geometries

This article investigates the effect of cylindrical obstacles with different dimensions inside the triangular cavity on natural convection heat transfer. This study considers three cavities, each of which has one, two, and three-cylinder barriers embedded inside it. The use of one or two cylindrical barriers has been investigated in many research, but in this research, in addition to the number of cylindrical barriers, their dimensions and sizes have been changed, and an alternating temperature function has been used at the base of the cavity. The considered nanofluid is Al2O3H2O, which contains aluminum oxide nanoparticles with a concentration of 5 %. In all three cavities, the velocity of the nanofluid in the walls is zero. The temperature in the lateral sides of the cavity has low-temperature faces. Instead of being constant or adiabatic, the temperature at its base is an alternating function (sinusoidal function with a frequency of 1.0 Hz.). In contrast, it is considered that the surfaces of the obstacles of the cylinders have zero velocity and are adiabatic. In this study, the governing equations of nanofluid flow behavior have been solved using the Galerkin finite element method and analyzed in the Rayleigh number range of 103 to 105. Because triangular cavities with different ratios are used to optimize multiple objectives and increase thermal performance in microchannels, the results show that the multiplicity of cylindrical obstacles in the triangular cavity causes the expansion of the nanofluid velocity range in the whole area, which itself causes the increase of the heat transfer surface, and with the increase of the Rayleigh number and the buoyancy force, the magnitude of the velocity inside the triangular cavity increases. In the triangular cavity containing three cylindrical barriers, the nanofluid's velocity range is low, but according to the velocity contours, its extent is greater than the other two cavities. Also, the average Nusselt number in this cavity is higher than other cavities.

Mixtures of self-propelled particles interacting with asymmetric obstacles.

In the presence of an obstacle, active particles condensate into a surface "wetting" layer due to persistent motion. If the obstacle is asymmetric, a rectification current arises in addition to wetting. Asymmetric geometries are therefore commonly used to concentrate microorganisms like bacteria and sperms. However, most studies neglect the fact that biological active matter is diverse, composed of individuals with distinct self-propulsions. Using simulations, we study a mixture of "fast" and "slow" active Brownian disks in two dimensions interacting with large half-disk obstacles. With this prototypical obstacle geometry, we analyze how the stationary collective behavior depends on the degree of self-propulsion "diversity," defined as proportional to the difference between the self-propulsion speeds, while keeping the average self-propulsion speed fixed. A wetting layer rich in fast particles arises. The rectification current is amplified by speed diversity due to a superlinear dependence of rectification on self-propulsion speed, which arises from cooperative effects. Thus, the total rectification current cannot be obtained from an effective one-component active fluid with the same average self-propulsion speed, highlighting the importance of considering diversity in active matter.

Numerical Study of the Effects of Roughness Coupled with Inclination on a Turbulent Flow around an Obstacle

In this study, we simulate the cooling of a microprocessor by thermal convection in three different shapes: a square, a trapezoidal, and a triangular shape. The latter is improved by a variety of types of roughness, including square roughness, triangular roughness Type 1, triangular roughness Type 2, and triangular roughness Type 3. The microprocessors are kept at a constant temperature, the air flow is constant, and the geometry is fixed. The physical phenomenon is simulated by the ANSYS software. The numerical results reported in this study cover the ranges of the obstacle’s angle of inclination, 0°≤θ≤45°, (square obstacles, θ=0°, trapezoidal obstacles, 0°<θ<45°, triangular obstacles, θ=45°) and Reynolds number, 2500≤Re≤10,000. The findings relate to streamlines, dynamic pressure (max), mean velocity, temperature field, mean Nusselt number (Nu/Nu0) profiles, local coefficient of friction (Cf/f0), mean coefficient of friction (f/f0) profiles, mean velocity field with roughness, and fluid temperature field with roughness. The aim of the study is to show the interaction between the roughness parameter and the obstacle geometry. In the case of a triangular obstacle, the contact between the cold air and the obstacle is significant downstream of the obstacle, which gives us good cooling, and the Nusselt number has an important value because the agitation of the flow increases convective heat transfer, and the coefficient of friction is low because the air flow is uniform.

Robot Motion Planning with Optimization-based Algorithm and Neural Network: Unsupervised Path Regression

Planning collision-free motions for robots is challenging in environments with complex obstacle geometries. In this study, we combine the optimization-based algorithm and neural network to obtain a short and collision-free path through unsupervised path regression. The network can help to predict an educated initial path for an optimization-based planner, which will converge to a better solution. We compare different path representations, world representations, and also their combinations to improve the result. The motion planning problem is extended from a sphere robot in a single 2D world to a more complex static arm robot in multiple worlds. Through our experiments, we can find that in multiple worlds, the relative path with the signed distance field is the best combination for both robots. This is not only proved by metrics of feasible rate and loss but also by the visualization in the map.

Routing Among Convex Polygonal Obstacles in the Plane

Given a set [Formula: see text] of [Formula: see text] pairwise disjoint convex polygonal obstacles in the plane, defined with [Formula: see text] vertices, we preprocess [Formula: see text] and compute one routing table at each vertex in a subset of vertices of [Formula: see text]. For routing a packet from any vertex [Formula: see text] to any vertex [Formula: see text], our scheme computes a routing path with a multiplicative stretch [Formula: see text] and an additive stretch [Formula: see text], by consulting routing tables at only a subset of vertices along that path. Here, [Formula: see text] is the number of obstacles of [Formula: see text] the routing path intersects, and [Formula: see text] depends on the geometry of obstacles in [Formula: see text]. During the preprocessing phase, we construct routing tables of size [Formula: see text] in [Formula: see text] time, where [Formula: see text] is an input parameter.

Optimal design of an array of porous obstacles in a partially heated channel using lattice Boltzmann method for the heat transfer enhancement

The present work investigates the heat transfer enhancement in a channel includes a number of porous obstacles. A partially heated channel is considered, and an array of porous blocks installed on the channel wall is used as an effective heat transfer enhancement mechanism. The flow and temperature fields are resolved using a well-tuned lattice Boltzmann method. An optimal design is obtained for the porous obstacles considering the blocks' height and pitch together with the permeability of the porous medium as the design parameters. In addition, the impact of Da on the thermal performance of the porous block is studied. The PEC number (Performance Evaluation Criteria), which simultaneously accounts for the pressure drop penalty and the heat transfer rate augmentation, is chosen as a proper thermal performance evaluation criteria. The obtained results show an optimum value for both blocks' height and pitch, which depends on the Da. Moreover, the impact of obstacle geometry and the distribution of porous material inside the channel is investigated on the thermal performance of the heat-removing system.

Experimental investigation of the effect of flexible/rigid flag on heat transfer

This experimental work investigated the heat transfer characteristics of rectangular channels equipped with a flexible flag vortex generator (FFVGs) and a rigid flag vortex generator (RFVGs). The FFVGs and RFVGs are mounted at the entrance of the channel using four different obstacle geometries. The experiments were performed in a rectangular duct with FFVGs and RFVGs under four different Reynolds numbers (9965, 19,930, 29,985, and 34,875), four different obstacle geometries (triangle-shaped obstacle (T-SO), cylinder-shaped obstacle (C–SO), rectangular-shaped obstacle (R–SO) and half cylinder-shaped obstacle (HC–SO), four different FFVGs and RFVGs lengths (L) (50 mm, 100 mm, 150 mm, and 200 mm), four different FFVGs and RFVGs width (w) (10 mm, 20 mm, 30 mm, and 45 mm), and two different FFVGs and RFVGs channel height clearance (c) (1 mm, and 4 mm). To reduce the number of trials, the Taguchi technique was utilized, thereby reducing the number of trials from 1024 to 16. The highest thermal performance factor was determined as approximately 1.32 in Case 12, which was observed in Case 12 with, l*=0.36, w*=0.036, c*=0.014, Re = 34,875, FFVGs, and R–SO. The heat transfer results of the FFVGs and RPVGs were compared with those of a smooth plate. The best heat transfer performance was obtained with the FFVGs. The presence of the vortex generators produced higher heat transfer coefficients than the smooth plate surfaces.

Stable model reduction for linear variational inequalities with parameter-dependent constraints

We consider model reduction for linear variational inequalities with parameter-dependent constraints. We study the stability of the reduced problem in the context of a dualized formulation of the constraints using Lagrange multipliers. Our main result is an algorithm that guarantees inf-sup stability of the reduced problem. The algorithm is computationally effective since it can be performed in the offline phase even for parameter-dependent constraints. Moreover, we also propose a modification of the Cone Projected Greedy algorithm so as to avoid ill-conditioning issues when manipulating the reduced dual basis. Our results are illustrated numerically on the frictionless Hertz contact problem between two half-disks with parameter-dependent radius and on the membrane obstacle problem with parameter-dependent obstacle geometry.

Backwards wave breaking by flow separation vortices under solitary waves

In this work, the backward wave breaking process by the presence of flow separation vortices under a solitary wave is studied. Based on a set of non-dimensional variables defined from the Buckingham Π theorem, a set of numerical experiments are performed in order to analyze the effect of varying the submerged obstacle geometry on the surrounding flow and free surface by using a RANS-VOF model. Model simulations are tested against available experiments showing a good performance of numerical results. The structure-submergence ratio and the structure-based Reynolds number modulate the type of breaking (collapsing-plunging). The structure aspect ratio defines the location and number of backward breaking points for rectangular structures and the breaking wave direction for triangular structures (either forward or backward). Moreover, when the flow separation vortex diameter is comparable to the local water depth a backward wave breaking process is originated. The vortex behaves as a rigid body that accelerates the flow at the upper side of the vortex, accumulating mass at the downstream side where a very large slope on the free surface makes the water fall backward due to gravity.

A User Centric Blockage Model for Wireless Networks

This paper proposes a cascade blockage model for analyzing the vision that a user has of a wireless network. This model, inspired by the classical multiplicative cascade models, has a radial structure meant to analyze blockages seen by the receiver at the origin in different angular sectors. The main novelty is that it is based on the geometry of obstacles and takes the joint blockage phenomenon into account. We show on a couple of simple instances that the Laplace transforms of total interference satisfies a functional equation that can be solved efficiently by an iterative scheme. This is used to analyze the coverage probability of the receiver and the effect of blockage correlation and penetration loss in both dense and sparse blockage environments. Furthermore, this model is used to investigate the effect of blockage correlation on user beamforming techniques. Another functional equation and its associated iterative algorithm are proposed to derive the coverage performance of the best beam selection in this context. In addition, the conditional coverage probability is also derived to evaluate the effect of beam switching. The results not only show that beam selection is quite efficient for multi-beam terminals, but also show how the correlation brought by blockages can be leveraged to accelerate beam sweeping and pairing.

Three-dimensional phase-field lattice-Boltzmann simulations of a rising bubble interacting with obstacles: Shape quantification and parameter dependence

Exploring the bubble dynamics in the presence of obstacles can improve understanding of mechanism, design, and operation of multiphase flow. However, large deformation and complex hydrodynamics during the bubble–obstacle interaction pose challenges for shape quantification and parameter dependence. In this work, the bubble–obstacle interaction is investigated by employing a conservative phase-field lattice-Boltzmann model implemented on a parallel platform. Two shape parameters, which are the combination of the bubble geometrical parameters, are defined to characterize the bubble deformation during rising, impacting, and sliding process. The effects of the flow parameters (Reynolds, Eötvös, and Morton numbers) and the obstacle geometry settings (size and layout) are discussed, and a multilinear correlation is established to obtain a thorough evaluation. The difference induced by spatial dimension is further discussed to illustrate the necessity of simulating three-dimensional liquid–gas flow. The results can help decode the intricate bubble dynamics and lay a foundation for developing physically informed models for predicting the bubble–obstacle interaction.

Numerical investigation of heat transfer performance of an air heater with delta flow obstruction

Air heaters are a vital component in many engineering systems, including room heating and agricultural dryers. The use of flow obstacles improves the convective heat transfer coefficient by interrupting the formation of a laminar sub-layer. In the previous studies reported, the thermal and frictional effects of various flow obstacle geometries were studied, but they are limited to non-inclined obstacles. The current research examines the thermal and hydraulic characteristics of air heaters with inclined and non-inclined delta shape obstacles using numerical techniques and compares the results with empirical predictions and literature data. The influence of flow rate and angle of attack (α) on Nusselt number (Nu) and friction factor (f) were evaluated using CFD for Reynolds numbers (Re) ranging from 5000 to 20,000 and for α ranging from 300 to 900. A rectangular duct (300 mm × 50 mm) with a constant heat flux of 800 W/m2 at the bottom surface of the air heater with delta obstructions of relative obstacle height (e/H) of 0.5 with a constant transverse (Pt/b) of 1.5 and longitudinal pitch (Pl/e) of 3 was considered. The Nu, f and Thermal Enhancement Factor (TEF) were calculated and investigated for various flow rates and attack angles. The predicted Nu and f values demonstrated a good agreement with empirical correlations, with an average variation of 5.68 percent and 7.2 percent, respectively. The CFD results were also consistent with earlier published experimental findings. The results indicate that using a delta obstruction enhances heat transfer rate considerably at the cost of increased pressure loss. The use of delta-shaped flow obstruction increases Nusselt number in the range of 71–162, with a 6–9.6 times increase in friction factor. A maximum TEF of 1.69 was obtained for the air heater with delta obstruction with α = 300 at Re = 5000.

Modeling of attenuation and suppression of cellular detonation in the hydrogen-air mixture by circular obstacles

The results of numerical study of the interaction of the gaseous detonation with the regular obstacle consisting of checkered elements with circular cross section are presented. The aim of this work is to identify and generalize the parameters affected the attenuation of a cellular detonation propagating in a premixed stoichiometric hydrogen-air mixture. Studies of such problems are aimed at studying issues related to explosion and fire safety in the operation of highly efficient gaseous fuels, which are currently very widespread. As a result, the dependencies of the leading shock wave propagation velocity on the obstacle geometry are obtained. The contribution of each of the considered parameters to the detonation wave velocity deficit is estimated. Maps of detonation suppression and re-initiation modes for varying barrier parameters are obtained.

Hydrogen detonation onset behind two obstructions with unequal blockage ratio and opening geometry

Experiments on detonation onset behind two solid obstructions with uneven blockage ratio (BR) and opening shape were carried out in premixed, stoichiometric, hydrogen-oxygen mixtures at 20 kPa. Three geometric features of the second obstruction (OB2) were investigated: the opening shape, BR, and minimum opening vertical dimension (d/λ). Obstructions with blockage ratio increase across the obstacle pair (40%–80% and 40%–60%) presented shorter detonation onset time than obstacle pairs with unvaried BR (40%–40%). Modifications in the second obstacle geometry for pairs with 40%–40% and 40%–80% blockage had minimal effect on DDT time and obstacle-induced shock strength. Conversely, obstacle pairs with 40%–60% blockage experienced significant variation depending on the geometry employed. Critical conditions of detonation initiation immediately behind the second obstacle were found to correlate with BR and effective opening dimension (deff/λ); For OB2 with 60% and 80% BR, DDT limits correlate well with the upper and lower limits constrained by D−deff2λ≥1 and deffλ≥1, respectively. The Taguchi analysis showed that the second obstacle blockage is the factor that most influenced early detonation onset, both the shape and opening dimension had minor effects. This finding confirms the importance of BR pattern for overpressure estimation during gaseous explosions.