Dynamic Motion Planning for Aerial Surveillance on a Fixed-Wing UAV

We present an efficient path planning algorithm for an Unmanned Aerial Vehicle surveying a cluttered urban landscape. A special emphasis is on maximizing area surveyed while adhering to constraints of the UAV and partially known and updating environment. A Voronoi bias is introduced in the probabilistic roadmap building phase to identify certain critical milestones for maximal surveillance of the search space. A kinematically feasible but coarse tour connecting these milestones is generated by the global path planner. A local path planner then generates smooth motion primitives between consecutive nodes of the global path based on UAV as a Dubins vehicle and taking into account any impending obstacles. A Markov Decision Process (MDP) models the control policy for the UAV and determines the optimal action to be undertaken for evading the obstacles in the vicinity with minimal deviation from current path. The efficacy of the proposed algorithm is evaluated in an updating simulation environment with dynamic and static obstacles.Comment: Accepted at International Conference on Unmanned Aircraft Systems 201

AN EXPERIMENTAL INVESTIGATION INTO THE EFFECT OF PARTICULATE MATTER ON NOx REDUCTION IN A SCR CATALYST ON A DPF

The study of NOx reduction across the SCRF® is presented in this report to understand the inlet and outlet NO, NO2, NH3 species from the SCRF®. The SCRF® is a prototype SCR catalyst on a Diesel Particulate Filter (DPF) that reduces NOx and PM at the downstream location. The SCRF® reduces the packaging volume of the aftertreatment components in order to reduce the cost, volume and weight of the aftertreatment system. A total of 12 experiments were performed on a Cummins ISB 2013 280 hp engine and the aftertreatment system. The tests were performed to investigate the NOx reduction performance of the SCRF® under various Particulate Matter loading. The loading phase has been divided into two stages: Stage 1 and Stage 2. Stage 1 begins after all the PM has been removed from the SCRF®, which is then followed by Stage 2 loading. The engine is run at 2400 rpm and 200 Nm load with different fuel rail pressures for a duration to achieve PM loadings of 0, 2, and 4 g/L (grams of PM per volume of the SCRF®) in the SCRF®. For the testing of the SCRF® without PM loading, a Catalyzed Particulate Filter (CPF) was placed before the SCRF®. After the loading phase, NOx reduction stage was run at different engine conditions. The engine speed and load conditions were selected for the NOx reduction stage, named as test points 1, 3, 6, and 8, in order to attain a wide range in space velocities, inlet temperatures and NO2/NOx ratios in the SCRF®, which are the major parameters determining NOx reduction efficiency in the SCRF®. The exhaust temperature varied from 206 to 443 °C, inlet NO2/ NOx ratio varied from 0.22 to 0.46, and space velocity varied from 13.5 to 48.2 k/hr. Urea was dosed in the decomposition tube before the SCRF® to determine the NOx conversion efficiency at different ammonia to NOx ratio (ANR) values. The ANR values considered for the NOx reduction and NH3 slip were 0, 0.8, 1, 1.2, and 1.2 repeat. The ANR of 1.2 was repeated in the urea dosing cycle. It was found that the NOx conversion efficiency across the SCRF® is maximum for test points 3 and 6 i.e. for the temperature range of 300-350 °C. The NO2/NOx ratio at those points was around 0.42-0.46. It is observed that the loading in the SCRF® does not affect the NOx conversion efficiency at low (205 °C) and high (440 °C) temperature points but affects in between. The NOx conversion efficiency improved with PM loading until 300°C SCRF® inlet temperature and decreased (with PM loading) after 350 °C. There is noticeable ammonia oxidation at temperatures above 400 °C in the SCRF® that affects NOx conversion efficiency [1]. At higher temperature of about 440 °C, NH3 slip is observed varying with PM loading in the SCRF®. With PM loading, NO2 assisted oxidation increases the concentration of NO [2] and affects the NOx conversion efficiency. It is concluded from the results that the NO2 concentration across the SCRF® decreased with PM loading and SCRF® temperature due to NO2 assisted PM oxidation. The impact of PM loading on NOx reduction in the SCRF® was insignificant below 300 °C. NOx conversion decreased by 3 – 5 % above 350 °C with increase in PM loading from 0 to 2 and 4 g/L, due to consumption of NO2 via passive oxidation of PM. The NOx concentration is not completely converted across the SCRF® at temperatures above 350 °C even if dosed with an ANR value of 1.2

Thermal and Hydraulic Performance of Finned Tube Heat Exchangers

This study numerically examines the heat transfer and pressure drop performance of finned tube heat exchangers with staggered and inline tube layout for a range of tube pitch. The first part of the thesis considers the case where the heat exchanger is placed in fully ducted airflow. The simulations indicate that the performance reduced considerably for the staggered tube layout with an increase in the tube pitch, but a minimal difference for the inline tube arrangement. The effects of other geometrical parameters like fin pitch and the number of tube rows are then presented. Finally, a correlation for fin and tube heat exchangers with inline tube layout is proposed based on 280 simulations for 70 different configurations. The proposed heat transfer correlation can describe the database within ±8% discrepancy while the friction factor correlation can correlate the dataset within a ±10% discrepancy. The mean deviations for heat transfer and friction factor correlations are 4.3% and 5.4%. An important factor that influences the performance of flat plate and finned tube heat exchangers is when there is bypass flow around the heat exchanger. The next section of this thesis numerically investigates the partially ducted inline fin and tube heat exchanger with side bypass. The effects of the side clearance and the Reynolds number on the heat transfer and the pressure drop performance of the heat exchanger are presented. The simulations indicate that the heat transfer performance depreciates by more than 25% for infinite side clearance. The study then compares the pressure difference observed for entry, exit and the friction pressure drop with the various correlations available in the literature. Finally, the heat transfer and pressure drop performance for staggered and inline tube layouts are compared.ThesisMaster of Applied Science (MASc

Teaching Matters: Investigating the Role of Supervision in Vision Transformers

Vision Transformers (ViTs) have gained significant popularity in recent years and have proliferated into many applications. However, their behavior under different learning paradigms is not well explored. We compare ViTs trained through different methods of supervision, and show that they learn a diverse range of behaviors in terms of their attention, representations, and downstream performance. We also discover ViT behaviors that are consistent across supervision, including the emergence of Offset Local Attention Heads. These are self-attention heads that attend to a token adjacent to the current token with a fixed directional offset, a phenomenon that to the best of our knowledge has not been highlighted in any prior work. Our analysis shows that ViTs are highly flexible and learn to process local and global information in different orders depending on their training method. We find that contrastive self-supervised methods learn features that are competitive with explicitly supervised features, and they can even be superior for part-level tasks. We also find that the representations of reconstruction-based models show non-trivial similarity to contrastive self-supervised models. Project website (https://www.cs.umd.edu/~sakshams/vit_analysis) and code (https://www.github.com/mwalmer-umd/vit_analysis) are publicly available.Comment: Website: see https://www.cs.umd.edu/~sakshams/vit_analysis. Code: see https://www.github.com/mwalmer-umd/vit_analysis. The first two authors contributed equally. Accepted to CVPR 2023 as conference pape

Enhancing M30 Grade Concrete: A Comparative Study of Hooked vs. Crimped Steel Fibers in Fly Ash Mixes

The realm of concrete offers vast opportunities for inventive applications, design, and construction methodologies, given its adaptability and cost-effectiveness. Its versatility in meeting diverse requirements has established it as a highly competitive building material. To address escalating structural demands and harsh environmental factors, new cementitious materials and concrete composites are continually being developed, followed by the need for enhanced durability and performance, as well as pressure to utilize industrial waste materials. The research explores the impact of incorporating fly ash and steel fiber into M30-grade concrete, alongside cement, coarse, and fine aggregate, through experimental methods, with the primary aim of determining optimal ingredient proportions for achieving desired strength. The study evaluates compressive strength variations with fly ash ranging from [10%] to [30%] while hooked and crimped steel fibers [ranging from 0% to 1.5%] in concrete, alongside cement, fine and coarse aggregate. Environmental considerations and the imperative to utilize industrial waste have significantly contributed to advancements in concrete technology and sustainability. Through meticulous analysis of results, meaningful inferences are made in relation to the strength attributes of fly ash fiber-reinforced concrete. Two sets of experiments were conducted, one altering fly ash content while maintaining fixed steel fiber content, and the other varying steel fiber content while keeping other parameters constant. The study aims to provide practical insights for engineers seeking cost-effective and sustainable building construction methods, adhering to specified norms (IS Code: 456-2000)

Effective Gesture Based Framework for Capturing User Input

Computers today aren't just confined to laptops and desktops. Mobile gadgets like mobile phones and laptops also make use of it. However, one input device that hasn't changed in the last 50 years is the QWERTY keyboard. Users of virtual keyboards can type on any surface as if it were a keyboard thanks to sensor technology and artificial intelligence. In this research, we use the idea of image processing to create an application for seeing a computer keyboard using a novel framework which can detect hand gestures with precise accuracy while also being sustainable and financially viable. A camera is used to capture keyboard images and finger movements which subsequently acts as a virtual keyboard. In addition, a visible virtual mouse that accepts finger coordinates as input is also described in this study. This system has a direct benefit of reducing peripheral cost, reducing electronics waste generated due to external devices and providing accessibility to people who cannot use the traditional keyboard and mouse

On designing light-weight object trackers through network pruning: Use CNNs or transformers?

Object trackers deployed on low-power devices need to be light-weight, however, most of the current state-of-the-art (SOTA) methods rely on using compute-heavy backbones built using CNNs or transformers. Large sizes of such models do not allow their deployment in low-power conditions and designing compressed variants of large tracking models is of great importance. This paper demonstrates how highly compressed light-weight object trackers can be designed using neural architectural pruning of large CNN and transformer based trackers. Further, a comparative study on architectural choices best suited to design light-weight trackers is provided. A comparison between SOTA trackers using CNNs, transformers as well as the combination of the two is presented to study their stability at various compression ratios. Finally results for extreme pruning scenarios going as low as 1% in some cases are shown to study the limits of network pruning in object tracking. This work provides deeper insights into designing highly efficient trackers from existing SOTA methods.Comment: Submitted at IEEE ICASSP 202