Low Speed Conditions Research Articles

RockSeg: A Novel Semantic Segmentation Network Based on a Hybrid Framework Combining a Convolutional Neural Network and Transformer for Deep Space Rock Images

Rock detection on the surface of celestial bodies is critical in the deep space environment for obstacle avoidance and path planning of space probes. However, in the remote and complex deep environment, rocks have the characteristics of irregular shape, being similar to the background, sparse pixel characteristics, and being easy for light and dust to affect. Most existing methods face significant challenges to attain high accuracy and low computational complexity in rock detection. In this paper, we propose a novel semantic segmentation network based on a hybrid framework combining CNN and transformer for deep space rock images, namely RockSeg. The network includes a multiscale low-level feature fusion (MSF) module and an efficient backbone network for feature extraction to achieve the effective segmentation of the rocks. Firstly, in the network encoder, we propose a new backbone network (Resnet-T) that combines the part of the Resnet backbone and the transformer block with a multi-headed attention mechanism to capture the global context information. Additionally, a simple and efficient multiscale feature fusion module is designed to fuse low-level features at different scales to generate richer and more detailed feature maps. In the network decoder, these feature maps are integrated with the output feature maps to obtain more precise semantic segmentation results. Finally, we conduct experiments on two deep space rock datasets: the MoonData and MarsData datasets. The experimental results demonstrate that the proposed model outperforms state-of-the-art rock detection algorithms under the conditions of low computational complexity and fast inference speed.

Lubrication analysis of hydrodynamic-static hybrid bearing with deep-shallow chambers considering thermal conduction

The oil film separates the shaft-bearing system to reduce the frictional force of contact surfaces with large temperature variations owing to thermal conduction. Multiple impact factors seriously affected the lubrication behavior of the bearing during actual working process. An applicable model regarding the lubrication analysis of a hydrodynamic-static hybrid bearing with deep-shallow chambers is proposed and validated with published literature. The lubrication behavior includes film pressure, load capacity, bearing stiffness and flow rate is numerically calculated with centered finite difference method by solving the Reynolds equation. The influence of film thickness and working temperature are considered, over a range of eccentricity ratio. Moreover, the temperature variation caused by thermal conduction is analyzed in details. To investigate the influence of thermal conduction on the lubrication behavior, the results show that the load capacity, bearing stiffness, friction power, and flow power significantly decline with the consideration of thermal conduction. This study proposes an accurate model that is helpful for the design of hydrodynamic-static hybrid bearings with deep-shallow chambers under low rotational speed, heavy load, and high temperature conditions.

Experimental study on the influence of fluid motion on hull resistance in stepped moonpool

A series of model tests are carried out to explore the influence of fluid motion on the hull resistance in the non-resonant state of the moonpool. The variations in total hull resistance under various wavelengths, wave steepness, and speed conditions are investigated based on regular waves. Considering the three navigational conditions of low speed (Fr=0.097), medium speed (Fr=0.13), and high speed (Fr=0.162). The two incident wave frequencies are consistent with the moonpool piston and the sloshing mode, respectively. In order to ascertain the effect of fluid motion on hull resistance in the non-resonant state of the moonpool, a new damping device is designed to reduce the amplitude of the fluid motion response and dissipate the energy of fluid motion in the moonpool. The variations of fluid motion response and hull resistance with and without a damping device in the moonpool are compared and analyzed. It can be discovered that vortex structure in the moonpool has a significant effect on the hull's additional resistance. During the test conditions of λ/LPP=0.46, the average added resistance effect of the moonpool in the case of Fr=0.097 is 5.76%; in the case of Fr=0.13, it is 7.23%; and in the case of Fr=0.162, it is 17.33%. The average decreases in fluid motion response amplitude in the moonpool are 54.52%, 62.8%, and 72.55%, respectively. Under the conditions of λ/LPP=1.43, the average added resistance effect of the moonpool in the case of Fr=0.13 is 8.7%, and in the case of Fr=0.162, it is 12.48%. The average decreases in fluid motion response amplitude in the moonpool are 15.10% and 43.70%, respectively. With the dissipation of the vortex structure and the decrease of the fluid motion response in the moonpool, the total resistance of the hull is also reduced. This study will provide a reference for the green and energy-saving design of drilling ships.

Aerodynamic Investigation and Simulation Studies on Wing Section of an Unmanned Aerial Vehicle Attached with Solar Plate

The paper investigates the aerodynamic performance and power requirement characteristics of wing sections integrated with high-lift airfoil to support the operation of solar-powered Unmanned Aerial vehicle (UAV). The flight mission is aimed to simulate the operation of solar-powered UAVs under low -speed environment. The research focuses on studying the aerodynamic effect of non-solar UAV wing model and solar UAV wing model for the varying angle of attack. The UAV wing models are tested using a subsonic wind tunnel to validate the aerodynamic characteristics at low-speed condition. The aerodynamic parameters such as coefficient of lift (Cl), coefficient of drag (Cd), coefficient of pressure (Cp), and the total power required to accelerate the solar UAV are studied to maintain steady level flight. The solar UAV and non-solar UAV wing models were subjected to a computational process to examine the pressure and velocity distributions for the aerodynamic performance analysis. Evident results show that the solar cells positioned at the flow separation region of the UAV wing model produces an aerodynamic efficiency rate of 5.45% and required 37.13W of minimum power compared to non-solar UAV at the Reynolds number of 9.8 106.

Performance analysis of diesel particulate filter thermoelectric conversion mobile energy storage system under engine conditions of low-speed and light-load

The thermal heat from diesel particulate filter (DPF) can generate electrical energy through the thermoelectric generator (TEG) which can be stored in mobile battery power energy storage system (MBPES). The DPF-TEG of MBPES system is a new technology proposed in this study, which is made up of the DPF system, heat exchanger (HEX), the thermoelectric module (TEM) and the battery. The effects of low-speed and light-load operating conditions on the DPF-TEG of MBPES system were studied. The low regeneration temperatures (823 K, 873 K, 923 K) and the high regeneration temperatures (1606 K, 1696 K, 1786 K) were selected to explore the thermoelectric conversion performance of DPF-TEG of MBPES system. The maximum output power is increased 55% with the velocity change from 6 m/s to 8 m/s at low regeneration temperatures. The DPF-TEG of MBPES system contains the 48 TEMs with external load 19.2 Ω, which can generate the maximum power output of 4.99 w/6 w/7.12 w of 823 K/873 K/923 K, 32.09 w/36.76 w/41.75 w of 1606 K/1696 K/1786 K. The output voltage of the 4 TEMs increased from 0.015837 V to 0.016172 V per 10 K temperature difference. The output power grew from 0.017714 w to 0.08057 w.

Improving the Aerodynamic Performance of WIG Aircraft with a Micro-Vortex Generator (MVG) in Low-Speed Condition

This present study investigated the potential of passive flow control to reduce induced drag by using a micro-vortex generator (MVG) at a backward-facing step (BFS) location. A wing-in-ground (WIG) craft is a fast watercraft that resembles a dynamically stabilised ship that can move or glide across the surface of water or land. Therefore, the wing of the WIG is designed to glide when in contact with water, which helps to decrease drag and enhance the lift of the overall vehicle. However, the existing design of the hull-fuselage of WIG tends to induce more drag during the flight, especially at a flow downstream of a BFS, which will cause inefficient fuel consumption over the distance travelled. MVG with the ramp type was chosen and tested at various angles (°) and heights (h). The angles (°) tested were 12°, 16°, and 24°, while the heights (h) tested were 0.4 δ, 0.6 δ, and 0.8 δ, where δ refers to the boundary layer height. The model was designed and fabricated using a 3D printer. The 3D model was tested in a subsonic wind tunnel at Re = 6.1 × 104 m−1 to 6.1 × 105 m−1 between 1 and 10 m/s. This study demonstrated that the most effective angle and height of MVG for reducing the drag coefficient were 16° and 0.6 δ, respectively. In comparison to an uncontrolled case, the drag coefficient decreased significantly by 38% compared to the baseline.

Friction Coefficient Characteristics of Typical Subway Brake Shoes and Brake Pads in Service

Brake pads and brake shoes are the main components of the friction pair of the subway air brake. At present, the average coefficient of friction is usually used as a criterion for evaluating the braking effect of pads and shoes. In this paper, by analyzing the braking process of the subway, it is inferred that the average friction coefficient has a poor evaluation effect under the low-speed common braking conditions, and a new alternative evaluation index, the equivalent average friction coefficient at low speed, is proposed. The conjecture is verified by the test bench test, and the feasibility of the low-speed equivalent average friction coefficient as an evaluation index under low-speed conditions is proved.

Research on the Vibration Behavior of Ring–Block Friction Pair Made of Materials of Water-Lubricated Rubber Bearing under Special Operating Conditions

A water-lubricated rubber bearing (WLRB) is prone to generate frictional vibration noise under special operating conditions, which seriously affects the acoustic stealth performance of warships and threatens their navigation safety. Meanwhile, the main factor affecting the frictional vibration behavior of a WLRB is the materials of the friction pair. Therefore, this work selects a friction pair composed of a copper ring and a rubber block as the research object and studies the frictional vibration behavior of the ring–block friction pair under low-speed and starting conditions. The real friction coefficient curve is used to establish a transient dynamic finite element analysis model for the ring–block friction pair. The effects of the load, friction coefficient, and Young’s modulus on the frictional vibration behavior under special operating conditions are studied. The analysis’s results show that the frequency of the medium-high frequency friction-induced vibration disappears under low-speed operating conditions when the friction coefficient is below 0.1. During the startup process, even if the friction coefficient is very low, the medium-high frequency friction-induced vibration still exists. The research results provide ideas for future theoretical research and guidance suggestions for engineering practice.

Effect of Graphite Filling Pore Structure Size on the Tribology Behaviors of Tin Bronze/45 Steel Pairs With Grease Under Low-Speed and Heavy Load Conditions

Effect of Graphite Filling Pore Structure Size on the Tribology Behaviors of Tin Bronze/45 Steel Pairs With Grease Under Low-Speed and Heavy Load Conditions

Study on Grinding Behavior Characteristics under Low-Speed Grinding Condition

In order to explore the crushing mechanism of minerals, this paper attempts to eliminate the throwing effect of media and study the grinding characteristics of minerals only under the action of abrasion force. In this paper, the method of removing the throwing state of media is to adjust the mill to a lower rotational speed, so that the grinding media are all in a cascading state. Three single-component pure minerals, quartz, pyrrhotite, and pyrite, commonly found in complex ores, were selected as research objects to study the grinding behavior characteristics of the three minerals only under the force of abrasion. The effects of mineral species, feed-particle sizes, grinding time, and other factors on the particle-size distribution and product-generation rate of grinding products are studied. The results show that from the particle-size distribution of grinding products, the yield of coarse particles is the highest, while the yield and t10 value of other fine particles are very low. The feed-particle size and the hardness of the mineral sample affect the grinding behavior. The product particle size is mainly 0.71 times the feed-particle size, and the other fine particle sizes generated are less than 0.5 times the feed-particle size.

Formation and steady state characteristics of flow field effect in the header of a stripping prior to cutting combine harvester with CFD

In order to analyze the formation mechanism of the flow field in the header of a stripping prior to cutting combine harvester and compare the steady characteristics of the flow field generated by flat and concave combs, this study combined bench tests and computational fluid dynamics (CFD) to analyze them. During the formation of the flow field, the airflow produced “bottoming out” and “vortex” and other phenomena. At high speed, the maximum velocity of the airflow generated by the flat comb was 10.39 m s−1 and that of the concave comb was 10.59 m s−1; the flow field generated by the concave comb was better than that generated by the flat comb. Significant pulsation effects were generated in the airflow at the rice inlet and return outlet; the pulsation intensity was positively correlated with the pulsation mean velocity. At the return outlet, the turbulence of the airflow generated by the concave comb rotation was higher than that of the airflow generated by the flat comb rotation for both low and high speed conditions. This study explores the characteristics of stripping loss in the header of a stripping prior to cutting combine harvester from the perspective of flow field, which provides ideas for the structural optimization of a stripping prior to cutting combine harvester and the study of stripping loss reduction in the later stage, and also provides a reference for the rational use of air flow in the rotating domain in engineering applications.

Experimental‐based study of gear vibration characteristics incorporating the fractal topography of tooth surface

AbstractMicroscopic roughness is inevitable on the gear meshing surface, which is also a key parameter affecting the dynamic response. The surface roughness exhibits self‐affine characteristics across multiscales. To explore the influence of surface fractal topography on the vibration amplitude of the gear system under different rotational speeds and loads, an experimental setup of spur gear transmission is devised. The fractal dimension and fractal roughness of the meshing surface are calculated by the power spectral density method. The relationships between gear response and fractal parameters are revealed experimentally. Results indicate that a rougher tooth surface, that is, a smaller fractal dimension or larger fractal roughness, corresponds to an intense vibration amplitude. The sensitivity of dynamic response to the tooth surface topography varies at different rotational speeds and loads. Under low speed and light load conditions, the fractal dimension and fractal roughness have a more obvious influence on the dynamic response of the gear transmission system. With the increase of speed and load, the macroworking conditions gradually become the main factor attributed to vibration amplitude.

Technological Readiness, Innovation, Entrepreneurship: Three Key Elements of Increasing the Competitiveness of Small and Medium-Sized Enterprises in Vietnam

"The purpose of the research is to analyze the factors and features that influence the development of the business environment in Vietnam, taking into account the technological readiness of higher educational institutions. The following methods were used to achieve research goals: descriptive, survey, comparative. The results of the paper determined that entrepreneurship training lies not only in improving the abilities and characteristics of students, forming the structure of the training program, communication system, startup and entrepreneurial ecosystem, but also in forming the structure of the technological readiness of the business. Technological readiness, innovation and entrepreneurship are the three key pillars of increasing the competitiveness of enterprises, which must necessarily be initiated by universities. It was determined that in the conditions of low innovation speed of the economy, the considered aspects of increasing the competitiveness of experts in the subject area require, first of all, the joint participation of the state and local authorities to accelerate innovative elements. The Vietnamese government needs to properly balance the modern trends of enterprises and the state as a whole in order to rationally organize the management of small and medium-sized enterprises, starting with higher educational institutions."

Tribological properties and synergetic self-lubricating mechanism of PS-PAO based nanocapsules with MoDTC addtives

With development of encapsulation technology, analysis of dependent nano-scaled microcapsule is significant to intensively understand self-lubrication behavior. In this paper, polystyrene (PS)-poly alpha olefin (PAO) capsules were synthesized with PAO as core and PS as shell. The diameter, shell thickness and encapsulated rate of PS-PAO4 were 381.51 ± 25.44 nm, 40 nm and 43.29 wt.%. The friction coefficient (COF) of PS-PAO4 by SRV friction test was 0.089, which played intermediate between PS nanosphere and PAO oil. Comprehensive analysis with Hamrock-Dowson equation and classical Stribeck curve manifested that the PS-PAO nanocapsules and PS nanospheres stayed in mixed lubrication regime, and PAO oil stayed in the boundary lubrication regime. Due to the absence of lubrication, PS dry friction and asperities contact status were more significant to determine the lubrication state of PS-PAO4 sample. The influence factors including load, operating temperature, PAO types and molybdenum dithiocarbamate (MoDTC) addtives were respectively investigated. A three-stage decline curve of PS-PAO4/MoDTC was found with final COF of 0.015, which the COF value decreased by 83.15% compared by PS-PAO4. The synergetic self-lubricating mechanism was mainly determined by asperity contacts, PS debris grinding, FeS tribofilm formation of MoDTC additives and counterparts, transfer film and third body formation by PS, MoDTC, PAO oil and counterparts. This work provides intensive understanding of nanocapsules for mixed lubrication regime and is expected to apply in ultrathin coating, liquid lubricant additives and functional polishing abrasives under heavy-duty and low speed conditions.

Conceptual Design of a Nonconstant Swept Flying Wing Unmanned Combat Aerial Vehicle

The design of unmanned combat aerial vehicles (UCAVs) is primarily governed by the low-observability requirement for military applications rather than aerodynamic performance. The conceptual design and optimization of UCAV models via size and shape variables for different missions in different flow regimes form a research area for military vehicle design. Flying wing UCAVs experience flow separation during takeoff and landing, and furthermore exhibit stability issues. The aerodynamic performance of these UCAVs can be significantly improved by redesigning their leading-edge sweep angle and wing planform. In the present work, the initial weight determination, aerodynamic sizing, and planform with and without inlet lip integration, and the conceptual design of a nonconstant leading-edge flying wing UCAV configuration are performed. Next, the obtained conceptual design is downscaled 1:20 to be used as a wind-tunnel model and optimized for low-speed conditions using a kriging-based surrogate model with a vortex-lattice method to maximize the lift-to-drag ratio. Later, the optimized design is validated using an open-source computational fluid dynamics code, OpenFOAM 8.0, to verify the accuracy of the surrogate model and to investigate the aerodynamic characteristics. The optimized UCAV design exhibited improved aerodynamic characteristics in terms of the lift-to-drag ratio. Furthermore, the aerodynamic performance and flowfield of the optimized UCAV model with and without inlet lip integration have been evaluated at low and high speeds.

Comparative Study of Magnet Temperature Estimation at Low Speeds Based on High-Frequency Resistance and Inductance

Interior permanent magnet synchronous motors have been widely used in electric vehicles. These motors employ Nd-Fe-B as the permanent magnet, which is vulnerable to temperature variations. Moreover, some features of Nd-Fe-B magnets are related to temperature, which can affect motor characteristics. Therefore, magnet temperature is an important parameter and methods for estimating it have been developed. In particular, a signal injection method has been developed for low-speed regions. In this method, two parameters are employed: high-frequency resistance and high-frequency inductance. In this paper, these two methods are compared to determine which parameter is more appropriate for estimations at low speeds and to reveal whether signal injection methods can be applied to the standstill condition. The comparison indicated that the high-frequency inductance-based method has a stronger correlation with the magnet temperature at low speed and standstill conditions than the high-frequency resistance-based method.

Analyzation of the Application Scenarios of Ackerman Geometry based on Vehicle Steering Model

A complete set of models about vehicle steering are established to testify the feasibility of Ackerman geometry applied in various scenarios. The relationship between different parameters from cars and how they affect the steering ability is studied by Python. Linear model and nonlinear model are built to adapt to small and big slip angle. The mechanism section is tested with data from two types of cars: BMW M3 and Chevrolet Cavalier. We find that M3 has a better steering capability since it can generate more lateral force with less sideslip. The relationship between slip angle and lateral force illuminates our research about Ackerman geometry. The result indicates that regular Ackerman principle is beneficial in the big wheel steering angle with low-speed conditions, because it can reduce the slip angle and tire-road interaction, making cornering smoother and reducing tire wear. However, in small wheel steering angle with high-speed conditions, the Ackerman principle has some limitations and should be amended, which adds to the slip angle and thus increase the lateral force to get better steering. That is basically the reason why Reverse Ackerman is widely applied in Formula 1.

Automotive Steering System and Its Controller Design for Intelligent Vehicles

<div>With the rapid development of intelligent vehicles technology, it is extremely urgent to solve environmental pollution and energy crisis. The electric intelligent vehicles technology can accelerate the world to move towards low carbonization and intelligence. In this article, one automatic steering system and its controller are designed with this electric vehicle as the verification platform. First, based on the digital mock-up (DMU) module of the CATIA digital prototype, the motion simulation of the automatic steering system is carried out. Then, the transient dynamics and fatigue analysis module from ANSYS Workbench 16.0 software is used to simulate and analyze the transmission mechanism. After verifying the reasonable strength of the real vehicle parts, the original platform steering system is reformed. Our intelligent vehicle uses a monocular charge-coupled device (CCD) to detect road marking lines and then employs a linear two degrees of freedom (2-DOF) vehicle model to establish a preview deviation model based on the visual navigation lane lines. A vehicle lateral control method combining fuzzy logic rules, adaptive proportional-integral-derivative (PID) control strategy, and preview deviation is designed. A lateral controller is built using Simulink software for lane tracking simulation, and a good tracking effect is obtained. Finally, the results of low-speed real vehicle tests show that the vehicle can stably track the target lane line at low-speed conditions.</div>

A Novel Geometry Optimization Approach for Multi-Recess Hydrostatic Bearing Pad Operating in Static and low-Speed Conditions Using CFD Simulation

The design of a hydrostatic bearing pad is limited to simple geometry using analytical equations or one-parameter optimization based on experimental data. This study proposes and investigates a new two-parameter method for estimating optimal hydrostatic bearing pad proportions—recess area and position, using Computational Fluid Dynamics (CFD). In this study, 3D static CFD quarter model of a multi-recess hydrostatic bearing pad assuming laminar flow is used. The CFD model was calibrated based on experimentally obtained results and the literature. The recess pressure and resulting load are evaluated for a variety of recess positions and areas. Performance factors are calculated and interpolated in the MATLAB environment. Using the proposed novel two-parameter optimization, the energetic loss was reduced by 20% compared to the classical one-parameter approach. This methodology allows versatile and effective design of optimal hydrostatic bearings operating in low-speed conditions to achieve minimum energetic loss.

Research on Tunnel-Boring Machine Main Bearing Fatigue Damage and Vibration Response

Based on the damage evolution equation of bearing steel, a user subroutine was developed to simulate the fatigue damage behavior of the TBM main bearing under the condition of low speed and heavy load. In addition, the damage evolution law of the main bearing in the time domain and the space domain was studied. Then, a nonlinear spring element was introduced to simulate the interaction between the roller raceway, and the vibration response of the TBM after the main bearing damage was studied using the transient dynamic method. The research shows that the damage risk of the raceway is greater than that of the roller, and the damage risk of the main pushing raceway is greater than that of the other two raceways. The damage of the main bearing will not only lead to the increase in the peak vibration response of the TBM but also cause more frequency components of the response. By monitoring the time domain index of vibration signal, the damage degree to the main bearing can be mastered in real time, providing a reference for the maintenance of the main bearing.