Hasil untuk "Mechanical engineering and machinery"

Milkias Berhanu Tuka, Seid Endris Ali

The increasing demand for electric power, coupled with rapid urbanization, necessitates a reliable and high-quality electricity supply to meet consumer expectations. However, existing passive distribution systems are inadequate to address the escalating power requirements, resulting in challenges such as increased power losses and suboptimal voltage profiles. In the base case scenario, the total active and reactive power losses were substantial, and many buses exhibited voltage magnitudes that fell outside acceptable limits. This study investigates the optimal placement and sizing of distributed generation (DG) resources to improve the performance of distribution feeders. A multi-objective optimization framework, utilizing a Genetic Algorithm (GA), was developed to minimize power losses and enhance voltage profiles. Load flow analysis was conducted using the Backward/Forward Sweep (BFS) method, allowing for precise evaluation of the distribution feeder under various DG configurations. Consequently, the study successfully enhanced the system through optimal DG allocation. Additionally, a comparative analysis was conducted to assess the performance of the proposed GA algorithm against other optimization techniques. The results indicate that, in nearly all cases, the GA method outperforms PSO by reducing system power losses and improving the voltage profile more effectively.

Matija Hoić, Mario Hrgetić, Ivan Ruškan et al.

The paper presents the design of an active seat suspension system for a medium-sized passenger vehicle (installation height of 180 mm), which is aimed at enhancing passenger comfort, with an emphasis on autonomous vehicle applications. The system is developed in two design variants based on Scott–Russell and Kempe mechanisms. The former is characterized by high rigidity and low friction, and it serves as a benchmark solution in this research. The latter is distinguished by cost-effectiveness and, thus, targeted for production vehicle applications once it is verified against the benchmark solution. Both designs are developed to satisfy the operational requirements derived from system computer simulations (suspension stroke of ±40 mm, speed of up to 0.5 m/s, and acceleration of up to 1 g), which are based on a half-car vehicle model extended with seat suspension dynamics and controlled by a linear quadratic regulator. The paper also outlines the electrical, measurement, and basic control subsystem of the overall active seat suspension mechatronic system. Finally, it presents experimental identification results to illustrate that the designed system complies with the specified requirements.

Yundie Guan, Xiangyu Zhang, Zheming Liang et al.

Abstract The intermittency and volatility of renewable energy have been major challenges in modern power systems. This paper proposes a self‐adaptive energy management strategy based on deep reinforcement learning (DRL) to integrate renewable energy sources into a system comprising compressed air energy storage, battery energy storage systems, and solid oxide fuel cells. However, the basic deep deterministic policy gradient algorithm lacks sensitivity to environmental changes, particularly when there is a mismatch in module capacity within the system. This limitation may affect the proper selection of the charging and discharging actions for the hybrid energy storage system. Thus, some modifications are dedicated to the careful replay buffer design in the basic algorithm, improving the ability to identify subtle changes in the reward function. The proposed method is also compared with other DRL methods to validate the feasibility and effectiveness. The simulation results demonstrate the compatibility of the improved algorithm with the proposed energy management strategy and better performance in terms of economic benefits.

Turja Nandy, Ronald A. Coutu, Rafee Mahbub

Microelectromechanical systems (MEMS) ohmic contact switches are considered to be a promising candidate for wireless communication applications. The longevity of MEMS switches is directly related to the reliability and performance of microcontacts. In this work, an improved microcontact test fixture with high actuation rates (KHz) and highly precise position control (nm) and force (nN) control was developed. Here, we collected microcontact performance data from initial contact tests (ICT) and microcontact reliability data from cold switched tests (CST). To perform these tests with our test fixture, we fabricated MEMS microcontact test structures with relatively high Young’s modulus electroplated Nickel (Ni)-based, fixed–fixed beam structure with Au/RuO₂ bimetallic microcontacts. These structures were characterized for forces ranging from 200–1000 µN in ICT tests. In a CST test, the tested microcontact survived more than 200 million cycles at a 1 KHz cycle rate, with a stable contact resistance value ranging between 3.8–5.2 Ω. These experiments validate the potentiality of our microcontact test fixture, and will facilitate further investigation on advanced microcontacts to enhance the MEMS switch’s reliability.

FENG Jianghua, TAN Bo, DOU Zechun et al.

With the continuous advancement of China's "dual carbon" goals and the ongoing optimization of the energy mix, the electrification of transportation equipment, as a low-carbon and environmentally-friendly approach, has become an important development trend in the transportation industry. This paper presents the exploration in high-power-density electrification technologies for transportation equipment, focusing on those in the chain-type key technology routes encompassing devices, components, equipment, systems and architectures. Taking products supplied by CRRC Zhuzhou Institute Co., Ltd. as an case study, detailed investigations were made into five key technologies for high-power-density design: high-frequency converters, customized devices, silicon-based equipment, structural integration, and diversified networking, and three high-power-density generic technologies: thermal management, electromagnetic compatibility, and reliability, highlighting their key roles in improving the performance, efficiency, and reliability of transportation equipment. The study summarizes the current research status concerning the development of transportation equipment towards higher power, lighter weight, and smaller size. For future development in high-power-density electrification technologies, this paper suggests a focus on continuous innovation and development in four areas: the innovation chain, intelligent systems, new power semiconductor device technologies, and safety. The research outcomes provide strong support for the green transformation and sustainable development of the transportation industry.

M. K. Mehta, M. Zaaijer, D. von Terzi

<p>Traditionally, wind turbine and wind farm designs have been optimized to minimize the cost of energy. Such a design would make sense when bidding in price-based auctions. However, in a future with a high share of renewables and zero subsidies, the wind farm developer is exposed to the volatility of market prices, where the price paid per kilowatt-hour of energy would not be constant anymore. The developer might then have to maximize the revenue earned by participating in different energy, capacity, or ancillary services markets. In such a scenario, a turbine designed for maximizing its market value could be more profitable for the developer compared to a turbine designed for minimizing the levelized cost of electricity (LCoE). This study is in line with this paradigm shift in the field of turbine and farm design. It is a continuation of a previous study conducted by the same authors <span class="cit" id="xref_paren.1">(<a href="#bib1.bibx31">Mehta et al.</a>, <a href="#bib1.bibx31">2024</a>)</span>, which explicitly focused on the drivers of turbine sizing with respect to LCoE. The goal of this study is to optimize the design for a new set of objective functions and analyze how various day-ahead market conditions and objectives drive turbine design. A simplified market model that can generate hourly day-ahead market prices is developed and coupled with a wind-farm-level multidisciplinary design analysis and optimization (MDAO) framework to evaluate key economic indicators of the wind farm. The results show how the optimum turbine design is driven by both the choice of the economic metric and the market scenario. However, an LCoE-optimized design is found to perform well with respect to profitability-based economic metrics like modified internal rate of return (MIRR) or profitability index (PI), indicating a limited need to redesign turbines for a specific day-ahead market scenario.</p>

André F. P. Ribeiro, Claudia Muscari

Abstract Simulating entire wind farms with an actuator line model requires significant computational effort, especially if one is interested in wake dynamics and wants to resolve the tip vortices. A need to explore unconventional approaches for this kind of simulation emerges. In this work, the actuator line method is implemented within a lattice‐Boltzmann flow solver, combined with a sliding mesh approach. Lattice‐Boltzmann solvers have advantages in terms of performance and low dissipation, while the sliding mesh allows for local refinement of the blade and tip vortices. This methodology is validated on a well‐documented case, the NREL Phase VI rotor, and the local refinement is demonstrated on the NREL 5 MW rotor. Results show good agreement with reference Navier–Stokes simulations. Advantages and limitations of the sliding mesh approach are identified.

ZHONG Hanwen, XIAO Lei, CHEN Wenguang et al.

Long wheelbase design of vehicle can effectively increase the standing area without increasing the body length, thus increasing the passenger capacity. Today, with the development of urbanization, the long wheelbase vehicle design has become a trend, but this poses new challenges to the low-speed trafficability and high-speed stability of vehicles. This paper takes the long wheelbase commercial vehicle as the research object. Based on the vehicle dynamics and suspension design theory, the author first designed key parameters of long wheelbase vehicle and built an 18 degrees of freedom (DOF) dynamics simulation model for the vehicle; then designed the four-wheel steering (4WS) control algorithm according to the design parameters of the vehicle, for achieving the control target that the side slip angle tends to zero; and finally researched the influence of front-wheel steering (FWS) control and four-wheel steering control on the dynamic performance of the vehicle under the steady-state circumferential conditions with different turning radiuses and steering wheel angle pulse conditions with different speeds. The simulation results show that, under the steady-state circumferential turning condition with a low-speed turning radius of R15, the four-wheel steering design reduces the passing space from 4.6 m to 3.9 m, effectively improving the tracking ability of the front and rear axles of the vehicle and enhancing the trafficability and safety of the vehicle, and under the pulse condition with a maximum speed of 100 km/h, reduces the peak lateral acceleration from 4 m/s2 to 1.5 m/s2 and the peak yaw rate from 11°/s to 3°/s. Therefore, under high-speed steering wheel angle pulse conditions, the four-wheel steering design can effectively reduce the dynamic indicators of the vehicle, such as side slip angle, lateral acceleration and yaw rate, and improve the safety, stability and comfort of the vehicle at high speed.

Christian Moisés Trujillo Córdova

La crisis ambiental por el cambio climático ha obligado a muchos Estados a dirigir esfuerzos hacia la transición medioambiental para reducir la probabilidad de ocurrencia de una situación con un impacto negativo sobre su población o medioambiente. El Perú no es la excepción. En tal sentido, surge la necesidad de identificar y categorizar sus distritos según un determinado riesgo socioambiental. Ante tal reto, se construyó e implementó una metodología cuantitativa multietápica, la cual hizo uso tanto del aprendizaje automatizado (supervisado y no supervisado) como de la econometría espacial. Los resultados de la metodología, visualizados a través de índices de riesgo emergentes, evidenciaron la existencia de 165 distritos considerados zonas con riesgo socioambiental (ZRS), ubicados en su mayoría en la franja costera. Finalmente, se concluye que el patrón y replicabilidad del modelo de desarrollo urbanístico en el Perú actualmente no es coherente con los esfuerzos de conservación y preservación del medioambiente.

Lin ZHANG, Yusuke SATO, Jiwang YAN

Fast tool servo (FTS) in ultra-precision diamond turning is an efficient technique for high-precision fabrication of freeform optics. However, the currently adopted constant scheme for control point sampling takes no account of the shape variation of the desired surface, which might lose some micro features and result in low form accuracy and non-uniform surface quality. Facing this issue, this manuscript proposes a novel adaptive control points sampling strategy, which improves the form accuracy and keeps as many as the micro surface features. In the optimization method, the sampling stepovers between two adjacent control points are actively adjusted to adapt to the surface profile variation. By adopting this method, the control point sampling induced interpolation error is constrained within the desired tolerance and eliminates the lack/over-definition of control points in the machining area. The feasibility of the proposed optimization method is demonstrated by both theoretical simulations and fabrication experiments of sinusoid freeform surfaces. Compared with the constant sampling method, both the theoretical predicted and experimental measured form error of the proposed method is remarkably reduced by about 35 % with the same amount of control points. This technique provides a new route to allocating control points in FTS diamond turning to achieve high form accuracy and machining efficiency in the fabrication of freeform optics.

Sameer Ali Alsibiani

In this study, roughened absorber plate and jet nozzle are simultaneously employed to enhance the efficiency of a solar based air heater. The impact of jet nozzle hole shape is comprehensively investigated for the mentioned system which have not been investigated before. Three-dimensional steady-state simulations of incompressible turbulent fluid flow and heat transfer are performed using the Reynolds-Averaged Navier-Stokes (RANS) equations to model the jet solar air heater (JSAH). Five different jet hole shapes (circular, triangular, square, hexagonal, and rectangular) are examined and results are compared with conventional structure. The thermal and hydraulic performance of the JSAH is assessed using a variety of geometric and operating parameters, including jet diameter ratio (dj/Dh), jet hole streamwise pitch (Lj/Dh), and Re number (Re). The results show that the ratio of (Nu/Nus) initially increases and then decreases as the hydraulic diameter of the jet holes increases. Circular jet holes consistently outperform other shapes, while rectangular and triangular jet holes perform poorly. The pressure penalty (f/fs) decreases with increasing (dj/Dh), with circular jet holes exhibiting the lowest value. Increasing the Reynolds number enhances heat transfer and pumping power but leads to a decrease in (Nu/Nus) and negatively affects the THPP of the JSAH compared to a conventional smooth solar air heater. The study also reveals that the THPP initially increases with streamwise pitch (Lj/Dh) but then declines, following the trend of (Nu/Nus). The results demonstrate up to 4.5 times higher Nusselt numbers with a jet solar air heater versus a smooth solar heater. A maximum thermal-hydraulic performance parameter of 1.64 indicates the proposed design's efficacy. This research furnishes critical insights into optimizing solar air heater performance by examining jet nozzle hole shape, streamwise pitch, and Reynolds number. It enables enhancing thermal efficiency and thermo-hydraulic performance.

Mani Teja Bodduluri, Torben Dankwort, Thomas Lisec et al.

Energy harvesting and storage is highly demanded to enhance the lifetime of autonomous systems, such as IoT sensor nodes, avoiding costly and time-consuming battery replacement. However, cost efficient and small-scale energy harvesting systems with reasonable power output are still subjects of current development. In this work, we present a mechanically and magnetically excitable MEMS vibrational piezoelectric energy harvester featuring wafer-level integrated rare-earth micromagnets. The latter enable harvesting of energy efficiently both in resonance and from low-g, low-frequency mechanical energy sources. Under rotational magnetic excitation at frequencies below 50 Hz, RMS power output up to 74.11 µW is demonstrated in frequency up-conversion. Magnetic excitation in resonance results in open-circuit voltages > 9 V and RMS power output up to 139.39 µW. For purely mechanical excitation, the powder-based integration process allows the realization of high-density and thus compact proof masses in the cantilever design. Accordingly, the device achieves 24.75 µW power output under mechanical excitation of 0.75 g at resonance. The ability to load a capacitance of 2.8 µF at 2.5 V within 30 s is demonstrated, facilitating a custom design low-power ASIC.

Shin’ya OBARA

In order to make an electric power of renewable energy source increase, development of a new transmission network is effective. However, it is because installation of a new transmission network takes a huge investment, operating technique regarding improvement of the utilization factor of a transmission network is investigated. On the other hand, stabilization of distribution electric power by hydrogen energy careers, such as ammonia or methyl-cyclohexane (MCH) is expected to contribute to the drastic increase in utilization factor of the transmission network. Moreover, because these hydrogen energy careers can store electric power, it is effective in making the reliability of the transmission network increase. The energy flow of the system accompanied by use of each energy career of ammonia or MCH is clarified, the examination method of the utilization factor of the transmission network with the electric power leveling by the hydrogen career was proposed. The proposal analysis method is applied to a transmission network of Wakkanai, the relation between the amount of introduction of renewable energy and the utilization factor of the transmission network, and the utilization factor of the transmission network using a hydrogen career were clarified.

Lemma Shallo, Getachew Sime

The main objective of this study is to investigate factors that determine the functionality of bio-digesters in southern Ethiopia. Data were collected through personal interview of adopter households using a semi-structured questionnaire and focus group discussions and key informant interviews. Results indicated the proportion of the functional status of digesters was ‘never operate’ (17.9%), ‘poor’ (19.4%), ‘fair’ (18.6%), ‘good’ (17.2%) and ‘excellent’ (26.9%). Sex of household head, household total income, institutional technical follow-up and support, and level of satisfaction with the biogas programme service significantly and positively influence the functionality of bio-digesters. Whereas, distance from residence to water source and to the nearest market for appliances significantly and negatively influence the functionality of digesters. Advances in these perspectives could improve the functionality of bio-digesters, the reputation of biogas technology among members of communities as well as help ensuring a sustainable energy security in rural Ethiopia.

Viacheslav Shemelin, Tomas Matuska

In the present work, the detailed mathematical model of a dual air/water solar collector (DAWC) has been developed and experimentally verified. To demonstrate the application of the DAWC, three buildings with different energy performance levels and three building locations were chosen in analyzed case studies. Four solar collector systems were compared with one another. The solar yield of the described systems was determined by simulation using the detailed theoretical model of DAWC. The results indicate that in the case of combining a domestic hot water preparation system and recirculating-air heating system based on DAWC, it is possible to achieve up to 30% higher solar energy yield compared to a conventional solar domestic hot water preparation system dependent on climate and building performance.

R. Rouhollahi, S. Baheri Islami, R. Gharraei et al.

Experimental investigation of Electrohydrodynamic developing falling film flow of transformer oil has been conducted within an inclined rectangular channel and hydrodynamic characteristics of the flow have been revealed. The electric field has been generated by five overhead thin wire electrodes connected to the positive high DC voltage on the air and the grounded plate electrodes which are placed upon the floor of the channel. It is the first time that the wavy behavior on a liquid falling film's interface has been created by this electrode configuration. A non-intrusive method has been used to measure the local flow structure by a high-speed camera, then statistical characteristics of the wavy falling film have been computed by image processing of the captured video frames. By applying 13-16 kV to the wire electrodes, the influence of EHD force on the wavy behavior of falling film has been conducted for Reynolds number 10-120 in the laminar-wavy regime at three different inclination angles 15◦, 30◦ and 45°. The vertical distance of the high-voltage wire electrodes to ground electrodes has been set to 14 mm. The liquid velocity, film thickness, and wave frequency have been measured for non-electrified and electrified falling film, and their results have been evaluated with other experimental studies and an acceptable agreement has been obtained. The results indicate that the proposed HV wire-grounded plate electrode configuration in this study does not disturb the original structure of the falling film and by intensifying the wavy behavior of laminar falling film can either suppress or enhance heat/mass transfer rate. The effects of the applied voltage on the frequency, velocity and film thickness of the falling liquid film have been also discussed in detail.

B. Lou, Y. Qiu, X. Long

Smoke temperature distribution in non-smoke evacuation under different mechanical smoke exhaust rates of semi-transverse tunnel fire were studied by FDS numerical simulation in this paper. The effect of fire heat release rate (10MW 20MW and 30MW) and exhaust rate (from 0 to 160m3/s) on the maximum smoke temperature in non-smoke evacuation region was discussed. Results show that the maximum smoke temperature in non-smoke evacuation region decreased with smoke exhaust rate. Plug-holing was observed below the smoke vent when smoke exhaust rate increased to a certain value. Smoke spreading distance can be divided into three stages according to changes of smoke exhaust rate. The maximum smoke temperature model concluded that the peak temperature rise at tunnel vault is proportional to 0.75 power of dimensionless fire power. The maximum temperature in non-smoke evacuation region decays exponentially with the increase of smoke exhaust rate. However smoke vent interval influences the dimensionless maximum temperature in non-smoke evacuation region slightly. Smoke vent interval influences the dimensionless maximum temperature in non-smoke evacuation region slightly.

Cenk Onan

One of the most important considerations to be considered in the design of energy efficient buildings is the thickness of the insulation to be applied to the building. In this study the existing building stock in Turkey has been investigated depending on parameters such as the height and the area. A model building has been created covering all of these buildings. Fuel emission reduction of combustion system was calculated in the case of insulation applied to this model building. Heat loss of the existing building stock and exhaust emissions and the contribution to the country's economy with the model building methodology are also determined. The results show that the optimum insulation thicknesses vary between 3.21 and 7.12 cm, the energy savings vary between 9.23 US$/m 2 and43.95 US$/m 2 , and the payback periods vary between 1 and 8.8 years depending on the regions. As a result of the study when the optimum insulation thickness is applied in the model building, the total energy savings for the country are calculated to be 41.7 billion US$. And also total CO 2 emissions for the country are calculated to be 57.2 billion kg CO 2 per year after insulation.

J.E. Stangroom