Search results
1 – 10 of over 1000Chaoyue Wang, Fujun Wang, Changliang Ye, Benhong Wang and Zhichao Zou
Tip leakage vortex flow (TLV) is a common flow phenomenon in the axial-flow hydraulic machinery. High-efficiency simulation of TLV is still not an easy task because of the complex…
Abstract
Purpose
Tip leakage vortex flow (TLV) is a common flow phenomenon in the axial-flow hydraulic machinery. High-efficiency simulation of TLV is still not an easy task because of the complex turbulent vortex-cavitation interactions. As an important basis of CFD, turbulence model directly affects the efficient computation of TLV. The purpose of this paper is to evaluate the newly developed MST turbulence model in predicting the TLV flows.
Design/methodology/approach
By using the MST turbulence model and the ZGB cavitation model, numerical simulations of the TLV generated by a NACA0009 hydrofoil were performed under the cavitation-free and cavitation conditions, and the results were compared with the available experimental data.
Findings
The important features of TLV are well captured by the MST-based simulation scheme, and the problem of under-predicting the cavitating TLV tube is well solved. Turbulent viscosity is reasonably adjusted in the TLV core regions, and the LES-like mode is activated, which is beneficial to obtain more turbulent information on the same URANS grids. The requirements of grid size and time step of the MST model are much lower than that of the LES method, thereby weighing a good balance between the simulation accuracy and computation cost.
Originality/value
The MST turbulence model is suitable for the high-efficiency simulation of the TLV flows, which can lay a good foundation for efficient engineering computations of the cavitating TLV in the axial-flow hydraulic machinery.
Details
Keywords
Compared to the traditional wireless network, the multi‐hop ad hoc wireless network is self‐configurable, dynamic, and distributed. During the past few years, many routing…
Abstract
Compared to the traditional wireless network, the multi‐hop ad hoc wireless network is self‐configurable, dynamic, and distributed. During the past few years, many routing protocols have been proposed for this particular network environment. While in wired and optical networks, multi‐protocol label switching (MPLS) has clearly shown its advantages in routing and switching such as flexibility, high efficiency, scalability, and low cost. However MPLS is complex and does not consider the mobility issue for wireless networks, especially for ad hoc wireless networks. This paper migrates the label concept into the ad hoc network and provides a framework for the efficient label routing protocol(LRP) in such a network. The MAC layer is also optimized with LRP for shorter delay, power saving, and higher efficiency. The simulation results show that the delay is improved significantly with this cross‐layer routing protocol.
Details
Keywords
Mohsen Sajadnia, Sajjad Dehghani, Zahra Noraeepoor and Mohammad Hossein Sheikhi
The purpose of this study is to design and optimize copper indium gallium selenide (CIGS) thin film solar cells.
Abstract
Purpose
The purpose of this study is to design and optimize copper indium gallium selenide (CIGS) thin film solar cells.
Design/methodology/approach
A novel bi-layer CIGS thin film solar cell based on SnS is designed. To improve the performance of the CIGS based thin film solar cell a tin sulfide (SnS) layer is added to the structure, as back surface field and second absorbing layer. Defect recombination centers have a significant effect on the performance of CIGS solar cells by changing recombination rate and charge density. Therefore, performance of the proposed structure is investigated in two stages successively, considering typical and maximum reported trap density for both CIGS and SnS. To achieve valid results, the authors use previously reported experimental parameters in the simulations.
Findings
First by considering the typical reported trap density for both SnS and CIGS, high efficiency of 36%, was obtained. Afterward maximum reported trap densities of 1 × 1019 and 5.6 × 1015 cm−3 were considered for SnS and CIGS, respectively. The efficiency of the optimized cell is 27.17% which is achieved in CIGS and SnS thicknesses of cell are 0.3 and 0.1 µm, respectively. Therefore, even in this case, the obtained efficiency is well greater than previous structures while the absorbing layer thickness is low.
Originality/value
Having results similar to practical CIGS solar cells, the impact of the defects of SnS and CIGS layers was investigated. It was found that affixing SnS between CIGS and Mo layers causes a significant improvement in the efficiency of CIGS thin-film solar cell.
Details
Keywords
Marian Lukaniszyn, Mariusz Jagiela and Rafal Wrobel
A brushless, permanent magnet, three‐phase disc‐type salient‐pole DC motor with co‐axial flux in the stator is considered. Electromechanical properties of a basic eight‐pole motor…
Abstract
A brushless, permanent magnet, three‐phase disc‐type salient‐pole DC motor with co‐axial flux in the stator is considered. Electromechanical properties of a basic eight‐pole motor are compared with those for a 16‐pole one of the same volume, in order to contrast the two potential candidates for variable‐speed, low‐cost drives. As a basis of the comparative analysis, 3D FEM magnetic field modelling and circuit analysis considering an electronic commutator are employed. Increasing the number of poles results in unfavourable raising in the switching frequency. The eight‐pole motor construction has been shown in simulations to have higher efficiency and lower power losses than its 16‐pole counterpart.
Details
Keywords
Feng Liang, Quanyong Xu and Ming Zhou
The purpose of this paper is to propose a quasi-three-dimensional (3D) thermohydrodynamic (THD) model for oil film bearings with non-Newtonian and temperature-viscosity effects…
Abstract
Purpose
The purpose of this paper is to propose a quasi-three-dimensional (3D) thermohydrodynamic (THD) model for oil film bearings with non-Newtonian and temperature-viscosity effects. Its performance factors, including precision and time consumption, are investigated.
Design/methodology/approach
Two-dimensional (2D), 3D and quasi-3D numerical models are built. The thermal and mechanical behaviors of two types of oil film bearings are simulated. All the results are compared with solutions of commercial ANSYS CFX.
Findings
The 2D THD model fails to predict the temperature and pressure field. The results of the quasi-3D THD model coincide well with those of the 3D THD model and CFX at any condition. Compared with the 3D THD model, the quasi-3D THD model can greatly reduce the CPU time consumption, especially at a high rotational speed.
Originality/value
This quasi-3D THD model is proposed in this paper for the first time. Transient mechanical and thermal analyses of high-speed rotor-bearing system are widely conducted using the traditional 3D THD model; however, the process is very time-consuming. The quasi-3D THD model can be an excellent alternative with high precision and fast simulation speed.
Details
Keywords
Nur Atiqah Hamzah, Mohd Ann Amirul Zulffiqal Md Sahar, Aik Kwan Tan, Mohd Anas Ahmad, Muhammad Fadhirul Izwan Abdul Malik, Chin Chyi Loo, Wei Sea Chang and Sha Shiong Ng
This study aims to investigate the effects of indium composition on surface morphology and optical properties of indium gallium nitride on gallium nitride (InGaN/GaN…
Abstract
Purpose
This study aims to investigate the effects of indium composition on surface morphology and optical properties of indium gallium nitride on gallium nitride (InGaN/GaN) heterostructures.
Design/methodology/approach
The InGaN/GaN heterostructures were grown on flat sapphire substrates using a metal-organic chemical vapour deposition reactor with a trimethylindium flow rate of 368 sccm. The indium composition of the InGaN epilayers was controlled by applying different substrate temperatures. The surface morphology and topography were observed using field emission scanning electron microscope (F.E.I. Nova NanoSEM 450) and atomic force microscopy (Bruker Dimension Edge) with a scanning area of 10 µm × 10 µm, respectively. The compositional analysis was done by Energy Dispersive X-Ray Analysis. Finally, the ultraviolet-visible (UV-Vis) spectrophotometer (Agilent Technology Cary Series UV-Vis-near-infrared spectrometer) was measured from 200 nm to 1500 nm to investigate the optical properties of the samples.
Findings
The InGaN/GaN thin films have been successfully grown at three different substrate temperatures. The indium composition reduced as the temperature increased. At 760 C, the highest indium composition was obtained, 21.17%. This result was acquired from the simulation fitting of ω−2θ scan on (0002) plane using LEPTOS software by Bruker D8 Discover. The InGaN/GaN shows significantly different surface morphologies and topographies as the indium composition increases. The thickness of InGaN epilayers of the structure was ∼300 nm estimated from the field emission scanning electron microscopy. The energy bandgap of the InGaN was 2.54 eV – 2.79 eV measured by UV-Vis measurements.
Originality/value
It can be seen from this work that changes in substrate temperature can affect the indium composition. From all the results obtained, this work can be helpful towards efficiency improvement in solar cell applications.
Details
Keywords
Nayyer Abbas Zaidi and Shafaat Ahmed Bazaz
– The purpose of this paper is to present the design of a microgripper system that comprises a dual jaw actuation mechanism with contact sensing.
Abstract
Purpose
The purpose of this paper is to present the design of a microgripper system that comprises a dual jaw actuation mechanism with contact sensing.
Design/methodology/approach
Interdigitated lateral comb-drive-based electrostatic actuator is used to move the gripper arms. Simultaneous contact sensing of the gripper jaws has been achieved through transverse comb-based capacitive sensor. The fabricated microgripper produces a displacement of 16 μm at gripper jaws for an applied actuation voltage of 45 V.
Findings
It is observed that the microgripper fails to operate for the maximum performance limits (70 μm jaws displacement) and produces uncontrolled force at the tip of the jaws > 45 V.
Originality/value
A novel behavioral model of the microgripper system is proposed using the fabricated dimensions of the system to carry out a detailed analysis to understand the cause of this failure. The failure analysis shows that the microgripper system failed to operate in its designed limits due to the presence of side instability in the designed combs structure. Our proposed failure model helps in redesigning the actuator to ensure its operation above 45 V so that the gripper jaw can be displaced to its maximum limit of 70 μm and also result in the increase of the controlled force from 250 to 303 μN at the microgripper jaws.
Details
Keywords
Sunil Kumar Tumma and Bheema Rao Nistala
The purpose of this paper is to design an on-chip inductor with high inductance, high-quality factor and high self-resonance frequency for the equivalent on-chip area using…
Abstract
Purpose
The purpose of this paper is to design an on-chip inductor with high inductance, high-quality factor and high self-resonance frequency for the equivalent on-chip area using fractal curves.
Design/methodology/approach
A novel hybrid series stacked differential fractal inductor using Hilbert and Sierpinski fractal curves is proposed with two different layers connected in series using vias. The inductor is implemented in Sonnet EM simulator using 180 nm CMOS standard process technology.
Findings
The proposed inductor reduces the parasitic capacitance and negative mutual inductance between the adjacent layers with significant improvement in overall inductance, quality factor and self-resonance frequency when compared with conventional series stacked fractal inductors.
Research limitations/implications
The fractal inductor is used to create high inductance in the single-layer process, but access to multilayers is restricted owing to unusual and expensive fabrication processes.
Practical implications
The proposed inductor can be used in implementation of low noise amplifier, voltage controlled oscillators and power amplifiers.
Originality/value
This paper introduces a combination of two fractal curves to implement a hybrid fractal inductor that enhances the performance of the inductor.
Details
Keywords
Xiongmin Tang, Tianhong Jiang, Weizheng Chen, ZhiHong Lin, Zexin Zhou, Chen Yongquan and Miao Zhang
How to use a simple and classical topology to provide a high-efficiency excitation voltage for dielectric barrier discharge (DBD) loads is one of the primary problems to be solved…
Abstract
Purpose
How to use a simple and classical topology to provide a high-efficiency excitation voltage for dielectric barrier discharge (DBD) loads is one of the primary problems to be solved for DBD application fields.
Design/methodology/approach
To address the issue, a set of modes that can generate a high-efficiency pulse excitation voltage in a full-bridge inverter are adopted. With the set of modes, the unique equivalent circuit of DBD loads and the parasitic parameter of the step-up transformer can be fully used. Based on the set of modes, a control strategy for the full-bridge inverter is designed. To test the performance of the power supply, a simulation model is established and an experimental prototype is made with a DBD excimer lamp.
Findings
The simulation and experimental results show that not only a high-efficiency excitation voltage can be generated for the DBD load, but also the soft switching of all power switch is realized. Besides this, with the set of modes and the proposed control strategy, the inverter can operate in a high frequency. Compared with other types of power supplies, the power supply used in the paper can fully take advantage of the potential of the excimer lamp at the same input power.
Originality/value
This work considers that how to use a simple and classical topology to provide a high-efficiency excitation voltage for DBD loads is one of the primary problems to be solved for DBD application fields.
Details
Keywords
The ability to simulate the effects of process technology on final product circuits has become virtually indispensable in modern VLSI production. It is especially significant as a…
Abstract
The ability to simulate the effects of process technology on final product circuits has become virtually indispensable in modern VLSI production. It is especially significant as a toot for controlling parametric yield by appropriate design centering and in determining the sensitivity of the electrical parameters to process control tolerances. The system demands the combined use of process simulation device simulation and circuit simulation all three of which rely heavily on computationally intensive numerical solution of partial differential equations. The severe computational overhead involved in ‘technology simulation TCAD)’ means it is generally expensive and limits the scope of statistical design centering and optimisation, which depend on a large number of simulations. A compromise solution is often resorted to by limiting simulation to one or two spatial dimensions, replacing numerical simulation by analytical approximations as implemented in the statistical process simulator: FABRICS 11, or combining numerical and analytical models as in the process/device simulator PRIDE.) This paper addresses the problem of simpler, higher efficiency TCAD evaluation by restricting the domain of the simulation and approximating the process/device characteristic relationship by a set of simple, computationally efficient empirical equations. These equations offer a high speed solution at the expense of decreasing accuracy away from the nominal process centre. Referred to as a ‘response surface model’, it is generated using the results of a small number of statistically designed TCAD simulations. As the process sample is centred around the nominal design parameters, the model can be used to statistically analyze the effects of process perturbations.