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1 – 10 of 495Dong Li, Bin Chen and Guo-Xiang Wang
The purpose of this paper is to present a numerical analysis of the laser surgery of port wine stain (PWS) with cryogen spray cooling to compare the treatment effect between pulse…
Abstract
Purpose
The purpose of this paper is to present a numerical analysis of the laser surgery of port wine stain (PWS) with cryogen spray cooling to compare the treatment effect between pulse dye laser and Nd:YAG laser, explain the incomplete clear of the lesion and optimize the laser parameter.
Design/methodology/approach
The complex structure of skin and PWS is simplified to a multi-layer skin model that consists of top epidermal layer and underneath dermis layer embedded with discrete blood vessels. The cooling effect of cryogen spray before laser firing is quantified by a general correlation obtained recently from the experimental data. The light distribution is modeled by the Monte Carlo method. The heat transfer in skin tissue is calculated by Pennes bioheat transfer model. The thermal damage of blood vessel is quantified by the Arrhenius damage integral.
Findings
For the vessel size studied (10-120 µm), pulse duration is recommended shorter than 6 ms. Large and deeply buried vessels, which may survive from 595 nm laser irradiation, can be coagulated by 1,064 nm laser due to its deep light penetration depth in skin. Furthermore, a desired uniform heating within the large vessel lumen can be achieved by 1,064 nm laser whereas 595 nm laser produce non-uniform heating.
Originality/value
The possible reason for the poor responding and incomplete clearance lesions is clarified. Laser wavelength and pulse duration are suggested to improve the clinical results.
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Hugo Rodriguez-Ignacio and Xose M. Lopez-Fernandez
The purpose of this paper is the numerical verification of the linearization coefficient ap proposed by Turowski for the calculation of the electromagnetic field distribution and…
Abstract
Purpose
The purpose of this paper is the numerical verification of the linearization coefficient ap proposed by Turowski for the calculation of the electromagnetic field distribution and therefore the stray losses inside magnetically saturated solid steel conductors.
Design/methodology/approach
The numerical verification is performed on a case study consisting of a simple current conductor sheet parallel to a solid steel plate. Numerical computations are compared with analytical calculations with and without inclusion of the semi-empirical Turowski’s coefficient.
Findings
Results confirm a good agreement between numerical values for steel with non-linear permeability and analytical ones applying Turowski’s coefficient. This is particularly powerful in the case of analytical calculation of the magnetic surface impedance (SI) to increase precision when hybrid methods are used. The concept of SI enables the establishment of hybrid approaches for the calculation of stray losses, combining the numerical methods (finite difference method, finite element method (FEM), etc.) together with the analytical formulation, gaining from the advantages of both methods.
Originality/value
Previous numerical analysis was focused on the field dependence on time for several depths inside solid steel. The aim of this paper is to investigate the electromagnetic field distribution inside solid steel on a representative FEM model and verify how the linearization coefficient ap proposed by Turowski works.
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Patricia Penabad‐Duran, Xose M. Lopez‐Fernandez, Janusz Turowski and Pedro M. Ribeiro
The purpose of this paper is to apply a 3D methodology to assess the heating hazard on transformer covers and present a practical tool to design amagnetic inserts arrangement.
Abstract
Purpose
The purpose of this paper is to apply a 3D methodology to assess the heating hazard on transformer covers and present a practical tool to design amagnetic inserts arrangement.
Design/methodology/approach
A practical 3D methodology linking an electromagnetic analytical formulation with thermal finite element method is used for computation. Such methodology allows the evaluation of the temperature on metallic device elements heated by electromagnetic induction. This is a 3D problem which in the case of power transformers becomes especially difficult to apply due to the discretization requirement into the thin skin depth penetration compared to big machine dimensions.
Findings
From the numerical solution of the temperature field, decisions on dimensions and different amagnetic inserts arrangements can be taken to avoid hot spots on transformer covers.
Research limitations/implications
Some parameters presented in the model as heat exchange coefficients and material properties are difficult to determine from formulae or from the literature. The accuracy of the results strongly depends on the proper identification of those parameters, which the authors adjust based on measurements.
Originality/value
Differing from previous works found in the literature, which focus their results in power loss computation methods, this paper evaluates losses in terms of temperature distribution, which is easier to measure and validate over transformer covers. Moreover, an experimental work is presented where the temperature distribution is measured over a steel cover plate and a cover plate with amagnetic insert.
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Phamella Reinert Tamanini Piccoli, Sérgio Henrique Lopes Cabral, Luiz Fernando de Oliveira, Odirlan Iaronka, Diogo Fernando Harmel, João Paulo Vieira and João Egídio Sapeli
This paper aims to present the proposition of a new experimental method for obtaining very crucial data of the structural steel that is used in the tank of oil filled power…
Abstract
Purpose
This paper aims to present the proposition of a new experimental method for obtaining very crucial data of the structural steel that is used in the tank of oil filled power transformers, namely, the volumetric losses and the magnetic permeability, both in function of the density of magnetic flux. Although these data are not usually available, they are fundamental for helping the transformer designer in avoiding the occurrence of hot spots in the transformer tank. The adoption of a conventional Epstein frame has restrictions because of the incompatibility between it and the samples of the steel.
Design/methodology/approach
The basis of the proposition is the same as that of the Epstein frame, with significant attention paid to the additional losses in the winding that creates the magnetic flux to the samples in the core. These losses can be significant and are created by the harmonics of current along the windings and are summed to the ohmic losses. For separating these winding losses from the magnetic losses, each sample is made as being the core of a toroidal 1:1 transformer. Thus, two tests with two identic of these toroidal transformers are necessary.
Findings
The proposed methodology is simple, because it is very similar to the classical tests of transformers (no-load and short-circuit tests). The process of separation of losses requires only a numerical fitting of curves for adjusting the winding losses as a function of the current amplitude, and the obtained results are coherent with the expected behavior of the magnetic losses and the magnetic permeability of a structural steel.
Research limitations/implications
The method gives very approximate results in comparison to those obtained using the Epstein frame. The influences of the temperature and/or of the skin effect have not been evaluated.
Practical implications
Practical, real and thus confident data of structural steel, such as the magnetic permeability and the volumetric losses (hysteresis and Foucault), become available for the transformer designer to take actions for not only reducing the tank losses but also for avoiding the occurrence of hot spots through computer simulation.
Originality/value
The proposition is very new, as it allows to test steel samples with a size that does not fit to a usual Epstein frame. It takes into account the real influence of harmonic of currents in the losses along the winding of a classical Epstein frame, which has not been so far mentioned. It allows obtaining data of structural steel that had not been considered important until now.
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Jens Benecke, André Linde and Stefan Dickmann
The purpose of this paper is to create a model to calculate the high frequency (HF) complex impedance of common low‐voltage DC motors from construction parameters to predict their…
Abstract
Purpose
The purpose of this paper is to create a model to calculate the high frequency (HF) complex impedance of common low‐voltage DC motors from construction parameters to predict their electromagnetic compatibility (EMC) emission behaviour and perform sensitivity analyses, and an optimization routine is developed to find combinations of construction parameters which best match a desired impedance curve.
Design/methodology/approach
The motor is divided into components. For each component, its electrical behaviour including parasitics is derived from material and geometry, and the electromagnetic interactions between components are defined. These results are then reproduced using inductances, capacitances, and resistors where applicable. Mathematical expressions are given to calculate their value from the material and geometrical parameters.
Findings
The complex impedance of DC motors can be accurately constructed from geometry and material parameters within a small range. The optimization routine successfully finds parameters to match a desired curve within specified parameter ranges. This can help finding a motor with lower conducted electromagnetic interference.
Originality/value
This analytically parameterized model constitutes a new way to describe electrical motors from an EMC perspective and define critical parameters.
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H. Ymeri, B. Nauwelaers, K. Maex and D. De Roest
New analytical approximation for the frequency‐dependent impedance matrix components of symmetric VLSI interconnect on lossy silicon substrate are derived. The results have been…
Abstract
New analytical approximation for the frequency‐dependent impedance matrix components of symmetric VLSI interconnect on lossy silicon substrate are derived. The results have been obtained by using an approximate quasi‐magnetostatic analysis of symmetric coupled microstrip on‐chip interconnects on silicon. We assume that the magnetostatic field meets the boundary conditions of a single isolated infinite line; therefore, the boundary conditions for the conductors in the structure are approximately satisfied. The derivation is based on the approximate solution of quasi‐magnetostatic equations in the structure (dielectric and silicon semi‐space), and takes into account the substrate skin‐effect. Comparisons with published data from circuit modeling or full‐wave numerical analyses are presented to validate the inductance and resistance expressions derived for symmetric coupled VLSI interconnects. The analytical characterization presented in this paper is well situated for inclusion into CAD codes in the design of RF and mixed‐signal integrated circuits on silicon.
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Klaus Roppert, Florian Toth and Manfred Kaltenbacher
The purpose of this paper is to examine a solution strategy for coupled nonlinear magnetic-thermal problems and apply it to the heating process of a thin moving steel sheet…
Abstract
Purpose
The purpose of this paper is to examine a solution strategy for coupled nonlinear magnetic-thermal problems and apply it to the heating process of a thin moving steel sheet. Performing efficient numerical simulations of induction heating processes becomes ever more important because of faster production development cycles, where the quasi steady-state solution of the problem plays a pivotal role.
Design/methodology/approach
To avoid time-consuming transient simulations, the eddy current problem is transformed into frequency domain and a harmonic balancing scheme is used to take into account the nonlinear BH-curve. The thermal problem is solved in steady-state domain, which is carried out by including a convective term to model the stationary heat transport due to the sheet velocity.
Findings
The presented solution strategy is compared to a classical nonlinear transient reference solution of the eddy current problem and shows good convergence, even for a small number of considered harmonics.
Originality/value
Numerical simulations of induction heating processes are necessary to fully understand certain phenomena, e.g. local overheating of areas in thin structures. With the presented approach it is possible to perform large 3D simulations without excessive computational resources by exploiting certain properties of the multiharmonic solution of the eddy current problem. Together with the use of nonconforming interfaces, the overall computational complexity of the problem can be decreased significantly.
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A. Aliferov and S. Lupi
The paper deals with the current density distributions in toroidal conductors of circular cross‐section.
Abstract
Purpose
The paper deals with the current density distributions in toroidal conductors of circular cross‐section.
Design/methodology/approach
A review of the analytical solutions existing in the literature only for the case of very thin skin depth is presented.
Findings
Results are given for different aspect ratios of torus. The accuracy of these analytical solutions is verified by comparison with numerical results. Finally, a set of numerical results are given for the same aspect ratios but different penetration depths of the electromagnetic wave in the conducting material.
Originality/value
The paper provides results for different penetration depths of electromagnetic wave in conducting material and different torus aspect ratios.
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Nicholas G. Dagalakis, Jae-Myung Yoo and Thomas Oeste
The purpose of this paper is a description of DITCI, its drop loads and sensors, the impact tools, the robot dynamic impact safety artifacts, data analysis, and modeling of test…
Abstract
Purpose
The purpose of this paper is a description of DITCI, its drop loads and sensors, the impact tools, the robot dynamic impact safety artifacts, data analysis, and modeling of test results. The dynamic impact testing and calibration instrument (DITCI) is a simple instrument with a significant data collection and analysis capability that is used for the testing and calibration of biosimulant human tissue artifacts. These artifacts may be used to measure the severity of injuries caused in the case of a robot impact with a human.
Design/methodology/approach
In this paper, we describe the DITCI adjustable impact and flexible foundation mechanism, which allows the selection of a variety of impact force levels and foundation stiffness. The instrument can accommodate arrays of a variety of sensors and impact tools, simulating both real manufacturing tools and the testing requirements of standards setting organizations.
Findings
A computer data acquisition system may collect a variety of impact motion, force and torque data, which are used to develop a variety of mathematical model representations of the artifacts. Finally, we describe the fabrication and testing of human abdomen soft tissue artifacts with embedded markers, used to display the severity of impact injury tissue deformation.
Research limitations/implications
DITCI and the use of biosimulant human tissue artifacts will permit a better understanding of the severity of injury, which will be caused in the case of a robot impact with a human, without the use of expensive cadaver parts. The limitations are set by the ability to build artifacts with material properties similar to those of various parts of the human body.
Practical implications
This technology will be particularly useful for small manufacturing companies that cannot afford the use of expensive instrumentation and technical consultants.
Social implications
Impact tests were performed at maximum impact force and average pressure levels that are below, at and above the levels recommended by a proposed International Organization for Standardization standard. These test results will be used to verify whether the adopted safety standards will protect interactive robots human operators for various robot tools and control modes.
Originality/value
Various research groups have used human subjects to collect data on pain induced by industrial robots. Unfortunately, human safety testing is not an option for human–robot collaboration in industrial applications every time there is a change of a tool or control program, so the use of biosimulant artifacts is expected to be a good alternative.
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Yang Tian, Dacian Tomus, Aijun Huang and Xinhua Wu
Limited research has attempted to reveal the different modes of the melt pool formation in additive manufacturing. This paper aims to study the mechanisms of surface roughness…
Abstract
Purpose
Limited research has attempted to reveal the different modes of the melt pool formation in additive manufacturing. This paper aims to study the mechanisms of surface roughness formation, especially on the aspect of melt pool formation which determine the surface profile and consequently significantly influence the surface roughness.
Design/methodology/approach
In this study, the conditions under which different modes of melt pool formation (conduction mode and keyhole mode) occur for the case of as-fabricated Hastelloy X using direct metal laser solidification (DMLS) are derived and validated experimentally. Top surfaces of uni-directionally built samples under various processing conditions are cut, grinded, polished and etched to reveal their individual melt pool morphologies. Similarly, up-skin (slope angle < 90°) and down-skin (slope angle > 90°) melt pool morphologies are also investigated to compare the differences. Surface tension gradients and resultant Marangoni flow, which dominate the melt flow in the melt pool, is also calculated to help better evaluate the melt pool shape forming.
Findings
Two types of melt pool formation modes are dominating in DMLS: conduction mode and keyhole mode. Melt pool formed by conduction mode generally has an aspect ratio of 1:2 (depth vs width) and is in elliptical shape. Appropriate selection of scanning laser power and speed are required to maintain a low characteristic length and width ratio to prevent ballings. Melt pool formed by keyhole mode has an aspect ratio of 1:1 or less. High-energy contour promotes formation of key-hole-shaped melt pool which fills the gaps between layers and smoothens the up-skin surface roughness. Low-energy contour scan is necessary for down-skin surface to form small melt pool profiles and achieve low Ra.
Originality/value
This paper provides valuable insight into the origins of surface quality problem of DMLS, which is a very critical issue for upgrading the process for manufacturing real components. This paper helps promote the understanding of the attributes and capabilities of this rapidly evolving three-dimensional printing technology and allow appropriate control of processing parameters for successful fabrication of components with sound surface quality.
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