Behavior Of Shields Research Articles

Experimental Investigation of the Effects of Aperture Ratio, Chamber Pressure and Soil Conditioning on the Clogging Behavior of EPB Shields

Earth pressure balance (EPB) shield excavation in cohesive strata frequently encounters cutterhead clogging, consuming time and economic costs. Engineering practice shows that cutterhead aperture ratio, soil chamber pressure and soil conditioning have important influences on the clogging behavior of EPB shields. In order to study these factors, a series of laboratory tests were conducted using a setup that can closely simulate the shield tunnelling process. The indicators analyzed were excavation speed, torque, specific energy and soil distribution on the cutterhead. The results indicate that cutterhead aperture and cutter arrangement are important factors in clogging potential. Clogging creates a significant reduction in excavation speed. Torque is not a sensitive parameter reflecting clogging because of the effect of the consolidated soil on the cutters. The presence of soil chamber pressure makes it difficult to remove the clogging through the shearing action of the excavation surface. The injection of a sufficient amount of foam can reduce the risk of shield clogging, but it may lead to an increase of soil adhesion on the cutterhead. The amount of soil that adheres to the cutterhead cannot be used as a classification criterion for clogging potential. Based on experimental phenomena and established studies, a mechanical model called ‘beam-bridge’ was proposed to study the behavior of the soil through the cutterhead opening and damage form of clogging. The results will help to the excavation control of EPB shields.

Modeling and validation of stray-field loss inside magnetic and non-magnetic components under harmonics-DC hybrid excitations based on updated TEAM Problem 21

Purpose This paper aims to propose and establish a set of new benchmark models to investigate and confidently validate the modeling and prediction of total stray-field loss inside magnetic and non-magnetic components under harmonics-direct current (HDC) hybrid excitations. As a new member-set (P21e) of the testing electromagnetic analysis methods Problem 21 Family, the focus is on efficient analysis methods and accurate material property modeling under complex excitations. Design/methodology/approach This P21e-based benchmarking covers the design of new benchmark models with magnetic flux compensation, the establishment of a new benchmark measurement system with HDC hybrid excitation, the formulation of the testing program (such as defined Cases I–V) and the measurement and prediction of material properties under HDC hybrid excitations, to test electromagnetic analysis methods and finite element (FE) computation models and investigate the electromagnetic behavior of typical magnetic and electromagnetic shields in electrical equipment. Findings The updated Problem 21 Family (V.2021) can now be used to investigate and validate the total power loss and the different shielding performance of magnetic and electromagnetic shields under various HDC hybrid excitations, including the different spatial distributions of the same excitation parameters. The new member-set (P21e) with magnetic flux compensation can experimentally determine the total power loss inside the load-component, which helps to validate the numerical modeling and simulation with confidence. The additional iron loss inside the laminated sheets caused by the magnetic flux normal to the laminations must be correctly modeled and predicted during the design and analysis. It is also observed that the magnetic properties (B27R090) measured in the rolling and transverse directions with different direct current (DC) biasing magnetic field are quite different from each other. Research limitations/implications The future benchmarking target is to study the effects of stronger HDC hybrid excitations on the internal loss behavior and the microstructure of magnetic load components. Originality/value This paper proposes a new extension of Problem 21 Family (1993–2021) with the upgraded excitation, involving multi-harmonics and DC bias. The alternating current (AC) and DC excitation can be applied at the two sides of the model’s load-component to avoid the adverse impact on the AC and DC power supply and investigate the effect of different AC and DC hybrid patterns on the total loss inside the load-component. The overall effectiveness of numerical modeling and simulation is highlighted and achieved via combining the efficient electromagnetic analysis methods and solvers, the reliable material property modeling and prediction under complex excitations and the precise FE computation model using partition processing. The outcome of this project will be beneficial to large-scale and high-performance numerical modeling.

The Shadow of a Gunman by Sean O’Casey, and :Juno and the Paycock by Sean O’Casey, and:The Plough and the Stars by Sean O’Casey

Reviewed by: The Shadow of a Gunman by Sean O’Casey, and :Juno and the Paycock by Sean O’Casey, and:The Plough and the Stars by Sean O’Casey Michael C. O’neill THE SHADOW OF A GUNMAN. By Sean O’Casey. Directed by Ciarán O’Reilly. Irish Repertory Theatre, New York City. January 31, 2019. JUNO AND THE PAYCOCK. By Sean O’Casey. Directed by Neil Pepe. Irish Repertory Theatre, New York City. March 21, 2019. THE PLOUGH AND THE STARS. By Sean O’Casey. Directed by Charlotte Moore. Irish Repertory Theatre, New York City. June 20, 2019. New York City’s Irish Repertory Theatre celebrated its thirtieth anniversary by devoting the second half of its 2018–19 season to Sean O’Casey, [End Page 107] staging his so-called “Dublin Trilogy” in repertory at the Irish Rep’s intimate space on West 22nd Street. Marking the first time in the New York area that The Shadow of a Gunman (1923), Juno and the Paycock (1924), and The Plough and the Stars (1926) have been performed in repertory, the productions captured the comic energy and relentless suffering of O’Casey’s characters, connecting contemporary audiences to the domestic turmoil and political upheaval that permeates these plays first staged by Dublin’s Abbey Theatre almost a century ago. An audacious undertaking by any measure, the Irish Rep’s productions maintained O’Casey’s legacy without challenging it, and instead embraced the novice playwright’s passions and developing ideas. This method allowed audiences a sense of how O’Casey’s early work, particularly his strong portraits of selfless, sometimes heroic women helped revolutionize theatre in Ireland and beyond. Click for larger view View full resolution James Russell (Donal Davoren) and Michael Mellamphy (Seumas Shields) in The Shadow of a Gunman. (Photo: Carol Rosegg.) Set in 1920 during the Irish War for Independence, The Shadow of a Gunman, under the direction of Ciarán O’Reilly, immediately thrust the audience into a confusing Dublin tenement flat governed by the guarded behavior and puzzling innuendo of the peddler Seumas Shields and his illegal tenant, the hapless poet Donal Davoren, who, according to tenement gossip, is secretly an IRA gunman. Although the acting ensemble provided vivid portraits of the nosey tenement dwellers, O’Reilly’s direction did little to help the audience distinguish them from one another; moreover, James Russell as Davoren complained so strongly when the neighbors interrupted his writing that he may have made it difficult for the audience to understand these denizens of an unfamiliar era as more than merely part of O’Casey’s microcosm of Dublin’s impoverished working class. O’Casey pokes fun at would-be poets, including his own youthful artistic pretensions, through Davoren, but Russell seemed to equate passion with yelling and never captured the modulation in the wonderful lines O’Casey has written for Davoren. Russell’s Davoren, however, stirred briefly to life in his first act encounter with Minnie Powell, played by Meg Hennessy as a potential “new woman” deprived by her lack of education from taking her place in a culture redefining itself. She imposed upon a receptive Davoren her simple preconceptions of a heroic ethos embodied by soldiers fighting against Britain. In feigning to share her revolutionary fervor, the duplicitous Davoren by the close of The Shadow of a Gunman ironically became a foil to Minnie, whose accidental death was quickly mythologized by tenement gossip as an act of heroism; meanwhile, in one of the production’s most genuine moments, Seumas [End Page 108] and Davoren realized their debt to Minnie for saving their lives must remain a secret they keep forever. Presented at the Irish Rep in 1995 and 2014, Juno and the Paycock remains O’Casey’s most popular play, and in terms of theatrical artistry, it is far more accomplished than The Shadow of a Gunman. The Atlantic Theatre Company’s artistic director, Neil Pepe, directed the production without much evidence of his customary visceral approach, reflecting instead the Irish Rep’s steady and unobtrusive directorial aesthetic. Pepe appropriately contrasted the mundane troubles of the Boyle family in 1924, however, against the insufferable loss of children to...

A New Approach to Calculate the Shielding Factor of Magnetic Shields Comprising Nonlinear Ferromagnetic Materials under Arbitrary Disturbances

To enable the realization of ultra-low magnetic fields for scientific and technological research, magnetic shielding is required to create a space with low residual magnetic field and high shielding factors. The shielding factors of magnetic shields are due to nonlinear material properties, the geometry and structure of the shields, and the external magnetic fields. Magnetic shielding is used in environments full of random realistic disturbances, resulting in an arbitrary and random external magnetic field, and in this case, the shielding effect is hard to define simply by the shielding factors. A new method to simulate and predict a dynamic internal space magnetic field wave is proposed based on the Finite Element method (FEM) combined with the Jiles-Atherton (JA) model. By simulating the hysteresis behavior of the magnetic shields and establishing a dynamic model, the new method can simulate dynamic magnetic field changes inside magnetic shields as long as the external disturbances are known. The shielding factors under an AC external field with a sine wave and certain frequencies are calculated to validate the feasibility of the new method. A real-time wave of internal magnetic flux density under an AC triangular wave external field is simulated directly with the new method versus a method that splits the triangular wave into several sine waves by a Fourier transform, divides the shielding factors, and then adds the quotients together. Moreover, real-time internal waves under some arbitrary fields are measured. Experimental internal magnetic flux density waves of a 4-layer magnetically shielded room (MSR) at the Harbin Institute of Technology (HIT) fit the simulated results well, taking experimental errors into account.

Numerical analysis of VVER-440/213 concrete biological shield under normal operation

The numerical approach for the coupled damage-creep modeling of concrete biological shield, which combines the current and the past knowledge regarding the effects of irradiation and temperature on concrete with the real measured and calculated neutron fluence and temperature distribution for VVER-440/213 reactors, is described in detail in this study. The proposed approach takes into account the real structural geometry as well as the real neutron fluence and temperature distribution and the latest knowledge about the effect of irradiation and temperature on concrete strength and stiffness. The radiation induced volumetric expansion and the thermal expansion of concrete are modeled. According to the results of the numerical simulation, the analyzed structure reaches critical damage within the time interval from 10.00 to 35.25 years of normal operation. The damage of the concrete biological shield of the VVER reactor will not affect the load-bearing function of the containment building, since the biological shield is self-bearing. The shielding properties of the biological shield may be reduced due to the appearance of the radial cracks, however, the concrete wall, which is situated right behind the biological shield, will ensure the necessary shielding. Therefore, the concrete biological shield of the VVER reactors can be considered as sacrificial structure and can be damaged without significant consequences. However, this study implies the importance of capability to predict the behavior of those PWR reactor biological shields which serve both the load-bearing and shielding purposes.

2D Simulator for Eddy Current Field Filters

Hall devices are magnetic field current sensors based on the Hall effect. A bias current is applied via contacts through the Hall plates which are placed along magnetic field. High frequency components affect the Hall plates in a non- linear manner, disturbing the uniform biasing current flow. This problem can be alleviated by the development of a flux shaping device. A CAD tool is presented here, which can simulate the behavior of shields with different shape in order to choose the one that may be optimally used.

Nonferromagnetic Open Shields at Industrial Frequency Rate

We have investigated some innovative geometric configurations for shielding extremely low-frequency (ELF) magnetic fields through nonferromagnetic materials. We define proper 2-D and 3-D finite-element (FE) models for the numerical computation of the shielding effectiveness of open conducting shields, in order to assess the mitigation of the magnetic field generated by a single-wire transmission line, two-wire t.l., or three-phase current excitation at industrial frequency rates. For the case of current conductors in air (i.e., in absence of the metallic shield) we validate our numerical model using the Biot-Savart law, while for the case of an infinite plane shield we exploit an analytical validation by means of a direct solution of the Maxwell's equations, with properly defined boundary conditions. We compare our experimental results with those found in literature and prove the accuracy of the computed shielding efficiency. After this preliminary validation of the numerical tool, we study the behavior of several nonplane open shields, characterized by different transversal profiles: by means of the FE model, we directly compare these innovative configurations to the plane one, thus showing that they can guarantee an increase of the shielding effectiveness at constant weight of the shield just by a simultaneous mitigation of both the two components of the magnetic field in the transversal plane. This feature is verified by means of experimental results, in which we have considered a finite shield with a current source constituted by a single long wire.

An ATP-EMTP-Based Model for Analysis of Shielding Properties of Ferromagnetic Cable Sheaths

Ferromagnetic materials, such as steel, are used for shielding of power and telecommunication cables. These shields often provide path for currents during faults or lightning and are important for the integrity and safety of electrical systems and devices. Since such currents might be with low- or high-frequency content, and of low or high intensity, ferromagnetic shield behavior might be quite different due to hysteresis. This paper describes a method for analyzing the dynamic behavior of ferromagnetic cable shields based on the Jiles model of hysteresis. The solution is implemented in ATP-EMTP, which allows one to analyze the complex behavior of ferromagnetic cable shields in conjunction with that of the other elements of the power system. Due to limitations of the model of hysteresis, application of the proposed model is limited to frequencies up to about 10 kHz. The model is illustrated for a practical 100-m-long cable.

Electromagnetic Behavior and Stress Analysis of BT Thermal Shields

The ATLAS detector is one of the huge detectors used on the future LHC at CERN. Its magnet system is composed of a barrel toroid (BT) and two end-cap toroids (ECT) inserted at the ends of the BT, of an inner solenoid and of an iron shield close to the inner bore of the BT. The coil cryogenic system is designed to cool down the thermal shields by helium gas at 80 K. In the event of any variation of the magnetic flux, eddy currents are induced in these shields. This paper presents the computations of eddy currents in the shields using a variational formulation of the problem in terms of the electric vector potential and a finite element method. The worst case - fast discharge into dump diodes and resistors - is presented in the electrical behavior section. The evolution of eddy currents is computed using this method. Finally, anchor points are determined in the mechanical analysis in order to minimize the mechanical stresses on the shields.

The validation of hydrocodes for orbital debris impact simulation

Orbital debris pose a danger for spacecraft in orbit. Protection against this threat is obtained by shielding. One or more shields placed at some distance from the structure to be protected can minimize the damage inflicted by projectiles at high velocity. The range of velocity between 0 and 8 km/s is well covered by tests. Unfortunately, the average velocity of debris in low earth orbit is above 10 km/s with a maximum velocity around 15 km/s. The methodology presented in this paper aims to validate the numerical approach. It will predict and extrapolate the behavior of multishock shields in the velocity range between 8 and 15km/s. The formation and propagation of the debris cloud, after perforation of the shields and the generation of damage in the backwall, are key factors. These phenomena are examined, discussed and illustrated with correlation between numerical simulation with EFHYD TM analytical formulae and test results.

Analytic solution of the transient behavior of radiation-backscattering heat shields

An analytic solution of the material response to combined radiative and convective heating is presented. The solution includes the equations of radiative transfer (within the material), coupled to a transient energy equation that contains both radiative and convective terms. The analysis allows for unlimited spectral detail, but assumes that within the range of applicability, the various material properties do not vary significantly with temperature. To facilitate development of the analytic solution, it is also assumed that scattering within the material dominates absorption, and that the exposed surface of the material does not ablate. The exposed surface boundary condition includes convective heating and spectral radiation, some of which is absorbed by the surface and some of which penetrates the surface.

Passive magnetic screening

It is shown that a passive magnetic shield for a 1.5-T whole-body magnet requires about 20 tons of iron. Moreover, to first order, the amount of shielding material is independent of the radius of the shield. The choice between a thick shield fitting tightly round the magnet and a thinner shield of larger radius is determined by considerations of available space and the need for the highest uniformity of field in the bore. Very high permeability materials such as mu-metal are useful only in special circumstances. Multiple shields are valuable if a high degree of shielding is required, but the spacing between the shields needs careful attention. Although exact reciprocity of internal and external shielding is not found in the general case, the degree of shielding will be of the same order in both cases. The complete behavior of cylindrical shields around superconducting magnets can be determined by analytical solution of Maxwell's equations; for less regular shapes, solutions may be determined numerically by computer.

Electromagnetic Pulse Transmission Through a Thin Sheet of Saturable Ferromagnetic Material of Infinite Surface Area

A numerical solution is presented for determining the shielding properties of a thin sheet of saturable ferromagnetic material of infinite surface area. Several examples are given to indicate the behavior of ferromagnetic shields in an intense electromagnetic environment. These examples illustrate that only a few numerical results are required to determine the electric field transmitted through the material for a given incident pulse of any amplitude.