Element Length Research Articles

Mathematical Morphology-Based Fault Detection in Radial DC Microgrids Considering Fault Current From VSC

The paper proposes a fast fault detection method for radial DC microgrids established on mathematical morphology (MM) denoising filters and detection principles utilizing only local measurements. The proposed fault detection algorithm utilizes the DC fault current signal from a Voltage Source Converter (VSC) and detects a fault. Problems related to communication delays are thus avoided, while preserving the low cost and computational burden. The proposed fault detection framework includes five different MM-based denoising filters, employed as pre-signal processing methods whose features are assessed and compared. The influence of selecting an appropriate type and length of a structuring element (SE) on the proposed method is analyzed. The developed fault detection method based on MM is used for extracting transient features and detecting pole-to-pole (PP) and pole-to-ground (PG) faults within milliseconds of their occurrence. The proposed method is demonstrated using simulation tests in MATLAB/Simulink. The results indicate that the proposed method enables reliable, accurate and fast detection of both the PP and the PG faults. Computer simulations are carried out to verify that the proposed method distinguishes faults from overload.

Thermal buckling of steel tube using finite element method

The present research work focuses on obtaining the critical buckling temperature (ΔTcri) of an offshore pipeline model from one-dimensional and three-dimensional finite element analysis. In this work, the pipeline model considered for analysis has a prismatic and hollow cross-section. The dimensions used for the pipeline model are: Length (L) = 360 mm, Outer Diameter (D) = 12 mm, and Thickness of the pipeline model (t) = 1 mm. The one-dimensional (1D) finite element analysis is conducted with proper element selection as BEAM188 element, and the three-dimensional (3D) finite element analysis is carried out using the SOLID186 element. The mesh element length or size for 1D analysis is 20 mm, while it is 1 mm for 3D analysis, as determined by a detailed convergence study on both 1D and 3D finite element models. The pinned–pinned boundary conditions used for 1D finite element analysis are (at × = 0 mm, u = 0 &v = 0; at × = 360 mm, u = 0 &v = 0). Similarly, the following boundary conditions are used for 3D finite element analysis: at z = 0 mm, u (x, y, 0) = 0, v (x, y, 0) = 0, and w (x, y, 0) = 0, and at z = 360 mm, u (x, y, 360) = 0, v (x, y, 360) = 0, and w (x, y, 360) = 0. The displacements along the ×,y, and z directions are represented in the 3D analysis as u, v, and w. The critical buckling temperature values (ΔTcri) obtained in the 1D and 3D thermal buckling analysis are (ΔTcri)1D = 72.06 °C and (ΔTcri)3D = 72.27 °C.

Effect of radial growth rate on wood properties variation of Sentang (Azadirachta excelsa) tree planted in Kelantan, Malaysia

Properties of Sentang wood planted in Kelantan, Malaysia, were studied, focusing on the effect of radial growth rate on variation in the fiber and vessel element dimensions, moisture content, density, shrinkage, bending, and compression strength at the breast height of the tree. The trees were categorized into slow-, average-, and fast-growth categories, based on their breast height diameter and standard deviation. The variations in properties were then examined from the pith to the bark. The fiber length and diameter tend to decrease until a certain distance from the pith, followed by an increase toward the bark. Contrastingly, the vessel element length and diameter tend to increase until a maximum size is reached and then exhibit a relatively constant size toward the bark. The fast-growing trees tended to have longer and larger fibers, while the slow-growing trees tended to have longer and larger vessel elements. In addition, the fast-growing trees tended to have a higher green moisture content and shrinkage, lower density, lower modulus of rupture (MOR), and lower compression strength. The results revealed that growth rate seems to influence the modulus of elasticity (MOE) less than the MOR and compression strength.

Calculation of Linear Buckling Load for Frames Modeled with One-Finite-Element Beams and Columns

Critical linear buckling load calculation is one of the possible ways to check structural stability. Structural analysis programs usually model beams and columns with just one element, but this is not enough to obtain an accurate value of the critical buckling load when the buckling mode is associated with an effective length that is less than twice the element length. This paper presents a method for the accurate calculation of the buckling load of frames modeled with only one finite element per structural element. For this purpose, a local correction is applied to some elements a few times until convergence is achieved. The validity of the presented method is confirmed by several examples ranging from simple canonical cases to large structures.

Transitional Strength Under Plasma: Precise Estimations of Astrophysically Relevant Electromagnetic Transitions of Ar7, Kr7, Xe7, and Rn7 Under Plasma Atmosphere++++

The growing interest in atomic structures of moderately stripped alkali-like ions in the diagnostic study and modeling of astrophysical and laboratory plasma makes an accurate many-body study of atomic properties inevitable. This work presents transition line parameters in the absence or presence of plasma atmosphere for astrophysically important candidates Ar7+, Kr7+, Xe7+, and Rn7+. We employ relativistic coupled-cluster (RCC) theory, a well-known correlation exhaustive method. In the case of a plasma environment, we use the Debye Model. Our calculations agree with experiments available in the literature for ionization potentials, transition strengths of allowed and forbidden selections, and lifetimes of several low-lying states. The unit ratios of length and velocity forms of transition matrix elements are the critical estimation of the accuracy of the transition data presented here, especially for a few presented for the first time in the literature. We do compare our findings with the available recent theoretical results. Our reported data can be helpful to the astronomer in estimating the density of the plasma environment around the astronomical objects or in the discovery of observational spectra corrected by that environment. The present results should be advantageous in the modeling and diagnostics laboratory plasma, whereas the calculated ionization potential depression parameters reveal important characteristics of atomic structure.

Design and Development of Parasitic Elements Loaded Quadband Frequency and Pattern Reconfigurable Antenna

Modern communication demands a low-profile, versatile antenna. In this paper, a low-profile antenna of size 38 × 40 × 0.787 m m 3 is proposed to reconfigure frequency and radiation pattern. The Rogers RT Duroid 5870 of dielectric constant 2.33 is used as a substrate. Frequency reconfiguration is achieved by connecting patches of different lengths corresponding to the resonant frequencies through three PIN diode switches. Switching on/off these three diodes results in frequency switching between four distinct frequency bands. The Yagi-Uda principle is utilized to alter the radiation pattern. Simple parasitic elements are loaded on either side of the radiating structure. Changing the electrical lengths of the parasitic elements using PIN diode switches facilitates pattern reconfiguration by making them behave as a reflector/director. The presented structure resonates at four distinct frequencies (5.3 GHz/3.82 GHz/2.77 GHz/2.2 GHz) with a maximum of three beam tilt angles for each resonating frequency. SMP1345-079LF PIN diode is used for switching operation. Biasing circuit has been designed to ensure RF and DC isolation. The proposed antenna offers acceptable radiation performance in all the switching states. The average measured gains are 2.43 dBi, 2.42 dBi, 3.5 dBi, and 3.29 dBi at 5.3 GHz, 3.82 GHz, 2.77 GHz, and 2.2 GHz, respectively. On an average, the proposed antenna exhibits the simulated efficiency of 81%. The proposed antenna is suitable for 5G communication as its bandwidth covers band 1, band 7, band 46, and band 77 of the 5G new radio (NR) standard. Fabrication and testing are done to validate the results.

Use of longitudinal wave in non-destructive methods: approach to foundation and retaining elements

Non-destructive tests (NDT) are used to verify the length or integrity of elements embedded in soils or rocks. These elements can be piles in foundations or nails and tiebacks in retaining walls. NDTs differ by the types of waves, ways to generate and receive the signal and to analyze data. Tests using sonic wave do not require a pre-installed pipe or wire and they are based on acoustic impedance theory. Despite its dissemination on piles, the application in retaining elements is recent and requires more studies to increase knowledge about these methods. This paper aims to present studies of sonic wave methods in foundation and retaining elements, presenting results, similarities, and differences. Studies from different dates are presented with their relevance, considerations for the different types of elements tested, objectives and methodologies used, to evidence the variables involved within this solution. The sonic test in foundation is widespread and has a greater number of studies. Withing this paper, the variables that interfere in the results of these methods were observed: the velocity of propagation of the sonic wave, the soil stiffness, the location of wave generation and reception and the type of hammer used, evidencing the necessity of further studies, especially in retaining elements.

Experimental and numerical investigations on novel post-tensioned precast beam-to-column energy-dissipating connections

This paper proposes novel self-centering post-tensioned hybrid connections (PTHC) with energy-dissipating elements, with assembly requiring grouting only once and convenient construction. To investigate the seismic performance of the hybrid connections, cast-in-place beam-to-column and assembled monolithic beam-to-column connection specimens were designed as comparison test specimens. Subsequently, four PTHC specimens with different test variables— restraint conditions of beam end, unbonded lengths of the energy-dissipating elements, energy-dissipating material, and initial prestress were designed and investigated by quasistatic experiments. The test results showed that the designed PTHC specimens had high energy dissipation capacity, good self-centering capacity, high ductility, and low accumulated damage. Concrete restraints at the beam end effectively restrained the buckling behavior of the energy-dissipating elements. Finally, numerical simulation models of the PTHC specimens were established to further investigate the effects of the design parameters on the bearing and energy dissipation capacity. Combined with the test results, the PTHC specimens were found to have good seismic resilience. Balancing the contributions of the energy-dissipating elements and prestress to the load carrying capacity appeared to be critical.

A Constant Properties Model for the Performance Estimation in Segmented Thermoelectric Generator Elements and Its Experimental Validation Using an n-Type Mg2Si0.3Sn0.7–Bi2Te2.7Se0.3 Segmented Leg

Segmenting multiple compatible thermoelectric (TE) materials can improve the conversion efficiency in thermoelectric generators (TEGs) compared to single-material TEGs. A model to accurately estimate the performance in segmented TEGs is essential for optimizing the geometric parameters. Constant properties models (CPMs) help in the quick estimation of the performance of TEGs working under large temperature differences using averaged material properties. This work discusses a CPM to predict the performance of single and segmented TEG elements using a combination of temperature-averaged and spatially-averaged TE properties. Spatial averaging requires the knowledge of the temperature profile across the TEG element length, which was obtained by solving the heat balance equation with a numerical integration approach as suggested by Ponnusamy et al. In this work, we develop the CPM for the segmented TEG elements (CPMS). The model predictions were validated experimentally from the performance evaluation of single Mg2(Si0.3Sn0.7)0.98Bi0.02 and segmented Mg2(Si0.3Sn0.7)0.98Bi0.02–Bi2(Te2.7Se0.3)0.98(CuI)0.02 TEG elements. Single and segmented TEG elements with Cu contacts were prepared by a hot-pressing technique. Both Mg2(Si0.3Sn0.7)0.98Bi0.02 and Bi2(Te2.7Se0.3)0.98(CuI)0.02 TE materials show peak zT > 1 in their measurement range. The experimental results show a maximum efficiency (ηmax) of ∼8.25% with 18% improvement for the segmented structure at ΔT ≈ 302 K. The improvement mainly originated from lower heat input (Qin) even though the maximum power output (Pmax) became lower by ∼30%. The performance prediction using the CPM matches well with <10% error for Pmax and ηmax for the single TEG element, and using the CPMS, the predictions were <10% error for Pmax and <25% error for ηmax for the segmented TEG element experimental results. This work demonstrates how CPMS can be used to predict device performance characteristics in segmented TEGs.

Variational multiscale method stabilization parameter calculated from the strain-rate tensor

The stabilization parameters of the methods like the Streamline-Upwind/Petrov–Galerkin, Pressure-Stabilizing/Petrov–Galerkin, and the Variational Multiscale method typically involve two local length scales. They are the advection and diffusion length scales, appearing in the expressions for the advective and diffusive limits of the stabilization parameter. The advection length scale has always been in the flow direction. The diffusion length scales in use have mostly been just element-geometry-dependent, but there is good justification for also making that direction-dependent, so that the spatial variation of the solution is taken into account somehow. The length scale in the solution-gradient direction, which was introduced in 2001, was intended for making sure that near solid surfaces, the element length in the surface-normal direction is selected even if that is not the minimum element length. It was also intended for making sure that in a 2D computation with a 3D mesh, there would be no dependence on the element length in the third direction. With the same objectives, and with better invariance properties, we are now introducing the direction-dependent diffusion length scale calculated from the strain-rate tensor. We accomplish those objectives, get invariance with respect to switching to a different inertial reference frame, and the element length in the surface-normal direction, even when the surface is undergoing rotation, is selected as the diffusion length scale.

Retaining Wall - Parametric Study of the Method of Reinforcement

Abstract The highway section on the D3 highway Hričovské Podhradie – Žilina – Strážov was carried out on the left branch of the highway body on the overpass and on the right branch on the embankment body. The stability of the embankment body was ensured by a geosynthetics reinforced retaining wall. The retaining wall was assembled from reinforced concrete prefabs, on which the uniaxial geogrids were attached. The article presents a numerical analysis of the deformations of this reinforced structure in the profile monitored by geotechnical monitoring. The results of the numerical analysis of the deformations of the retaining wall were confronted with geotechnical monitoring measurements. Geotechnical monitoring measurements confirmed the reality of the numerical model of the retaining wall. Verification of the reality of the numerical model of the retaining wall made it possible to use this model for a parametric study of the influence of the reinforcement method on the deformation of the face of the reinforced retaining wall. In the parametric study, the effects of the change in the horizontal length and vertical spacing of the reinforcement elements, as well as their interaction with the backfill soil on the deformation values of the face of the retaining wall are analyzed.

Testing Carlquistian hypotheses on the functional significance of vessel element length

Summary While total vessel length is widely recognized as being of fundamental functional significance, opinion is more divided regarding the potential functional importance of vessel element length, a variable that Sherwin Carlquist regarded as functionally significant. We show that vessel element length can, as Carlquist predicted, affect vessel resistance to deformation. Perforation plates are locally thickened annuli, so tubes with annuli resist deformation better than those without, and tubes with closely-spaced annuli resist deformation better than those with distantly spaced ones. However, there is a tradeoff between deformation resistance and conductance. With a comparative analysis across more than 1000 species of angiosperms, we show that both vessel element length and the areas of individual inter-conduit pits scale positively with vessel diameter. Such covariation is expected if plants are to maintain conductance as they grow taller. Congruent with Carlquist’s thinking, we found that species with vessel elements that are exceptionally short tend to grow in drylands, whereas those with vessel elements that are exceptionally long tend to grow in moist climates. Finally, we show evidence suggesting that selection on vessel element length is an important determinant of imperforate tracheary element length. Conversely, the evidence for selection on imperforate tracheary element length affecting vessel element length appears to be weaker. These results seem sufficient to establish that, whatever the functional importance of total vessel length, vessel element length is a variable of functional significance in its own right, congruent with Sherwin Carlquist’s long-held views.

2X2 MICROSTRIP PATCH ARRAY BEAM STEERING ANTENNA WITH PIN DIODES

This paper introduces a novel design of a 2x2 microstrip patch array beam steering antenna integrated with pin diodes. The antenna system enables dynamic control over the beam direction, allowing for efficient wireless communication in various applications. By incorporating pin diodes, the electrical length of the patch elements can be modified, resulting in beam steering capabilities. The antenna operates in the 1.8 – 3 GHz band frequency range, utilizing cost-effective FR4 substrate material. Simulation and experimental evaluations demonstrate the antenna's performance, including return loss, radiation pattern, and beam steering range. This research contributes to the advancement of beam steering antenna technology, providing a practical and affordable solution for enhancing wireless communication systems.

Scalable and Conflict-Free NTT Hardware Accelerator Design: Methodology, Proof, and Implementation

Number Theoretic Transform (NTT) is useful for the acceleration of polynomial multiplication, which is the main performance bottleneck in the next-generation cryptographic schemes. Different NTT based cryptographic algorithms have different security settings. The diverse application scenarios introduce different cost-performance trade-offs and hardware constraints. Motivated by the emerging demand for more versatile NTT hardware accelerators, we propose a new design methodology that can generate area-efficient and high-performance NTT accelerators for any length and modulus of NTT polynomials and single processing element (PE) or PE array with a varying number of layers. The proposed NTT accelerator architecture pivots on a conflict-free memory access pattern for adaptation to different combinations of security and PE array configuration parameters. The proposed memory access pattern is formally proved to be conflict-free for any parametric configurations. The criterion for read-after-write conflict without pipeline stall is also established. Our proposed design methodology can produce NTT accelerators with single PE or multi-layer PE array for different polynomial size and modulus, with hardware area and computational efficiency comparable to accelerators customized for a fixed set of parameters. Our proposed methodology produces parameterized accelerator with higher scalability than the existing parameterized accelerator design. On average, the accelerators generated by our proposed method are 71.4% more area-time efficient. Up to 30.7% area-time reduction over the most area-time efficient state-of-the-art scalable NTT accelerator can be achieved for the same security parameters.

Single angle steel member damage under static and fatigue axial tension loads

Sections of steel elements are subject to damage owing to factors such as sudden loads, tearing, or corrosion. This affects the efficiency of the steel element in terms of its load capacity or number of load cycles when subjected to fatigue load. Experimental tests were performed on five specimens of single-angle sections with various degrees of damage to the unconnected leg in the middle of the element length under static load. A finite element (FE) simulation was performed on 25 specimens with the same amount of damage as in the experimental tests under static and fatigue loads. The maximum load capacity and corresponding elongation under static load were measured in the FE simulation specimens and compared with the results. The results proved the high accuracy of the FE modeling of steel elements with damage to the unconnected leg of a single-angle section. For the section with damage to a depth of 80% of the depth of the unconnected angle leg, the maximum load capacity decreased by 67.5%. Damage also affected the number of load cycles. The percentage of decrease did not exceed 5% with damage up to 40% of the depth of the unconnected leg, but it increased to 57% with damage at 80% of the depth. It is therefore important to use the stress concentration factor when calculating the number of load cycles in damaged sections.

Novel Approach of Airfoil Shape Representation Using Modified Finite Element Method for Morphing Trailing Edge

This study presents a novel approach to parameterize the geometry of a morphing trailing-edge flap that allows its aerodynamics to be optimized while capturing the expected structural behavior of the flap. This approach is based on the finite frame element method, whereby the initial flap surface is defined as a structure with constraints that are similar to those of a morphing flap with passive skin. The initial shape is modified by placing a series of distributed loads on the surface. The finite frame element method is modified with rigid rotation corrections to maintain the initial element length without requiring nonlinear calculations and to achieve accurate surface-length results by only solving the linear FEM equations twice. The proposed method enables the shape of the morphing flaps to be rapidly formulated while maintaining the initial upper surface-length and trailing-edge angle. The constraints are inherently integrated into the algorithm, eliminating the need for unnecessary feasibility checks during the aerodynamic optimization. By using the proposed airfoil parameterization method, a case study was conducted by using a genetic algorithm to optimize the lift-to-drag ratio of the NACA 23012 airfoil flap starting at 0.7c with 10 degrees of deflection. The optimizer resulted in a structurally feasible morphing flap that achieved a 10% increase in the lift-to-drag ratio in the optimized angle of attack range.

THE INFLUENCE OF PARAMETERS OF EARTHMOVING MACHINES ON THE DESIGN SOLUTIONS OF BARRETTE PILES

The article deals with the analysis of publications on the arrangement of barrette foundations. It indicates that the bearing capacity of a barrette is determined mainly by the resistance behind its lateral surface, and if it is larger, maybe, it will increase the bearing capacity of the barrette. The use of barrettes with a cross-sectional shape is more relevant than rectangular (square) one. Nowadays, rectangular (square), X-shaped, T-shaped, L-shaped, H-shaped, Y-shaped and C-shaped barrettes can be used in construction. The geometric dimensions of the barrettes depend on the size of a grab unit or a milling unit. A theoretical study of the parameters of the most common types of earthmoving machines, namely a hydraulic grab and a hydromill, was carried out. The technical characteristics of hydraulic grabbers were analyzed: KHD series (CASAGRANDE S.P.A.), GB series (BAUER Maschinen GmbH), HSG series (LIEBHERR Maschinen GmbH), GH series (SOILMEC S. P.A.) and technical characteristics of hydromills: FD series (CASAGRANDE S.P.A.), BC series (BAUER Maschinen GmbH), LSC series (LIEBHERR Maschinen GmbH), SH series (SOILMEC S.P.A.). The intervals of variations were determined in the geometric dimensions of a single gripper, which is arranged with the help of a grab unit and milling unit. It allowed to determine the possible variations in the geometric dimensions of rectangular (square), X-shaped, T-shaped, L-shaped, H-shaped, Y-shaped, and C-shaped barrettes with cross-sectional dimensions. According to the obtained results, the width of a separate linear element of the barrette can vary from 420 to 1800 mm during the use of a grab unit and from 64 to 2000 mm during the use of a milling unit. The length of a single line element of barrette can vary from 2200 mm to 4200 mm during the use of a grab unit and from 2200 mm to 3200 mm during the use of a milling unit. The obtained results will allow to optimize the design process of barrette foundations and avoid additional specification of their dimensions at the installation stage.

Features of Nonlinear Calculation of Bending Rods Partially Supported on Elastic Foundation

The paper investigates the results of solving spatial contact problems on the free support of bending rods (hereinafter referred to as beams) on elastic quarter-space and octant of space. The objectives of the study include determining the stress state of contact pads, obtaining a picture of the distribution of contact stresses over them, and studying the features that arise when solving these contact problems. The main solution method is the method of B. N. Zhemochkin, based on the discretization of contact areas by replacing a continuous contact with a point one. This approach allows us to reduce the contact problem to the calculation of a statically indeterminate system using well-developed methods of structural mechanics. The mathematical model of the contact problems to be solved is built on the assumption of linear elastic (geometric and physical linearity) work of both the bending element and the elastic foundation. Since in the process of deformation the end sections of the beam element can break away from the support areas, the contact problems to be solved belong to the group of contact problems with a previously unknown contact area. The design schemes of such problems are constructively nonlinear, and their calculation is carried out by iterative methods. Based on the results of solving the considered contact problems, it has been found that with a geometrically symmetrical support of the beam element on the left and right on elastic quarter-spaces (space octants) with equal support areas, but different mechanical characteristics, as well as symmetrical loading, the values of support reactions, considering them as resultants of contact stresses on the left and right contact pads, and the coordinates of the points of their application are not equal to each other. The solution of the contact problem leads to a similar result in the case of a bending beam element resting on the elastic quarter-space on one side, and on the edge of the space octant on the other. In addition, a constant torque appears along the entire length of the beam element, indicating that the beam element is in a torsional transverse bending condition.

Performance analysis of heat pipe-cooled two-stage thermoelectric air conditioner

A detailed model of heat pipe-cooled two-stage thermoelectric (TE) air conditioner is established. The performance is analysed comprehensively including the cooling power, coefficient of performance (COP), thermodynamic perfectibility and extreme temperature difference. The influences of key parameters including working current, distribution ratio of TE elements and heat pipe parameters are analysed by numerical simulation. The working current and the TE element number ratio are optimized for the maximum cooling power and the maximum COP respectively. The influences of the cross-sectional area, the length of the TE element and the temperature difference on the optimal variables and optimal performance is obtained. The results show the refrigeration performance of the TE air conditioner can be effectively improved by heat pipe cooling. The two-stage mode can effectively improve the refrigeration temperature difference. The extreme temperature difference can be improved from 60 K to 110 K.

Electromagnetic and RF pulse design simulation based optimization of an eight-channel loop array for 11.7T brain imaging.

Optimization of transmit array performance is crucial in ultra-high-field MRI scanners such as 11.7T because of the increased RF losses and RF nonuniformity. This work presents a new workflow to investigate and minimize RF coil losses, and to choose the optimum coil configuration for imaging. An 8-channel transceiver loop-array was simulated to analyze its loss mechanism at 499.415 MHz. A folded-end RF shield was developed to limit radiation loss and improve the efficiency. The coil element length, and the shield diameter and length were further optimized using electromagnetic (EM) simulations. The generated EM fields were used to perform RF pulse design (RFPD) simulations under realistic constraints. The chosen coil design was constructed to demonstrate performance equivalence in bench and scanner measurements. The use of conventional RF shields at 11.7T resulted in significantly high radiation losses of 18.4%. Folding the ends of the RF shield combined with optimizing the shield diameter and length increased the absorbed power in biological tissue and reduced the radiation loss to 2.4%. The peak of the optimal array was 42% more than the reference array. Phantom measurements validated the numerical simulations with a close match of within 4% of the predicted . A workflow that combines EM and RFPD simulations to numerically optimize transmit arrays was developed. Results have been validated using phantom measurements. Our findings demonstrate the need for optimizing the RF shield in conjunction with array element design to achieve efficient excitation at 11.7T.