Equal Angles Research Articles

Assessment of design procedures for the buckling resistance of hot-rolled steel equal leg angles under concentric and eccentric compression

This work presents an extensive advanced numerical study calibrated with recent experimental results available in the literature on the buckling behavior of hot-rolled steel angles under concentric and eccentric compression to support the ongoing revision in Europe of the design rules for angles concentrically and eccentrically loaded in compression. The numerical results were used for the assessment of existing design procedures commonly applied in practice (Eurocodes and AISC), as well as new recently proposed recommendations. In general, the current analytical rules do not present good agreement with the experimental and calibrated numerical results, even showing unsafe results for some slenderness ranges. In case of fixed members in eccentric compression, these design rules are extremely conservative, reaching ratios rN (numerical versus analytical resistances) in excess of 2. The new proposals resulting from the project ANGELHY present an improved agreement with the numerical results, showing that they may efficiently replace the current design rules in the Eurocodes. However, for concentric compression, a reliability assessment shows that the required partial factor is γM1* = 1.1.

Stab lesion of the L4/L5 intervertebral disc in the rat causes acute changes in disc bending mechanics

Low-back pain often coincides with altered neuromuscular control, possibly due to changes in spine stability resulting from injury or degeneration, or due to effects of nociception. The relative importance of these mechanisms, and their possible interaction, are unknown. In spine bending, the bulk of the load is borne by the IVD, yet the acute effects of intervertebral disc (IVD) injury on bending mechanics have not been investigated. In the present study, we aimed to quantify the acute effects of a stab lesion of the disc on its mechanical properties, because such changes can be expected to elicit compensatory changes in neuromuscular control. L4/L5 spinal segments were collected from 27 Wistar rats within two hours after sacrifice and stored at −20℃. Following thawing, bending tests were performed to assess the intersegmental angle-moment characteristics. Specimens were loaded in right bending, left bending and flexion, before and after a stab lesion of the IVD fully penetrating the nucleus pulposus. In the angle-moment curves, we found reduced moments at equal bending angles after IVD lesion in left bending, right bending and flexion. Peak stiffness, peak moment, and hysteresis were significantly decreased (by 7.8–27.7 %) after IVD lesion in all directions. In conclusion, L4/L5 IVD lesion in the rat caused small to moderate acute changes in IVD mechanical properties. Our next steps will be to evaluate the longer term effects of IVD lesion on spine mechanics and the neural control of trunk muscles.

Simulation of the Hydraulic Performance of Parallel Pivot Weirs with Different Angles

Pivot weirs are one of the most important structures for regulating the water level in rivers and canals. These weirs are constructed with one or more gates in a row in the waterways. Changing the angle of each gate is done individually with an independent system. Based on available information, the hydraulic performance of this type of weirs (especially in several gates and different angles) in different operational conditions has not been investigated. In present study, pivot weirs with two gates are simulated using Ansys CFX software with the angles of 27.8 to 90 degree and the discharges between 40 to 130 L/s. Further, the importance of the open space between the two adjacent weirs with different angles (lack of retail wall) and its hydraulic behavior have been studied. The model was calibrated based on valid laboratory data and using the K-ϵ turbulence model. Therefore, the weirs with equal angles were studied in the first step. In this case, the effective discharge angle coefficient was studied and its maximum value compared to the vertical angle was obtained 1.076 for the angle of 52°. Furthermore, relationships for discharge coefficient versus upstream water depth were developed. In the next step, the effective length of the crest was found to be increases by 30% under unequal angles operation and the discharge coefficient raised by 1.3 to 2.4 times. Also, it was recognized that, in case of two weirs with unequal angles, about 26% to 69% of the flow passes through the distance between the two weirs. Therefore, the performance of unequal angles operation seems to be more effective in controlling the water level and discharge in different conditions and especially in flood events.

Demodulation method of orbital angular momentum vortex wave by few fields sampled on an extremely small partial aperture in radiation region

In this paper, a demodulation method of electromagnetic wave carrying orbital angular momentum (OAM) has been developed by using few electric fields sampled on an extremely small portion of the whole circumference in the radiation region. Considering that the field of the OAM wave is naturally of the form of exp (ilφ) in the far-field region, the matrix pencil method is used to extract the magnitude terms and the exponential terms according to the real and imaginary parts of the fields sampled on a small portion of the whole circumference, and further, the mode purities corresponding to the desirable OAM modes can be easily solved. The proposed demodulation method only uses four sampling electric fields with the sampling angle ranges of 3.3° and 9° to well demodulate the mode purities of the OAM waves with the single mode and the mixed dual-mode, respectively. The prototype of a dual uniform circular array with the equal divergent angle for the OAM waves of the modes l = 1 and l = 2 is fabricated and measured. Good agreement between the simulation and the measurement is observed to verify the proposed demodulation method.

Effects of Deposition Rate on Local Stability of Wire Arc Additively Manufactured Outstand Elements

AbstractA great focus is currently being placed on the development of applications of Wire Arc Additive Manufacturing (WAAM) in structural engineering. To facilitate this development, an experimental programme investigating the effects of the deposition rate on WAAM 316LSi stainless steel outstand elements has been conducted. Equal angle section (EAS) stub columns with four different cross‐sectional slendernesses were produced using WAAM. For each slenderness, four different deposition rates were employed; hence, overall, sixteen EAS stub columns were produced, 3D scanned and tested to examine their local stability. To keep the heat input constant between all cases, for each deposition rate, the travel speed was varied accordingly. Alongside the EAS specimens, tensile coupon testing was conducted to determine the material properties corresponding to each deposition rate. The tensile coupons were extracted at three different orientations (0°, 45° and 90°) relative to the deposition direction in order to investigate the degree of material anisotropy. In the present paper, following the description of the EAS stub column test results, the applicability of current Eurocode design rules and the Continuous Strength Method for the prediction of their design strength is assessed.

Metasurface modulator of frequency diverse multi-mode OAM beams with equal divergence angle for coincidence imaging

Traditional multi-mode orbital angular momentum (OAM) beams suffer from low energy efficiency in detection since the divergence angle tends to increase with increasing order of the OAM mode. Thus, OAM beams with equal divergence angle are highly desirable. In this paper, a frequency-diverse multi-mode (FDMM) OAM modulator with approximately equal divergence angle is proposed. The modulator is composed of an OAM modulation metasurface and a spatial filter (SF) with narrow passband. Firstly, the OAM modulation metasurface is designed based on multiple ring-like regions with different radii in the metasurface aperture. Each mode of OAM beam is generated at a corresponding frequency point in one region. Thus, the metasurface aperture can generate different modes of OAM beams at different frequencies (i.e., FDMM OAM beams) simultaneously. Then, the SF with narrow passband is proposed through synthesizing multi-layer frequency selective metasurfaces, aiming to reduce interferences between different modes of OAM beams. Finally, the FDMM OAM modulator is realized by superposing the SF on the OAM modulation metasurface. The FDMM OAM modulator can generate six modes of OAM beams (i.e., , and modes) at 12.5 GHz, 13.0 GHz and 13.6 GHz, respectively. A multi-mode OAM coincidence imaging model based on the FDMM OAM modulator is established. The simulation and experiment results show that the proposed FDMM OAM modulator can be used for target reconstruction and the coincidence imaging performance can be improved assisted by an optimization algorithm.

Issues of Developing Equal-Strength Two-Layer Spherical Rubber-Metal Hinges

Development of equal-strength two-layer spherical rubber­metal hinges (RMH), described in the paper, is associated with the problem that with an equal thickness of the layers of rubber bushings and an equal opening angle, there is a significant difference in their radial stiffness and relative deformation of the rubber. With hinge dimensions corresponding to those of the hinges used in the undercarriage of locomotives, there is a difference in relative deformation of inner and outer bushings by about 1,5 times. As a result, it is proposed to determine the load capacity of spherical two-layer RMH by the value of relative deformation of the rubber of the most loaded bushing. Also, studies have been carried out on the possibilities of creating a uniformly deformable design of a spherical two-layer RMH.To determine the characteristics of a spherical rubber-metal hinge, applied digital computer modelling based on the finite element method. A proposed parametrised geometric model of a spherical two-layer RMH and a finite element model of an elastic bushing offer the ratio of radial stiffnesses of outer and inner bushings, which is close to the preliminarily determined one, based on the equations of the theory of elasticity in displacements in a spherical coordinate system.It has been established that to achieve uniform elasticity by changing the opening angle, the opening angle of the outer reinforcement of RMH should be approximately 1,5 times less than the opening angle of the inner one. This makes it possible to reduce the width of outer reinforcement of RMH by 25 % but raises the problem of strength and rigidity of outer edges of intermediate reinforcement. Also, equal elasticity of hinge bushings can be achieved due to their different thicknesses, while to achieve non-uniform stiffness of bushings within ± 5 %, it is required to ensure that deviation of the intermediate cage diameter during hinge manufacture is less than ± 0,1 %.The obtained research results prove the practical possibility of creating an equally strong (with equal bushing rigidity) spherical two-layer RMH. The issue of searching for a compromise design of RMS, acceptable from the point of view of loading of the intermediate cage and of the requirements for manufacturing accuracy, requires further study.

Structural design and flow field characteristics analysis of a new spin-on multi-hole jet drill bit for radial horizontal wells

In order to improve the rock breaking and drilling capacity of the jet bit in radial drilling, a new spin-type multi-hole jet bit was designed. The RNG K-ε turbulence model is used to analyze the flow characteristics of the internal and external flow fields of the designed jet bit, and the influence of the rotational speed and nozzle distribution on the flow field characteristics of the jet bit is analyzed to provide a basis for the design and structural parameter optimisation of the jet bit in radial horizontal wells. The results show that the internal flow field of the jet bit can be divided into four zones: the forward jet zone, the bottomhole overflow zone, the reverse overflow zone and the low-speed reverse flow zone. The reverse jet consists of six straight jets uniformly distributed along the circumferential direction and arranged at equal angles around the axis of the rotating body in the flow field. The reverse jet also impinges on the well wall to form an overflow zone, which provides self-propulsion and acts as a reaming agent. As the injection distance increases, the axial velocity rapidly decreases to zero and the decay velocity of the three groups of jets gradually approaches at the impact wall. Rotational speed has an effect on the decay of the flow velocity at the centre of the forward jet axis. When the angle of inclination is very small, the rotational speed has almost no effect on the decay of the axial velocity of the jet. The greater the angle of inclination, the greater the linear angular velocity at the jet exit, the more the jet mixes with the surrounding crossflow, the faster the dissipation of jet energy and the faster the jet decays along the axis. Controlling the magnitude of the rotational speed has to be taken into account in the design. Initially, the optimum values of the different structural parameters were determined as the central nozzle coinciding with the drill axis, the central forward nozzle deflection angle of 20°, the external nozzle deflection angle of 20° and the external nozzle tension angle of 15°.

Performance evaluation of turbulent circular heat exchanger with a novel flow deflector-type baffle plate

Experiments were conducted to investigate the performance of an axial flow tubular heat exchanger with a novel swirl flow of air created by the addition of circular baffle plates featuring trapezoidal air deflectors with various inclination angles. The tubes remained in identical longitudinal arrangement and maintained constant heat flux over their surface. Each baffle plate contained four deflectors with an equal inclination angle, generating an air swirl inside the circular duct containing the heated tubes that improved the air-side turbulence and thus the rate of heat transfer from the tubes' surfaces. The pitch ratio of the baffle plates was varied, and the Reynolds number was kept in the range of 16000–28000. Results from the study showed an average 7.4% improvement in performance enhancement criteria when the exchanger was fitted with a baffle plate featuring a deflector inclination angle of 30° and operated under counter flow conditions when compared to a parallel flow arrangement operating under similar experimental conditions.

An enhanced instantaneous angular speed estimation method by multi-harmonic time–frequency realignment for wind turbine gearbox fault diagnosis

Gearboxes are one of the most critical transmission devices in wind turbines (WTs). Order tracking (OT) of variable-speed WT gear is a powerful means to carry out fault diagnosis. Since it is difficult to install a tachometer or encoder for gearboxes with limited structural space, it is impossible to obtain the instantaneous angular speed (IAS) of the gearbox. In recent years, many tacholess techniques have been presented to estimate instantaneous phase from vibration signals for OT. However, their performance needs to be further improved to get a more exact diagnosis result. To solve this issue, this paper presents an enhanced IAS estimation approach for WT tacholess order tracking (TLOT), which is available for accurate IAS estimation of the rotating shaft, so that TLOT can be more effectively conducted under conditions of large speed variation and background noise. An improved cost function algorithm is designed to extract the IAS from the vibration signal. A Vold–Kalman filter and Hilbert transform are combined to calculate the instantaneous phase. Afterwards, the raw non-stationary vibration signal is resampled at an equal angle increment, and the envelope order spectrum is calculated from the resampled signal for fault diagnosis of the WT gearbox. The main innovating idea of this approach is to improve the traditional cost function ridge-extraction method by introducing gradient information based on probability and multi-harmonic time–frequency realignment, which makes the IAS estimation process more accurate and overcomes the limitations of traditional IAS estimation techniques. The effectiveness of the presented approach is demonstrated by using a vibration signal measured from real-world WT gearboxes, and the validation results demonstrate that the presented approach surpasses some state-of-the-art methods in IAS estimation accuracy and efficiency.

An optimization method for surface urban heat island footprint extraction based on anisotropy assumption

The footprint (FP) is the main indicator used to quantitatively analyse the surface urban heat island (SUHI) effect. Currently, SUHI FP extraction methods ignore the interference caused by the city shape and are mostly based on the isotropic expansion assumption, resulting in an exaggerated range. Therefore, a new approach for an optimization schema that leverages the assumptions of angle segmentation and anisotropy is proposed herein. This method divides an urban area and its buffer rings into 16 sectors with equal central angles and selects appropriate land surface temperature (LST) curves for an exponential decay fit. The final FP was determined using the SUHI extension distance and the reference rural LST. To verify the effectiveness of this method, SUHI FPs of 27 cities in the central region of the Yangtze River Delta (YRD) were extracted during the summer of 2019, and the results were compared with those derived from traditional methods. The results showed that the FPs calculated using this method were more detailed because they minimized the influence of urban shape, topography, and the surrounding landscape. Moreover, this method played a vital role in revealing the effect of the land use allocation outside urban area on the SUHI effect. This state-of-the-art method is useful for unveiling SUHI spatial distribution patterns and for providing scientific support for land planning for sustainable urban development.

Material properties and local stability of WAAM stainless steel equal angle sections

An experimental study has been carried out to investigate the material properties and local stabilities of outstand WAAM 316L stainless steel plates. A series of equal angle section (EAS) stub columns and corresponding sample plates for tensile coupon extraction were fabricated employing two sets of manufacturing parameters in order to achieve two print thicknesses. The tensile coupons were extracted from the sample plates along different printing directions, and the tensile test results indicated a high degree of anisotropy while displaying satisfactory material ductility according to the Eurocode 3 requirements. The EAS stub columns covered a wide range of plate slendernesses and their geometric profiles were 3D laser scanned and analysed prior to the compression tests. The failure modes and load carrying capacities of the WAAM EAS stub columns were analysed, showing generally lower resistances compared to conventional rolled counterparts in the high slenderness range. Assessed against the test data, the Continuous Strength Method is shown to be suitable for designing stocky WAAM stainless steel plates. For the design of slender WAAM stainless steel plates, the effective width equation in Eurocode 3 is shown to be applicable, however, the calculation should be based on the new characteristic geometric dimension proposed. Based on this, it is further demonstrated that the thicker printing strategy adopted in the current study would have a higher effective thickness to overall thickness ratio, hence more efficient builds than the thinner printing strategy.

Behaviour of back-to-back built-up cold-formed steel equal angles with complex edge stiffeners under axial compression

The application of built-up cold-formed steel (CFS) structures becoming popular in civil engineering fields such as trusses, bridges, transmission towers and railway coaches. This work presents the numerical analysis of axially compressed back-to-back built-up CFS equal angle sections. A nonlinear finite element (FE) model was developed that considered geometric imperfections, material nonlinearity, and intermediate fastener. The published experimental test data were used to compare the FE model, and the results shown good agreement. The effect of the slenderness ratio and edge stiffening direction on the axial strength of back-to-back built-up CFS equal angle sections is investigated by using parametric study.

Experimental study of impinging jets of gelled and liquid fluids

This work presents an experimental study on spray formation by unlike impingement of gelled ethanol with liquid water and liquid ethanol, and a comparison with spray formation by like impingement of gelled ethanol. High-speed shadowgraphy was utilized to analyze collision sheets, instabilities, breakup lengths and particles of sprays formed by colliding jets with 0.80 mm diameter with equal momentum and different collision angles and flow conditions. For unlike jet impingement, the sheet evolution and disintegration showed a mixture of patterns found in Newtonian and non-Newtonian fluids, such as complex structures with rails, holes, fishbone, detaching beads and ligaments. Regime transition for unlike impingement configurations is faster than for like impingement, consequently the breakup lengths for unlike impingement were significantly shorter than for like impingement. In general, the breakup lengths decreased for larger We or larger jet momentum values and increased for lower impingement angles. Despite the improvement in the atomization caused by unlike configurations, small ligaments remained in all sprays formed by unlike jets. The particle sizes and geometries for the different configurations were evaluated and compared in terms of circularity, percent area and Feret diameter. No significant differences of the spray regions were observed between the two unlike impingement settings.

A numerical algorithm to model wall slip and cavitation in two-dimensional hydrodynamically lubricated contacts

Hydrodynamic lubrication takes a fundamental role in mechanical systems to reduce energy losses and prevent mechanical breakdown. The analytic instrument usually adopted to describe hydrodynamic lubrication is the Reynolds equation, which in its simplest statement for monophase lubricants and with assuming no fluid slip at the walls, is a linear equation in the hydrodynamic pressure. However, this classical linear Reynolds equation cannot reflect all the lubricant characteristics in engineered surfaces (e.g. superhydro(oleo)phobic surfaces and textured surfaces). In these cases, the effect of two critical factors, such as wall slip and cavitation, need to be considered, introducing non-linearities in the system. In order to tackle this issue, a modified two-dimensional Reynolds equation is introduced, able to capture both the cavitation presence, via a complementary mass-conserving model, and wall slippage, starting from the multi-linearity description introduced by Ma et al. (2007). In addition, an alternative model for the slippage at the wall is proposed by modifying the multi-linearity wall slip model to improve accuracy and computational cost. In this new model, the possible slip directions are limited to three, separated by equal angles, with the slip occurring only along the first direction, and the other directions, then, used to iteratively adjust the direction of slippage, until a suitable convergence criterion is satisfied. The proposed mathematical model is validated versus results available in literature with tests performed on (i) journal bearings, (ii) slider bearings, (iii) squeeze dampers, and (iv) surface textured bearings. By conducting these tests, the proposed alternative wall slip model is proved to be up to one order of magnitude more computational efficient than the original multi-linearity wall slip model.

Design and Analysis of a Multi-Knuckle Coupled Grasper With Equal Angles at Each Knuckle During Motion

Abstract In this study, a coupled multi-knuckle mechanical finger was designed. The finger is composed of same-structured knuckles in a connecting link structure, and the knuckles can be combined arbitrarily. The coupling motion is completed under the drive of a single actuator. First, the influences of the angular relationship between the knuckles and working stroke of the knuckles on the actual grasping range of the finger were evaluated, and the kinematic analysis of the knuckle was performed using the closed-loop vector method. Next, an optimization design method based on a genetic algorithm was proposed, which considered the angular relationship as the objective function to optimize the knuckle, which is illustrated with an example. The angle between each pair of knuckles is approximately constant and equal, which indicates that the finger has an approximately circular envelope curve. Subsequently, the finger motion simulation was carried out to verify the optimization design results and evaluate the error in the finger grasping process. The grasper is capable of completing accurate envelopes on cylinders with diameters ranging from 38.97 mm to 127.60 mm. Finally, the prototype of the manipulator was constructed according to the parameters obtained in the optimization design example. The feasibility of the design was verified through a grasping experiment using beakers and other objects. It provides a reference for angle optimization and envelope curve design of the grasper.

Resolution Analysis of Coincidence Imaging Based on OAM Beams With Equal Divergence Angle

The multi-mode orbital angular momentum (OAM) beams can be effectively applied in target detection when the divergence angles are equal. The resolution threshold of the coincidence imaging system with multi-mode OAM is analyzed assisted by the subspace projection method. First, the relationship between the imaging resolution and the correlation function (CF) of the measurement mode is obtained based on the first-order correlation algorithm for the multi-mode OAM-based coincidence imaging (MM-OAMCI). Then, the feature vector of each imaging unit is extracted to distinguish the imaging point in the discretized imaging plane. Finally, the resolution threshold is given based on three factors, i.e., the feature vector, the noise, and the reconstruction algorithm. Specifically, the resolution of the MM-OAMCI system is determined by the deployment of the transmitting array, the reconstruction algorithm and the noise caused by the system design, the imaging modeling, and the environment noise. The super-resolution capability of the multi-mode OAM coincidence imaging system is validated by the simulations and experiments. The imaging results show that the resolutions in elevation and azimuth of the reconstructed image can be improved largely compared with the traditional microwave coincidence imaging (TMCI) methods, which is consistent with the theoretical analysis results.

Rebar Replacement in Severely Damaged RC Bridge Column Plastic Hinges: Design Criteria and Experimental Investigation

This paper presents a procedure for rehabilitating plastic hinges with damaged/fractured weldable longitudinal rebars in severely damaged reinforced concrete (RC) bridge columns and possible improvements regarding connection protection and plastic hinge development. Damaged/fractured longitudinal rebars are replaced with new rebar segments, and the basis of this approach involves connecting intermediate machined parts to the original longitudinal rebars by welding with an off-the-shelf steel equal angle. The proposed rehabilitation design procedure is based on capacity design principles, with equations that define the new geometries and required ductility, and it is validated experimentally on three 1∶6-scale RC circular column specimens. Compared with the original columns, the ductility capacity of the rehabilitated columns increased from 39% to 58%, and the energy dissipation (equivalent viscous damping ratio) increased from approximately 50% to 250%. The base shears of the rehabilitated columns were smaller than those of the original columns owing to the reduction in the rebar area; thus, shear failure was avoided, and the demand on the foundation was reduced. The rehabilitation procedure, by adopting a welding connection that is easily performed on site and concentrates the damage in the new rebar segments, promises to be a quick, simple, reliable, and effective means to improve the ductility and shear capacity of RC bridge columns without using mechanical couplers or changing the column dimensions.

Effect of Screw Head- and Hook-on Bond Behavior of Flamingo Shear Reinforcing Technique in Concrete

An alternative reinforcing shear technique was proposed during this work in place of the traditional vertical stirrups. Three reinforced concrete beams with dimensions of (200 * 300) mm and a length of 1800 mm were used. A reference control beam with traditional vertical stirrups (RCWS) and two beams reinforced with flamingo with a fixed angle of 45° and free ends (50% and 50%) from effective depth were used, while the main variable was the bonding process with concrete using a screw head (FWS) and hook (FWH). In the flamingo technique, the hook was used and the screw head was used at an equal angle of 130 degrees. A significant improvement was found in the shear capacity of the beam compared to the reference sample. Also, using a screw head made the shear capacity 13.22% higher than using a hook and improved the shear ductility, final deflection, and crushing behavior of beams made with the flamingo technique.

Analisis Destruction Test Tower Sutet dibandingkan dengan Software Ms Tower dan SAP 2000

The transmission line system which is currently growing rapidly in Sumatra, requires a reliable interconnection network to meet the electricity demand for the West Sumatra region. PT. PLN as a provider of electricity businesses in Indonesia conducted planning and destruction tests to design a new model Extra High Voltage Transmission Line (SUTET) tower with specification of 66.6 meters height, slim type tower, 275 kV, lattice BB+15, quadrapole zebra (435/55 mm2) 2 cct. This research aims to study tower collapse behavior caused by working loads, analyze and compare the suitability level of tower deformation and natural frequency among MS Tower, SAP 2000 space truss analysis, SAP 2000 space frame analysis with destruction test results. SAP 2000 space frame deformation analysis shows that the tower is unstable in the Leg section. The analysis of natural frequency and the mode shape in the SAP 2000 space frame analysis is close to the value of the natural frequency destruction test with a deviation of 30%. The tower collapse occurred due to imperfection geometry on the legs section, resulting in a global collapse. Improvements in the form of adding equal angle to the hip bracing were carried out, the result was able to withstand a load case load of 9870 up to 100%. Space frame analysis on SAP 2000 is closer to MS Tower, this can be seen from the deformation and natural frequency values that approach each other from the two analyses.