Search Results (40)

Double-suction centrifugal pumps are extensively employed in industrial applications owing to their high efficiency, low vibration, superior cavitation resistance, and operational durability. This study analyzes how impeller oblique cutting angles (0°, 6°, 9°, 12°) affect a double-suction pump at a fixed 4% trimming ratio and constant average post-trim diameter. Numerical simulations and tests reveal that under low-flow (0.7Q_d) and design-flow conditions, the flat-cut (0°) minimizes reflux ratio and maximizes efficiency by aligning blade outlet flow with the mainstream. Increasing oblique cutting angles disrupts this alignment, elevating reflux and reducing efficiency. Conversely, at high flow (1.3Q_d), the 12° bevel optimizes outlet flow, achieving peak efficiency. Pressure pulsation at the volute tongue (P11) peaks at the blade-passing frequency, with amplitudes significantly higher for 9°/12° bevels than for 0°/6°. The flat-cut suppresses wake vortices and static–rotor interaction, but oblique cutting angle choice critically influences shaft-frequency pulsation. Entropy analysis identifies the volute as the primary loss source. Larger oblique cutting angles intensify wall effects, increasing total entropy; pump chamber losses rise most sharply due to worsened outlet velocity non-uniformity and turbulent dissipation. The flat-cut yields minimal entropy at Q_d. These findings provide a basis for tailoring impeller trimming to specific operational requirements. Furthermore, the systematic analysis provides critical guidance for impeller trimming strategies in other double-suction pumps and pumps as turbines in micro hydropower plants. Full article

In the framework of the MATIM project, an acoustic test campaign was conducted on a platform derived from a commercial-class quadcopter within the CIRA semi-anechoic chamber. A dedicated rotor rig allowed systematic measurements of thrust, torque, and shaft speed together with near- and far-field noise using ten calibrated 1/2-inch precision microphones. Three configurations were examined: an isolated rotor, the same rotor mounted on an aluminium quadcopter plate, and the full four-rotor assembly. The resulting data set, acquired over 3000–8000 rpm, documents the azimuthal directivity and radial decay of tonal and broadband noise while separating motor, propeller, and installation contributions. Analysis shows that a nearby rigid plate scatters part of the sound field towards frontal and oblique observers and produces a shielding effect in the rotor plane. The combined operation of four rotors further redistributes energy and broadens blade-passing frequency harmonics. The database is intended as a benchmark for aeroacoustics codes and for the development of reduced-order models. Full article

Among the biggest challenges in modern manufacturing techniques is deliberately shaping the surface layer of a part to suit the conditions in which it will be used. The degree of difficulty increases with the increase in the functional requirements of the items to be manufactured and with the complexity of the technology developed. Hybrid machining processes allow functional surfaces to be shaped by combining different machining operations into a single operation. The values of the amplitude and length parameters of the resulting surface geometrical texture are largely determined by the technological parameters of the combined machining operations. However, it is the tool guidance and kinematic–geometric conditions during the hybrid machining process that are responsible for the surface texture. This paper describes the results of an investigation into the influence of the milling tool guidance strategy during shaping milling and tooling guidance during burnishing of workpieces made of 42CrMo4 steel tempered to a hardness of 35 ± 2 HRC—a material commonly used in the construction of machine parts. It was shown that running the burnishing with two crossing passes oriented obliquely to the marks left by the cutter was the most favourable of the burnishing strategies tested. Full article

In a supersonic flow, disturbances of different parameters arise. These perturbations can have a significant impact on the interaction of the flow with the surface. When gas flow passes through a shock wave, perturbations are transformed depending on the initial parameters of the flow. Therefore, it is important to be able to correctly assess the intensity of these transformations. In this work, for the first time, a method has been proposed that allows us to estimate the dynamics of variation of disturbances of flow parameters when passing through an oblique shock wave. The influence of the shock wave inclination angle β, Mach number, intensity of disturbances of velocity, density, temperature, and pressure in front of the shock wave on perturbations of the flow parameters behind the shock wave was investigated. The Mach numbers ranged from 1.2 to 10 and the shock wave inclination angle varied from 15° to 90°. It was shown that the interaction of a supersonic gas flow with an oblique shock wave has a significant effect on the transformation of the perturbations of the flow parameters. The perturbations of temperature and pressure behind the shock wave increase significantly with the increasing angle β and Mach number in front of the shock wave. With the increasing Mach number, the velocity perturbations behind the shock wave first increase, then decrease, passing through a maximum, and afterwards the flow becomes more stable. Full article

The transmittance characteristics and the band structure of photonic heterostructures consisting of four distinct dielectric materials are analyzed using the transfer matrix method. An enhanced band structure of such crystals is discovered. It is shown that the band structure is strongly influenced by the arrangement of unit cells in the periodic building blocks of the crystals. The transmission spectra are evaluated for varying layer thicknesses and incident angles to investigate their impact on wave propagation. The symmetrical results for periodicities, sub-layer thickness, and oblique incident angles indicate robust bandgaps with blue shifting and enhanced transmission. Moreover, the periodicity in different cases, followed by the period, has also shown to have a great impact on the emergence of multiple bandgaps. The photonic bandgap and frequency are associated with the lattice elements of the unit cell, shifting naturally as a fundamental property of the structure, which has been achieved by the alteration of unit cells. Hence, the proposed photonic heterostructures offer significant potential for developing efficient band-stop and band-pass filters, facilitating their use in multi-functional integrated optical circuits within the Terahertz spectrum. Full article

Since one of the effective methods for producing the form-cutting tools used in the form-turning process involves utilizing a wire cut machine, the effect of the geometric characteristics of the form contour on reducing the negative effects of the recast layer was investigated in this research. The basic assumption of the components for each type of profile form is based on a combination of four modes, i.e., concave arc, convex arc, flat surface, and oblique surface. Based on this, samples were fabricated as cutting tools with three different radii: a convex arc, a concave arc, and a flat surface. During the wire electrical discharge machining (WEDM) operation, one-pass mode was used to create a rough surface, two passes resulted in a semi-finished surface, and three passes resulted in a finished surface. Furthermore, the difference between the surface quality of the recast layer in the two areas above the workpiece or the wire entry point and the bottom area of the workpiece or the wire exit point was studied. Finally, the effect of the direction, size of the curvature and the number of passes in the electric discharge process of the wire on the recast layer was shown, and it was observed that with the increase in the number of passes in WEDM, the thickness of the recast layer was reduced, along with the uniformity of the cutting contour section in the areas close to the cutting region. The entry of the wire was greater than that in the areas near the exit of the wire. Full article

The highway network is densely distributed in the southeast coast of China. Highway subgrades passing through soft soil areas often produce large settlements, resulting in pavement cracking, bridgehead jumping, and other diseases. In order to study the effect of three trenchless treatment technologies of oblique jet grouting pile (JGP), lateral displacement limiting pile (LDLP), and load reducing pipe (LRP), centrifugal model tests were carried out under three treated conditions and without treatment. Based on the data of pore water pressure and settlement in the range of the half embankment model and outside the embankment, the settlement characteristics of highway soft soil foundation during the test simulation were studied, and the characteristics of different treatment methods were compared. The high level of pore water pressure corresponds to the rapid development of settlement. The average settlement during the existing operation period accounts for 96.7% of the total settlement of the simulation period, and the settlement does not converge. The methods can effectively inhibit the development of settlement, and each has its own characteristics: the LRP method does not involve foundation treatment, so its settlement characteristics are closest to that without treatment. The LDLP method can obviously limit the settlement within the embankment range and the pore water dissipation. The JGP method enhances the synergistic deformation ability of the embankment and significantly decreases the differential settlement. Full article

Aiming at the problem of the wheat straw and stubble of the previous crop blocking the opener during the operation of the summer peanut no-tillage seeder under straw incorporation modes, an oblique stubble-cutting and side-throwing anti-blocking device that can simultaneously cut the stubble and throw the straw was designed. The structure and working principle of the device were clarified, and the key structure of the anti-blocking device was designed through theoretical analysis. According to the kinematics analysis of the rotary blade cutting and throwing of the root–soil composite, the key factors affecting the operation quality of the device and the range of values were determined. The quadratic orthogonal rotation combination design test was carried out with the motion inclination angle, bending angle, and advancing velocity as the test factors, and the straw clearance rate, stubble-cutting rate, and operation power consumption as the indexes. The discrete element simulation test was carried out in EDEM. The significance test of the test results was carried out in Design-Expert, and the influence of each factor on the test index and the interaction between the factors were determined. Then the regression model was optimized by multi-objective function, and the optimal parameter combination was obtained as follows: The motion inclination angle was 22°, the bending angle was 58°, and the advance velocity was 7.7 km/h. At this time, the straw clearance rate of the seedling belt was 92.55%, the root stubble-cutting rate was 95%, and the operation power consumption was 1.80 kW. The field test shows that the machine had good passing capacity, the straw clearance rate of the seedling belt was 91.04%, the root stubble-cutting rate was 92.98%, and the operation power consumption of the single group of stubble cutting device was 1.92 kW. The difference between the field test results and the simulation test was less than 6%, which met the local agronomic requirements and proved that the anti-blocking device had good operation quality. Full article

Libration and precession are different body forces that are ubiquitous in many rapidly rotating systems, particularly in geophysical and astrophysical flows. Libration is a modulation of the background rotation magnitude, whereas precession is a modulation of the background rotation direction. Assessing the consequences of these body forces in large-scale flows is challenging. The Ekman number, the ratio of the rotation time scale to the viscous time scale quantifying the rotation speed, is extremely small, leading to extremely thin and intense shear layers in the flows even when the amplitudes of the body forces are very small. We consider the consequences of libration and precession numerically in a geometrically simple container, a cube, which lends itself to very efficient, accurate, and robust numerical treatment, with the axis of rotation passing through opposite vertices, so that all walls of the cube are at oblique angles to the rotation axis. This results in the geometric focusing of inertial wavebeams reflecting off the walls, whereby the energy density of the wavebeams increases along with the magnitude of their wavevector. The nature of this focusing depends on the forcing frequency but not on the body force. In the inviscid setting, wavebeams form infinitesimally thin vortex sheets, and their energy density becomes unbounded upon focusing. We present linear inviscid ray tracing to set the scene for the focusing of wavebeams and then consider viscous problems at an Ekman number that is typical of current state-of-the-art laboratory experiments. We begin by considering the linear responses, which are comprised of focusing viscous shear layers, of which their details are mostly captured via ray tracing, and particular solutions accounting for the body forces. These have complicated spatio-temporal structures, which differ for libration and precession. Increasing the forcing amplitude from zero introduces nonlinear interactions, enhances the focusing effects via vortex tilting and stretching when the shear layers reflect at the walls, and also introduces temporal superharmonics and a mean flow. When the magnitude of the mean flow is within a few percent of the magnitude of the instantaneous flow, instabilities breaking the spatio-temporal symmetries set in. These are localized in the oscillatory boundary layers where the reflections are concentrated and introduce broadband dynamics in the boundary layers, with additional inertial wavebeams emitted into the interior. The details again depend on the specifics of the body forces. Full article

In this paper, a patch array antenna with wideband circular polarization and high gain is proposed by utilizing a hybrid metasurface (MS). A corner-cut slotted patch antenna was chosen as the source due to the possible generation of CP mode. The hybrid MS (HMS), consisting of a receiver MS (RMS) arranged in a 2 × 2 array of squared patches and a linear-to-circular polarization conversion (LCPC) MS surrounding it was then utilized as the superstrate driven by the source. The LCPC MS cell is a squared-corner-cut patch with a 45° oblique slot etched, which has the capability for wideband LCPC. The LCPC unit cell possesses wideband PC capabilities, as demonstrated by the surface current analysis and S-parameter simulations conducted using a Floquet–port setup. The LP EM wave radiated by the source antenna was initially received by the RMS, then converted to a CP wave as it passed through the LCPC MS, and ultimately propagated into space. To further enhance the LCPC properties, an improved HMS (IHMS) was then proposed with four cells cut at the corners, based on the original HMS design. To verify this design, both CMA and E-field were utilized to analyze the three MSs, indicating that the IHMS possessed a wideband LCPC capability compared to the other two MSs. The proposed antenna was then arranged in a 2 × 2 array with sequential rotation to further enhance its properties. As demonstrated by the measurements, the array antenna achieved an S11 bandwidth of 60.5%, a 3 dB AR bandwidth of 2.85 GHz, and a peak gain of 15.1 dBic, all while maintaining a low profile of only 0.09λ₀. Full article

Research on the excavation mechanical properties of underpass tunnels has already had certain results, but only a few of them consider the effects of dynamic and static loads on the excavation mechanical properties of underground tunnels at the same time; particularly, there is a lack of research investigating double-line highway tunnels with angled underpasses of existing railway tunnels. In this paper, based on the tunnel project of the new double-line Shiqian Highway Tunnel passing under the Hurong Railway with an oblique angle, based on the method of over-advance geological prediction and investigations into the palm face surrounding the rock, the rock degradation caused by dynamic and static loads is quantified using the perturbation system. Additionally, the mechanical parameters of the rock under the influence of dynamic and static load coupling in the influence area of the cross-tunneling project are determined using the Hoek–Brown criterion, and the mechanical characteristics of the excavation of a tunnel under the double-lane highway tunnel passing under the existing railroad are constructed with the mechanical characteristics of the double-lane highway tunnel, taking into consideration the influence of the dynamic and static load coupling in a three-dimensional model. The results show that, in line with the new tunnel rock movement law for the top of the arch sinking, the bottom plate bulging, the side wall outward movement, the height and width of the arch, and the bottom plate arch show an increase with the tunnel excavation, while the side wall rock displacement effect is smaller; the left and right line tunnel disturbed area of the rule of change is similar; the existing tunnel bottom plate displacement is larger than the top plate and the left and right side wall, under the influence of the excavation time step. Typical profile point displacement is mainly determined by the distance from the excavation surface; von Mises stress extremes are observed in the top plate and side walls of the existing tunnel, which occur in the tunnel structure, and there are unloading and pressure-bearing zones in the bottom plate; the new tunnel has the same rock disturbance angle under the four calculation conditions and, based on the displacement control criterion, the excavation method is preferred and the upper and lower step blasting excavation method is recommended. Full article

The Fabry–Perot interferometer (FPI) plays a crucial role as the frequency discriminator in the incoherent Doppler wind lidar. However, in the practical receiver system, reflections occurring between optical elements introduce non-normal incident components in the light beams passing through the FPI. This phenomenon results in the deformation of the FPI transmission spectral lines. Based on that, a theoretical model has been developed to describe the transmission spectrum of the FPI when subjected to obliquely incident light beams with a divergence angle. By appropriately adjusting the model parameters, the simulated transmission spectrum of the FPI edge channels can coincide with the experimentally measured FPI spectral line. Subsequently, the impact of deformations in the transmission spectrum of the two edge channels on wind measurements is evaluated. The first implication is a systematic shift of 30.7 m/s in line-of-sight (LOS) wind velocities. This shift is based on the assumption that the lidar echo is solely backscattered from atmospheric molecules. The second consequence is the inconsistency in the response sensitivities of Doppler frequency shift between Rayleigh signals and Mie signals. As a result, the lidar system fails to fully achieve its initial design objectives, particularly in effectively suppressing interference from Mie signals. The presence of aerosols can introduce a significant error of several meters per second in the measurement of LOS wind velocity. Full article

To extend the wideband performance of high-order band-pass filtering applications, optimized designs with knitted structures based on traditional miniaturized frequency-selective surfaces (FSSs) are proposed in this paper. The presented miniaturized FSSs consist of multiple metallic capacitive layers, knitted inductive layers, and substrates. In contrast to the conventional high-order miniaturized FSSs composed of metallic frames, patches, and substrates, the optimized miniaturized FSSs replace the original metallic wire frames with knitted structures. Both proposed modified miniaturized FSSs achieve a flat pass-band from 5.5 GHz to 10.3 GHz with a 3 dB bandwidth of 71.6% under vertical incidence. The unit cells have dimensions of 0.16 λ₀ × 0.16 λ₀ × 0.284 λ₀ and 0.16 λ₀ × 0.16 λ₀ × 0.279 λ₀, respectively, where λ₀ is the free space wavelength at 7.9 GHz, which is the center frequency of the operating band. Numerical simulations and measurements demonstrate that the proposed modified miniaturized FSSs exhibit excellent wideband performance with clean transition bands around the pass-band during oblique incidence and are suitable for applications such as radomes, where wideband filtering is essential for covering multi-band functions of radar or communication instruments. Full article

In December 2021, we presented a prototype of a fast ionosonde for vertical sounding based on the usage of publicly available radio-electronic components. This approach led to a major reduction in the cost of the created device. We called our development ION-FAST, which characterizes the key feature of the ionosonde: the possibility of continuous operation at a speed of one ionogram per second, which is required to study the rapid processes of redistribution of the electron concentration during heating experiments. In May 2022, an ionosonde for vertical sounding of the ionosphere, developed at the Radiophysical Research Institute of Nizhni Novgorod (NIRFI), was put into continuous operation at the SURA facility. This report provides a description of the improvements made to the prototype over the last year and the path to be passed from idea to implementation. The results of the first months of the prototype’s operation (especially the results of the supporting optic experiment in August 2022), as well as prospects for further use and modernization, are provided. In addition, the realization of the oblique chirp-sounding receiver prototype as an extension of the proposed diagnostic platform’s functionality, including the first results, is presented. Full article

The MPW that emits from a tunnel’s exit when a high-speed train passes through is a serious environmental problem which increases rapidly with the speed of the train. To alleviate the MPW problem at 400 km/h, the aerodynamic effects caused by the hood located at the entrance or exit of a tunnel are studied by numerical method, and the influences of hood geometry, such as an enlarged cross-section, oblique entrance, and opening holes on the MPW, are also investigated. The research indicates that the enlarged cross-section of the hood at the entrance and exit of the tunnel has opposite effects on the MPW, and the oblique section can alleviate the MPW by extending the rising time of the compression wave and increasing the spatial angle at the hood exit. The pressure gradient can be mitigated through delaying the rising of the compression wave by opening holes on the side wall of the hood, and the relief effects of the holes can reduce the MPW further. The MPW problem when a train passes through a tunnel at 400 km/h can be effectively alleviated by an optimized oblique enlarged hood with opening holes, even up to train speeds of 500 km/h. Full article