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Noise Reduction Using Synthetic Microjet Excitation in Supersonic rectangular Jets

APPLIED SCIENCES-BASEL 2025年第3期15卷 1180-1180页

作者： Marques, Michael Singh, Surabhi Lyrintzis, Anastasios Golubev, Vladimir Embry Riddle Aeronaut Univ Dept Aerosp Engn 1 Aerosp Blvd Daytona Beach FL 32114 USA

This work explores a potential methodology for rectangular jet noise reduction that employs nozzle unsteady microjet excitation. Using high-fidelity computational studies and spectral analyses, major jet noise sources impacted by the applied actuation are identified. A heated supersonic rectangular jet is considered with a nozzle aspect ratio of 2:1 at a Mach number of 1.5. The current study essentially validates the hypothesis of a previous reduced-order analysis that predicted jet noise reduction through jet excitation at the harmonic or subharmonic of the dominant frequency associated with jets' large-scale structures. Such noise reduction was attributed to the excitation-induced nonlinear energy exchange between the coherent modes. In the current study, the synthetic microjet actuation of the jet plume shear layer using 1% of the jet mass flow rate is implemented at the excitation ports located at the nozzle lip and directed along the jet axis. A resulting jet noise reduction of up to 4 dB at the peak radiation angle is predicted. An analysis of the near-field Spectral Proper Orthogonal Decomposition (SPOD) results provides further insights into the impact of jet actuation on the modification of jet flow structures, thus addressing the effectiveness of the proposed noise control methodology.

关键词： rectangular jet noise control synthetic microjet high-fidelity study

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Combination of Phase Rotation SM-OOK and rectangular, Cross, Octagonal SD-8QAMs for MIMO Systems

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IEICE TRANSACTIONS ON COMMUNICATIONS 2025年第3期E108B卷 282-293页

作者： Ida, Yuta Maruta, Kazuki Ohira, Yasuaki Kuroda, Sho Matsumoto, Takahiro Yamaguchi Univ Grad Sch Sci & Technol Innovat Ubeshi 7558611 Japan Tokyo Univ Sci Fac Engn Tokyo 1258585 Japan Kagoshima Univ Grad Sch Sci & Engn Kagoshima 8900065 Japan FX Syst Corp Osakashi 5300011 Japan

In cooperative systems for multi-antenna techniques, multiple-input multiple-output (MIMO) is essential to enhance the system capacity. For the transmission technique of MIMO systems, there is the combination of the space division multiplexing (SD) and the spatial modulation (SM), and the bit error rate (BER) performance is improved by using the channel ranking QR decomposition with M algorithm maximum likelihood detection (CR-QRM-MLD). And then, the transmission for the phase rotation SM on-off keying (PR-SM-OOK) and the rectangular SD8QAM is also effective by using the CR-QRM-MLD with the simultaneous and separated searches. On the other hand, there are several assignments of the constellation for the 8QAM, but they are not evaluated in the SDSM-MIMO. Therefore, in this paper, we propose the combination of the PR-SM-OOK and the rectangular, cross, octagonal SD-8QAMs for MIMO systems.

关键词： MIMO PR-SM-OOK rectangular cross and octagonal SD-8QAMs

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Experimental Study on the Performance of Gradient Pores Density Metal Foam in a rectangular Channel

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HEAT TRANSFER 2025年第3期54卷 2127-2139页

作者： Hasan, Mohammed H. Saihood, Raed G. Univ Baghdad Dept Mech Engn Baghdad Iraq

Various approaches are employed to enhance the heat transfer coefficient and Nusselt number inside the channels. One of the techniques employed for these enhancements is the utilization of porous media. In the current article, a practical investigation of forced convection heat transfer in a rectangular cross-section channel (0.05 x 0.1 m2) with 0.25 m length is conducted. A heater with a heat flux range (450-6000 W/m2) is imposed under a copper plate, and the other sides are covered by insulation layers. The air is considered as a working fluid with Re (600-2100). The test section is fully filled with gradient pores per inch (PPI) metal foam by taking three different pores densities PPI (10, 20, and 40 PPI) and studying its effects on the temperature of copper plate, the local heat transfer coefficient, average Nusselt number, pressure drop, friction factor, and the performance factor. Three cases were studied inside the channel: one empty case and two with gradient pore density case A (40-20-10) PPI and case B (10-20-40) PPI. The results showed that inserting the metal foam inside the channel improves h and Nu. Case B appeared the best of this improvement in h and Nu by 12% and 25%, respectively, compared with that in case A. While the friction factor was the same for two cases A and B. So, the performance factor in case B showed an improvement of around 25% and 50% in comparison to case A and the empty case, respectively.

关键词： channel flow convection gradient metal foam performance PPI rectangular

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Soft-Computing for 3D Failure Envelope of rectangular Skirt Foundations in Heterogeneous Clays

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GEOTECHNICAL AND GEOLOGICAL ENGINEERING 2025年第3期43卷 1-22页

作者： Vichai, Katavut Tran, Duy Tan Keawsawasvong, Suraparb Jamsawang, Pitthaya Thammasat Univ Thammasat Sch Engn Dept Civil Engn Res Unit Sci & Innovat Technol Civil Engn Infrastr Pathum Thani Thailand Ho Chi Minh City Univ Transport Inst Civil Engn 02 Vo Oanh Ho Chi Minh City Vietnam King Mongkuts Univ Technol North Bangkok Soil Engn Res Ctr Dept Civil Engn Bangkok 10800 Thailand

This work investigates the failure envelope of a rectangular skirt foundation in non-homogeneous clays based on the new novel soft-computing approach that combines FELA simulation and tree machine learning models, including decision tree (DT), random forest (RF), and gradient boosting (GB) models. The impacts of embedment depth (D/B), shape ratio (L/B), and soil heterogeneity (kappa) that affect the failure envelope of the rectangular skirt foundation under combined loading conditions, including the vertical load (V), horizontal load (H), and moment (M), are investigated. Furthermore, decision trees, random forests, and gradient boosting are selected to consider the relationships between the investigated parameters and the failure envelope capacity (V/Asu, H/Asu, M/ALsu). To facilitate practical application, the numerical findings are given in the form of design charts and tables. The efficiency of the tree models is determined through regression parameters (i.e., R2, RMSE, MSE, and MAE) combined with a Taylor chart. As a result, the decision tree model is suggested as the best model (R2 = 0.999) for predicting the failure envelope of rectangular skirt foundations. Additionally, the failure mechanism of rectangular skirt footing in heterogeneous clay under combined loading (V, H, M) has been examined, enhancing the design of engineers in practice.

关键词： Skirt foundation rectangular Non-homogeneous clay FELA Machine learning

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A Novel Case of Cooling and Heating in rectangular Lid-Driven Cavities: Interplay of Richardson Numbers in Streamlines and Isotherms

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PROCESSES 2025年第2期13卷 432-432页

作者： Gonzalez-Zamudio, Edgar Alexandro Olivares-Robles, Miguel Angel Andrade-Vallejo, Andres Alfonso Inst Politecn Nacl Secc Estudios Posgrad & Invest Escuela Super Ingn Mecan & Elect Unidad Culhuacan Ciudad De Mexico 04430 Mexico

The thermal and dynamic behavior of SiO2 nanofluid was studied in a rectangular lid-driven cavity using the finite difference method. A non-adiabatic lid and a hot section at the bottom wall were considered in different heating and cooling cases. Three novel study cases were studied: a standard temperature at Th (heat conduction through the left-side walls), a high hot temperature, 2Th (heat conduction through the left-side walls), and a 2Tc high cold temperature (heat conduction through right-side walls). The Richardson number was varied between 10 and 100, and the lid direction. With a Richardson number of 10, the streamlines in the different cases tended to the formation of a central vortex with small vortices on the side walls, and the isotherms tended to a central one near the lower wall's heated section and the homogenized temperature in the center of the cavity. At a Richardson number of 100, the streamlines produced a division in the cavity through a central vortex due to the heating of the bottom wall;this affected the isotherms, generating a prominent one in the center of the cavity and others near it. The generating decreased in the temperature near the bottom and top walls but increased in the middle of the cavity. The standard temperature case tended to behave similarly to the high cold temperature case but presented different temperatures, while the high hot temperature case generally maintained a slightly different behavior. These effects were more noticeable with the lid direction opposite X.

关键词： nanofluid rectangular lid driven Richardson number

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rectangular sharp-crested weir calibration for low head and clinging flow regime

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IRRIGATION SCIENCE 2015年第2期33卷 131-139页

作者： Zhang, Xin Yuan, Linjuan Yan, Peng Li, Jiazhen He, Xiangli China Agr Univ Coll Water Resources & Civil Engn Beijing 100083 Peoples R China China Inst Water Resources & Hydropower Res Dept Hydraul Beijing Peoples R China

The classical head-discharge relation for rectangular sharp-crested weirs is applicable only to free flow conditions, not valid at low head when flow becomes clinging. Based on experimental data for eight sharp-crested rectangular weirs of different sizes, a new method for calculating discharge at the low head bistable and clinging flow regime was proposed in this study. In the bistable zone, the head-discharge relationship can be covered partly by the classical weir-discharge equations of free flow. The discharge coefficient is quite similar to Rehbock's equation for free flow with a surface tension term. In the clinging flow regime, the head had to be transformed into an equivalent head obtained by regression. All the regression parameters were about the same for the weirs of different sizes. In the clinging zone, discharge was also directly proportional to weir width, while unit width discharge was directly proportional to the square of head, independent of weir height. The errors of model-predicted discharge were less than 10 % for more than 90 % of the data points. Therefore, the proposed method for discharge of clinging flow is applicable to rectangular sharp-crested weirs at very low head, while the classical formulas often fail under these flow conditions.

关键词： rectangular rectangular weirs Directly proportional sharp-crested weirs free flow flow regime discharge coefficient low head

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rectangular dielectric-rod fed by metallic waveguide

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IEE PROCEEDINGS-MICROWAVES ANTENNAS AND PROPAGATION 2002年第2期149卷 92-97页

作者： Ando, T Yamauchi, J Nakano, H Hosei Univ Coll Engn Tokyo 1848584 Japan

A rectangular dielectric-rod antenna fed by a metallic waveguide is numerically investigated. with emphasis on the mechanism of the gain variation with rod length. Before studying the mechanism, impedance matching between a dielectric rod and a metallic waveguide is performed by introducing a simple technique in which a portion of the rod is inserted into the waveguide. return loss of greater than 15 dB is obtained over a frequency bandwidth of 11%. The amplitude and phase distributions of the field near the rod are investigated, The field is decomposed into a surface wave propagating along the rod and an unguided wave radiating near the feed end. Calculations show that the phase interaction between the surface and unguided waves occurs near the rod. The gain increase with rod length is explained in terms of the expansion of the equiphase region in the terminal aperture regarded as a secondary Huygens plane.

关键词： rectangular clamping lever Phase distribution surface waves frequency band widths rod Waveguide Device Component gain variation

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rectangular patch resonator with laminated ground plane

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IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION 1995年第12期43卷 1361-1368页

作者： Kiang, JF Department of Electrical Engineering National Chung Hsing University Taichung Taiwan

In this paper, we analyze the effect of a laminated ground plane on the resonance frequency of rectangular patch resonators. We model each lamina of the ground plane as an anisotropic layer and use a transition matrix to relate the tangential field components in different laminae. An integral equation is formulated in the spectral domain, and Galerkin's method is applied to solve the integral equation for the resonance frequencies of the patch resonator. A perturbation approach is also derived for comparison. The effects of substrate dielectric are studied, The resonance frequency variation thus obtained will be useful in designing patch resonators attached to composite laminated surfaces.

关键词： rectangular Ground plane Resonator Device Component resonant frequencies Spectral domain S matrix

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rectangular cavity-based perfect dual-band absorber with wide incidence angle in terahertz region

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APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING 2018年第12期124卷 1-6页

作者： Lu, Xiaojie Xiao, Zhongyin Shanghai Univ Key Lab Special Fiber Opt & Opt Access Networks Shanghai Inst Adv Commun & Date Sci Sch Commun & Informat EngnJoint Int Res Lab Spec Shanghai 200072 Peoples R China

In this paper, a dual-band perfect metamaterial absorber(MA) based on rectangular cavity with wide incidence angle is proposed in the terahertz region. The unit of the absorber is composed of three different size rectangular cavities which are placed vertically on a metal plate. The numerical results show that the MA has two distinctive absorption bandwidths from 3.7586 to 4.0977THz and 5.7635 to 6.0746THz, respectively, with both absorption rates larger than 90%. Besides, the resonant frequency can be calculated based on rectangular cavity theory, which provides a design guideline for MA of such type. The theoretical predictions of the resonance frequencies have excellent agreements with the simulation ones. What's more, the physical mechanism of the perfect absorption can be explained based on the distribution of E-field in the absorber and the standing wave theory. Our results provide a new way on realizing perfect absorption based on rectangular cavity.

关键词： Perfect absorbers terahertz rectangular absorption angle of incidence Mission Assurance resonant frequencies rectangular cavity Dual band metal plates

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rectangular jet impingement heat transfer on a vehicle windshield

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JOURNAL OF THERMOPHYSICS AND HEAT TRANSFER 2002年第1期16卷 154-157页

作者： Roy, S Nasr, K Patel, P AbdulNour, B Kettering Univ Dept Engn Mech Flint MI 48503 USA Ford Motor Co Technol Dev Dept Dearborn MI 48120 USA

This Note addressed numerical and experimental studies of a pair of rectangular air jets impinging on an inclined surface. Experimental measurements of surface temperatures, using liquid crystals, yielded a map of local heat transfer coefficients between the surface and the incoming jet for an imposed heat flux. Corresponding three-dimensional numerical simulation has been performed using a finite volume algorithm for obtaining detailed temperature and flow distributions. The numerical simulation correlated reasonably well with the experimental results and further explained the flow characteristics and thermal patterns. A detail comparison of 34 locations under the heating pad validated the numerical predictions within 1-3℃ of the measured temperature values. Further investigation should aim for the defogging/defrosting analysis in the flow.

关键词： rectangular Numerical flow characteristics local heat transfer coefficient HEAT PAD jet impingement numerical simulation AIR JETS maps Liquid Crystals flow field Pairing Windscreen Heat flux Surfaces

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