Mechanics

Averaged Heat Fluxes Densities During Condensation and Evaporation of a Water Droplet

Kristina BIKNIENĖ — 2024-04-23

This study is intended for experimental investigation of the influence of boundary conditions on the intensity of phase transformations and heat transfer processes in a suspended water droplet. The results of the dynamics of the averaged heat fluxes densities during the droplet phase change cycle are presented and analysed. The influence of the droplet initial temperature, the surrounding air flow temperature and the additional humidity in the air flow were defined in separate regimes of the droplet phase transformations cycle. The experiments performed demonstrated that the parameters of the air flow surrounding the suspended water droplet affect the intensity of heat fluxes in the droplet throughout whole its phase change cycle. It was experimentally claimed that the initial temperature of the water droplet has no influence on the droplet heat and mass transfer processes in the equilibrium evaporation regime. The obtained results showed that most intensity heat flux densities are at the beginning of the droplet phase change cycle when condensation process occurs on the droplet’s surface in case with biggest amount of additional humidity in the surrounding air flow. This is very important in technologies of cleaning and heat recovery from flue gases.

Effects of Weld Heat Input on Mechanical Characteristics of Low Carbon Sheet Steels

Sait Ozmen ERUSLU — 2024-04-23

This study focuses on examining the variation in mechanical characteristics of low-carbon sheet steels when they are subjected to heat input from Tungsten Inert Gas (TIG) welding. The weld heat input parameters, such as welding speed and current, were controlled through the TIG welding process. A finite element analysis was performed to evaluate the couple field thermomechanical effects of the weld heat line, using the Gauss heat flux approach for thermal heat variation across the weld heat-affected zone. The numerical study yielded results for weld heat-affected deflection, residual stress, and modal analysis through the finite element model. It was found that the ductility decreased and hardness increased in the fusion zone, as a function of weld current and speed. The residual stresses and their zone of influence, as determined by weld line parameters, were found to be key factors affecting deflection and natural frequencies in structural aspects of low carbon sheet steels.

Research on Complementary Filtered Attitude Solution Method for Quadcopter Based on Double Filter Preprocessing

Linlin ZHANG — 2024-04-23

In the attitude calculation process of quadrotor, the traditional pre-filtering method has degraded the attitude solving accuracy due to incomplete denoising of accelerometer and gyroscope measurements. Therefore, a complementary filtered attitude solution method based on double filter pre-processing is proposed to address this problem. First, the signal decomposition, hard threshold denoising, and signal reconstruction of the accelerometer and gyroscope acquired data are performed using the Haar real-time wavelet filtering algorithm. The reconstructed signal is then filtered by the infinite impulse response ( IIR ) low-pass filtering algorithm to remove the residual high-frequency noise and complete the dual filtering preprocessing. Next, the gyroscope data is corrected with accelerometer data according to the complementary filtering algorithm. Finally, the corrected data are used to solve the quaternion and thus the attitude angle by combining the Longacurta method. The results show that the dual filtering preprocessing method can further reduce the noise in the measurements of accelerometer and gyroscope. The attitude angle results calculated by the proposed method in the static and dynamic hovering states of the four-rotor aircraft have a small degree of dispersion, which can effectively improve the accuracy of attitude calculation.

Vibration Characteristics Analysis of Twin-Screw Compressor Shell Based on the Fluid-Solid Coupling Method

Yayin HE — 2024-04-23

Under the action of the flow field force and the constraint reaction force of the negative rotor and the positive rotor, the twin screw compressor shell will produce vibration, which will affect the life of the parts and produce noise. The rotors restraint reaction force are calculated by fluid-structure coupling method. The shell inherent frequency is solved by modal analysis, and the shell resonance is analyzed during the rotors meshing process. On this basis, the flow field force and rotor constraint reaction force are used as the compressor shell vibration excitation sources, and the vibration response of the compressor shell under the action of excitation force is studied. The research results can provide some reference for the optimized design of compressor shell structure.

Investigating the Impact of Flow Profile on Heat Transfer in Nanofluid Flow: A Numerical Study

Bilal LITOUCHE — 2024-04-23

Assessing the profitability of an energy system requires careful consideration of various factors, including fluid characteristics, geometry shape, and operating conditions. This study investigates the influence of sinusoidal rib shapes, with different space ratios (e/b) ranging from 0 to 1, on heat transfer in nanofluid flow. The channel's upper surface is subjected to a uniform heat flux, employing Al2O3 nanofluid as the working fluid and varying Reynolds numbers from 5000 to 20000. Additionally, the effect of aluminum nanoparticle volume fraction, ranging from 0 to 6%, is analyzed. Simulation results indicate that the performance of the corrugated surface in the channel is significantly influenced by rib shapes and their geometrical parameters. The highest Performance Evaluation Criteria (PEC) index is achieved for ribs with a space ratio (e/b) of 0 at Reynolds number of 5000 and a volume fraction of 6% nanoparticles. Furthermore, the average Nusselt number shows an increasing trend with higher particle volume fraction and Reynolds numbers.

Experimental Study of Vibration Isolation Using Electromagnetic Damping

Easu DAKSHNAMOORTHY — 2024-04-23

This study presents an experimental investigation focused on the reduction of vibrations using electromagnetic damping techniques. The objective is to explore the effectiveness of electromagnetic damping in mitigating undesirable vibrations and enhancing system stability. A single-degree vertically constrained spring-mass system, two pairs of electromagnets, Lab VIEW software, an accelerometer, DAQ card were used for the experimentation. SWG 17 and SWG19 coil electromagnets were used in different conditions of energization to evaluate the effectiveness of the electromagnetic damping system. The parameters such as excitation frequency, vibration amplitude, and electromagnetic damping force are systematically varied and their effects on vibration isolation are analysed. The results demonstrate that the electromagnetic damping system effectively isolates base induced vibrations across a range of frequencies and amplitudes. The experimental data reveal that at lower frequencies, upto 6Hz the amplitude of RMS acceleration was same as that of the system without energizing the electromagnet and at higher frequencies, above 10 Hz, all 2V,4V and 6V of energized electromagnets in the SDVC system showed negligible variation in the RMS amplitude of acceleration. A substantial isolation of top plate was observed at higher frequencies of base excitation.

Study on the Thermal Sensitivity of Anisotropic Thin Sheets: Application to Hot Bulge Tests

Aboulbaba ELADEB — 2024-04-23

This article presents a study on the thermal sensitivity of anisotropic thin sheets, focusing specifically on their behavior during hot bulge tests. Anisotropic materials exhibit different mechanical properties in different directions, and understanding their response to thermal loading is crucial for various engineering applications.

The experimental investigation involves subjecting thin sheets of anisotropic materials to controlled thermal conditions and measuring their response. The hot bulge test, a well-established method, is employed to analyze the behavior of the sheets under elevated temperatures. This test involves applying a controlled internal pressure to a heated circular and elliptical specimen, causing it to deform and form a bulge.

Through this study, the thermal sensitivity of anisotropic thin sheets is characterized by analyzing the bulge height, bulge profile, and strain distribution. The influence of various factors, such as temperature, material anisotropy, and loading rate, is examined to understand their effects on the sheet's response.

Experimental results reveal significant variations in the thermal sensitivity of anisotropic thin sheets, depending on the material's orientation and temperature. The study demonstrates that certain orientations exhibit greater sensitivity to thermal loading, leading to distinct bulge profiles and strain distributions.

Furthermore, numerical simulations are conducted using finite element analysis to validate and complement the experimental findings. The simulation models incorporate the anisotropic material properties and the thermal boundary conditions, enabling a comprehensive understanding of the thermal sensitivity behavior observed experimentally.

The outcomes of this study provide valuable insights into the thermal behavior of anisotropic thin sheets, particularly in the context of hot bulge tests. The findings contribute to the knowledge base of material characterization and can aid in the design and optimization of structures and components subjected to thermal loading, where anisotropic materials are involved.

Vibration Analysis of Porous Functionally Graded Material Truncated Conical Shells in Axial Motion

Weiwei XIAO — 2024-04-23

In this study, a vibration equation for axially moving truncated conical thin shells made of functionally gradient materials with uniformly and non-uniformly distributed pores has been established based on classical thin shell theory. The free vibration and dynamic response solutions are obtained using the Galerkin method. The effects of axial velocity, half cone angle, ceramic material mass composition, material component index, and internal porosity on the free vibration and dynamic response of mentioned shells were analyzed and discussed. The results show that the increase of axial velocity, half cone angle, and material composition index all decrease the natural frequency of the truncated conical shell but amplify its dynamic response, and the rise of the mass fraction of the ceramic material increases the natural frequency of the truncated conical shell but reduces the dynamic response. The results also demonstrate that compared with non-uniformly distributed pores, the effects of uniformly distributed pores on the shells’ dynamic responses are more evident under axial motion.

Effect of Structural Parameters on the Jet Formation and Penetration Capability of Small Caliber Shaped Charges

Yongjie XU — 2024-04-23

Take small caliber high explosive antitank cartridge as research platform, establish 35mm diameter warhead model. Numerical simulation for the process of shaped charge jet forming and penetrating the target has been done through explosion mechanics analysis software AUTODYN. Effect of liner thickness, cone angle and charging length-diameter ratio on shaped charge jet performance has been analyzed. And the optimal combination of the structural parameters of the shaped charge has been determined by orthogonal optimum design. Results show that optimized shaped charge structure can penetrate 105mm steel target under simulation conditions and the maximum penetration depth of main charge in the explosion test is 100mm, the average value of penetration depth is 86.67mm. The minimum and average of relative error between results of static explosion test and numerical simulation are 4.76% and 17.46% respectively. The research results can provide theoretical and technical support for the optimization design and engineering application of small caliber shaped charge.

Physical-Model-Based Assessment of Reduction of Hydraulic Forces Acting on Channel Bed through Advanced Energy Dissipator Design

Petr ŠTEMBERK — 2024-04-23

The hydraulic engineering designers focus on shaping up the flow regime so that the greatest energy dissipation is ensured. On the other hand, the structural designers focus on load bearing capacity and durability of the structural components which may contradict the focus of the hydraulic experts. Such a case may occur when the spillway chute floor slab must be thin due to the limited spaces. Then, the dynamic load acting on the chute floor slab may compromise its long-term operation. The dynamic forces are created by the violent turbulences which may even coincide with the natural frequency of the reinforced concrete floor slab. Therefore, the objective of this paper is a complex approach to small-scale physical model testing which makes use of the latest rapid-prototyping techniques and the particle image velocimetry, and which in the end allows to estimate the magnitude of the dynamic hydraulic forces acting on the channel bed. The newly developed organic-shape energy dissipators play a key role in reducing the kinetic energy of water through its enhances aeration. The proposed method on a small scale can assist favorably the design process of real-scale hydraulic reinforced concrete structures.