Robotic Systems and Applications
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Creep modeling of asperities on joint surface and its effect on joint surface stiffness
Get PDFCreep of the asperities on joint surface will change the stiffness characteristics of joint surface. Based on creep mechanics, a novel creep model of asperities between two rough surfaces is established from a microscopic point of view in this paper. The change of joint stiffness caused by creep of asperities under constant pre-tightening force is analyzed. The results show that the creep of the asperities leads to the increase of the stiffness of the joint surface with the increase of time when the joint force is constant. Moreover, the influence of key parameters of joint surface on creep of asperities is further studied. It is found that the change rate of joint stiffness increases with the increase of initial contact distance and contact area. According to the proposed creep model and the findings in this paper, more accurate stiffness characteristics of joint surface can be achieved for analysis of dynamic and static characteristics of structures with time
Dynamic characteristics of aero-engine’s rotor under large maneuvering flight
Get PDFIn view of the large maneuvering overload of the rotor system in Unmanned Aerial Vehicle (UAV), the dynamic characteristics of rotor system under large maneuvering overload conditions were analyzed in this paper. The finite element model of rotor system under large maneuvering overload was first established by Timoshenko beam element theory and finite element method. The motion differential equations of the rotor system were derived by Lagrange equation, and the additional damping matrix, stiffness matrix and excitation force were obtained. Critical speeds and unbalance response were calculated by characteristic equation method and Newmark-β numerical integration method respectively. The calculation results showed that the additional damping and stiffness leaded the critical speeds of the rotor system to change under large maneuvering flight, and the additional excitation force resulted in a certain static displacement of the whirling orbits
Near-field acoustic holography for high-frequency weak sound sources under low signal-to-noise ratio
Get PDFThe mechanical noise in the cabin of the ship is so large that the leakage of high-pressure fluid is not easily noticed. In view of this situation, a near-field acoustic holography for high-frequency weak sound source under low signal-to-noise ratio is proposed. The method uses the empirical mode decomposition method to add weights to the time-domain sampling signals of each array element, and then uses the plane equivalent source near-field acoustic holography combined with compressive sensing to find the holographic surface acoustic pressure distribution. The simulation and experiment show that this method has certain feasibility under low signal-to-noise ratio, and the results are better than the method based on Fourier transform and the traditional boundary element method. It is of positive significance to apply it to engineering practice
Dynamic analysis of towing operation with military tracked recovery vehicle
Get PDFThe present work is focused upon development of multi-body dynamic (MBD) models of a military tracked recovery and towed vehicles in Adams Tracked Vehicle (ATV) toolkit, and carrying out the dynamic analysis of towing operation with the vehicles. Towing is one of the important recovery operations for the military recovery vehicle, which is generally carried out on plain terrain conditions. However, it is also desired to tow another vehicle of similar weight class over certain gradients as well. In this regard, it is required to assess the structural rigidity of the tow bar assembly, while negotiating the gradients. The finite element models of the tow bars have been developed in Abaqus/CAE, from which the modal information is extracted. The finite element models of the tow bars have been integrated with the MBD model of the recovery and towed vehicles in ATV through Adams/Flex. The dynamic analyses of towing operation with the existing tow bar assembly, have been carried out over different gradients, based on which required design modifications have been proposed to minimize the relative angular motion between the tow bars while descending the gradient. With an objective of further weight reduction and enhanced gradient climbing capability, suitable recommendations have further been provided to modify the tow bar assembly design. Dynamic simulations were carried out with the modified tow bar assembly design, through which higher gradients could be negotiated with reduced tow bar assembly weight. The above dynamic analyses have provided a base platform for arriving at the standard operating procedure of carrying out the towing operation in practice. The analyses have also established a framework for future design of tow bar assemblies under the influence of a three dimensional vehicle dynamic environment
An extrusion simulation of an aluminum profile by porthole die
Get PDFThe aluminum alloys are ideal material because of their corrosion resistance, recycling ability, high specific strength and especially low density for lightweight structures of transportation, aerospace, automotive industries. Hot extrusion process is the most used metal forming method for obtaining a variety of aluminum alloy profiles. The demand for large cross section, multi cavity and thin wall profiles has been increasing with the development of the industry and extrusion method is key solution for producing complex profiles with high productivity. These profiles are generally extruded by porthole dies. The extrusion process by porthole die is complicated and die design has great importance for the quality of the extruded product. Design of the porthole die should give optimum material flow and homogenous temperature distribution both for obtaining desired profile and eliminating die scrap. The measuring the temperature and material flow is not possible for closed die formation and it is so important to estimate both material flow, temperature change in the die. For this aim, an extrusion simulation of a porthole die for standard aluminum profile was investigated in this study with the support of HyperXtrude Inspire Extrude Metal 2019 software, which is specialized for FEM calculations of extrusion process. Each step of extrusion process was simulated. Aluminum AA6063 material was used for simulations, the process temperature was 4500 °C and punch velocity was selected as 5 mm/sec. Finally, the FEM results were obtained and the temperature distribution, pressure distribution, billet interface and relative die exit speed results were analyzed
Comparative vibration analysis on IC engine with biodiesel and multi-walled carbon nanotube
Get PDFSound and vibration caused in the engine due to combustion process may affect the users. One of the vital qualities of diesel fuel is high sound and vibration. The vibration of the engine is one of the primary factors in engine structure and maintenance. Vibration estimation on the engine block, cylinder head is a non-intrusive strategy and has been utilized effectively for fault prediction of diesel engines. The vibration signals along with signal processing techniques are utilized to highlights the features that are sensitive to faults. In this work, experimental tests have been carried out to assess the vibration of a diesel engine with diesel, 20 % biodiesel (Ethyl Ester of ground nut acid oil EEGOA) and 30 ppm Multi-walled Carbon Nano tubes with 20 % biodiesel (MWCNT30ppm B20EEGAO) at various load (20 %, 40 %, 60 %, 80 % and 100 %). Digital Vibration Meter Model: Equinox-VM 6360 is utilized to gauge the vibration in three unique positions, one is cylinder head of the engine, second one is crank of the engine, and third one is bottom of the engine. In this work, the vibration is measured in terms of acceleration. The MWCNT30ppm B20EEGAO blend demonstrates the lower vibration compared with different blends
Modal analysis application for the problemof gamma-ray spectrometers resolution improving
Get PDFThe cryostat of gamma-ray spectrometer with HPGe detector cooled by Stirling cycle cryocooler is under consideration. The natural frequencies and modes shapes for components involved to oscillatory systems distinguished in dynamic model of cryostat were calculated by Solidworks simulation. The results obtained for the gamma-ray spectrometer “Monolith” produced by BSI, represent its specific modal portrait and allow identification the components of electrical noise due to microphone effect. The absence of resonant amplification due to coincidence between the harmonics of cryocooler operating frequency and the natural frequencies of the cryostat components is an important condition for reducing the influence of microphonics. The results obtained by modal analysis are also useful for assessing the influence of external mechanical disturbances, such as shocks, external vibration or audible noise
Research on vibration displacement test method for large-caliber artillery muzzle
Get PDFIn order to solve the problem of muzzle vibration displacement test of large caliber under high elevation, this paper presents a test method by two high-speed photography. The method fully considers the influence of the muzzle torsion on the measurement results, and accurately obtains the three-dimensional vibration displacement of the muzzle of the large caliber artillery. Finally, through the result analysis, the accuracy of the measurement results can reach 0.1 mm, which shows the advantage of the sub-pixel-based high-speed camera processing method in the muzzle vibration displacement test of the conventional artillery. This paper proposes an innovative test method that accurately measures the vibration displacement of the muzzle using a non-contact method
Construction of 12 DOFs spur gear coupling dynamic model
Get PDFA 12-degree-of-freedom (DOF) spur gear dynamic model is constructed, which is coupled by the mesh gear pair and the gearbox. The construction method of spur gear coupling dynamic model, based on lumped mass method, is better than finite element method, due to higher modeling efficiency. The work would be benefit to spur gear coupling dynamic modeling and analyses
Dynamics similarity design and verification of rotor system
Get PDFIn order to study the dynamics similarity of original model similar to normal model, the similarity criteria and the similarity ratio of the normal and original models for the rotor system were derived by the dimension analysis method. ANSYS was used to numerically calculate the critical speeds, modal shapes and harmonic response of the original and normal models of rotor system. The analysis results show that, for the rotor system, the dynamic characteristics of the normal and original models satisfy the requirement of the similarity criteria perfectly. The dynamic characteristics of the original model can be predicted accurately by the corresponding normal model