Vibrational Dynamics in crystalline 4-(dimethylamino) benzaldehyde: Inelastic Neutron Scattering and Periodic DFT Study

The structure and dynamics of crystalline 4-(dimethylamino) benzaldehyde, 4DMAB, are assessed through INS spectroscopy combined with periodic DFT calculations. The excellent agreement between experimental and calculated spectra is the basis for a reliable assignment of INS bands. The external phonon modes of crystalline 4DMAB are quite well described by the simulated spectrum, as well as the modes involving low-frequency molecular vibrations. Crystal field splitting is predicted and observed for the modes assigned to the dimethylamino group. Concerning the torsional motion of methyl groups, four individual bands are identified and assigned to specific methyl groups in the asymmetric unit. The torsional frequencies of the four methyl groups in the asymmetric unit fall in a region of ca. 190 ± 20 cm−1, close to the range of values observed for methyl groups bonding to unsaturated carbon atoms. The hybridization state of the X atom in X-CH3 seems to play a key role in determining the methyl torsional frequency.

Arrangement Optimization and Crashworthiness Analysis of B-Pilla Solder Joint Based on Collision Safety

Through hyperworks and Lsdyna, the side impact simulation of the vehicle model with Q&P980 class B-pilla is carried out. The middle part of B-pillar is the main part to bear the impact load, which corresponds to the occupant's chest and abdomen. The invasive displacement and the speed are large and the change trend is basically the same. After the optimization of the B-pillar weld solder joint layout, the number of solder joints was reduced by 23.61%, the structural static stiffness and the first-order torsional frequency were improved, the collision performance remained basically unchanged, and the body assembly cost was reduced.

Research on Torsional Property of Body-In-White Based on Square Box Model and Multiobjective Genetic Algorithm

In order to assess the performance of a vehicle in the conceptual design stage, a square box model was proposed to predict the torsional stiffness and the first-order torsional frequency of Body-in-White. The structure of Body-in-White was decomposed into eight simple structural surfaces, from which a square box model was constructed. Based on the finite element method, modified shear stiffness of each simple structure surface was calculated and the torsional stiffness was obtained. Then, simple structural surfaces of Body-in-White were constructed into an eight degree-of-freedom series spring system to calculate the first-order torsional frequency. Furthermore, a multiobjective genetic algorithm was used to determine the thickness and structural reinforcement of panels with small stiffness, so as to achieve the goal of increasing the stiffness while reducing the mass of the panel. The result shows that the optimal values of thickness are reduced by around 9.9 percent without affecting their performance by the proposed method. Compared to the prediction results obtained with the complicated numerical simulation, the relative error of the square box model in predicting the torsional stiffness is 6.04 percent and in predicting the first-order torsional frequency is 0.95 percent, indicating that the prediction model is effective.

Wind Resistant Analysis of 5000m Hyperbolic Parabolic Spatial Mixed Cable Suspension Bridge

Combined with the engineering background of a 5000-meter Strait Suspension Bridge, the configuration study of the hyperbolic parabolic space cable suspension bridge was carried out, and the ANSYS finite element analysis model was established to analyze and study the structural internal force and dynamic modal characteristics. The research shows that the hyperbolic parabolic space mixed cable suspension bridge has excellent spatial stiffness and wind stability performance, its torsional frequency and torsional frequency ratio are significantly improved, the critical wind speed of flutter is greatly improved. In order to further improve the wind stability of the hyperbolic parabolic space mixed cable suspension bridge, temporary wind resistance cable measures adopted during strong typhoons are proposed. This method can ensure that the 5000-meter-level hyperbolic parabolic space mixed cable suspension bridge has the ability to withstand 120 m / s rare extreme typhoons.

Modeling Considerations for Testing Full-Scale Offshore Wind Turbine Nacelles With Hardware-in-the-Loop

When compared to open-loop configuration, full-scale wind turbine nacelle testing with Hardware-In-the-Loop (HIL) configuration allows for coupled electro-mechanical as well as full operational certification tests with the native nacelle controllers. This configuration requires a full turbine real-time simulation running in parallel to the nacelle under test. In this study, a baseline simulation model is used to investigate the nacelle fidelity necessary to capture dynamic characteristics of interest while meeting the real-time requirements. The same model is also utilized to understand the influence of different boundary conditions seen by the nacelle when mounted on a test bench without a rotor, tower, and platform. The results show that the torsional dynamics are mainly governed by the flexibility of the main shaft and the gearbox supports. It is also demonstrated that the abstraction of the nacelle leads to a torsional frequency shift and higher frequency content in component responses necessitating compensation techniques for proper implementation of HIL testing.

Aeroelastic Response of Suspended Pedestrian Bridges Made of Laminated Wood and Hemp

The work described in this paper investigated, by calculating critical flutter speed, the aeroelastic response of suspended pedestrian bridges made of a laminated wood structure and hemp cables and compared them to bridges with a steel structure and harmonic steel cables. Critical flutter speed was estimated using a numerical two degree of freedom (2-DOF) generalized deck model based on finite-element modal analysis. The critical flutter speeds of two sets of 25 different structural configurations, obtained by varying the deck chord and the permanent deck loads, made of steel and of laminated wood respectively, were estimated using experimental flutter derivatives obtained from 30 wind tunnel experiments. One of the most significant results was that pedestrian bridges made of laminated wood and hemp have a higher torsional frequency than those made of steel and that this affects critical flutter speed. A case study was performed and discussed by analyzing the structural and aeroelastic response of a 250 m pedestrian bridge with a 12 m deck chord and two approximately 32 m tall towers.

Spectral Dynamic Analysis of Torsional Vibrations of Thin-Walled Open Section Beams Restrained Against Warping at One End and Transversely Restrained at the Other End

The present paper deals with spectral dynamic analysis of free torsional vibration of doubly symmetric thin-walled beams of open section. Spectral frequency equation is derived in this paper for the case of rotationally restrained doubly-symmetric thin-walled beam with one end rotationally restrained and transversely restrained at the other end. The resulting transcendental frequency equation with appropriate boundary conditions is derived and is solved for varying values of warping parameter and the rotational and transverse restraint parameter. The influence of rotational restraint parameter, transverse restraint parameter and warping parameter on the free torsional vibration frequencies is investigated in detail. A MATLAB computer program is developed to solve the spectral frequency equation derived in this paper. Numerical results for natural frequencies for various values of rotational and transverse restraint parameters for various values of warping parameter are obtained and presented in both tabular as well as graphical form showing the influence of these parameters on the first fundamental torsional frequency parameter.

Torsional vibration of functionally graded carbon nanotube reinforced conical shells

The present study deals with the free torsional vibration of a composite conical shell made of a polymeric matrix reinforced with carbon nanotubes (CNTs). Distribution of CNTs across the thickness of the conical shell may be uniform or functionally graded. Five different cases of functionally graded reinforcements are considered. First-order shear deformable shell theory compatible with the Donnell kinematic assumptions is used to establish the motion equations of the shell. These equations are two coupled equations which should be treated as an eigenvalue problem. The generalized differential quadrature method is used to obtain a numerical solution for the torsional frequency parameters and the associated mode shapes of the shell. After validating the results of this study for the cases of isotropic homogeneous cone and annular plates, parametric studies are carried out to analyze the influences of geometrical characteristics of the shell, volume fraction of CNTs, and grading profile of the CNTs. It is shown that volume fraction of CNTs is an important factor with regard to torsional frequencies of the shell; however, grading profile does not change the torsional frequencies significantly.