Numerical analysis of flow noises in the square cavity vortex based on computational fluid dynamics

In order to study turbulence conditions in an underwater square cavity, the large eddy simulation method was adopted to analyze flow field distributions in the cavity as well as its development and pressure pulsation characteristics at some key positions. MATLAB was also adopted to realize Fast Fourier Transform of signals in time domain and obtain pressure pulsation levels in frequency domain. Based on the analyzed results, pressure pulsation characteristics of key points in the cavity were further discussed. The results showed that pressure pulsation frequencies and characteristics were different with different positions in the square cavity and were closely related with relevant vortex motion states. It was found through comparisons with the experimental results, that pressure pulsation simulation had a good consistency with the experiment when the analyzed frequency was more than 31.5 Hz. As a result, feasibility and accuracy of numerical simulation and Fourier analysis methods were verified. Finally, a numerical model of square cavity in near sound field was built, and sound source intensity distributions at two frequency points were extracted. It could be found that the sound source intensity was large at the rear-edge step, which was consistent with the intensity distribution of vortices. Therefore, reliability of the numerical model in this paper was indirectly verified in the results

Full-spectrum noise prediction of the high-speed train head under multi-physics coupling excitations based on statistical energy analysis

The force between wheels and rails of the high-speed train was firstly extracted and applied into the computational model of radiation noises of wheels and rail respectively. As a result, the radiation noise of wheels and rails was obtained. As can be seen from the result, radiation noises of wheels had an obvious directivity on the body surface, while radiation noises of rails had an obvious periodicity on the body surface. With the increase of the analyzed frequency, both directivity and periodicity were shown more obviously. Then the aerodynamic model of the high-speed train was established, and the pressure and velocity distributions on the train surface were computed. The maximum pressure was at the tip of the nose of the high-speed train, the maximum velocity was at the transition of the cabin, and more serious eddy was in the rear of the high speed train. Based on the computed pressure distribution, the aerodynamic noise was distributed evenly on the entire body surface, which was gradually increased with the increasing analyzed frequency. Finally, the wheel radiation noise, rail radiation noise and aerodynamic noise were extracted as excitations and applied into the SEA (Statistical Energy Analysis) model of the high-speed train, in order to compute its full-spectrum noise under multi-physics coupling excitations. The computational result was compared with the experimental result. It was presented that the difference of average sound pressure level (SPL) was 2.8 dB between the experimental and numerical simulations within the entire analytical frequency band. The SEA model with considering the multi-physics coupling was effective

Numerical analysis and optimization of wheel vibrations and radiation noises of the high-speed train

Finite element and boundary element models of the standard wheel, damping wheels and S-type damping wheels were established and compared. The radial vibration and axial vibration of the standard wheel could be reduced to decrease the vibro-acoustic radiation. Regarding damping wheels and S-type damping wheels, the coupling between the radial vibration and axial vibrations of 1 pitch circle could be reduced to decrease the radiation noise. The vibration acceleration in the tread, rim and web plate was significantly improved after applying damping in the standard wheel. If the web plate was changed into S-type structure, the vibration acceleration of the wheel at three positions was further reduced. The radiation noise of S-type damping wheels was significantly improved. The radiation noise of the web plate was significantly greater than that of the tread, which was caused by the larger radiation area of the web plate

Numerical optimization of vehicle noises in multi-peak frequency points based on hybrid genetic algorithm and simulated annealing

The finite element model of Body in White was built, and the corresponding modes were computed in this paper. These computational modes were then compared with experimental results. The small errors showed that the accuracy of the finite element model can satisfy the computational requirements. Based on the verified finite element model, acoustic cavities in the vehicle were extracted to build a boundary element model. Sound pressure levels at all passengers in the vehicle were then computed, compared and analyzed. Results indicated that the sound pressure curve had 6 peak noises. Using the characteristic frequency weight coefficient and field point weight coefficient, the body panels which made large acoustic contributions to the comprehensive sound field under multi-characteristic frequencies were determined. Finally, the improved genetic algorithm based on simulated annealing was used to optimize the key body panels, and peak noises at researched field points after the optimization were further computed. The computational results were compared with those of the original structure, which presented that the noise was improved at most frequency points in the spectrum and peak noises were suppressed obviously

Numerical calculation of the interior noise for the high-speed transportation under coupled multi-physical field excitations

A finite element model of a high-speed transportation was constructed, including its body in white (BIW), and traction system. And an analytical scheme on the interior structural radiation noise of a high-speed transportation was proposed under coupled multi-physical-field excitation. Rigid multi-body dynamics, boundary element method and large-eddy simulation were employed to extract secondary suspension forces, railway noise and surface pressure fluctuations, respectively, which were coupled with the structural modals to obtain the structural vibration response and noise. The experiment of vibration and noise for the high-speed transportation was conducted at speed of 350 km/h. A measuring point of vibration was randomly selected on the floor. The tendency and amplitude of its vibration velocity level and noise obtained from the experiment and simulation agreed well with each other, which validated the precision of numerical model and coupled multi-physical-field excitation

Dynamic characteristics of pipe-soil interaction for steel catenary riser in touchdown zone

Steel catenary riser (SCR) is one of the most popular and economic risers in the development of deep-water oil and gas field. As a difficulty in the SCR design, the pipe-soil interaction at the touchdown zone is affected by the soil strength, riser diameter, upper floating body, and other factors. Conventionally, the pipe-soil interaction was mainly studied based on the static response of the riser under a linear seabed which was inconsistent with the actual situation. Therefore, a dynamic characteristic model was built in the paper for more realistic simulation of the pipe-soil interaction. And experiments were conducted to verify the reliability of the numerical model. Based on the verified model, the dynamic process of the nonlinear time-domain was analyzed. Different parameters, such as the soil strength and dynamic loads, were changed to analyze their effects on the pipe-soil interaction in the whole process which provided a certain foundation for the SCR design

Experiment and simulation research of the ground-borne vibration for a high-speed train

In order to study the effect of the operational loads on the ground-borne vibration of the high-speed train, a train-track coupling model with considering the vertical and horizontal effects is established and applied to calculate the impact of different operational speeds on vibration acceleration. As shown in the results, the vibration acceleration is largely affected by different frequencies generated from different train speeds. By means of an indoor dynamic triaxial test, the impact of different vibration frequencies of a train on soil body is simulated. And a large number of medium- and low-frequency vibration tests are conducted according to the settings of load form, drainage requirement and vibration number of train vibration loads. The experimental results are analyzed to study the effect of different frequencies on dynamic characteristics, and a dynamic strain-time calculation formula, that takes the frequency factor into consideration, is proposed. Meanwhile, the improved formula that considered frequency is substituted into the finite element model (FEM) of the train, so as to analyze the impact of different vibration frequencies on the settlement, is applied. As shown in the results, the proposed improved formula, that considered the frequency, is good at prediction. The effect of vibration efficiency on the engineering can be reflected by a simulated high-speed train model. Based on the simulation model, a reinforcement measure is conducted for the ground-borne, and it is calculated that the settlement is obviously reduced and the service time of the train ground-borne is increased. This paper can provide a reference for a theoretical research and engineering practice

APPLICATION OF NOVEL CLONAL ALGORITHM IN MULTIOBJECTIVE OPTIMIZATION

In this paper, a novel clonal algorithm applied in multiobjecitve optimization (NCMO) is presented, which is designed from the improvement of search operators, i.e. dynamic mutation probability, dynamic simulated binary crossover (D-SBX) operator and hybrid mutation operator combining with Gaussian and polynomial mutations (GP-HM) operator. The main notion of these approaches is to perform more coarse-grained search at initial stage in order to speed up the convergence toward the Pareto-optimal front. Once the solutions are getting close to the Pareto-optimal front, more fine-grained search is performed in order to reduce the gaps between the solutions and the Pareto-optimal front. Based on this purpose, a cooling schedule is adopted in these approaches, reducing the parameters gradually to a minimal threshold, the aim of which is to keep a desirable balance between fine-grained search and coarse-grained search. By this means, the exploratory capabilities of NCMO are enhanced. When compared with various state-of-the-art multiobjective optimization algorithms developed recently, simulation results show that NCMO has remarkable performance.Multiobjective optimization, immune algorithm, clonal selection, hybrid mutation