Applied Mechanics and Materials Vols. 166-169

Abstract: This paper presents an active vibration control scheme for uncertain structural system. The state feedback controller is designed in term of Hinf robust control theory and the optimal solu- tion is obtained by using LMI convex optimal technique. A numerical example of three-degree-of- freedom system is taken to verify the proposed approach.The simulations demonstrate the effective- ness and feasibility.

Abstract: With the characteristics of low noise, low vibration, high reliability and long life, Screw Compressor is the indispensable main equipment which widely used in petrochemical field. The abnormal vibration of Compressor will affect normal operation of the host, lead to damage of some main parts such as Compressor and motor and at the same time it’s an unneglectable hidden trouble for equipment’s safe operation. This article takes the data acquisition of vibration and the analyses of shake for two Ammonia Refrigeration Piston Compressors, and study at the reason about shock then take the effective shockproof treatment plan. All these ensure the stable running of the facility.

Abstract: From the basic equations of dynamics, the precise expression of the relationship ,which was between the horizontal natural frequency and pressure load of the simply supported beam and the beam fixed at both ends with vertical pressures, was obtained. The approximate expression of the relationship, which was between the horizontal natural frequency and pressure load of the beam fixed at both ends with vertical pressures, derived from the variational methods. By comparing the precise numerical solution and the approximate solution of the beam fixed at both ends with vertical pressures, the conclusion of approximate linear relationship that was between the square of the natural frequency and axial force of the beam fixed at both ends with vertical pressures was got. Through theoretical and experimental comparing, the difference between the approximate solution and the accurate numerical solution was small, which could meet the requirements of accuracy on engineering. On this basis, as long as the natural frequencies of the structure at two load conditions are measured by experimental methods, elastic buckling load of the compressed beam can be identified.

Abstract: The flexural strength of steel fiber reinforced prestressed concrete slab (SFRPCS) with different steel fiber volume ratio (0%, 1%, 2%) is obtained according to four-point bend test, which reveals that the addition of steel fiber can retard the crack growth and enhance the flexural strength of SFRPCS. With the results of fatigue experiment, the damage forms of SFRPCS is analyzed, strain amplitude-cycle ratio curves are obtained and the plastic strain energy of SFRPCS with different steel fiber volume ratio during fatigue process is calculated. It is shown that after 80% fatigue life, the more of the steel fiber volume ratio, the less of the strain amplitude increment, which proves the addition of steel fiber can prevent the concrete matrix from cracking and improve the fatigue performance of SFRPCS, and the plastic strain energy curve of SFRPCS shows obviously three- stage development.

Abstract: Based on simplified theory model of injected fluid structure, select steel plate as maintenance structure and water as test equipment of liquid production, do field tests of explosion and analyze explosion resistance performance of structure. The results show that the injected fluid structure has good explosion resistance performance and that its cutting-wave ratio reaches to about 85%. It provides experimental basis for explosion resistance performance of injected fluid structure in the explosion load.

Abstract: By using the key technology of wireless sensor networks, a stress test system was designed, which takes the M2110 wireless sensor networks as a platform. Based on the hardware design and software design of TinyOS2.0 sensor nodes and gateway nodes, the signal transmission performance of wireless sensor networks for the stress test system was tested and researched. In the visual conditions, the maximum communication distance of M2110 wireless node is up to 601 meters. In the non-visual conditions, M2110 wireless node also has a certain signal transmission capacity. On the situation of multi-hop nodes network, the success rate of data transfer has relation to the transmission rate of data packet and the number of hops for nodes.

Abstract: The structural safety alarming based on signal energy is carried out in this study with the aiding of wavelet packet transform (WPT). The structural dynamic responses are computed by using Newmark-beta algorithm and then decomposed to obtain the signal energy distribution at different levels. A damage detection approach based on signal energy by using wavelet packet transform is developed in this study to detect the damage event of a simply-supported beam. A WPT component energy (WPCE) index is proposed to construct the damage vectors for damage identification. A beam structure is taken as an example to examine the feasibility and validity of the proposed approach. The results from this study demonstrate that the detection approach proposed can accurately identify the damage event in the structure.

Abstract: The evaluation on damage event of a beam structure is carried out in this study through an integration of knowledge in damage detection and signal process. A damage detection approach based on wavelet packet transform (WPT) is developed by decomposing and reconstructing the structural dynamic responses to obtain the signal energy distribution at different levels. The WPT coefficients are reconstructed to extract the signals in various frequency ranges and determine the signal energy in different frequency bands. A WPT component energy index is proposed to establish the slope vector as well as curvature vector and then the judge on the slope vector and curvature vector can indicate the damage event. Parametric study is carried out to investigate the relationship between the index amplitude and the damage extent. The results from this study demonstrate that the detection approach proposed can accurately identify the damage event in the structure.

Abstract: Structural stability problem is the key problem in design of steel structural. The structural stability behavior of suspended dome is investigated by employing a computation model of the Kiewitt suspend-dome with a span of 92m. ANSYS were used in the investigation. The load-displacement path of the structure is studied by using the Newton-Raphson and arc-length method. The parameters that affect the structural elastic-plastic ultimate load-carrying capacity such as rise to span ratio, height of struts, and prestress of the cables below were analyzed. Some conclusions are drawn that improving the prestress can’t improve the ultimate load-carrying capacity and higher rise to span ratio, heights of struts can improve the ultimate load-carrying capacity.

Abstract: Based on the numerical calculation and the theoretical formula for crack width,a new semi-numerical and semi-theoretical calculation formula for crack width of beam was given. By using this new formula,finite element method and theoretical method is combined. The method has been validated with the beam, it is indicated that the proposed method can be used to calculate the crack width of beam accurately and efficiently.