Based on the viberation of bouncing,pitching and rolling directions,the vertical dynamics model of levitation chassis was established,and the equations of motion of the model were derived.A simulation program was designed to simulate the vibration dynamic characteristics of the levitation chassis for a certain latest middle and low speed maglev vehicle.The structure decoupling function of levitation chassis was further studied,especially the influence of elastic constraints between the maglev vehicle specific left and right module,and evidences were provided for designing the restraint parameters of module rolling.
The vibration environments in launching process were the worst of satellite's life cycle.In order to better the mechanical environments of satellite in launching stage,improve the reliability of satellite launches and reduce the cost of satellite,the whole spacecraft isolation technique has been attached great importance in all countries.Whole spacecraft isolation technique can effectively isolate the vibration transformed from rocket to satellite,improving the mechanical environment and increase the reliability in launching stage.System's passivity has close contact with its dissipative and stability,the key problem of passive control was to make the system passive,the positive real lemma makes an equivalence relationship between positive real conditions in frequency-domain and corresponding positive real condition of statespace in time-domain,thus the passivity was equivalent to positive realness for linear systems.An active control system was designed based on passive theory,positive real control and LMI inequality method for a new orbicular box-type vibration isolator.Simulation results show that the designed controller has effective vibration suppression and strong robustness.
Abstract Mishrif carbonate formation is widely developed in Iraq and other areas of Middle East. When it comes to carbonate reservoir water injection development, the high heterogeneity commonly existed in carbonate reservoirs makes water flow complicated and performance of water injection differed from reservoir to reservoir. The existence of high permeability stripes and zones would make the problem more complicated and always result water early break through and poor sweep of the reservoir. Water injection pilots started recently in Mishrif carbonate reservoirs in M Field and N Field in southern Iraq. The objectives of these pilots were to investigate the feasibility to conduction water flooding in the Mishrif carbonate reservoirs, including test the injectivity and its change through time, sweep efficiency, responses from offset producers, investigate the methods that can be applied to tackle the problems brought by high permeability zones in water injection. The pilots were carried out in two different well patterns in the two fields, one is inverted nine spots pattern and the other is vertical-horizontal well pattern with vertical well as injector. In one pilot, separated injection was applied to avoid water channeling and improved producer performance. 3D numerical model was applied to track and monitor water sweep during the pilot. It was found out that directional connectivity and high permeability zones were developed in these reservoirs and resulted in early water breakthrough and quick increase of water cut in offset producers. This effect impact vertical and lateral sweep greatly and lower recovery potential in future field water flooding development if not well learned and handled. The challenges are to make description of these directional connectivity and distribution of high permeability zones in reservoir description and modeling and find effective ways in field operations to avoid the negative impact of them in field scale water flooding. To tackle the challenges, integrated reservoir study of multi-discipline is necessary in order to make full description of high permeability zones and reservoir heterogeneity and understand their mechanism on water sweep. It is suggested to pay additional attention to high permeability zone as a key factor in reservoir development of these kinds of reservoirs and integrated the study results into the design of field development plan in an early stage, to narrow the uncertainties brought by them and reduce development risks.
Based on the theory and method of the active design for point meshing tooth surfaces, the writer uses the advantages of convenient and flexible of tooth surfaces active design techniques to analyze the meshing action of point-contact tooth surfaces. The paper analyzes the impacts of tooth meshing in detail. It has very important guiding significance for understanding the rule of tooth surfaces meshing and the design of point-contact tooth surfaces.
The exposure of recycled concrete (RCA) to a sulphate environment in cold regions makes it crucial to overcome the freeze–thaw cycling effects of recycled concrete. Based on steel and basalt fiber reinforced recycled concrete, the freeze–thaw cycle resistance of recycled concrete was studied by exposure to a sulphate environment. The mass loss, dynamic elastic modulus loss and compressive strength loss of the specimens were studied through freeze–thaw cycle experiments. SEM techniques were used to explore the effect of fiber distribution on the freeze–thaw resistance of recycled concrete. The freeze–thaw mechanism of the basalt fiber and steel fiber recycled concrete exposed to a sulphate environment has also been summarized. The results show that, based on the sulphate environment, the composite fiber recycled concrete has a higher stability in terms of mass loss and relative dynamic modulus of elasticity than single fiber concrete. The compressive strength of S0.9RC (recycled concrete with 0.9% steel fibers) and BF5.5RC (recycled concrete containing 5.5 kg/m3 basalt fibers) increased by 8.62% and 13.62%, respectively, compared to normal recycled concrete after 28 days of maintenance; and after 150 freeze–thaw cycles, the compressive strength increased by 41.39% and 47.54%, respectively; compared to ordinary natural aggregate concrete, the compressive strength of S0.9RC and BF5.5RC increased by 32.90% and 27.36%, respectively. The compressive strength of the S1.5BF7.5RC (recycled concrete with 1.5% steel fibers and 7.5 kg/m3 basalt fibers) composite basalt fiber–steel fiber concrete also increased by 42.82%. SEM techniques indicated that the basalt fiber in the recycled concrete exhibited fracture damage, which inhibited the development of microcracks within the concrete. When the recycled concrete is subjected to coupled sulphate and freeze–thaw cycles, freezing occurs from the outside in, with ice crystals extending along the cracks into the matrix. Prior to freezing, a negative pressure is created by the compression of the air and the contraction of the salt solution, which pulls the external solution inwards. The brine is in a state where ice and water coexist during the continuous cooling process. The salt solution migrates from the inside to the outside during heating and melting.
Abstract The existence of high energetic density material depends more on their kinetic stability. The synthesis reactions of CN 7 – by experimentally known N 3 CN and N 3 – were studied. The barrier of CN 7 – towards dissociation was theoretically calculated as 31.6 kcal⋅mol −1 . The data, calculated at the CCSD(T)//B3LYP/6‐311+G(3df,2p) theoretical level, rised to 38.9 kcal⋅mol −1 when CN 7 H was formed by adding hydrogen anion to CN 7 – , indicating significant improvement in stability. The potential energy surfaces of N 7 C R ( R = CH 3 , NH 2 , F, and Cl) system were also investigated, and the lowest kinetic barrier is 36.3 kcal⋅mol −1 , 35.7 kcal⋅mol −1 , 23.5 kcal⋅mol −1 , and 28.5 kcal⋅mol −1 , respectively. Moreover, the energy gap (E g ) of azidotetrazolates (N 7 C R ) system was calculated by frontier molecular orbital theory to verify the stability.
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