Abstract:Solar energy is a kind of rich, clean, and renewable energy, which has the potential to alleviate the energy crisis and environmental problems of the world. Due to the high energy density in space without the influence of weather and nighttime, an important way to obtain large amounts of solar energy in the future is to construct space solar power stations (SSPSs). However, the dynamics and control of the SSPSs are challenges to scientists and engineers, because SSPSs are ultra-large and ultra-flexible spacecraft that operate for decades with accurate attitude pointing requirement. The main purpose of this paper is to review the main results on conceptual designs, dynamics, and control of SSPSs. Firstly, the background and development history of SSPSs were briefly introduced. Meanwhile, the main conceptual designs of SSPSs were summarized. Then, the dynamic and control studies of SSPSs during their serving period were outlined, including dynamic modelling methods, effects of space perturbations, numerical simulation methods, orbital and attitude control, and structural vibration control. It is found that the studies of dynamics and control of SSPSs are still at the initial stage. The previous researches mainly focused on the simplified dynamic models of the SSPSs, such as rigid bodies, beams, and plates. Another focus is on the control of orbit, attitude, or structural vibration of SSPSs separately, despite the coupling effects among them. Nevertheless, the coupled orbit-attitude-structure models in space environment and coordinated orbit-attitude-structure control still need further developments. Finally, some future directions on dynamics and control of SSPSs were given.

Abstract:To solve the problem of the best observation region fast automous prediction for lunar ultra-long wave interferometer, this article makes use of improved binary search method. During the mission period of lunar ultra-long wave interferometer, numerical solutions to relative real-time position of sun, earth, moon and the interferometer are known by the orbit prediction algorithm on board, so the prediction problem is equal to the one-dimension boundary search problem with the assumption. Frequently-used one-dimesion search methods for extremum, such as binary search, golden section search, and fibonacci search, were improved so that they could be applied to the boundary search problem. The specific improvement was to reduce search range by rough search firstly and then design new convergence criterion to find the accurate time when the interferometer gets in or out of the best observation region. Finally, search efficiency of the above methods was assessed by comparing the search time and calculation in the same precision requirement. According to the simulation results, the search time and calculation amount of the improved binary search were both slightly higher than half of those of the other methods. So improved binary search whose search efficiency is significantly better than that of the improved Fibonacci method and the golden section method can be applied to fast autonomous prediction of the best observation for lunar ultra-long wave interferometer.

Abstract:Due to the lightweight requirements of spacecraft structures, the application of large flexible space truss structure has become increasingly widespread. Since it has low-damping and large-flexible features, large oscillation is easy to be motivated on the orbit and it will affect the normal operation of the spacecraft. A finite-time control scheme based on terminal sliding-mode technique is developed to suppress the vibration of the sensor/actuation-integrated space intelligent truss structure. Based on the modal decoupling characteristics of independent modal space control theory, the extended state observer is utilized to estimate the general system disturbances consisted of external disturbances and model perturbations in real-time. Then, the terminal sliding-mode controller is designed based on "linear dynamics compensation" method. Compared with the traditional finite-time controller based on homogeneous method, simulation results show that the proposed vibration suppression controller can reduce the modal vibration amplitude caused by transient disturbance force and periodic disturbance force significantly in a shorter settling time. The proposed controller has good robustness and finite time vibration convergence characteristics.

Abstract:Inter-satellite information interaction is the basis of satellite formation attitude coordination control. To reduce the amount of inter-satellite interaction information and meet the constraints of resource and communication bandwidth limitation, an event-triggered relative attitude distributed adaptive control algorithm is proposed based on the Euler-Lagrange attitude dynamics model of satellite formation. Event-triggered function is designed by utilizing inter-satellite state deviation and associative matrix, etc. Event is triggered and data is updated when function value satisfies the condition, and control algorithm is designed by utilizing information of event time during non-event time, thus the satellite formation attitude consensus coordination control is transformed into an event-triggered control problem. Update frequency of control input and the amount of inter-satellite interaction information are reduced effectively. Leader-follower satellite formation system using proposed control algorithm is proved to be globally asymptotic stable based on the Lyapunov theory. Event-triggered time sequence will not produce Zeno behavior, i.e. a lower bound exists during inter-event time. Numerical simulations were performed to verify the effectiveness of event-triggered adaptive control algorithm, which was in turn compared with a conventional one. Simulation results show that the proposed control algorithm significantly reduces update frequency of control input and the amount of inter-satellite interaction information, meet the constraints of energy on board and inter-satellite communication ability, and ensures control performance of closed loop system at the same time.

Abstract:In the powered phase, spinning missiles are affected by not only aerodynamic forces and moments, but also variable mass characteristics and jet. In order to investigate the dynamic characteristics of spinning missiles in the powered phase, the jet damping effect was modeled and analyzed. Firstly, spinning missiles were modeled as continuous particle systems. The dynamics equations of spinning missiles considering aerodynamic moments, jet damping effect, and variable mass characteristic were established. Then, the characteristics of the spin speed and coning motion under the jet damping effect and nonlinear variable mass characteristics were theoretically analyzed respectively. Moreover, based on the sufficient and necessary condition for stability of coning motion, the expressions of spin speed, quasi-attack-angle and quasi-sideslip-angle were derived under the combined influence of jet damping effect and aerodynamic moments. Finally, the results of theoretical analysis were verified by numerical simulations. The theoretical analysis and numerical simulation results show that the variable mass characteristics and jet damping effect affect the missile's spin speed and coning motion. To keep spin speed constant, the radius of grain should be slightly smaller than that of the engine nozzle. The jet damping effect increases the damping of coning motion, which is advantageous to coning motion stability. Nonlinear variations of mass characteristics can make cone motions converge faster. The variable mass characteristics and jet damping effect cannot be ignored in design and analysis.

Abstract:This study is carried out to investigate the distributed chattering reduction finite-time containment control for multiple Euler-Lagrange systems with systems model uncertainties and external disturbances. Firstly, by defining containment control error variables and choosing an appropriate high-order finite-time sliding variable, a distributed finite-time containment control algorithm was designed. To reduce chattering, the sign function term was included in the derivative of the control law and the continuous control output was obtained by definite integral. Besides, adaptive estimation laws were proposed to approximate the upper bound of the model uncertainties and external disturbances. Based on the graph theory and matrix theory, it is demonstrated that the systems are stable in finite time and the estimation to model uncertainties and external disturbances is effective by Lyapunov method. Finally, simulation results show the effectiveness of the control law.

Abstract:For common methods of investigating the vortex motion evolution experiment in a towing tank, a cross-flow plane is usually illuminated by the laser sheet, and vortex motion photos taken by the CCD camera which is placed on one side of the end face of the towing tank are usually analyzed. However, this method only contributes to investigating vortex planar motion. For offering further insight into its spatial evolution process, a new method named Lagrangian section method is developed to extract and restructure the three-dimensional complex vortex system structure. The method is based on the Lagrangian theory to depict the flow field, combined with the image processing technology of Matlab software to transform vortex motion photos into digital ones. Owing to Galilean transformation, their spatial relative locations are determined by considering the trailer speed and the camera shooting interval. After they are arranged logically, the three-dimensional spatial structure of the vortex system is restructured well to depict the real physical structure. The new method can help people cognize the evolution phenomenon on three-dimensional complex vortex system directly and comprehend vortex interaction mechanism better. Compared to common research technique, it has the characteristics of high cost performance.

Abstract:Transform-invariant group-sparse regularization with directional total variation is an efficient method to solve the super-resolution problem in the regions with highly structured straight edges which is deformed from the real urban scenes and space scenes. Total variation, however, probably leads to staircase artifacts, which may affect the result of super-resolution to large extent. In this paper, we present a new method by mixing different regularizers, especially by combining wavelet analysis with the Transform invariant directional total variation objective function. This allows us to simultaneously recover textures and local geometry structures, particularly highly structured straight edges. To solve this hybrid regularization problem with different norms, we used the idea of templates for first-order conic solvers, and derived the solution of the whole object function that we proposed. Experiments on same real image collections show that our method is more effective than prior works.

Abstract:A spectra calibration method and a radionuclide identification method are developed for the improvement of the adaptability to the nuclear detector measurement in complex environment. In view of the low identification rate of multiple nuclides caused by γ-ray energy spectrum shifting with temperature change, we propose a radionuclide identification method based on sparse representation and multi-task learning. Firstly, a transfer matrix was constructed to represent the environment variation affecting currently measured spectra. Then, the model of the measurement spectra was established, which was used to describe the instantaneous superposition of scale copies of individual nuclide sub-spectra in standard spectra library. Thus, the problem of radionuclide identification was transformed into the problem of sparse decomposition of various radionuclides. In order to solve this non-convex optimization problem, the multi-task learning method based on alternating direction multiplier method (ADMM) was developed to optimize the transfer matrix and decompose the sparse matrix simultaneously. The feasibility and effectiveness of the developed method were verified by some experiments, in which the measurement environment of CsI (Tl) detector was simulated by using the programmable temperature and humidity chamber and the real radioactive spectrum data of 11 kinds of nuclides and typical mixed nuclides were measured, respectively. Meanwhile, the single and mixed nuclide data of 27 kinds of nuclides were used, which are specified by the simulation IAEA of Monte Carlo analysis software Geant4. The experiment results show that the developed method can accurately identify a variety of commonly used nuclides even at temperature range of -20~50℃.

Abstract:To solve the problem of overload-recoil when launching the high muzzle velocity grenade by grenade machine gun system (GMGS), a new effective technology of reducing the recoil force using laval nozzle device with double chambers is presented, and the device is designed and applied to the GMGS. Based on unsteady one-dimensional gas dynamic theory, the interior ballistic duration and after-effect period gas dynamics equations of the recoil device were derived. The rationality of the built mathematical model was validated by contrasting the test date and simulation results. The gas pressure of back chamber, front chamber, gas operated device and nozzle chamber was calculated and the variation laws were analyzed. The bore pressure and muzzle velocity of laval nozzle device with double chambers and conventional weapons were compared. The distribution of gas parameter in nozzle with time and the distribution of gas parameter in nozzle with position were selectively analyzed. The influence of launching performance of laval nozzle with double chambers were discussed. The results show that the GMGS can achieve low recoil launching by setting reasonable parameters of the laval nozzle device with double chambers, while the projectile velocity is unaffected.

Abstract:The forward reachable set of a control system at a certain time is the set of states that can be reached at this time from the initial state. In order to solve the forward reachable set of a nonlinear control system, numerical methods for ordinary differential equations was used to discretize the continuous control system. Since the reachable set of a continuous system can be approximated by its discrete counterpart, a grid projection method based on optimization technology was proposed to approximate the reachable set. In this method, uniformly distributed grid points were placed and projected to the boundary of reachable set for a discrete control; each projection problem corresponded to an optimization problem; by solving these problems the approximated description of the reachable set was obtained. Theoretical analysis proves that the smaller the grid interval, the smaller the approximation error. Finally, numerical results verified the effectiveness of the proposed method, which were compared with those of the DFOG(distance fields on grids) method in literature. The research shows that the grid projection method can effectively handle control systems with non-convex reachable sets. Compared with the DFOG method, the method gets uniform distributed boundary points, solves less optimization problems and uses less computation time.

Abstract:As the interception probability and interception efficiency of anti-missile system consistently increased, the probability for a single ballistic missile breaking the anti-missile system to achieve the attack task is gradually decreasing, thereafter comes the strategy multi-ballistic missile cooperative attack. The cooperative attack of multi-ballistic missile during the free flight segment is easy to achieve, with the missile called warhead at this stage. To solve the problem of modeling and output consensus of cooperative attack for multiple warheads(hereinafter referred to as multi-warhead)in the free-flight segment of ballistic missile, a three-dimension nonlinear state space model for multi-warhead space motion in the free-flight segment is established. On this basis, the characteristic of the model and the challenges brought by the nonlinear dynamic of the model to the cooperative attack of multi-warhead receives detailed analysis. To deal with the above challenges and realize the output consensus of the cooperative attack architecture for leader-followers multi-warhead, a kind of cooperative acceleration command signal is designed for the followers by using the input-output feedback linearization control theory, and the effectiveness of the designed command signal is verified by detailed numerical simulation. The result of simulation shows that the output consensus of cooperative attack architecture for leader-followers multi-warhead is realized under the given performance requirement on all axes of the leader's launch coordinate system. The faster the velocity of leader varies and the larger the real part modulus value of convergence coefficient is, the faster the convergence speed of velocity tracking error and the smaller the velocity tracking error will be. Finally, the performance of the output consensus will be even better.

Abstract:In order deal with the attitude control of assembled spacecraft whose moment of inertia is unknown, a spacecraft combination attitude control algorithm, which is independent of accurate dynamic model, was designed based on model-free control method. Firstly, a model-free adaptive control equation was derived based on date driven control method of a single input and single output discrete-time system. Then, the model-free adaptive control method was introduced to the attitude control of the assembled spacecraft, and the model-free adaptive controller was derived. In addition, the attitude control process was optimized based on the dynamics characteristics of the combined spacecraft. Finally, the model-free adaptive control algorithm and the control process optimization algorithm were simulated under the background of the operation after target capturing. The results show that the designed model-free adaptive algorithm is feasible, and it can achieve precise control of assembled spacecraft whose inertial parameter is unknown. By optimizing the control process, fast convergence of attitude control can be achieved with a higher accuracy.

Abstract:A path tracking control algorithm based on the improved line-of-sight guidance algorithm and adaptive sliding-mode heading control algorithm is proposed. Based on the Lyapunov and cascade theory, the proposed path tracking control system is proved to be uniform globally asymptotic stable (UGAS) when the target tasks are all achieved. Compared to the traditional line-of-sight guidance algorithm, the improved guidance algorithm in the paper can realize the real-time estimation and compensation of the drift angle by introducing the adaptive observer. At the same time, the design of the forward-looking distance makes the manipulation of the underactuated USV more flexible. Based on the maneuvering model and parameters identification of the USV called "sturgeon 03", the path tracking contrast simulations were carried out on MATLAB/SIMULINK software. The simulation results show that the path tracking algorithm proposed in the paper has more dynamic performance and less steady-state error than the traditional LOS guidance algorithm. Then, the sea-field test using the USV called "sturgeon 03" confirms that, under the action of the tracking control algorithm, the USV can track the desired path accurately, and the track error is relatively small during the whole tracking.

Abstract:To study the characteristics of low velocity ball water entry cavity and the effect of cavity on ball dynamic characteristics, a cavity was modeled based on the principle of independence of the cavity sections expansion. A high-speed video camera was used to observe the process of ball water entry at different velocities and the process of cavity formation. The effect of cavity formation on jet flow and dynamic characteristics of the ball as well as the cavity dynamic characteristics were analyzed. The results showed that the formed cavity had an great effect on the jet flow. The jet was sputtered in the form of a water column when the cavity was not formed. After the stable cavity was formed, the jet was sputtered around before the surface closure and sputtered upward after the surface closure. The ball acceleration changed complexly due to the changed of ball water entry velocity, the formation of cavity and the impact force. The drag coefficient decreased when the cavity was formed. The change of the cavity section area was obtained using the proposed cavity model, which was verified by the experiment results. The time of cavity formation at different depth has little difference and the cavity section has a larger maximum area at small depth.

Abstract:To investigate the change rule of multiphase flow characteristics in the turning motion of supercavitation vehicle, the RANS equation is solved based on the finite volume method and VOF multiphase flow model. Combined with the dynamic mesh technology, an unsteady numerical simulation study is conducted. By comparing the numerical simulation results with the calculation results based on Logvinovich independence principle, the effectiveness of the numerical simulation method is validated. The influence of rotate center of vehicle on the cavity shape and that of turning radiuses on the hydrodynamic characteristics of vehicle for the turning motion are analyzed by the numerical simulation. The results show that the numerical simulation method of dynamic mesh can simulate the cavitary shape of the turning motion of the supercavitation vehicle better. The rotation center of the vehicle has an important influence on the wetting area on the inner or outer surface of the turning radius of the vehicle. The valley environment of the vehicle makes the shape of the super cavity tail appear inclined double vortex tubes under the combined action of gravity and inertial force. During the turning motion, when the wetting area appears on the surface of the vehicle, the fluid dynamics of the vehicle will have a small amplitude fluctuation. The fluid dynamics tends to be stable with the wetting area increasing. And the trajectory radius of the turning motion has a great influence on the fluid dynamics of the vehicle. The smaller the turning radius is, the greater the influence is.

Abstract:To investigate the water-entry cavity and the dynamic characteristics of the revolution body, the Fluent was adopted for the multiphase flow and the movement of the water-entry revolution body with the dynamic mesh. The effectiveness of the numerical method was verified by comparing the numerical results with the experimental results. Based on the method, the flow field characteristics during the oblique water entry of the revolution body with different velocities and angles is studied. Results show that in the same water depth, the diameters of the water-entry cavity increased slightly as the velocity of water entry increased, and decreased as the angle of water entry increased. The velocity of water entry had a great influence on the pressure distribution in the flow field. The maximum pressure of the flow field increased as the water-entry velocity increased for the same water depth. The angle of water entry had little influence on the maximum pressure of the flow field near the revolution body, but the minimum pressure increased as the water entry angle increased. When the angle of the water entry was larger, the point of the maximum pressure in the generatrix of the cone shifted to the right endpoint gradually, but its value had little difference. The drag coefficient peak value differed slightly with increasing the velocity of water entry, but became larger as the angle of water entry increased. The stable drag coefficient became larger with the increase of water-entry velocity.

Abstract:To study the influence regularity of the tail fin on the bubble flow pattern, the hydrodynamic characteristics of fins of supercavitation projectile were performed in water tunnel. The rationality of the test scheme was fully demonstrated. The test system of ventilation cavitation flow was constructed based on the high-speed water tunnel. Base on the basic shape of the projectile and the similarity theory, the tail force measurement test model was designed. Meanwhile, to change the relative location between the fins and the cavitation, the cavitation size or the model attitude was adjusted. The hydrodynamic characteristics of fins of supercavitation projectile were studied by changing the test conditions. The influence regularity of the tail fin on the bubble flow pattern and its hydrodynamic characteristics under different puncture conditions were obtained. The results show that the formation of secondary cavitation at the top and the side of the tail fin after the puncture of the tail significantly changed the shape of the main cavitation, and the impact of the tail fin on the main cavitation became more obvious with the increase of the puncture height. The hydrodynamic characteristics of the tail fin mainly came from the wetting part of the leading edge, and the lift coefficient and the drag coefficient increased significantly with the increase of the puncture height. The drag coefficient and the lift coefficient under puncture conditions increased linearly with the attack angle. The results can provide references for the optimization design of the shape of the supercavitation projectile and trajectory prediction.

Abstract:To investigate the effects of boundary conditions and geometric properties on dynamic characteristics of axially functionally graded beams, Gauss-Lobatto sampling and Chebyshev polynomials are used to discretize deformation fields of the beams, and the discrete governing equations are obtained by utilizing Chebyshev spectral method and Lagrange's equation. After employing projection matrices, classical as well as elastic boundary conditions are incorporated in the governing equations. The effects of various parameters, such as material gradient index, cross-sectional area, and attached tip mass on the vibration of the beams are analyzed. The results show that these effects differ for different boundary conditions. As the taper ratio increases, the first natural frequency of the cantilever beam increases simultaneously. While for the beams with other boundary conditions, their natural frequencies decrease. With the raising of the material gradient index, the first natural frequency of the cantilever beam increases firstly and then decreases, but other frequencies all increase. But for the fixed-fixed beam, its first two natural frequencies decrease, the third and the fourth increase. For the pinned-pinned beam, all natural frequencies increase with increasing material index. When the elastic support becomes stiffer, all natural frequencies increase with a step. The effect of the rotational spring is more pronounced than the translational spring when the elastic supports are of low stiffness. The attached tip mass makes the natural frequencies smaller and this effect appears more pronounced for higher modes.

Abstract:To overcome the premature problem of the traditional flower pollination algorithm, a novel niche flower pollination algorithm is proposed by combining the niche strategy with flower pollination algorithm. It is designed for the parameter inversion of the space fractional order diffusion equation, so as to provide some theoretical basis for the pollutants source identification and air pollution prevention. Firstly, twenty multimodal functions were selected to verify the performance of the flower pollination algorithm and its improved algorithm. Then, we carried out direct simulation with implicit finite difference scheme. Based on the forward simulation results, the flower pollination algorithm and the improved algorithm were applied to invert the source term and the diffusion coefficients of the space fractional differential equation. The sensitivity analysis of the proposed algorithms regarding initial interval, perspectives of population and transition probability has also been completed. Furthermore, the anti-noise properties of the proposed algorithms were discussed. The numerical results demonstrate that the improved flower pollination algorithm has achieved a higher precision and accuracy.

Abstract:The open-circuit voltage of a solar cell is one of the key parameters for conversion efficiency. In order to contactlessly and quantitatively image the open-circuit voltage of solar cells, in this paper, the relationship between the luminescence intensity and the open-circuit voltage (V_oc) of solar cells was firstly simulated by finite element technique (FEM). Secondly, the V_oc images of a crystalline silicon (c-Si) solar cell and a multicrystalline silicon (mc-Si) solar cell were quantitatively investigated by lock-in carrierography (LIC) as well as the existed photoluminescence (PL) method. In order to validate the imaging method, Sun-V_oc was employed to measure the open-circuit voltage of the crystalline silicon (c-Si) solar cell and the multicrystalline silicon (mc-Si) solar cell. Finally, the open voltage images of GaAs solar cells irradiated by 1 MeV electrons with different fluences were studied by LIC. The result shows: the averaged V_oc values by both imaging methods were in good agreements with the results measured by Sun-V_oc, and the average values of LIT and PL for two kinds of solar cells differed less than 1% compared with Sun-V_oc. Furthermore, the V_oc image by LIC was consistent with PL. Compared to PL measurements, LIC has a higher signal-to-noise-ratio (SNR) as well as a simpler detection process. The V_oc degradation of electron irradiation GaAs solar cells measured by LIC was in a good agreement with electrical measurement.Therefore, LIC could provide a possible approach to achieve more quantitative characterization of spatially resolved information and a new method to investigate the irradiated solar cell for space use.

Abstract:To explore the evidence supporting campus environmental design for physical activity promotion in cold climates, empirical studies based on Theory of Evidence-based Design and Social-ecological Model were conducted in 9 campuses located in the northeast of China. Accordingly, the impacts of different domains of campus environment on students' winter physical activity have been defined by questionnaire surveys. Cross-sectional comparisons between physical activity level in winter and other seasons, and subjective evaluation in 9 campuses have been studied by descriptive statistical analysis; correlations between campus environment elements and students' winter physical activity have been defined by multiple linear regression. The results revealed: both the frequency and amount of physical activity conducted in winter are lower than those in other seasons; the quality of campus environmental elements evaluated in winter is less desirable than in other seasons, specifically the ratings of climate-protection, walkable accessibility, traffic safety and winter activity safety are relatively lower than other elements; in winter, some elements (destination variety, public-transit choice variety, street network connectivity, environmental quality of walking routines, walking-assisted facility presence and crime safety) are positively correlated with the transportation-related physical activity, while some (ice and snow threatens and air pollution) are negatively related with it; there is no obvious correlation between campus environment and recreation-related physical activity. Based on the statistical findings, design indications of campus design and the relative importance of campus environmental elements for physical activity promotion can be inferred reasonably, to be more specific, elements such as campus destinations, walking routines, crime safety, walking-assisted facilities and campus public transit are proved to be more important.

Abstract:To study the driving characteristics of air conditioning behavior, a field survey study was carried out in 28 dormitory rooms during the summer in 2016 in Beijing. Indoor temperature, humidity, occupants' presences at their rooms and their actions on air conditioners were measured. A questionnaire survey was conducted to investigate the driving forces of occupants' actions to turn on or turn off room air conditioners. The field survey data was grouped based on the driving forces to trigger air conditioning behaviors, and individual driving characteristics of air conditioning behavior were described as probability with driving force together with the characteristic parameters using an action-based behavior model. Moreover, driving characteristic parameters were analyzed and probability curves were subdivided under different driving forces. Two to four new probability curves were developed and the corresponding characteristic parameters were determined for each subdivision under different driving forces, which presented a quantitative description about driving characteristics of air conditioning level at group level. The results in this study are useful for further study of driving characteristics of air conditioning behavior on a large scale.

Abstract:The thermal inertia index D is the key parameter in the thermal stability model of the building based on the harmonic analysis method. To reveal the effect mechanism of D on the heat flow fluctuation in the enclosure structure, the relationship between D and the attenuation and the number of temperature waves was given, based on the theoretical analysis and solution of the heat transfer process of the building envelope under the periodic unsteady thermal action. Then the effect of D on the attenuation and delay of temperature wave in the enclosure structure is analyzed by numerical simulation method. Finally, the key influence of D on the calculation of thermal stability parameters was analyzed, such as violent fluctuating layer thickness, the thermal storage coefficient of inner surface, the attenuation multiplier and the delay time. The results show that there is a quantitative relationship between D and the attenuation of temperature wave and the number of temperature waves in the enclosure. For the same type of enclosure structure, when D value increases, the attenuation and the delay time become greater. As the number of temperature waves in the enclosure structure increases, and the thermal stability become better. For different forms of multilayer enclosure structure, the larger the D value is, the longer the delay time is, and the attenuation ratio is related to the arrangement of the material layer, and the external insulation can obtain more attenuation multiple. Using D=1 to determine the thickness of violent fluctuating layer provides a new idea for thermal storage design of building envelope. The calculation of the thermal storage coefficient of inner surface is mainly related to the thickness of violent fluctuating layer. The theoretical basis for the improvement of the physical meaning of the thermal inertia index from the qualitative description to the quantitative description is provided.

Abstract:Water muffler can effectively attenuate the noise of the pipeline system. In order to calculate the transmission loss (TL) of the water muffler accurately, the acoustic field of the water muffler was analysed based on the acoustic solid interaction model. The acoustic solid interaction effect of different structural parts on the acoustic performance of the expansion chamber muffler filled with water was studied. The TL of the water muffler was predicted with the ratio of elastic wall thickness to radius which equals to 1. The obtained results were compared with the analytical solutions and the numerical results of the case with rigid wall, which is used to validate the accuracy of the adopted acoustic solid interaction approach. On the other hand, the results based on the two dimensional axisymmetric model and the complete model were compared to validate the feasibility of the present method. The numerical results show that the decrease of the water muffler's structure thickness caused the enhancement of interaction between the solid and the water, leading to obvious effects of the elastic wall on the muffler's acoustic characteristics. The interaction between the circumferential wall and the water made the TL curve of the expansion chamber move to the lower frequency band. The interaction between the end wall and the water caused the resonance peak and the inverse one of the TL curve, which is related to the eigenfrequency of the end chamber wall. The acoustic solid interaction between the expansion cavity wall and the water made the acoustic pressure appear three dimensional high order wave in the lower frequency range, and increased the amount of noise elimination. The interaction between the pipe and the water had little effect on the acoustic performance of the water muffler.

Abstract:Lab-scale simultaneously anaerobic ammonia oxidation and denitrification (SAD) process was operated in Municipal Waste Water Treatment Plant (WWTP). Sewage treated by A/O and nitrification process was served as substance to start up anaerobic ammonia oxidation filter reactor. Adding organic carbon-source to influent was served as substance to start up SAD filter reactor after successful start-up of Anammox reactor. Glucose was selected as organic carbon-source because it is harmless and inexpensive. The result show that SAD process performed well with 10, 20, and 30 mg/L Glucose added to effluent sewage at ambient temperature and average total nitrogen concentration of effluent was 9.16, 8.10, and 6.41 mg/L. Compared with Anammox process, SAD process performed better and total nitrogen concentration in effluent decreased 16-42 percents. Stability of SAD process was destroyed and SAD process turned to denitrification process when 30 mg/L Glucose was added in influent sewage in winter. Ammonia in effluent increased from 0.5 mg/L to 6.2 mg/L. The results indicate that temperature has superior effect on SAD process. The total nitrogen concentration in effluent varied from 6.5 to 8.5 mg/L when concentration of Glucose decreased to 20 mg/L. In winter, the effluent of SAD process reached the 1A level of integrated discharge standard of water pollutants applied in Beijing City.