基于器间测量的火星进入过程实时高精度导航

精确着陆于火星特定目标区域是未来火星着陆探测的关键技术。面向火星精确着陆需求,研究火星进入过程中基于器间测量的实时高精度导航方法具有重要意义。该方法利用火星已有的环绕探测器,在着陆器接近进入过程中,通过无线电链路获得量测信息,结合器上滤波算法实时估计着陆器的位置与速度状态。仿真结果显示该导航方法可有效提高进入过程中的导航精度。

基于轨道动力学特性的小天体物理参数感知方法

感知小天体物理参数是小天体探测任务的重要科学目标。针对无人系统在深空探测领域的应用,研究基于轨道动力学特性的小天体物理参数感知方法,建立小天体物理参数与探测器轨道动力学的联系,将小天体物理参数感知问题转化为动力学参数估计问题。首先,采用不规则形状小天体引力场球谐系数模型建立在双探测器绕飞小天体过程中的轨道动力学模型;其次,基于器间测距信息建立小天体引力场与自旋参数感知系统;然后,以器间测距作为感知系统的输入信息,获得引力场模型系数、自旋角速度以及探测器位置速度的最优估计;最后,通过数值仿真验证所提出方法的有效性。分析表明,通过动力学估计方法,可以在不规则引力场下实现高精度自主定轨,并感知出小天体高阶引力场与自旋角速度。

Application of Spatial Filtering Techniques in the Measurement of the Velocity

As one of the interesting optical techniques for measurements of the velocity,the spatial filtering method is treated briefly in this paper.We shown theoretical analysis and calculation of spatial filtering velocimetry,and discussed two-dimensional measurements of the velocity.About the data processing,we used A/D conversion and interfaced with a microcomputer,so that the data can be processed automatically by the microcomputer.The preliminary experiment was performed and the experimental results show the usefulness of the present method for measurements of the velocity.

Design of capacitance sensor system for void fraction measurement

Simulation and optimization were applied to a capacitive sensor system based on electrical tomography technology. Sensors, consisting of Morgantown Energy Technology Center (METC) axial synchro driving guard electrodes and two sets of detecting electrodes, make it possible to obtain simultaneously two groups of signals of the void fraction in oil-gas two-phase flow. The computational and experimental results showed that available sensors, charactered by high resolution and fast real-time response can be used for real-time liquid-gas two-phase flow pattern determination.

Dynamic Crowd Loading Test on Tibetan Ancient Structures

The field test of a typical Tibetan ancient structure instrumented with displacement and acceleration transducers was conducted to measure time histories due to crowd walking and running. The test case is introduced firstly. The displacement time histories are then used to analyze the dynamic property such as fundamental frequency of vertical vibration and damping ratio of the test structure, and the acceleration time histories are applied to evaluate the floor vibration serviceability. The floor interaction and comparison of human walking and running are also discussed. Some valuable conclusions are given.

Ambient noise during rough weather and cyclones in the shallow Bay of Bengal

This paper presents ambient noise analysis during rough weather, using time series measurements from an automated noise measurement system in the shallow southwest Bay of Bengal during October–November 2010. The period witnessed low-pressure events including depressions and cyclones, with JAL cyclone passing close to the measurement site. The time series noise level shows a shift in mid-October, after which deep depressions and cyclones formed, with an average increase of 5–10 dB in the lower band and 2–3 dB in the higher band of frequencies. Furthermore, correlation between noise level and wave height(data from wave rider buoy deployed at the site) for sea state scale 3 and above shows good correlation with an increase in noise level with increase in wave height, the effect being most pronounced at 0.5 kHz. The noise captured during JAL was analysed to identify the spectrum components due to convective precipitation and heavy wind/wave activity and shows anomalously high levels during the crossing of the cyclone. Rain noise spectra from the rain bands associated with the wall of the cyclone are reported. This has been correlated with radar refl ectivity measurements to ascertain the presence of rain, and discriminate between convective and stratiform types. Also, vertical directionality pattern of ambient noise during JAL showed clearly distinct surface contributions. On the whole, knowledge of ambient noise fields during high sea states and precipitation is useful in optimizing SONAR performance. The findings at the study site have been compared with measurements from other shallow water locations during rough weather.

Mixing time in stirred vessels: A review of experimental techniques

Mixing time is de fined as the time required for achieving a certain degree of homogeneity of injected tracer in a unit operation vessel. It has been used as a key parameter for assessing the performance of a mixing system. From an experimental standpoint, several techniques have been developed for measuring the mixing time. Based on the disturbances to fl ow, they can be classi fied into two groups: non-intrusive and intrusive. However, depending on the type of data generated, they can be also classi fied into direct measurements and indirect measurements(Eulerian and Lagrangian). Since the techniques available for measuring mixing times in an agitated tank do not provide the same information, its choice depends on several factors, namely: accuracy, reproducibility,suitability, cost, sampling speed, type of data, and processing time. A review of the experimental techniques reported in the literature in the last 50 years for the measurement of mixing time in stirred vessels under single and gas–liquid fl ow conditions with Newtonian and non-Newtonian fl uids in the laminar and turbulent regime is made, and a comparison between these techniques is also presented.

Using a 3D Interval Type-2 Fuzzy Interpolation System to Improve Modeless Robots Measurement and Calibration Accuracy

This paper is an extended research for a novel technique used in the pose error compensations of the robot and manipulator calibration process based on an IT2FEI （interval type-2 fuzzy error interpolation） method. Robot calibrations can be classified into model-based and modeless methods. A model-based calibration method normally requires that the practitioners understand the kinematics of the robot therefore may pose a challenger for field engineers. An alternative yet effective means for robot calibration is to use a modeless method; however with such a method there is a conflict between the calibration accuracy of the robot and the number of grid points used in the calibration task. In this paper, an interval type-2 fuzzy interpolation system is applied to improve the compensation accuracy of the robot in its 3D workspace. An on-line type-2 fuzzy inference system is implemented to meet the needs of on-line robot trajectory planning and control. The simulated results given in this paper show that not only robot compensation accuracy can be greatly improved, but also the calibration process can be significantly simplified, and it is more suitable for practical applications.

Irradiation-Induced Embrittlement of Inconel 600 Flux Detectors in CANDU Reactors

Post-irradiation examination of encapsulated INCONEL 600 coiled flux detectors that had failed after several years of service in a CANDU reactor showed that many of the detector wires inside the carrier rod were broken. It was concluded that failure occurred because the He cover gas was lost and replaced by air. Because He is a better thermal conductor than air, and because nuclear heating is significant, the temperature of the assembly increased. The examination showed that those parts of the INCONEL 600 detector wires that had operated at the highest temperature were the most severely embrittled. Parts of the same detector wires that were operating at lower temperatures remained ductile. The temperature dependence for the embrittlement of INCONEL 600 material can be explained in terms of the transition from recombination-dominated to sink-dominated reaction-rate kinetics for point defect accumulation at sinks. Cavity formation and accumulation at grain boundaries could weaken the material and result in the observed brittle intergranular failure.

Using Spatial Data Mining to Predict the Solvability Space of Preconditioned Sparse Linear Systems

The solution of large sparse linear systems is one of the most important problems in large scale scientific computing. Among the many methods developed, the preconditioned Krylov subspace methods [1] are considered the preferred methods. Selecting an effective preconditioner with appropriate parameters for a specific sparse linear system presents a challenging task for many application scientists and engineers who have little knowledge of preconditioned iterative methods. The purpose of this paper is to predict the parameter solvability space of the preconditioners with two or more parameters. The parameter solvability space is usually irregular, however, in many situations it shows spatial locality, i.e. the parameter locations that are closer in parameter space are more likely to have similar solvability. We propose three spatial data mining methods to predict the solvability of ILUT which make usage of spatial locality in different ways. The three methods are MSC （multi-points SVM classifier）, OSC （overall SVM classifier）, and OSAC （overall spatial autoregressive classifier）. The experimental results show that both MSC and OSAC can obtain 90% accuracy in prediction, but OSAC is much simpler to implement. We focus our work on ILUT preconditioner [2], but the proposed strategies should be applicable to other preconditioners with two or more parameters.

Analytical investigation for stress measurement with the rheological stress recovery method in deep soft rock

Due to the difficulty and weakness of current stress measurement methods in deep soft rock, a new rheological stress recovery method of the determination of the three-dimensional(3D) stress tensor is proposed. It is supposed that rock stresses will recovery gradually with time and can be measured by embedding transducers into the borehole. In order to explore the applicability and accuracy of this method, analytical solutions are developed for stress measurement with the rheological stress recovery method in a viscoelastic surrounding rock, the rheological properties of which are depicted as both the Burger's model and a 3-parameter solid model. In such conditions, explicit analytical expressions for predicting time-dependent pressures on the transducer are derived. A parametric analysis is then adopted to investigate the influences of the grout solidification time and the mechanical properties of the grout layer. The results indicate that this method is suitable for stress measurement in deep soft rock, the characteristics of which are soft, fractured and subjected to high geo-stress.

Summability results for operator matrices on topological vector spaces

Basic summability results are established for matrices of linear and some nonlinear mappings between topological vector spaces.

Investigation of electrons inside the satellite by the Geant4 simulation

The measurement of the electron radiation inside the satellite is important for engineering and space environment researches.The particle radiation detectors (PRD) on board CBERS-1 and CBERS-2 made great contribution to understanding of the space environment.Then,what is the radiation relationship between inside and outside the satellite? The Monte Carlo simula-tion with Geant4 was implemented to study the problem.The boundaries of the energy bins of 0.5 and 2 MeV were precisely corresponding to outside energies of 0.99 and 2.52 MeV,respectively.Besides the changes of the energy bins,the fluxes inside were smaller than those of the corresponding bins outside.The spectrum inside the satellite was harder than that outside.An indicator was that the flux ratio of the high energy bin to the low energy bin increased more than 20% from outside to inside.The geometric factor (GF) relates to the incident energy of electrons.By using the AE-8 model to derive the incident spec-trum,the GFs of the low and high energy bins were 1.15 and 0.70 cm2 sr,respectively.GF of the low energy bin was larger than that of the high energy bin.But they were both smaller than the previous results.It was due to the scattering,straggle and shielding effects.

Study on Sensitivity Improving of Fiber Bragg Grating Based pH Sensor

The key factor of the sensitivity in the FBG-based pH sensor is analyzed in detail. A multi-thin-layer structure of the gel coated cover was proposed and implemented with a special process. The sensors with the coated thickness of 420 ~m, 500 ~m, and 580 ~m were built up, respectively. The corresponding spectral shifts of 0.08nm, 0.13nm, and 0.22nm were detected when the pH sensors were soaked in the pH value of 3-9. Meanwhile, the sensor with the gel layer thickness of 580 ~tm was measured in the optimum measurement time period with the pH value changing from 3-12, in which the detected sensitivity of 52pm/pH was achieved in the pH range of 6-12.