Mechanism design and dynamic analysis of a large-scale spatial deployable structure for space mission

Currently, little is known about the spatial and temporal variability of rice (Oryza sativa L.) yield patterns. This information is needed before implementing any site-specific management strategy. The objective of this research was to characterize the spatial and temporal yield variability of rice grown in commercial fields in California. Rice cultivars M-202 and Koshihikari were grown and managed by a cooperating farmer, who collected yield monitor data over a 4-yr period. Alternative methods of data quality analysis were applied to the data. To evaluate temporal variability, yields from different years must be placed on a common grid. The appropriate size for these grids was tested. Large-scale spatial structure was determined using median polish while small-scale spatial structure was evaluated by computing variograms of the yield residuals after subtracting the trends. Temporal variability was determined using two approaches: (i) computation of the variance among years of the original, trend, and residual yield values at fixed points in the field and (ii) cluster analysis of the standardized trend yield values. Results from the study showed that the grid density necessary to capture the spatial variability depended on site and year. Trend surface spatial behaviors depended on year, indicating a lack of temporal stability. Variograms showed strong spatial structure of yield residuals. Cluster analysis reduced the considerable complexity in a sequence of yield maps of these fields to a few general patterns of variations among years.

Kinematic of symmetric deployable scissor-hinge structures with integral mechanism mode

There has been increasing demand for larger space structures to satisfy the requirements of astrophysics missions. However, storage space for payloads in satellites is limited, so deployable structures are used in most space missions to minimize storage space and consequently, to reduce launch costs. This work proposes a deployable truss structure which can improve the packaging efficiency of the existing truss structure. The main feature of the proposed structure is that it can be stored in a flat form. Each unit consists of Scissor-like Elements (SLEs) and the whole structure is deployed in a three-dimensional form with a simple mechanism. The detailed configurations and mechanism of the proposed structure are discussed. The geometric constraints for folding the proposed structure into a planar form were analyzed. A kinematic analysis to describe the motion of the structure was also performed. Then the packaging efficiency with respect to length, which is an important performance index of such deployable structures, was analyzed and compared with a typical truss structure.

Accounting for spatial dependence improves relative abundance estimates in a benthic marine species structured as a metapopulation

Away from continental boundaries, the variability of the global ocean is often dominated by eddies. Despite this interior turbulence, ocean boundary pressures on opposing sides of a basin can vary coherently over interannual to decadal timescales, while exhibiting large-scale (∼10⁴ km) spatial structure. As part of the OceanBound project, we investigate how boundary pressure differences reflect meridional transport anomalies in the Atlantic and use an adjoint model to track potential sources of variability.In the ECCO state estimate, we find that boundary pressure differences across the Atlantic account for 60–90% of the meridional transport variability, both on interannual and subannual timescales. This result is consistent at most latitudes, excluding the equatorial region.Adjoint model simulations allow us to quantify the linear sensitivity of across-basin pressure differences to surface forcing. We focus on two latitude ranges where boundary pressure estimates of meridional transport variability are particularly robust. The first is centred at 26.5°N, aligning with the RAPID array, and the second at 26.5°S, overlapping with the SAMBA array. In both cases, we identify surface winds above the continental shelf as the dominant driver of boundary pressure variability, whereas surface buoyancy forcing plays a negligible role.Sensitivity fields derived from the adjoint model are used to reconstruct the Atlantic boundary pressure differences and, consequently, the significant geostrophic component of meridional transport variability. Forward perturbation experiments further reveal potential mechanisms underlying these sensitivities, as well as any non-linear behaviours.

To identify the damaged beams in large-scale spatial structure, a damage indicator based on virtual axial strain calculated from mode shape vectors was proposed. The damage detection process was performed based on the dynamic simulation flowchart. Firstly, random signals were used for excitation and the damage was simulated by decreasing beam elasticity modulus. Then, the NEWMARK-β precision direct integral method was appreciated for calculating time history response. Finally, the frequency-domain decomposition method only using output response signal was selected for modal parameter estimation. A double-layer grid structure was taken as example for verifying the damage detection method. Results indicate that the proposed indicator was insensitive to environmental noise and capable of localizing multiple damaged members in space structure without the baseline data.

Spatial structure analysis and kriging of dichlorodiphenyltrichloroethane residues in topsoil from Tianjin, China

This paper proposes a direct three-dimensional (3D) numerical method in time domain for seismic soil-structure interaction (SSI) analysis of spatial grid structure. First, a finite element model including soil, foundation and typical spatial grid structure is developed. Then, the precisions of equivalent viscous-spring artificial boundary element (VSABE) and size effect of site soil region are discussed. Finally, under different site types, time history analyses for models with or without considering SSI effect are implemented respectively under horizontal seismic excitation. The results show that VSABE has the same precision as infinite element boundary and plane size of truncated soil region can be five times of structure plane size for SSI analysis of spatial grid structure. Moreover, except for hard site, it is shown that horizontal acceleration and displacement of spatial grid roof increases substantially when SSI effect is considered. Therefore, it is suggested that SSI influence should be taken into account in engineering design of spatial grid structure.

Controlled shape-morphing metallic components for deployable structures

A defining feature of mechanical metamaterials is that their properties are determined by the organization of internal structure instead of the raw fabrication materials. This shift of attention to engineering internal degrees of freedom has coaxed relatively simple materials into exhibiting a wide range of remarkable mechanical properties. For practical applications to be realized, however, this nascent understanding of metamaterial design must be translated into a capacity for engineering large-scale structures with prescribed mechanical functionality. Thus, the challenge is to systematically map desired functionality of large-scale structures backward into a design scheme while using finite parameter domains. Such "inverse design" is often complicated by the deep coupling between large-scale structure and local mechanical function, which limits the available design space. Here, we introduce a design strategy for constructing 1D, 2D, and 3D mechanical metamaterials inspired by modular origami and kirigami. Our approach is to assemble a number of modules into a voxelized large-scale structure, where the module's design has a greater number of mechanical design parameters than the number of constraints imposed by bulk assembly. This inequality allows each voxel in the bulk structure to be uniquely assigned mechanical properties independent from its ability to connect and deform with its neighbors. In studying specific examples of large-scale metamaterial structures we show that a decoupling of global structure from local mechanical function allows for a variety of mechanically and topologically complex designs.

In order to improve the large-scale complex spatial structure sensor placement, this paper puts forward an optimal sensor placement method for the tower structure based on key components. According to this method, different probabilities of the structure system’s reliability degree caused by the same damage degree of components are firstly calculated; then component weight coefficients are introduced to measure the relative importance of various components in the whole structure system; the key components of the structure system are defined according to the value of weight coefficients; then modal parameters are adopted to analyze the damage sensitivity of the key components and to find out the vibration modes and measuring points sensitive to the damage of key components, thus to finish the sensor placement. Fully considering the structure characteristics, this method can solve the optimization issues, including the quantity of measurement points and the position, and avoid the complex iterative algorithm and modal expansion error, so it contributes to better controlling the structure state. Finally, through the calculation example of a communication tower, the feasibility and the validity of the method are proved.

As opposed to conventional, static structures, transformable structures possess a transformational capacity enabling them to efficiently respond to altered boundary conditions, such as climatic conditions, different locations, varying functional requirements, or emergency situations. Generally, this capacity is provided through built-in mobility (structural mechanisms) or by means of assembly/disassembly of its constitutive members (kit-of-parts systems). The former group demonstrates kinematic properties that allow them to rapidly respond to changing needs by folding, expanding, or by any other form of deployment. Generally they come in the form of lightweight deployable structures that can easily transform between different configurations. This makes them fit for temporary, mobile applications or for adding adaptable sub-structures to buildings. In what follows, the research performed at the Vrije Universiteit Brussel by the Transform Research Group, the Lightweight Structures Lab, and the Mechanics of Materials and Constructions research group (MeMC), all collaborating on lightweight deployable structures, is presented. Through six case studies, diverse possibilities of deployable structures in architectural and structural engineering are explored. Key aspects concerning the design, analysis and construction of mobile, as well as adaptable constructions, are explained. Finally, conclusions are drawn on the intricate relationship between the geometric configuration, the kinematic behaviour and Mobile and Rapidly Assembled Structures IV 1 doi:10.2495/MAR140011 www.witpress.com, ISSN 1743-3509 (on-line) WIT Transactions on The Built Environment, Vol 136, © 2 014 WIT Press the structural response of lightweight deployable structures.

Computational methods have been successfully applied in structural analysis and drawings of large spatial structures. However, there are still huge challenges in performing conceptual design of structures using computers as what human brain is able to do. A computational method, named performance-based structural synthesis has been proposed and validated to generate and realize planar truss structures. However, it is insufficient for more general spatial truss structures whose geometries and load-carrying requirements are more complex compared with those of planar truss. Therefore, this computational synthesis method based on planar shape grammar was extended and presented in this paper to generate three-dimensional spatial truss structures through building 3D shape grammars and multi-objective hybridized optimization algorithm. Meanwhile techniques of load-generation were employed in the structural synthesis method to realize its engineering application. In the aspect of structural configuration, the method integrates structural topology, geometry and section size allocation; in the aspect of structural design and optimization, it takes into account the combining effects of safety, economy, construction and architectural elegance. Thus the structure generated by this synthesis method must be the best design in terms of the overall structural performance and cost compared with that obtained by traditional design method.

The creep effect becomes significantly pronounced when a steel structure has prolonged exposure to fire. To investigate the influence of creep on displacement, stress, and fire resistance time of spatial grid structure subjected to fire, a square pyramid spatial grid structure was taken as the research object. The element tangent stiffness matrix considering creep effect was derived, and a series of numerical simulation models were established with two constitutive models of materials, a creep model and an elastoplastic model. A comparative analysis of whether to consider creep effects was performed, aiming to assess the differences in the structural response and fire resistance duration of the spatial grid structure subjected to fire. The analysis indicates that the creep effects on both displacement and stress can be disregarded for structural fire durations under 0.5 h, however, once the fire duration exceeds 0.5 h, structural deformation increases significantly, especially when the creep is considered, and the stresses in members decreased significantly, therefore, the influence of creep must be considered in the fire analysis of spatial grid structures to avoid unsafe predictions. The research results aim to provide valuable references for the analysis of spatial grid structure fire responses and post-fire assessments of structures.

In the past, the progressive collapse resulting from local failures during accidents has caused many tragedies and loss of life. Although long-span spatial grid structures are characterised by a high degree of static indeterminacy, the sudden failure of key members may lead to a catastrophic progressive collapse. For this reason, it is especially necessary to research the progressive collapse resistance capacity of long-span spatial grid structures. This paper presents an evaluation method of important members and a novel dynamic analysis method for simulating the progressive collapse of long-span spatial grid structures. Engineering cases were analysed to validate these proposed method. These proposed methods were eventually implemented in the progressive collapse analysis of the main stadium for the Universiade Sports Center. The roof of the structure was concluded to have good resistance against progressive collapse. The novel methods provide results close to practice and are especially suitable for the progressive collapse analysis of long-span spatial grid structures.