Showing papers in "Journal of Aerospace Engineering in 1994"
TL;DR: This paper presents a robust hybrid genetic algorithm for optimization of space structures using the augmented Lagrangian method that can be applied to a broad class of optimization problems.
Abstract: This paper presents a robust hybrid genetic algorithm for optimization of space structures using the augmented Lagrangian method. An attractive characteristic of genetic algorithm is that there is no line search and the problem of computation of derivatives of the objective function and constraints is avoided. This feature of genetic algorithms is maintained in the hybrid genetic algorithm presented in this paper. Compared with the penalty function-based genetic algorithm, only a few additional simple function evaluations are needed in the new algorithm. Furthermore, the trial and error approach for the starting penalty function coefficient and the process of arbitrary adjustments are avoided. There is no need to perform extensive numerical experiments to find a suitable value for the penalty function coefficient for each type or class of optimization problem. The algorithm is general and can be applied to a broad class of optimization problems.
270 citations
TL;DR: Two concurrent augmented Lagrangian genetic algorithms for optimization of large structures utilizing the multiprocessing capabilities of high-performance computers such as the Cray Y-MP 8/864 supercomputer are presented.
Abstract: In a recent article, the writers presented an augmented Lagrangian genetic algorithm for optimization of structures. The optimization of large structures such as high-rise building structures and space stations with several hundred members by the hybrid genetic algorithm requires the creation of thousands of strings in the population and the corresponding large number of structural analyses. In this paper, the writers extend their previous work by presenting two concurrent augmented Lagrangian genetic algorithms for optimization of large structures utilizing the multiprocessing capabilities of high-performance computers such as the Cray Y-MP 8/864 supercomputer. Efficiency of the algorithms has been investigated by applying them to four space structures including two high-rise building structures. It is observed that the performance of both algorithms improves with the size of the structure, making them particularly suitable for optimization of large structures. A maximum parallel processing speed of 7.7 is achieved for a 35-story tower (with 1,262 elements and 936 degrees of freedom), using eight processors. 9 refs.
234 citations
TL;DR: In this paper, the authors developed a method of analysis for inflated fabric beams that is analogous to the shear-moment method, based on basic assumptions about the state of stress in the fabric of the inflated beam.
Abstract: The use of inflatable structures has often been proposed for aerospace applications. The advantages of such structures include low launch weight and easy assembly. To consider using inflated fabric beams in aerospace applications, an accurate and efficient method of structural analysis must be developed. This paper develops a method of analysis for inflated fabric beams that is analogous to the shear-moment method. The bending model is developed from basic assumptions about the state of stress in the fabric of the inflated beam. The resulting model shows that the bending behavior of inflatable fabric beams is identical to conventional solid elastic beams as long as the beam fabric remains unwrinkled. Experimental data were obtained and verify the static bending model for beams with length/diameter ratios greater than 10.
110 citations
TL;DR: In this article, a systematic procedure is presented to assign Cartesian coordinate frames for the links (joints) of an excavator and the homogeneous transformation matrices that relate two adjacent coordinate frames are given.
Abstract: To use construction machines effectively in the dark, severe weather, or hazardous and/or unhealthy environments, their operations should be controlled automatically. It can be realized if the kinematics and dynamics of the machine are understood. To help achieve this goal, the kinematics of specific construction machines—excavators (backhoes and loaders)—are investigated here. A systematic procedure is presented to assign Cartesian coordinate frames for the links (joints) of an excavator. Then, the homogeneous transformation matrices that relate two adjacent coordinate frames are given. The kinematic relations of the pose (position and orientation) of the bucket, the joint shaft angles, and the lengths of the cylinder rods in the hydraulic actuators for an excavator are studied. Explicit expressions for the forward and backward (inverse) kinematic relations are presented. Then, the corresponding kinematic velocity relations for the excavators are developed. The kinematic relations presented provide the f...
78 citations
TL;DR: The integrated structural and control optimization problem is formulated by including constraints on displacements, stresses, and closed-loop eigenvalues and the corresponding damping factors and then parallel algorithms are presented for integrated optimization of structures on shared-memory multiprocessors such as the CRAY YMP 8/864 supercomputer.
Abstract: Optimization of combined structural and control systems is a complex problem requiring an inordinate amount of computer-processing time, especially the solution of the eigenvalue problem of a general unsymmetric square real matrix with complex eigenvalues and eigenvectors, which is frequently used in such problem. The few algorithms presented in the literature thus far have been applied to small structures with a few members and controllers only. Parallel processing on new-generation multiprocessor computers provides an opportunity to solve large-scale problems. In this paper, the integrated structural and control optimization problem is formulated by including constraints on displacements, stresses, and closed-loop eigenvalues and the corresponding damping factors. Then, parallel algorithms are presented for integrated optimization of structures on shared-memory multiprocessors such as the CRAY YMP 8/864 supercomputer. In particular, parallel algorithms are presented for the solution of complex eigenvalue problems encountered in structural control problems using the method of matrix iteration for dominant eigenvalue(s). The solution is divided into two parts. The first part is the iteration for dominant eigenvalue(s) and the corresponding eigenvector(s) and the second part is the reduction of the matrix to obtain the smaller eigenvalue(s) and the corresponding eigenvector(s).
68 citations
TL;DR: The feasibility of pneumatic transfer for the movement of regolith at a lunar base is evaluated in this paper, where both horizontal and vertical transfer is studied, and the results show that the choking velocity for 150-micron glass spheres was determined to be 1/2 to 1/3 the velocity required at 1 g.
Abstract: The feasibility of pneumatic transfer for the movement of regolith at a lunar base is evaluated. Operation of pneumatic conveying systems at partial (lunar and Mars) gravity on NASA's KC-135 aircraft allowed the determination of some key parameters necessary for the design of an operable system. Both horizontal and vertical transfer is studied. In the vertical experiment, the choking velocity for 150-micron glass spheres was determined to be 1/2 to 1/3 the velocity required at 1 g. Pressure drops were reduced by roughly the same amount. Determination of the saltation velocity in the horizontal run was problematic, but qualitatively similar results were obtained. Comparison of the partial g results to 1-g behavior and theoretical analysis is made.
32 citations
TL;DR: Judicious combination of microtasking, macrotasking, and autotasking is explored with the goal of achieving a vectorized and multitasking algorithm for optimization of a large structure with maximum speedup performance.
Abstract: Various multitasking approaches are investigated for optimization of large space structures. Judicious combination of microtasking, macrotasking, and autotasking is explored with the goal of achieving a vectorized and multitasked algorithm for optimization of a large structure with maximum speedup performance. Speedup results are presented and compared for three space truss structures, with 526, 1,046, and 3,126 members. The processing time required for optimization of large structures increases exponentially with the size of the structure (number of design variables). Example 3 of this paper has 3,126 members and 2,226 displacement degrees of freedom. Development of efficient concurrent algorithms utilizing the unique architecture and capabilities of high‐performance computers results in substantial reduction in the overall execution time.
24 citations
TL;DR: In this paper, a new airfoil-design concept was developed to produce greater lift coefficients over a much broader range of operational angles of attack, to improve or eliminate stall at virtually all operational airspeeds, to increase functional lift-to-drag ratios over a greater range of operations, and to be adaptable for aircraft of both the fixed-wing and the rotarywing types.
Abstract: The research in this paper is the result of an experimental study regarding a new airfoil‐design concept, which is developed to produce greater lift coefficients over a much broader range of operational angles of attack, to improve or eliminate stall at virtually all operational airspeeds, to increase functional lift‐to‐drag ratios over a greater range of operational angles of attack, and to be adaptable for aircraft of both the fixed‐wing and the rotary‐wing types. The writer has combined his effort with L. L. Smith, and a U.S. Patent, entitled “Airfoil,” Patent No. 4,606,519, was obtained on August 19, 1986. Patents were also obtained or are pending in other countries. The experimental results, obtained by using the new airfoil‐design concept, have been compared with experimental results obtained from a conventional NACA 23012 airfoil. Flight performance tests by using a 2.134‐m (7.0 ft) model and remote‐control devices, as well as flow‐separation studies, were also performed. The results were compared ...
23 citations
TL;DR: In this paper, the authors used the direct stiffness method within a symbolic manipulation framework to transform the lattice structure to an equivalent single-layer grid, and then using existing expressions to obtain the desired equivalent plate.
Abstract: Deployable structures can be stored in a compact, folded configuration and are easily deployed into load-bearing, open forms. Hence, they are suitable for applications where speed and ease of erection and reusability are desired. The structures investigated here are prefabricated space frames made of so called scissor-like elements, sets of two straight bars connected to each other by a pivot. These structures are stress-free and self-standing in both their folded and deployed configurations, thus overcoming major disadvantages of previous designs. This study deals with deployable structures that are flat and subjected to normal loads in their deployed configuration. Although the behavior for that loading case is linear, the availability of an equivalent continuum model for stiffness prediction is desirable because it can significantly reduce the computational effort during preliminary design. The derivation of such a model is not straightforward because of the unorthodox geometry and the rotations allowed by the hinged and pivotal connections. This problem is addressed by first applying the direct stiffness method within a symbolic manipulation framework to transform the lattice structure to an equivalent single-layer grid, and then using existing expressions to obtain the desired equivalent plate. The model exhibits good accuracy and convergence characteristics for uniform loads.
17 citations
TL;DR: The analysis aspects of the 23,000-line FORTRAN program VICONOPT are described in this paper, where the longitudinal continuity of typical wing and fuselage panels is closely approximated by the solutions are for the infinitely long structure obtained by repeating a bay and its supports longitudinally.
Abstract: The analysis aspects of the 23,000‐line FORTRAN program VICONOPT are described. Overall stiffness matrices assembled from the earlier exact VIPASA flat plate stiffnesses are optionally coupled by Lagrangian multipliers to find critical buckling loads, or natural frequencies of undamped vibration, of prismatic assemblies of anisotropic flat plates with arbitrarily located point supports or simple transverse supporting frames. The longitudinal continuity of typical wing and fuselage panels is closely approximated because the solutions are for the infinitely long structure obtained by repeating a bay and its supports longitudinally. Any longitudinally invariant in‐plane plate stresses are permitted, and very rapid solutions are guaranteed by numerous refinements, including multilevel substructuring and a method for repetitive cross sections that is exact for regular polygons used to represent cylinders. Modal displacements and stresses in or between plies of laminated plates are calculated and plotted, with values being recovered at all nodes of substructures. Comparison with usual approximate finite‐element methods confirms that, for comparably converged solutions, VICONOPT is typically between 100 and 104 times faster.
16 citations
TL;DR: In this paper, the utilization of soil traditionally involves the compaction of the insitu or previously loosened material, which plays an important role in the construction of foundations of roads and buildings.
Abstract: Soil plays an important role in the construction of foundations of roads and buildings. The utilization of soil traditionally involves the compaction of the insitu or previously loosened material t...
TL;DR: In this paper, a piecewise continuous Timoshenko beam model was used for the dynamic analysis of a tapered beam-like structure, and the transfer matrix method was used to relate all elements as a whole.
Abstract: Distributed parameter modeling may offer a viable alternative to the finite‐element approach for modeling large flexible space structures. In addition, the introduction of the transfer matrix method to the continuum modeling process provides a very useful tool to facilitate the distributed parameter model applied to more complex configurations. This paper proposes a piecewise continuous Timoshenko beam model, which was used for the dynamic analysis of a tapered beam‐like structure. Instead of the arbitrarily assumed shape functions used in a finite‐element analysis, the closed‐form solution of the Timoshenko beam equation was used. Application of the transfer matrix method was used to relate all elements as a whole. Using the corresponding boundary conditions and compatibility equations, a characteristic equation for the global tapered beam was produced and natural frequencies derived. The results from this analysis were compared to those obtained from a conventional finite‐element analysis. While compara...
TL;DR: In this paper, a preliminary design for a lunar outpost shelter is presented, and early enabling technologies are identified to facilitate an understanding of lunar shelter designs from an integrated system standpoint, and the design methodology is explored.
Abstract: The construction of an outpost on the Moon in which humans can live and work for periods exceeding six months will require special countermeasures to adapt to the hostile environment present at the lunar surface. Various inherent dangers such as meteoroids, galactic cosmic radiation, solar proton events, and large thermal extremes will drive the design configuration of the outpost. Other considerations such as lunar soil mechanics, equipment performance, mass delivery, risk, reliability, and tele-operability act strongly as constraints that shape and control the design alternatives. Analysis of these fundamental relationships have resulted in lunar civil engineering guidelines, which are unique to this domain, and these in turn have pointed to research areas needing further attention. A preliminary design is presented for a lunar outpost shelter. Additionally, the design methodology is explored, and early enabling technologies are identified to facilitate an understanding of lunar shelter designs from an integrated system standpoint. 17 refs.
TL;DR: In this article, the authors present an alternative based on using one of the fundamental means to move objects, namely ropes and cables, which can be used to lift and haul heavy loads for long distances with high levels of reliability.
Abstract: The establishment of an efficient transportation system is key to any human development on Earth or in space. Different technologies for transporting humans and goods have been developed, the diversity of which indicates that individual concepts have specific strengths and weaknesses. So far, transportation on the Moon has utilized a wheel-based vehicle, the lunar rover. Present concepts for transporting goods and people in a lunar base of the future are generally based on using wheels and traction. While such systems have many advantages for a variety of applications, the hauling of heavy goods will require the preparation of stable and trafficable roadways, a challenging and potentially expensive undertaking. This paper presents an alternative based on using one of the fundamental means to move objects, namely ropes and cables. Because of their inherent characteristics, ropes have been used to lift and haul heavy loads for long distances with high levels of reliability. This mature and constantly perfected technology, not well known in this car-oriented society, has been investigated for its use as a true alternative to the traditional wheel-based transportation systems. As will be shown, innovative applications of cable-based technologies may in effect provide many opportunities to leverage the differences between the Earth and the Moon for the purpose of creating efficient engineering products.
TL;DR: Doppler global velocimetry as discussed by the authors is a nonintrusive flow diagnostics instrumentation system, which is capable of making simultaneous, three-component velocity measurements within a selected measurement plane at video camera rates.
Abstract: A new nonintrusive flow diagnostics instrumentation system, Doppler global velocimetry, is presented. The system is capable of making simultaneous, three-component velocity measurements within a selected measurement plane at video camera rates. These velocity images can provide the researcher with spatial and temporal information about the flow field in a global sense. The investigation of a vortical flow above a 75-degree delta wing comparing standard three-component, fringe-type laser velocimetry measurements with Doppler global velocimetry measurements is presented.
TL;DR: In this paper, a preliminary design concept for a weldable joint for on-orbit assembly of large space structures is described, which was designed for ease of assembly, for structural efficiency, and to allow passage of fluid along the member through the joint.
Abstract: A preliminary design concept for a weldable joint for on-orbit assembly of large space structures is described. The joint was designed for ease of assembly, for structural efficiency, and to allow passage of fluid (for active cooling or other purposes) along the member through the joint. The members were assumed to consist of graphite/epoxy tubes which were bonded 2219-T87 aluminum alloy end fittings for welding on-orbit to nodes of the same alloy. A modified form of gas tungsten arc welding was assumed to be the welding process. The joint was designed for the thermal and structural loading associated with a 37 m diameter tetrahedral truss intended as an aerobrake for a mission to Mars. It was concluded that the assembly process could lock large loads into the truss members and that the assembly robot could be required to exert large forces while aligning pairs of nodes during assembly. It was also concluded that the connections between the composite struts and the aluminum fittings will be subjected to very high service stresses due to the effects of differential thermal expansion.
TL;DR: In this article, a refined higher order shear deformation theory for linear and geometrically nonlinear behavior of fiber-reinforced angle-ply composite and sandwich laminates is established.
Abstract: A refined higher order shear deformation theory for linear and geometrically nonlinear behavior of fiber‐reinforced angle‐ply composite and sandwich laminates is established. Laminae material is assumed to be linearly elastic, homogeneous and isotropic/orthotropic. The theory accounts for nonlinear quadratic variation of transverse shear strains through the thickness of the laminate and higher order terms in Green's strain vector in the sense of von Karman. A simple C0 finite‐element formulation of this theory is then presented with a total Lagrangian approach, and a nine node Lagrangian quadrilateral element is chosen with nine degrees of freedom per node. Numerical results are presented for linear and geometrically nonlinear analyses of multilayer angle‐ply composite and sandwich laminates. The theory is shown to predict displacements and stresses more accurately than first‐order shear deformation theory. The results are compared with available closed‐form and numerical solutions of plate theories and t...
TL;DR: In this paper, a thermoviscoplastic finite element method employing the Bodner-Partom constitutive model is used to investigate the response of simplified thermal-structural models to intense local heating.
Abstract: A thermoviscoplastic finite element method employing the Bodner-Partom constitutive model is used to investigate the response of simplified thermal-structural models to intense local heating. The computational method formulates the problem in rate form and advances the solution in time by numerical integration. The thermoviscoplastic response of simplified structures with prescribed temperatures is investigated. With rapid rises of temperature, the nickel alloy structures display initially higher yield stresses due to strain rate effects. As temperatures approach elevated values, yield stress and stiffness degrade rapidly and pronounced plastic deformation occurs.
TL;DR: In this article, high frequency Space Shuttle liftoff data are treated by autoregressive (AR) and auto-gressive-moving-average (ARMA) digital algorithms, which provide useful information on the spectral densities of the data.
Abstract: High frequency Space Shuttle liftoff data are treated by autoregressive (AR) and autoregressive-moving-average (ARMA) digital algorithms. These algorithms provide useful information on the spectral densities of the data. Further, they yield spectral models, which lend themeselves to incorporation into the concept of the random response spectrum. This concept yields a reasonably smooth power spectrum for the design of structural and mechanical systems when the available data bank is limited. Due to the nonstationary of the liftoff event, the pertinent data are split into three slices. Each of the slices is associated with a rather distinguished phase of the liftoff event, in which stationarity can be expected. The presented results are preliminary in nature; they aim to call attention to the availability of the discussed concepts and to the need to augment the Space Shuttle data bank as more flights are completed.
TL;DR: It is concluded that the speedup due to microtasking is improved substantially with an increase in the size of the problem.
Abstract: Mathematical optimization of space trusses in a vector/parallel processing environment is the subject of this paper. Parallel processing is achieved through microtasking and the use of the CRAY CFT77 compiler directives. Speed-up results are presented for four space-truss examples. It is concluded that the speedup due to microtasking is improved substantially with an increase in the size of the problem.
TL;DR: The Next Generation Space Telescope (NGST) as discussed by the authors uses active optics in the form of a steerable secondary mirror to compensate for the motion of the vehicle without necessitating the reorientation of the whole structure.
Abstract: The pointing control system of the Hubble Space Telescope (HST) represents the current state of the art for the precision control of a large spacecraft. The proposed Next Generation Space Telescope (NGST) will require an order-of-magnitude increase in pointing resolution over that of HST. The use of active optics in the form of a steerable secondary mirror has been proposed for NGST in order to satisfy these requirements. An introduction to some of the design concepts associated with the decision of the NGST, including a description of the proposed vehicle, a description of the pertinent design parameters, and a description of the types of disturbances to which it may be subjected, is given herein. A companion paper provides a description of a feasibility study conducted to evaluate the use of a control system for the implementation of “beam steering” to compensate for the motion of the vehicle without necessitating the reorientation of the whole structure.
TL;DR: In this article, a construction robot is proposed for accomplishing a variety of cleaning tasks in construction, such as spraying, cleaning, and finishing of surfaces, where a force sensor can be used not only to monitor the force acting at the contact points, but also to identify the uncertainties of the unstructured construction environment.
Abstract: Basic surface treatment tasks on construction sites that can be performed by robots include the spraying, cleaning, and finishing of surfaces. In the present paper, a construction robot is proposed for accomplishing a variety of cleaning tasks in construction. Specifically, the force‐control problem in cleaning a surface is studied. The paper shows that a force sensor can be used not only to monitor the force acting at the contact points, but also to identify the uncertainties of the unstructured construction environment. A different formulation for the external force is presented. With this formulation, the external force on the end‐effector is presented as a function of the contact force, contact torque, and constraint conditions, but not the actuated torque in the joint space. Therefore, the force‐control problem is simplified to compensate for the external force and to exert a desired force. One advantage of this approach is that the original PID position control loop of an industrial robot is retaine...
TL;DR: In this paper, the authors demonstrate the feasibility of satisfying the pointing stability requirements by sensing the guide-star position and steering the optical path of the telescope with the active secondary mirror, and a two-degree-of-freedom model is constructed to examine the behavior of the system subject to typical spacecraft excitations.
Abstract: The pointing control system of the Hubble Space Telescope (HST) represents the current state of the art for the precision control of a large spacecraft. The proposed Next Generation Space Telescope (NGST) will require an order‐of‐magnitude increase in pointing resolution over that of HST. The use of active optics in the form of a steerable secondary mirror has been proposed for NGST to satisfy these requirements. The primary motivation for this study was to demonstrate the feasibility of satisfying the pointing‐stability requirements by sensing the guide‐star position and steering the optical path of the telescope with the active secondary mirror. To study the requirements of the control system, a two‐degree‐of‐freedom model that retains the rigid‐body mode of the telescope as well as its first oscillatory mode was constructed. The corresponding optimal control law was developed and implemented in a discrete manner to examine the behavior of the system subject to typical spacecraft excitations.
TL;DR: In this article, a structural analysis is performed for the rim support of a pressurized off-axis paraboloidal membrane that serves as a space-based solar concentrator, and a properly designed tension element can reduce the maximum bending moment by more than a factor of 2.
Abstract: A structural analysis is performed for the rim support of a pressurized off‐axis paraboloidal membrane that serves as a space‐based solar concentrator. The function of the elliptical rim support is to take up the tensile forces created by the stretched membrane. This paper extends earlier load and deformation analyses to include the effect of a tension element added along the major axis of the ellipse. Such an element, in the form of a string or cable, restrains the tendency for increased ovality of the rim support under load without seriously interfering with the packaging and deployment of the device, at negligible added mass. The internal forces and moments and the deformations resulting from the membrane‐applied loads have been calculated. The analysis has shown that a properly designed tension element can reduce the maximum bending moment by more than a factor of 2. The deformations are reduced by more than a factor of 20.
TL;DR: In this paper, the authors investigate the damage containment capability of simple composite laminates of two graphite-epoxy systems: T300/5208 and AS/3501•6.
Abstract: Damage in composite laminates caused by low‐velocity impact may produce significant reductions in compressive strength. Lockheed conducted an experimental program to investigate the damage‐containment capability of simple composite laminates of two graphite‐epoxy systems: T300/5208 and AS/3501‐6. Four different lay‐ups, including two hybrid laminates, were investigated for each material system. Results are presented for comparison. Laminates with Kevlar layers, especially where the layer is on the surface of the laminate, demonstrate better impact resistance.
TL;DR: In this paper, an optimization procedure was developed to address the complex and conflicting requirements associated with the design of high-speed proprotor aircraft, where the key technical issues were maintenance of propulsive efficiency and aeroelastic stability in high speed cruise without deteriorating figure of merit in hover.
Abstract: An optimization procedure has been developed to address the complex and conflicting requirements associated with the design of high‐speed proprotor aircraft. Since the key technical issues are maintenance of propulsive efficiency and aeroelastic stability in high‐speed cruise without deteriorating figure of merit in hover, rotor aerodynamic performance and aeroelastic analysis are coupled, inside a closed loop, to the optimizer. The discipline couplings provide actual blade air‐loads, during hover and cruise, and also provide realistic blade designs. The propulsive efficiency in high‐speed cruise is used as the objective function. Constraints are also imposed on the aeroelastic stability in axial flight and the rotor figure of merit in hover. Both structural and planform design variables are used. The optimization procedure yields significant improvements in the aerodynamic characteristics of the rotor. Off‐design performance studies, conducted with the optimum blade, show overall design improvements.
TL;DR: In this article, an assessment of the outcome of lowering the internal pressure for a lunar structure is presented that accounts for human physiology, plant growth, mechanical equipment for gas circulation, structural aspects, leak rate, decompression, flammability, combustion, and economic issues.
Abstract: Design and construction of a structure on the Moon requires addressing a host of issues not encountered on Earth. Since there is no atmosphere on the Moon, a lunar structure must contain an artificial atmosphere. One critical design issue is the magnitude of the pressure of this atmosphere. Much of the current literature on the design of lunar structures assumes a pressure of 101.3 kPa (14.7 psi), corresponding to that at sea level on Earth, which is an order of magnitude larger than any other loading on the structure. An assessment of the outcome of lowering the internal pressure for a lunar structure is presented that accounts for human physiology, plant growth, mechanical equipment for gas circulation, structural aspects, leak rate, decompression, flammability, combustion, and economic issues. Options for the magnitude and content of an internal atmosphere for a lunar structure are given. Results clearly show that there is a great savings if the pressure is lowered by an amount that does not greatly affect the inhabitants physiology or safety.
TL;DR: Several algorithms for linear and nonlinear static analysis, as well as dynamic finite-element analysis, are examined, showing decomposition algorithms are shown to have a decided advantage over element-by-element preconditioned conjugate gradient algorithms.
Abstract: The finite-element method has proven to be an invaluable tool for analysis and design of complex, high-performance systems, such as those typically encountered in the aerospace or automotive industries. However, as the size of the finite-element models of such systems increases, analysis computation time using conventional computers can become prohibitively high. Parallel processing computers provide the means to overcome these computation-time limits, provided the algorithms used in the analysis can take advantage of multiple processors. The writers have examined several algorithms for linear and nonlinear static analysis, as well as dynamic finite-element analysis. The performance of these algorithms on an Alliant FX/80 parallel supercomputer has been investigated. For single load-case linear static analysis, the optimal solution algorithm is strongly problem dependent. For multiple load cases or nonlinear static analysis through a modified Newton-Raphson method, decomposition algorithms are shown to have a decided advantage over element-by-element preconditioned conjugate gradient algorithms. For eigenvalue/eigenvector analysis, the subspace iteration algorithm with a parallel decomposition is shown to achieve a relatively high parallel efficiency. 12 refs.
TL;DR: In this article, the development of design criteria for lunar structures must begin soon in order to establish adequate criteria, and some of the items that need consideration in such criteria are discussed.
Abstract: The development of design criteria for lunar structures must begin soon in order to establish adequate criteria. Some of the items that need consideration in such criteria are discussed. The categorization of the structures will provide designers with information on the purpose and level of complexity of the structure. Various construction materials and structure types that will be critical for the design of lunar structures, are considered. The environment of the moon and its possible effects on structures are presented and lead to the development of a few load cases that need to be considered in design. A probabilistic format for the criteria and design lifetimes are also discussed.
TL;DR: In this article, three types of ceramics (monolithic glasses, glass fibers, and glass-ceramics) produced from lunar simulants were used to understand and optimize the mechanical properties of these materials on the moon.
Abstract: A variety of products made from lunar resources will be required for a lunar ourpost. These products might be made by adapting existing processing techniques to the lunar environment, or by developing new techniques unique to the moon. In either case, processing techniques used on the moon will have to have a firm basis in basic principles of materials science and engineering, which can be used to understand the relationships between composition, processing, and properties of lunar-derived materials. These principles can also be used to optimize the properties of a product, once a more detailed knowledge of the lunar regolith is obtained. Using three types of ceramics (monolithic glasses, glass fibers, and glass-ceramics) produced from lunar simulants, we show that the application of materials science and engineering principles is useful in understanding and optimizing the mechanical properties of ceramics on the moon. We also demonstrate that changes in composition and/or processing can have a significant effect on the strength of these materials.