This research investigates the strength of composite lattice cylindrical and conical shells under axial compressive loads. The lattice structures are composed of circumferential and helical members, whose cross-sections are rectangular. The failure modes of both cylindrical and conical composite lattice shells are examined. New design constraints to achieve weight efficient structures with high failure loads is presented. Two main failure modes, general buckling as a shell and excessive shear stress in the members, are considered. The main emphasis is placed on the effects of geometrical configuration of the structure and the manufacturing process. Filament winding was used as the method of construction to automate the fabrication process and to minimize manufacturing costs. Numerical results are obtained by finite element analysis which are compared with experimental solutions. The motivation of the present work was to find the optimal winding pattern to which filament winding can be easily applied and still provide the highest strength to weight ratio. The final result of this research includes the numerical and experimental analysis of composite lattice cylindrical and conical shells via filament-winding. This work provides an understanding of composite lattice structures that will be useful in preliminary design of such structures.
In this research, an analysis technique is developed to model orthotropic composite toroids and optimize the fiber layup, accounting for the natural variation in thickness due to fiber stacking. The behavior of toroids is difficult to model using membrane shell theories due to a singularity in the strain-displacement relations occurring at the toroid crest that yields discontinuous displacement results. A technique is developed here where the constitutive properties of multilayered toroidal shells are determined using lamination theory, and the toroid strains and line loads are determined using finite element analysis. The toroid strains are rotated into the fiber directions, allowing the fiber stress and transverse stress distributions to be determined for each layer. The fiber layup is modified heuristically until an optimum is found. An optimum is reached when the maximum fiber and transverse direction stresses of each shell layer are equal, minimizing wasted fibers and excess weight. Test cases are analyzed to verify the accuracy of the finite element model and an example composite toroid with Kevlar/epoxy material properties is optimized. The analysis technique developed here can decrease the time and cost associated with the development of orthotropic toroidal pressure vessels, resulting in lighter, cheaper, and more optimal structures. The models developed can be expanded to include a steel liner and a broader range of fiber winding patterns.
This paper describes the development, implementation, and functionality of an interactive multimedia, online eBook designed to enhance the learning experience of students studying basic concepts in engineering thermodynamics. The eBook is case-based and covers the same material addressed in a typical engineering thermodynamics textbook. It is comprised of 42 case problems. Each case covers a specific concept in engineering thermodynamics and is presented in four parts: Case Introduction, Theory, Case Solution, and Simulation. The first three parts introduce a case to students, present required concepts to solve the case problem, and apply the concepts to solve the case problem. Graphics, diagrams, animations, sounds, and hypertext are used to present these materials in a rich interactive and dynamic method. The fourth part provides an opportunity for students to experience a simulation by modifying parameters of the case problem. The eBook is published through the Internet at www.eCourses.ou.edu and any instructor or engineering student can access the material without cost or conditions. The content can be used as a stand-alone tool for distance learning, a supplementary material for traditional classes, or a just-in-time learning tool for those who want to review a specific topic in engineering thermodynamics.
This paper proposes an engineering analysis environment that allows remote users to conduct three-dimensional finite element analysis collaboratively through the Internet. Java and Java 3D were chosen to develop the working prototype due to their advantages of platform-independence and network supporting. The environment allows remote users to work collaboratively on the same analysis object simultaneously. It reads the geometric data generated by the collaborative geometric modeling environment. The user can interact directly with the geometric model to perform operations, such as applying, editing, and deleting boundary conditions and forces. The operations are propagated among the team members, which creates a distributed shared environment. The commands are transmitted instead of the generated data, and thus the network traffic associated with the collaboration is minimized. Different from classical server/client models, the environment adopts a strategy in which the client-side application has full analysis capabilities while the server only manages communication. The essential features for distributed collaboration are discussed. The actual design consideration of the working prototype is presented to help illustrate the complexity and development of the collaborative environment. The environment is open to the public at www.vcity.ou.edu.
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