291 research outputs found
Anomalous response of an elastic-plastic structural model to impulsive loading
No full textTo simulate the response of a pin-ended elastic-plastic beam, a nonlinear structural model, i.e., a double-tier-spring model is analyzed to follow its deformation process after it is subjected to impulsive loading. After examining the first integral of the equation of motion, in the final elastic vibration, combined with other conditions, a region in the parameter's map is found in which the anomalous behavior (i.e., a negative-negative vibration) appears. This model is proved to be equivalent to the Shanley-type model adopted in previous analyses, but the present approach provides new results in a more complete way.SCI(E)EI0ARTICLE4868-8735
RECONSIDERATION AND SOME NEW RESULTS FOR THE CIRCULAR BEAM IMPACT PROBLEM.
No full textA quadrant circular beam subjected to radial impact in its own plane at its tip by a rigid mass analyzed previously by the authors is reexamined. By adding some new terms representing the effect of the travelling plastic hinge on the change in the direction of velocities, revised basic equations are constructed, and then solved numerically. Some numerical results are given, and attention is drawn to the distribution of energy dissipated, especially when the ratio of the tip mass to the beam mass is large.EI04221-228
Experimental investigation on the dynamic behaviour of aluminum foam sandwich plate under repeated impacts
No full textEngineering structures in marine and vehicle are frequently subjected to repeated impact loadings. The damage can't be neglected during the accumulation of deflection caused by the repeated impacts. In this paper, the dynamic behaviour of aluminum foam sandwich plate (AFSP) under repeated impacts was investigated by impact tests using INSTRON 9350 Drop Tower. The penetration behavior of front face and back face are compared. Meanwhile, the relationships between deflections of face sheets with impact number as well as the loading-unloading process during repeated impacts are analyzed. Results showed that, the permanent deflections of the front face and back face increased gradually, while the increments decreased until the crack occurred on the front face sheet. The damage modes of front face and back face were different. The impact number (Np) for penetration of front fact and residual number (Nr) for perforation of back face both decreased in exponential form with the increase of impact energy. It implied that the back face sheet still has residual load-carrying capacity even if the front face sheet became cracked.</p
PLASTIC HINGE POSITION IN A CIRCULAR CANTILEVER WHEN STRUCK NORMAL TO ITS PLANE BY A CONSTANT JET AT ITS TIP.
No full textA rigid/perfectly plastic circular cantilever, when struck normal to its plane by a jet of constant force at it tip, is analyzed to determine the relationship between the magnitude of the jet force and the location of the plastic collapse cross-section. Due to the interaction of bending and torsion in circumstances where beam inertia is important, two modes for a generalized plastic hinge may be found to form in the curved beam; the stability of these modes is examined. Some numerical results are given to facilitate understanding of related pipe-whip problems.EI03143-154
An Investigation on the Meanings of Xue Pan’s Role in The Dream of the Red Chamber
No full text在《紅樓夢》的研究中，薛蟠一向乏人注目，一般評論或將其與其他紈?子弟合而論述，斥責其惡行劣跡，未見其個人明顯特質，或視其為丑角，而忽略了作者對此一角色含藏了極大的巧思與苦心。 深受魏晉名士思想影響，崇尚自然的曹雪芹，在薛蟠的角色中寄寓了「率真」的思想，和賈寶玉一樣具有其類似性的意義，但是在「情」、「欲」的特質中，他和賈寶玉有不同的表現，如此在率真的角色意義上，又和賈寶玉形成陽陰的對比，暗喻倒轉中國傳統「氣性論」「貴陽而賤陰」的傳統。他除了和賈府諸紈?形成對照，更和薛寶釵的禮教典型分別有「相互對待的態度－率直現真與規謹內斂」、「內在性格的對顯－熱與冷」的對比。而其所具有的「情悟」經驗，正襯托出寶玉在塵世「情悟」歷程，故此一角色，其實具有極特殊的意義。In the studies of The Dream of the Red Chamber, Xue Pan has rarely been noticed. Some critics regard him as a playboy, blaming his misbehaviors and neglecting his unique characteristics, whereas others see him as a clown. Both views ignore the author's great intention behind this character. This paper suggests that as in the case of Jia Bao-yu, Cao Xue-qin also portrays Xue Pan in line with his idea of “naturalness” (shuaizhen). Accordingly the two characters occupy a similar place in the vision of the novel. However, in their attitudes toward affection and desire, Xue and Jia are very different. Cao depicts this difference by invoking the contrast between yang (embodied in Xue) and yin (embodied in Jia), thus presenting an implicit reversal of the traditional qi-based doctrine of human nature which praises yang over yin. Apart from serving as a contrast to other playboys in the novel, Xue Pan also stands in sharp contrast to Xue Bao-chai: while the former is marked by his genuineness toward other people and his warn temperament, the latter is noted for her conformism and cool temperament. Finally, Xue Pan's enlightening experience in the realm of affections (qingwu) offers great illuminations on the unfolding processes of Jia Bao-yu's similar enlightenment. This suggests that Xue indeed assumes a highly significant role in The Dream of the Red Chamber
Relationship Between Financial Aid Policies, Practices and Procedures at Texas Public Colleges and Universities
No full textThe economic success of the state of Texas is dependent upon future market participants having access to higher education. The ability of Texas citizens to access higher education is dependent upon access to financial aid resources to pay for higher education. Much is known about the impact of particular financial aid outcomes on access and persistence in higher education. However, very little is known about whether institutional financial aid processes (i.e. the policies, practices and procedures used by financial aid administrators) affect financial aid outcomes for students. This is especially true in Texas. The study that follows was a retrospective study related to financial aid and student access to higher education. Specifically, the research examined the relationship between financial aid processes (policies, practices and procedures)and outcomes (financial aid awards) at Texas public institutions of higher education. This study explored (1) whether there were definable patterns in financial aid outcomes for students at Texas public institutions; (2) whether these patterns varied by institutional type; (3) whether there were patterns in the financial processes used by financial aid administrators at these institutions; (4) whether these patterns varied by institutional type; and (5) whether there were definable relationships between the financial aid outcomes and the processes used by financial aid administrators at Texas public institutions. To investigate these questions, the researcher (1) extracted and analyzed financial aid award data obtained from the statewide Financial Aid Database System (FADS) maintained by the Texas Higher Education Coordinating Board; (2) surveyed financial aid administrators at Texas public colleges and universities regarding institutional financial aid processes (survey derived from the 2001 Survey of Undergraduate Financial Aid Policies, Practices and Procedures (SUFAPP) developed by the National Association of Student Financial Aid Administrators); and (3) identified financial aid award outcomes and determined from the survey database whether definable patterns of institutional financial aid processes existed. This research was significant as it examined relationships between processes (institutional policies, practices and procedures) and outcomes (financial aid awards to students) and provided structural models illustrating those relationships which (1) were state specific and (2) would be useful to financial aid administrators in evaluating the impact of their processes on outcomes for their students.financial,aid,financing,higher,education,college,undergraduate,survey,policies,practices,procedures,university,universities,public,institutions,study
Characterization and Testing of a MEMS-Vaporizing Liquid Microthruster for Small Satellite Propulsion
No full textActive propulsion is required in order to further develop the capabilities of small satellites like CubeSats. At TU Delft a micropropulsion system is being developed based on a Vaporizing Liquid Microthruster (VLM), using liquid water as propellant. This research presents the manufacturing, characterization and testing of an existing VLM-design. It focuses on the thruster component of the propulsion system, which is called the MEMS-VLM. The breadboard model consists of an inlet module, multiple heating chamber modules and a nozzle, integrally manufactured using MEMS-technology. The heating chamber modules consist of flow channels etched in silicon, of which the walls support silicon carbide heaters. These heaters are suspended in the center of the cross-section. The nozzle is a two-dimensional convergent-divergent duct. Characterization and testing of the MEMS-VLMis done in a bottom-up approach. First, the geometry and electrical properties of the flow channels and heaters are characterized, after which the performance of the heating chamber and the nozzle are independently studied by models and experiments. In order to facilitate manufacturing, minor changes are implemented to the design of the nozzle, electrical interface and fluidic interface. With these changes, successful manufacturing of theMEMS-VLM is achieved. Microscope images show significant but acceptable deviations between design dimensions and manufacturing results. Furthermore, resistance measurements of the heaters indicate partial mechanical failures in 20 out of 154 measured heaters. The thermal behavior of the heating chamber is studied by means of analytical models for conduction and radiation and a one-dimensional steady state model for convection. The conduction study shows that the chamber wall temperature is homogeneous, while the suspended heaters formhot spots. The convection model is used to study whether sufficient heat transfer can be expected to fully vaporize the propellant flow. It is found that at a chamber wall temperature as little as 10 K above the boiling point, full vaporization can be expected. An experimental setup is made to test the heating chamber, ultimately attempting to validate the design and the performance models. The ability to power the heaters with constant current and measure the mass flow, pressure and dissipated power is demonstrated. Furthermore, amethod to determine the local chamber temperature based on the resistance of the heaters is presented. However, current leaks and partial mechanical failures are detected in the heaters during tests with nitrogen gas, which compromise the ability to operate with liquid water. Hence, full validation of the heating chamber models could not be achieved. With respect to future designs it is recommended to change to metallic heaters, which are placed outside the chamber. The silicon chamber wall then serves as a heat exchanger. It is furthermore recommended to change the capping wafer material to glass, so that the boiling process can be studied optically. A second experimental campaign is done to determine the performance of the nozzle, which is described by the discharge factor CD, the Isp-efficiency ´I sp and the thrust coefficient CF . Nozzle performance tests are carried out in vacuum, using gaseous nitrogen as propellant. The pressure is adapted in order to match the Reynolds number in the nozzle throat to the designed operating conditions. At a measurement Reynolds numbers of Rem ¼ 1400 the performance quality factors are found to be CD ¼ 0.68§0.06 (discharge factor), ´I sp ¼ 0.3§0.05 (Isp-efficiency) and CF ¼ 0.33§0.06 (thrust coefficient). The poor performance is primarily explained by excessive friction and rarefaction losses in the divergent section of the nozzle and are expected to improve when increasing the Reynolds number and when decreasing the expansion ratio. Design validation of the MEMS-VLM could not be achieved, as on various aspects the design is rejected. Nonetheless, the experimental approach has been successful in revealing critical design recommendations and demonstrating the ability to test a microthruster, improving the understanding and advancing the development of micropropulsion at TU Delft.Aerospace EngineeringSpace Engineerin
- …
