Identification of nonlinear vibrating structures: Part I -- Formulation

A self-starting multistage, time-domain procedure is presented for the identification of nonlinear, multi-degree-of-freedom systems undergoing free oscillations or subjected to arbitrary direct force excitations and/or nonuniform support motions. Recursive least-squares parameter estimation methods combined with nonparametric identification techniques are used to represent, with sufficient accuracy, the identified system in a form that allows the convenient prediction of its transient response under excitations that differ from the test signals. The utility of this procedure is demonstrated in a companion paper

Identification of nonlinear vibrating structures: Part II -- Applications

A time-domain procedure for the identification of nonlinear vibrating structures, presented in a companion paper, is applied to a "calibration" problem which incorporates realistic test situations and nonlinear structural characteristics widely encountered in the applied mechanics field. The "data" set is analyzed to develop suitable, approximate nonlinear system representations. Subsequently, a "validation" test is conducted to demonstrate the range of validity of the method under discussion. It is shown that the procedure furnishes a convenient means for constructing reduced-order nonlinear nonparametric mathematical models of reasonably high fidelity in regard to reproducing the response of the test article under dynamic loads that differ from the identification test loads

Competing Interactions among Supramolecular Structures on Surfaces

A simple model was constructed to describe the polar ordering of non-centrosymmetric supramolecular aggregates formed by self assembling triblock rodcoil polymers. The aggregates are modeled as dipoles in a lattice with an Ising-like penalty associated with reversing the orientation of nearest neighbor dipoles. The choice of the potentials is based on experimental results and structural features of the supramolecular objects. For films of finite thickness, we find a periodic structure along an arbitrary direction perpendicular to the substrate normal, where the repeat unit is composed of two equal width domains with dipole up and dipole down configuration. When a short range interaction between the surface and the dipoles is included the balance between the up and down dipole domains is broken. Our results suggest that due to surface effects, films of finite thickness have a none zero macroscopic polarization, and that the polarization per unit volume appears to be a function of film thickness.Comment: 3 pages, 3 eps figure

Evaluation of on-line pulse control for vibration suppression in flexible spacecraft

A numerical simulation was performed, by means of a large-scale finite element code capable of handling large deformations and/or nonlinear behavior, to investigate the suitability of the nonlinear pulse-control algorithm to suppress the vibrations induced in the Spacecraft Control Laboratory Experiment (SCOLE) components under realistic maneuvers. Among the topics investigated were the effects of various control parameters on the efficiency and robustness of the vibration control algorithm. Advanced nonlinear control techniques were applied to an idealized model of some of the SCOLE components to develop an efficient algorithm to determine the optimal locations of point actuators, considering the hardware on the SCOLE project as distributed in nature. The control was obtained from a quadratic optimization criterion, given in terms of the state variables of the distributed system. An experimental investigation was performed on a model flexible structure resembling the essential features of the SCOLE components, and electrodynamic and electrohydraulic actuators were used to investigate the applicability of the control algorithm with such devices in addition to mass-ejection pulse generators using compressed air

ANALISIS KETERKAITAN RAGAM TEKNIK UKIR TATAH TEMBAGA TERHADAP KEMUNGKINAN BENTUK YANG DIHASILKAN DALAM PERTIMBANGAN DESAIN

AbstractCopper handicrafts made by craftsmen in Tumang village, Boyolali Regency, are well known in various cities on Java. it is inseparable from the process and manufacturing techniques that continue to be maintained, that is forging and carving techniques.The design results of the craft products made tends to use traditional design style, and require a long time for the making. The purpose of this research is to produce a new design form with a simpler carving pattern and allow for a faster production process time. The simplification of the production process allows the making of products with more quantity. The main research method used is direct observation of the process ofmaking carvings by metal carving experts at craft centers. The results of this new design form can accelerate the production process because it can be made without going through a forging process.AbstrakKerajinan tembaga yang dibuat oleh para pengrajin di desa Tumang kabupaten Boyolali sudah cukup dikenal di berbagai kota di pulau Jawa. Hal tersebut tidak lepas dari proses dan teknik pembuatannya yang terus dipertahankan, yaitu teknik tempa dan teknik ukir. Hasil bentuk desain dari produk kerajinan yang dibuat lebih cenderung menggunakan gaya desain tradisional, dan membutuhkan waktu yang cukup lama dalam pembuatannya. Tujuan dari penelitian ini adalah menghasilkan bentuk design baru dengan bentuk pola ukir yang lebih sederhana dan memungkinkan waktu proses produksi yang lebih cepat. Penyederhanaan proses produksi memungkinkan menghasilkan produk dengan kuantitas lebih banyak. Metode utama penelitian yang digunakan adalah observasi langsung terhadap proses pembuatan ukiran oleh ahli ukir logam di sentra kerajinan. Hasil bentuk desain baru inimempercepat proses produksi karena dapat dibuat tanpa melalui proses tempa

The Effectiveness of Using Response- based Strategy in Enhancing Students' Levels of Engagement, Motivation, Problem-solving Skills, and Critical Thinking

The study analyzed the efficacy of response-based teaching tactics in enhancing students' levels of engagement, motivation, problem-solving skills, and critical thinking by utilizing data and a mixed-methods research methodology. There was a total of 30 students in the sample, 15 of whom were assigned to each of the two groups (response-based techniques and conventional instruction). Researchers also looked at how factors like teacher background and technological sophistication influenced the success of these techniques in the classroom. The students participated in a pre-test to define a starting point and a post-test to evaluate growth throughout the study. The efficacy of the response-based tactics was determined by statistical analysis using t-tests, ANOVA, and Cohen's d. Teacher and student demographics, as well as information about classroom practises and the usage of technology, were gathered through an online survey. Student perceptions of their own problem-solving and critical-thinking skills, as well as their level of classroom participation and motivation, were also probed in the survey. Both quantitative and qualitative approaches were employed to gather and analyze the data for this study. In terms of improving students' interest, motivation, problem-solving skills, and critical thinking, the results demonstrated that response-based teaching tactics were superior to more conventional methods. However, it was discovered that teacher traits and technology use influenced the efficacy of the response-based tactics. The findings also suggested that response-based teaching tactics might be useful in online classrooms, with the caveat that the success of such strategies would depend on the specific nature of the strategies employed and the specific features of the technology tools used. Conclusions from the study indicate that using response-based teaching methodologies can improve students' interest, motivation, problem-solving skills, and critical-thinking capacities. This study's methodology and statistical methods can serve as a foundation for other studies in this field. Keywords: response-based teaching strategies, traditional teaching approaches, student engagement, student motivation, problem-solving skills, critical thinking abilities DOI: 10.7176/JEP/14-27-10 Publication date:September 30th 2023

Institutional Change in the Syrian Rangelands

Summaries During the past forty years, the Syrian rangelands have been the focal point of government interventions. These had four major components: assertion of state ownership over rangelands, settlement and transformation of herders into farmers, formal reorganization of the Bedouin population into range improvement and sheep husbandry cooperatives, and development of rangeland reserves. Each of these interventions has had many implications for livestock production, on rangeland management as well as on the livelihood strategies of herding households and communities. In 1994, the Syrian government took a major decision by banning cultivation in rangelands and committed itself to enhancing livestock production through better conservation, improvement and management of rangeland resources. The ban on cultivation, which is transforming sheep production systems and livelihood strategies of herding communities, is forcing herding communities to devise new strategies for overcoming their production constraints. Under present range conditions, it is clear that herding communities cannot stay there all year round and have, necessarily, to seek alternative feed resources. This article asks the questions: are herding communities likely to revert to old Bedouin livestock production systems based on trans?humance and reciprocity or will they opt to use more individualistic and market?based feed resources? Are feed access strategies differentiated by livestock ownership? How will these changes affect their production systems and livelihood strategies

System Identification and Seismic Performance Evaluation of Earth Dams

A system identification technique is developed to provide dynamic properties of earth dams from their seismic records. The technique is utilized to assess the capabilities and limitation of analytical models in terms of dynamic nonlinear constitutive relationships as well as damping. The technique is based on the least square method using Gaussian hypothesis. Earth dams are modeled as a three-dimensional nonhomogeneous visco-elasto-plastic soil structure. The forward problem is solved using a Galerkin-Ritz formulation in which the solution is expanded using basis function, which is selected to be the eigenmodes. The spatial variation of the excitation is considered by using global shape functions defined on the boundary domain to interpolate the input motion on the dam boundaries using recorded motion at discrete locations. The constitutive model is used to accommodate the nonlinear path dependent behavior of the dam material as well as coupling between different constituent of the soil mixture. The model is implemented using Druker-Prager multi-yield surface model and linear Kelvin-Voigt model. Application to instrumented dams, in recent earthquake, showed significant match between the recorded response and the optimal estimated response