Random Response of a Strongly Nonlinear Oscillator with Internal and External Excitations

A second order oscillator with nonlinear restoring force and nonlinear damping is considered: it is subject to both external and internal (parametric) excitations of Gaussian white noise type. The nonlinearities are chosen in such a way that the associated Fokker-Planck-Kolmogorov equation is solvable in the steady state. Different choices of some system parameters give rise to different and interesting shapes of the joint probability density function of the response, which in some cases appears to be multimodal. The problem of the determination of the power spectral density of the response is also addressed by using the true statistical linearization method.

Appropriate solid waste management system in Quelimane (Mozambique):study and design of a small-scale center for plastic sorting with wastewater treatment

Appropriate solid waste management(SWM)strategies are necessary to avoid severe environmental and sanitary impacts,especially in low-income countries.Such strategies are most likely to succeed whether implementing actors are supported by scientific research.In this paper,the results of a collaboration between local authorities and researchers are presented and discussed that are the assessment of waste generation in the city of Quelimane(Mozambique),integrating existing and field-collected data and the design of a small-scale center for plastic sorting to complement the SWM system of the city.The center is expected to receive about 0.3-0.4 t/day of plastic waste(5%-7%of the overall amount of plastic waste daily produced in Quelimane).As long-term sustainability represents a typical issue,simplicity of operation was a leading principle in the design of the center;moreover,the design included a treatment plant(WWTP)for generated wastewater,whose management is usually neglected in such interventions.Among others,natural wastewater treatment(constructed wetlands)has been chosen for its affordability.Noteworthy,the so-conceived WWTP appears as a novelty in the scientific literature associated with small-scale plastic sorting plants.The system is designed to treat an average flow of 6 m3/day and consisted of a septic tank followed by a subsurface flow constructed wetland.Overall,the COD(chemical oxygen demand)and TSS(total suspended solids)removal higher than 80%and 90%were estimated,respectively.Based on this work,both the center and the WWTP were successfully realized,which are waiting to become operational.In the authors’opinion,the implemented procedure could become a reference for broader investigations and surveys.