On the inversion of describing functions in nonlinear system analysis

Nonlinear mechanical vibrations are widely found in engineering structures. Traditional linear analysis methods are failing to meet the growing requirements of analysis accuracy. Because of the complexity of nonlinear system, there is no general method for nonlinear system analysis. Based on the describing function method, a polynomial inversion method may be used in nonlinear system identification. Using this method, the measured DF can be inverted into the form of force which has a clearer physical meaning and is easier to use for parameter fit. A MDOF system with two types of nonlinearities at the same location is studied to demonstrate this method

Aeroelastic two-level optimization for preliminary design of wing structures considering robust constraints

AbstractAn aeroelastic two-level optimization methodology for preliminary design of wing structures is presented, in which the parameters for structural layout and sizes are taken as design variables in the first-level optimization, and robust constraints in conjunction with conventional aeroelastic constraints are considered in the second-level optimization. A low-order panel method is used for aerodynamic analysis in the first-level optimization, and a high-order panel method is employed in the second-level optimization. It is concluded that the design of the abovementioned structural parameters of a wing can be improved using the present method with high efficiency. An improvement is seen in aeroelastic performance of the wing obtained with the present method when compared to the initial wing. Since these optimized structures are obtained after consideration of aerodynamic and structural uncertainties, they are well suited to encounter these uncertainties when they occur in reality

Genetic Marker Discovery for Gene Map Construction in the Pacific White Shrimp (Litopenaeus vannamei)

The Pacific White Shrimp (Litopenaeus vannamei) is important to the aquaculture industry and as a food source, but only limited genome information exists. The demand for specific shrimp broodstocks with high disease resistance and growth rate is increasing so the construction of a genetic map with easily usable genetic markers is a high priority. Using all the available public genomics information, a largescale discovery effort for single nucleotide polymorphism (SNP) genetic markers has produced the identification of 1,576 SNPs in 545 unique contigs. The genotyping work will be performed on the standardized Sequenom TM platform on a ready-to-use shrimp resource family, which will be used to develop a shrimp genetic map, as well as facilitate the mapping of quantitative trait locus (QTL) for growth rate and disease resistance

Candidate Gene Discovery for Retained Testicles in Dogs

Cryptorchidism, or retained testicles, is one of the most common congenital developmental defects in purebred dogs. DNA markers called single nucleotide polymorphisms (SNPs) are being used to investigate the associations between 21 candidate genes and cryptorchidism in Siberian huskies. We found the genes COL2A1, HOXA10, INSL3 and TIMP1 tended to be associated with cryptorchidism in Siberian huskies. The results will help to find the causative mutations in the future and will be useful in dog breeding programs to reduce the incidence of cryptorchidism

Efficient hybrid algorithms to solve mixed discrete-continuous optimization problems: A comparative study

Purpose: – In real world cases, it is common to encounter mixed discrete-continuous problems where some or all of the variables may take only discrete values. To solve these non-linear optimization problems, it is very time-consuming in use of finite element methods. The purpose of this paper is to study the efficiency of the proposed hybrid algorithms for the mixed discrete-continuous optimization, and compares it with the performance of Genetic Algorithms (GA). Design/methodology/approach: – In this paper, the enhanced multipoint approximation method (MAM) is utilized to reduce the original nonlinear optimization problem to a sequence of approximations. Then, the Sequential Quadratic Programming (SQP) technique is applied to find the continuous solution. Following that, the implementation of discrete capability into the MAM is developed to solve the mixed discrete-continuous optimization problems. Findings: – The efficiency and rate of convergence of the developed hybrid algorithms outperforming GA are examined by six detailed case studies in the ten-bar planar truss problem and the superiority of the Hooke-Jeeves assisted MAM algorithm over the other two hybrid algorithms and GAs is concluded. Originality/value: – The authors propose three efficient hybrid algorithms: the rounding-off, the coordinate search, and the Hooke-Jeeves search assisted MAMs, to solve nonlinear mixed discrete-continuous optimization problems. Implementations include the development of new procedures for sampling discrete points, the modification of the trust region adaptation strategy, and strategies for solving mix optimization problems. To improve the efficiency and effectiveness of metamodel construction, regressors φ defined in this paper can have the form in common with the empirical formulation of the problems in many engineering subjects