Optimal Equivalent Model Research Articles

An optimised equivalent modelling approach for LMRP/BOPs in the global dynamic analysis of deepwater risers

ABSTRACT Lower marine riser package/blowout preventers (LMRP/BOPs) play a crucial role in transferring the dynamic loads from the slim drilling risers to the subsea wellhead (SW). Generally, the LMRP/BOPs are usually modelled as the combination of pipe and mass elements in the finite element analysis. In this paper, an optimised equivalent modelling approach for LMRP/BOPs was proposed to improve the calculation accuracy of dynamic cyclic bending moment of SW. In the proposed methodology, the equivalent model of LMRP/BOPs was established based on the deformation analysis of the local fine model of LMRP/BOPs. Using the Newton–Raphson method, the equivalent model was optimised to acquire the optimal equivalent model of LMRP/BOPs. A case study indicated the modelling accuracy of LMRP/BOPs was improved by 14.6% compared to the conventional approach by using the proposed approach, thus the calculation accuracy of the dynamic cyclic bending moment of SW was improved accordingly.

A rapid quantification method for the screening indicator for β-thalassemia with near-infrared spectroscopy

Near-infrared (NIR) spectroscopy combined with chemometrics was applied to rapidly analyse haemoglobin A2 (HbA2) for β-thalassemia screening in human haemolysate samples. The relative content indicator HbA2 was indirectly quantified by simultaneous analysis of two absolute content indicators (Hb and Hb∙HbA2). According to the comprehensive prediction effect of the multiple partitioning of calibration and prediction sets, the parameters were optimized to achieve modelling stability, and the preferred models were validated using the samples not involved in modelling. Savitzky-Golay smoothing was firstly used for the spectral pretreatment. The absorbance optimization partial least squares (AO-PLS) was used to eliminate high-absorption wave-bands appropriately. The equidistant combination PLS (EC-PLS) was further used to optimize wavelength models. The selected optimal models were I=856nm, N=16, G=1 and F=6 for Hb and I=988nm, N=12, G=2 and F=5 for Hb∙HbA2. Through independent validation, the root-mean-square errors and correlation coefficients for prediction (RMSEP, RP) were 3.50gL−1 and 0.977 for Hb and 0.38gL−1 and 0.917 for Hb∙HbA2, respectively. The predicted values of relative percentage HbA2 were further calculated, and the calculated RMSEP and RP were 0.31% and 0.965, respectively. The sensitivity and specificity for β-thalassemia both reached 100%. Therefore, the prediction of HbA2 achieved high accuracy for distinguishing β-thalassemia. The local optimal models for single parameter and the optimal equivalent model sets were proposed, providing more models to match possible constraints in practical applications. The NIR analysis method for the screening indicator of β-thalassemia was successfully established. The proposed method was rapid, simple and promising for thalassemia screening in a large population.

Packaging Parameters Analysis for the Fatigue Reliability of Stacked Chip Ball Grid Array by Using the Optimal Equivalent Solder Balls

A global/local method with the modified sub‐modeling approach of the two‐parametric optimal equivalent volume solder balls is introduced to predict the deformation and reliability of the package. The equivalent solder balls as exhibit in this method can obviously reduce the required elements/nodes quantities to enhance computing efficiency. A package model of wire‐bonded stacked chip ball grid array under cyclic thermal loading is used as a test vehicle to verify the influences of design factors by fatigue life indicator. Comparing the proposed method with the global fine mesh model, it is found that the difference in the accumulated strain energy density is merely 5.77%, but the optimal equivalent model has highly saved 90% finite element analysis required elements, which means the adopted method can effectively replace the global fine mesh model because both results are in accordance with each other. Using design of experiments to efficiently verify each factor influence with their cross‐coupling effects, this paper adopts two kinds of response surface methods that confirm the fatigue life of the proposed approach can be improved by as much as 123.7% for the dual response surface method and 126.3% for the mixed response surface method when comparing with the baseline model. In addition, the optimization of generic algorithm for both response surface methods is demonstrated in this study. From the reviews of factor coupling effects, it is concluded that the response surface method is eligible to achieve the optimum design for package reliability improving. Copyright © 2013 John Wiley & Sons, Ltd.

A simplified model for coupled horizontal and rocking vibrations of embedded foundations

For a foundation–soil system undergoing coupled horizontal and rocking motions, a simplified mass–spring–dashpot model is proposed to simulate unbounded soil. Through three equivalent criteria, a group of equivalent models are established for the foundation–soil system. An optimal equivalent model is then determined to represent the best simplified model. The method proposed to develop the optimal equivalent model may be more efficient than lengthy optimization techniques used by most existing models. The dynamic responses of the foundation–soil system using the optimal equivalent model are compared with those obtained by the half-space theory and by the existing lumped-parameter models. A validation of the proposed model in time domain is also provided. Since the coupling of horizontal and rocking motions is adequately considered, the optimal equivalent model is found to have more accurate results than most existing models. It is also found that the rotational responses of embedded foundations subjected to a harmonic rocking moment may be significantly underestimated without considering the coupling behavior. This proposed method may be effectively applied to practical engineering problems.

Simple Models of Foundation-Soil Interactions

This study aims to develop a series of simplified mass-spring-dashpot model to simulate unbounded soil for a foundation-soil system subjected to vertical, horizontal, rocking and torsional motions. A group of equivalent models are established by using three equivalent criteria and the coupling of horizontal and rocking motions is also considered. An optimal equivalent model is then determined to represent the best simplified model. The dynamic responses of the foundation-soil system using the optimal equivalent model are compared with those obtained by the half-space theory and by the lumped-parameter models. Since the coupling of horizontal and rocking motions is adequately considered, the optimal equivalent model is found to have more accurate results than most existing models. Moreover, the proposed model is also applied to a time-history analysis for a building-soil interaction system subjected to horizontal excitations. This proposed method may be effectively applicable to practical soil-structure interaction problems.

진피세포의 조성이 인공피부의 기저막과 표피형성에 미치는 영향

최근 유럽연합에서는 동물실험을 통하여 검증된 성분을 함유하고 있는 화장품에 대하여 판매를 금지할 것을 선언하였다. 그리하여 동물실험을 대체할 동물실험 대체모델의 개발이 필요해졌다. 인공피부는 화장품, 의약품 및 의료기기의 안전 테스트에 있어서 아주 중요한 시스템이다. 본 연구에서는 기저막과 표피를 가지고 있는 최적의 인공피부를 만들기 위한 시도를 하였다. 이러한 목적으로 중간엽줄기세표(MSCs, mesenchymal stem cells)와 지방전구세포를 진피세포인 섬유모세포와 혼합하여 진피대체물을 만들었다. 기저막과 표피의 형성은 면역조직화학 염색(immunohistochemical stains)을 통하여 확인하였다. 여러 가지 모델 중에서, 중간엽줄기세포를 혼합한 모델에서 표피의 두께가 제일 두꺼웠으며 또한 PCNA와 involucrin의 분포가 실제 사람피부와 비슷하였다. 결론적으로, 본 연구의 결과는 진피대체물에 중간엽줄기세포를 혼합한 인공피부가 동물실험 대체모델로 개발될 수 있다는 점을 제시한다. European Union prohibited the marketing of cosmetic products containing constituents that have been examined through animal experiments. Thus, non-animal test models are needed to replace animal experiments. The reconstructed skin models are important as a test system for cosmetic, pharmaceutical, and medical device safety testing. In the present study, we tried to develop an optimal skin equivalent model containing basement membrane and epidermis. For this purpose, we used mesenchymal stem cells (MSCs) and/or preadipocytes as well as fibroblasts as the dermal matrix cells. The formation of basement membrane and epidermis was verified by immunohistochemical stains. Among various models, the epidermis was thickest when MSCs were used in the dermal matrix. Furthermore, PCNA and involucrin distribution showed that dermal matrix with MSCs resembled human skin. Therefore, skin equivalents with MSCs could be developed as a non-animal test model to replace animal experiments.

Electrochemical impedance spectroscopy characterization of mercaptopropionic acid capped ZnS nanocrystal based bioelectrode for the detection of the cardiac biomarker—myoglobin

3-Mercaptopropionic acid (MPA) capped ZnS nanocrystals (ZnS(MPA)) are covalently attached to a self assembled monolayer (SAM) of 3-aminopropyltriethoxysilane (APTES) on an indium-tin-oxide (ITO) coated glass plate. The protein antibody, anti-myoglobin (Ab-Mb), is covalently linked to free carboxyl groups present on ZnS(MPA) nanocrystals via carbodiimide coupling reaction to form a bioelectrode (Ab-Mb(BSA)/ZnS(MPA)/APTES/ITO-glass). This bioelectrode has been characterized using atomic force microscopy (AFM), contact angle measurements, cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The optimal equivalent circuit model that matches the impedimetric responses of the bioelectrode describes three distinct regions: the electrolyte solution resistance (Rs), the double layer capacitance (Cdl) and the specific charge transfer resistance (Ret). The EIS measurements revealed that the Ret increases considerably with no significant change in Cdl after immunoreaction with protein specific antigen myoglobin, Ag-Mb, so that the prepared bioelectrode can be used for the detection of Ag-Mb. The bioelectrode exhibits an electrochemical impedance response to Ag-Mb, in a linear range from 10ng to 1μgmL−1 phosphate buffer solution (pH 7.4) with a Ret sensitivity of 117.36Ωcm2 per decade.

Electrochemical impedance spectroscopy characterization of nanoporous alumina dengue virus biosensor

The Faradaic electrochemical impedance technique is employed to characterize the impedance change of a nanoporous alumina biosensor in response towards the specific binding of dengue serotype 2 (Denv2) viral particles to its serotype 2-specific immunoglobulin G antibody within the thin alumina layer. The optimal equivalent circuit model that matches the impedimetric responses of the sensor describes three distinct regions: the electrolyte solution (Rs), the porous alumina channels (including biomaterials) (Q1, R1) and the conductive electrode substrate layer (Q2, R2). Both channel resistance R1 and capacitance Q1 change in response to the increase of the Denv2 virus concentration. A linear relationship between R1 and Denv2 concentration from 1 to 900 plaque forming unit per mL (pfu mL−1) can be derived using Langmuir–Freundlich isotherm model. At 1pfu mL−1 Denv2 concentration, R1 can be distinguished from that of the cell culture control sample. Moreover, Q1 doubles when Denv2 is added but remains unchanged in the presence of two other non-specific viruses — West Nile virus and Chikungunya virus indicates biosensor specificity can be quantitatively measured using channel capacitance.

A response-based simplified model for vertical vibrations of embedded foundations

A simplified damped oscillator model is proposed to simulate unbounded soil for the vertical vibration analysis of rigid embedded foundations. Based on the dynamic responses of a foundation–soil system, an optimal equivalent model is determined as the best simplified model. Magnification responses of a foundation–soil system simulated by the optimal equivalent model are well consistent with those obtained by the half-space theory and by a widely used computer program even as embedment depth or vibrating mass increases. The optimal equivalent model utilizing only three parameters can result in responses as accurate as the existing models, which use more parameters. This proposed method uses much simpler procedure than optimization techniques used by most existing discrete models. This proposed method may also be easily and accurately applied to practical soil–structure interaction analysis.

Non‐iterative equivalent linearization of inelastic SDOF systems for earthquakes in Japan and California

AbstractThe seismic performance of existing structures can be assessed based on nonlinear static procedures, such as the Capacity Spectrum Method. This method essentially approximates peak responses of an inelastic single‐degree‐of‐freedom (SDOF) system using peak responses of an equivalent linear SDOF model. In this study, the equivalent linear models of inelastic SDOF systems are developed based on the constant strength approach, which does not require iteration for assessing the seismic performance of existing structures. To investigate the effects of earthquake type and seismic region on the equivalent linear models, four ground‐motion data sets—Japanese crustal/interface/inslab records and California crustal records—are compiled and used for nonlinear dynamic analysis. The analysis results indicate that: (1) the optimal equivalent linear model parameters (i.e. equivalent vibration period ratio and damping ratio) decrease with the natural vibration period, whereas they increase with the strength reduction factor; (2) the impacts of earthquake type and seismic region on the equivalent linear model parameters are not significant except for short vibration periods; and (3) the degradation and pinching effects affect the equivalent linear model parameters. We develop prediction equations for the optimal equivalent linear model parameters based on nonlinear least‐squares fitting, which improve and extend the current nonlinear static procedure for existing structures with degradation and pinching behavior. Copyright © 2010 John Wiley & Sons, Ltd.

Simplified model for torsional foundation vibrations

A simplified model is presented to simulate unbounded soil for torsional foundation vibration problems. Based on the criterion of equivalent displacement response, a group of equivalent models are developed for a foundation-soil system. An optimal equivalent model is then determined to represent the best simplified model. The parameters of the optimal equivalent model may be obtained by a much easier and more efficient method than lengthy optimization techniques used by most existing lumped-parameter models. The dynamic torsional responses of the foundation-soil system using the optimal equivalent models are very consistent with those obtained by the half-space theory and by the existing models. With fewer parameters, the optimal equivalent model is also found to be as accurate as most existing models. This proposed method may be effectively applied to practical torsionally vibrating problems involving soil–structure interaction.

Simplified Model for Vertical Vibrations of Surface Foundations

A simplified model for simulating unbounded soil in the vertical vibration problems of surface foundations is presented. The model comprises a mass, a spring, and a dashpot without any internal degree of freedom. By considering three equivalent criteria, a group of equivalent models is established for a foundation-soil system. An optimal equivalent model is then determined to represent the best simplified model. The parameters of the optimal equivalent model may be obtained by a much easier and more direct method than the optimization technique used by existing models. The dynamic responses of the foundation-soil system using the optimal equivalent models are also compared with those obtained by the half-space theory and by the existing lumped-parameter models. The optimal equivalent model is found to have more accurate results than existing discrete models especially for responses at resonant frequencies. This proposed method may be easily applied to practical problems involving soil-structure interaction such as machine foundation vibration and seismic structural analysis.