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Journal of Rock Mechanics and Geotechnical Engineering 2022年第3期14卷 714-730页

作者： Akshay Kumar Gaurav tiwari Department of Civil Engineering IIT KanpurIndia

An efficient resampling reliability approach was developed to consider the effect of statistical uncertainties in input properties arising due to insufficient data when estimating the reliability of rock slopes and tunnels.This approach considers the effect of uncertainties in both distribution parameters(mean and standard deviation)and types of input properties.Further,the approach was generalized to make it capable of analyzing complex problems with explicit/implicit performance functions(PFs),single/multiple PFs,and correlated/non-correlated input properties.It couples resampling statistical tool,i.***.jackknife,with advanced reliability tools like Latin hypercube sampling(LHS),Sobol’s global sensitivity,moving least square-response surface method(MLS-RSM),and Nataf’s transformation.The developed approach was demonstrated for four cases encompassing different types.Results were compared with a recently developed bootstrap-based resampling reliability approach.The results show that the approach is accurate and significantly efficient compared with the bootstrap-based approach.The proposed approach reflects the effect of statistical uncertainties of input properties by estimating distributions/confidence intervals of reliability index/probability of failure(s)instead of their fixed-point estimates.Further,sufficiently accurate results were obtained by considering uncertainties in distribution parameters only and ignoring those in distribution types.

关键词： Statistical uncertainty Resampling reliability Moving least square response surface(MLSRSM) Sobol’s global sensitivity Correlation coefficient

Reliability assessment of deep excavations in spatially random cohesion weakening friction strengthening massive rocks:Application to nuclear repositories

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Underground Space 2023年第6期13卷 48-73页

作者： Akshay Kumar Gaurav tiwari Department of Civil Engineering Indian Institute of Technology KanpurKanpurUttar Pradesh 208016India

An augmented methodology is developed to estimate the reliability of deep excavations along spatially variable massive rock masses using the cohesion weakening friction strengthening(CWFS)model.Sensitive parameters of the CWFS model were initially identified using Sobol’s global sensitivity analysis based on their influence on the displacements and excavation damage zone around excavations.The probability of failure was estimated by performing Mont–Carlo Simulations on random finite difference models of excavations generated via MATLAB-FLAC2D coupling,considering the spatial variation of these sensitive parameters.Spatial variation was modeled by generating anisotropic random fields of sensitive CWFS parameters via the recently developed Fourier series method and updated correlations suggested by Walton(2019).The proposed methodology was demonstrated for a proposed deep nuclear waste repository to be located in Canada.Results from the developed methodology were systematically compared with those of traditional reliability(ignoring spatial variation)and deterministic methods(ignoring uncertainty).Although the developed methodology was computationally complex,it was judged to be the most realistic due to the realistic consideration of heterogeneous distributions of rock properties.Traditional methodologies underestimate/overestimate the excavation performance due to negligence of uncertainty and spatial variability.Finally,a parametric analysis was performed using developed methodology by varying the initial friction angle,scale of fluctuations(SOFs)and dilation angle.The effect of initial friction angle was observed to be more pronounced on the probability of failures as compared to SOFs and dilation angle.Similar observations were made related to the excavation damage zone(EDZ)development quantified using yield area ratio.

关键词： Deep excavations Brittle failures CWFS model Sobol’s sensitivity Moving least square response surface Fourier series random field

Rate-dependent mechanical behavior of jointed rock with an impersistent joint under different infill conditions

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Journal of Rock Mechanics and Geotechnical Engineering 2022年第5期14卷 1380-1393页

作者： Sachin Kumar Gaurav tiwari Venkitanarayanan Parameswaran Arghya Das Department of Civil Engineering Indian Institute of TechnologyKanpurIndia

Transition in the rate-dependent mechanical response of rock was investigated due to the presence of impersistent joint with different infill conditions.Four types of samples,i.***.intact,jointed with no grouting,jointed and grouted with cement,and jointed and grouted with epoxy,were fabricated using model material.A series of dynamic split Hopkinson pressure bar(SHPB) tests was conducted on prepared samples with strain rates varying between 53-130 salong with static uniaxial compression tests(10s).Progression of fracture/failure along samples was monitored using high-speed imaging and digital image correlation(DIC).Strength was observed to be significantly lower for jointed samples as compared to intact samples.However,the increasing trend of strength with strain rates remained similar for all types of samples.Epoxy was observed to be a better grout due to greater improvement in the strength of epoxy grouted jointed samples than cement grouted samples under both static and dynamic conditions.Significant changes were observed in fracture behavior(initiation,pattern and mechanism)with strain rate for intact and jointed unfilled/grouted samples.Fracturing was dominated by shear and tensile cracks at high strain rates compared to tensile cracks at low strain rates in all samples.Unlike static loading conditions,the location of cracks initiation shifts away from joint tips with increasing strain rate and depending upon existing infill conditions(unfilled/grouted).

关键词： Jointed rocks Grouted joint Dynamic loading Strain rates

Review of the crushing response of collapsible tubular structures

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Frontiers of Mechanical Engineering 2020年第3期15卷 438-474页

作者： Vivek PATEL Gaurav tiwari Ravikumar DUMPALA Department of Mechanical Engineering Visvesvaraya National Institute of TechnologyNagpur 440010India

Studies on determining and analyzing the crushing response of tubular structures are of significant interest,primarily due to their relation to safety.Several aspects of tubular structures,such as geometry,material,configuration,and hybrid structure,have been used as criteria for evaluation.In this review,a comprehensive analysis of the important findings of extensive research on understanding the crushing response of thin-walled tubular structures is presented.Advancements in thin-walled structures,including multi-cell tube,honeycomb and foam-filled,multi wall,and functionally graded thickness tubes,are also discussed,focusing on their energy absorption ability.An extensive review of experimentation and numerical analysis used to extract the deformation behavior of materials,such as aluminum and steel,against static and dynamic loadings are also provided.Several tube shapes,such as tubes of uniform and nonuniform(tapered)cross sections of circular,square,and rectangular shapes,have been used in different studies to identify their efficacy.Apart from geometric and loading parameters,the effects of fabrication process,heat treatment,and triggering mechanism on initiating plastic deformation,such as cutouts and grooves,on the surface of tubular structures are discussed.

关键词： monolithic structure crashworthiness energy absorber static and dynamic loadings multicellular tube structure filled tube

A Bayesian multi-model inference methodology for imprecise momentindependent global sensitivity analysis of rock structures

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Journal of Rock Mechanics and Geotechnical Engineering 2024年第3期16卷 840-859页

作者： Akshay Kumar Gaurav tiwari Department of Civil Engineering Indian Institute of Technology(IIT)KanpurKanpur208016India

Traditional global sensitivity analysis(GSA)neglects the epistemic uncertainties associated with the probabilistic characteristics(i.***.type of distribution type and its parameters)of input rock properties emanating due to the small size of datasets while mapping the relative importance of properties to the model response.This paper proposes an augmented Bayesian multi-model inference(BMMI)coupled with GSA methodology(BMMI-GSA)to address this issue by estimating the imprecision in the momentindependent sensitivity indices of rock structures arising from the small size of input data.The methodology employs BMMI to quantify the epistemic uncertainties associated with model type and parameters of input properties.The estimated uncertainties are propagated in estimating imprecision in moment-independent Borgonovo’s indices by employing a reweighting approach on candidate probabilistic models.The proposed methodology is showcased for a rock slope prone to stress-controlled failure in the Himalayan region of India.The proposed methodology was superior to the conventional GSA(neglects all epistemic uncertainties)and Bayesian coupled GSA(B-GSA)(neglects model uncertainty)due to its capability to incorporate the uncertainties in both model type and parameters of properties.Imprecise Borgonovo’s indices estimated via proposed methodology provide the confidence intervals of the sensitivity indices instead of their fixed-point estimates,which makes the user more informed in the data collection efforts.Analyses performed with the varying sample sizes suggested that the uncertainties in sensitivity indices reduce significantly with the increasing sample sizes.The accurate importance ranking of properties was only possible via samples of large sizes.Further,the impact of the prior knowledge in terms of prior ranges and distributions was significant;hence,any related assumption should be made carefully.

关键词： Bayesian inference Multi-model inference Statistical uncertainty Global sensitivity analysis(GSA) Borgonovo’s indices Limited data

Assessment of the ballistic response of honeycomb sandwich structures subjected to offset and normal impact

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Defence Technology（防务技术） 2023年第10期28卷 56-73页

作者： Nikhil Khaire Gaurav tiwari Vivek Patel M.A.Iqbal Department of Mechanical Engineering Indian Institute of Technology DelhiNew Delhi110016India Department of Mechanical Engineering Visvesvaraya National Institute of TechnologyNagpur440026India School of Mechanical Engineering Dr.Vishwanath Karad MIT World Peace UniversityPune411038India Department of Civil Engineering Indian Institute of Technology RoorkeeRoorkee247667India

In the present study,experimental and numerical investigations were carried out to examine the behavior of sandwich panels with honeycomb cores.The high velocity impact tests were carried out using a compressed air gun.A sharp conical nosed projectile was impacted normally and with some offset distance(20 mm and 40 mm).The deformation,failure mode and energy dissipation characteristics were obtained for both kinds of loading.Moreover,the explicit solver was run in Abaqus to create the finite element model.The numerically obtained test results were compared with the experimental to check the accuracy of the modelling.The numerical result was further employed to obtain strain energy dissipation in each element by externally running user-defined code in Abaqus.Furthermore,the influence of inscribe circle diameter and cell wall and face sheet thickness on the energy dissipation,deformation and failure mode was examined.The result found that ballistic resistance and deformation were higher against offset impact compared to the normal impact loading.Sandwich panel impacted at 40 mm offset distance required 3 m/s and 1.9 m/s more velocity than 0 and 20 mm offset distance.Also,increasing the face sheet and wall thickness had a positive impact on the ballistic resistance in terms of a higher ballistic limit and energy absorption.However,inscribe circle diameter had a negative influence on the ballistic resistance.Also,the geometrical parameters of the sandwich structure had a significant influence on the energy dissipation in the different deformation directions.The energy dissipation in plastic work was highest for circumferential direction,regardless of impact condition followed by tangential,radial and axial directions.

关键词： Honeycomb sandwich structure Offset impact Energy dissipation characteristic Deformation and failure mode Geometry effect

Seaweed nutraceuticals and their therapeutic role in disease prevention

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Food Science and Human Wellness 2019年第3期8卷 252-263页

作者： Abirami R.Ganesan Uma tiwari gaurav Rajauria School of Applied Sciences College of EngineeringScience and TechnologyFiji National UniversityFiji School of Science Institute of Technology SligoBallinodeCo.SligoIreland School of Agriculture and Food Science University College DublinLyons Research FarmCelbridgeCo.KildareIreland

There is a growing interest that bioactive compounds from seaweed can play a major therapeutic role in disease prevention in humans.Seaweed bioactives including polysaccharides,pigments,fatty acids,polyphenols and peptides have been proven to possess various beneficial biological properties that could potentially contribute to functional food and nutraceutical development.These bioactive are explored for functional properties such as antioxidant,antibacterial,anticancer,antidiabetic,antitumor,antiviral,anti-inflammatory and anticoagulant properties,both in an in-vitro and in-vivo model system.This review critically examines the existing scientific knowledge on primary and secondary metabolites from seaweed and their functional properties for health-related conditions.It presents an update on the most recent evidence relating to their effect on health-related conditions and their action on cellular metabolism.Recent advancement and challenges for seaweed bioactive as a nutraceutical in relation to their biocompatibility and bioavailability to understand their therapeutic development is discussed.

关键词： Functional ingredients Glucose metabolism Lipid metabolism Macroalgae Bioavailability

Robust Optimization Method of Cylindrical Roller Bearing by Maximizing Dynamic Capacity Using Evolutionary Algorithms

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Journal of Harbin Institute of Technology(New Series) 2022年第5期29卷 20-40页

作者： Kumar gaurav Rajiv tiwari Twinkle Mandawat Department of Mechanical Engineering Indian Institute of Technology GuwahatiGuwahati 781039India

Optimization of cylindrical roller bearings(CRBs)has been performed using a robust design.It ensures that the changes in the objective function,even in the case of variations in design variables during manufacturing,have a minimum possible value and do not exceed the upper limit of a desired range of percentage variation.Also,it checks the feasibility of design outcome in presence of manufacturing tolerances in design variables.For any rolling element bearing,a long life indicates a satisfactory performance.In the present study,the dynamic load carrying capacity C,which relates to fatigue life,has been optimized using the robust design.In roller bearings,boundary dimensions(i.e.,bearing outer diameter,bore diameter and width)are standard.Hence,the performance is mainly affected by the internal dimensions and not the bearing boundary dimensions mentioned formerly.In spite of this,besides internal dimensions and their tolerances,the tolerances in boundary dimensions have also been taken into consideration for the robust optimization.The problem has been solved with the elitist non-dominating sorting genetic algorithm(NSGA-II).Finally,for the visualization and to ensure manufacturability of CRB using obtained values,radial dimensions drawing of one of the optimized CRB has been made.To check the robustness of obtained design after optimization,a sensitivity analysis has also been carried out to find out how much the variation in the objective function will be in case of variation in optimized value of design variables.Optimized bearings have been found to have improved life as compared with standard ones.

关键词： cylindrical roller bearing optimization robust design elitist non-dominating sorting genetic algorithm(NSGA-II) fatigue life dynamic load carrying capacity

Further contribution to the Neogene petrified wood forest of Mizoram, India

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科学通报 2013年第S1期58卷 104-110页

作者： MEHROTRA Rakesh Chandra tiwari R P SRIVASTAVA gaurav SHUKLA Anumeha Birbal Sahni Institute of Palaeobotany Department of Geology Mizoram University

Mizoram, a state situated in the northeast corner of India, is very rich in fossil woods belonging to the Tipam Group(Late Miocene-Early Pliocene in age). Four new fossil woods, namely Swintonioxylon hailakandiense Prakash & Tripathi, Bombacacioxylon tertiarum Mehrotra et al., gen. et sp. nov., Dipterocarpoxylon jammuense Guleria et al. and Bischofia palaeojavanica Awasthi are described from there. They resemble the modern taxa, namely Swintonia Griff.(Anacardiaceae), Dipterocarpus C.F. Gaertn.(Dipterocarpaceae), Bischofia Blume(Euphorbiaceae) and the taxa of the family Bombacaceae. The distribution of the modern equivalents of the present and previously described taxa indicates the existence of warm and humid climate in Mizoram during the depositional time.

关键词： fossil wood Tipam Group angiosperms northeast India palaeoclimate

Aspergilloma in a Pulmonary Hydatid

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World Journal of Cardiovascular Surgery 2013年第3期3卷 108-110页

作者： Nikhil tiwari Ramesh Kaushik gaurav Kumar Gautam Ganguly Shabaz Hasnain Department of Cardiothoracic Surgery Military Hospital (CTC) Pune India

Aspergilloma infection in the lung can occur in preexisting cavities and is usually seen after tuberculosis, pulmonary infarction and bronchestasis. Occassionally aspergilloma has been reported within a hydatid cyst. We describe a patient with aspergilloma formed within cyst hydatid. The primary symptom in this patient was recurrent hemoptysis. In this 42-year-old male, the diagnosis was established by HRCT chest. Treatment consisted of postero-lateral thoracotomy with a bilobectomy of lower and middle lobe. Aspergilloma is an unusual complication of hydatid cyst and results from the deterioration of local defence against opportunistic infections.

关键词： Tuberculous Cavity Lung Hydatid Cyst Aspergilloma