Investigating the Hull Girder Strength of the MST-3 Vessel Using Finite Element Analysis

This paper focuses on the numerical method for the geometrically nonlinear buckling analysis of truss with initial member length imperfection. The solution of nonlinear buckling problem of truss with imperfection using a displacement-based finite element is dependent on the imperfection implemented. Generally, the operation of incorporating the initial imperfection to the master stiffness equation develops by master-slave elimination method, penalty augmentation method or Lagrange multiplier adjunction methods. Obviously, the initial imperfection considerably increases the difficulty in finite element formulation nonlinear buckling problem. This research proposes a novel approach to formulate the nonlinear buckling problem of truss with imperfection using mixed finite element method. The mixed balanced equation of truss is formulated using the principle of stationary potential energy. The paper presents novel mixed finite truss element, including initial member length imperfection, considering large displacement. Using the arc length technique, the research develops a new incremental-iterative algorithm for solving the nonlinear buckling problem of truss with initial imperfection in different cases of model formulation, including displacement-based finite element and mixed finite element formulation. The numerical test is presented to investigate the equilibrium path for plan truss with initial member length imperfection. The calculation results in solving problem formulated in both displacement and mixed finite model are converged showing the efficiency and reliability of the proposed method.

Background: The non-linear finite element method with initial geometric imperfection is compulsory to capture the shear buckling behavior of the Corrugated Web Steel Plate Girder (CWSPG). These initial geometry imperfections can come from the slender structure that cannot maintain its perfect shape or lousy quality during the assembly process. Most researchers generate the initial geometry imperfection from the elastic buckling modes that may not represent the randomness in the geometric imperfection. Therefore, there is a need to develop a method to generate random initial geometry imperfection without carrying out elastic buckling modes from the analysis. Objectives: This paper investigated the shear buckling behavior of CWSPG using non-linear finite element analysis and proposed a method to generate the initial geometric imperfection using the random material imperfection. Methods: The random material properties for each meshed element follow a statistically random normal distribution of the material yield strength. The initial geometric imperfection is generated from the first second-order analysis with random material properties (using the in-house 3D-NLFEA package) to the point where the expected buckling shape is obtained. The final deformed geometry from the first second-order analysis is then scaled down to be used as the initial geometric imperfection. Results: The proposed method requires the scaling value such that the first buckling load from the available experimental test result and the one from the numerical model are at the same level. The proposed method was able to capture the shear buckling behavior of the CWSPG and was sensitive to the element’s size. The minimum size of the element required normalized with the element thickness was found to be less than four to maintain the accuracy for both the peak and residual load of the CWSPG specimen. Conclusion: The proposed method shows excellent agreement in predicting the peak load and the post-buckling behavior of the available test results. Therefore, the proposed method can be used as an alternative method to capture the buckling load of the CWSPG specimen.

Effect of geometric imperfections on the ultimate moment capacity of cold-formed sigma-shape sections

From the recent literature, it is revealed that pipe bend geometry deviates from the circular cross-section due to pipe bending process for any bend angle, and this deviation in the cross-section is defined as the initial geometric imperfection. This paper focuses on the determination of collapse moment of different angled pipe bends incorporated with initial geometric imperfection subjected to in-plane closing and opening bending moments. The three-dimensional finite element analysis is accounted for geometric as well as material nonlinearities. Python scripting is implemented for modeling the pipe bends with initial geometry imperfection. The twice-elastic-slope method is adopted to determine the collapse moments. From the results, it is observed that initial imperfection has significant impact on the collapse moment of pipe bends. It can be concluded that the effect of initial imperfection decreases with the decrease in bend angle from 150∘ to 45∘. Based on the finite element results, a simple collapse moment equation is proposed to predict the collapse moment for more accurate cross-section of the different angled pipe bends.

This paper is concerned with the approach to implementing the Penalty function method for imposing multi-freedom constraints in geometrically nonlinear analysis of imperfect trusses based on mixed finite element formulation. Using a finite element model based on displacement formulation, it is required to incorporate both the dependent boundary relations and initial length imperfection to the nonlinear master stiffness system of equations for solving the geometrically nonlinear problem of imperfect truss with multi-freedom constraints. For decreasing the mathematical complexion of the incorporating process, the author proposes a novel mixed finite truss element considering initial imperfection, used in building the model for solving the geometrically nonlinear problem of truss with multi-freedom constraints. The modified nonlinear stiffness equation is constructed by employing the penalty function method to convert a constrained problem into an unconstrained problem by extremizing the augmented energy function established based on the proposed mixed finite element formulation. For solving the nonlinear equilibrium equation of imperfect trusses with multi-freedom constraints, the incremental equilibrium equation is constructed, and the incremental-iterative algorithm for calculation is established utilizing the arc-length method, used for writing the calculation program for investigating geometrically nonlinear behavior of imperfect truss with multi-freedom constraints. The results of the numerical test show the influence of initial imperfection and choosing weight values on the equilibrium path of the truss.

Finite Element simulations are often used to study the reliability of solder joints subjected to thermal cycling. Packaging configurations are becoming more complex to accommodate better functionality and performance. Increased complexity leads to several challenges for FE models including difficulties modeling thin layers and interfaces, as well as keeping the total numbers of nodes and elements to reasonable levels so that computation times can be practical. To reduce the use of high-density meshes and to relax the restrictions of nodal connections, the technique of Multi-Point Constraints (MPC) is often used in finite element analysis. In the MPC method, constraints are enacted between different degrees of freedom of the model to simply transition between finely and coarsely meshed regions. MPC algorithms require additional DOF constraints on a FE model; and extra contact nodes/elements are deployed between the interfaces of contacting elements. MPC methods can be implemented with materials having linear or nonlinear mechanical behavior. The accuracy and efficiency of MPC-based finite element simulations for electronic packages have not been evaluated completely in the literature. In this work, an improved MPC based FE modeling strategy was developed for BGA packages to reduce the total number of elements (including both conventional and MPC elements), and thus reduce the simulation time. In addition, the new method can improve the simulation accuracy relative to models prepared using conventional meshing strategies. The proposed technique allows for different types of mesh patterns (circular pattern from solder joint and rectangular patterns from other component) to be connected in a package assembly while reducing the overall number of elements in the model. The proposed approach works with both symmetric and non-symmetric solder ball arrays, and achieves a good balance between simulation cost and simulation accuracy.

The hatch corner of ship is the most prone area for stress concentration, which makes the fatigue problem of hatch corner particularly serious, and becomes a position that is easily damaged. Firstly, the hot spot stress method based on surface extrapolation is introduced, and the hatch corner of a bulk carrier is selected as the research object, the scale model test is designed and carried out, the finite element model is established, and the parameters of the corner form and different transition radii are analyzed. The CCS calculation specification evaluates the fatigue strength of hatch corner, and compares the test results with the finite element calculation results. The results show that the hot spot stress method has good adaptability to the fatigue assessment of hatch corner, and the fatigue strength evaluation of hatch corner needs to select the corresponding S–N curve according to the position of the maximum hot spot stress. The form of corner and the increase of transition radius are of great significance for alleviating stress concentration effect and improving fatigue life of corner, which provides reference for fatigue resistance and optimal design of hatch corner structure.

Margin plate is a part of bottom construction that joint the floor and frame construction of the ship, so the inner bottom plate will be installed cut off on the margin plate. Lately the bottom construction of the ship tends not to use the margin plate. The ship is currently built with an inner bottom plate continuously from the left side to the right side of the ship.This study aims to determine the transversal and longitudinal strength ratio of ships with and without margin plate. The analysis was carried out by using Finite Element Method so-called ANSYSTM. The result shows if the loadvariatied 0.2 x maximum load on the calculation of the transverse strength of the ship, the stress value on the ship model with a margin plate was 9.6242 (N/mm2) and on the ship model without margin plate was 8.4739 (N/mm2) under conditions 100%. The results of the comparison due to bottom load averaged 15.82%. The difference in stress due to the effect of deck loads was an average of 13.49% while the effect of side loads was on average 8.74%. The longitudinal strength of the ship was also a varied of every increase of 0.2 x maximum moment with a review point of meeting between bottom plate and bilga plate for the ship model without margin plates using the Multi Point Constraint (MPC) method looking for results in sagging conditions of 12,443 (N / mm2) and the hogging condition was -11.045 (N / mm2) at 100% x maximum moment load conditions. So that the ship model with a margin plate sagging condition was 23,189 (N / mm2) and hagging condition was -20,585 (N / mm2). The results showed the stress that occurred in the ship model without using margin plate was better to withstand the transverse and longitudinal strength of the ship compared to the ship model with the margin plate.

Dynamic impact analysis of the grid structure using multi-point constraint (MPC) equation under the lateral impact load

An experimental study on out-of-plane inelastic buckling strength of fixed steel arches

The in-plane mechanical properties of honeycomb paperboard were analyzed and simulated by ANSYS software with finite element analysis method. This paper also explored and optimized finite element modeling method of honeycomb paperboard structure and obtained the equivalent stress distribution maps of honeycomb paperboard in different displacement loads. The mechanical properties and deformation mode of the honeycomb paperboard in the in-plane compression conditions were also analyzed. The results show that longitudinal compressive strength is greater than the lateral compressive strength. The compression deformation mode is different when compressing but appears with the same four stages. The results of finite element analysis have good equivalence with the experimental ones. This paper also revealed the honeycomb paperboard in-plane mechanical properties, deformation and destruction mechanism, further extended the research scope of honeycomb paperboard, and promoted the application of finite element method in the analysis of honeycomb paperboard.

Concrete-filled steel tubes subjected to axial compression: Life-cycle based performance

This research aims to determine the longitudinal strength of passenger ship which was converted from Landing Craft Tank with 54 m of length as stated by BKI (Biro Klasifikasi Indonesia / Indonesian Classification Bureau). Verification of strength value is done to 4 (four) loading conditions which are (1) empty load condition during sagging wave, (2) empty load condition during hogging wave, (3) full load condition during sagging wave and (4) full load condition during hogging wave. Analysis is done using Finite Element Analysis (FEA) software by modeling the entire part of passenger ship and its loading condition. The back and upfront part of ship centerline were used as the boundary condition. From that analysis it can be concluded that the maximum stress for load condition (1) is 72,393 MPa, 74,792 MPa for load condition (2), 129,92 MPa for load condition (3), and 132,4 MPa for load condition (4). Longitudinal strength of passenger ship fulfilled the criteria of empty load condition having smaller stress value than allowable stress which is 90 MPa, and during full load condition with smaller stress value than allowable stress which is 150 MPa. Analysis on longitudinal strength comparison with entire ship plate thickness variation of ± 2 mm from initial plate was also done during this research. From this research it can be concluded that plate thickness reduction causes the value of longitudinal strength to decrease, while plate thickness addition causes the value of longitudinal strength to increase.

Study of thermal buckling behavior of plain woven C/SiC composite plate using digital image correlation technique and finite element simulation

Normal procedure for assessing the hull strength of a ship shaped Floating Production Unit (FPU) is to use a rule based approach recommended by the classification societies. In this approach the vertical and horizontal wave bending moments and shear forces are calculated based on formulae prescribed in the rules. The difference between the hull's total carrying capacity and the rule prescribed wave related quantities provide the envelope of the still water moments and shear forces. The loading conditions are developed such that the still water envelope is not exceeded. Although this method can reasonably predict the longitudinal hull strength the following important issues are not addressed.The transverse strength of the hull.The stresses at the interface of the hull and add-on structures like living quarters, riser porch, heavy production modules etc which are common in a FPU.The stresses at the corner of large deck openings. The above issues can only be addressed effectively through a Finite Element (FE) based approach. In this approach a coarse mesh integrated model of the hull including the add-on structures is prepared. The envelope values of the wave dynamic pressures, accelerations etc. are obtained from the formulae presented in the rules. These are then multiplied with appropriate factors also prescribed in the rules to obtain their simultaneously occurring values. These loads along with the gravity loads are first applied on a beam model representing the hull to obtain the actual moments at the target locations. The difference between the target moment and actual moment is applied as concentrated end moments to achieve the target values. The areas of high stress reported in the coarse mesh analysis are further refined and studied in a local analysis by employing boundary displacement methods. In this paper the above procedure has been discussed in detail and selected results have been presented to establish the effectiveness of this analysis procedure. A detail hydrodynamic based analysis is necessary for an optimum site specific strength assessment of a FPU. But a cost-effective, although slightly conservative assessment (since the rule based design strength quantities correspond to north Atlantic conditions) can be done by the rule based approach using finite element. The authors believe that the methodology and results reported in this paper for a specific FPU will help in understanding the rule based analysis procedure of other ship type FPUs. Introduction A primary requirement of a floating vessel is to ensure the global longitudinal and transverse strength adequacy of the structure to resist the gravity, buoyancy, environmental and motion induced loads for the site specific environment. For an ocean going vessel it is normal practice to use the Rule Based approach specified by the classification societies. The longitudinal strength of the vessel is characterized by the maximum moment and shear force at any cross-section of the vessel considering both the Stillwater and the Wave effects. In the rule-based approach, the longitudinal wave effects of the vessel are calculated using essentially prescribed empirical formulae without performing any hydrodynamic analysis for the waves.