Non-linear ultrasonic technique to assess fatigue damage in structural steel

2006 ◽  
Vol 55 (2) ◽  
pp. 199-202 ◽  
Author(s):  
S PALITSAGAR ◽  
S DAS ◽  
N PARIDA ◽  
D BHATTACHARYA
Keyword(s):  
Structural Steel ◽  
Fatigue Damage ◽  
Ultrasonic Technique ◽  
Non Linear

A Method for Fatigue Evaluation of Trimaran Cross Structure With the Influence of Slamming

2017 ◽  
Author(s):  
Zhe Li ◽  
Huilong Ren ◽  
Kai Jin
Keyword(s):  
Stress Response ◽  
Fatigue Strength ◽  
Fatigue Damage ◽  
Linear Response ◽  
Operating Conditions ◽  
Wave Load ◽  
Hull Structure ◽  
Non Linear ◽  
Slamming Load ◽  
Cross Structure

Slamming is a highly non-linear phenomenon between hull structure and wave. Due to the special structure of trimaran, the slamming mode is extremely different from that of traditional vessel. Besides bow emergence and enter, the slamming phenomenon of the out shell at the cross structure is also obvious. In conventional hull structure fatigue strength evaluation, the slamming load is usually not considered. However, the slamming problem is unavoidable at danger load cases, and the stress concentration of the trimaran cross structure is serious. So it is dangerous to ignore the existence of slamming in serious load cases when evaluating the structural fatigue strength. Therefore, it is necessary to study the contribution of slamming load to fatigue damage. In this paper, a practical method for calculating and analyzing is presented to consider the effect of slamming on the fatigue strength of the trimaran cross structure to ensure that the fatigue life of the structure is closer to the true value. According to the linear theory, the relative motion and relative speed of the hull in wave and the stress response of the wave load on the structure are calculated firstly. Then, the stress response of the non-linear out shell slamming force is calculated. The linear response and non-linear response are combined. And the stress response time history under the combined action of slamming and wave load are obtained. Finally, the fatigue damage of the structure under dangerous operating conditions is calculated by the rain flow counting method. And the contribution value of the slamming load to the structural damage degree is calculated. The paper will put forward some reference suggestions for fatigue study calculation and evaluation of Trimaran cross structure with the influence of slamming.

A Non-Linear Fatigue Damage Model for Concrete in Tension

1995 ◽  
Vol 4 (4) ◽  
pp. 362-379 ◽  
Author(s):  
Idelin Molinas Vega ◽  
M. Asghar Bhatti ◽  
Wilfrid A. Nixon
Keyword(s):  
Fatigue Damage ◽  
Damage Model ◽  
Non Linear

ALKALI ACTIVATED FLY ASH BASED CONCRETE: EVALUATION OF CURING PROCESS USING NON-LINEAR ULTRASONIC APPROACH

2021 ◽  
pp. 1-26
Author(s):  
Arash Nikvar-Hassani ◽  
Hamad N. Alnuaimi ◽  
Umar Amjad ◽  
Saptarshi Sasmal ◽  
Lianyang Zhang ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Unconfined Compressive Strength ◽  
Curing Process ◽  
Ultrasonic Technique ◽  
Ultrasonic Signals ◽  
Non Linear ◽  
Ultrasonic Techniques ◽  
Alkali Activated ◽  
Testing And Evaluation

Abstract This paper investigates the applicability of nondestructive testing and evaluation (NDT&E) method using ultrasonic signals to monitor the curing of alkali activated fly ash based concrete (AAFC). The evaluation was carried out on AAFC specimens with two different water/binder (W/B) ratios of 0.3 and 0.5 and after curing at 60 °C for 7, 14 and 28 days, respectively. The signals are recorded and analyzed using linear and non-linear ultrasonic techniques. The results show that the non-linear ultrasonic technique has a clear advantage over the linear ultrasonic technique when monitoring the curing of AAFC specimens with the lower W/B ratio. However, the specimens with the higher W/B ratio do not undergo proper curing and therefore do not show clear distinctions between the curing times measured from the two ultrasonic techniques. The unconfined compressive strength (UCS) of the AAFC specimens at different W/B ratios and curing times is also measured. The UCS results showed a good correlation with the ultrasonic results.

The Effects of Modelling Techniques and Data Uncertainty in Wellhead Fatigue Life Calculation

2012 ◽  
Author(s):  
Dara Williams ◽  
John Greene
Keyword(s):  
Finite Element ◽  
Fatigue Life ◽  
Fatigue Damage ◽  
Environmental Data ◽  
Nonlinear Load ◽  
Soil Response ◽  
Load Response ◽  
Highly Nonlinear ◽  
Non Linear ◽  
The Impact

Offshore oil and gas exploration continues to move into deeper and more harsh environments and consequently the response of drilling riser systems and associated fatigue loading transmitted to the wellhead and conductor system are of key importance in the design of offshore wells. In addition the presence of ageing infrastructure in mature areas combined with requirements for future workover operations requires careful consideration of both past and future fatigue damage accumulation. In order to estimate remaining fatigue life for the wellhead and conductor the accumulation of damage from each stage of a drilling campaign and phase of operation of a well, including workover and completion operations, must be considered. Thus a detailed global finite element analysis of the impact of riser response, under wave and vortex induced vibration (VIV), on the conductor and wellhead structure is of critical importance. Traditional engineering evaluation methods to estimate fatigue of wellhead systems in offshore regions with limited availability of environmental data may result in an over estimation of fatigue damage accumulated in the wellhead. Any assumptions regarding fatigue current profiles can also lead to over-prediction of fatigue damage in the wellhead. This can have implications for the planning of future workover operations and may also lead to unnecessary over-design of the system. A further limitation of traditional wellhead fatigue evaluation criteria lies in the assumptions regarding riser tensioner system load response. These methods do not account for the highly nonlinear load response of the tensioner system and can thus significantly underestimate fatigue damage contribution. This paper presents a more detailed wellhead fatigue analysis methodology to incorporate new analysis techniques, as used for a number of recent applications, to assess with a greater level of refinement the impact of the riser motions on the wellhead fatigue. Specifically this methodology incorporates the generation of a detailed global finite element model of the riser and wellhead system to include detailed non-linear riser tensioner system models, accurate models of the wellhead and conductor, detailed non-linear soil response characteristics and the use of more refined current data as input to VIV calculations. The details of the riser and wellhead system model are presented and the conservatisms associated with traditional modeling methods with regard to VIV and riser tensioner load variations are discussed. A number of case studies are presented to illustrate the effects of various data assumptions and simplifications on estimated wellhead fatigue.

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