m1 h in .NET Development QR Code in .NET m1 h

m1 h using .net vs 2010 tomake qr code jis x 0510 with web,windows application GS1 DataBar Overview (7.11). where () = g amma function; and k = total number of stress levels, as de ned in Eq. (7.4).

In a case where the long-term stress ranges arise from a series of short-term sea states following the Rayleigh distribution, the fatigue damage accumulation can be calculated for the different loading conditions involved and a bilinear or two-sloped S N curve application, as follows [for symbols not speci ed below, see Eq. (7.3)] 2 m1 I,J 2 2moi j m1 c D = fo Td ri j 1 1+ A1 2 2 2moi j i=1, j=1 2 2moi j + A2.

m2 2 1+ 2 c 2 2moi j , (7.12). where ri j = .net vs 2010 qr barcode relative number of stress cycles in short-term conditions i, j; A1 , m1 = S N fatigue parameters typically for N < 107 ; A2 , m2 = S N fatigue parameters typically for N 107 ; I = total number of sea-state conditions; J = total number of wave headings; and moi j = zero spectral moment of stress response process. In some FLS design cases, one part of the fatigue damage may arise from a particular process of fatigue actions, but another fatigue damage for the same hot spot area may be caused by yet another different process of fatigue actions.

In this case, the combination of fatigue damages from two different fatigue processes must be considered in an adequate manner because a linear superposition may not necessarily provide conservative FLS assessment (Lotsberg 2005). To combine fatigue damages from two different dynamic processes, DNV-RPC206 (DNV 2006) suggests using the following equation when one-sloped S N curve is applied for fatigue damage calculations: D = D1 n2 1 n1 + n2 D1 n1. D2 n2 (7.13). where D1 = f atigue damage due to one dynamic process; D2 = fatigue damage due to another dynamic process; n1 = mean zero up-crossing frequency for one dynamic process; n2 = mean zero up-crossing frequency for another dynamic process; and m = inverse slope of one-sloped S N curve. It is considered that both D1 and D2 are also calculated applying the corresponding one-sloped S N curves. However, when two-sloped S N curves are applied, for example, so that highcycle fatigue is likely dominant, it is considered that the main contribution to overall.

Fatigue Limit-State Design fatigue dama ge will be from the region of N Nc . In this regard, Eq. (7.

13) may still be applicable for this case but with the inverse slope of two-sloped S N curve at N Nc , for example, m = 5.0 as de ned in Tables 7.6 and 7.

7 (Lotsberg 2005). 7.10 High-Cycle Fatigue versus Low-Cycle Fatigue Typically, fatigue damage of offshore structures is likely due to high-cycle fatigue actions that are considered to have an associated number of loading cycles that are more than 104 .

It may be considered that fatigue initiated with a number of cycles less than 104 is low-cycle fatigue and vice versa for high-cycle fatigue. Most guidance and practices for FLS assessment and design presented in codes and standards, as well as in this chapter, are associated with high-cycle fatigue. It is important to realize that action effects (e.

g., stresses) related to low-cycle fatigue more likely involve plasticity at structural details (hot spot areas), but those due to high-cycle fatigue mostly remain in the elastic regime. Therefore, low-cycle fatigue analysis must apply the action effects obtained by taking account of nonlinear material behavior.

Offshore structures are normally designed for other types of limit states such as ULS so that a suf cient factor of safety is achieved for extreme environmental and operational conditions as well as in normal service. Although the effects of stresses due to local notches or at structural details (hot spot areas) are usually not accounted for in ULS design, it is considered that the ULS design results in a structure wherein the stress ranges during extreme actions are themselves limited to few in number. However, it is to be noted that low-cycle fatigue must certainly be considered when dynamic actions with low-cycle fatigue are frequent.

In fact, the loading and unloading cycle is quite frequent in FPSOs when compared to many trading tankers, and the resulting hull girder loading variations can also be signi cant, as shown in Figure 6.1 of 6. Similar scenarios may also need to be considered for trading tankers in particular cases (Urm et al.

2004). 7.11 Time-Variant Fatigue Crack Propagation Models Fatigue cracking damage has been a primary source of costly repair work for aging structures.

Such cracking damage has been found primarily in welded joints and local areas of stress concentrations; for example, at the weld intersections of longitudinals, frames, and girders. Initial defects may also be formed in the structure by fabrication procedure and may conceivably remain undetected over time. Under a cyclic loading or even monotonic extreme loading, cracks and defects may propagate and become larger with time.

Because cracks of a large enough size can conceivably lead to the catastrophic failure of the structure, it is essential to properly consider and establish relevant crack-tolerant design procedures for structures in addition to implementation of close-up survey and maintenance strategy. For reliability assessment of aging structures under extreme loads, it is often necessary to take into account a known (existing or premised or anticipated) crack on the ultimate limit-state analysis as a parameter.
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